# The Kinematic and Dynamic Properties of HBC 494’s Wide-Angle Outflows

Austen Fourkas1,2, Dary Ruíz-Rodríguez2, Lee G. Mundy1, Jonathan P. Williams3
1Department of Astronomy, University of Maryland, 4296 Stadium Dr, College
Park, MD 20742, USA
2National Radio Astronomy Observatory, 520 Edgemont Rd, Charlottesville, VA
22903, USA
3Institute for Astronomy, University of Hawai‘i at Mānoa, 2680 Woodlawn Dr.,
Honolulu, HI 96822, USA E-mail<EMAIL_ADDRESS>0000-0001-7387-3898
0000-0003-3573-8163 0000-0002-8876-0690 0000-0001-5058-695X

(Accepted XXX. Received YYY; in original form ZZZ)

###### Abstract

We present Atacama Large Millimeter/sub-millimeter Array (ALMA) Cycle-5
observations of HBC 494, as well as calculations of the kinematic and dynamic
variables which represent the object’s wide-angle bipolar outflows. HBC 494 is
a binary FU Orionis type object located in the Orion A molecular cloud. We
take advantage of combining the ALMA main array, Atacama Compact Array (ACA),
and Total Power (TP) array in order to map HBC 494’s outflows and thus,
estimate their kinematic parameters with higher accuracy in comparison to
prior publications. We use 12CO, 13CO, C18O, and SO observations to describe
the object’s outflows, envelope, and disc, as well as estimate the mass,
momentum, and kinetic energy of the outflows. After correcting for optical
opacity near systemic velocities, we estimate a mass of $3.0\times 10^{-2}$
$\mathrm{M}_{\sun}$ for the southern outflow and $2.8\times 10^{-2}$
$\mathrm{M}_{\sun}$ for northern outflow. We report the first detection of a
secondary outflow cavity located approximately $15\arcsec$ north of the
central binary system, which could be a remnant of a previous large-scale
accretion outburst. Furthermore, we find CO spatial features in HBC 494’s
outflows corresponding to position angles of $\sim 35\degr$ and $\sim
145\degr$. This suggests that HBC 494’s outflows are most likely a composite
of overlapping outflows from two different sources, i.e., HBC 494a and HBC
494b, the two objects in the binary system.

###### keywords:

stars: winds, outflows – submillimetre: stars – stars: kinematics and dynamics
– stars: pre-main-sequence

††pubyear: 2023††pagerange: The Kinematic and Dynamic Properties of HBC 494’s
Wide-Angle Outflows–A

##  1 Introduction

Young stellar objects (YSOs) primarily gain mass due to accretion of material
from their large stellar envelope onto a protostellar disc (Hartmann & Kenyon,
1996). However, mass and luminosity predictions based on constant accretion
models do not align with measured values for multiple YSOs (Kenyon et al.,
1990; Audard et al., 2014). As first proposed by Kenyon et al. (1990), the
‘luminosity problem’ highlights the difference between predicted and observed
luminosity values. FU Orionis stars (FUors) serve as a solution to the
luminosity problem, as their non-constant accretion rates are able to resolve
differences in theory and observation. FUors are a subclass of Class 0 and I
YSOs which display characteristic large-scale accretion outbursts resulting in
changes to brightness, bolometric luminosity, and the object’s spectral energy
diagram (SED) (Herbig, 1966). Specifically, accretion rates during outbursts
can increase by up to 1000 times in comparison to quiescent epochs
($10^{-7}\rightarrow 10^{-4}$
$\mathrm{M}_{\sun}\,\,\mathrm{y}\mathrm{r}^{-1}$), and the star may accrete up
to 0.01 $\mathrm{M}_{\sun}$ during an outburst (Audard et al., 2014; Andrews &
Williams, 2005). The large amount of disc material accreted onto the protostar
during an outburst event can increase a FUor’s optical brightness by 3-6 mag,
and lead to bolometric luminosity increases of between 50 and 500
$\mathrm{L}_{\sun}$ (Audard et al., 2014).

While luminosity and magnitude changes serve as observational evidence for the
occurrence of outbursting events, the mechanisms which trigger these events
are yet to be completely constrained (Cieza et al., 2018). Possible
outbursting mechanisms include: thermal instabilities in the disc (Bell & Lin,
1994), disc fragmentation (Andrews & Williams, 2005; Zhu et al., 2012), tidal
interactions between the protostellar disc and a companion object (Lodato &
Clarke, 2004; Bonnell & Bastien, 1992), and a combination of gravitational and
magneto-rotational instabilities (Armitage et al., 2001; Zhu et al., 2009).

As accretion from the protostellar disc onto the central protostar proceeds,
streams of molecular material called outflows are created and propagate
perpendicular to the disc in opposite directions. The creation and propagation
of these flows are closely linked to the magnetic field generated by the
central protostar and how this field interacts with the protostellar disc. The
wind created by a magnetized disc, called the disc-wind, carries angular
momentum away from the protostar through the bipolar outflows (Pudritz & Ray,
2019). While disc-winds assume that outflows stem from the surface of the
disc, other models suggest that interactions between the inner edge of the
disc and the magnetosphere of the central protostar are the primary driver of
outflows. Magnetic field changes at these radii cause material to be ejected
centrifugally through open field lines, and the wind generated in conjunction
with the X-ring is called an X-wind (Pudritz & Ray, 2019). Along with
impacting the accretion rate of material onto the central protostar, stellar
outflows can also entrain and disperse envelope material away from the central
object, thus impacting the object’s final mass, and evolutionary pathway.

By observing and analysing an FU Ori type object’s outflows, its large-scale
accretion outburst mechanism can be better constrained along with its
evolutionary pathway. Specifically, interferometric millimetre/sub-millimetre
arrays with both long and short baselines can aid in observing FU Ori type
objects due the presence of both large and small-scale emission in such
systems. Greater baseline lengths are able resolve emission from the
protostellar disc, as well as outflow cavities and bow-shocks, while shorter
baselines image the envelope emission and material which fills the
aforementioned cavities.

This study focuses on HBC 494, a binary FU Ori type object located at a
distance of $414\pm 7$ pc in the Orion A molecular cloud with a systemic
velocity of
$V_{$\mathrm{s}\mathrm{y}\mathrm{s}$}=4.3\,${km}\,\mathrm{s}^{-1}$$ (Menten et
al., 2007). HBC 494 was initially correlated with optical and infrared
brightness increases in the reflection nebulae Re50 and Reipurth 50 N
(Reipurth, 1985; Reipurth & Bally, 1986). Nogueira et al. (2023) were able to
resolve both objects in the binary, HBC 494a and HBC 494b, with a separation
of approximately 75 au. They report that HBC 494a has a dust mass of 1.4
$\mathrm{M}_{J}$ and a gas mass of 143.5 $\mathrm{M}_{J}$, while HBC 494b has
a dust mass of 0.3 $\mathrm{M}_{J}$ and a gas mass of 28.7 $\mathrm{M}_{J}$.
Furthermore, they report that HBC 494a is likely the primary object in the
binary, as along with its mass, it is approximately 5 times brighter than HBC
494b. HBC 494 also presents extraordinarily wide bipolar outflows (Ruíz-
Rodríguez et al., 2017, hereon RR17). With an opening angle of 150 degrees,
HBC 494’s outflows are at least 20$\%$ wider than early interferometric
observations suggest, as Class I YSO outflows were typically observed with
opening angles angles between 30 and 125 degrees (e.g., Arce & Sargent, 2006;
Klaassen et al., 2016; Cieza et al., 2018). Recent studies have revealed,
however, that wide angle outflows are more common amongst Class 0 and I YSOs
than previously thought (e.g. Hsieh et al., 2023). Nevertheless, HBC 494’s
outflows present interesting structure, shape, and possible origin, all of
which will be discussed in this work. Initial observations of HBC 494’s
outflows presented in RR17 only made use of the ALMA main array, making it
difficult to accurately estimate outflow parameters. Specifically, these
observations were limited by poor UV-plane coverage at short baselines, thus
filtering out flux from large-scale structure and causing outflow parameters
to be underestimated. In this paper we improve upon the results presented in
2017 through improvements to observations with regard to sensitivity and field
of view (FOV), as well as an updated analysis and calculation procedure.

We present ALMA Cycle-5 observations of HBC 494. 12CO (J=2-1), 13CO (J=2-1),
C18O (J=2-1), and SO (J=6-5) are all used to trace different regions of the
protostar and its surrounding environment. We make use of the ALMA main array
(12-m array) as well as a combination of the main array, Total Power array
(single-dish, 12-m diameter), and Atacama Compact Array (7-m array), which
will be called the ‘combination array’ for the remainder of this paper. The
use of both long and short baselines in the combination array prevents spatial
filtering normally present in ALMA 12-m array observations. The Cycle-5
observations traced a larger extent of the outflow in comparison to prior
observations due to the use of X-field mosaicing instead of a single pointing
for imaging (Fig. 1). Specifications of our ALMA observations are described in
section 2, while observational and computational results are presented in
sections 3 and 4, respectively. A discussion of results and important
conclusions are given in sections 5 and 6.

##  2 Observations

We obtained ALMA Cycle-5 Band 6 observations toward HBC 494 with a centre
position of $\alpha$ (J2000) = 05h 40m 27.45s ; $\delta$ (J2000) =
-07o27${\arcmin}$30.05${\arcsec}$. The spectral windows targeted 12CO (J =
2-1), 13CO (J = 2-1), C18O (J = 2-1), SO (J = 6(5)-5(4)), DCN (J = 3-2), SiO
(J= 5-4), 13CS (J = 5-4) and continuum at rest-frame frequencies of 230.588,
220.398, 219.560, 219.949, 217.238, 217.104, 231.220, and 232.50 GHz,
respectively (see Table 1).

Table 1: Spectral windows. Line | Rest Freq. | 12-m | 7-m | TP
---|---|---|---|---
Bandwidth | Channel | Bandwidth | Channel | Bandwidth | Channel
[GHz] | [MHz] | [$\\#$] | [MHz] | [$\\#$] | [MHz] | [$\\#$]
SiO J=5-4 | 217.105 | 58.5 | 480 | 62.5 | 512 | 62.5 | 512
DCN J=3-2 | 217.238 | 58.5 | 480 | 62.5 | 512 | 62.5 | 512
H2CO J=3(2,1)-2(2,0) | 218.760 | 58.5 | 480 | 62.5 | 512 | 62.5 | 512
C18O J=2-1 | 219.560 | 58.5 | 960 | 62.5 | 1024 | 62.5 | 1024
SO J=6(5)-5(4) | 219.949 | 58.5 | 960 | 62.5 | 1024 | 62.5 | 1024
13CO J=2-1 | 220.398 | 58.5 | 960 | 62.5 | 1024 | 62.5 | 1024
12CO J=2-1 | 230.55 | 117.2 | 960 | 62.5 | 1024 | 125 | 1024
13CS J=5-4 | 231.221 | 117.2 | 960 | 125 | 1024 | 125 | 1024

The correlator for these spectral windows was set to have bandwidths between
58.5 MHz and 2000 MHz. In order to image HBC 494 with a full coverage from
0.5${\arcsec}$ to the map size of 30″, we make use of the ALMA combination
array. By combining the 12-m, 7-m, and TP data, the observations are sensitive
to emission from disc to outflow scales. Table 2 summarizes the observational
logs for this project.

HBC 494 was observed (project ID: 2017.1.00015.S PI: J. Williams) using the
compact (baselines $\sim$ 55 to 91 m) and the extended configurations, C43-2
(15 - 315 m) and C43-5 (15 - 1400 m), on 2017 October 31, 2018 Jan 21, and
July 12, respectively (Table 2). The field of view of 60″ $\times$ 60″ was
covered by a mosaic of 27 pointings (12-m array). The shorter UV distance
range was fulfilled by ACA observations using a 7 pointing mosaic (7-m array)
with a maximum detectable size of 30″, and the TP observations covered the
larger-scale emission over the entire mapped region.

Table 2: Observational details. Array | Observation | Bandpass | Flux | Phase | Time On | Median PWV
---|---|---|---|---|---|---
Date | Calibrator | Calibrator | Calibrator | Source [mm:ss] | [mm]
12-m $\times$ 44 | 21-Jan-2018 | J0607-0834 | J0607-0834 | J0541-0541 | 17:21 | 0.98
12-m $\times$ 43 | 12-Jul-2018 | J0542-0913 | J0522-3627 | J0542-0913 | 08:48 | 2.25
7-m $\times$ 11 | 31-Oct-2017 | J0522-3627 | J0607-0834 | J0607-0834 | 34:45 | 1.43
7-m $\times$ 11 | 01-Nov-2017 | J0522-3627 | J0607-0834 | J0607-0834 | 34:11 | 0.58
TP | 03-May-2018 | J0542-0913 | J0542-0913 | J0542-0913 | 38:01 | 0.63
TP | 04-May-2018 | J0542-0913 | J0542-0913 | J0542-0913 | 38:01 | 0.71
TP | 06-May-2018 | J0542-0913 | J0542-0913 | J0542-0913 | 38:01 | 1.40
TP | 15-May-2018 | J0607-0834 | J0607-0834 | J0607-0834 | 38:01 | 0.89

###  2.1 Data Calibration and Reduction

Data were calibrated using the standard calibration script in the CASA
software package (Version 4.7.2- Cycle-5). In order to concatenate all data
sets, we initially converted the TP map into visibilities by using the Total
Power to Visibilities (TP2VIS)111https://github.com/tp2vis/distribute package
that runs on the CASA platform (Koda et al., 2019, and references therein). We
adopt the root-mean-square (rms) noise in the TP map as the optimal weight of
the TP visibilities. For line imaging, we initially subtracted the continuum
emission by fitting a first-order polynomial to the continuum in the UV-plane.
After subtracting continuum emission determined at the emission-free channels,
we then combined the 12-m, 7-m, and TP data in UV space using the CASA task
concat and deconvolved them jointly. We determined weights of the visibility
data using the task statwt. Unfortunately, the sensitivity of the extended
configuration C43-5 from Cycle-5 observations is not optimal for the
combination. We attempted to combine the 12-m, 7-m, and TP data by
concatenating the visibility data together using different weights; however,
the resulting rms became higher when including the C43-5 array. We opted to
not include these observations in the final products. Nevertheless, for
completeness, we list in Table 2 the Cycle-5 C43-5 array observations.

After concatenating the visibility data, the reduction process was done using
the TCLEAN task with a multi-scaled deconvolver of 0, 20, 60, which applies an
iterative procedure with a decreasing threshold parameter to automatically
mask regions during the cleaning process (e.g. Kepley et al., 2020). To
achieve a good balance between sensitivity and angular resolution, the Briggs
weighting parameter R was set to 0.5 for the spectral-line image cubes. The
spectral data cubes were constructed on a 640 $\times$ 640 pixel grid with
0.05" pixel size, and with 0.18 km s-1 velocity resolution.

The broadband (2 GHz baseband) 232.5 GHz visibility was imaged by using the
TCLEAN algorithm and applying similar imaging parameters as mentioned above.
The analysis in this work, however, is focused mainly on the line data
detected towards HBC 494, see section 3.

Figure 1: Moment-0 maps of 12CO integrated between LSR velocities of -11 and
23.56 ${km}\,\mathrm{s}^{-1}$. This figure illustrates the improvements made
to both sensitivity and field of view by using both the combination array and
mosaic pointings. The left image shows a Cycle-5 combination array observation
of 12CO at a field of view of approximately one square arcminute, while the
right image shows a Cycle-5 main array observation of 12CO at a field of view
of approximately 400 square arcseconds, which is equal to the field of view of
previously recorded ALMA Cycle-2 observations presented in RR17. The
combination array synthesised beam is shown in white at the bottom left of the
first image with a size of 1.85 $\times$ 1.23 arcseconds and position angle of
-67.2$\degr$. The main array synthesised beam is shown in white at the bottom
left of the second image with a size and position angle of 1.55 $\times$ 1.09
arcseconds and -68.8$\degr$, respectively. The white contours at the centre of
each image represent continuum emission centred at 232.5 GHz, and is shown at
levels of 0.25 and 0.75 times the maximum intensity of 0.11 Jy/beam. The
continuum beam is shown in the top left of each frame as a green ellipse, and
has an angular size of 1.50 $\times$ 1.07 arcseconds and a position angle of
-66.8$\degr$.

##  3 Observational Results

###  3.1 12CO observations

12CO emission is the primary tracer of HBC 494’s outflow material, and as
such, we created a data cube covering LSR velocities from -20 to 33.82
${km}\,\mathrm{s}^{-1}$. The cube can be split into three velocity sections:
blueshifted, systemic, and redshifted. Blueshifted emission is present from
-20 to 3.4 ${km}\,\mathrm{s}^{-1}$; emission near systemic velocities is
present between 3.58 and 5.2 ${km}\,\mathrm{s}^{-1}$, and redshifted emission
is present from 5.38 to 33.82 ${km}\,\mathrm{s}^{-1}$.

In order to reveal the large outflow structure traced by blueshifted and
redshifted 12CO emission, we integrate over two velocity ranges: -11 – 3.4
${km}\,\mathrm{s}^{-1}$ and 5.38 – 23.56 ${km}\,\mathrm{s}^{-1}$ for
blueshifted and redshifted emission, respectively. These velocity ranges do
not encompass the full extent of the aforementioned data cube, as outflow
emission is not present near the minimum and maximum velocities of the cube.
The results of these velocity channel integrations (moment-0 maps) are
presented in Figure 2. Figure 2a shows that a blueshifted outflow cavity wall
is detected with an extension of approximately 27${\arcsec}$ to the southeast
(labelled A), and a fainter structure 13${\arcsec}$ long is detected on the
southwestern side (labelled B). Figure 2b shows the northern, redshifted
outflow cavity. In comparison to the southern outflow cavity, the northern
cavity shows a more uniformly parabolic shape with extension in the eastern
and western arms of 11${\arcsec}$ (labelled C) and 18${\arcsec}$ (labelled D),
respectively. The two prior outflows will hereon be called the primary
northern and southern outflow cavities, respectively. A secondary outflow
cavity is traced approximately 15${\arcsec}$ north of the central binary
(labelled E). Due to its location, it is possible that this cavity is the
result of a previous accretion outburst. Additionally, the misalignment
between the southern cavity and the two northern cavities suggests an overlap
of two sets of outflows from different origins (i.e., HBC 494a and HBC 494b),
and is explained further in section 3.5.

Figure 2c shows an integration over the full velocity range which highlights
the parabolic shape of the southern and northern outflow cavities, as well as
the secondary northern cavity. An asymmetry between the eastern and western
features of each primary outflow is seen in the centre of the figure. A $\sim
5.5{\arcsec}$ long and $\sim 1{\arcsec}$ wide ‘bar’ (indicated by an arrow) of
emission extends eastwards from the central binary with a position angle of
67$\degr$, and is more than twice as intense as the more extended regions of
each outflow. This bar could represent an overlap between the northern and
southern outflows, as the eastern arms of both outflows appear to begin their
separation at the end of this bar. It is also possible that this asymmetry is
further evidence of overlapping outflows from the two objects in HBC 494’s
binary system, which likely have differing position angles from one another.

Figure 2: Moment-0 maps of blueshifted 12CO emission integrated between
velocities of -11 – 3.4 ${km}\,\mathrm{s}^{-1}$ (2a – left), redshifted
emission between velocities of 5.38 – 23.56 ${km}\,\mathrm{s}^{-1}$ (2b –
centre), and both velocity ranges to encompass the northern and southern
outflow (2c – right). The letters A-E in shown in the above figures correspond
to the following features: A – eastern blueshifted wall, B – western
blueshifted wall, C – eastern redshifted wall, D – western redshifted wall, E
– the secondary cavity. The white contours at the centre of each image
represent continuum emission centred at 232.5 GHz at levels of 0.25 and 0.75
times the maximum detected intensity of 0.11 Jy/beam. The white ellipse in the
bottom left corner of each image represents the synthesised beam, which has an
angular size of 1.85 $\times$ 1.23 arcseconds and a position angle of
-67.2$\degr$. The continuum beam is shown in the top left of each frame as a
green ellipse, and has an angular size of 1.50 $\times$ 1.07 arcseconds and a
position angle of -66.8$\degr$.

The blueshifted outflow increases in both extension and intensity as channel
velocities approach the systemic value, with the ambient cloud becoming
prevalent at 1.6 ${km}\,\mathrm{s}^{-1}$ (Fig. 20). The velocity evolution of
the southern outflow cavity is shown in greater detail in Figure 3, which
displays emission from the southern cavity between -2.54 and 3.76
${km}\,\mathrm{s}^{-1}$ with a channel spacing of 0.18
${km}\,\mathrm{s}^{-1}$. The eastern arm shows significant emission at channel
velocities ranging from -11 and 3.76 ${km}\,\mathrm{s}^{-1}$; however, the
western arm only displays emission from -2.54 to 3.76 ${km}\,\mathrm{s}^{-1}$.
Indicated by arrows towards the bottom of the figure, emission near the base
of the outflow lobe at velocities between 2.5 and 3.58 ${km}\,\mathrm{s}^{-1}$
follows the curvature the southern cavity, and separates into two distinct
lobes of emission along its eastern and western walls. While the intensity of
these two lobes is similar, their extension in relation to the southern
outflow cavity is not. Specifically, the southwestern emission lobe extends to
the end of its corresponding outflow arm, while the southeastern lobe extends
approximately half way down the eastern arm.

Figure 3: An individual channel map of blueshifted 12CO emission between
velocities of -2.54 and 3.76 ${km}\,\mathrm{s}^{-1}$. The western arm of the
southern outflow can be seen more prevalently as channel velocity increases.
The green arrows shown towards the bottom of the figure highlight the lobes of
emission present near the base of the outflow cavity. The central contours in
each panel display continuum emission centred at 232.5 GHz at levels of 0.25
and 0.75 times the maximum recorded intensity of 0.11 Jy/beam. The white
ellipse in the bottom left corner of each panel represents the synthesised
beam, which has a size and position angle of 1.85 $\times$ 1.23 arcseconds and
-67.2$\degr$, respectively. The green ellipse in the top left corner of each
panel represents the continuum emission beam with a size of 1.50 $\times$ 1.07
arcseconds and a position angle of -66.8$\degr$.

As velocities increase from systemic values, both northern outflow arms extend
away from the central binary towards the north east. Figure 4 shows per-
channel 12CO emission in the redshifted velocity range, specifically between
5.02 and 9.34 ${km}\,\mathrm{s}^{-1}$ with a channel spacing of 0.18
${km}\,\mathrm{s}^{-1}$. A large cloud of material appears to be pushed
upwards in the northern outflow cavity. Beginning at the front of this
velocity range and becoming more prevalent as channel velocity increases, this
cloud becomes separated from the central binary, continues to propagate
upwards, and morphs into the secondary northern outflow cavity. At the same
time, the two northern outflow arms begin to take shape; however, extension
does not occur in the same velocity channels for both arms, nor does it occur
at the same rate. The western arm reaches its maximum projected extension
within 0.18 ${km}\,\mathrm{s}^{-1}$ of the emission cloud becoming detached
from the central binary. In contrast, the eastern arm does not extend until 7
${km}\,\mathrm{s}^{-1}$. Approaching 9.34 ${km}\,\mathrm{s}^{-1}$, emission
from the secondary northern outflow cavity dissipates and the two northern
outflow arms are seen clearly.

Figure 4: A channel-by-channel map of redshifted 12CO emission at velocities
between 5.02 and 9.34 ${km}\,\mathrm{s}^{-1}$. The white contours visible at
the centre of each panel represent continuum emission centred at 232.5 GHz at
levels of 0.25 and 0.75 times the maximum detected intensity of 0.11 Jy/beam.
The green and white ellipses shown at the top and bottom left of each panel,
respectively, represent the 12CO continuum and synthesised beams. These beams
maintain an angular size of 1.85 $\times$ 1.23 and 1.50 $\times$ 1.07
arcseconds, and position angles of -67.2$\degr$ and -66.8$\degr$,
respectively.

Redshifted emission present between 5.38 and 9.16 ${km}\,\mathrm{s}^{-1}$ is
mimicked between 9.34 and 13.84 ${km}\,\mathrm{s}^{-1}$ at lower intensity. In
other words, the outflow/emission shapes seen between 5.38 and 9.16
${km}\,\mathrm{s}^{-1}$ are also present between 9.34 and 13.84
${km}\,\mathrm{s}^{-1}$ with lower overall intensity in each channel. This
phenomenon is displayed in Fig. 5, which shows a channel map of 12CO emission
towards the tail-end of the redshifted velocity range (9.34 to 13.66
${km}\,\mathrm{s}^{-1}$) with a channel spacing of 0.18
${km}\,\mathrm{s}^{-1}$. As channel velocities increase towards the tail end
of the data cube, the secondary northern cavity dissipates while the primary
northern cavity remains prevalent. The primary cavity maintains its shape and
intensity up to 23.56 ${km}\,\mathrm{s}^{-1}$, at which point it quickly
disappears.

Figure 5: An individual channel map of redshifted 12CO emission at velocities
between 9.34 and 13.66 ${km}\,\mathrm{s}^{-1}$. The white contours shown in
the centre of each frame represent continuum emission centred at 232.5 GHz at
levels of 0.25 and 0.75 times the maximum detected intensity of 0.11 Jy/beam.
The green and white ellipses shown at the top and bottom left of each panel,
respectively, represent the 12CO continuum and synthesised beams. These beams
maintain an angular size of 1.85 $\times$ 1.23 and 1.50 $\times$ 1.07
arcseconds, and position angles of -67.2$\degr$ and -66.8$\degr$,
respectively.

###  3.2 13CO observations

To trace the stellar envelope, as well as interactions between the envelope
and HBC 494’s outflows, we produced a 13CO data cube encompassing emission
from -20 to 33.82 ${km}\,\mathrm{s}^{-1}$ with a channel width of 0.18
${km}\,\mathrm{s}^{-1}$. Although 13CO detections are most prevalent near the
systemic velocity ($4.3\pm 0.7$ ${km}\,\mathrm{s}^{-1}$), emission is
generally present between 2.14 and 11.5 ${km}\,\mathrm{s}^{-1}$. As with 12CO
emission, 13CO detections can be separated into three different velocity
ranges: blueshifted (2.14 – 3.40 ${km}\,\mathrm{s}^{-1}$), systemic (3.58 –
5.02 ${km}\,\mathrm{s}^{-1}$), and redshifted (5.2 – 11.32
${km}\,\mathrm{s}^{-1}$). Figure 6 displays a velocity integration between
2.14 and 11.32 ${km}\,\mathrm{s}^{-1}$. There are two notable features in this
figure, the first being the concentration of envelope material around the
central binary system, and a cloud of material north of the binary. The former
feature illustrates outflow material and the stellar envelope near systemic
velocities, while the latter is indicative of interactions between the stellar
envelope and the secondary northern outflow cavity.

Figure 6: A moment-0 map of 13CO emission as observed by the ALMA combination
array, and integrated between 2.14 and 11.32 ${km}\,\mathrm{s}^{-1}$. White
contours representing 232.5 GHz continuum emission are shown at the centre of
the frame at levels of 0.25 and 0.75 times the maximum intensity of 0.11
Jy/beam. The synthesized beam is shown in the bottom left of the frame with a
size of 1.77 $\times$ 1.30 arcseconds, and a position angle of -72.3$\degr$.
In addition, the continuum beam is shown in green in the top left corner, and
maintains a size of 1.50 $\times$ 1.07 arcseconds and a position angle of
-66.8$\degr$.

In order show how 13CO detections change across a range of velocity channels,
Figure 7 displays emission between 2.14 and 11.32 ${km}\,\mathrm{s}^{-1}$ with
spacing of 0.54 ${km}\,\mathrm{s}^{-1}$.

Figure 7: A channel map of 13CO emission detected between 2.14 and 11.32
${km}\,\mathrm{s}^{-1}$, with each frame at a velocity spacing of 0.54
${km}\,\mathrm{s}^{-1}$. The white contours at the centre of each frame
represent continuum emission centered at 232.5 GHz at levels of 0.25 and 0.75
the maximum detected intensity of 0.11 Jy/beam. The synthesized beam is shown
as a white ellipse in the bottom left of each frame, and has an angular size
and position angle of 1.77 $\times$ 1.30 arcseconds and -72.3$\degr$,
respectively. The continuum beam is shown in the top left by a green ellipse
with an angular size of 1.50 $\times$ 1.07 arcseconds and a position angle of
-66.8$\degr$

Firstly, blueshifted emission at velocities between 2.14 and 3.4
${km}\,\mathrm{s}^{-1}$ traces an interaction between the western arm of the
southern outflow and material from the stellar envelope. Emission in this
region shifts from the southwest towards the northeast with increasing size as
velocity approaches the systemic value. 13CO emission also takes the shape of
the southern outflow as traced with 12CO at 3.04 and 3.22
${km}\,\mathrm{s}^{-1}$, indicating that envelope material is entrained within
the wide-angle wind of the outflow, a conclusion consistent with observations
from RR17. A wing of emission is also seen on HBC 494’s western side at these
velocities, although there is no overlap between either of the primary
outflows and this wing at blueshifted, systemic, or redshifted velocities. As
mentioned in section 3.1, the western arm of the southern outflow shows much
less extension than its eastern counterpart, specifically at velocities where
13CO detections are prominent, meaning that the stellar envelope could be
obfuscating it from view. Alternatively, a compact region of 13CO could be
entrained in this arm of the outflow, thus making it appear as a clump rather
than mirroring the shape of the eastern arm.

Near systemic velocities ($4.3\pm 0.7$ ${km}\,\mathrm{s}^{-1}$), 13CO
continues to trace envelope motion, extending further towards the northeast
approaching redshifted velocities. Interactions between each of the primary
outflows and the stellar envelope may also be accentuating this feature at the
extremes of this velocity range. 13CO emission reaches its largest angular
area within this velocity range at approximately $50\arcsec\times 50\arcsec$.
Starting at 4.48 ${km}\,\mathrm{s}^{-1}$, along with rotating envelope
emission in the northwest, 13CO takes the shape of the primary cavity as
observed with 12CO. This continues up to 6.82 ${km}\,\mathrm{s}^{-1}$ when
13CO emission dissipates and the envelope is no longer detected. Significant
interactions between the secondary cavity and envelope material are also
observed upwards of 8.8 ${km}\,\mathrm{s}^{-1}$.

A ‘wave’ of emission propagates upwards at increasing velocities, which most
likely represents envelope material entrained in the secondary outflow’s wind.
13CO emission entrained in both the primary and secondary northern outflow
cavities maintains a much larger opening angle in comparison to material
entrained at blueshifted velocities, possibly due to an interaction between
the outflows of HBC 494a and HBC 494b.

###  3.3 C18O observations

We produced a combination array C18O data cube encompassing velocities
identical to those in the 13CO data cube, again using a channel width of 0.18
${km}\,\mathrm{s}^{-1}$. Because they both trace the stellar envelope, as well
as interactions between the envelope and outflow cavities, C18O exhibits very
similar detection velocities to 13CO. Emission is detected between 2.32 and
11.14 ${km}\,\mathrm{s}^{-1}$, with the most intense and extended detections
observed near systemic velocity (Fig. 8).

Figure 8: A channel map of C18O emission detected between 2.14 and 11.32
${km}\,\mathrm{s}^{-1}$, with each frame at a velocity spacing of 0.54
${km}\,\mathrm{s}^{-1}$. The white contours at the centre of each frame
represent continuum emission centred at 232.5 GHz at levels of 0.25 and 0.75
the maximum detected intensity of 0.11 Jy/beam. The synthesised beam is shown
as a white ellipse in the bottom left of each frame, and has an angular size
and position angle of 1.78 $\times$ 1.28 arcseconds and -74.6$\degr$,
respectively. The continuum beam is shown in the top left by a green ellipse
with an angular size of 1.50 $\times$ 1.07 arcseconds and a position angle of
-66.8$\degr$

Blueshifted emission at velocities between 2.86 and 3.4
${km}\,\mathrm{s}^{-1}$ traces the motion of the stellar envelope envelope, as
well as material entrained by the eastern arm of the primary southern outflow.
Emission in this velocity range also shows the wing of material directly west
of HBC 494 observed with 13CO, although with less extension and intensity –
most likely due to C18O tracing high-density regions of the envelope. Near
systemic velocities, C18O is able to trace the shape of the stellar envelope.
Specifically, channels with velocities between 4.12 and 5.02
${km}\,\mathrm{s}^{-1}$ show the greatest extension of the envelope, as well
as a strong resemblance to 13CO emission in the same velocity range.

Interactions between high-density envelope regions and the primary northern
outflow are traced at 5.02 – 6.28 ${km}\,\mathrm{s}^{-1}$. Material present at
5.02 ${km}\,\mathrm{s}^{-1}$ forms into bands that appear on either side of
HBC 494 and propagate upwards with increased intensity as channel velocity
increases to 5.92 ${km}\,\mathrm{s}^{-1}$. At this velocity, the bands
coalesce into a clump of material which is visible up to 6.28
${km}\,\mathrm{s}^{-1}$. This clump of material is also seen in the same
velocity range in 12CO and 13CO images, and is likely due to the mixing of two
different outflows with differing position angles. This phenomenon is
discussed further in section 5.3. This clump, as well as the bands of
material, are also seen in 13CO observations in the same velocity range,
although with greater overall extension and higher intensity compared to C18O
(Fig. 9).

Figure 9: Two individual channel maps of C18O (left) and 13CO (right) emission
between channel velocities of 5.02 and 5.92 ${km}\,\mathrm{s}^{-1}$. The white
contours at the centre of each frame represent continuum emission centred at
232.5 GHz at levels of 0.25 and 0.75 times the maximum detected intensity of
0.11 Jy/beam. The green ellipse in the top left of each frame represents the
continuum beam, which has an angular size of 1.50 $\times$ 1.07 arcseconds and
a position angle of -66.8$\degr$. The white ellipses visible in the bottom
left of each frame in the left and right images represent the C18O and 13CO
synthesised beams, respectively. The former has an angular size of 1.78
$\times$ 1.28 arcseconds and a position angle of -74.6$\degr$, while the
latter maintains an angular size of 1.77 $\times$ 1.30 arcseconds and a
position angle of -72.3$\degr$.

These bands are also detected with nearly identical shapes from 9.34 to 9.88
${km}\,\mathrm{s}^{-1}$, although with much lower intensity (Fig. 21).

###  3.4 SO observations

SO traces shocked material (e.g. Jørgensen et al., 2004), with detections
present from 1.6 up to 10.6 ${km}\,\mathrm{s}^{-1}$. To map these detections,
we created a data cube with the same velocity range as the three prior
isotopologues (-20 – 33.82 ${km}\,\mathrm{s}^{-1}$) with a channel width of
0.18 ${km}\,\mathrm{s}^{-1}$. SO is able to trace the central object, as well
as certain portions of the secondary northern outflow cavity.

Beginning with the former, emission is present in two distinct velocity
ranges: 1.6 to 5.02 ${km}\,\mathrm{s}^{-1}$, and 6.1 to 9.52
${km}\,\mathrm{s}^{-1}$ (Figs. 22 $\&$ 23). At the front end first range SO
appears as a small lobe at the southwest of HBC 494, which grows in both size
and intensity as channel velocity approaches the systemic value. Additionally,
SO shifts from the southwest to the northeast, similar to the motion of 13CO
and C18O in this velocity range.

At 3.58 ${km}\,\mathrm{s}^{-1}$ two distinct lobes form with a position angle
near that of HBC 494’s constituent objects, and are present up to 4.3
${km}\,\mathrm{s}^{-1}$ (Nogueira et al., 2023). However, these lobes do not
align with continuum observations of the circumstellar disc, either in their
position or separation. HBC 494a and HBC 494b maintain a separation of
approximately 75 au (Nogueira et al., 2023), while the observed SO lobes are
separated on average by 830 au. The lobes are also displaced to the south of
HBC 494 in all velocity channels where they are intense enough to be seen
despite their northeastward motion. Figure 10 shows a channel map of SO
emission between 1.6 and 4.3 ${km}\,\mathrm{s}^{-1}$, and illustrates the
velocity evolution of the aforementioned lobes as well as their displacement
from continuum observations.

Figure 10: An individual channel map of SO emission between velocities of 1.6
and 4.3 ${km}\,\mathrm{s}^{-1}$. The white contours at the centre of each
frame represent continuum emission centred at 232.5 GHz, and are shown at
levels of 0.25 and 0.75 times the maximum detected intensity of 0.11 Jy/beam.
The SO synthesised beam and continuum emission beam are shown in the bottom
and top left of each frame, respectively. The former maintains a size and
position angle of 1.81 $\times$ 1.28 arcseconds and -72.3$\degr$, while the
latter has a size of 1.50 $\times$ 1.07 arcseconds and a position angle of
-66.8$\degr$.

SO emission in this velocity range is also spatially coincident with intense
13CO regions, suggesting that envelope interactions could be responsible for
the asymmetric distribution of SO near the disc (Fig. 24). The SO emission
shapes shown in the prior two figures are also present from 6.1 to 9.7
${km}\,\mathrm{s}^{-1}$, although with lower intensity and extension. In
addition to mimicking emission seen in the prior velocity range, SO emission
in these channels also closely resembles 13CO surrounding the central binary,
again with lower intensity and extension.

As for the secondary northern outflow cavity, detections are present in two
distinct velocity ranges: 5.02 to 6.28 ${km}\,\mathrm{s}^{-1}$ and 9.34 to
10.6 ${km}\,\mathrm{s}^{-1}$. In both of these ranges SO primarily traces the
eastern portion of the cavity, with very limited emission present on the
western side (Fig. 11).

Figure 11: Two channel maps of SO emission between 5.2 and 6.1
${km}\,\mathrm{s}^{-1}$ (left) and 9.7 and 10.6 ${km}\,\mathrm{s}^{-1}$
(right). Shown in the centre of each frame are white contours which represent
continuum emission, and are at levels of 0.25 and 0.75 times the maximum
detected intensity of 0.11 Jy/beam. The bottom and top left of each frame also
show the synthesized and continuum beams, respectively. The former has an
angular size of 1.81 $\times$ 1.28 arcseconds and a position angle of
-72.3$\degr$, while the latter has an angular size of 1.50 $\times$ 1.07
arcseconds and a position angle of -66.8$\degr$.

The outflow regions traced by SO are also highlighted by 13CO and C18O in the
same velocity channels, suggesting that SO surrounding the circumstellar disc
may have been entrained in the wind of a previous accretion outburst.

###  3.5 P-V Diagrams

In order to scrutinise the kinematics and spatial distribution of the detected
molecules tracing the bipolar lobes, we build Position-Velocity (P-V) diagrams
perpendicular to the position of the binary system, and along the outflow axis
traced by the blueshifted 12CO emission, i.e., position angles (P.A.) of $\sim
35\degr$, and $\sim 145\degr$, respectively. The position angles used for the
cuts are shown in Figure 12.

Figure 12: The moment-0 map displayed in Figure 2c with two overlaid P.A.
lines. These lines represent the cuts used to generate the P-V diagrams shown
in Figures 13 and 14.

Figure 13 displays the resulting P-V diagram cuts perpendicular to the
position of the binary system. 12CO clearly traces material characteristic of
outflow/infall motions near the central binary system (e.g. Tobin et al.,
2012) with strong blueshifted emission self-absorbed, and an extended emission
detected in the velocity range 4.3 $\leq$ Vsys $\leq$ 6.0 km s-1. The latter
feature is associated with emission from the secondary northern cavity. On the
other hand, the 13CO P-V diagram displays mainly Keplerian velocities that may
be associated with winds or material close to and interacting with the binary
star. In Fig. 13, the dashed white lines represent the expected Keplerian
velocities for a system of 8 M☉ at an inclination of $\sim 65\degr$, a
distance to the object of 414 pc, and a Vsys of $\sim$ 4.3 km s-1 (RR17).
These Keplerian curves place an upper limit of 8 M☉ for the central stellar
masses, HBC 494a and HBC 494b. In addition, and similar to 12CO, an extended
13CO feature is extracted along a position angle of $\sim 35\degr$. In a
similar way to 13CO, and with expected higher densities, C18O emission traces
a combination of rotating and envelope/outflow material as seen in Fig. 13c.
With a more compacted extension, SO emission displays outflowing velocities
tracing material towards the central object together with an extra redshifted
component that belongs to ejected material.

The most striking feature of the P-V diagram analysis is the extent of the
13CO and SO emission detected as a positive spatial offset ($\sim$ 4.3 km s-1
– redshifted emission). The blue dashed lines in Fig. 13b display Keplerian
velocities generated with similar parameters as described above except for a
positive offset of $\sim$ 4.3 km s-1 added in the final outcome. The velocity
components of 13CO and SO trace a similar region where the expelled material
possibly – after a massive and powerful outburst – preserved rotational motion
while expanding. The lack of a symmetric infall signature at a negative offset
may come from asymmetrical infall and non-uniformity of the molecular cloud.

The P-V cuts also reveal a systematic velocity difference between symmetric
positions from the central binary system axis and the secondary northern
cavity. Figure 14 displays P-V diagrams of the 12CO, 13CO, and C18O emission
extracted along a position angle of $\sim 145\degr$, i.e., along the outflow
axis traced by blueshifted emission (RR17). It is worth noting that there is a
redshifted feature that extends toward the northwestern direction from an
offset of $\sim$ 10$\arcsec$ to $\sim$ 20$\arcsec$ with a velocity range
between $\sim$ 4.5 and 5.5 km s-1. This elongated feature, which is indicated
in Fig. 14 with a magenta arrow, is associated with emission from the
secondary northern cavity. This suggests that either the molecular outflows
exhibit intermittency or a molecular flow that erupted in two distinct epochs.

Also, the position and velocity gradients suggest that the redshifted 12CO,
13CO, and C18O emission traces an overlapping of two northern lobes (the
redshifted lobe) with different position angles. It means that it is possible
that HBC 494a and HBC 494b are associated with molecular outflows with
different rotational axes and opening angles. Inspection of individual
channels in the data cubes shows that 12CO and 13CO lines likely trace
misaligned outflows with rotational axes of 35$\degr$ and 145$\degr$.
Nevertheless, it is difficult to evaluate and separate the amount of molecular
emission corresponding to each lobe of the bipolar outflows.

Figure 13: P-V diagrams of the 12CO, 13CO, C18O, and SO emission obtained
perpendicular to the binary system, i.e., P.A. $\sim 35\degr$.

Figure 14: P-V diagrams of the 12CO, 13CO, and C18O emission obtained along
the outflow rotational axis of P.A. $\sim 145\degr$

##  4 Analysis

###  4.1 Outflow kinematics

Because observations recorded with the combination array are able to detect
large-scale emission more effectively than main array observations alone, we
are able to more accurately determine the kinematic and dynamical properties
of HBC 494’s outflows. In order to determine the mass, momentum, kinetic
energy, and luminosity of each primary outflow, as well as the secondary
northern cavity, we make use of techniques detailed in Dunham et al. (2014)
and references therein. Our calculations incorporate the H2 column density
$N_{$\mathrm{H}_{2}$}$, mean molecular weight per hydrogen molecule
$\mu_{$\mathrm{H}_{\mathrm{2}}$}$ (assumed to be 2.8 for a gas composed of
71$\%$ hydrogen, 27$\%$ helium, and 2$\%$ metals by mass), the mass of a
hydrogen atom $m_{$\mathrm{H}$}$, and the area per pixel
$A_{$\mathrm{p}\mathrm{x}$}$, to calculate the mass per pixel per velocity
channel $M_{$\mathrm{v}\mathrm{,}\mathrm{p}\mathrm{x}$}$:

$M_{$\mathrm{v}\mathrm{,}\mathrm{p}\mathrm{x}$}=N_{$\mathrm{H}_{\mathrm{2}}$}m_{$\mathrm{H}$}\mu_{$\mathrm{H}_{\mathrm{2}}$}A_{$\mathrm{p}\mathrm{x}$}.$
(1)

Column density values are calculated using the methods described in Dunham et
al. (2014) appendix C. Specifically, we use the CO column density
$N_{$\mathrm{C}\mathrm{O}$}$, and an abundance ratio of CO relative to H2 of
$X_{$\mathrm{C}\mathrm{O}$}=10^{-4}$ to infer $N_{$\mathrm{H}_{2}$}$. The
CO/H2 abundance ratio is based on the 13CO/H2 ratio of $2\times 10^{-6}$
provided in Ripple et al. (2013), and then scaled to CO using the 12CO/13CO
ratio of 62 from Langer & Penzias (1993). This CO/H2 abundance is consistent
with other publications using the same analysis procedures (e.g. Hsieh et al.,
2023; Plunkett et al., 2015). The $N_{$\mathrm{C}\mathrm{O}$}$ calculation is
also dependent on the excitation temperature of CO,
$T_{$\mathrm{e}\mathrm{x}$}$. We performed one set of calculations using
$T_{$\mathrm{e}\mathrm{x}$}=20$ K, and another using
$T_{$\mathrm{e}\mathrm{x}$}=50$ K, as these temperatures best represent HBC
494’s outflows and allow for straightforward comparison between this work and
RR17. The total mass of each outflow is then calculated by integrating
$M_{$\mathrm{v}\mathrm{,}\mathrm{p}\mathrm{x}$}$ across all pixels and
velocities in which outflow emission is detected above a 3$\sigma$ threshold.

Analogous to their respective classical calculations, the momentum and kinetic
energy of each pixel in a given velocity channel are given by

$P_{$\mathrm{v}\mathrm{,}\mathrm{p}\mathrm{x}$}=M_{$\mathrm{v}\mathrm{,}\mathrm{p}\mathrm{x}$}|v-v_{$\mathrm{s}\mathrm{y}\mathrm{s}$}|$
(2)

and

$K_{$\mathrm{v}\mathrm{,}\mathrm{p}\mathrm{x}$}=\frac{1}{2}M_{$\mathrm{v}\mathrm{,}\mathrm{p}\mathrm{x}$}|v-v_{$\mathrm{s}\mathrm{y}\mathrm{s}$}|^{2}$
(3)

where again integrating over all relevant pixels and channels produces the
total momentum and kinetic energy of the outflow (Plunkett et al., 2015). In
addition, we make estimates of the characteristic extension and velocity for
the northern and southern outflows. To determine the characteristic extension
for an outflow, we average the length of multiple prominent features, namely
the emission wings, cavity filling material, and other emission swept away
from the ambient cloud. After accounting for all of these features, we find
that the blueshifted outflow has a characteristic extension of 17$\arcsec$,
while the redshifted outflow has an extension of 20$\arcsec$. The
characteristic velocity is equal to the momentum of the outflow divided by its
mass ($V_{$\mathrm{c}\mathrm{h}\mathrm{a}\mathrm{r}$}=P/M$). With these values
in place, the dynamical age of each outflow can be found with
$T_{$\mathrm{d}\mathrm{y}\mathrm{n}$}={R_{$\mathrm{c}\mathrm{h}\mathrm{a}\mathrm{r}$}}/{V_{$\mathrm{c}\mathrm{h}\mathrm{a}\mathrm{r}$}}$.
Finally, we provide estimates for outflow mass-loss rate
($\dot{M}=M/T_{$\mathrm{d}\mathrm{y}\mathrm{n}$}$), luminosity
($L=K/T_{$\mathrm{d}\mathrm{y}\mathrm{n}$}$), and force
($F=\dot{M}/V_{$\mathrm{c}\mathrm{h}\mathrm{a}\mathrm{r}$}$).

To isolate all relevant outflow emission, kinematic and dynamical variable
calculations made use of two regions: one encompassing the southern outflow at
blueshifted velocities, and one encompassing the northern outflow at
redshifted velocities. These regions also serve to exclude emission from HBC
494’s disc. Furthermore, velocity channels which showed no emission from
either the blueshifted or redshifted outflow, or which showed significant
ambient cloud contamination, were excluded from calculations. Velocity
channels between -8.3 and 2.32 ${km}\,\mathrm{s}^{-1}$ were integrated for
blueshifted outflow calculations, and channels between 7.0 and 23.56
${km}\,\mathrm{s}^{-1}$ were integrated for redshifted outflow calculations.

###  4.2 Corrections

####  4.2.1 Opacity

Due to 12CO and 13CO being optically thick near systemic velocity, outflow
masses and other dynamical properties can be underestimated if optical depth
effects are not properly accounted for. Using methods detailed in Dunham et
al. (2014), Zhang et al. (2016), and Hsieh et al. (2023), we first correct the
optical depth of the 13CO line using C18O, and then use the corrected 13CO
data to correct 12CO. The calculations necessary for these corrections are
prefaced by the assumptions that excitation temperature and beam-filling
factors are equivalent for each of the three lines, and that all emission is
in local thermal equilibrium (LTE). With a dipole moment of 0.11D, CO is
easily thermalized, and thus follows a Boltzmann distribution (Scuseria et
al., 1991). Due to this easy thermalization, it is valid to assume that 12CO,
13CO, and C18O have identical excitation temperatures and are in LTE, which
greatly simplifies column density calculations. The 13CO correction process
begins by determining the ratio of the mean brightness temperature between
13CO and C18O, which can be stated as the following:

$\frac{T_{$\mathrm{m}\mathrm{b}\mathrm{,}\mathrm{1}\mathrm{3}$}(v)}{T_{$\mathrm{m}\mathrm{b}\mathrm{,}\mathrm{1}\mathrm{8}$}(v)}=\frac{1-\exp(-\tau_{v,13})}{1-\exp(-\tau_{v,18})}.$
(4)

$T_{$\mathrm{m}\mathrm{b}\mathrm{,}\mathrm{1}\mathrm{3}$}$ and
$T_{$\mathrm{m}\mathrm{b}\mathrm{,}\mathrm{1}\mathrm{8}$}$ are the brightness
temperatures of 13CO and C18O respectively, while $\tau_{v,13}$ and
$\tau_{v,18}$ represent the respective opacities of the two isotopologues. As
opposed to 12CO and 13CO, C18O is generally found to be optically thin (Kong
et al., 2018), and thus the brightness temperature ratio can be approximated
to

$\frac{T_{${mb,13}$}(v)}{T_{${mb,18}$}(v)}=X_{13,18}\frac{1-\exp(-\tau_{v,13})}{\tau_{v,13}}$
(5)

in which X13,18 is the abundance ratio of 13CO to C18O, and is taken to be 8.7
in accordance with Wilson & Matteucci (1992). Equation 5 can then be
rearranged to produce the 13CO correction factor, $C(v)_{13}$:

$C(v)_{13}=\frac{\tau_{v,13}}{1-\exp(\tau_{v,13})}\approx
X_{13,18}\frac{T_{$\mathrm{m}\mathrm{b}\mathrm{,}\mathrm{1}\mathrm{8}$}(v)}{T_{$\mathrm{m}\mathrm{b}\mathrm{,}\mathrm{1}\mathrm{3}$}(v)}.$
(6)

This factor stems from the formula for calculating column density as a
function of brightness temperature

$N_{2}=\frac{1}{\beta}\frac{8\pi
k{\nu^{2}}}{A_{21}hc^{3}}\int{T_{$\mathrm{B}$}dv}$ (7)

in which the correction factor is given by $\beta$ (Williams, 2021):

$\beta=\frac{1-\exp(-\tau_{\nu})}{\tau_{\nu}}.$ (8)

The corrected 13CO line is generated by multiplying the original line by the
correction factor across corresponding velocity channels such that
$T_{$\mathrm{m}\mathrm{b}\mathrm{,}\mathrm{1}\mathrm{3}$}(v)^{\prime}\equiv{C(v)_{13}T_{$\mathrm{m}\mathrm{b}\mathrm{,}\mathrm{1}\mathrm{3}$}(v)}$.
The new 13CO data cube is now representative of optically thin emission, and
can then be used to correct the 12CO line. Specifically, this method can be
replicated with 12CO in place of the uncorrected 13CO line, the corrected 13CO
line in place of C18O line, and an abundance ratio of
$X_{$\mathrm{1}\mathrm{2}\mathrm{,}\mathrm{1}\mathrm{3}$}=62$ to produce the
final opacity-corrected 12CO data cube.

In order to calculate the brightness temperature ratio for a given velocity
channel, all emission was first masked above 3$\sigma$ in order to increase
the channel’s signal-to-noise ratio and prevent division by small values. Once
masked, pixel-wise division was performed in corresponding velocity channels
to determine the brightness temperature ratio for two given spectral lines. In
order to calculate the weighted mean and standard deviation of the brightness
temperature ratios in each channel we applied the weighting scheme described
in Zhang et al. (2016). To properly incorporate high signal-to-noise pixels
into the correction process, weights followed an inverse-squared
proportionality to the uncertainty in the brightness temperature ratio for
each pixel within a channel. Once weighting was applied to each pixel, the
average brightness temperature ratio for each channel was determined through
the weighted mean, with uncertainty given by the weighted standard deviation.
To determine the brightness temperature ratio, and thus the optical depth, for
13CO in channels where C18O was not prominent, we fit a second order
polynomial to channels near systemic velocity in which 13CO is optically thick
(Fig. 15).

Figure 15: The weighted mean brightness temperature ratio between 13CO and
C18O as a function of $v-v_{$\mathrm{s}\mathrm{y}\mathrm{s}$}$. Each blue
point represents those considered in the fitting process, while those in red
were not included due to improper optical depth in 13CO. The data points used
to generate the orange parabola encompass velocities between -1.14 and 1.02
${km}\,\mathrm{s}^{-1}$.

The fit used is

$\frac{T_{13}}{T_{18}}=(1.96\pm 0.27)+(1.76\pm
0.61)(v-v_{$\mathrm{s}\mathrm{y}\mathrm{s}$})^{2}$ (9)

which has a reduced $\chi^{2}$ value of 0.08. The same process was performed
with 12CO and the opacity-corrected 13CO line. A strong self absorption
feature present in low velocity 12CO channels makes
$\frac{T_{$\mathrm{m}\mathrm{b}\mathrm{,}\mathrm{1}\mathrm{2}$}}{T_{$\mathrm{m}\mathrm{b}\mathrm{,}\mathrm{1}\mathrm{3}$}}$
a poor indicator of optical depth. To avoid the impacts of these self-absorbed
channels we exclude emission at velocities between 3.22 and 5.02
${km}\,\mathrm{s}^{-1}$ from the $\frac{T_{12}}{T_{13}^{\prime}}$ fitting
process. This exclusion process resulted in the best-fitting polynomial

$\frac{T_{12}}{T_{13}^{\prime}}=(0.24\pm 0.22)+(0.45\pm
0.07)(v-v_{$\mathrm{s}\mathrm{y}\mathrm{s}$})^{2}$ (10)

with a reduced $\chi^{2}$ value of 0.12 (Fig. 16). The fits for both sets of
spectral lines are truncated at their respective abundance ratios, meaning
that the correction factors for 13CO and 12CO have a lower limit of 1.

Figure 16: The weighted mean brightness temperature ratio between 12CO and
opacity-corrected C13O as a function of
$v-v_{$\mathrm{s}\mathrm{y}\mathrm{s}$}$. Again, points in blue represent
those used in the fitting process, while those in red were excluded. Points
used to generate the fit encompass velocity channels between -3.48 and 2.82
${km}\,\mathrm{s}^{-1}$.

####  4.2.2 Inclination

In addition to opacity corrections, we also take the inclination of HBC 494
into account when calculating variable estimates, as without them such values
can be underestimated by up to factors of 2. Ideally, inclination can be
determined using the ratio of the disc’s major axis to its minor axis;
however, this technique assumes that the disc is circular, flat, and thin
(Hsieh et al., 2023). Due to its binary nature, and the fact that the
observations used in this analysis do not resolve HBC 494’s individual
components, we were unable to make use of this technique. However, the high-
resolution images presented in Nogueira et al. (2023) are able to effectively
resolve both objects in the binary, and thus we take HBC 494a’s reported
inclination ($i=37.16\degr$) to be the inclination of the system. We apply a
series of inclination-based corrections using the trigonometric relationships
provided in Dunham et al. (2014), which are shown in Table 3 alongside the
optical depth correction factors. The results of these two correction
processes are listed in Table 4.

Table 3: Inclination and opacity correction factors. Property |  Inclination Dependence |  Incl. Correction Factor $i=37.16\degr$ | Opacity Correction Factors | Combined Correction Factor
---|---|---|---|---
Blueshifted | Redshifted | Blueshifted | Redshifted
Outflow Mass | N/A | N/A | 14.3 | 7.6 | 14.3 | 7.6
Mass-loss rate | $\sin{i}/\cos{i}$ | 0.80 | 9.5 | 6.0 | 7.6 | 4.5
Outflow Momentum | $1/\cos{i}$ | 1.3 | 10.1 | 6.1 | 12.5 | 7.8
Outflow Kinetic energy | $1/\cos^{2}{i}$ | 1.6 | 6.0 | 4.3 | 9.5 | 6.8
Outflow Luminosity | $\sin{i}/\cos^{3}{i}$ | 1.2 | 3.8 | 3.4 | 4.5 | 4.0
Outflow Force | $\sin{i}/\cos^{2}{i}$ | 0.95 | 7.0 | 4.8 | 6.6 | 4.4
Characteristic Velocity | $1/\cos{i}$ | 1.3 | 0.7 | 0.8 | 0.8 | 1.0
Characteristic Extension | $1/\sin{i}$ | 1.7 | N/A | N/A | 1.7 | 1.7
Dynamical Time | $\cos{i}/\sin{i}$ | 1.3 | 1.4 | 1.3 | 1.9 | 1.6
Table 4: Outflow properties according to excitation temperature using Cycle-5
data.

Excitation Temperature | Property | Blueshifteda | Redshiftedb | Units
---|---|---|---|---
Uncorr.c | Incl.d | Opacity + Incl.e | Uncorr. | Incl. | Opacity + Incl.
| Mass | 2.1 | 2.1 | 30 | 3.7 | 3.7 | 28 |  $10^{-3}\,$M☉
20 K | Mass loss rate | 2.1 | 1.6 | 16 | 5.5 | 4.1 | 25 |  $10^{-7}\,$M${}_{\sun}\,$yr-1
Momentum | 0.83 | 1.0 | 10 | 1.8 | 2.3 | 14 |  $10^{-2}\,$M${}_{\sun}\,${km}\,\mathrm{s}^{-1}$$
Kinetic energy | 4.3 | 6.8 | 41 | 11 | 18 | 77 |  $10^{41}\,$ergs
Luminosity | 0.36 | 0.43 | 1.8 | 1.4 | 1.7 | 5.6 |  $10^{-4}\,$L☉
Force | 0.84 | 0.80 | 5.3 | 2.7 | 2.6 | 13 |  $10^{-6}\,$M${}_{\sun}\,${km}\,\mathrm{s}^{-1}\,\mathrm{y}\mathrm{r}^{-1}$$
Char. Velocity | 4.0 | 5.0 | 3.4 | 5.0 | 6.3 | 4.9 | ${km}\,\mathrm{s}^{-1}$
Char. Extension | 0.04 | 0.07 | 0.07 | 0.03 | 0.06 | 0.06 | pc
| Dynamical Time | 9.8 | 13 | 19 | 6.7 | 8.9 | 11 |  $10^{3}$ yr
| Mass | 3.7 | 3.7 | 53 | 6.6 | 6.6 | 51 |  $10^{-3}\,$M☉
50 K | Mass loss rate | 3.8 | 2.8 | 28 | 9.8 | 7.4 | 45 |  $10^{-7}\,$M${}_{\sun}\,$yr-1
Momentum | 1.5 | 1.9 | 18 | 3.3 | 4.1 | 25 |  $10^{-2}\,$M${}_{\sun}\,${km}\,\mathrm{s}^{-1}$$
Kinetic energy | 7.7 | 12 | 74 | 20.2 | 32 | 140 |  $10^{41}\,$ergs
Luminosity | 0.65 | 0.77 | 3.2 | 2.5 | 3.0 | 10 |  $10^{-4}\,$ L☉
Force | 1.5 | 1.4 | 9.5 | 4.9 | 4.7 | 22 |  $10^{-6}\,$M${}_{\sun}\,${km}\,\mathrm{s}^{-1}\,\mathrm{y}\mathrm{r}^{-1}$$
Char. Velocity | 4.0 | 5.0 | 3.4 | 5.0 | 6.3 | 4.9 | ${km}\,\mathrm{s}^{-1}$
Char. Extension | 0.04 | 0.07 | 0.07 | 0.03 | 0.06 | 0.06 | pc
| Dynamical Time | 9.8 | 13 | 19 | 6.7 | 8.9 | 11 |  $10^{3}$ yr

  * a

Emission integrated between -8.3 and 2.32 ${km}\,\mathrm{s}^{-1}$.

  * b

Emission integrated between 7.0 and 23.56 ${km}\,\mathrm{s}^{-1}$.

  * c

Variable calculations performed with neither inclination nor opacity
corrections.

  * d

Inclination-corrected properties based on an angle of $i=37.16\degr$.

  * e

Properties with inclination and opacity corrections applied.

##  5 Discussion

###  5.1 Comparison of parameter estimations and observations

When comparing the results presented in this work to those using the Cycle-2
observations, it is crucial to recognize the differences between the observing
cycles and analysis techniques used here and in RR17. Starting with the
differences in analysis techniques, the most notable change is the inclusion
of 13CO opacity corrections using the 13CO/C18O brightness temperature ratio.
Along with correcting the 13CO data cube, we also use a different scheme to
isolate the additional 12CO outflow emission brought on by the Cycle-5 field
of view. Prior work used a mask to remove all emission from the central
binary, but included all pixels encompassing both outflows. This method relies
on a careful choice of velocity channel integration ranges so as to not
include emission from the redshifted outflow in calculations involving the
blueshifted outflow, and vice-versa. This method does not work in our case, as
the larger Cycle-5 field of view introduces material that is unrelated to
either of the outflows in multiple velocity channels. This being the case, it
was necessary to create masks to remove emission not related to the outflows.
To generate the masks used in our analysis, we constructed two 12CO moment-0
maps using the integration ranges described in section 4.1 and created regions
which excluded emission from the central binary and only encompassed each
individual outflow. Additionally, RR17 used a 12CO/H2 abundance ratio of
$X_{$\mathrm{C}\mathrm{O}$}=5.6\times 10^{-6}$, while we adopt the value
$X_{$\mathrm{C}\mathrm{O}$}=1\times 10^{-4}$ for our analysis. We also make
use of the inclination correction process described in Plunkett et al. (2015),
while the inclination of HBC 494 was not considered in RR17.

For simplicity, and to directly compare the Cycle-2 and Cycle-5 observations,
we applied the analysis techniques discussed in section 4 to the Cycle-2 12CO
(J=2-1), 13CO (J=2-1), and C18O (J=2-1) data cubes. Details of this
observation program can be found in RR17 section 2. We adopt the velocity
integration limits from RR17, using channels between -5.25 and 1.5
${km}\,\mathrm{s}^{-1}$ for the blueshifted outflow and channels between 7.0
and 16.5 ${km}\,\mathrm{s}^{-1}$ for the redshifted outflow. The results of
this analysis are shown in Table 5.

Table 5: Outflow properties according to excitation temperature using Cycle-2
data.

Excitation Temperature | Property | Blueshifteda | Redshiftedb | Units
---|---|---|---|---
Uncorr.c | Incl.d | Opacity + Incl.e | Uncorr. | Incl. | Opacity + Incl.
| Mass | 0.34 | 0.34 | 7.9 | 0.43 | 0.43 | 7.8 |  $10^{-3}\,$M☉
20 K | Mass loss rate | 0.68 | 0.52 | 10.1 | 1.7 | 1.3 | 18.0 |  $10^{-7}\,$M${}_{\sun}\,$yr-1
Momentum | 0.17 | 0.22 | 4.3 | 0.27 | 0.34 | 4.7 |  $10^{-2}\,$M${}_{\sun}\,${km}\,\mathrm{s}^{-1}$$
Kinetic energy | 1.0 | 1.6 | 25 | 2.0 | 3.2 | 32 |  $10^{41}\,$ergs
Luminosity | 0.17 | 0.20 | 2.7 | 0.7 | 0.8 | 6.1 |  $10^{-4}\,$L☉
Force | 0.35 | 0.34 | 5.5 | 1.1 | 1.1 | 11 |  $10^{-6}\,$M${}_{\sun}\,${km}\,\mathrm{s}^{-1}\,\mathrm{y}\mathrm{r}^{-1}$$
Char. Velocity | 5.2 | 6.5 | 5.4 | 6.3 | 8.0 | 6.0 | ${km}\,\mathrm{s}^{-1}$
Char. Extension | 0.03 | 0.04 | 0.04 | 0.02 | 0.03 | 0.03 | pc
| Dynamical Time | 5.0 | 6.5 | 7.9 | 2.5 | 3.3 | 4.3 |  $10^{3}$ yr
| Mass | 0.60 | 0.60 | 14 | 0.77 | 0.77 | 14 |  $10^{-3}\,$M☉
50 K | Mass loss rate | 1.2 | 0.93 | 18.1 | 3.1 | 2.4 | 32.3 |  $10^{-7}\,$M${}_{\sun}\,$yr-1
Momentum | 0.31 | 0.39 | 7.7 | 0.49 | 0.61 | 8.4 |  $10^{-2}\,$M${}_{\sun}\,${km}\,\mathrm{s}^{-1}$$
Kinetic energy | 1.8 | 2.8 | 45 | 3.6 | 5.7 | 57 |  $10^{41}\,$ergs
Luminosity | 0.30 | 0.35 | 4.8 | 1.2 | 1.4 | 11 |  $10^{-4}\,$ L☉
Force | 0.64 | 0.60 | 9.8 | 2.0 | 1.9 | 19 |  $10^{-6}\,$M${}_{\sun}\,${km}\,\mathrm{s}^{-1}\,\mathrm{y}\mathrm{r}^{-1}$$
Char. Velocity | 5.2 | 6.5 | 5.4 | 6.3 | 8.0 | 6.0 | ${km}\,\mathrm{s}^{-1}$
Char. Extension | 0.03 | 0.04 | 0.04 | 0.02 | 0.03 | 0.03 | pc
| Dynamical Time | 5.0 | 6.5 | 7.9 | 2.5 | 3.3 | 4.3 |  $10^{3}$ yr

  * a

Emission integrated between -5.25 and 1.5 ${km}\,\mathrm{s}^{-1}$.

  * b

Emission integrated between 7.0 and 16.5 ${km}\,\mathrm{s}^{-1}$.

  * c

Variable calculations performed with neither inclination nor opacity
corrections.

  * d

Inclination-corrected properties based on an angle of $i=37.16\degr$.

  * e

Properties with inclination and opacity corrections applied.

Observations presented in the prior publication were limited in sensitivity,
UV coverage, and FOV, resulting in underestimated kinematic and dynamical
variable values. In order to quantify the increases in emission due to the
inclusion of the ALMA Total Power and Atacama Compact arrays, we make a per-
channel comparison of Cycle-5 12CO data cropped to the Cycle-2 field of view
($19\arcsec\times 19\arcsec$) against original Cycle-2 12CO data (Fig. 17).
The Cycle-2 data was not corrected for primary beam attenuation, and to
account for this, we divided each channel of the 12CO data cube by a two-
dimensional Gaussian with a FWHM=$25\arcsec$ and a maximum of one Jy/beam. We
found the sum of all 12CO emission per channel in each of the two cubes and
divided by the synthesised beam area to produce the total Jy in each channel.
Comparing the total per-channel emission in these velocity ranges, blueshifted
Cycle-5 emission is more intense by factors of 3.11-55.24 with a mean ratio of
8.35. Within the redshifted velocity range, Cycle-5 emission is more intense
by factors of 4.30-9.90, with the mean ratio being 4.46.

In addition to the increases in emission brought by the inclusion of the ALMA
Total Power and Atacama Compact arrays, current variable calculations also
encompass wider velocity ranges. The blueshifted range is larger by a total of
3.87 ${km}\,\mathrm{s}^{-1}$, while the redshifted range is larger by 7.31
${km}\,\mathrm{s}^{-1}$. The combination of increased emission in each channel
along with widened velocity ranges for both outflows lead to prominent
increases in every estimated variable. Furthermore, the increased field of
view of the Cycle-5 observations allows for the full extension of each outflow
to be seen. Cycle-2 12CO observations display the eastern and western walls of
the blueshifted outflow with an extensions of $12\arcsec$ and $5\arcsec$
respectively, while Cycle-5 observations show the same walls with extensions
of $27\arcsec$ and $13\arcsec$. Similar increases are seen with the redshifted
outflow, as the eastern arm increases in extension from $9\arcsec$ to
$11\arcsec$ and the western arm increases from $6\arcsec$ to $18\arcsec$
between observation cycles. To quantify the extra emission provided by the
Cycle-5 field of view, we produced a mass spectrum of each outflow wing using
Cycle-5 12CO data at its original field of view ($60\arcsec\times 60\arcsec$)
and cropped to the Cycle-2 field of view (Fig. 18). As with the prior average
intensity comparison, the Cycle-5 field of view provides significantly more
emission for each of the four outflow wings in comparison to previous
observations. The total mass for the blueshifted and redshifted outflow wings
increases by factors of 3.6 and 2.6, respectively, due to the increase in
field of view.

Figure 17: The total intensity of Cycle-2 12CO and Cycle-5 12CO data at a
field of view of $19\arcsec\times 19\arcsec$. The velocity integration ranges
used in current kinematic calculations, as well as those provided in RR17, as
shown as dashed grey lines. Figure 18: The per-channel mass for each outflow
wing over their respective velocity integration ranges.

The changes between observation cycles lead to noticeable differences between
the calculations performed with Cycle-2 data and those performed with Cycle-5
data. Firstly, uncorrected and inclination-only corrected Cycle-2 values are
lower in comparison to their Cycle-5 counterparts, a trend which aligns with
the aforementioned differences between the two cycles. However, the opacity
correction process leads to higher force, luminosity, and characteristic
velocity values when using the Cycle-2 data. The increases to these values are
driven by two factors: the opacity correction process, and the characteristic
velocity calculation. The parabolic fits used to produce each Cycle-2
correction factor were flatter than those found in the Cycle-5 process,
meaning that every Cycle-2 velocity channel received a significant correction,
which then lead to higher variable estimates. Additionally, the use of fewer
velocity channels in the Cycle-2 calculations leads an increased momentum/mass
ratio, which directly leads to a higher characteristic velocity. This issue
propagated throughout the calculation process and led to increases in
luminosity and force. Nevertheless, we report the most accurate calculations
for HBC 494’s outflows through use of the ALMA main, ACA, and TP arrays.

###  5.2 Comparison with similar objects

Along with the comparisons made between current and prior observations
regarding HBC 494’s outflows, a comparison between HBC 494 and similar objects
(i.e., Class 0 and I YSOs, FU Ori objects) can reveal additional information
related to HBC 494’s outflows and their evolution. We first compare HBC 494 to
the numerous objects reported in Hsieh et al. (2023), a study which details 21
Class 0, I, and flat spectrum YSOs using ALMA Cycle-6 observations. This study
makes use of three spectral lines reported in our work, namely 12CO (J=2-1),
13CO (J=2-1), and C18O (J=2-1), and also makes use of the same computational
methods for determining outflow parameters. Most notably, they report the
total outflow mass of the selected Class 0 YSOs to be between 0.5 and 0.9 M☉,
and the total outflow mass of the selected Class I YSOs to be between 1.5 and
2.9 M☉. To determine these values, they produce a mass spectrum for each
outflow using a combination of 12CO, 13CO, and C18O. 12CO emission is used to
determine mass in high-velocity channels that lack ambient cloud
contamination. As cloud emission becomes more prevalent, 13CO is used in low-
velocity channels, and C18O is used in channels closest to the systemic
velocity. We apply this technique using a 13CO/H2 ratio of
$X_{$\mathrm{1}\mathrm{3}\mathrm{,}\mathrm{H}_{2}$}=2\times 10^{-6}$, and a
C18O/H2 ratio of $X_{$\mathrm{1}\mathrm{8}\mathrm{,}\mathrm{H}_{2}$}=2\times
10^{-7}$ (Hsieh et al., 2023). For the blueshifted outflow we integrate 12CO
between -8.3 and 2.32 ${km}\,\mathrm{s}^{-1}$, 13CO between 2.5 and 3.04
${km}\,\mathrm{s}^{-1}$, and C18O between 3.22 and 3.4
${km}\,\mathrm{s}^{-1}$. For the redshifted outflow we integrate C18O between
4.66 and 4.84 ${km}\,\mathrm{s}^{-1}$, 13CO between 5.02 and 6.82
${km}\,\mathrm{s}^{-1}$, and 12CO between 7 and 23.56 ${km}\,\mathrm{s}^{-1}$.
Making use of the opacity corrected 12CO and 13CO data cubes, we produce a
total outflow mass of 0.63 M☉, which places HBC 494 in the centre of the Class
0 YSO range.

It is important to note that the objects selected for this study were chosen
specifically for their singular nature, meaning that outflow characteristics
stemming from HBC 494’s binarity are not present, especially with regard to
outflow opening angle. Hsieh et al. (2023) notes that opening angle generally
increases as a YSO evolves, with the largest opening angles coming from the
flat-spectrum sources in their study. Specifically, they report opening angles
of between $\sim 15\degr$ and $\sim 130\degr$, with the latter reported for
the flat-spectrum source HOPS 200. The aforementioned trend could indicate
that HBC 494’s binarity may be at least partly responsible for this
phenomenon, as it maintains a larger outflow angle than any of the objects
documented in this publication.

Comparisons of HBC 494’s disc to other FUor discs can also provide useful
information about the system. FU Ori discs were studied in depth in Cieza et
al. (2018), specifically those of V883 Ori, V2775 Ori, and V1118 Ori. Cieza et
al. (2018) also includes early observations of HBC 494; however, their
observations do not resolve the discs of HBC 494a and HBC 494b individually.
They conclude that FUor discs have masses between 80 and 600
M${}_{$\mathrm{J}\mathrm{u}\mathrm{p}$}$, while EXor discs – a type of object
similar to FUors with less intense outbursting events – have masses between
0.5 and 40 M${}_{$\mathrm{J}\mathrm{u}\mathrm{p}$}$. According to Nogueira et
al. (2023) HBC 494a has a disc mass (gas + dust) of $\sim 145$
M${}_{$\mathrm{J}\mathrm{u}\mathrm{p}$}$, while HBC 494b has a disc mass of
$\sim 29$ M${}_{$\mathrm{J}\mathrm{u}\mathrm{p}$}$, a value consistent with
EXor type objects. While disc mass alone cannot provide a definitive
classification for HBC 494b, it can aid in characterising HBC 494’s outflows
as a whole. Based on the aforementioned Cycle-2 observations, HBC 494 was
thought to present a single set of wide-angle outflows. However, we now
believe that HBC 494’s outflows are a composite of outflows from HBC 494a and
HBC 494b. If possible, untangling the outflows from these two sources may also
reveal important properties of each individual object, providing additional
information about their specific classifications. Future work can perhaps
focus on the orbital evolution of HBC 494, as well as how the individual
outflows from its constituent objects impact the system as a whole.

###  5.3 The secondary cavity

The existence of HBC 494’s secondary cavity could be indicative of multiple
phenomena. Firstly, it is possible that this cavity represents a previous
outflow from HBC 494 that was expelled outwards due to an accretion
outbursting event. The cavity is observed most prevalently at velocities
between 6.1 and 8.98 ${km}\,\mathrm{s}^{-1}$, and at lower intensity between
10.24 and 13.66 ${km}\,\mathrm{s}^{-1}$. Accounting for HBC 494’s inclination
of $i=37.16\degr$, the cavity is seen at a distance of $24.9\arcsec$ north of
the central binary, indicating that it was expelled between 5,300 and 6,200
years ago. These values can provide us with an estimate of when a previous
outburst occurred, as Hartmann & Kenyon (1996) claims that outburst events
must occur multiple times over an interval of $\sim 10^{5}$ years, although a
prior outburst has not been observed from HBC 494.

Secondly, the shape of the cavity may serve as additional evidence for
overlapping outflows from HBC 494’s binary components. The outflows from HBC
494a and HBC 494b, both of which have different position angles, could be the
cause of both the primary and secondary cavities’ wide opening angle and
shape, as well as the wings of emission seen in blueshifted 13CO and C18O
observations, which are highlighted in Fig. 19. This figure shows two features
which evidence outflows with differing position angles: a set of eastern and
western outflow wings (green arrows) and a clump of material created by the
interaction between outflows from HBC 494a and HBC 494b (cyan arrows). The
clump of material is situated in between the position angles for the two
suggested outflows. A similar clump of material is seen in 12CO and
corresponds with the northern regions between the two outflow position angles,
indicating that a comparable interaction is occurring within the northern
outflow cavity. The cavity also shows clear interactions between HBC 494’s
northern outflow as observed with 12CO, 13CO, and C18O. These interactions are
evidenced by similar emission shapes between the three lines at velocities at
which the secondary cavity is detected (8.98 – 10.6 ${km}\,\mathrm{s}^{-1}$).
Detections at these velocities, specifically with 13CO and C18O, indicate that
the northern side of the system is more embedded in the stellar envelope than
the southern side, as 13CO and C18O also trace the envelope.

Figure 19: Two channel maps of 13CO (top) and C18O (bottom) which highlight
two distinct features with coloured arrows. Specifically, the green arrows
highlight a set of outflow wings present on either side of the binary, and the
cyan arrows show material representative of an interaction between outflows
from HBC 494a and HBC 494b. The white contours seen at the centre of each
frame in both channel maps represent continuum emission centred at 232.5 GHz
at levels of 0.25 and 0.75 times the maximum intensity of 0.11 Jy/beam. The
white ellipse in the bottom left of each frame shows the synthesised beam,
which maintains an angular size of 1.77 $\times$ 1.30 arcseconds and a
position angle of -72.3$\degr$ for 13CO, and 1.78 $\times$ 1.28 arcseconds and
-74.6$\degr$ for C18O. The green ellipse shown in the top left of each
represents the continuum beam, which has an angular size of 1.50 $\times$ 1.07
arcseconds and a position angle of -66.8$\degr$.

While the specific classification of HBC 494b is currently unknown, it is
likely to be a Class 0/I protostar, meaning that outflow interactions may be
possible (Connelley et al., 2008; Nogueira et al., 2023). Additionally,
misaligned outflows from binary YSO systems are also noted at length in Lee et
al. (2016). They report on the outflows of nine binary or higher-n YSOs, and
determine outflow position angle differences of between $6\degr$ and $90\degr$
with a median difference of $61\degr$. It is important to note that the
observed systems maintain much larger separations than HBC 494, as the minimum
separation between any two objects in this study is 1,863 au – nearly 25 times
greater than the separation between HBC 494a and HBC 494b. The gravitational
influence of HBC 494’s components on one another may be responsible for the
large difference in position angle between the two outflow sets.

##  6 Conclusions

We present ALMA Cycle-5 observations of 12CO, 13CO, C18O, and SO, all of which
are able to trace different features of HBC 494. To improve upon the results
presented in RR17, current observations used a combination of the ALMA main,
Total Power, and Atacama Compact arrays to increase sensitivity to large-scale
emission and reduce spatial filtering. Through image mosiacing, we were also
able to greatly improve the field-of-view of our ALMA observations, as those
presented in RR17 were limited to single-pointing images. These improvements
in observations led to two important results:

  1. 1.

For the first time in HBC 494’s observational history, a secondary outflow
cavity was observed above the northern primary cavity. We believe that the
cavity was launched upwards from the central binary as the result of a prior
accretion outburst. Additionally, it serves as evidence of an overlap between
outflows stemming from HBC 494’s constituent objects. The cavity has a
dynamical age between 5,300 and 6,200 years, which is in line with the time-
scales of repeated accretion outburst events (Hartmann & Kenyon, 1996). P-V
diagrams made at angles of $35\degr$ and $145\degr$ reveal that outflows from
HBC 494a and HBC 494b are misaligned. This misalignment serves as an
explanation as to why the primary outflows present an uncharacteristically
wide opening angle. The secondary cavity displays a similarly wide opening
angle, suggesting that interactions between the two sets of outflows aided in
shaping the secondary cavity.

  2. 2.

The full extent of HBC 494’s outflows has also been observed for the first
time. The southern primary outflow maintains an asymmetric parabolic shape,
with its eastern arm showing much greater extension and intensity in
comparison to the western arm. The northern primary outflow, however, is much
more symmetric in both extension and intensity. The secondary northern cavity
mimics the shape of its primary counterpart, although its western arm shows
higher intensity than its eastern arm. The asymmetry shown in the primary and
secondary outflow cavities, both in shape and emission intensity, could be
useful in determining the origins of the secondary cavity and is currently a
point of further investigation.

In combination with improved observations, we also present kinematic and
dynamical variable estimations using the methods described in Dunham et al.
(2014). To perform such calculations, we find the mass of each pixel in a
given velocity channel based on a series of assumptions regarding excitation
temperature, optical depth, and beam filling factors. Specifically, the CO
dipole moment allows for 12CO and 13CO to be easily thermalized, and thus can
be represented by the Boltzmann distribution. From this, we assume that all
emission is in LTE and maintains the same excitation temperature. To find the
total outflow mass, we integrate over all pixels and velocity channels in
which outflow emission is detected above a $3\sigma$ cutoff, which is
determined using the RMS of each data cube. Optical depth effects can lead to
underestimations of kinematic and dynamical variables, and thus must be
corrected for. To do so, we use the brightness temperature ratio between 13CO
and C18O to apply an initial correction to the 13CO data cube, and then
calculate the same ratio between 12CO and the corrected 13CO. The second set
of corrections are then applied to the 12CO data cube, and the calculation
process is performed again. Without corrections applied, we estimate the mass
of the southern primary outflow to be between $2.1\times 10^{-3}$ and
$3.7\times 10^{-3}$ $\mathrm{M}_{\sun}$ based on assumed excitation
temperatures of 20 K and 50 K. With corrections, these values increase to
$3.0\times 10^{-2}$ $\mathrm{M}_{\sun}$ and $5.3\times 10^{-2}$
$\mathrm{M}_{\sun}$, respectively. For the northern primary outflow, the
uncorrected mass is estimated to be between $3.7\times 10^{-3}$ and $6.6\times
10^{-3}$ $\mathrm{M}_{\sun}$, while corrected estimates are between $2.8\times
10^{-2}$ and $5.1\times 10^{-2}$ $\mathrm{M}_{\sun}$. The large increases to
each physical parameter created by the correction process are in line with
those presented in Dunham et al. (2014). The variable estimates made using
Cycle-5 data are larger than those using Cycle-2 data, as the use of the ALMA
main, Total Power, and Atacama Compact arrays has allowed us to resolve a much
greater amount of emission in comparison to prior observations. The use of
image mosaicing also contributed to the increased variable estimates, as HBC
494’s outflows were observed to their full extent.

## Acknowledgments

This research was supported through the National Radio Astronomy Observatory’s
(NRAO) summer student program in Charlottesville, VA. Additional contributions
were made by the Department of Astronomy at the University of Maryland (UMD)
in College Park, MD. AF thanks Dr Andrew Harris and Dr Melissa Hayes-Gehrke
from UMD for their revisions of this research, and Dr Jim Braatz from the NRAO
for his efforts in organizing and running the NRAO summer student program.
Lastly, AF thanks Dr John Fourkas and Dr Amy Mullin from UMD for their
continued support of this research. This paper makes use of the following ALMA
data: ADS/JAO.ALMA$\\#$2017.1.00015.S. ALMA is a partnership of ESO
(representing its member states), NSF (USA) and NINS (Japan), together with
NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in
cooperation with the Republic of Chile. The Joint ALMA Observatory is operated
by ESO, AUI/NRAO and NAOJ. The National Radio Astronomy Observatory is a
facility of the National Science Foundation operated under cooperative
agreement by Associated Universities, Inc.

## Data Availability

The data underlying this paper are available in the ALMA archive at
https://almascience.nrao.edu under project code 2017.1.00015.S.

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##  Appendix A Extra channel maps

Figure 20: An individual channel map of blueshifted 12CO emission between
-11.0 and 2.68 ${km}\,\mathrm{s}^{-1}$. Each frame is spaced by 0.72
${km}\,\mathrm{s}^{-1}$. The white contours in the centre of each panel
represent continuum emission centred at 232.5 GHz shown at 0.25 and 0.75 times
the maximum recorded intensity of 0.11 Jy/beam. The synthesised beam is shown
in the bottom left of each panel by a white ellipse with a size and position
angle of 1.85 $\times$ 1.23 arcseconds and -$67.2\degr$, respectively. The
continuum beam is represented by a green ellipse in the top left corner of
each panel, with a size of 1.50 $\times$ 1.07 arcseconds and a position angle
of -$66.8\degr$. Figure 21: An individual channel map of redshifted C18O
between 9.34 and 9.88 ${km}\,\mathrm{s}^{-1}$. The white contours represent
continuum emission centred at 232.5 GHz at levels of 0.25 and 0.75 times the
maximum of 0.11 Jy/beam. The C18O synthesised beam is shown in the bottom left
of each frame in white, while the continuum beam is shown in green at the top
left of each frame. The two beam have sizes and positions angles of 1.78
$\times$ 1.28 arcseconds and -74.6$\degr$, and 1.50 $\times$ 1.07 arcseconds
and -66.8$\degr$, respectively. Figure 22: A channel map of SO emission
between velocities of 1.6 and 5.02 ${km}\,\mathrm{s}^{-1}$. The white contours
at the centre of each frame represent continuum emission centred at 232.5 GHz,
and are shown at levels of 0.25 and 0.75 times the maximum detected intensity
of 0.11 Jy/beam. The SO synthesised beam and continuum emission beam are shown
in the bottom left and top left of each frame, respectively. The former
maintains a size and position angle of 1.81 $\times$ 1.28 arcseconds and
-72.3$\degr$, while the latter has a size and position angle of 1.50 $\times$
1.07 arcseconds and a position angle of -66.8$\degr$. Figure 23: A channel map
of SO emission between velocities of 6.1 and 9.52 ${km}\,\mathrm{s}^{-1}$. The
white contours at the centre of each frame represent continuum emission
centred at 232.5 GHz, and are shown at levels of 0.25 and 0.75 times the
maximum detected intensity of 0.11 Jy/beam. The SO synthesised beam and
continuum emission beam are shown in the bottom left and top left of each
frame, respectively. The former maintains a size and position angle of 1.81
$\times$ 1.28 arcseconds and -72.3$\degr$, while the latter has a size and
position angle of 1.50 $\times$ 1.07 arcseconds and a position angle of
-66.8$\degr$. Figure 24: An individual channel map of 13CO emission between
1.6 and 4.3 ${km}\,\mathrm{s}^{-1}$ with SO emission overlaid as a white
contour at levels of 5, 7,5, and 10 times the maximum detected intensity of
0.11 Jy/beam. The 13CO synthesised beam is shown as a white ellipse in the
bottom left of each frame, and has an angular size and position angle of 1.77
$\times$ 1.30 arcseconds and -72.3$\degr$, respectively. Likewise, the SO
synthesised beam is shown as a green ellipse in the top left of each frame
with an angular size of 1.81 $\times$ 1.28 arcseconds and a position angle of
-72.3$\degr$.