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# Spectral Survey
of the Star Formation Region DR21OH
in the 4 mm Wavelength Range

S. V. Kalenskii  Lebedev Physical Institute, Astro Space Center,
84/32 Profsoyuznaya st., Moscow, GSP-7, 117997, Russia  E. A. Mikheeva
Lebedev Physical Institute, Astro Space Center,
84/32 Profsoyuznaya st., Moscow, GSP-7, 117997, Russia  Sternberg Astronomical
Institute, Moscow State University,
Universitetsky pr., 13, Moscow 119234, Russia

###### Abstract

The results of a spectral survey of the region of massive star formation
DR21OH in the 4-mm wavelength range are presented. Sixty-nine molecules and
their isotopologues have been detected, ranging from simple diatomic or
triatomic species such as SO, SiO and CCH, to complex organic molecules such
as CH3OCHO or CH3OCH3. The obtained results qualitatively repeat the results
of the survey of the same source at 3 mm. The inventories of molecules found
at 3mm and 4mm overlap to a great extent. However, at 4 mm we found a number
of species that have no allowed transitions in the 3-mm wavelength range, e.g.
DCN, DNC, or SO+. The bulk of the molecules detected at 4 mm are those that
are common for dense cores, e.g., HC3N or CH3CCH, but some of the detected
species are typical for hot cores. The latter include complex organic
molecules CH3OCHO, CH3CH2OH, CH3OCH3, etc. However, the detected emission of
these molecules probably arises in a gas heated to 30 K only. Nine molecules,
including complex species CH3C3N, CH3CH2CN, CH3COCH3, were found by spectral
line stacking. This demonstrates the prospects of the method in the study of
molecular clouds.

##  1 INTRODUCTION

The high-mass star-forming region DR21OH is located within a giant molecular
cloud in the Cygnus X complex. The distance to the complex, obtained from the
trigonometric parallaxes of H2O and CH3OH masers, is 1.4 kpc rygl12 . DR21OH
is a part of a massive dense cloud elongated in the north-south direction for
approximately 4 pc harvey86 ; hennemann12 . Within the cloud, there is a chain
of Young Stellar Objects (YSOs) also elongated in the north-south direction.
In addition to DR21OH, this YSO chain includes a powerful radio continuum
source, the bright HII region DR21, which gives the entire cloud its name
harvey86 , as well as the infrared sources W75S-FIR1, W75S-FIR2, and
W75S-FIR3. The bolometric luminosity of the DR21OH region is approximately
$5\times 10^{4}$ solar luminosities harvey77 , and the total mass is about
$10^{4}$ solar masses.

The region is located three angular minutes north of the DR21 HII-region and
consists of four main clouds designated DR21OH Main (DR21OH M), DR21OH North
(DR21OH N), DR21OH West (DR21OH W), and DR21OH South (DR21OH S), surrounded by
molecular gas with a clumpy structure mangum91 ; mangum92 . The DR21OH M
cloud, in turn, consists of two dense cores, MM1 and MM2, whose emission
maxima are located 8 seconds apart in the northeast-southwest direction. These
cores are observed both in molecular lines and in the continuum in the mm,
submm and IR bands padin89 ; mangum91 ; mangum92 . Zapata et al. zapata12
observed DR21OH M at 1.4 mm wavelength using the SMA interferometer and
separated MM1 and MM2 into nine more compact clumps, designated SMA1 – SMA9.
The main physical parameters of MM1 and MM2 were determined by Mangum et al.
mangum91 . The bolometric luminosity of MM1 is $1.7\times 10^{4}$ solar
luminosities, its mass is 350 solar masses, and its dust temperature is 58 K.
The upper limit on the bolometric luminosity of MM2 is $1.3\times 10^{4}$
solar luminosities; MM2 has a mass of 570 solar masses; the dust temperature
is 30 K. The systemic velocity of DR21OH M is about $-3$ km s-1, but spectral
details with LSR velocities about $9$ km s-1 are observed toward this cloud.
These details are related to a cloud that probably collides with DR21 dickel78
; dobashi19 . According to Mangum et al mangum92 , the radial velocities of
the MM1 core and several neighbouring clumps are close to the systemic
velocity and fall in the interval from -4.4 km s-1 to -2.2 km s-1, while the
velocities of the MM2 core and other clumps fall in the interval from 0 km s-1
to -1 km s-1. However, according to the spectra reported in minh12 , in the
direction of the hot core MM1b (see next paragraph), the lines of 34SO, HC3N
and some other molecules have maxima at velocities around 0 km s-1.

An indication of active star formation in DR21OH M is the existence of strong
OH, H2O and CH3OH masers genzel77 ; norris82 ; batrla88 . In addition, bipolar
outflows in CO, CS, SiO, H2CO, H2CS lines have been observed in this region
lai03 ; zapata12 ; orozco19 . However, despite many indications of an actively
proceeding process of high-mass star formation, no compact HII regions are
found in DR21OH-M, and the hot cores found by Minh et al. minh12  in the MM1
direction and labelled MM1a and MM1b are not as pronounced as the hot cores in
sources like Sgr B2, W51e1/e2, G34.26+0.15, etc. These facts indicate that the
protostars in DR21OH M are at the early stages of evolution. Nevertheless, in
this source, we can search for COMs (complex organic molecules), which appear
in the gas phase due to various non-thermal desorption mechanisms, as well as
due to evaporation of dust mantles in hot postshock gas the lobes of high-
velocity outflows.

A spectral survey of DR21OH at 3 mm wavelengths was carried out by Kalenskii
and Johansson (2010) kalenskii10a  with the 20-m radio telescope of the Onsala
Space Observatory (Sweden). The whole DR21OH M region fell within the
telescope beam. Lines of 78 molecules were detected, most of them typical of
dense clouds. The rotational temperatures of most of the detected molecules
proved to be about 20 – 30 K, but the rotational temperature of SO2 was 186 K.
An even higher rotational temperature, 252 K, was obtained from methanol lines
with upper level energies above 100 K. Some of the detected molecules were
COMs - oxygen-containing CH3OH, CH3OCHO, CH3OCH3, nitrogen-containing CH3CN,
CH3CH2CN and others.

The detection of these molecules shows that DR21OH is a promising source to
search for COMs. However, a number of molecules important for astrochemistry
do not have allowed transitions in the 3-mm wavelength range and must be
searched for in other spectral bands. Some molecules — CH2NH, DC3N, HCCN —
have been found at 3 mm only presumably and their detections should be
confirmed or denied. Therefore, when the 4 mm wavelength range receiver
appeared at the Onsala Observatory, we carried out a spectral survey of DR21OH
in this range as well.

##  2 Observations

The observations were carried out in April and May 2018 on the 20-m
millimeter-wave radio telescope of the Onsala Space Observatory (Sweden) in
parallel with the spectral survey of the star-forming region W51e1/e2 (project
O2017b-04) and are described in detail in kalen22 . The spectral range of the
survey was 68 – 88 GHz. The dual beam switching with a beam throw of 11 arcmin
in azimuth was used. The main beam width at half-power (HPBW) at 86 GHz was
$43^{\prime\prime}$. The antenna was pointed toward MM1
(R.A.=$20^{h}39^{m}01.1^{s}$, DEC=$42^{o}22^{\prime}48^{\prime\prime}$;
J2000). The entire DR21OH M cloud falls within the beam. Pointing errors were
checked using SiO maser observations at 86 GHz and did not exceed
$5^{\prime\prime}$. The data were calibrated by applying the chopper-wheel
method. The system noise temperature mainly varied between $\sim 200--500$ K,
but in the final observing sessions, between $\sim 300$ K and $\sim 1200$ K. A
fast Fourier transform spectrometer consisting of four sections, two sections
for each polarisation plane, was connected to the receiver backend. The full
analysis bandwidth was 4 GHz. The frequency resolution was 76.294 kHz,
corresponding to a velocity resolution of 0.28 km s-1 at 83 GHz. During data
processing, the resolution was smoothed to $0.305$ MHz (1.1 km s-1 at 83 GHz).
For 75% of the survey range, the $1\sigma$ noise level did not exceed 0.003 K,
increasing slightly (to 0.006K) toward the edges of the range.

This project served as a test for the new Bifrost control system, which
controls the observations in automatic mode.

The data were processed using the Grenoble Observatory’s CLASS software
package111https://www.iram.fr/IRAMFR/GILDAS using the WEEDS extension.

##  3 Results

Source spectrum in the frequency range 68–88 GHz was obtained. A part of it is
reproduced in Fig. 1. Many radio lines of different molecules were detected.
The primary identification of the detected lines was done using the Lovas
database of molecular lines detected in space lovas09
222http://physics.nist.gov/restfreq. However, some detected lines were absent
from this database. Part of the absent lines have been found and identified by
Kalenskii et al. kalen22 . The CDMS muller01 ; muller05  and JPL pickett
spectral line catalogs were used to identify the others. However, eight lines
remained unidentified.

Practically all detected thermal lines have maxima at velocities near $-3$ km
s-1. No lines with maxima near 9 km s-1 were detected. The lines of H2CO at
72837.948 MHz and HC5N at 85201.346 MHz are non-Gaussian and were approximated
by two components each, with the radial velocities of the stronger components
being near the system velocity and those of the weaker components being near
$-1$ km s-1. It is possible that the remaining lines of these and some other
molecules are also double lines, but the signal-to-noise ratio achieved does
not allow us to separate them into components.

At 80578.283 MHz, we detected the $1_{1,0}-1_{1,1}$ HDO line, which has a
radial velocity at maximum of 0.066 km s-1. However, the line identification
cannot be considered reliable because only one line of this molecule has been
detected. To verify the identification, it is best to observe the
$2_{1,1}-2_{1,2}$ HDO line at 241561.550 MHz.

The radial velocity of the $N,J=2,2-1,1$ 34SO line is -0.92 km s-1, but the
width of this line is very large (9.28 km s-1). It is probably blended with
some unidentified line and the parameters given in the table are related to
the whole blend.

Thus, it is not possible to separate the contributions of the different
sources in our data. We can only conclude that most of the detected emission
arises in the MM1 core and/or other objects with radial velocities close to
the systemic velocity. In order to distinguish the contributions of individual
cores, it is necessary to observe DR21OH with high spatial resolution.

A total of 69 molecules and their isotopic species were found at 4 mm, ranging
from simple di- or triatomic molecules such as SO, SiO, and CCH, to complex
organic compounds, CH3CN, CH3OCH3 or CH3CH2OH. The list of detected molecules
is given in Table 1; molecules found by spectral line stacking (see Section 4)
are shown in italics.

A significant fraction of the results are qualitatively similar to those of
the 3 mm survey. The lists of molecules detected at 3 mm and 4 mm overlap to a
large extent. The bulk is the species that are frequently observed in dense
cores, such as HC3N, SO, OCS, etc. However, a notable fraction of the detected
molecules are characteristic of hot cores. In particular, COMs such as
CH3OCHO, CH3OCH3, CH3CH2OH, CH3COCH3 are found, which, according to modern
concepts, are formed in icy dust mantles and enter the gas phase during
evaporation of mantles in hot cores or their sputtering by shock waves.
However, it is well known that e.g., methanol, which is also formed in dust
mantles, was also found in dense clouds and even dark clouds. All the lines of
COMs we have detected (except several methanol lines) arise at transitions
between levels with excitation energies less than 100 K. Therefore it is
possible that these lines arise in dense cores and not in hot regions (see
Subsection 3.1 for further discussion of this issue).

Apart from neutral molecules, various molecular ions – HC18O+, HC17O+, H13CO+,
DCO+, etc. have been found. These ions, besides diffuse clouds, are often
present in dense clouds with high optical absorption, where the primary
sources of ionization are cosmic rays and X-ray radiation from protostars
((see padovani09, , and references in this article)).

Several deuterated compounds were found, including the deuterated
cyanoacetylene DC3N, which was only presumably found at 3 mm. The detection of
two other molecules presumably found at 3 mm, CH2NH and HCCN, was not
confirmed.

###  3.1 Rotation diagrams

Rotation diagrams (RDs) are a widely used method for estimating the
temperature of interstellar gas and are described in a large number of papers
(e.g. blake, ). If several optically thin lines of the same molecule are
found, then the column densities at the upper energy levels of these lines,
divided by the statistical weights of the levels ($N_{u}/g_{u}$), can be
estimated. Under the Local Thermodynamic Equilibrium (LTE), the points on the
plot of $\log(N_{u}/g_{u})$ versus $E_{u}/k$, where $E_{u}$ is the upper level
energy, $k$ is the Boltzmann constant, lie on a straight line, the slope of
which is inversely proportional to the temperature. This temperature is called
rotational temperature ($T_{rot}$). Since in molecular clouds LTE, if it
exists, is achieved due to collisions with H2 molecules, the rotational
temperature often turns out to be close to the kinetic one. The point of
intersection with the Y axis makes it possible to estimate the column density
of the molecule.

We plotted an RD for each molecule with four or more isolated spectral lines
detected333Excluding molecules whose individual spectral features are
hyperfine components of the same rotational transition with practically the
same upper-level energies. These diagrams are shown in Fig. 2, and determined
parameters are presented in Table 2. The RDs for four molecules: methyl
acetylene (CH3CCH), methyl cyanide (CH3CN), cyanodiacetylene (HC5N), and
ketene (CH2CO) demonstrate only slight point scattering around the
approximating lines. The rotational temperatures fall within a narrow range,
27–42 K. This result is in a good agreement with the estimates of the kinetic
temperature of MM2 (32 K), as well as of all other cores in DR21OH, except
MM1, obtained by Mangum et al. mangum92  from VLA observations of ammonia
lines. Since symmetric-top molecules CH3CCH and CH3CN are good ”thermometers”
of the interstellar gas askne ; loren , we believe that the temperature of the
bulk of the gas in DR21OH is about 30–40 K.

The RD for methanol (CH3OH) clearly shows the existence of two components. The
first of them dominates the lines with $E_{u}/k<100$ K (low-energy component),
and the second dominates the lines with $E_{u}/k>100$ K (high-energy
component). The low-energy lines are approximated by a straight line
corresponding to $T_{rot}=19$ K, and the high-energy lines, by a straight line
corresponding to $T_{rot}=298$ K. It is natural to interpret this diagram in
such a way that low-energy lines appear in cold regions and high-energy lines,
in hot regions. This interpretation is in agreement with the results of SMA
observations of Minh et al. minh12  and Orozco-Aguilera et al. orozco19 . They
found that methanol emission originates in hot cores MM1a and MM1b and in the
lobes of a bipolar outflow south of MM1, elongated into the west-east
direction for a distance of approximately $24^{\prime\prime}$, which at a
distance to the source of 1.4 kpc corresponds to a distance projection on the
picture plane of 0.15 pc. Low-energy lines that do not require high
temperatures to arise are likely to occur in both of these regions; in
addition, more extended emission regions, filtered out by the SMA array, may
exist. High-energy lines may appear in a gas with a temperature on the order
of 300 K, i.e., in hot cores discovered by Minh et al. minh12 . However, this
interpretation can be slightly modified. Figure 2, the bottom row shows a
model RD constructed from the methanol lines we observed for the case when all
their optical depths are high and therefore the brightness temperatures are
the same. The sizes of the emitting region are chosen equal to the sizes of
the hot core MM1a ($1.6^{\prime\prime}\times 1.1^{\prime\prime}$) minh12 , the
temperature of the region is chosen to be 100 K. Note that the resulting
rotational temperature does not depend on the kinetic temperature of the
source, but the position of the points along the Y axis depends on this
parameter – the higher the temperature, the higher the points are located.
This RD strongly resembles the diagram plotted from actually observed high-
energy lines, and the obtained value of $T_{rot}$ almost coincides with the
rotational temperature of the observed high-energy component. Therefore,
observed high-energy lines may be optically thick. In this case, the source
temperature must be high because otherwise, it is problematic to obtain a
large optical depth of lines with $E_{u}/k\sim 300-400$ K; however, it can
differ greatly from the obtained value $T_{rot}=298$ K.

The rotational temperatures for CH3CHO, CCS, and c-C3H2 fall within the range
7–11 K. This can mean either that these molecules exist in a colder medium
than CH3CCH, CH3CN, and HC5N, or that the rotational level populations of
these molecules are not thermalized by collisions. To deal with this issue, we
modeled the c-C3H2 (cyclopropenylidene) emission for a number of source
parameter sets using the Large Velocity Gradient (LVG) method with the RADEX
code radex . The temperature was fixed at 32 K. The best agreement with the
observations was obtained for the following parameter sets:
n${}_{\symoperators H2}=2\times 10^{5}$ cm3 and N${}_{\symoperators
c-C3H2}=6.4\times 10^{12}$ cm-2. The rotation diagram for this set of
parameters is shown in Fig. 2 on the bottom right plot. It is very similar to
the rotation diagram plotted from the observed c-C3H2 lines and gives the same
rotational temperature (7 K). Therefore, we believe that the c-C3H2 emission
arises at the same gas temperature as the CH3CCH, CH3CN, and HC5N emission;
the H2 number density in the emitting region is about 2$\times 10^{5}$ cm-3,
and c-C3H2 column density is about $6.4\times 10^{12}$ cm-2.

Unfortunately, it is impossible to carry out such modelling for ethanal
(CH3CHO) and thioethenylidene (CCS) because of the absence of collisional
constants for these molecules. As for CH3CHO, we assume that the low
rotational temperature of this molecule is due to deviations of the level
populations from LTE. The reason is as follows: ethanal is a prolate slightly
asymmetric top. The same type of molecule is methanol, whose excitation was
studied by Kalenskii & Kurtz kk16 . We believe that the rotation diagrams of
two molecules of the same type may have the same regularities. Kalenskii and
Kurtz kk16  showed that the rotational temperature obtained from the
$J_{K}-(J-1)_{K}$ methanol lines with the same $J$ and different $K$ values is
lower than the kinetic temperature when H2 number density is lower than
$\lesssim 10^{8}$ cm-3 and depends on the H2 number density rather than on
temperature. In our survey, only such lines of CH3CHO444Except for the
$2_{1,2}-1_{0,1}E$ line were found, so it is natural to assume that just the
set of lines caused the low rotational temperature.

Sulfur dioxide emission on the SMA maps of Minh et al. minh12  is strongly
concentrated toward the hot cores MM1b and MM1b. However, we obtained a
rotational temperature of SO2 equal to 48 K. Therefore one can assume that we
observed SO2 emission that arises in regions with moderate gas temperature.
However, if the warm region radiating in the sulfur dioxide lines is compact,
it is not clear why it is not visible in the maps of Minh et al. If it is
extended, it is not clear why it is not revealed in the rotation diagrams of
CH3CN, CH3CCH, and HC5N. To deal with this question, we have modelled the
emission of the SO2 molecule with RADEX and found that, in a wide range of
molecular gas parameters the rotational temperature of sulfur dioxide,
determined from the transitions we observed, turned out to be much lower than
the kinetic temperature. Therefore, our results do not indicate the existence
of sources with gas temperatures on the order of 50 – 60 K and do not
contradict the assumption that sulfur dioxide emission arises in hot cores.
However, while the maps of Minh et al minh12  are dominated by emission from
the MM1b core, the radial velocities of the lines detected by us are close to
the systemic velocity that is characteristic of the MM1a core (see
Introduction). It is natural to assume that the contribution of the MM1a core
to these lines dominates. This difference in results may be due, for example,
to the fact that Minh et al. observed higher energy transitions than those
detected by us. While the energies of the upper levels of the lines observed
by Minh et al. are of the order or higher than 200 K, similar values for the
lines detected by us are of the order or lower than 120 K. If MM1a is colder
than that of MM1b, it is possible that the emission of MM1a will be stronger
in low-energy lines and that of the MM1b, in high-energy lines. Reliable
measurements of the temperature of MM1a and MM1b are needed to test this
assumption555The alternative assumption of the existence, in addition to MM1a,
of some other hot region of gas with a velocity close to the systemic velocity
seems unlikely for the same reasons as the assumption of the existence of a
region with a temperature of about 50 K.

###  3.2 Column densities determined from single lines.

When it was not possible to construct a rotation diagram, we determined the
column density of the molecule from single lines, assuming LTE. Exactly the
same procedure was used as in the analysis of the survey of DR21OH at 3 mm
kalenskii10a . Knowledge of the integrated intensity of a molecular line makes
it possible to determine the column density at the upper level of the observed
transition. Using this value, assuming LTE, and knowing the rotational
temperature, one can calculate the total column density of the molecule.
Rotational temperature cannot be determined from observations of a single line
and must be chosen based on extraneous considerations. In this work, we
assumed this temperature to be equal to the kinetic temperature of the gas in
extended regions (32 K).

Many of the molecules that have been detected — COMs CH3OCHO, CH3CH2OH,
CH3OCH3, etc. — according to current concepts, are formed in the mantles of
dust grains and rapidly pass into the gas phase as a result of mantle
evaporation or sputtering in shock-heated gas. However, such molecules are
observed not only in hot cores but, albeit with less abundances, in dense
cores and even dark clouds (e.g. agundez23 ; spezzano ). In observations with
low spatial resolution, the contribution of cold regions may dominate, as
usually they are much more extended than hot cores. From our data, taken in
one direction, it is impossible to determine where the emission of the
detected COMs arises in compact hot cores or in extended dense clouds. In the
case of methanol, which is also a COM that forms on dust grains, we see two
components: a cold and a hot (see Subsection 3.1). In low-energy lines, the
contribution of the cold component predominates. The lines of all other COMs
found at 4 mm are low-energy, so it is natural to assume that they originate
mainly in cold gas. Therefore we took the rotational temperature equal to 32 K
in all cases.

For a number of molecules, the detected lines are hyperfine components of the
same rotational transition. It is impossible to construct a rotation diagram
from such lines because the energies of their upper levels practically
coincide. For many molecules – H2CO, HC3N, OCS, etc. only two spectral lines
were found. In addition, for C4H, CCS, and CH3CHO, low rotational
temperatures, obtained from the rotational diagrams, indicate strong
deviations from LTE, which could distort the column densities. In each of
these cases, we determined the column density for each line, assuming
$T_{rot}=32$ K, and found the average value.

Column densities determined from single lines are given in Table 3. The last
11 lines show the column densities of molecules determined by spectral-line
stacking (see Section 4). The third column shows the relative abundance of
molecules. The H2 column density was determined from the integrated intensity
of the $1-0$ C18O line, taken from the results of the DR21OH spectral survey
at 3 mm kalenskii10a . The abundance of C18O was taken equal to $10^{-7}$,
which approximately corresponds to the average value of the abundance of C18O
in dense cores (see Fig. 18 in baras21 ). With this abundance of C18O, the H2
column density turned out to be equal to $3\times 10^{23}$ cm-2.

The obtained abundances are given in Tables 2 and 3. For seven molecules
(H13CN, H13CO+, HC18O+, SO, 34SO, HCS+, OCS), these abundances can be compared
with the values obtained for a large number of dense cores by Rodriguez-Baras
et al. baras21 . Their paper shows the dependencies of molecular abundances on
various cloud parameters, including density. For all seven molecules, a
negative correlation between the density and abundance was found in baras21 .
The abundances obtained by us correspond to density intervals from $\sim
10^{4}$ to $\sim 10^{5}$ cm-3. This is lower than the density obtained by us
from CCS lines (see Subsection 3.3.1) and by 2 orders of magnitude lower than
the densities obtained from dust emission by Mangum et al. mangum91  in MM1
and MM2. This discrepancy may be a consequence of the structure of the source.
Mangum et al. estimated the density in clumps MM1 and MM2. It is possible that
the CCS emission appears at the periphery of the clumps, where the density is
lower, while the emission of the seven listed molecules occurs in an even more
rarefied interclump medium. However, the fact that the abundances of all seven
molecules correspond to approximately the same density, which is lower than
that obtained from the CCS lines, makes the following explanation more likely.
Figure 18 in the paper baras21  shows that the interval of C18O abundances in
dense cores is about an order of magnitude. Probably, in DR21OH-M C18O
abundance is close to the lower boundary of this interval, i.e., approximately
three times lower than the average value. In this case, the abundance of
molecules in Table 2 and 3 is overestimated by a factor of three. The results
of Rodriguez-Baras et al. baras21  show that in this case the actual
abundances of H13CN, H13CO+, HC18O+, SO, 34SO, HCS+ and OCS in DR21OH
correspond to a density range of approximately $3\times 10^{4}-3\times 10^{5}$
cm-3, which does not contradict the density obtained from the CCS lines.

##  4 Spectral line stacking

If the abundance of a molecule in a molecular cloud is below $\sim
10^{-11}-10^{-12}$, then, as a rule, with the state-of-art equipment it is
impossible to detect the radio lines of this molecule in a reasonable
observing time. However, often the number of lines of the molecule falling
within the observed frequency range is very large, reaching hundreds or
thousands. This is especially true for complex molecules. In this case, it is
possible to stack these lines and for the aggregate spectral detail to obtain
a signal-to-noise ratio higher than that achieved for the strongest lines of
the sought-for molecule. Therefore, spectral line stacking (SLS) makes it
possible to find even the molecules whose lines are not visible. This method
was first applied to search for molecules by Johansson et al. johansson .
Kalenskii and Johansson kalenskii10a ; kalenskii10b  used SLS to analyze the
results of surveys of star-forming regions DR21OH and W51e1/e2 in the 3-mm
wavelength range and expanded the lists of detected molecules666Johansson et
al. and Kalensky and Johansson called this method ”composite averages”. A
13-atom molecule benzonitrile (C6H5CN) and several other, even more complex
molecules, have been discovered in space for the first time using SLS kalen17
; mcguire18 ; loomis .

The method is described in a number of papers johansson ; kalenskii10a ;
loomis ; however, the technique used here differs in detail from those used in
these works. Therefore in this section, we present our approach.

When searching for a molecule using SLS, the Lines of Other Molecules (LOMs)
are interferences that can lead to a spurious ”detection” of the sought-for
molecule. This can occur due to random coincidences in frequency between LOMs
and the lines of the sought-for molecule. The impact of LOMs had to be
minimised. For this purpose, we excluded from further consideration the parts
of the spectrum occupied by LOMs. This was done as follows: first, the model
spectrum (MS) of all already detected molecules in DR21OH was built. For this
purpose, we used the WEEDS extension of the CLASS software, which, in turn,
assumes LTE. The source temperature was assumed to be 32 K. The frequencies
and other necessary parameters of the LOMs were taken from the spectral line
catalogs CDMS muller01 ; muller05  and JPL pickett . The column densities for
calculating line intensities were taken from Tables II and III. The widths of
all lines were taken to be 4.24 km s-1, which is the mean FWHM in DR21OH
according to our data.

This MS makes it possible to exclude all frequency ranges occupied by the
emission of already detected molecules. For this purpose, we marked every
frequency interval where the MS brightness temperature exceeds the noise rms
of the observed spectrum provided that the maximum MS brightness temperature
within this interval exceeds 2 rms. Then the width of each such interval was
increased by 20% to account for the possible differences in line widths. The
spectral lines of the sought-for molecule that fell into these intervals were
excluded from consideration. In addition, the observed emission within these
frequency intervals was replaced by noise with the same rms as the noise rms
of the observed spectrum. This is necessary for the correct assessment of the
weights with which the lines are stacked (see Appendix).

Next, narrow sections of the same width (200 channels, which corresponds to a
bandwidth of 61 MHz), centered on the frequencies of the sought-for molecule
lines, were cut out from so prepared broadband source spectrum and stacked
with weights chosen in a certain way (the construction of a stacked spectrum
is described in more detail in the Appendix). The weights depend on the
rotational temperature of the sought-for molecule, which is unknown in
advance. Therefore at the first stage, the stacked spectra were built for
seven temperatures: 9.375, 18.75, 37.5, 75, 150, 225, and 300 K. These
temperatures were chosen because just for them JPL and CDMS catalogs provide
molecular partition functions777Partition functions of some molecules for
2.725, 5.0, 500, and 1000 K are additionally given in the Cologne catalog, but
we didn’t build stacked spectra for these temperatures..

As a result, seven stacked spectra are obtained for the sought-for molecule
(see Fig. 3). If the molecular emission is present in the observed spectrum, a
spectral feature appears in the center of the stacked spectrum, which we call
a stacked line (SL). The signal-to-noise ratio for SL in the stacked spectrum
is higher than this ratio even for the strongest lines of the sought-for
molecule in the observed spectrum.

We performed this procedure for all molecules whose spectral line data are
available in the JPL and CDMS databases. As a result, several dozens of
stacked lines were detected. However, for each source and frequency range,
there is a certain confusion level, upon reaching which the observer is faced
with a situation when weak lines of different molecules can have practically
the same frequency. When observing at the millimeter wavelengths using the
state-of-art equipment, it is quite possible to reach the confusion level or
come close to it. This can lead to spurious detections, an example of which is
the ”discovery” of glycine kuan , subsequently criticized by Snyder et al.
snyder . Therefore, each detected SL should be additionally tested. We applied
two tests for this purpose. The first of them is as follows: one can build a
model stacked spectrum (MSS) using MS instead of the observed spectrum. If the
detection is spurious and SL is a result of a random superposition of weak
lines of already detected molecules, then it must appear on the MSS as well.
The absence of SL on the MSS is an argument in favor of the statement that the
detection of the sought-for molecule is real.

Snyder et al. snyder  proposed criteria for a molecule to be reliably
detected, which can be summarized as follows: (1) many lines of this molecule
must be detected; (2) the ratio of line intensities must correspond to some
rotational temperature depending on the source parameters. In particular, the
lines that, according to their spectral characteristics, should be reliably
detected, must be detected. The method of spectral line stacking fundamentally
does not allow the application of these criteria. Instead, we used the fact
that line weights are chosen based on line parameters and rotational
temperature and repeatedly applied the following procedure as a second test:
for the molecule under test, we did stacked spectra with randomly selected
weights. If the SL on the ”correct” stacked spectrum appears due to the
emission of the sought-for molecule, stacking with random weights will weaken
the SL or lead to its disappearance. But if the SL appears due to a random
coincidence in the frequency of weak lines of other molecules, such stacking
can both weaken and strengthen the SL.

If an SL successfully passes both tests, the molecule is considered to be
detected. Its column density was estimated, and its emission was added to the
model spectrum. The column density was estimated as follows: first, some a
priori column density $N^{a}$ was assigned to this molecule, then a model
spectrum of only this molecule was constructed (specific model spectrum), and
the stacked spectrum was built from this model spectrum. Then the molecule
column density $N_{mol}$ can be found from the obvious equation:

$N_{mol}=\frac{T_{R}^{sl}}{T_{R}^{sm}}\cdot N^{a}$ (1)

where $T_{R}^{sl}$ is the SL brightness temperature and $T_{R}^{sm}$ is the
brightness temperature of the stacked line, constructed from the specific
model spectrum. An example of the comparison of the ”observed” and ”specific”
SLs is presented in Fig. 4.

The column densities of two molecules found by the traditional method, ethyl
alcohol (CH3CH2OH) and dimethyl ether (CH3OCH3), determined from single lines
are extremely unreliable. The reasons are as follows. As concerns ethyl
alcohol, only one weak line with poorly determined parameters was found. As
for dimethyl ether, all its lines are grouped into blends, and it is
impossible to determine the parameters of single lines. Therefore, we
determined the column densities of these molecules in the same way as the
column densities of molecules found by spectral line stacking. The results are
shown in Table 3.

Nine molecules (see Table 1) passed both tests. However, the SL integrated
intensity of three of them is small (less than its five errors), so the
detection of these molecules is still questionable and should be further
tested.

##  5 Summary

The results of a survey of the region of massive star formation DR21OH in the
4 mm wavelength range are presented. Sixty-nine molecules and their
isotopologues have been detected, ranging from simple diatomic or triatomic
molecules, such as SO, SiO, CCH, to complex species such as CH3OCHO or
CH3OCH3. A notable part of the results qualitatively repeats the results of
the survey of the same source at 3 mm. The lists of molecules found at 3 mm
and 4 mm are broadly overlapped. The bulk of the molecules detected at 4 mm
are commonly found in dense cores, e.g., HC3N or CH3CCH. Rotation diagrams
constructed from CH3CN, CH3CCH, and HC5N lines showed that the gas temperature
in DR21OH is on the order of 30–40 K.

Eighteen of the detected species are COMs. According to modern concepts, these
molecules are formed in the mantles of interstellar dust grains and appear in
the gas phase either as a result of mantle evaporation in hot cores around
protostars or due to nonthermal desorption in colder gas. Unfortunately, from
the data of our single-position survey, it is impossible to unambiguously
establish in which regions the observed emission of COMs arises, in hot cores
or in the surrounding gas, like the emission of the other detected molecules.
Only for methanol (CH3OH) we found a number of high-energy transitions and
separated two components, cold and hot. The cold component produces low-energy
lines with level energies below 100 K, while the hot component produces high-
energy lines with level energies above 100 K. Low-energy lines can appear in
the same regions as the CH3CCH, CH3CN, HC5N lines. High-energy lines can
appear in gas with temperatures above 100 K, e.g., in hot cores discovered by
Minh et al. minh12 . All other COMs demonstrate only low-energy lines, which
presumably originate in colder gas.

The column densities and the abundances of the detected molecules were
estimated. For a number of simple molecules, the abundances agree with those
that are typical for dense clouds at an H2 number densities of the order of
$10^{4}-10^{5}$ cm-3.

Nine molecules, including COMs CH3C3N, CH3CH2CN, CH3COCH3, were found using
spectral-line stacking. This fact demonstrates that spectral line stacking may
be a useful tool for the analysis of broadband spectra.

###### Acknowledgements.

SVK was financially supported through the Ministry of Science and Higher
Education of the Russian Federation grant No. 075-15-2021-597, and EAM,
through the Russian State program GZ019ASC009 109.61. The authors are grateful
to P. Bergman and A. O. H Olofsson (Onsala Space Observatory) for help with
the application and observations and to an anonymous referee for helpful
comments. The Onsala Space Observatory national research infrastructure is
funded through Swedish Research Council grant No. 2017-00648. This paper makes
use of NASA’s Astrophysical Data System as well as the following data sets:
Observed Interstellar Molecular Microwave Transitions (lovas09, ), the Cologne
Database for Molecular Spectroscopy (muller01, ; muller05, ), the JPL Spectral
Line Catalog (pickett, );

##  Appendix A Line stacking procedure

This Appendix describes the process of spectral-line stacking itself when the
sought-for molecule and the rotational temperature have already been chosen.
LTE is assumed elsewhere in this section. First, from the JPL or CDMS catalog
we selected the lines of the sought-for molecule, whose frequencies fall
within the range of the survey. From the obtained inventory we excluded the
lines whose frequency errors and/or upper-level energies exceed some threshold
values. In this work, the threshold for the frequency error was set equal to
0.5 MHz. Near the low-frequency boundary of the survey band, this value
corresponds to 2.1 km s-1, i.e., to the mean half-width at half maximum of the
lines in DR21OH. The threshold for the upper-level energy was set equal to
1000 K.

Further, using the line parameters from the catalogs, we searched for the
strongest line at the chosen rotational temperature (hereinafter referred to
as the reference line). When the column density of the molecule is unknown, we
cannot find the brightness temperatures of molecular lines, but assuming LTE
we can find the brightness temperature ratios. This is enough to correctly
determine the line weights.

Intensity $I$ (cm-1/(molecule/cm2)), presented in the JPL and CDMS catalogs
for each molecular line is proportional to the maximum optical depth of the
line $\tau^{max}$:

$I=\frac{\kappa_{\nu}}{f(\nu)\cdot n}=\frac{\tau(\nu)}{f(\nu)\cdot
N}\propto\frac{\tau^{max}\Delta\nu}{N}$ (2)

where $N$ is the column density of the molecule, $\tau(\nu)$ is the optical
depth of the line as a function of frequency, $f(\nu)$ is the normalized
function describing the line profile, $\Delta\nu$ is the line width (FWHM).
From here, one can find the maximum optical depth of the line (up to a certain
coefficient, which depends on $N$ and is the same for all lines). Further,
among the selected lines, the strongest one is found, that is, the line with
the largest optical depth. Some optical depth value is assigned to this line.
Then, the optical depths of the remaining lines can be found using the
relation:

$\tau_{i}^{max}=\tau_{ref}^{max}\times
I_{i}/I_{ref}\times\frac{\nu_{i}}{\nu_{ref}}$ (3)

It is assumed here that the widths of all lines in velocity units are the
same, in which case $\Delta\nu_{i}\propto\nu_{i}$. Knowing the optical depth
$\tau_{i}$, one can find the amplitude of each line, $\Delta T_{i}$, using the
well-known relation:

$\Delta T_{i}=(T_{ex}-T_{bg})\times(1-exp(-\tau_{i}))$ (4)

where $T_{ex}$ and $T_{bg}$ are the Rayleigh–Jeans equivalent temperatures of
excitation and microwave background. The excitation temperature under LTE is
equal to the chosen rotational temperature.

When the brightness temperature of each line is known, one can calculate the
ratios $R_{i}=T_{i}/T_{ref}$, where $T_{ref}$ is the brightness temperature of
the reference line and $T_{i}$ is the brightness temperature of the $i-$th
line. All lines with $R_{i}\lesssim 0.01$ are excluded from further
consideration. Then, from the observed spectrum we cut out narrow bands
centered on the frequencies of selected lines and divided the brightness
temperatures in each band by the relevant $R_{i}$. After this procedure, the
brightness temperatures of the lines in all narrow-band spectra became
approximately the same, and the noise rms increased proportionally to $R_{i}$.
The narrow-band spectra were stacked with weights inversely proportional to
the spectrum noise dispersion and the weight of the strongest line equal to
unity, and the results were divided by the sum of the weights. With this
method, the SL amplitude turns out to be approximately equal to the reference
line amplitude, and the noise level is less than that in the original spectrum
by $\sqrt{\sum(w_{i})}$ times.

The sizes of the sources in which we are looking for new molecules are
unknown. If we assume that these sizes are comparable to the main beam width,
then the weak lines that appear in such sources should be optically thin. The
optical depth of the strongest line $\tau_{ref}^{max}$ is set equal to 0.1 by
default, and in this survey, we keep this value of the maximum optical depth.
The exact value of the optical depth provided that $\tau_{ref}^{max}<<1$, does
not matter for calculating the weights. However, compact sources may fall into
the telescope beam. For example, in our observations, it was hot cores MM1a
and MM1b. The sizes of these sources are much smaller than the beam width, and
even weak lines arising in these cores may be optically thick. In this case,
the choice of line weights, made on the assumption that the lines are
optically thin, is no longer optimal. Therefore, at the final stage, one
should repeat SLS abandoning the assumption that the lines are optically thin.
We rebuilt all stacked spectra, setting the maximum optical depth of the
reference line of each molecule to be equal to 10. However, no new molecule
was found as a result of this procedure.

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Figure 1: DR21OH spectrum in the frequency range 69200–69500 MHz. The spectrum
is fully available in the electronic form.

Figure 2: Rotation diagrams plotted from lines found at 4 mm. RDs for
methanol: upper panel – plotted from the observed transitions; lower panel –
model RD plotted from the same transitions when they are optically thick. RDs
for cyclopropenylidene: upper panel – plotted from the observed transitions;
lower panel – plotted from the results of RADEX modeling ($T_{kin}=32$ K,
N${}_{\symoperators c-C3H2}=6.4\times 10^{12}$ cm-2, $n_{\symoperators
H2}=2\times 10^{5}$ cm-3)

Figure 3: Stacked spectra of methylcyanoacetylene (CH3C3N) for seven rotation
temperatures. N – the number of stacked lines, SoW – the sum of weights of
stacked lines.

Figure 4: The thin solid line is the synthetic spectrum of
methylcyanoacetylene (CH3C3N), constructed from observational data. The thick
solid line is a similar synthetic spectrum built using the model spectrum of
the source (MSS), which includes all detected molecules, except for
methylcyanoacetylene. The dotted line is a synthetic spectrum constructed from
a spectral model that includes only methylcyanoacetylene.

Table 1: Molecules found in the DR21OH star-forming region Diatomic  |  NS, SiO, 29SiO, 30SiO, 30Si18O?, 34SO, SO, SO+
---|---
Triatomic  |  CCH, 13CCH, C13CH, CCD, CCS, DCO+, DCN, DNC, HCO, HDO, HNO, HC18O+, HC17O+, HCS+, H13CN, HC15N, H13CO+,N2O, N2D+, OCS, O13CS?, OC34S?, SO2
Four-atom  |  l-C3H, C3S?, H2CO, H${}_{2}^{13}$CO, H2CS, HOCO+, HOCN?, D2CS, NH2D
Five-atom |  c-C3H2, l-C3H2, C4H, CH2CO, CH2CN, DC3N, H13CCCN, HC13CCN, HCC13CN, t-HCOOH, HC3N
Six-atom |  CH3CN, CH3OH, 13CH3OH, CH3SH, NH2CHO
Seven-atom |  CH3CCH, CH3CHO, CH2CHCN, CH3NH2, HC5N
Eight-atom |  CH3OCHO, C2H3CHO, CH3C3N,
Nine-atom  |  C2H5OH, CH3OCH3, CH3CH2CN, CH3C4H?
Ten-atom |  CH3COCH3

Table 2: Rotational temperatures, column densities, and abundances of
molecules obtained using rotation diagrams. Numbers in brackets show $1\sigma$
errors.

Molecule | $T_{rot}$ | $N_{mol}$ |  $N_{mol}/N_{H_{2}}$1
---|---|---|---
| (K) | ($10^{13}$ cm-2) | ($10^{-10}$)
C4H | 8.9(0.8) | 15(3.0) | 5(1)
c-C3H2 | 7.1(0.9) | 1.3(0.53) | 0.4(0.2)
CCS | 11.4(2.0) | 0.73(0.28) | 0.2(0.1)
CH3CCH | 35.6(3.9) | 66(9.4) | 22(3)
HC5N | 28.7(1.6) | 0.68(0.08) | 0.2(0.02)
CH3CN | 31.3(1.6) | 2.5(0.18) | 0.8(0.06)
CH3CHO | 9.7(2.2) | 2.5(0.86) | 0.8(0.3)
CH3OH | 19(4) | 110(100) | 37(33)
CH3OH2 | 298(196) | 170(170) | –
CH2CO | 46.1(3.8) | 4.5(0.35) | 1.5(0.1)
SO2 | 49.4(7.4) | 21(4.1) | –

${}^{1}-N_{H_{2}}=3\times 10^{23}$ cm-2 (see Subsection 3.1).
2–abundance is not given because the size of the hot region and the column
density of hydrogen in it are unknown.

Table 3: Column densities of molecules determined from single lines  Molecule | Column density | $N_{mol}/N_{H_{2}}$
---|---|---
| ($10^{12}$ cm-2) | ($10^{-11}$)
13CCH | 34 | 10.5
C13CH | 47 | 14.5
CCH | 2133 | 660
C4H | 94 | 29.1
CCD | 118 | 36.5
CCS | 10 | 3.1
CH2CHCN | 3 | 1.0
CH2CN | 1 | 0.3
CH3CHO | 115.8 | 35.8
CH3OCH3 | 110 | 34.1
CH3OCHO | 100.3 | 31.1
CH3OH | 3359.5 | 1040.1
D2CS | 1.9 | 0.6
DC3N | 0.7 | 0.2
DCN | 24.1 | 7.5
DCO+ | 3.4 | 1.1
DNC | 8.4 | 2.6
H13CCCN | 1.1 | 0.4
H13CN | 43.9 | 13.6
H13CO+ | 18.3 | 5.6
l-C3H2 | 0.9 | 0.3
H2CO | 582.2 | 180.2
H2CS | 136.6 | 42.3
H${}_{2}^{13}$CO | 23.8 | 7.4
HC13CCN | 1.5 | 0.5
HC15N | 9.5 | 2.9
HC18O+ | 2.7 | 0.8
HCC13CN | 1.3 | 0.4
HC3N | 58.4 | 21.9

Table 3: (continued)  Molecule | Column density | $N_{mol}/N_{H_{2}}$
---|---|---
| ($10^{12}$ cm-2) | ($10^{-11}$)
HCO | 83.2 | 25.8
t-HCOOH | 24.2 | 7.5
HCS+ | 11.5 | 3.6
HDO | 10.1 | 3.1
HN13C | 15.9 | 4.9
HNO | 16.7 | 5.2
N2D+ | 1.1 | 0.4
NH2CHO | 1.1 | 0.4
NS | 91.6 | 28.4
OCS | 101.7 | 31.5
29SiO | 1.5 | 0.5
34SO | 25 | 7.8
SO | 405.4 | 125.5
SO+ | 36.8 | 11.4
SiO | 24.2 | 7.5
l-C3H | 7.9 | 2.5
l-C3H2 | 0.9 | 0.3
CH3C3N | 1.1 | 0.4
CH3CH2CN | 1.2 | 0.4
CH3CH2OH | 36 | 11.1
C3S | 0.3 | 0.1
13CH3OH | 59 | 18.3
CH3C4H | 4.5 | 1.4
CH3OCH3 | 125 | 38.7
CH3SH | 36 | 11.1
CH2CN | 1.4 | 0.4
OC34S | 4.9 | 1.5
C2H3CHO | 1.8 | 0.5

Table 4: Spectral lines of the DR21OH M star formation region in the 4-mm wavelength range.  Frequency | Molecule | Transition | $\int T_{R}dV$ | $V_{LSR}$ | $\Delta V$ | $T_{R}$ | Notes
---|---|---|---|---|---|---|---
(MHz) |  |  | (K km s${}^{-1})$ | (km s-1) | (km s-1 ) | (K) |
68305.68 | CH3OH | $1_{1,0}-2_{0,2}E$ | 0.27(0.04) | -2.92(0.61) | 9.40(1.63) | 0.0265 |
68354.502 | CH3CCH | $4_{3}-3_{3}$ | 0.13(0.02) | -3.33(0.05) | 3.98(0.00) | 0.0314 | bl
68361.035 | CH3CCH | $4_{2}-3_{2}$ | 0.30(0.02) | -3.33(0.05) | 3.98(0.00) | 0.0714 | bl
68364.955 | CH3CCH | $4_{1}-3_{1}$ | 0.67(0.02) | -3.33(0.05) | 3.98(0.00) | 0.1586 |
68366.262 | CH3CCH | $4_{0}-3_{0}$ | 0.81(0.02) | -3.33(0.05) | 3.98(0.06) | 0.1901 |
68699.381 | H2CS | $2_{0,2}-1_{0,1}$ | 0.69(0.02) | -3.08(0.07) | 4.27(0.17) | 0.152 |
68972.154 | SO2 | $6_{1,5}-6_{0,6}$ | 0.81(0.02) | -3.03(0.09) | 6.00(0.22) | 0.1275 | rw
69002.890 | NS | $J=3/2-1/2\leavevmode\nobreak\ F=5/2-3/2e$ | 0.45(0.02) | -2.76(0.07) | 3.73(0.08) | 0.1123 |
69017.895 | NS | $J=3/2-1/2\leavevmode\nobreak\ F=3/2-3/2e$ | 0.18(0.02) | -2.76(0.07) | 3.73(0.00) | 0.0452 |
69037.336 | NS | $J=3/2-1/2\leavevmode\nobreak\ F=3/2-3/2e$ | 0.17(0.02) | -2.76(0.07) | 3.73(0.00) | 0.0415 |
69040.324 | NS | $J=3/2-1/2\leavevmode\nobreak\ F=1/2-1/2e$ | 0.11(0.01) | -2.76(0.07) | 3.73(0.00) | 0.0279 |
69227.183 | HC5N | $26-25$ | 0.31(0.02) | -2.73(0.14) | 4.56(0.27) | 0.065 |
69281.115 | CCS | $N_{J}=5_{6}-4_{5}$ | 0.33(0.02) | -3.23(0.10) | 3.99(0.24) | 0.078 |
69330.592 | NS | $J=3/2-1/2\leavevmode\nobreak\ F=3/2-3/2\leavevmode\nobreak\ f$ | 0.14(0.01) | -3.38(0.19) | 3.77(0.38) | 0.035 |
69408.371 | SO+ | ${}^{2}\Pi_{1/2}\leavevmode\nobreak\ J=3/2-1/2e$ | 0.17(0.02) | -2.92(0.20) | 4.24(0.87) | 0.0380 |
69411.943 | NS | $J=3/2-1/2\leavevmode\nobreak\ F=5/2-3/2f$ | 0.46(0.02) | -3.36(1.31) | 3.71(0.31) | 0.1158 |
69437.850 | NS | $J=3/2-1/2\leavevmode\nobreak\ F=1/2-1/2\leavevmode\nobreak\ f$ | 0.14(0.02) | -3.33(0.16) | 3.22(0.42) | 0.040 |
69485.223 | NS | $J=3/2-1/2\leavevmode\nobreak\ F=3/2-1/2\leavevmode\nobreak\ f$ | 0.17(0.01) | -3.23(0.11) | 2.99(0.29) | 0.052 |
69575.923 | SO2 | $1_{1,1}-0_{0,0}$ | 0.42(0.02) | -2.99(0.57) | 5.20(0.05) | 0.0752 |
69746.720 | H2CS | $2_{1,1}-1_{1,0}$ | 0.91(0.01) | -3.19(0.03) | 4.10(0.07) | 0.209 |
69783.846 | SO+ | ${}^{2}\Pi_{1/2}\leavevmode\nobreak\ J=3/2-1/2f$ | 0.11(0.01) | -3.17(0.11) | 2.55(0.26) | 4.195 |
70534.033 | H13CCCN | $8-7$ | 0.11(0.01) | -3.45(0.18) | 3.72(0.52) | 0.0279 |
71024.781 | H${}_{2}^{13}$CO | $1_{0,1}-0_{0,0}$ | 0.24(0.01) | -3.19(0.10) | 4.49(0.25) | 0.0499 |
71889.596 | HC5N | $27-26$ | 0.31(0.01) | -3.02(0.10) | 4.51(0.22) | 0.0640 |

Table 4:  (continued)  Frequency | Molecule | Transition | $\int T_{R}dV$ | $V_{LSR}$ | $\Delta V$ | $T_{R}$ | Notes
---|---|---|---|---|---|---|---
(MHz) |  |  |  (K km s${}^{-1})$ |  (km s-1) |  (km s-1 ) | (K) |
72039.331 |  DCO+ | $1-0$ | 0.54(0.02) | -2.99(0.05) | 3.56(0.13) | 0.1416 |
72107.721 | CCD | $1-0\leavevmode\nobreak\ J=5/2-3/2\leavevmode\nobreak\ F=7/2-5/2$ | 0.26(0.02) | -3.35(0.18) | 5.19(0.54) | 0.048 |
72187.708 | CCD | $1-0\leavevmode\nobreak\ J=3/2-3/2\leavevmode\nobreak\ F=5/2-5/2$ | 0.08(0.01) | -2.87(0.15) | 3.69(0.22) | 0.021 | new
72189.726 | CCD | $1-0\leavevmode\nobreak\ J=3/2-1/2\leavevmode\nobreak\ F=3/2-5/2$ | 0.08(0.01) | -2.87(0.15) | 3.69(0.22) | 0.020 | new
72323.789 | CCS | $J_{N}=6_{5}-5_{4}$ | 0.11(0.01) | -3.25(0.14) | 3.41(0.18) | 0.031 |
72409.092 |  H2CO | $5_{1,4}-5_{1,5}$ | 0.28(0.01) | -2.78(1.98) | 4.89(0.02) | 0.0544 |
72413.484 | DCN | $1-0\leavevmode\nobreak\ F=1-1$ | 0.75(0.01) | -3.67(0.01) | 4.30(0.02) | 0.1752 |
72414.905 | DCN | $1-0\leavevmode\nobreak\ F=2-1$ | 1.26(0.01) | -3.67(0.01) | 4.30(0.02) | 0.292 |
72417.030 | DCN | $1-0\leavevmode\nobreak\ F=0-1$ | 0.25(0.01) | -3.67(0.01) | 4.30(0.02) | 0.0584 |
72475.074 |  HC13CCN | $8-7$ | 0.18(0.01) | -3.07(0.18) | 5.90(0.46) | 0.0293 |
72482.055 |  HCC13CN | $8-7$ | 0.14(0.01) | -3.02(0.19) | 4.63(0.38) | 0.0290 |
72758.235 |  SO2 | $6_{0,6}-5_{1,5}$ | 0.86(0.02) | -3.31(0.04) | 4.77(0.11) | 0.1696 | rw
72783.818 |  HC3N | $8-7$ | 6.52(0.02) | -3.20(0.01) | 4.32(0.01) | 1.4191 | bw,rw
72835 | U |  | 0.11(0.01) | -3.38(0.07) | 2.01(0.12) | 0.052 | new
72837.948 |  H2CO | $1_{0,1}-0_{0,0}$ | 5.87(0.12) | -4.19(0.03) | 2.97(0.04) | 1.86 | bw
|  |  | 3.43(0.12) | -1.30(0.04) | 2.88(0.05) | 1.12 |
72976.779 | OCS | $6-5$ | 0.37(0.01) | -3.05(0.07) | 4.10(0.15) | 0.0855 |
73577.454 |  CH3CN | $4_{3}-3_{3}$ | 0.11(0.01) | -3.27(0.02) | 4.26(0.00) | 0.0244 |
73584.545 |  CH3CN | $4_{2}-3_{2}$ | 0.32(0.01) | -3.27(0.02) | 4.26(0.00) | 0.0694 |
73588.801 |  CH3CN | $4_{1}-3_{1}$ | 0.81(0.01) | -3.27(0.02) | 4.26(0.00) | 0.1787 | bl
73590.220 |  CH3CN | $4_{0}-3_{0}$ | 0.92(0.01) | -3.27(0.02) | 4.26(0.03) | 0.2020 | bl
73722.376 |  CH3OCH3 | $9_{2,7}-9_{1,8}EE$ | 0.14(0.02) | -5.12(0.68) | 11.79(1.23) | 0.0109 |
+73720.490 |  CH3OCH3 | $9_{2,7}-9_{1,8}AE+EA$ |  |  |  |  |
+73724.261 |  CH3OCH3 | $9_{2,7}-9_{1,8}AA$ |  |  |  |  |
74551.988 |  HC5N | $28-27$ | 0.28(0.01) | -3.06(1.37) | 4.35(0.08) | 0.0594 |
74891.681 |  CH3CHO | $4_{1,4}-3_{1,3}A^{++}$ | 0.25(0.01) | -3.27(1.87) | 4.35(0.18) | 0.0536 |

Table 4:  (continued)  Frequency | Molecule | Transition | $\int T_{R}dV$ | $V_{LSR}$ | $\Delta V$ | $T_{R}$ | Notes
---|---|---|---|---|---|---|---
(MHz) |  |  |  (K km s${}^{-1})$ |  (km s-1) |  (km s-1 ) | (K) |
74924.137 |  CH3CHO | $4_{-1,4}-3_{-1,3}E$ | 0.22(0.01) | -3.27(2.41) | 3.59(0.23) | 0.0571 |
75366 | U |  | 0.05(0.013) | -3.27(0.23) | 2.66(0.58) | 0.018 | m
75862.92 |  CH3SH | $3_{0}-2_{0}A+$ | 0.16(0.02) | -2.63(0.90) | 13.21(1.80) | 0.0115 |
+75864.43 |  CH3SH | $3_{0}-2_{0}E$ |  |  |  |  |
75921 | U |  | 0.08(0.02) | -3.57(0.93) | 8.05(1.67) | 0.001 | m
76117.43 |  C4H |  17/2$-$15/2 | 0.21(0.01) | -3.02(0.08) | 3.10(0.19) | 0.0620 |
76156.02 |  C4H |  15/2$-$13/2 | 0.20(0.01) | -3.06(0.07) | 3.10(0.16) | 0.0613 |
76198.724 |  l-C3H | $2P1/2J=7/2-5/2,F=4-3f$ | 0.089(0.009) | -2.96(0.16) | 3.269(0.17) | 0.0257 | bl
76199.925 |  l-C3H | $2P1/2J=7/2-5/2,F=4-3f$ | 0.072(0.008) | -2.96(0.16) | 3.269(0.00) | 0.0206 | bl
76204.198 |  l-C3H | $2P1/23-2J=7/2-5/2\leavevmode\nobreak\ F=4-3$ | 0.041(0.008) | -2.96(0.16) | 3.269(0.00) | 0.0117 |
76205.108 |  l-C3H | $2P1/23-2J=7/2-5/2\leavevmode\nobreak\ F=3-2$ | 0.046(0.008) | -2.96(0.16) | 3.269(0.00) | 0.0132 |
76247.312 |  CH3OH | $11_{1,10}-10_{2,9}A^{-}$ | 0.12(0.01) | -3.15(0.19) | 4.03(0.43) | 0.0282 |
76305.717 | DNC | $1-0$ | 0.91(0.01) | -3.20(0.02) | 4.12(0.05) | 0.2066 |
76362.194 |  CH3OCH3 | $7_{2,5}-7_{1,6}AE+EA$ | 0.044(0.010) | -3.43(0.35) | 4.56(0.00) | 0.0090 | m
76364.277 |  CH3OCH3 | $7_{2,5}-7_{1,6}EE$ | 0.067(0.010) | -3.43(0.35) | 4.56(0.45) | 0.0137 |
76412.158 |  SO2 | $10_{1,9}-9_{2,8}$ | 0.27(0.01) | -2.53(0.17) | 6.22(0.39) | 0.0402 |
76460 | U |  | 0.17(0.01) | -5.12(0.04) | 1.32(0.12) | 0.120 |
|  |  | 0.20(0.02) | -2.00(0.10) | 2.69(0.31) | 0.068 |
76509.628 |  CH3OH | $5_{0,5}-4_{1,3}E$ | 0.75(0.01) | -2.99(0.04) | 5.40(0.09) | 0.1313 |
76866.437 |  CH3CHO | $4_{0,4}-3_{0,3}E$ | 0.36(0.01) | -3.21(0.06) | 4.29(0.14) | 0.0787 |
76878.958 |  CH3CHO | $4_{0,4}-3_{0,3}A^{++}$ | 0.36(0.01) | -3.13(0.06) | 4.04(0.16) | 0.0832 |
77038.605 |  CH3CHO | $4_{2,3}-3_{2,2}A^{--}$ | 0.08(0.01) | -3.62(0.20) | 3.50(0.46) | 0.0223 |
77107.86 |  N2D+ | $1-0\leavevmode\nobreak\ F1=1-1$ | 0.045(0.008) | -3.16(0.16) | 3.20(0.00) | 0.0131 |

Table 4:  (continued)  Frequency | Molecule | Transition | $\int T_{R}dV$ | $V_{LSR}$ | $\Delta V$ | $T_{R}$ | Notes
---|---|---|---|---|---|---|---
(MHz) |  |  |  (K km s${}^{-1})$ |  (km s-1) |  (km s-1 ) | (K) |
77109.61 |  N2D+ | $1-0\leavevmode\nobreak\ F1=2-1$ | 0.074(0.008) | -3.16(0.16) | 3.20(0.20) | 0.0215 |
77112.2 |  N2D+ | $1-0\leavevmode\nobreak\ F1=0-1$ | 0.025(0.007) | -3.16(0.16) | 3.20(0.00) | 0.0074 | hfs
77125.695 |  CH3CHO | $4_{2,2}-3_{2,1}$ | 0.26(0.04) | -4.63(0.15) | 6.13(0.38) | 0.040 |
+77126.418 |  CH3CHO | $4_{2,3}-3_{-2,2}$ |  |  |  |  |
77214.360 |  HC5N | $29-28$ | 0.28(0.01) | -2.97(0.09) | 4.65(0.19) | 0.0556 |
77218.295 |  CH3CHO | $4_{2,2}-3_{2,1}A^{++}$ | 0.09(0.01) | -3.05(0.32) | 5.35(0.78) | 0.0160 |
77731.725 | CCS | $6,6-5,5$ | 0.16(0.01) | -2.95(0.13) | 4.27(0.31) | 0.0348 |
78603.670 |  30Si18O | $2-1$ | 0.047(0.01) | -2.98(0.60) | 5.00(1.21) | 0.009 | m
79099.313 |  CH3CHO | $4_{1,3}-3_{1,2}E$ | 0.32(0.01) | -3.34(0.05) | 4.28(0.12) | 0.0704 |
79150.172 |  CH3CHO | $4_{1,3}-3_{1,2}$ | 0.34(0.01) | -3.37(0.07) | 4.86(0.28) | 0.0656 |
79350.476 |  H13CCCN | $9-8$ | 0.12(0.01) | -2.98(0.17) | 4.51(0.33) | 0.0252 |
79876.711 |  HC5N | $30-29$ | 0.27(0.01) | -2.70(0.18) | 5.12(0.13) | 0.0488 |
80076.644 |  CH2CO | $4_{1,4}-3_{1,3}$ | 0.25(0.01) | -3.15(0.06) | 3.73(1.69) | 0.0637 |
80479.940 |  CH2CN | $4-3\leavevmode\nobreak\ J=11/2-9/2$ | 0.04(0.006) | -4.62(0.18) | 2.37(0.90) | 0.016 | m
80490 | U |  | 0.05(0.01) | -4.89(0.23) | 2.97(0.48) | 0.015 |
80578.283 | HDO | $1_{1,0}-1_{1,1}$ | 0.072(0.010) | 0.066(8.05) | 6.76(1.40) | 0.010 | di,bl?
80723.186 |  c-C3H2 | $4_{2,2}-4_{1,3}$ | 0.046(0.009) | -3.68(0.44) | 4.74(0.75) | 0.0091 |
80820.409 |  CH2CO | $4_{2,3}-3_{2,2}$ | 0.030(0.007) | -3.24(0.13) | 3.50(0.00) | 0.0082 |
80824.314 |  CH2CO | $4_{2,2}-3_{2,1}$ | 0.024(0.007) | -3.24(0.13) | 3.50(0.00) | 0.0063 |
80832.107 |  CH2CO | $4_{0,4}-3_{0,3}$ | 0.11(0.01) | -3.24(0.13) | 3.50(0.17) | 0.0283 |
80993.257 |  CH3OH | $7_{2,6}-8_{1,7}A^{-}$ | 0.14(0.01) | -2.62(2.04) | 6.62(3.10) | 0.0192 |
81477.49 | HNO | $1_{0,1}-0_{0,0}$ | 0.12(0.01) | -3.25(1.19) | 3.20(0.42) | 0.0344 |
81505.208 | CCS | $7,6-6,5$ | 0.31(0.01) | -3.23(0.32) | 3.53(0.06) | 0.0834 |
81534.125 |  HC13CCN | $9-8$ | 0.12(0.01) | -2.68(1.60) | 4.74(0.19) | 0.0236 |

Table 4:  (continued)  Frequency | Molecule | Transition | $\int T_{R}dV$ | $V_{LSR}$ | $\Delta V$ | $T_{R}$ | Notes
---|---|---|---|---|---|---|---
(MHz) |  |  |  (K km s${}^{-1})$ |  (km s-1) |  (km s-1 ) | (K) |
81541.981 |  HCC13CN | $9-8$ | 0.12(0.01) | -2.66(1.73) | 3.77(1.13) | 0.0287 |
81586.229 |  CH2CO | $4_{1,3}-3_{1,2}$ | 0.24(0.01) | -3.00(0.42) | 3.67(3.11) | 0.0617 |
81881.462 |  HC3N | $9-8$ | 6.22(0.01) | -3.12(0.00) | 4.44(0.00) | 1.3159 |
82093.555 |  c-C3H2 | $2_{0,2}-1_{1,1}$ | 0.47(0.01) | -3.05(0.03) | 3.45(0.11) | 0.1266 |
82395.089 |  l-C3H2 | $4_{1,4}-3_{1,3}$ | 0.06(0.004) | -2.59(0.07) | 2.20(0.76) | 0.0237 |
82539.375 | U |  | 0.15(0.01) | -2.13(0.10) | 3.26(0.26) | 0.0440 |
|  |  | 0.049(0.008) | 0.79(0.10) | 1.71(0.22) | 0.0267 |
82966.201 |  c-C3H2 | $3_{1,2}-3_{0,3}$ | 0.19(0.01) | -2.89(0.08) | 3.84(0.17) | 0.0453 |
83163 | U |  | 0.11(0.01) | -3.78(0.14) | 3.99(0.31) | 0.0261 |
83207.51 |  CH2CHCN | $9_{1,9}-8_{1,8}$ | 0.021(0.004) | -2.73(0.25) | 2.39(0.52) | 0.0084 |
83217 | U |  | 0.09(0.01) | -4.03(0.13) | 3.64(0.31) | 0.024 |
83584.282 |  CH3CHO | $2_{-1,2}-1_{0,1}E$ | 0.05(0.01) | -2.88(0.23) | 3.15(0.48) | 0.0136 |
83688.086 |  SO2 | $8_{1,7}-8_{0,8}$ | 0.80(0.01) | -2.79(0.03) | 6.40(0.08) | 0.1179 | rw
83900.570 | HOCN | $4_{0,4}-3_{0,3}$ | 0.04(0.01) | -3.74(0.22) | 3.02(0.62) | 0.0139 | di
83933.681 |  l-C3H2 | $4_{1,3}-3_{1,2}$ | 0.06(0.01) | -2.71(0.16) | 2.47(0.59) | 0.0211 |
84119.329 |  13CCH | $1-0\leavevmode\nobreak\ 3/2-1/2\leavevmode\nobreak\ F=2,2.5-1,1.5$ | 0.07(0.01) | -3.02(0.17) | 3.66(0.33) | 0.017 |
84410.693 |  34SO | $N,J=2,2-1,1$ | 0.13(0.01) | -0.92(0.37) | 9.28(0.94) | 0.0128 | bl
84423.706 |  CH3OH | $13_{-3,11}-14_{-2,13}E$ | 0.05(0.01) | -3.76(0.15) | 2.69(0.35) | 0.0165 |
84429.815 |  DC3N | $10-9$ | 0.08(0.01) | -2.67(0.28) | 4.49(0.73) | 0.016 |
84449.102 |  CH3OCHO | $7_{2,6}-6_{2,5}E$ | 0.03(0.01) | -2.49(0.00) | 5.82(0.00) | 0.0054 | m
84454.787 |  CH3OCHO | $7_{2,6}-6_{2,5}A$ | 0.04(0.01) | -2.49(0.43) | 5.82(0.51) | 0.0065 | m
84521.206 |  CH3OH | $5_{-1,5}-4_{0,4}E$ | 0.85(0.04) | 0.43(0.00) | 0.89(0.00) | 0.9033 | mas
|  |  | 0.005(0.005) | 0.16(0.01) | 0.76(0.01) | 0.0066 | mas
|  |  | 2.27(0.11) | -0.70(0.05) | 2.62(0.16) | 0.8144 | mas
|  |  | 3.65(0.12) | -3.84(0.05) | 3.77(0.21) | 0.9108 | mas

Table 4:  (continued)  Frequency | Molecule | Transition | $\int T_{R}dV$ | $V_{LSR}$ | $\Delta V$ | $T_{R}$ | Notes
---|---|---|---|---|---|---|---
(MHz) |  |  |  (K km s${}^{-1})$ |  (km s-1) |  (km s-1 ) | (K) |
84542.331 |  NH2CHO | $4_{0,4}-3_{0,3}$ | 0.031(0.006) | -3.55(0.27) | 3.21(0.75) | 0.0091 |
84727.691 |  c-C3H2 | $3_{2,2}-3_{1,3}$ | 0.07(0.01) | -3.39(0.23) | 4.14(0.98) | 0.0161 |
84745.998 |  30SiO | $2-1\leavevmode\nobreak\ v=0$ | 0.15(0.01) | -3.97(0.21) | 7.21(0.79) | 0.0198 |
84865.166 |  O13CS | $7-6$ | 0.03(0.008) | -4.73(0.78) | 5.68(1.40) | 0.006 | m
85139.104 | OCS | $7-6$ | 0.55(0.01) | -2.86(0.03) | 4.63(0.07) | 0.1108 |
85153.931 |  D2CS | $3_{0,3}-2_{0,2}$ | 0.023(0.007) | -3.46(0.40) | 3.00(1.14) | 0.0073 | di
85162.223 |  HC18O+ | $1-0$ | 0.43(0.01) | -3.35(0.03) | 3.93(0.07) | 0.1016 |
85201.346 |  HC5N | $32-31$ | 0.25(0.02) | -3.89(0.13) | 2.72(0.26) | 0.089 |
|  |  | 0.14(0.02) | -0.93(0.22) | 2.55(0.38) | 0.053 |
85229.27 |  C13CH | $1-0\leavevmode\nobreak\ 3/2-1/2\leavevmode\nobreak\ F=2,2.5-1,1.5$ | 0.09(0.01) | -2.93(0.11) | 4.26(0.16) | 0.0205 |
85232.76 |  C13CH | $1-0\leavevmode\nobreak\ 3/2-1/2\leavevmode\nobreak\ F=2,1.5-1,0.5$ | 0.07(0.01) | -2.93(0.11) | 4.26(0.00) | 0.0149 |
85247.65 |  C13CH | $1-0\leavevmode\nobreak\ 3/2-1/2\leavevmode\nobreak\ F=1,0.5-0,0.5$ | 0.035(0.006) | -2.93(0.11) | 4.26(0.00) | 0.0078 |
85256.96 |  C13CH | $1-0\leavevmode\nobreak\ 3/2-1/2\leavevmode\nobreak\ F=1,1.5-0,0.5$ | 0.06(0.01) | -2.93(0.11) | 4.26(0.00) | 0.0133 |
85265.507 |  t-CH3CH2OH | $6_{0,6}-5_{1,5}$ | 0.06(0.01) | -2.12(0.41) | 5.89(0.53) | 0.0094 |
85307.459 |  C13CH | $1-0\leavevmode\nobreak\ 1/2-1/2\leavevmode\nobreak\ F=1,1.5-1,1.5$ | 0.06(0.006) | -2.62(0.23) | 4.20(0.44) | 0.014 |
85338.906 |  c-C3H2 | $2_{1,2}-1_{0,1}$ | 1.51(0.01) | -3.08(0.01) | 3.72(0.01) | 0.3807 |
85347.869 |  HCS+ | $2-1$ | 0.71(0.01) | -3.01(0.09) | 3.93(0.01) | 0.1694 |
85442.6 |  CH3CCH | $5_{3}-4_{3}$ | 0.26(0.00) | -3.24(0.01) | 4.09(0.00) | 0.0587 |
85450.765 |  CH3CCH | $5_{2}-4_{2}$ | 0.43(0.00) | -3.24(0.01) | 4.09(0.00) | 0.0978 |
85455.665 |  CH3CCH | $5_{1}-4_{1}$ | 1.02(0.00) | -3.24(0.01) | 4.09(0.00) | 0.2348 |
85457.299 |  CH3CCH | $5_{0}-4_{0}$ | 1.27(0.01) | -3.24(0.01) | 4.09(0.01) | 0.2910 |
85531.512 |  HOCO+ | $4_{0,4}-4_{1,3}$ | 0.03(0.006) | -3.41(0.28) | 2.78(0.63) | 0.011 | m
85568.074 |  CH3OH | $6_{-2,5}-7_{-1,7}E$ | 0.10(0.01) | -3.41(0.14) | 4.08(0.37) | 0.0238 |

Table 4:  (continued)  Frequency | Molecule | Transition | $\int T_{R}dV$ | $V_{LSR}$ | $\Delta V$ | $T_{R}$ | Notes
---|---|---|---|---|---|---|---
(MHz) |  |  |  (K km s${}^{-1})$ |  (km s-1) |  (km s-1 ) | (K) |
85634.00 |  C4H | $9-8\leavevmode\nobreak\ J=19/2-17/2$ | 0.17(0.01) | -2.85(0.03) | 2.60(0.04) | 0.0631 |
85672.57 |  C4H | $9-8\leavevmode\nobreak\ J=17/2-15/2$ | 0.16(0.01) | -2.85(0.03) | 2.60(0.00) | 0.0561 |
85656.418 |  c-C3H2 | $4_{3,2}-4_{2,3}$ | 0.039(0.005) | -3.67(0.18) | 3.20(0.75) | 0.0113 |
85715.424 |  CH2CHCN | $9_{2,7}-8_{2,6}$ | 0.03(0.006) | -3.42(0.28) | 2.71(0.50) | 0.010 |
85759.188 |  29SiO | $2-1v=0$ | 0.20(0.01) | -3.29(0.11) | 6.44(0.01) | 0.0292 |
85926.270 |  NH2D | $1_{1,1}-1_{0,1}$ | 0.99(0.02) | -2.94(0.06) | 7.09(0.15) | 0.131 | hfs
86054.967 |  HC15N | $1-0$ | 1.23(0.01) | -3.02(0.02) | 4.60(0.01) | 0.2512 |
86093.983 | SO | $N,J=2,2-1,1$ | 2.27(0.01) | -2.59(0.01) | 5.33(0.03) | 0.3997 |
86181.413 | CCS | $N,J=7,6-6,5$ | 0.13(0.01) | -2.98(0.13) | 3.72(0.33) | 0.0337 |
86338.736 |  H13CN | $1-0\leavevmode\nobreak\ F=1-1$ | 1.95(0.01) | -3.38(0.00) | 4.56(0.00) | 0.4028 |
86340.176 |  H13CN | $1-0\leavevmode\nobreak\ F=2-1$ | 3.06(0.01) | -3.38(0.00) | 4.56(0.01) | 0.6308 |
86342.255 |  H13CN | $1-0\leavevmode\nobreak\ F=0-1$ | 0.71(0.01) | -3.38(0.00) | 4.56(0.00) | 0.1474 |
86546.18 | t-HCOOH | $4_{1,4}-3_{1,3}$ | 0.10(0.01) | -3.11(0.22) | 4.56(0.74) | 0.0214 |
86615.602 |  CH3OH | $7_{2,6}-6_{3,3}A^{--}$ | 0.11(0.01) | -3.17(0.23) | 3.67(0.57) | 0.0283 |
86670.82 | HCO | $1_{0,1}-0_{0,0}\leavevmode\nobreak\ 3/2-1/2\leavevmode\nobreak\ F=2-1$ | 0.51(0.00) | -2.53(0.02) | 2.87(0.03) | 0.1667 |
86708.35 | HCO | $1_{0,1}-0_{0,0}\leavevmode\nobreak\ 3/2-1/2\leavevmode\nobreak\ F=1-0$ | 0.36(0.01) | -2.53(0.02) | 2.87(0.00) | 0.1172 |
86754.288 |  H13CO+ | $1-0$ | 4.10(0.01) | -3.35(0.00) | 4.09(0.00) | 0.9428 |
86777.43 | HCO | $1_{0,1}-0_{0,0}\leavevmode\nobreak\ 1/2-1/2\leavevmode\nobreak\ F=1-1$ | 0.31(0.01) | -2.85(0.04) | 2.92(0.07) | 0.1009 |
86805.75 | HCO | $1_{0,1}-0_{0,0}\leavevmode\nobreak\ 1/2-1/2\leavevmode\nobreak\ F=0-1$ | 0.13(0.01) | -2.85(0.04) | 2.92(0.00) | 0.0409 |
86846.995 | SiO | $2-1\leavevmode\nobreak\ v=0$ | 1.70(0.02) | -3.27(0.26) | 4.59(0.26) | 0.3483 |
|  |  | 1.52(0.02) | -3.40(0.26) | 16.60(0.26) | 0.0859 |
86902.947 |  CH3OH | $7_{2,5}-6_{3,4}A^{++}$ | 0.09(0.01) | -3.34(0.15) | 3.48(0.67) | 0.0236 |
87057.258 |  HC17O+ | $1-0\leavevmode\nobreak\ F=7/2-5/2$ | 0.14(0.01) | -3.21(0.30) | 6.47(0.80) | 0.0200 |
+87056.966 |  HC17O+ | $1-0\leavevmode\nobreak\ F=3/2-5/2$ |  |  |  |  |
+87058.294 |  HC17O+ | $1-0\leavevmode\nobreak\ F=5/2-5/2$ |  |  |  |  |
87090.859 |  HN13C | $1-0\leavevmode\nobreak\ F=2-1$ | 1.73(0.01) | -2.97(0.01) | 4.32(0.03) | 0.3771 |
87143.198 |  CH3OCHO | $7_{3,4}-6_{3,3}E$ | 0.09(0.01) | -3.74(0.37) | 5.66(0.76) | 0.0141 |
87163 | U |  | 0.05(0.007) | -3.42(0.14) | 1.95(0.38) | 0.024 |

Table 4:  (continued)  Frequency | Molecule | Transition | $\int T_{R}dV$ | $V_{LSR}$ | $\Delta V$ | $T_{R}$ | Notes
---|---|---|---|---|---|---|---
(MHz) |  |  |  (K km s${}^{-1})$ |  (km s-1) |  (km s-1 ) | (K) |
87284.156 |  C2H | $1-0\leavevmode\nobreak\ 3/2-1/2\leavevmode\nobreak\ F=1-1$ | 1.03(0.00) | -2.78(0.02) | 3.70(0.01) | 0.2624 |
87313 | U |  | 0.17(0.01) | -5.11(0.09) | 2.97(0.12) | 0.0539 |
87316.925 |  C2H | $1-0\leavevmode\nobreak\ 3/2-1/2\leavevmode\nobreak\ F=2-1$ | 7.10(0.01) | -3.01(0.00) | 4.23(0.00) | 1.5753 |
87328.624 |  C2H | $1-0\leavevmode\nobreak\ 3/2-1/2\leavevmode\nobreak\ F=1-0$ | 4.19(0.01) | -3.01(0.00) | 4.23(0.00) | 0.9312 |
87398 | U |  | 0.04(0.01) | -4.73(0.21) | 1.70(0.43) | 0.020 |
87402.004 |  C2H | $1-0\leavevmode\nobreak\ 1/2-1/2\leavevmode\nobreak\ F=1-1$ | 4.32(0.01) | -3.01(0.00) | 4.23(0.00) | 0.9580 |
87407.165 |  C2H | $1-0\leavevmode\nobreak\ 1/2-1/2\leavevmode\nobreak\ F=0-1$ | 2.14(0.01) | -3.01(0.00) | 4.23(0.00) | 0.4748 |
87446.512 |  C2H | $1-0\leavevmode\nobreak\ 1/2-1/2\leavevmode\nobreak\ F=1-0$ | 1.18(0.01) | -3.01(0.00) | 4.23(0.00) | 0.2615 |
87863.63 |  HC5N | $33-32$ | 0.20(0.01) | -2.83(0.12) | 5.01(1.11) | 0.0381 |