# JWST Observations of the Enigmatic Y Dwarf WISE 1828+2650: I. Limits to a
Binary Companion

Matthew De Furio Department of Astronomy, University of Michigan, Ann Arbor,
MI 48109, USA  Ben Lew Bay Area Environmental Research Institute, Moffett
Field, CA 94035, USA  NASA Ames Research Center, Mountain View, CA  Charles
Beichman NASA Exoplanet Science Institute, Infrared Processing and Analysis
Center (IPAC)  Jet Propulsion Laboratory, California Institute of Technology,
Pasadena, CA 91125  Thomas Roellig NASA Ames Research Center, Mountain View,
CA  Geoffrey Bryden Jet Propulsion Laboratory, California Institute of
Technology, Pasadena, CA 91125  David Ciardi NASA Exoplanet Science Institute,
Infrared Processing and Analysis Center (IPAC)  Jet Propulsion Laboratory,
California Institute of Technology, Pasadena, CA 91125  Michael Meyer
Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA
Marcia Rieke Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
Alexandra Greenbaum IPAC, Caltech, 1200 E. California Blvd., Pasadena, CA
91125, USA  Jarron Leisenring Steward Observatory, University of Arizona,
Tucson, AZ 85721, USA  Jorge Llop-Sayson California Institute of Technology,
1200 E. California Blvd., Pasadena, CA 91125, USA  Marie Ygouf Jet Propulsion
Laboratory, California Institute of Technology, Pasadena, CA 91125  Loic
Albert Université de Montréal, Montréal,Quebec H3C 3J7, Canada,  Martha Boyer
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218,
USA  Daniel Eisenstein  Harvard-Smithsonian Center for Astrophysics, 60 Garden
St, Cambridge, MA 02138, USA  Klaus Hodapp  University of Hawaii, Hilo,
HI,96720  Scott Horner  NASA Ames Research Center, Mountain View, CA  Doug
Johnstone NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Rd,
Victoria, BC, V9E 2E7, Canada  Department of Physics and Astronomy, University
of Victoria, Victoria, BC, V8P 5C2, Canada  Doug Kelly  Steward Observatory,
University of Arizona, Tucson, AZ 85721, USA  Karl Misselt  Steward
Observatory, University of Arizona, Tucson, AZ 85721, USA  George Rieke
Steward Observatory, University of Arizona, Tucson, AZ 85721, USA  John
Stansberry Space Telescope Science Institute, 3700 San Martin Drive,
Baltimore, MD 21218, USA  Erick Young Universities Space Research Association,
425 3rd Street SW, Suite 950, Washington DC 20024

(Accepted February 21, 2023)

###### Abstract

The Y-dwarf WISE 1828+2650 is one of the coldest known Brown Dwarfs with an
effective temperature of $\sim$300 K. Located at a distance of just 10 pc,
previous model-based estimates suggest WISE1828+2650 has a mass of $\sim$5-10
$\,M_{\rm J}$, making it a valuable laboratory for understanding the
formation, evolution and physical characteristics of gas giant planets.
However, previous photometry and spectroscopy have presented a puzzle with the
near-impossibility of simultaneously fitting both the short (0.9-2.0 $\mu$m)
and long wavelength (3-5 $\mu$m) data. A potential solution to this problem
has been the suggestion that WISE 1828+2650 is a binary system whose composite
spectrum might provide a better match to the data. Alternatively, new models
being developed to fit JWST/NIRSpec and MIRI spectroscopy might provide new
insights. This article describes JWST/NIRCam observations of WISE 1828+2650 in
6 filters to address the binarity question and to provide new photometry to be
used in model fitting. We also report Adaptive Optics imaging with the Keck 10
m telescope. We find no evidence for multiplicity for a companion beyond 0.5
AU with either JWST or Keck. Companion articles will present low and high
resolution spectra of WISE 1828 obtained with both NIRSpec and MIRI.

††journal: ApJ

monthyearday []

##  1 Introduction

The WISE mission (Wright et al., 2010) identified cool brown dwarfs (BDs)
using their very red ([3.4]–[4.6] or hereafter W1-W2) colors (Kirkpatrick et
al., 2011). The most extreme of these objects, with effective temperatures
$T_{\rm eff}$ $<$500 K, have been typed as Y dwarfs (Cushing et al., 2011;
Kirkpatrick et al., 2012). With W1-W2$>$4.2 mag, WISEP J182831.08+265037.8
(hereafter WISE 1828+2650) was identified as one of the reddest of this small
group of only two dozen Y dwarfs. Follow-up photometry and spectroscopy with
the Hubble Space Telescope (HST), the Spitzer Space Telescope, and various
ground-based facilities found weak emission between 1.0-1.7 $\mu$m marked by
absorption due to H2O, CH4 and NH3 (Cushing et al., 2011), extremely weak
emission in the $K$ band (2.2 $\mu$m), followed by a sharp rise out to 5
$\mu$m.

Astrometry from Keck, Spitzer and HST determined distances to the WISE Y dwarf
sample ranging from 5-15 pc (Beichman et al., 2013; Martin et al., 2018;
Kirkpatrick et al., 2019). With distances serving to constrain the absolute
luminosity and typical ages of 3-10 Gyr inferred from their transverse
motions, it was possible to fit the photometry and spectroscopy to
evolutionary models to estimate masses from 5-10 $\,M_{\rm J}$. Beichman et
al. (2014) and Kirkpatrick et al. (2019) put WISE 1828+2650 at a distance of
of 9.93$\pm$0.23 pc and suggested an effective temperature of 400K and a mass
around 5 $\,M_{\rm J}$.

Table 1: JWST NIRCam Observing Parameters (PID:#1189)  Instrument | Filter Pair | Readout | Groups/Int | Ints/Exp | Dithers | Total Time (sec)
---|---|---|---|---|---|---
NIRCam | F115W & F335M (CH4) | MEDIUM | 4 | 10 | 4 | 1632
NIRCam | F140M (H2O, CH4) & F360M | MEDIUM | 4 | 10 | 4 | 1632
NIRCam | F162M (ref for F140M) & F470N (H2) | MEDIUM | 4 | 10 | 4 | 1632

WISE 1828+2650 has proven to be exceptional even within the unusual class of Y
dwarfs. Its extreme W1-W2 color, the difficulty in simultaneously fitting
models to the 1-2 and 3-5 $\mu$m photometry, and WISE 1828+2650’s position at
least 1 mag above the Y/T dwarf locus in the H-W2 color-magnitude diagram
(Kirkpatrick et al., 2019, Figure 8) highlighted the challenges of making
satisfactory models for such cold objects. Leggett et al. (2013, 2017)
suggested that WISE 1828+2650 might be a binary system which would account for
at least 0.75 mag of its separation from the Y/T locus. Most recently, Cushing
et al. (2021) used 0.7-1.7 $\mu$m HST spectroscopy and a new generation of
models (Marley et al., 2021, the Sonora Bobcat models) to bolster the idea
that WISE 1828+2650 is an unresolved binary consisting of roughly equal mass
objects with $T_{\rm eff}$$\sim$275-350 K. However, there remain challenges
with the model ages ($<$1 Gyr for a single object) and the subsolar values of
[M/H] $\sim-0.5$ and [C/O] $\sim-0.6$ required to fit the existing data
(Cushing et al., 2021).

With the expectation that JWST would help resolve these theoretical
difficulties, we set out a program of imaging and spectroscopy, particularly
in the key 3-10 $\mu$m region. The JWST NIRCam imaging data permit a search
for faint companions at separations and sensitivity levels not previously
possible as well as anchoring the fluxes of the the higher-spectral resolution
NIRSpec data. The spectroscopy provides critical diagnostics of physical
conditions, composition, the presence or absence of clouds, and surface
gravity in the 3-5 $\mu$m region where Y dwarfs emit most of their energy.

This paper describes NIRCam imaging in six filters spanning 1-5 $\mu$m
undertaken by the NIRCam Guaranteed Time Observation (GTO) team under
PID#1189. Companion papers will give results from NIRSpec and MIRI
spectroscopy, and from a deep NIRISS search for a close companion. $\S$2
describes the observations and $\S$3 the data reduction procedures and
results. $\S$4 addresses the search for and limits to the presence of a close
companion to WISE 1828+2650 while $\S$5 presents fits to the spectral energy
distribution of WISE 1828+2650 and estimates of derived physical parameters.
The paper ends with a search for wide field companions ($\S$6) and concluding
remarks.

Table 2: NIRCam Photometry

Filter | F${}_{\nu}(\mu$Jy)1 | Magnitude
---|---|---
F090W | 0.078$\pm$0.005(0.015) | 26.16$\pm$0.20
F115W | 0.311$\pm$0.005(0.03) | 24.39$\pm$0.10
F162M | 1.29$\pm$0.009(0.13) | 22.25$\pm$0.10
F335M | 2.41$\pm$0.013(0.24) | 20.23$\pm$0.10
F360M | 34.2$\pm$0.05(3.4) | 17.19$\pm$0.10
F470M | 340.4$\pm$0.62(34) | 14.16$\pm$0.10
F480M2 | 326$\pm$0.14(32) | 14.21$\pm$0.10
J (1.25 $\mu$m) | 0.65$\pm$0.23 | 23.48$\pm$0.23
H (1.65 $\mu$m) | 0.83$\pm$0.21 | 22.73$\pm$0.13
K (2.16 $\mu$m) | 0.27$\pm$0.08 | 23.48$\pm$0.36
Spitzer/IRAC (3.55 $\mu$m) | 48.1$\pm$1.0 | 16.92$\pm$0.02
Spitzer/IRAC (4.55 $\mu$m) | 335.5$\pm$6.71 | 14.32$\pm$0.02
WISE W2 (4.62 $\mu$m) | 310$\pm$14 | 14.35$\pm$0.05

.

Note. — 1 First quoted uncertainty reflects only photometric accuracy based on
aperture photometry. Values in parenthesis include an average 10% calibration
uncertainty at all wavelengths estimated from the average of successive
iterations of the calibration values (PHOTMJYSR and PIXAR_SR) available at
MAST. The values listed here use image files created on 2022-11-11 using
calibration software version 11.16.14 and photometric reference data from
jwst_nircam_photom_0114.fits. Values below the solid line come from ground and
space missions as given in (Martin et al., 2018; Liu et al., 2016; Kirkpatrick
et al., 2019, 2021). 2Observation obtained using the NIRISS instrument

Figure 1: left) A color-composite image of 3 NIRCam filters, F162M, F335M and
F470N showing one extremely red object at the expected position of WISE
1828+2650. right) a zoom-in on the position of WISE 1828+2650.

##  2 Observations and Data Reduction

Table 1 describes the observing parameters for this program, using the long
and short wavelength modules of NIRCam to observe WISE 1828+2650
simultaneously in a combination of narrow, medium and wide filters between 0.9
and 4.7 $\mu$m. Data were obtained on 2022-07-28 UTC. The NIRISS full frame
imager was used to obtain a long exposure in the F480M filter in a deep search
for a close companion. The NIRISS results will be presented separately, but
the photometry at that wavelength is presented here for comparison with
models. NIRSpec and MIRI spectroscopy were also obtained at this time and are
discussed separately.

NIRCam images in the six wavelength bands and the single NIRISS band were
downloaded from the Mikulski Archive for Space Telescopes (MAST) at the Space
Telescope Science Institute, specifically the ”…i2d.fits” files which are the
result of mosaicing the four dither positions obtained at each wavelength. The
specific observations analyzed can be accessed via
https://archive.stsci.edu/doi/resolve/resolve.html?doi=10.17909/jxva-9x26
(catalog DOI). Figure 1 shows a three- color, full-frame NIRCam image of the
field around WISE 1828+2650 and is composed of images obtained at F162M
(blue), F335M (green) and F470M (red) with a close-up around the position of
WISE 1828+2650. Only one object in the frame appears with the highly red color
characteristic of a cool Y dwarf.

##  3 Analysis

The values listed here use image files created on 2022-11-11 using calibration
software version 11.16.14 and photometric reference data from
jwst_nircam_photom_0114.fits.

###  3.1 Photometry

Table 2 shows the results of standard aperture photometry using the
astropy/photutils package (Astropy Collaboration et al., 2013, 2018, 2022;
Bradley et al., 2020) with the image files created on 2022-11-11 and the
calibration software version 11.16.14 with photometric reference data from
jwst_nircam_photom_0114.fits. We selected an aperture size corresponding to
70% encircled energy and the appropriate aperture correction from the CRDS
database111https://jwst-crds.stsci.edu/. The F090W filter was the weakest
detection with the total flux dependent on the selected aperture due to the
poorly defined Point Spread Function. For small apertures with encircled
energy $<$ 50%, the flux estimates in F090W were variable at the 20-30% level.
Beyond encircled energy of 50%, the flux estimates were consistent at the 10%
level, shown in the total uncertainty in Table 2. We adopted a large radius of
9.25 pixels encircling 85% of the total energy for the F090W filter. We also
obtained photometry using the NIRISS imager in full frame mode (Willott et
al., 2022) using the same procedure as described above.

Figure 2 shows the JWST results along with previous data from Spitzer, WISE,
HST and Keck (Kirkpatrick et al., 2011; Leggett et al., 2015; Kirkpatrick et
al., 2019; Cushing et al., 2021). WISE 1828+2650 is detected at high signal-
to-noise (SNR) in all filters with statistical uncertainties of just a few
percent. However, we adopt a higher level of uncertainty for the absolute
calibration in the model fitting. Successive MAST releases of these data from
August-November 2022 have shown significant variations in the absolute
calibration of the NIRCam filters used here. We adopt a uniform 10%
uncertainty for the absolute photometric calibration in all filters.

We note the consistency between the JWST data and previous observations
although different passbands can be expected to yield significant differences
given the highly structured nature of the SED of cool BDs. The close agreement
between multiple facilities at the wavelengths of peak emission around 4-5
$\mu$m is consistent with the general lack of variability in the brightness of
WISE 1828+2650. Brooks et al. (in preparation) investigated the variability of
several hundred cold BDs observed in the Kirkpatrick et al. (2021) astrometric
program using Spitzer. For WISE 1828+2650 they found a limit of 3% ($3\sigma$)
to the variability in IRAC Ch2 ([4.5]) in 28 observations spanning almost 8
years. A model fit based on the cloudless Sonora-Bobcat models (Marley et al.,
2021) is also plotted and will be discussed in $\S$ 5.

Figure 2: The figure shows a combination of the new JWST photometry (large red
circles), previous ground- based and space-based observations (large blue
circles) (Kirkpatrick et al., 2011; Leggett et al., 2015; Kirkpatrick et al.,
2019), and in the 1-2 $\mu$m region the HST spectrum (Cushing et al., 2021,
thin blue line). Horizontal bars denote the widths of the various filters. As
discussed further in $\S$ 5, we also plot as a thin grey line a cloudless
Sonora (Bobcat) spectrum smoothed to R$\sim$3000 for the best fitting, binary
object solution (Table 4). The black circles with dashed lines denote
predicted fluxes as integrated over the relevant passbands for each filter
(Marley et al., 2021).

###  3.2 Astrometry

As described in (Kirkpatrick et al., 2019),WISE 1828+2650 has a high proper
motion ($\sim$1″/yr), mostly in right ascension, and a parallax corresponding
to a distance of 9.93$\pm$0.23 pc. The values listed in Table 3 were used to
establish the pointing of the NIRCam, NIRSpec and MIRI observations in this
program.

The F360M image was used to obtain the position of WISE 1828+2650. The high
signal to noise ratio in this filter would imply a nominal positional accuracy
of FWHM/(2$\times$SNR) $<$ 5 milli-arcseconds (mas) where FWHM is the Full
Width at Half Maximum of the Point Spread function. We calculated both center-
of-mass and 2-D Gaussian fits to obtain the image centroid which yielded
nominal accuracy of $<$0.1 pixel or $<$6 mas. Information in the FITS header
was used to convert the pixel location into celestial coordinates (J2000,
2022.5699) as given in Table 3222The astrometric distortion correction in the
MAST processing used the file crds://jwst_nircam_distortion_0158.asdf

A comparison of the NIRCam positions of 31 unsaturated, proper-motion
corrected Gaia stars ($20\,{\rm mag}>{\rm Gmag}>$14 mag) across the
4′$\times$4′ field showed a small offset of order the measurement uncertainty
with dispersion of $(\Delta\alpha,\Delta\delta)$= 10$\pm$10, 7$\pm$6) mas,
demonstrating that the reference frame is accurate to $\sim$5-10 mas. However,
Figure 3 shows that there remains some coherent distortions across the field
of view.

Figure 3: Differences in the positions of 31 Gaia DR3 stars (selected for
negligible parallactic motions and corrected for proper motion) relative to
the positions observed by JWST in F360M. Individual Gaia stars are shown as
black symbols with the arrow showing the difference in pixels (63 mas), scaled
by a factor of 200 for visibility. The position of WISE 1828+2650 is shown as
a red star. The colors in the image and the color bar encode the magnitude of
deviation in mas. The maximum Gaia-JWST difference is 27 mas with an average
of 10 mas and dispersion of 10 mas.

The predicted position of WISE 1828+2650 was calculated at the JWST epoch
incorporating stellar parallax (Smart & Green, 1977) using the rectangular
coordinates of JWST’s location in the solar system as given in the FITS header
(reversed to give the coordinates of the Sun). The uncertainty in the F360M
position is the combination of the centroid uncertainty and the uncertainty in
the reference frame derived from the Gaia stars, $\pm$2 mas, for a combined
uncertainty of $\pm$4.4 mas. The difference in the predicted vs observed
positions is within the uncertainties derived from a Monte Carlo run in which
the Kirkpatrick et al. (2021) values were varied according to their quoted
uncertainties. The Monte Carlo distribution yielded uncertainties at the JWST
epoch of 6.4 mas in right ascension and declination. The Predicted-JWST
position difference is consistent with the existing parallax and proper motion
values for WISE 1828+2650.

Table 3: NIRCam Astrometry of WISE 1828

Observatory | Epoch | RA | Dec | Parallax | $\mu_{RA}$ | $\mu_{DEC}$
---|---|---|---|---|---|---
| (MJD) | RA (Equinox=J2000) | (Equinox=J2000) | (mas) | (mas/yr) | (mas/yr)
Spitzer1 | 57094.09 | 277.131096 ($\pm$2 mas) | 26.844069($\pm$2 mas) | 100.3$\pm$2 | 1016.5$\pm$0.8 | 169.3$\pm$0.8
|  | 18h28m31.463s | +26o50′38.65″ |  |  |
JWST (predicted) | 59788.5143 | 277.1334156 ($\pm$6 mas) | 26.8444348 ($\pm$6 mas) |  |  |
|  | 18h28m32.020s | +26o50′39.965″ |  |  |
JWST (F360M) | 59788.5143 | 277.1334164 ($\pm$10 mas) | 26.8444334 ($\pm$10 mas) |  |  |
|  | 18h28m32.020s | +26o50′39.960″ |  |  |
$\Delta$Spitzer-JWST(pred) |  |  $-$7.45″ |  $-$1.32″ |  |  |
$\Delta$JWST (Pred-Obs) |  | 2.5$\pm$12 mas | -5.1$\pm$8.2 mas |  |  |
Gaia-JWST differences3 (mas) |  | 10.4$\pm$10.2 (1.8) | 6.8$\pm$5.1 (0.9) |  |  |

Note. — 1Kirkpatrick et al. (2019). 2Absolute astrometric accuracy estimated
by measurements of nearby Gaia stars. 3 Difference in positions between 31
proper-motion corrected Gaia stars and their JWST values. The value in
parenthesis is $\sigma\\_{mean}$ for the sample and represents an estimate of
the overall precision of reference frame.

##  4 Search for Close Companions

###  4.1 Near-IR Observations

Previous observations with Keck and HST revealed no evidence for multiplicity
at the level of 0.1″ (Beichman et al., 2013), corresponding to orbital
separations of $>$1 AU for equal brightness components. However, the Keck
observations were done with the 40 mas/pixel wide-field camera mode with a
typical resolution of $\sim 0.16\arcsec.$ New Keck observations were obtained
2022-Sep-08 UT with NIRC2 behind the laser guide star adaptive optics system
(Wizinowich et al., 2000) in the narrow-field camera mode with a pixel scale
of $0.009942\arcsec$.

Observations of WISE 1828+2650 were made in the $H$ filter
$(\lambda_{o}=1.633;\Delta\lambda=0.296~{}\mu$m) with an integration time of
300 seconds per frame in a standard 3-point dither pattern that is used with
NIRC2 to avoid the noisier lower-left quadrant. The transparency and seeing
during the night was highly variable and not all frames detected the BD. A
total of 12 frames at 300 seconds each were acquired yielding a total on-
source integration time of 3600 seconds.

The science frames were flat-fielded and sky-subtracted. The flat fields were
generated from a median average of dark subtracted flats taken on-sky. The
flats were normalized such that the median value of the flats is unity. The
sky frames were generated from the median average of the dithered science
frames; each science image was then sky-subtracted and flat-fielded. The
reduced science frames were combined into a single combined image using a
intra-pixel interpolation that conserves flux, shifts the individual dithered
frames by the appropriate fractional pixels, and median-coadds the frames. The
final resolutions of the combined dithers was determined from the full-width
half-maximum of the point spread functions: 7.1 pixels = 0.071″.

The sensitivity of the final combined AO image was determined by injecting
simulated sources azimuthally around the primary target every $20^{\circ}$ at
separations of integer multiples of the central source’s FWHM. The brightness
of each injected source was scaled until standard aperture photometry detected
it with $5\sigma$ significance. The resulting brightness of the injected
sources relative to WISE 1828+2650 set the contrast limits at that injection
location. The final $5\sigma$ limit at each separation was determined from the
average of all of the determined limits at that separation, and the
uncertainty on the limit was set by the rms dispersion of the azimuthal slices
at a given radial distance. The Keck data have a sensitivity close-in of
$\Delta H\approx 1.5$ mag at 0.071″; the final sensitivity curve for the Keck
image is shown in (Figure 4). No close-in stellar companions were detected and
the FWHM of the WISE 1828+2650 is consistent with the brighter nearby star to
the southeast (Gaia DR3 4585337218702066560). WISE 1828+2650 is $\Delta
H=3.4\pm 0.2$ mag fainter than Gaia DR3 4585337218702066560.

Figure 4: Keck NIR AO imaging and sensitivity curve for WISE 1828+2650 taken
in the $H$ filter. We can recover a companion at a contrast of $\sim 1.5$
magnitudes relative to the BD at separations greater than 0.071″. Inset: Image
of the central portion of the NIRC2 image.

The $H$-band magnitude of WISE 1828+2650 as measured by the Keck data is
$H=22.9\pm 0.2$ mag. Using the JWST F162M filter as a proxy for the H-band
filter, this measurement is consistent with the infrared photometry determined
directly from the JWST images (see Table 2).

###  4.2 NIRCam Observations

Although the aperture of JWST is smaller than that of Keck, JWST offers a
highly stable point spread function (PSF) and much greater sensitivity at
wavelengths where cold BDs are brightest. For the JWST data reported here, the
best combination of spatial resolution and SNR in the JWST data comes in the
F360M filter. A simple Gaussian fit of the image of WISE 1828+2650 compared to
fits of two nearby stars shows no evidence for extent: FWHM(WISE 1828+2650)=
$0.150\pm 0.001$″ compared with $0.153\pm 0.001$″and $0.150\pm 0.001$″for the
two stars.

We explored the data further by constructing realistic models of the PSF and
searching for a potential companion at all separations within 0.25”. Anderson
& King (2000) and Anderson (2016) developed a novel technique applicable to
multiple instruments on HST where they construct an “effective” PSF (ePSF)
from bright single stars within a given image. The ePSF is intended to
describe the contemporaneous realization of the theoretical PSF on the
detector pixels given the wavefront during the observation. They build the
ePSF first by identifying a sample of many bright stars in the image that
appear to be singles and without contamination from cosmic rays or other
stars. These stars are all centered at various positions within their peak
pixel, giving many samplings of the distribution of flux of the center of the
PSF. The initial ePSF is then generated by interpolating each PSF by the
factor of user-defined oversampling, and taking the median. Then, an iterative
process begins, comparing the ePSF to all stars in the sample, evaluating the
median residual, and adding that on to the ePSF model. For our case, we
generated an ePSF model 4x oversampled, as recommended in Anderson (2016),
after 20 iterations of the ePSF calculation, over 9x9 detector pixels. This
analysis was performed using publicly available PSF building tools from the
python package photutils (Bradley et al., 2020).

We chose the F360M data to perform this analysis as the number of bright
sources in the F470N data was small which limits the production of a
reasonable ePSF model. Also, the diffraction limit in F470N is 30% larger than
in F360M, limiting the sensitivity to close companions. We also avoid the
F335M filter due to the low signal to noise of WISE 1828+2650. Of the four
pointings, two had reliable data for WISE 1828+2650 without nearby cosmic rays
or bad pixels contaminating its flux. Within each integration, we constructed
a separate ePSF model from 57 and 63 separate stars (integration number 2 and
4, respectively), excluding WISE 1828+2650 from the sample.

Figure 5: Top row: WISE 1828+2650 cutout in F360M filter on the left, ePSF
single model in center, and residuals on the right. Bottom row: WISE 1828+2650
cutout in F360M filter on the left, ePSF binary model in center, and residuals
on the right. Units are in DN/s and the axes are in detector pixels
(0.063”/pixel). We used the level 2 pipeline product *cal.fits files to
perform this analysis.  Figure 6:  Shown is the difference in log-evidence
between the binary-PSF model and single-PSF model performed on artificial
binaries, made from the ePSF models. The threshold for strong evidence of the
binary model fit over the single model fit is shown with a solid line
(corresponding to a difference of 5). The diffraction limit and half the
diffraction limit at 3.6 microns are shown for comparison as the vertical
dash-dotted and dashed lines, respectively.

We then made a double-PSF fitting code that takes a cutout array of the data
as input (here a 9x9 pixel array centered around WISE 1828+2650) and then fits
the best-fit binary model using the ePSF, an approach similarly implemented on
HST (De Furio et al., 2019). We use the python module PyMultiNest (Buchner et
al., 2014) that performs the Nested Sampling Monte Carlo analysis using
MultiNest (Feroz et al., 2009) to derive the best-fit binary ePSF model to the
data, by maximizing our chi-sqaured likelihood statistic. Our model consists
of six parameters: x and y center of the primary, flux normalization of the
primary, separation between the centers of the primary and secondary, the
position angle of the center of the secondary relative to the primary, and the
difference in magnitude between the secondary and primary. We define flat
priors with -1.5 $\leq$ xcen $\leq$ 1.5, -1.5 $\leq$ ycen $\leq$ 1.5, 0.0 $<$
flux normalization $<$ 40.0, 0.01 $\leq$ separation $\leq$ 4.0 pixels, 0.0
$\leq$ position angle $<$ 360.0, and 0.01 $\leq$ difference in magnitude
$\leq$ 6.0 mag.

To both images of WISE 1828+2650 in F360M in question, the code converges to
the edge of the prior in separation (4 pixels) and approaching that in
difference in magnitude (5.6 and 5.8 mags in each). If instead we force the
code to fit within the core of the PSF (0.01 $\leq$ separation $\leq$ 2.0
pixels) and exclude wide separations, the best fit converges to
0.14${}^{+0.04}_{-0.03}$ pixels in separation and
$\Delta$mag=2.44${}^{+0.34}_{-0.36}$ in Frame #2, and 0.28${}^{+0.13}_{-0.06}$
pixels in separation and $\Delta$mag=3.06${}^{+0.74}_{-0.68}$ in Frame #4
(errors are 68% confidence interval). See Figure 5 for the comparison of our
binary PSF model to the data.

Figure 7: Binary model parameters from the recovery of a companion injected at
1.25 pixels in separation (Sep), a position angle (PA) of 90 degrees, and a
contrast (Dmag) of 1.0 (left) and 3.5 (right) mag relative to the primary.
These artificial binaries were constructed from empirical PSFs of NIRCam in
the F360M filter. X and Y are the central pixel coordinates of the primary and
Norm is the flux normalization of the primary.

However, our binary PSF-fitting code will always find a best fit binary
solution regardless of whether a true binary is present. If the object in
question is a single point source, the code will either fit a companion to the
brightest residuals in the background (e.g. the 4 pixels in separation and
$\Delta$mag $\sim$ 5.5-6 mag initial fit) or to the residuals in the core of
the source as models are photon-noise limited and have uncertainty (e.g. the
resulting best fit when forced to fit a companion at separations $<$ 2
pixels).

In order to determine whether we can recover a companion with these values, we
constructed many artificial binaries from the ePSF models at various
separations and differences in magnitude with the same signal to noise as our
F360M data. Then, we ran our double-PSF fitting code and a modified version
that just fits a single PSF (3 variables: xcen, ycen, and flux normalization)
on those same artificial binaries. PyMultiNest also calculates the evidence of
the model in question by integrating over the posteriors. Trotta (2008) define
a difference in the log-evidence between two models of 5 as being strong
evidence for one model over another (with a probability of 0.993 that the
higher evidence model is preferred). For a given companion at some separation
and difference in magnitude, we compare the log-evidence of the binary-PSF
model to that of the single-PSF model.

In Figure 6, we show the log-evidence difference between the binary and single
ePSF model fits based on separation and difference in magnitude of our
artificial binaries. We define our sensitivity as the point where the
difference in log-evidence between the binary and single PSF models equals 5.
With our binary fitting tool and ePSF models, we can resolve companions down
to $\sim$ 0.8 F360M pixels (0.05″) in separation for an equal brightness
companion and are sensitive to companions at $\Delta$mag=2.5 beyond 2 F360M
pixels (0.126″). See Figure 7 for the posteriors for a fit to a binary at 1.25
pixels in separation and $\Delta$mag=1.0 and 3.5 . For the $\Delta$mag=3.5
companion, the parameters (separation, position angle, and difference in
magnitude) are unconstrained.

In addition, we fit a single PSF model to the WISE 1828+2650 data set. The
difference in log-evidence between the single and binary PSF models is 3.5,
less than the threshold for a detection. In Fig. 5, we show both the single
and binary PSF models compared to the data, demonstrating how the binary fit
does not significantly improve the residuals. Therefore, we are confident that
the best-fit binary model solution to WISE 1828+2650 in the F360M filter is
not a true detection of a companion, and that we can rule out an equal mass
companion beyond 0.5 au and a $\Delta$mag=2.5 companion beyond 1.25 au.
Fainter companions at larger separations can also be ruled out although these
would not help resolve the problem of excess brightness of WISE 1828+2650
relative to model predictions. Such models generally require an equal mass
system as discussed below ($\S$5).

The incidence of binarity among BDs is generally low, 10%-30%, compared with
higher mass stars (Burgasser et al., 2007; Raghavan et al., 2010). While less
is known about the multiplicity of the coldest T/Y BDs, there is evidence that
the incidence of binarity may be even lower than for warmer BDs, with Opitz et
al. (2016) failing to find any companions in the range of 0.5-2 AU among the
five Y dwarfs they examined with AO imaging. Similarly, Fontanive et al.
(2018) estimated a companion frequency $<$ 10% for T-Y dwarfs with separations
tightly peaked at 3 AU, e.g. Luhman 16 AB (Luhman, 2013). However, it should
be noted that separations $\leq$ 3 AU are not well explored. If indeed WISE
1828+2650 is a binary as inferred from the spectral modeling presented by
Cushing et al. (2021), then high resolution JWST NIRSpec spectra may reveal a
double lined system, given an appropriate orbital plane inclination.
Furthermore, two 5-10 $\,M_{\rm J}$ objects orbiting at 0.5 AU would have a
period of 3-5 years and a typical orbital velocity of $\sim$5 km/s which might
be discernible in multiple epochs of high SNR spectra to yield masses for the
two objects.

##  5 The Spectral Energy Distribution and Model Fits

The broad wavelength coverage of JWST NIRCam photometry from 1 to 5µm is ideal
for characterizing the spectral energy distribution (SED) and inferring the
bulk atmospheric properties of BDs. We include thirteen ground- and space-
based photometric points (i.e, Table 2) in our spectral energy distribution
fitting. We considered a number of models for this comparison: Sonora Bobcat
and Cholla (Marley et al., 2021), ATMO (Phillips et al., 2020) chemical-
equilibrium (CEQ) models, ATMO chemical non-equilibrium models with strong
vertical mixing (CNEQ-strong), and the Linder et al. (2019) models. We
selected cloudless Sonora
models333https://zenodo.org/record/1309035#.YwqSGbTMKUk,444https://zenodo.org/record/5063476#.YwqSTrTMKUk
as the most up to date compared, e.g. with older COND models, or the recent
Linder et al. (2019) models which are limited to low mass objects ($<$2
$\,M_{\rm J}$). The Sonora Cholla models do not go to sufficiently low
temperatures for this study and the ATMO 2020 models gave similar results but
with higher reduced chi-squares than the Sonora Bobcat models.

We defer discussion of the new Leggett et al. (2021) models to a companion
paper on the NIRSpec low and high resolution spectroscopy (Lew et al in
preparation). Leggett et al. (2021) noted that their new model failed to fit
the total luminosity of WISE 1828+2650 as a single object and assumed an equal
mass binary.

We used the Sonora model grid that comprises temperatures from 200 to 600 K,
gravities from log(g) of 3.0 to 5.5 $\,\mathrm{m}s^{-2}$, metallicities [M/H]
from -0.5 to 0.5. The ATMO model grid assumes an atmosphere with solar
metallicity and span a range of temperature from 100 K to 900 K and of gravity
from $10^{2.5}\,\mathrm{c}ms^{-2}$ to $10^{5.5}\,\mathrm{c}ms^{-2}$. The ATMO
chemical non-equilibrium models with strong vertical mixing assume an eddy
diffusion coefficient of $10^{6}\,\mathrm{c}m^{2}s^{-1}$ at a gravity of
$10^{4.5}\,\mathrm{c}ms^{-2}$ and decreases with higher gravity (see Figure 1
in Phillips et al. 2020. We linearly interpolated the models to construct a
model spectra grid with a smaller spacing in temperature, gravity, and
metallicity. We adopt a distance of 9.93 pc reported by Kirkpatrick et al.
(2019).

In the model fitting process, we examined two cases: a single object or a
binary with different temperatures. For the SED fitting, we performed the
least-squares fit to the thirteen photometric points. For the binary case, we
require the two objects to share the same age and metallicity. To enforce the
equal-age constraints, we first calculate the age based on the free parameters
temperature $T_{1}$ and gravity $g_{1}$ of one component of the binary using
the Sonora evolution model. We then calculate the expected gravity $g_{2}$ of
the second component based on the calculated age and sampled temperature
$T_{2}$ of this object. Therefore, both components of the binary share the
same age, where $g_{2}$ is thus a derived value based on $T_{1},g_{1},T_{2}$
and $M$. We calculate the chi-squared values of the binary models over the
grid of temperature, gravity, metallicity, and radius of the binary
components. We use the bootstrapping method to estimate the uncertainties of
the fitted parameters. With the bootstrapping method, we randomly re-sample
the thirteen photometric points for 10,000 times and refit the models to the
resampled datapoints with the least squares method. We then calculate the 99.7
percentile range of the fitted parameters as the 3$\sigma$ confidence ranges,
as shown in Table 4.

In Table 4 and Figure 8, we show the best-fit parameters and display the
corner plots associated with the fits to show the correlation between the
parameters in our SED fitting. In the binary case, the chi-squared map
suggests that the primary shares a similar temperature ($\Delta T<$50K) to the
secondary when both components have non-negligible radii ($R_{1}$ and
$R_{2}>0$). We also calculate the combined radius, which is the square root of
the sum of the two radii squared ($\sqrt{R_{1}^{2}+R_{2}^{2}}$), for the
binary case. The combined radius is moderately constrained, with a 99.7
percentile range of 1.15-2.83 $R_{J}$ and a median value of 1.67$R_{J}$, where
the best-fit radius of the single model is 1.67$R_{J}$. Both the single and
binary fits favor effective temperature of around 330K, low metallicity ([M/H
= -0.5]), and low gravity ($\log(g)=4$). However, the best fit models suggest
that the single model requires a lower mass object (2$\,M_{\rm J}$), while the
binary model requires two higher mass objects ($\sim$4$\,M_{\rm J}$). Our
single model has a lower reduced $\chi^{2}$ than the binary model, although
both are too high to adequtely represent the data. We note that the best-
fitted radius of 1.67 $R_{J}$ in the single BD case may be unphysically large,
and that an equal-temperature binary may be preferred in this case, as
suggested in previous studies of WISE 1828+2650 (e.g., Beichman et al., 2013;
Leggett et al., 2013, 2017; Cushing et al., 2021; Leggett et al., 2021)

Figure 8: The reduced chi-squared maps of the photometry fitting results for
both the single object case (left) and the binary case (right). Both models
fitting results suggest WISE 1828+2650 has a temperature of around 330K, low
metallicity, and low gravity. The blue crosses mark the location with the
lowest chi-squared values that are listed in Table 4. The white-colored
regions in the plots are either outside of the considered temperature range
(i.e., T + $\Delta T>$600K) or incompatible with the Bobcat evolution model
grid.

A striking characteristic of the SED fits for both the single and binary cases
is their predicted youth, with best-fit ages between 0.3-0.7 Gyr which is at
odds with the likely dynamical age of WISE 1828+2650, although these young
ages are not well constrained in our model. As previously noted (Beichman et
al., 2014), WISE 1828+2650 is not associated with any known young cluster.
This original conclusion is bolstered by application of the Banyan $\Sigma$
tool555www.exoplanetes.umontreal.ca/banyan/banyansigma.php? (Gagné et al.,
2018) which puts the probability that WISE 1828+2650 is a field object at 99%
independent of its as yet unknown radial velocity. We expect WISE 1828+2650 to
have an age in the 2-4 Gyr range given its tangential velocity (Beichman et
al., 2013), consistent with the mean age of 2.3 Gyr for a sample of BDs in the
solar neighborhood (Dupuy & Liu, 2017), contrary to our modeling of the SED.

Based on the best-fit models, we extrapolate the flux density beyond the
observed wavelength regions and estimate the bolometric luminosity. The
estimated bolometric luminosity has $\log(L/L_{\odot})$ of around -6.5, as
listed in Table 2. The bolometric luminosity of $\log(L/L_{\odot})=$ -6.5 is
similar to the expected luminosity of a $\sim$400K object at 1Gyr. Our
calculations indicate that the JWST broadband photometry covers about 16% of
the bolometric luminosity, while the composite photometry comprising JWST,
2MASS, WISE, and Spitzer photometry accounts for around 55% of the bolometric
luminosity.

The discrepancy between models for cold BDs at long and short wavelengths is
well known (Beichman et al., 2014) with models which fit well at long
wavelengths failing to fit at short wavelengths and vice versa. This failure
is prominent in our fits to the WISE 1828+2650 data, independent of
metallicity or multiplicity. In all cases, the models, which fit reasonably at
4-5 $\mu$m, fail badly at 1 $\mu$m with the models being a factor of $\sim$2
brighter than observed at 1 $\mu$m. Another striking feature is that both the
F335M and F360M data points sit significantly above the predictions suggesting
that the absorption in this part of the spectrum is less than expected.
Further exploration of the possible temperature-pressure profile and
atmospheric chemistry, such as those models in Leggett et al. (2021), is
essential to understand the atmospheric processes that drive the longstanding
challenges in fitting the flux at near-IR and mid-IR wavelengths.

The SED fits to new JWST observations using two independent sets of models
leave us in the uncomfortable position of either accepting a single object
much younger than expected dynamically, or a near equal-mass binary system for
which the NIRCam data finds no evidence at separations $>$0.5 AU. Potentially
the NIRSpec’s high resolution spectroscopy will reveal a double-lined system
which might resolve this problem. However, whether WISE 1828+2650 turns out to
be a double, Figure 2 and the high $\chi^{2}$ values indicate significant
deviations between the models and the emission of WISE 1828+2650.

At the fitted effective temperature of around 300K, it is possible that
sulfide, chloride, and water clouds form near or within the photosphere and
affect the emission spectra (e.g., Morley et al., 2012, 2014b, 2014a).
However, Cushing et al. (2021) SED fitting results with Morley et al. (2014b)
cloud models at solar metallicity give a higher reduced chi square than that
with Sonora bobcat cloudless models with subsolar metallicity. Further
exploring cloudy models under various atmospheric chemistry and metallicity is
essential to understand the role of clouds in shaping the SED of WISE
1828+2650. It is possible that the rotation rate and observed inclination of
WISE 1828+2650 cause significant luminosity deviations from a typical BD of
similar temperature. Deviations as high as 20% have been estimated in
comparing pole-on vs. equator-on viewed BDs at high rotation rates (Lipatov et
al., 2022), but it is currently unknown if this effect occurs for WISE
1828+2650 . Important clues will come from the NIRSpec and MIRI spectroscopic
observations spanning 1-12 $\mu$m at low and high resolution which are
currently being analyzed.

Table 4: Spectral Model Fits to Photometry

| Primary | Secondary |  |  |  |  |  |
---|---|---|---|---|---|---|---|---
| Teff | log g | Mass | Radius | Teff | log g | Mass | Radius | Metallicity | Age | Reduced | Degs. of |  $\log$ ($L/L_{\odot}$)
| (K) | (cgs) | (MJup) | (RJup ) | (K) | (cgs) | (MJup) | (RJup) | [M/H] | ($\times 10^{9}$yr) | $\chi^{2}$ | Freedom |
Sonora Cloudless models
best-fit single | 325 | 3.6 | 2 | 1.83 |  |  |  |  | -0.5∗ | 0.3 | 180 | 9 | -6.49$\pm$ 0.03
99.7$\%$ CI | 309–405 | 3.0–5.5 | 0.6–13 | 1.1–2.0 |  |  |  |  | -0.5 | 0.01–7 |  |  |
best-fit binary | 337 | 4.0 | 4.4 | 1.38 | 330 | 4.0 | 4.1 | 0.90 | -0.5∗ | 0.7 | 231 | 7 | -6.49$\pm$0.04
99.7$\%$ CI | 316–413 | 3.0–4.8 | 0.6–20 | 0.4–2 | 268–395 | 3.5–4.8 | 0.6–20 | 0–2 | -0.5 | 0.03–10 |  |  |
ATMO Chemical Equilibrium models
best-fit single | 300 | 4.0 | 3.7 | 2 |  |  |  |  | 0 (fixed) | 1.0 | 256 | 10 | -6.45$\pm$ 0.06
99.7$\%$ CI | 287–359 | 3.0–5.1 | 0.5–13 | 2–2 |  |  |  |  | - | 0.02–8.5 |  |  |
best-fit binary | 300 | 3.6 | 1.5 | 1.9 | 300 | 3.6 | 1.7 | 1.4 | 0 (fixed) | 0.3 | 287 | 8 | -6.36$\pm$0.05
99.7$\%$ CI | 279–400 | 3.0–4.8 | 0.5–20 | 0.4–2 | 279–400 | 3.0–4.8 | 0.5–20 | 0–2 | - | 0.02–10 |  |  |
ATMO Chemical Non-equilibrium models with strong mixing
best-fit single | 294 | 4.3 | 5.5 | 2.0 |  |  |  |  | 0 (fixed) | 2.4 | 303 | 10 | -6.46$\pm$ 0.06
99.7$\%$ CI | 259–359 | 3.0–5.0 | 0.5–11 | 2.0–2.0 |  |  |  |  | - | 0.02–9.9 |  |  |
best-fit binary | 270 | 4.0 | 4.2 | 2 | 270 | 4.0 | 4.2 | 2 | 0 (fixed) | 2.1 | 320 | 8 | -6.38$\pm$0.09
99.7$\%$ CI | 253–340 | 3.0–4.6 | 0.5–13 | 2–2 | 253–340 | 3.0–4.6 | 0.5–13 | 2–2 | - | 0.03–9.9 |  |  |

Note. — 1 The fitted parameters and the corresponding 99.7$\%$ percentile
ranges for the single and binary objects cases. The mass, radius, and the
secondary object’s gravity are derived from the fitted parameters using the
Bobcat evolution models. ∗The fitted metallicity is at the lower bound of
metallicity grid.

Figure 9:  Color-Color plot for point sources detected in all three bands
seeded with a high SNR detection in F360M. Blue circular symbols are sources
in the WISE 1828+2650 field (WISE 1828+2650 is in the upper right corner), the
light blue crosses represent the progression of BDs from Kirkpatrick et al.
(2019) plotted in using H band, Spitzer IRAC Ch1 and Ch2 similar to the JWST
filters. Visual examination of the F360M image shows that four JWST sources
that lie above the BD locus are slightly extended, very red galaxies. The
lines denote sequence of early L to late T dwarfs based on Sonora Models
(Marley et al., 2021). The colors denote values of log(g) (black, 3.0, blue,
4.0, red, 5.0). The line type denotes different values of [Fe/H]=(0,thick;
-0.5,dashed; and +0.5 dotted).

##  6 A Search for Brown Dwarf Companions in the Entire Field

The large field of view and great sensitivity of NIRCam are two of the
instrument’s great strengths. In addition to searching for a close companion
we also looked for additional BD candidates which might or might not be
associated with WISE 1828+2650. For example, Nonino et al. (2023) made a
serendipitous discovery of a T dwarf (T${}_{eff}\sim$600 K) at a distance of
$\sim 0.5$ kpc in a deep survey field adjacent to Abell 2744.

We used the source catalogs provided by Level-3 processing from STScI for our
6 filters. We selected F360M unconfused point sources (the ”is_extended” flag
set to FALSE and the nearest neighbor distance $\geq$ 1″) with SNR$\geq$10\.
To avoid unreliable sources which appear at the edges of the field due to
having less than the full coverage of 4 dither positions, we selected objects
only within the central $2^{\prime}\times 2^{\prime}$ of the final F360M
image. We selected sources in the other 5 filters (SNR$\geq$5) in the same way
and used the F360M objects as seeds for band merging using a radius of 0.2″.
We adopted the catalog values of aperture photometry based on 70% encircled
value with pipeline-provided aperture correction. To enable a search for L,T
and Y BDs we focused on filters optimized to find cold objects, requiring
detections at F360M, F162M and F470N. Figure 9 shows 63 sources meeting these
criteria. Sources around 0.5$>$[F360M]–[F470N]$>$0 and $0<$ [F162M]–[F470N]
$<2$ mag are likely stars with spectral types as cool as M9 or galaxies
(Pecaut & Mamajek,
2013)666https://www.pas.rochester.edu/~emamajek/EEM_dwarf_UBVIJHK_colors_Teff.txt.

Figure 9 shows only one object in the color space occupied by BDs, WISE
1828+2650 itself in the upper right corner of the plot. Finally, there are 4
other red objects with colors around [F162M]–[F470N] $>$2 mag (Table 5). A
sixth source with [F360M]–[F470N]$\sim 1.2$ lies below the BD locus and
appears to be contaminated by confusion with a nearby object. Visual
inspection and measured FWHM of the four red objects shows two to be extended
(Table 5). A more detailed examination of the images and comparison with the
predicted WebbPSF777https://webbpsf.readthedocs.io/en/latest/ image size shows
that #2 and #4 have FHWM in the F360M image of 0.23″and 0.43″, respectively,
compared with other point sources in the field (0.15″in the mosaicked images)
and the WebbPSF FHWM of 0.12-0.13″(Table 5). A third, #5, may be slightly
extended 0.18″. The other two, #1 and #6, are point-like or only very slightly
extended. Source #3 is WISE 1828+2650. Extra-galactic objects with similar
colors are being found in on-going deep imaging programs and are suggestive of
a new class of highly dust obscured galaxy (Hainline et al, in preparation).

Figure 9 includes colors from a large sample of BDs from Kirkpatrick et al.
(2021) using H-band, IRAC C1 and Ch2 as analogs for the JWST filters. The plot
also includes loci of six different Sonora BD models evaluated in the JWST
filters and ranging in surface temperature, gravity, and metallicity:
$300<T_{Eff}<1700$ K, log(g) of (3,4,5), and [Fe/H] of ($-$0.5,0,+0.5). The
comparison between the models and the Kirkpatrick sample show the well known
problem that as the BDs become cooler, the models have a progressively harder
time fitting the data.

The conclusion of this search and visual inspection of the six JWST images is
that there are no obvious cool BD candidates in the WISE 1828+2650 field, but
that there are a significant number of galaxies.

Table 5: Highly Red Sources in WISE 1828+2650 Field

Label | RA20001 | DEC20001 | F090W2 | F115W2 | F162M2 | F335M2 | F360M2 | F470N2 | FWHM3
---|---|---|---|---|---|---|---|---|---
1 | 277.138408(60.) | 26.8286435(55.) | 1.06$\pm$0.00769 | 4.08$\pm$0.00955 | 0.911$\pm$0.00908 | 6.23$\pm$0.0223 | 5.66$\pm$0.0218 | 4.24$\pm$0.0982 | 0.15″
| 18h28m33.22s | 26d49m43.12s | 23.33$\pm$0.0078 | 21.59$\pm$0.0025 | 22.62$\pm$0.011 | 19.2$\pm$0.0039 | 19.15$\pm$0.0042 | 18.92$\pm$0.025 |
2 | 277.160802(20.) | 26.8420123(16.) | 0.172$\pm$0.00651 | 0.545$\pm$0.00633 | 0.975$\pm$0.00975 | 2.$\pm$0.0113 | 2.27$\pm$0.0122 | 2.5$\pm$0.0747 | 0.23″
| 18h28m38.59s | 26d50m31.24s | 25.3$\pm$0.04 | 23.78$\pm$0.013 | 22.55$\pm$0.011 | 20.43$\pm$0.0061 | 20.14$\pm$0.0058 | 19.5$\pm$0.032 |
34 | 277.133408(26.) | 26.8444326(4.3) | 0.078$\pm$0.005 | 0.311$\pm$0.00446 | 1.29$\pm$0.00857 | 2.41$\pm$0.0132 | 34.2$\pm$0.0511 | 340.$\pm$0.619 | 0.15″
| 18h28m32.02s | 26d50m39.96s | 26.16$\pm$0.20 | 24.39$\pm$0.015 | 22.25$\pm$0.0072 | 20.23$\pm$0.0059 | 17.19$\pm$0.0016 | 14.16$\pm$0.002 |
4 | 277.16172(24.) | 26.8470549(26.) | 0.0796$\pm$0.00708 | 0.323$\pm$0.00663 | 0.562$\pm$0.00985 | 1.93$\pm$0.0112 | 2.14$\pm$0.012 | 2.55$\pm$0.0752 | 0.44″
| 18h28m38.81s | 26d50m49.4s | 26.14$\pm$0.093 | 24.34$\pm$0.022 | 23.15$\pm$0.019 | 20.47$\pm$0.0063 | 20.2$\pm$0.0061 | 19.48$\pm$0.032 |
5 | 277.138946(24.) | 26.8479253(5.9) | N/A | 0.23$\pm$0.0043 | 1.27$\pm$0.00946 | 4.85$\pm$0.0166 | 5.39$\pm$0.0176 | 7.1$\pm$0.098 | 0.18″
| 18h28m33.35s | 26d50m52.53s | N/A | 24.71$\pm$0.02 | 22.26$\pm$0.008 | 19.47$\pm$0.0037 | 19.2$\pm$0.0035 | 18.36$\pm$0.015 |
65 | 277.152549(430.) | 26.8653645(380.) | 2.42$\pm$0.00887 | 3.94$\pm$0.0116 | 9.63$\pm$0.0276 | 6.41$\pm$0.0218 | 2.34$\pm$0.0225 | 4.31$\pm$0.0968 | 0.15″
| 18h28m36.61s | 26d51m55.31s | 22.44$\pm$0.004 | 21.63$\pm$0.0032 | 20.06$\pm$0.0031 | 19.17$\pm$0.0037 | 20.11$\pm$0.01 | 18.91$\pm$0.024 |

Note. — 1Epoch 2022.5699, uncertainties in milliarcseconds in parentheses;
2Top line is flux density in $\mu$Jy, the second line is corresponding Vega
magnitude.3Full width at Half Maximum in F360M. This is to be compared with
the FWHM of the WebbPSF of 0.17″. 4Source is WISE1828+2650. 5Source to
confusion with a nearby object.

##  7 Conclusion

This examination of the new 1-5$\mu$m NIRCam data for WISE 1828+2650 has
confirmed what has been previously known about this source. It remains among
the reddest and most challenging of the Y dwarfs to fit using existing models.
Both the high SNR data at F360M and the data from the Keck telescope at 1.6
$\mu$m have failed to reveal a near-equal mass companion beyond 0.5 AU. If, as
has been suggested, a binary system offers a better chance of fitting the
photometric models, the companion must orbit very close to WISE 1828+2650
itself, $<$0.5 AU. Such a companion might reveal itself through double lines
in the spectroscopy. However, as described above, even the binary model fails
to provide an improved fit to the existing photometric data. Further insights
into the properties of this enigmatic object will come with the analysis of
the NIRCam and MIRI spectroscopic data forthcoming shortly in other
publications.

##  8 Acknowledgements

We must first acknowledge the many years of effort by thousands of scientists,
engineers and administrators who made JWST such a dramatic success, exceeding
many of its most important requirements. This international collaboration
should be an inspiration to us all. The NIRCam team at the University of
Arizona and Lockheed Martin’s Advanced Technology Center brought great skill,
expertise and dedication to realize the full power of this instrument. M. De
Furio is grateful for support from NASA through the JWST NIRCam project though
contract number NAS5-02105 (M. Rieke, University of Arizona, PI).

We wish to thank Davy Kirkpatrick for valuable discussions about WISE 1828.
Some of the research described in this publication was carried out at the Jet
Propulsion Laboratory, California Institute of Technology, under a contract
with the National Aeronautics and Space Administration. M. De Furio benefited
from support from JPL’s Strategic University Research Partnership (SURP). Doug
Johnstone is supported by NRC Canada and by an NSERC Discovery Grant. L.A.
acknowledges support by the Canadian Space Agency under contract
9F052-170914/001/MTB.

Some of the data presented herein were obtained at the W. M. Keck Observatory,
which is operated as a scientific partnership among the California Institute
of Technology, the University of California and the National Aeronautics and
Space Administration. The Observatory was made possible by the generous
financial support of the W. M. Keck Foundation. The authors wish to recognize
and acknowledge the very significant cultural role and reverence that the
summit of Maunakea has always had within the indigenous Hawaiian community. We
are most fortunate to have the opportunity to conduct observations from this
mountain.

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