Abstract
We present Gemini Observatory follow-up J-band and K-band photometry for a sample of 16 T/Y dwarf candidates discovered by the Backyard Worlds: Planet 9 citizen science project. The Gemini observations were taken with Gemini-North using the Near-Infrared Imager instrument between 2017 September and 2018 March. Obtaining near-infrared photometry of very cold brown dwarfs is important for enabling and prioritizing future spectroscopic follow-up, particularly in the context of JWST spectroscopy of T and Y dwarfs.
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1. Introduction
The Backyard Worlds citizen science project (M. J. Kuchner et al. 2017) has been performing a crowdsourced visual inspection search for cold, nearby brown dwarfs since early 2017 using 3–5 μm unWISE coadds (A. M. Meisner et al. 2019). A key objective of Backyard Worlds has been to fill in the census of late-T and Y dwarfs in the solar neighborhood (e.g., S. Leggett et al. 2019; J. D. Kirkpatrick et al. 2024). Among numerous candidate LTY-type Backyard Worlds discoveries (e.g., A. M. Meisner et al. 2020b), we identified a sample of 16 high-priority objects based on their combination of very red WISE W1 − W2 colors (or color lower limits) and/or large proper motions (a proxy for nearness), plus visibility from northern latitudes. For this set of 16 objects, we obtained Gemini-North/Near-Infrared Imager (NIRI; K. W. Hodapp et al. 2003) J-band and K-band photometry, as an early first step in estimating photometric spectral types and temperatures for this sample. For all but four of our sample members, the discovery reference is A. M. Meisner et al. (2020b); the four exceptions are J010650.61+225159.1, J043309.27+100903.9 (A. M. Meisner et al. 2020a), J105553.59−165216.3 (C. G. Tinney et al. 2018), and J170127.19+415803.3 (J. D. Kirkpatrick et al. 2021).
2. Gemini Observations and Data Reductions
Our Gemini photometry derives from the Gemini Fast Turnaround (FT) programs GN-2017B-FT-9 and GN-2018A-FT-103 (PI: Wisniewski). The Gemini observations were acquired on 7 different nights spanning from 2017 September 29 to 2018 March 29. We reduced the Gemini data using the DRAGONS software package (K. Labrie et al. 2023), and identified the counterpart to each WISE-based brown dwarf candidate using the proper motion solution from CatWISE2020 (F. Marocco et al. 2021). For all but three targets the NIRI images were calibrated using UKIRT Hemisphere Survey (UHS; S. Dye et al. 2018) or Vista Hemisphere Survey (VHS; R. G. McMahon et al. 2013) data for point sources in the field with magnitudes between 15 and 18. For the remaining three targets (1525+60, 1553+69, 2059+66) the zero-points determined from the observations on the same night of our other targets, which did have survey coverage, were used. Magnitudes were determined using aperture photometry with concentric sky annuli; uncertainties are dominated by sky noise. Apertures with diameters of 0
9–23 were used, depending on the brightness of the source, seeing, and crowding of the field. Table 1 provides the magnitudes derived for photometric detections in our T/Y dwarf candidate sample.
Table 1. J-band and K-band Photometry
| WISE J | Spectral | Literature | Gemini | UT Date | New Measurements | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| R.A. Decl. | Type [Ref. a ] | J | σJ | K | σK | Ref. b | Program | (YYYYMMDD) | J | σJ | K | σK |
| 002909.89+190516.9 | [T7] [Me20a] | 17.81 | 0.04 | ⋯ | ⋯ | UHS | GN-2017B-FT-9 | 20170929 | 17.96 | 0.03 | 18.70 | 0.05 |
| 010650.61+225159.1 | [T6.5] [Me20b] | 17.41 | 0.03 | 17.97 | 0.22 | UHS | GN-2017B-FT-9 | 20170929 | 17.52 | 0.03 | 18.00 | 0.07 |
| 035733.81+070557.5 | [T6.5] [Me20a] | 17.66 | 0.05 | ⋯ | ⋯ | UHS | GN-2017B-FT-9 | 20170929 | 17.88 | 0.04 | 18.29 | 0.05 |
| 043309.27+100903.9 | [T8] [Me20b] | 17.94 | 0.04 | ⋯ | ⋯ | UHS | GN-2017B-FT-9 | 20171005 | 18.00 | 0.03 | 18.64 | 0.06 |
| 050238.26+100750.1 c | [T9] [Me20a] | 18.90 | 0.11 | ⋯ | ⋯ | UHS | GN-2017B-FT-9 | 20171003 | 18.95 | 0.04 | 19.94 | 0.07 |
| 105553.59−165216.3 | T9: [Ti18] | 20.71 | 0.21 | ⋯ | ⋯ | K21 | GN-2018A-FT-103 | 20180329 | 20.77 | 0.06 | ⋯ | ⋯ |
| 152529.08+605356.3 | [T9] [Me20a] | 19.56 | 0.10 | ⋯ | ⋯ | L21 | GN-2018A-FT-103 | 20180318 | 19.81 | 0.03 | ⋯ | ⋯ |
| 155349.98+693355.2 | sdT4 [Me21] | 19.17 | 0.03 | ⋯ | ⋯ | M23 | GN-2018A-FT-103 | 20180329 | 19.12 | 0.03 | ⋯ | ⋯ |
| 160516.72+002138.0 | [T8.5] [Me20a] | 19.02 | 0.12 | ⋯ | ⋯ | UHS | GN-2018A-FT-103 | 20180329 | 19.21 | 0.04 | ⋯ | ⋯ |
| 163932.74+184049.0 | [T9.5] [Me20a] | ⋯ | ⋯ | ⋯ | ⋯ | ⋯ | GN-2018A-FT-103 | 20180329 | 20.66 | 0.04 | ⋯ | ⋯ |
| 170127.19+415803.3 | [T8.5] [Ki21] | 19.66 | 0.08 | ⋯ | ⋯ | K21 | GN-2018A-FT-103 | 20180318 | 19.95 | 0.03 | ⋯ | ⋯ |
| 201833.63−141720.7 | [T9] [Me20a] | 19.13 | 0.11 | ⋯ | ⋯ | VHS | GN-2018A-FT-103 | 20180329 | 18.80 | 0.03 | ⋯ | ⋯ |
| 205921.90+662725.2 | [T8] [Me20a] | ⋯ | ⋯ | ⋯ | ⋯ | ⋯ | GN-2017B-FT-9 | 20170929 | 18.93 | 0.05 | 19.74 | 0.06 |
| 221841.38+143003.1 | [T7.5] [Me20a] | 19.14 | 0.12 | ⋯ | ⋯ | UHS | GN-2017B-FT-9 | 20171001 | 19.16 | 0.05 | 20.13 | 0.19 |
| 221859.33+114644.7 | [T7.5] [Me20a] | 17.94 | 0.06 | ⋯ | ⋯ | UHS | GN-2017B-FT-9 | 20171006 | 17.96 | 0.03 | 18.95 | 0.05 |
| 224319.56−145857.3 | [Y0] [Me20a] | 21.14 | 0.26 | ⋯ | ⋯ | L21 | GN-2017B-FT-9 | 20170929 | 20.75 | 0.10 | 20.65 | 0.20 |
Notes. Columns J, σJ , K, and σK are in magnitudes. All magnitudes are on the Vega system. New J-band and K-band measurements are all on the MKO bandpass system. "Ref." in the column headers is an abbreviation for "Reference."
a Ki21 = J. D. Kirkpatrick et al. (2021), Me20a = A. M. Meisner et al. (2020b), Me20b = A. M. Meisner et al. (2020a), Me21 = A. M. Meisner et al. (2021), Ti18 = C. G. Tinney et al. (2018). Photometric spectral type estimates are enclosed in square brackets whereas spectroscopic classifications are not. b K21 = J. D. Kirkpatrick et al. (2021), L21 = S. K. Leggett et al. (2021), M23 = A. M. Meisner et al. (2023), UHS = S. Dye et al. (2018), VHS = R. G. McMahon et al. (2013). c 050238.26+100750.1 has a low signal-to-noise ratio spectrum from A. M. Meisner et al. (2020b), which gives a spectral type limit of >T6 for this object.3. Conclusion
In the time since our Gemini data were proposed/taken, many targets benefited from the public release of the UHS or VHS data, in which these objects were detected. Nevertheless, we present new J-band detections for two brown dwarfs, and significantly improved measurements for nine; we present new K-band detections for eight brown dwarfs, and a significantly improved measurement for one. The Gemini follow-up presented herein will represent a valuable addition to ongoing compilations of near-infrared photometry for the coldest brown dwarfs (e.g., S. K. Leggett et al. 2021).
Acknowledgments
Based on observations obtained at the international Gemini Observatory, a program of NSF NOIRLab, which is managed by AURA under a cooperative agreement with the U.S. National Science Foundation on behalf of the Gemini Observatory partnership. We are grateful for the privilege of observing the Universe from Maunakea, a place that is unique in both its astronomical quality and its cultural significance.
Software: DRAGONS, WiseView (D. Caselden et al. 2018).