More Like this

1. CWISE J105512.11+544328.3: A Nearby Y Dwarf Spectroscopically Confirmed with Keck/NIRES

   https://doi.org/10.3847/1538-4357/ad0043  

   Robbins, Grady; Meisner, Aaron M; Schneider, Adam C; Burgasser, Adam J; Kirkpatrick, J Davy; Gagné, Jonathan; Hsu, Chih-Chun; Moranta, Leslie; Casewell, Sarah; Marocco, Federico; et al (November 2023, The Astrophysical Journal)

   Abstract Y dwarfs, the coolest known spectral class of brown dwarfs, overlap in mass and temperature with giant exoplanets, providing unique laboratories for studying low-temperature atmospheres. However, only a fraction of Y dwarf candidates have been spectroscopically confirmed. We present Keck/NIRES near-infrared spectroscopy of the nearby (d≈ 6–8 pc) brown dwarf CWISE J105512.11+544328.3. Although its near-infrared spectrum aligns best with the Y0 standard in theJband, no standard matches well across the fullYJHKwavelength range. The CWISE J105512.11+544328.3 NH₃-H= 0.427 ± 0.0012 and CH₄-J= 0.0385 ± 0.0007 absorption indices and absolute Spitzer [4.5] magnitude of 15.18 ± 0.22 are also indicative of an early-Y dwarf rather than a late-T dwarf. CWISE J105512.11+544328.3 additionally exhibits the bluest Spitzer [3.6]−[4.5] color among all spectroscopically confirmed Y dwarfs. Despite this anomalously blue Spitzer color given its low luminosity, CWISE J105512.11+544328.3 does not show other clear kinematic or spectral indications of low metallicity. Atmospheric model comparisons yield a log(g) ≤ 4.5 andT_eff≈ 500 ± 150 K for this source. We classify CWISE J105512.11+544328.3 as a Y0 (pec) dwarf, adding to the remarkable diversity of the Y-type population. JWST spectroscopy would be crucial to understanding the origin of this Y dwarf’s unusual preference for low-gravity models and blue 3–5μm color. 

   more » « less
2. Redder than Red: Discovery of an Exceptionally Red L/T Transition Dwarf

   https://doi.org/10.3847/2041-8213/acb0cd  

   Schneider, Adam C.; Burgasser, Adam J.; Bruursema, Justice; Munn, Jeffrey A.; Vrba, Frederick J.; Caselden, Dan; Kabatnik, Martin; Rothermich, Austin; Sainio, Arttu; Bickle, Thomas P.; et al (January 2023, The Astrophysical Journal Letters)

   Abstract We present the discovery of CWISE J050626.96+073842.4 (CWISE J0506+0738), an L/T transition dwarf with extremely red near-infrared colors discovered through the Backyard Worlds: Planet 9 citizen science project. Photometry from UKIRT and CatWISE give a (J−K)_MKOcolor of 2.97 ± 0.03 mag and aJ_MKO− W2 color of 4.93 ± 0.02 mag, making CWISE J0506+0738 the reddest known free-floating L/T dwarf in both colors. We confirm the extremely red nature of CWISE J0506+0738 using Keck/NIRES near-infrared spectroscopy and establish that it is a low-gravity, late-type L/T transition dwarf. The spectrum of CWISE J0506+0738 shows possible signatures of CH₄absorption in its atmosphere, suggesting a colder effective temperature than other known, young, red L dwarfs. We assign a preliminary spectral type for this source of L8γ–T0γ. We tentatively find that CWISE J0506+0738 is variable at 3–5μm based on multiepoch WISE photometry. Proper motions derived from follow-up UKIRT observations combined with a radial velocity from our Keck/NIRES spectrum and a photometric distance estimate indicate a strong membership probability in theβPic moving group. A future parallax measurement will help to establish a more definitive moving group membership for this unusual object. 

   more » « less
3. An Investigation of New Brown Dwarf Spectral Binary Candidates From the Backyard Worlds: Planet 9 Citizen Science Initiative

   https://doi.org/10.3847/1538-3881/acffc1  

   Bravo, Alexia; Schneider, Adam C; Bardalez_Gagliuffi, Daniella; Burgasser, Adam J; Meisner, Aaron M; Kirkpatrick, J Davy; Faherty, Jacqueline K; Kuchner, Marc J; Caselden, Dan; Sainio, Arttu; et al (November 2023, The Astronomical Journal)

   Abstract We present three new brown dwarf spectral-binary candidates: CWISE J072708.09−360729.2, CWISE J103604.84−514424.4, and CWISE J134446.62−732053.9, discovered by citizen scientists through the Backyard Worlds: Planet 9 project. Follow-up near-infrared spectroscopy shows that each of these objects is poorly fit by a single near-infrared standard. We constructed binary templates and found significantly better fits, with component types of L7+T4 for CWISE J072708.09−360729.2, L7+T4 for CWISE J103604.84−514424.4, and L7+T7 for CWISE J134446.62−732053.9. However, further investigation of available spectroscopic indices for evidence of binarity and large amplitude variability suggests that CWISE J072708.09−360729.2 may instead be a strong variability candidate. Our analysis offers tentative evidence and characterization of these peculiar brown dwarf sources, emphasizing their value as promising targets for future high-resolution imaging or photometric variability studies. 

   more » « less
4. Discovery of the Remarkably Red L/T Transition Object VHS J183135.58-551355.9

   https://doi.org/10.3847/1538-3881/ad4b16  

   Bickle, Thomas P; Schneider, Adam C; Gagné, Jonathan; Faherty, Jacqueline K; Rothermich, Austin; Vos, Johanna M; Suárez, Genaro; Kirkpatrick, J Davy; Meisner, Aaron M; Kuchner, Marc J; et al (July 2024, The Astronomical Journal)

   Abstract We present the discovery of VHS J183135.58−551355.9 (hereafter VHS J1831−5513), an L/T transition dwarf identified as a result of its unusually red near-infrared colors (J−K_S= 3.633 ± 0.277 mag;J−W2 = 6.249 ± 0.245 mag) from the VISTA Hemisphere Survey and CatWISE2020 surveys. We obtain low-resolution near-infrared spectroscopy of VHS J1831−5513 using the Magellan Folded port InfraRed Echellette spectrograph to confirm its extremely red nature and assess features sensitive to surface gravity (i.e., youth). Its near-infrared spectrum shows multiple CH₄absorption features, indicating an exceptionally low effective temperature for its spectral type. Based on proper-motion measurements from CatWISE2020 and a photometric distance derived from itsK_s-band magnitude, we find that VHS J1831−5513 is a likely (∼85% probability) kinematic member of theβPictoris moving group. Future radial velocity and trigonometric parallax measurements will clarify such membership. Follow-up mid-infrared or higher-resolution near-infrared spectroscopy of this object will allow for further investigation as to the cause(s) of its redness, such as youth, clouds, and viewing geometry. 

   more » « less
5. Brown Dwarf Retrievals on FIRE!: Atmospheric Constraints and Lessons Learned from High Signal-to-noise Medium-resolution Spectroscopy of a T9 Dwarf

   https://doi.org/10.3847/1538-4357/ace32e  

   Hood, Callie E; Fortney, Jonathan J; Line, Michael R; Faherty, Jacqueline K (August 2023, The Astrophysical Journal)

   Abstract Brown dwarf spectra offer vital testbeds for our understanding of the chemical and physical processes that sculpt substellar atmospheres. Recently, atmospheric retrieval approaches have been successfully applied to low-resolution (R∼ 100) spectra of L, T, and Y dwarfs, yielding constraints on the chemical abundances and temperature structures of these atmospheres. Medium-resolution (R∼ 10³) spectra of brown dwarfs offer additional insight, as molecular features are more easily disentangled and the thermal structure of the upper atmosphere is better probed. We present results from a GPU-based retrieval analysis of a high signal-to-noise, medium-resolution (R∼ 6000) FIRE spectrum from 0.85 to 2.5μm of the T9 dwarf UGPS J072227.51–054031.2. At 60× higher spectral resolution than previous brown dwarf retrievals, a number of novel challenges arise. We examine the effect of different opacity sources, in particular for CH₄. Furthermore, we find that flaws in the data like errors from order stitching can bias our constraints. We compare these retrieval results to those for anR∼ 100 spectrum of the same object, revealing how constraints on atmospheric abundances and temperatures improve by an order of magnitude or more with increased spectral resolution. In particular, we can constrain the abundance of H₂S, which is undetectable at lower spectral resolution. While these medium-resolution retrievals offer the potential of precise, stellar-like constraints on atmospheric abundances (∼0.02 dex), our retrieved radius is unphysically small ( $R={0.50}_{-0.01}^{+0.01}$R_Jup), indicating shortcomings with our modeling framework. This work is an initial investigation into brown dwarf retrievals at medium spectral resolution, offering guidance for future ground-based studies and JWST observations. 

   more » « less