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Abstract Using Keck Planet Imager and Characterizer high-resolution (R∼ 35,000) spectroscopy from 2.29 to 2.49μm, we present uniform atmospheric retrievals for eight young substellar companions with masses of ∼10–30MJup, orbital separations spanning ∼50–360 au, andTeffbetween ∼1500 and 2600 K. We find that all companions have solar C/O ratios and metallicities to within the 1σ–2σlevel, with the measurements clustered around solar composition. Stars in the same stellar associations as our systems have near-solar abundances, so these results indicate that this population of companions is consistent with formation via direct gravitational collapse. Alternatively, core accretion outside the CO snowline would be compatible with our measurements, though the high mass ratios of most systems would require rapid core assembly and gas accretion in massive disks. On a population level, our findings can be contrasted with abundance measurements for directly imaged planets withm< 10MJup, which show tentative atmospheric metal enrichment compared to their host stars. In addition, the atmospheric compositions of our sample of companions are distinct from those of hot Jupiters, which most likely form via core accretion. For two companions withTeff∼ 1700–2000 K (κAnd b and GSC 6214–210 b), our best-fit models prefer a nongray cloud model with >3σsignificance. The cloudy models yield 2σ−3σlowerTefffor these companions, though the C/O and [C/H] still agree between cloudy and clear models at the 1σlevel. Finally, we constrain12CO/13CO for three companions with the highest signal-to-noise ratio data (GQ Lup b, HIP 79098b, and DH Tau b) and report and radial velocities for all companions.
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RV Measurements of Directly Imaged Brown Dwarf GQ Lup B to Search for Exosatellites
Abstract GQ Lup B is one of the few substellar companions with a detected cicumplanetary disk (CPD). Observations of the CPD suggest the presence of a cavity, possibly formed by an exosatellite. Using the Keck Planet Imager and Characterizer (KPIC), a high-contrast imaging suite that feeds a high-resolution spectrograph (1.9–2.5µm,R∼35,000), we present the first dedicated radial velocity (RV) observations around a high-contrast, directly imaged substellar companion, GQ Lup B, to search for exosatellites. Over 11 epochs, we find a best and median RV error of 400–1000 m s−1, most likely limited by systematic fringing in the spectra due to transmissive optics within KPIC. With this RV precision, KPIC is sensitive to exomoons 0.6%–2.8% the mass of GQ Lup B (∼30MJup) at separations between the Roche limit and 65RJup, or the extent of the cavity inferred within the CPD detected around GQ Lup B. Using simulations of HISPEC, a high resolution infrared spectrograph planned to debut at W.M. Keck Observatory in 2026, we estimate future exomoon sensitivity to increase by over an order of magnitude, providing sensitivity to less massive satellites potentially formed within the CPD itself. Additionally, we run simulations to estimate the amount of material that different masses of satellites could clear in a CPD to create the observed cavity. We find satellite-to-planet mass ratios ofq> 2 × 10−4can create observable cavities and report a maximum cavity size of ∼51RJupcarved from a satellite.
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- PAR ID:
- 10544150
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astronomical Journal
- Volume:
- 168
- Issue:
- 4
- ISSN:
- 0004-6256
- Format(s):
- Medium: X Size: Article No. 175
- Size(s):
- Article No. 175
- Sponsoring Org:
- National Science Foundation
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