Informed systematic method to identify variable mid and late-T dwarfs

Abstract

The majority of brown dwarfs show some level of photometric or spectro-photometric variability in different wavelength ranges. This variability allow us to trace the 3D atmospheric structures of variable brown dwarfs and directly-imaged exoplanets with radiative-transfer models and mapping codes. Nevertheless, to date, we do not have an informed method to pre-select the brown dwarfs that might show a higher variability amplitude for a thorough variability study. In this work, we designed and tested near-infrared spectral indices to pre-select the most likely variable mid- and late-T dwarfs, which overlap in effective temperatures with directly-imaged exoplanets. We used time-resolved near-infrared Hubble Space Telescope Wide Field Camera 3 spectra of a T6.5 dwarf, 2MASS J22282889--431026, to design our novel spectral indices. We tested these spectral indices on 26 T5.5--T7.5 near-infrared SpeX/IRTF spectra, and we provided eight new mid- and late-T variable candidates. We estimated the variability fraction of our sample in $38_{-30}^{+4}$%, which agrees with the variability fractions provided by Metchev, et. al, (2015) for mid-to late-T dwarfs. In addition, two of the three previously known variables in our SpeX spectra sample are flagged as variable candidates by our indices. Similarly, all seven known non-variable in our sample are flagged as non-variable objects by our indices. These results suggest that our spectral indices might be used to find variable mid- and late-T brown dwarf variables. These indices may be crucial in the future to select cool directly-imaged exoplanets for variability studies.

Accepted for publication in AJ. 17 pages, 12 figures, 3 tables

References in corpus (14)

• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• Fingering convection and cloudless models for cool brown dwarf atmospheres
• Strong Brightness Variations Signal Cloudy-to-Clear Transition of Brown Dwarfs
• Discovery of 11 New T Dwarfs in the Two Micron All-Sky Survey, Including a Possible L/T Transition Binary
• Vertical Atmospheric Structure in a Variable Brown Dwarf: Pressure-dependent Phase Shifts in Simultaneous Hubble Space Telescope-Spitzer Light Curves
• SpeX Spectroscopy of Unresolved Very Low Mass Binaries. II. Identification of Fourteen Candidate Binaries with Late-M/Early-L and T Dwarf Components
• Let the Great World Spin: Revealing the Stormy, Turbulent Nature of Young Giant Exoplanet Analogs with the Spitzer Space Telescope
• Spitzer Variability Properties of Low-Gravity L Dwarfs
• Variability of the Lowest Mass Objects in the AB Doradus Moving Group
• A Search for Photometric Variability in L and T type Brown Dwarf Atmospheres
• Cloud Atlas: Rotational Spectral Modulations and potential Sulfide Clouds in the Planetary-mass, Late T-type Companion Ross 458C
• A High-Contrast Search for Variability in HR 8799bc with VLT-SPHERE
• Benchmarking Substellar Evolutionary Models Using New Age Estimates for HD 4747 B and HD 19467 B
• Revealing the Vertical Cloud Structure of a young low-mass Brown Dwarf, an analog to the beta-Pictoris b directly-imaged exoplanet, through Keck I/MOSFIRE spectro-photometric variability

Cited by in corpus (1)

• VIRAC2: NIR Astrometry and Time Series Photometry for 500M+ Stars from the VVV and VVVX Surveys