TY - JOUR
T1 - Spectral Variability of Two Rapidly Rotating Brown Dwarfs
T2 - 2MASS J08354256-0819237 and 2MASS J18212815+1414010
AU - Schlawin, E.
AU - Burgasser, Adam J.
AU - Karalidi, T.
AU - Gizis, J. E.
AU - Teske, J.
N1 - Funding Information:
We thank the anonymous referee for useful improvements and corrections to this work. We thank Vivien Parmentier for useful discussions on cloud versus spotted temperature models. Funding for E Schlawin is provided by NASA Goddard Spaceflight Center. The material is based upon work supported by the National Aeronautics and Space Administration under grant No.NNX15AI75G. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France; NASA’s Astrophysics Data System Bibliographic Services; and the M, L, T, and Y dwarf compendium housed at http:// DwarfArchives.org; the SpeX Prism Libraries at http://www. browndwarfs.org/spexprism. 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. Facility: IRTF (SpeX).
Publisher Copyright:
© 2017. The American Astronomical Society. All rights reserved.
PY - 2017/11/10
Y1 - 2017/11/10
N2 - L dwarfs exhibit low-level, rotationally modulated photometric variability generally associated with heterogeneous, cloud-covered atmospheres. The spectral character of these variations yields insight into the particle sizes and vertical structure of the clouds. Here, we present the results of a high-precision, ground-based, near-infrared, spectral monitoring study of two mid-type L dwarfs that have variability reported in the literature, 2MASS J08354256-0819237 and 2MASS J18212815+1414010, using the SpeX instrument on the Infrared Telescope Facility. By simultaneously observing a nearby reference star, we achieve <0.15% per-band sensitivity in relative brightness changes across the 0.9-2.4 μm bandwidth. We find that 2MASS J0835-0819 exhibits marginal (≲0.5% per band) variability with no clear spectral dependence, while 2MASS J1821+1414 varies by up to ±1.5% at 0.9 μm, with the variability amplitude declining toward longer wavelengths. The latter result extends the variability trend observed in prior HST/WFC3 spectral monitoring of 2MASS J1821+1414, and we show that the full 0.9-2.4 μm variability amplitude spectrum can be reproduced by Mie extinction from dust particles with a log-normal particle size distribution with a median radius of 0.24 ∼m. We do not detect statistically significant phase variations with wavelength. The different variability behavior of 2MASS J0835-0819 and 2MASS J1821 +1414 suggests dependencies on viewing angle and/or overall cloud content, underlying factors that can be examined through a broader survey.
AB - L dwarfs exhibit low-level, rotationally modulated photometric variability generally associated with heterogeneous, cloud-covered atmospheres. The spectral character of these variations yields insight into the particle sizes and vertical structure of the clouds. Here, we present the results of a high-precision, ground-based, near-infrared, spectral monitoring study of two mid-type L dwarfs that have variability reported in the literature, 2MASS J08354256-0819237 and 2MASS J18212815+1414010, using the SpeX instrument on the Infrared Telescope Facility. By simultaneously observing a nearby reference star, we achieve <0.15% per-band sensitivity in relative brightness changes across the 0.9-2.4 μm bandwidth. We find that 2MASS J0835-0819 exhibits marginal (≲0.5% per band) variability with no clear spectral dependence, while 2MASS J1821+1414 varies by up to ±1.5% at 0.9 μm, with the variability amplitude declining toward longer wavelengths. The latter result extends the variability trend observed in prior HST/WFC3 spectral monitoring of 2MASS J1821+1414, and we show that the full 0.9-2.4 μm variability amplitude spectrum can be reproduced by Mie extinction from dust particles with a log-normal particle size distribution with a median radius of 0.24 ∼m. We do not detect statistically significant phase variations with wavelength. The different variability behavior of 2MASS J0835-0819 and 2MASS J1821 +1414 suggests dependencies on viewing angle and/or overall cloud content, underlying factors that can be examined through a broader survey.
KW - brown dwarfs
KW - stars: atmospheres
KW - stars: individual (2MASS J08354256-0819237, 2MASS J18212815+1414010)
KW - stars: late-type
KW - techniques: spectroscopic
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UR - http://www.scopus.com/inward/citedby.url?scp=85034588919&partnerID=8YFLogxK
U2 - 10.3847/1538-4357/aa90b8
DO - 10.3847/1538-4357/aa90b8
M3 - Article
AN - SCOPUS:85034588919
VL - 849
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2
M1 - 163
ER -