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Title: Characterizing the Cloud Decks of Luhman 16AB with Medium-resolution Spectroscopic Monitoring

Abstract

We present results from a two-night R ∼ 4000 0.9–2.5 μ m spectroscopic monitoring campaign of Luhman 16AB (L7.5 + T0.5). We assess the variability amplitude as a function of pressure level in the atmosphere of Luhman 16B: the more variable of the two components. The amplitude decreases monotonically with decreasing pressure, indicating that the source of variability—most likely patchy clouds—lies in the lower atmosphere. An unexpected result is that the strength of the K i absorption is higher in the faint state of Luhman 16B and lower in the bright state. We conclude that either the abundance of K i increases when the clouds roll in, potentially because of additional K i in the cloud itself, or that the temperature–pressure profile changes. We reproduce the change in K i absorption strengths with combinations of spectral templates to represent the bright and the faint variability states. These are dominated by a warmer L8 or L9 component, with a smaller contribution from a cooler T1 or T2 component. The success of this approach argues that the mechanism responsible for brown dwarf variability is also behind the diverse spectral morphology across the L-to-T transition. We further suggest that the L9–T1 part ofmore » the sequence represents a narrow but random ordering of effective temperatures and cloud fractions, obscured by the monotonic progression in methane absorption strength.« less

Authors:
;  [1];  [2];  [3];  [4]
  1. The University of Western Ontario, Centre for Planetary and Space Exploration, 1151 Richmond Street, London, ON N6A 3K7 (Canada)
  2. Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822-1839 (United States)
  3. Carnegie Institution of Washington DTM, 5241 Broad Branch Road NW, Washington, DC 20015 (United States)
  4. Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Ave. Gran Bretaña 1111, Playa Ancha, Casilla 53, Valparaíso (Chile)
Publication Date:
OSTI Identifier:
22679701
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 849; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTRA; ABUNDANCE; AMPLITUDES; ATMOSPHERES; CLOUDS; HEAT EXCHANGERS; METHANE; PRESSURE DEPENDENCE; RANDOMNESS; RESOLUTION; STARS

Citation Formats

Kellogg, Kendra, Metchev, Stanimir, Heinze, Aren, Gagné, Jonathan, and Kurtev, Radostin, E-mail: kkellogg@uwo.ca, E-mail: smetchev@uwo.ca. Characterizing the Cloud Decks of Luhman 16AB with Medium-resolution Spectroscopic Monitoring. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA8E4F.
Kellogg, Kendra, Metchev, Stanimir, Heinze, Aren, Gagné, Jonathan, & Kurtev, Radostin, E-mail: kkellogg@uwo.ca, E-mail: smetchev@uwo.ca. Characterizing the Cloud Decks of Luhman 16AB with Medium-resolution Spectroscopic Monitoring. United States. doi:10.3847/1538-4357/AA8E4F.
Kellogg, Kendra, Metchev, Stanimir, Heinze, Aren, Gagné, Jonathan, and Kurtev, Radostin, E-mail: kkellogg@uwo.ca, E-mail: smetchev@uwo.ca. Wed . "Characterizing the Cloud Decks of Luhman 16AB with Medium-resolution Spectroscopic Monitoring". United States. doi:10.3847/1538-4357/AA8E4F.
@article{osti_22679701,
title = {Characterizing the Cloud Decks of Luhman 16AB with Medium-resolution Spectroscopic Monitoring},
author = {Kellogg, Kendra and Metchev, Stanimir and Heinze, Aren and Gagné, Jonathan and Kurtev, Radostin, E-mail: kkellogg@uwo.ca, E-mail: smetchev@uwo.ca},
abstractNote = {We present results from a two-night R ∼ 4000 0.9–2.5 μ m spectroscopic monitoring campaign of Luhman 16AB (L7.5 + T0.5). We assess the variability amplitude as a function of pressure level in the atmosphere of Luhman 16B: the more variable of the two components. The amplitude decreases monotonically with decreasing pressure, indicating that the source of variability—most likely patchy clouds—lies in the lower atmosphere. An unexpected result is that the strength of the K i absorption is higher in the faint state of Luhman 16B and lower in the bright state. We conclude that either the abundance of K i increases when the clouds roll in, potentially because of additional K i in the cloud itself, or that the temperature–pressure profile changes. We reproduce the change in K i absorption strengths with combinations of spectral templates to represent the bright and the faint variability states. These are dominated by a warmer L8 or L9 component, with a smaller contribution from a cooler T1 or T2 component. The success of this approach argues that the mechanism responsible for brown dwarf variability is also behind the diverse spectral morphology across the L-to-T transition. We further suggest that the L9–T1 part of the sequence represents a narrow but random ordering of effective temperatures and cloud fractions, obscured by the monotonic progression in methane absorption strength.},
doi = {10.3847/1538-4357/AA8E4F},
journal = {Astrophysical Journal},
number = 1,
volume = 849,
place = {United States},
year = {Wed Nov 01 00:00:00 EDT 2017},
month = {Wed Nov 01 00:00:00 EDT 2017}
}