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Title: Weather on Other Worlds. IV. Hα Emission and Photometric Variability Are Not Correlated in L0–T8 Dwarfs

Abstract

Recent photometric studies have revealed that surface spots that produce flux variations are present on virtually all L and T dwarfs. Their likely magnetic or dusty nature has been a much-debated problem, the resolution to which has been hindered by paucity of diagnostic multi-wavelength observations. To test for a correlation between magnetic activity and photometric variability, we searched for H α emission among eight L3–T2 ultra-cool dwarfs with extensive previous photometric monitoring, some of which are known to be variable at 3.6 μ m or 4.5 μ m. We detected H α only in the non-variable T2 dwarf 2MASS J12545393−0122474. The remaining seven objects do not show H α emission, even though six of them are known to vary photometrically. Combining our results with those for 86 other L and T dwarfs from the literature show that the detection rate of H α emission is very high (94%) for spectral types between L0 and L3.5 and much smaller (20%) for spectral types ≥L4, while the detection rate of photometric variability is approximately constant (30%–55%) from L0 to T8 dwarfs. We conclude that chromospheric activity, as evidenced by H α emission, and large-amplitude photometric variability are not correlated. Consequently, dust cloudsmore » are the dominant driver of the observed variability of ultra-cool dwarfs at spectral types, at least as early as L0.« less

Authors:
;  [1];  [2];  [3]
  1. Department of Physics and Astronomy and Centre for Planetary Science and Exploration, The University of Western Ontario, London, Ontario N6A 3K7 (Canada)
  2. Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)
  3. The University of Arizona, Department of Astronomy, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)
Publication Date:
OSTI Identifier:
22663621
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 840; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMPLITUDES; APPROXIMATIONS; CLOUDS; CORRELATIONS; DETECTION; DUSTS; DWARF STARS; EMISSION; MASS; PHOTOMETRY; RESOLUTION; ROTATION; STARS; SURFACES; WAVELENGTHS

Citation Formats

Miles-Páez, Paulo A., Metchev, Stanimir A., Heinze, Aren, and Apai, Dániel, E-mail: ppaez@uwo.ca. Weather on Other Worlds. IV. Hα Emission and Photometric Variability Are Not Correlated in L0–T8 Dwarfs. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA6F11.
Miles-Páez, Paulo A., Metchev, Stanimir A., Heinze, Aren, & Apai, Dániel, E-mail: ppaez@uwo.ca. Weather on Other Worlds. IV. Hα Emission and Photometric Variability Are Not Correlated in L0–T8 Dwarfs. United States. doi:10.3847/1538-4357/AA6F11.
Miles-Páez, Paulo A., Metchev, Stanimir A., Heinze, Aren, and Apai, Dániel, E-mail: ppaez@uwo.ca. Wed . "Weather on Other Worlds. IV. Hα Emission and Photometric Variability Are Not Correlated in L0–T8 Dwarfs". United States. doi:10.3847/1538-4357/AA6F11.
@article{osti_22663621,
title = {Weather on Other Worlds. IV. Hα Emission and Photometric Variability Are Not Correlated in L0–T8 Dwarfs},
author = {Miles-Páez, Paulo A. and Metchev, Stanimir A. and Heinze, Aren and Apai, Dániel, E-mail: ppaez@uwo.ca},
abstractNote = {Recent photometric studies have revealed that surface spots that produce flux variations are present on virtually all L and T dwarfs. Their likely magnetic or dusty nature has been a much-debated problem, the resolution to which has been hindered by paucity of diagnostic multi-wavelength observations. To test for a correlation between magnetic activity and photometric variability, we searched for H α emission among eight L3–T2 ultra-cool dwarfs with extensive previous photometric monitoring, some of which are known to be variable at 3.6 μ m or 4.5 μ m. We detected H α only in the non-variable T2 dwarf 2MASS J12545393−0122474. The remaining seven objects do not show H α emission, even though six of them are known to vary photometrically. Combining our results with those for 86 other L and T dwarfs from the literature show that the detection rate of H α emission is very high (94%) for spectral types between L0 and L3.5 and much smaller (20%) for spectral types ≥L4, while the detection rate of photometric variability is approximately constant (30%–55%) from L0 to T8 dwarfs. We conclude that chromospheric activity, as evidenced by H α emission, and large-amplitude photometric variability are not correlated. Consequently, dust clouds are the dominant driver of the observed variability of ultra-cool dwarfs at spectral types, at least as early as L0.},
doi = {10.3847/1538-4357/AA6F11},
journal = {Astrophysical Journal},
number = 2,
volume = 840,
place = {United States},
year = {Wed May 10 00:00:00 EDT 2017},
month = {Wed May 10 00:00:00 EDT 2017}
}
  • We have monitored 12 T dwarfs with the Kitt Peak 2.1 m telescope using an F814W filter (0.7-0.95 μm) to place in context the remarkable 10%-20% variability exhibited by the nearby T dwarf Luhman 16B in this wavelength regime. The motivation was the poorly known red optical behavior of T dwarfs, which have been monitored almost exclusively at infrared wavelengths, where variability amplitudes greater than 10% have been found to be very rare. We detect highly significant variability in two T dwarfs. The T2.5 dwarf 2MASS 13243559+6358284 shows consistent ∼17% variability on two consecutive nights. The T2 dwarf 2MASS J16291840+0335371 exhibits ∼10% variability thatmore » may evolve from night to night, similarly to Luhman 16B. Both objects were previously known to be variable in the infrared, but with considerably lower amplitudes. We also find evidence for variability in the T6 dwarf J162414.37+002915.6, but since it has lower significance, we conservatively refrain from claiming this object as a variable. We explore and rule out various telluric effects, demonstrating that the variations we detect are astrophysically real. We suggest that high-amplitude photometric variability for T dwarfs is likely more common in the red optical than at longer wavelengths. The two new members of the growing class of high-amplitude variable T dwarfs offer excellent prospects for further study of cloud structures and their evolution.« less
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