J/A+A/629/A145 L9-T3.5 brown dwarfs light curves (Eriksson+, 2019)
Detection of new strongly variable brown dwarfs in the L/T transition.
Eriksson S.C., Janson M., Calissendorff P.
<Astron. Astrophys. 629, A145 (2019)>
=2019A&A...629A.145E 2019A&A...629A.145E (SIMBAD/NED BibCode)
ADC_Keywords: Stars, brown dwarf ; Photometry, infrared
Keywords: brown dwarfs - stars: individual: 2MASS J22153705+2110554 -
stars: variables: general - stars: low-mass - infrared: stars -
techniques: photometric
Abstract:
Brown dwarfs in the spectral range L9-T3.5, within the so called L/T
transition, have been shown to be variable at higher amplitudes and
with greater frequency than other field dwarfs. This strong
variability allows for the probing of their atmospheric structure in
3D through multi-wavelength observations for studying the underlying
physical mechanisms responsible for the variability. The few known
strongly variable dwarfs in this range have been extensively studied.
Now, more variables such as these need to be discovered and studied to
better constrain atmospheric models. This is also critical to better
understand giant exoplanets and to shed light on a number of possible
correlations between brown dwarf characteristics and variability.
Previous studies suggest an occurrence rate for strong variability
(peak-to-peak amplitudes >2%) of up to 39% among brown dwarfs within
the L/T transition. In this work, we aim to discover new strong
variables in this spectral range by targeting ten previously
unsurveyed brown dwarfs.
We used the NOTCam at the Nordic Optical Telescope to observe 11
targets, with spectral types ranging from L9.5 to T3.5, in the J-band
during October 2017 and September 2018. Using differential aperture
photometry, we then analysed the light curves for significant
variability using Lomb-Scargle periodogram algorithms and least
squares fitting.
We report first discoveries of strong and significant variability in
four out of the ten targets (false alarm probability <0.1%),
measuring peak-to-peak amplitudes up to 10.7±0.4% in J for the T1
dwarf 2MASS J22153705+2110554, for which we observe significant light
curve evolution between the 2017 and 2018 epochs. We also report a
marginally significant detection of strong variability, and confirm
that the well known 2MASS J01365662+0933473 is still strongly variable
three years after the last reported epoch. Finally, we present an
extensive multi-epoch catalogue of strong variables reported in the
literature and discuss possible correlations that are identifiable
from the catalogue.
We significantly add to the number of known strong variables, and
through Poisson statistics infer an occurrence rate for strong
variability among L9-T3.5 brown dwarfs of 40+3219%, which is
in agreement with previous estimates. The new variables identified in
this work are also excellently suited for extensive multi-wavelength
observations dedicated to probing the 3D structure of brown dwarf
atmospheres.
Description:
The observations listed in the observation log (Table 2) took place
between 2017-2018 with the NOTCam instrument at the 2.5m Nordic
Optical Telescope (NOT), located at Observatorio del Roque de los
Muchachos on La Palma.
NOTCam was used with the J filter (1.165-1.328um) in wide field
imaging mode, where the 1024x1024 detector has a pixel scale of
0.234" resulting in a 40x40 field of view.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 96 11 Identifier, SpT and colour information for
targets observed in this work
table2.dat 72 15 Observation log observations using NOT/NOTCam J
lc/* . 15 Individual light curves
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Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 23 A23 --- Target Target name (2MASS JHHMMSSss+DDMMSSs) (1)
25- 34 A10 --- CName 2MASS ID Compact ID (2)
36- 50 A15 --- SpType Spectral type (3)
52- 55 A4 --- Ref Reference for discovery and Spectral type (4)
57- 61 F5.2 mag Jmag 2MASS J magnitude
63- 66 F4.2 mag e_Jmag rms uncertainty on Jmag
67 A1 --- n_Jmag [d] Note on Jmag (5)
69 A1 --- l_Ksmag Limit flag on Ksmag
70- 74 F5.2 mag Ksmag 2MASS Ks magnitude
76- 79 F4.2 mag e_Ksmag ? rms uncertainty on Ksmag
80 A1 --- n_Ksmag [d] Note on Ksmag (5)
82 A1 --- l_J-Ks Limit flag on J-Ks
83- 86 F4.2 mag J-Ks 2MASS J-Ks colour index
87 A1 --- n_J-Ks [d] Note on J-Ks (5)
89- 92 F4.1 pc Dphot ? Photometric distance (6)
94- 96 F3.1 pc e_Dphot ? rms uncertainty on Dphot
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Note (1): For this work we have chosen to use 2MASS identifiers whenever
possible and alternate designations (from e.g. the PSO, SIMP or WISE surveys)
might be used in discovery references.
Note (2): Compact ID entries in the table are of the form JHHMM+DDMM and in
running text also frequently referred to as JHHMM.
Note (3): Possible binarity indicated in parenthesis with question mark.
Note (4): References as follows:
1 = Andrei et al. (2011AJ....141...54A 2011AJ....141...54A)
2 = Artigau et al. (2006ApJ...651L..57A 2006ApJ...651L..57A)
3 = Best et al. (2015, Cat. J/ApJ/814/118)
4 = Kellogg et al. (2017, Cat. J/AJ/154/112)
5 = Kellogg et al. (2015AJ....150..182K 2015AJ....150..182K)
6 = Kirkpatrick et al. (2011, Cat. J/ApJS/197/19)
7 = Robert et al. (2016ApJ...830..144R 2016ApJ...830..144R)
8 = Schneider et al. (2016, Cat. J/ApJ/817/112)
Note (5): d: MKO magnitudes from Best et al. (2015, Cat. J/ApJ/814/118)
instead of 2MASS.
Note (6): Photometric distances from Robert et al. (2016ApJ...830..144R 2016ApJ...830..144R).
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- Target Target name (2MASS JHHMMSSss+DDMMSSs) (1)
25- 34 A10 --- CName Target name (2MASS JHHMMSSss+DDMMSSs) (1)
36- 45 A10 "date" Obs.date Observation date (start of the night where the
observation was executed)
47- 50 F4.2 h Deltat Time span
52- 54 I3 s texp Exposure time
56- 59 F4.2 --- SDraw Standard deviation of the normalized raw
target light curve obtained from aperture
photometry (2)
61- 72 A12 --- FileName Name of the table with light curves in
subdirectory lc
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Note (1): Targets observed during NOT programs 56-002 and 57-006, listed in
descending (compact) 2MASS ID. For more target information see Table 1.
Note (2): Shown here as an indicator of the quality of the observing conditions,
with detailed plots of the normalised reference light curve, sky counts and
airmass being available in Appendix A. For observations where texp was changed
shortly after the beginning of the run, the listed SD value is based on the
frames using the final texp.
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Byte-by-byte Description of file: lc/*
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Bytes Format Units Label Explanations
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1- 20 F20.18 h Time Elapsed time
22- 39 F18.16 --- RFlux Relative flux
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Acknowledgements:
Simon Eriksson, simon.eriksson(at)astro.su.se
(End) Patricia Vannier [CDS] 10-Sep-2019