J/A+A/501/1059 Infrared spectra of 9 T dwarfs (del Burgo+, 2009)
Physical parameters of T dwarfs derived from high-resolution near-infrared
spectra.
del Burgo C., Martin E.L., Zapatero-Osorio M.R., P.Hauschildt.
<Astron. Astrophys. 501, 1059 (2009)>
=2009A&A...501.1059D 2009A&A...501.1059D (SIMBAD/NED BibCode)
ADC_Keywords: Stars, dwarfs ; Spectra, infrared
Keywords: stars: fundamental parameters - stars: atmosphers -
stars: low-mass, brown dwarfs
Abstract:
Aims: We determine the effective temperature, surface gravity and
projected rotational velocity of nine T dwarfs from the comparison of
high-resolution near-infrared spectra and synthetic models, and
estimate the mass and age of the objects from state-of-the-art models.
Methods: We use the AMES-COND cloudless solar metallicity models
provided by the PHOENIX code to match the spectra of nine T-type field
dwarfs observed with the near-infrared high-resolution spectrograph
NIRSPEC using ten echelle orders to cover part of the J band from
1.147 to 1.347µm with a resolving power R∼20000. The projected
rotational velocity, effective temperature and surface gravity of the
objects are determined based on the minimum root mean square of the
differences between the modelled and observed relative fluxes.
Estimates of the mass and age of the objects are obtained from
effective temperature-surface gravity diagrams, where our results are
compared with existing solar metallicity models.
Results: The modelled spectra reproduce quite well the observed
features for most of the T dwarfs, with effective temperatures in the
range of 922-1009K, and surface gravities between 104.1 and
104.9cm/s2. Our results support the assumption of a dust free
atmosphere for T dwarfs later than T5, where dust grains form and then
gravitationally sediment into the low atmosphere. The modelled spectra
do not accurately mimic some individual very strong lines like the KI
doublet at 1.2436 and 1.2525µm. Our modelled spectra does not match
well the observed spectra of the two T dwarfs with earlier spectral
types, namely SDSSp J125453.90-012247.4 (T2) and 2MASS
J05591914-1404488 (T4.5), which is likely due to the presence of
condensate clouds that are not incorporated in the models used here.
By comparing our results and their uncertainties to evolutionary
models, we estimate masses in the interval ∼5-75MJ for T dwarfs
later than T5, which are in good agreement with those found in the
literature. We found apparent young ages that are typically between
0.1 and a few Gyr for the same T dwarfs, which is consistent with
recent kinematical studies.
Description:
High-resolution near-infrared spectra in the J-band of nine T dwarfs
were obtained using the Keck II telescope and the NIRSPEC
spectrograph.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 73 9 List of studied stars
fig/* . 9 Individual FITS files corresponding to the
reduced data (heliocentric velocity corrections
are not applied)
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 24 A24 --- Name Simbad name
26- 27 I2 h RAh Simbad right ascension (J2000)
29- 30 I2 min RAm Simbad right ascension (J2000)
32- 35 F4.1 s RAs Simbad right ascension (J2000)
37 A1 --- DE- Simbad declination sign (J2000)
38- 39 I2 deg DEd Simbad declination (J2000)
41- 42 I2 arcmin DEm Simbad declination (J2000)
44- 45 I2 arcsec DEs Simbad declination (J2000)
47- 73 A27 --- FileName Name of the FITS file in subdirectory fig
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Acknowledgements:
Carlos del Burgo, cburgo(at)cp.dias.ie
(End) Patricia Vannier [CDS] 15-May-2009