Bibcode
Del Burgo, C.; Martín, E. L.; Zapatero Osorio, M. R.; Hauschildt, P. H.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 501, Issue 3, 2009, pp.1059-1071
Fecha de publicación:
7
2009
Revista
Número de citas
34
Número de citas referidas
30
Descripción
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 1.347 μm with a resolving power R˜20 000. 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 922-1009 K, and
surface gravities between 104.1 and 104.9 cm
s-2. 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 K i
doublet at 1.2436 and 1.2525 μm. 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
≈5-75~MJ 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.
Reduced NIRSPEC spectra of the nine T-type dwarfs are available
electronically in fits format at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/1059