Physical parameters of T dwarfs derived from high-resolution near-infrared spectra

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 1.347 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 10 4.1 and 10 4.9 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 M J 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.

Prospects of stellar abundance studies from near‐IR spectra observed with the E‐ELT

“…They discuss the relative behavior of spectral features through the sequence of stars and brown dwarfs. Del Burgo et al (2009) determine physical parameters of T dwarfs based on NIR-SPEC spectra, and find, as expected, that T dwarfs later than T5 have dust free atmospheres due to dust sedimentation.…”

Physical parameters of a sample of M dwarfs from high-resolution near-infrared spectra

“…See [6] for a detailed description of the method. Table 1 shows the results for the eleven M dwarfs, where the spectral type (SpT) is indicated together with v rot sini, T eff , logg and the values found in the literature.…”

“…We have recently applied the technique of matching theoretical spectra to high-resolution data to derive the physical properties of a sample of nine T dwarfs (see [6]). Here we present a preliminary study of 11 out of the 40 late-M dwarfs of our sample observed with the instrument NIRSPEC (see [7]) on the Keck II telescope.…”

Radial velocity observations of VB10

“…The values (V shift ) are listed in Table 1; (3) Radial velocity measurements (V r ) were done on echelle orders that were free of any telluric lines; (4) In order to obtain absolute heliocentric velocity we took into account zero-point shifts errors and corrected for diurnal and annual velocities. The second column in Table 1 shows heliocentric radial velocities for all epochs; (5) the absolute radial velocity was calculated independently using a theoretical procedure followed by del Burgo et al [8]. The value of 34.05 ± 0.30 km/s obtained through these calculations compares well with those from the table (see Table 1 in del Burgo et al in this proceedings); (6) The table suggests radial velocity variability with an amplitude of 1 km/s.…”