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Measuring physical properties of pre-main sequence stars using high resolution infrared spectroscopy
textPhysical properties of preāmain sequence stars and their disks are measured
from high resolution nearāinfrared spectra. A new fitting technique using spectral
synthesis models has been developed to find the best fit to fully resolved K band
absorption lines, allowing measurements of the stellar effective temperature, rate
of rotation, and amount of nonāstellar continuum excess from infrared emission
by the circumstellar disk. An IDL fitting routine selects the best spectral synthesis
model by the RMS minimum to the residuals of the fits, and has been validated by
observations of MK standards. This new technique has been applied to a sample
of preāmain sequence stars in the Ļ Ophiuchi dark cloud to obtain accurate effective
temperatures, continuum veilings, and some of the first measurements of vsini
rotations in highly extincted young stars from 2.2 Āµm spectra. In two sources, a
new spectroscopic technique to measure surface gravity has been applied using line
flux ratios in high resolution spectra at 2.2 Āµm and 2.3 Āµm, leading to the first luminosity
measurements that are independent of extinction and only weakly dependent
on continuum excess. Previous assumptions of no continuum excess at J (1.2 Āµm)
upon which the photometrically determined luminosities are based, are called into
question with these new results. In the absence of strong magnetic fields, the ages
of these objects inferred from stellar evolutionary model tracks on the HR diagram
reveals an older age (6ā9 Myr) from spectroscopically determined luminosities than
from the photometry of the same objects.
Another useful application of high resolution spectroscopy is the detection
of binary systems. Characterization of binary systems offers a direct way to obtain
mass and relative mass information. With a sensitivity down to ~0.5 km s-1
, we
have measured precision radial velocities of the sources in our Ophiuchus sample,
resulting in the discovery of one short period (P <
1 yr) preāmain sequence binary
(GSS29). This system has been subsequently monitored to determine its orbital
characteristics (P = 145 d, v2 = 29 km s -1
) and constrain the mass (M1 + M2
~1.8 Mā ). We find the dominant spectral line component to be the less massive (and
cooler) star. The more massive star is mostly featureless because it is hotter and
rotating fast. More observations are required to better constrain these preliminary
results.Astronom