Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011ess.....2.2205s&link_type=abstract
American Astronomical Society, ESS meeting #2, #22.05
Astronomy and Astrophysics
Astronomy
Scientific paper
About 20 sub-stellar companions with large separations (> 50 AU) to their young primary stars and brown dwarfs are confirmed by both common proper motion and late-M / early-L type spectra. The origin and early evolution of these objects is still under debate. While often these sub-stellar companions are regarded as brown dwarfs, they could possibly also be massive planets, the mass estimates are very uncertain so far. They are companions to primary stars or brown dwarfs in young associations and star forming regions like Taurus, Upper Scorpius, the TW Hya association, Beta Pic moving group, TucHor association, Lupus, Ophiuchus, and Chamaeleon, hence their ages and distances are well known, in contrast to free-floating brown dwarfs.
Here we present how mass estimates of such young directly imaged companions can be derived, using e.g. evolutionary models, which are however currently almost uncalibrated by direct mass measurements of young objects. An empirical classification by medium-resolution spectroscopy is currently not possible, because a spectral sequence that is taking the lower gravity into account, is not existing. This problem leads to an apparent mismatch between spectra of old field type objects and young low-mass companions at the same effective temperature, hampering a determination of temperature and surface gravity independent from models. We show that from spectra of the objects, using the advantages of light concentration by an AO-assisted integral field spectrograph, temperature, extinction, metallicity and surface gravity can be derived using non-equilibrium radiative transfer atmosphere models as comparison and that this procedure as well allows a mass determination in combination with the luminosities found by the direct observations, as has recently been done by us for several young sub-stellar companions, as e.g. GQ Lup, CT Cha or UScoCTIO 108.
Neuhäuser Ralph
Schmidt Tobias
Seifahrt Andreas
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