Towards the Astrophysics of Protostars via IR Spectroscopy

Tom Greene
NASA Ames Research Center

Very little is known about the embryonic stellar cores of accreting
protostars. Their high extinctions (Av >= 40 mag) make them impossible
to study via optical spectroscopy with even the largest telescopes.
However, we have recently made progress towards understanding these
objects via high-resolution (R ~ 20,000) near-IR absorption line
spectroscopy using the IRTF and Keck telescopes. We have found that
these very young stellar cores have temperatures, radii, and surface
gravities which are similar to somewhat older T Tauri stars. However,
protostars have much higher continuum veilings, indicating very high mass
accretion rates. Interestingly, their spectra are dominated by
stellar-like features, and there is little evidence that any of their
absorption lines form in circumstellar disks. Protostars also appear
to be rotating much more quickly than T Tauri stars, so they must lose
about half of their angular momenta in only about 100,000 yr. It is
plausible that this can be done via magnetic coupling between protostars
and their disks. These first glimpses into the astrophysics of
protostars will also allow us to construct the first ever H-R diagrams
which show the true zero-point of stellar evolution