High-Resolution Near-IR Spectroscopy of Protostars with Large Telescopes

Abstract

It is now possible to measure absorption spectra of flat-spectrum and Class I protostars using D ≥ 8m telescopes equipped with sensitive cryogenic IR spectrographs. For the first time ever, our latest high-resolution (R ~ 20,000) Keck NIRSPEC data reveal that Class I protostars are indeed low-mass stars with pre-main-sequence or dwarf-like features. However, Class I and flat-spectrum protostars differ from T Tauri stars in that protostars have much higher IR veilings (r _k ≥ 1 − 3+) and they are rotating quickly, v sin i > 20 km s⁻¹. Interestingly, absorption spectra of low-mass protostars show stellar — not disk — absorption features. Our observations should also be able to probe whether protostellar photospheres have different physical structures than T Tauri stars, as predicted by theoretical models which account for accretion effects. There is much work to be done in this field, and the VLT can contribute immensely.