Quantitative near-infrared spectral analysis of young OB stars

Abstract

We have recently obtained moderate resolution (R${\sim}$8,000–12,000) high signal-to-noise H- and K-band spectroscopy of a number of optically visible, well studied OB stars (Hanson et al. 2005) to test the reliability of a pure near-infrared quantitative analysis (Repolust et al. 2005). The analysis of 25 of these OB stars via near-infrared spectra alone using the NLTE line-blanketed model atmosphere code FASTWIND (Puls et al. 2005) has proved successful at constraining stellar and wind parameters, consistent with results from previous optical analyses of these stars. This opens the door to quantitative analysis of OB stars at an extraordinarily young age, while they are still heavily enshrouded in their birth cocoons. Because the analysis requires good quality spectra at both H and K band, present 8-m class telescopes limit us to sources which are not extremely embedded ($A_V < 30$). As a first example, we present a preliminary analysis of the heavily reddened ($A_V = 25$), early-O star ionizing the UCHII region, G29.96-0.02. Challenges facing such an analysis include contributions from excess thermal emission from circumstellar material (disks, etc.) which weaken or even eliminate photospheric lines used in the analysis, nebular contamination in several of the principle H and He lines and crowding or general confusion in these very young and typically complex regions. Spectrographs coupled with state of the art adaptive optics will be extremely useful in minimizing these challenges, and may allow even fairly complex regions to be directly studied.