The Spectroscopy of Protostars with IGRINS – Characterizing Protostellar Accretion Using Br γ Emission*

Through the University of Toledo’s NSF-REU program, this research aims to determine intrinsic stellar parameters and characterize accretion activity in protostars using Brackett-γ (Br γ) emission. High-resolution near-infrared spectra were obtained with the Immersion GRating INfrared Spectrograph (IGRINS), and data reduction was performed using the IGRINS Pipeline Package (PLP) v3.1.

Our analysis focuses on the K-band spectral range (2.08–2.35 μm), excluding low-SNR regions in the H-band and near the band edges. To derive fundamental stellar parameters including effective temperature (T_eff), surface gravity (log g), rotational velocity (v sin i), radial velocity (v_r), and K-band veiling (r_k) we fit observed spectra with synthetic models from the BT-Settl (CIFIST) library of precomputed stellar atmospheres.

Spectral fitting is conducted using a Markov Chain Monte Carlo (MCMC) method via the emcee package, enabling us to explore the probability distributions of stellar parameters and quantify associated uncertainties. In parallel, we analyze the Br γ emission line at 2.166 μm to investigate protostellar accretion. The line profile and luminosity are used to infer accretion properties, using the observed correlation between Br γ and accretion luminosity (Alcalá et al. 2017). This approach enables simultaneous characterization of both stellar and accretion properties, crucial for understanding early stellar evolution and disk accretion.