Spectroscopic Observation of Wolf-Rayet Stars: Study of Expansion Velocity and Mass Loss as Contributors of Interstellar Matter Enrichment

Abstract

Wolf-Rayet (WR) stars exhibit broad emission lines in their spectra. Based on the featured lines, they are classified into three types: nitrogen-rich WN, carbon-rich WC, and oxygen-rich WO. Broad emission lines indicate high expansion velocity and also previous studies showed that WR stars possessed higher mass-loss rates compared with another type of stars. Thus, it is suggested that the expansion velocity and the mass loss of WR stars play a role in the enrichment of interstellar matter. Our observations were conducted between July 2018 and June 2019 using NEO-R1000 (R∼1000) spectrograph with spectral range 4500-7000Å at the Bosscha Observatory and consisted of WN and WC type stars. Data reduction and expansion velocities determination were carried out using IRAF with longslit-transform routine and Gaussian fitting respectively. To obtain mass-loss rates, we compared our observed spectra with models provided by Potsdam Wolf-Rayet Models (PoWR). In several cases, the contribution of WR stars can be directly observed as Wolf-Rayet nebulae, whose structures are influenced by the high expansion velocity of the nearby WR stars. Assuming that the total of WR stars in the Milky Way is ∼ 2600, we estimated that the population release ∼ 0.507 M⊙ of material annually into Galactic environment.