NEAR ULTRAVIOLET AND OPTICAL SPECTROSCOPY STUDY OF 11 GALACTIC WOLF-RAYET STARS: DERIVATION OF PHYSICAL PARAMETERS OF WOLF-RAYET STARS

• Main Author: Danang Setyo Budi, Bakuh
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/73580
• Institution: Institut Teknologi Bandung

Wolf-Rayet stars are one of the first emission-lined astronomical objects discovered by Charles Joseph ´Etienne Wolf and Georges-Antoine-Pons Rayet at the Observatory Paris in 1867 while conducting a survey of three stars in the constellation Cygnus by spectroscopy. They found an oddity in the spectrum of the three stars, there was a wide, bright emission lines between the continuum for easy viewing. This emission line is presumed originally derived from hydrocarbons. It is now known that Wolf-Rayet stars are abundant unusual helium, carbon, or nitrogen when compared to typical stars. The spectrum of a Wolf-Rayet star has a continuum profile that originates from large optical depth and assume to follows Planck’s law, and the resulting emission profile of the extended atmosphere through the process of photoionization, recombination, etc. The continuum profile of a Wolf-Rayet star is similar to continuum of class O stars which indicates Wolf-Rayet stars have hot temperatures (>10 000 K), therefore LTE atmospheric modeling (Local Thermal Equilibrium) does not apply. In addition, several P-Cygni emission profiles indicate an expanding atmosphere. Classification the Wolf-Rayet star class differs from the temperature-based Morgan-Keenan classification effectiveness and luminosity. Classification of this class of stars based on the degree of ionization and line strength some emission lines of helium, carbon, nitrogen, and/or oxygen. In this final project, several physical parameters are derived from 11 galacticWolf- Rayets representing each sub-class using GAO-ITB RTS observations with the NEO R-1000 low-resolution spectrograph and the International Ultraviolet Explorer data archive (IUE) with low-resolution spectrographs SWS and LWS. Atmospheric modeling of Wolf-Rayet stars uses blackbody radiation modeling and the Postdam Wolf-Rayet (PoWR) model. Prior to modeling, several separate analyzes were required, each with the aim of determining the parallax distance parameters of Wolf-Rayet stars using Gaia DR3 data and the terminal velocity of stellar winds through the P-Cygni profile using spectrum data from the International Ultraviolet Explorer data archive (IUE) with the SWS high-resolution spectrograph. Based on the analysis, the parameters of distance, temperature, radius, luminosity, terminal velocity of the stellar wind, and mass loss rate have been derived which have values not far from the reference. However, there are severa samples of Wolf-Rayet stars that have large deviations from the reference, one of which is caused by the sample being a double star. The existence of a partner star which is a class O star will dissolve the emission lines of Wolf-Rayet stars and make the spectrum modeling less accurate.