04/13/2021
By Sayantan Bhattacharya

The Kennedy College of Sciences, Department of Physics & Applied Physics, invites you to attend a master's thesis defense by Sayantan Bhattacharya entitled "Optical Spectroscopic Monitoring Of BH+WR HMXB: IC10 X-1."

The defense will be held on Monday, April 26 at noon via Zoom. Please contact Silas Laycock for meeting information if you are interested in attending.

Committee Members:

  • Silas G. T. Laycock, Department of Physics & Applied Physics, UMass Lowell
  • Ofer Cohen, Department of Physics & Applied Physics, UMass Lowell
  • Nishant Agarwal, Department of Physics & Applied Physics, UMass Lowell

Abstract: Stellar-mass black holes(BH) are one of the most interesting objects in Astrophysics. Their importance increases manifold when they're in a high mass x-ray binary system(HMXB) i.e the companion is a massive star like a Wolf-Rayet(WR) star. Such an interesting eclipsing HMXB system with a stellar-mass BH and a WR star named IC 10 X-1 has been featured in the present work. In general, mass and other parameters for binary systems can be calculated by creating radial velocity profiles from the stars' spectral lines. Similar initiatives using a Helium emission line(He II 4686) had resulted in a mass of 24 Solar mass of the black hole in IC 10 X-1, which makes it the most massive stellar-mass black hole. But, later a surprising finding shows that the X-ray eclipse is not aligned with the optical radial velocity measurements from the Helium emission line. This puts the previous mass determination in question. It can be assumed that either the BH is being eclipsed by a trailing shock or the He II line fails to track the motion of the BH and originates somewhere in the ionized wind of the star. Hence, we need to look for some higher excitation emission lines(Carbon or Nitrogen) in the spectra that originate deeper in the wind and tracks the true motion of the star, which requires more signal-to-noise ratio(SNR) than achievable in a single spectrum. Hence, we need to phase-wise stack more spectra to achieve the desired SNR.

This motivated us to proceed with this spectroscopic monitoring campaign of IC 10 X-1. It has been one of the major targets to many GEMINI observations of this galaxy, spanning from 2001 to 2019. Presented herein is the analysis of all-optical spectra from the GEMINI/GMOS archive(2001-2019). The goal of this project has been to understand the stellar wind structure and calculating the true binary parameters. This source belongs to a group of systems that can be the progenitors of gravitational wave sources i.e NS+NS, BH+BH, or NS+BH hence proper understanding of systems like IC 10 X-1 is of paramount interest.