Photometric Stellar Variability in the Galactic Center

TL;DR

This study used speckle imaging over 10 years to identify and analyze variable stars in the Galactic Center, revealing orbital characteristics and potential binary systems, and constraining the presence of accretion disks around Sgr A*.

Contribution

First long-term speckle imaging variability survey of the Galactic Center with detailed analysis of stellar variability and implications for black hole accretion structures.

Findings

Identified at least 15 variable stars within 5" of the Galactic Center.

Measured the orbital period of IRS 16SW as approximately 19.45 days.

Found no evidence of flares or dimming in OB stars near Sgr A*, constraining accretion disk models.

Abstract

We report the results of a diffraction-limited, photometric variability study of the central 5"x5" of the Galaxy conducted over the past 10 years using speckle imaging techniques on the W. M. Keck I 10 m telescope. Within our limiting magnitude of mK < 16 mag for images made from a single night of data, we find a minimum of 15 K[2.2 micron]-band variable stars out of 131 monitored stars. The only periodic source in our sample is the previously identified variable IRS 16SW, for which we measure an orbital period of 19.448 +- 0.002 days. In contrast to recent results, our data on IRS 16SW show an asymmetric phased light curve with a much steeper fall-time than rise-time, which may be due to tidal deformations caused by the proximity of the stars in their orbits. We also identify a possible wind colliding binary (IRS 29N) based on its photometric variation over a few year time-scale which is likely due to episodic dust production. None of the 4 LBV candidates in our sample show the characteristic large increase or decrease in luminosity, however, our time baseline is too short to rule them out as LBVs. Among the remaining variable stars, the majority are early-type stars and three are possibly variable due to line of sight extinction variations. For the 7 OB stars at the center of our field of view that have well-determined 3-dimensional orbits, we see no evidence of flares or dimming of their light, which limits the possibility of a cold, geometrically-thin inactive accretion disk around the supermassive black hole, Sgr A*.