Optical and UV Light Curves of the Accretion Disk Corona Source 4U 1822-371

TL;DR

This study presents new UV and optical light curves of the eclipsing low-mass X-ray binary 4U 1822-371, revealing the necessity of an optically-thick accretion disk corona in modeling its eclipses.

Contribution

First time combined UV spectrograms and optical/IR light curves for 4U 1822-371, updating ephemeris and emphasizing the role of an optically-thick ADC in eclipse modeling.

Findings

UV eclipses require an optically-thick ADC in models

Updated ephemeris for eclipse timings

New UV and optical light curves obtained

Abstract

The eclipsing low-mass X-ray binary 4U is the prototypical accretion disk corona (ADC) system. We have obtained new time-resolved UV spectrograms of 4U with the Hubble Space Telescope and new V- and J-band light curves with the 1.3-m SMARTS telescope at CTIO. We present an updated ephemeris for the times of the optical/UV eclipses. Model light curves do not give acceptable fits to the UV eclipses unless the models include an optically-thick ADC.