Modeling UX Ursae Majoris: An abundance of challenges

TL;DR

This paper develops a detailed model of the UX UMa system's spectra, incorporating multiple components and addressing complex absorption effects, to better understand its optical and UV emissions.

Contribution

The study introduces a comprehensive system model for UX UMa that accounts for variable absorption and emission features, improving spectral fitting accuracy over previous models.

Findings

Successful fit of optical and UV spectra with the model

Identification of the 'iron curtain' effect near the Balmer limit

Evidence of time-variable absorption affecting spectral fits

Abstract

We present a system model for optical and far UV spectra of the nova-like variable UX UMa involving a white dwarf, secondary star, gas stream, hot spot and accretion disk using our code BINSYN and based on an initially adopted system distance. Calculated SED intensity data successfully fit successive tomographically-extracted annuli longward of the Balmer limit but require a postulated `iron curtain' shortward of the Balmer limit that is applied to the annulus section closest to the secondary star, while postulated recombination emission fills in the model SED shortward of the Balmer limit and is applied to the annulus section more remote from the secondary star. The same model fits $UBV$ 1954 light curves by Walker and Herbig. Fits to $HST$ $FOS$ spectra are approximate but require assumed time-variable changes in the SED. Comparable effects, possibly involving variable absorption, afflict $FUSE$ spectra.