Photometry of two DQ white dwarfs - search for spots

TL;DR

This study investigates the presence of stellar spots on two cool DQ white dwarfs through photometric observations, aiming to explain spectral modeling discrepancies, but finds no evidence of variability caused by spots.

Contribution

The paper introduces a photometric method to search for stellar spots on DQ white dwarfs and assesses the likelihood of spot detection, addressing spectral modeling challenges.

Findings

No variability detected in the observed white dwarfs

Estimated detection probabilities for hypothetical spots

Discussion of alternative explanations for spectral modeling issues

Abstract

Aims. The intensity profiles of the C_2 Swan bands in cool DQ white dwarfs cannot be adequately fitted with models that otherwise succesfully reproduce spectral features of the molecule CH in these stars. Initial modelling showed that a two-component atmosphere in the style of a spot might be able to solve the problem. Methods. We photometrically observed the two cool DQ white dwarfs GJ1117 and EGGR78 to search for variability caused by stellar spots. Results. We have not found any such variability, but we estimate the effects of hypothetical spots on lightcurves. We also estimate detection probabilities for spots in different configurations. Alternative explanations of the problem are needed and briefly discussed.