A 33 year constancy of the X-ray coronae of AR Lac and eclipse diagnosis of scale height

Kavli Affiliate: David P. Huenemoerder

| First 5 Authors: Jeremy J. Drake, Peter Ratzlaff, Vinay Kashyap, David P. Huenemoerder, Bradford J. Wargelin

| Summary:

Extensive X-ray and extreme ultraviolet (EUV) photometric observations of the
eclipsing RS CVn system AR Lac were obtained over the years 1997 to 2013 with
the Chandra X-ray Observatory Extreme Ultraviolet Explorer. During primary
eclipse, HRC count rates decrease by ~40%. A similar minimum is seen during one
primary eclipse observed by EUVE but not in others owing to intrinsic source
variability. Little evidence for secondary eclipses is present in either the
X-ray or EUV data, reminiscent of earlier X-ray and EUV observations. Primary
eclipses allow us to estimate the extent of a spherically symmetric corona on
the primary G star of about 1.3Rsun, or 0.86Rstar, and indicate the G star is
likely brighter than the K component by a factor of 2-5. Brightness changes not
attributable to eclipses appear to be dominated by stochastic variability and
are generally non-repeating. X-ray and EUV light curves cannot therefore be
reliably used to reconstruct the spatial distribution of emission assuming only
eclipses and rotational modulation are at work. Moderate flaring is observed,
where count rates increase by up to a factor of three above quiescence.
Combined with older ASCA, Einstein, EXOSAT, ROSAT and Beppo-SAX observations,
the data show that the level of quiescent coronal emission at X-ray wavelengths
has remained remarkably constant over 33 years, with no sign of variation due
to magnetic cycles. Variations in base level X-ray emission seen by Chandra
over 13 years are only ~10%, while variations back to pioneering Einstein
observations in 1980 amount to a maximum of 45% and more typically about 15%.

| Search Query: ArXiv Query: search_query=au:”David P. Huenemoerder”&id_list=&start=0&max_results=10

Read More

Leave a Reply