An atmospheric model for UZ Librae from mean Hα-line profiles

Abstract

Abstract. We present the results from fitting a semi-empirical atmospheric model including a chromosphere and a transition region to the mean (seasonal) Balmer Hα line profiles of the RS CVn-type K0-giant UZ Librae. As a first step, a static 1D spherical model was applied to the mean component of the Hα-emission core and its profile. The main result of the fitting is that the transition region begins at a log mass depth of −1.8 g cm −2 at a temperature of 7400 K (approximately 3000 K warmer than the photosphere) and then has a steep increase to the peak temperature of ≈10 6 K. A stellar model in plane-parallel mode with "partial-frequency redistribution" option in the line transfer gave roughly the best fit. Subsequently, two-Gaussian fitting of the phase-dependent Hα-line profiles yields a complex velocity field. The radial velocities, from both the absorption reversal and the main emission component, display rotational and/or orbital modulation. The largest differences between consecutive line profiles occur mostly in the red line wings, suggesting the existence of both an inward-pointed velocity field and sporadic radiation events possibly related to flares. The total Hα emission, as derived from the equivalent width, possibly also displays rotational modulation. Indirect evidence is presented for the existence of circumstellar matter in form of an Hα absorption shell. Finally, a preliminary elemental abundance analysis suggests sub-solar metallicity of [M/H] ≈ −0.5 dex based on ATLAS models, or −0.7 dex based on PHOENIX models.

Wiyn Open Cluster Study. Lxxi. Spectroscopic Membership and Orbits of NGC 6791 Sub-Subgiants

“…Blueshifted Hα emission was also observed by van den Berg, Verbunt & Mathieu (1999) in the M67 SSG, S1063. We suggest this feature might be similar to the broad blueshifted Hα component detected in RS CVn-type giants and attributed to extended prominence material or outflow structures of the chromosphere (e.g., Zboril, Strassmeier & Avrett 2004;Biazzo et al 2006). However, the other SSG in M67, S1113, has Hα emission centered on the velocity of the primary star and two of the SSGs in NGC 6791 do not have Hα emission features, so blueshifted Hα emission is not a universal property of SSGs.…”

Photospheric and chromospheric active regions on three single-lined RS CVn binaries

“…When the active regions are facing the observer, the blueshifted chromospheric network would be "overwhelmed" by broad but symmetrical Hα profile due to the chromospheric plages. A systematic blue-shift of the broad Hα emission component was observed by Zboril et al (2004) in the very active RS CVn binary UZ Librae and explained in terms of velocity fields in the chromosphere.…”

X‐Ray and Ultraviolet Spectroscopy of Intermediate‐Mass, First Crossing Giants

“…Densities in the range 10 12 Y10 13 cm À3 are equivalent to those found in the upper chromospheres of very active giant stars (e.g., Zboril et al 2004). If hot coronal gas at such densities is fully confined, then magnetic fields of order 500 G would be required and the cooling times would be seconds, necessitating continual energy input (e.g., Phillips et al 1996).…”