Inga Kamp — Page 6 | Searcharxiv

arXiv2002

Do dusty A stars exhibit accretion signatures in their photospheres?

We determined abundances of O, Ca, Fe, Ba and Y for a sample of dusty and dust-free A stars, taken from the list of Cheng et al. (1992). Five of the stars have an infrared-excess due to circumstellar dust. Ongoing accretion from their circumstellar surroundings might have modified the abundances in the photospheres of these stars, but our results clearly show, that there is no difference in the photospheric composition of the dusty and dust-free stars. Instead all of them show the typical diffusion pattern which diminishes towards larger rotational velocities.

astro-ph↗

arXiv2001

On the gas temperature in circumstellar disks around A stars

In circumstellar disks or shells it is often assumed that gas and dust temperatures are equal where the latter is determined by radiative equilibrium. This paper deals with the question whether this assumption is applicable for tenous circumstellar disks around young A stars. In this paper the thin hydrostatic equilibrium models described by Kamp & Bertoldi (2000) are combined with a detailed heating/cooling balance for the gas. The most important heating and cooling processes are heating through infrared pumping, heating due to the drift velocity of dust grains, and fine structure and molecular line cooling. Throughout the whole disk gas and dust are not efficiently coupled by collisions and hence their temperatures are quite different. Most of the gas in the disk models considered here stays well below 300 K. In the temperature range below 300 K the gas chemistry is not much affected by T_gas and therefore the simplifying approximation T_gas = T_dust can be used for calculating the chemical structure of the disk. Nevertheless the gas temperature is important for the quantitative interpretation of observations, like fine structure and molecular lines.

astro-ph↗

arXiv1998

Dusty and dust-free A stars

We present preliminary results of our search for circumstellar absorption features in the Ca K lines based on high S/N observations obtained with the ESO CAT/CES system.

astro-ph↗