Do dusty A stars exhibit accretion signatures in their photospheres?

Abstract

Abstract. 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.

The interferometric diameter and internal structure of Sirius A

“…At the present status of our observational constraints on Sirius A, it is impossible to decide if overshoot exists or not in the central convective core. Note that our model gives a surface abundance of [M/H] Sirius = −0.32 dex which agrees with the abundance of the oxygen found by Kamp et al (2002). Finally, if Sirius A is able to excite radial modes of oscillation, we predict the mean large frequency spacing ∆ν 0 to be ranging between 81 and 82 µHz This is the primary observable of asteroseismology, and corresponds to the difference between the frequencies of oscillation modes with consecutive radial order n (see Table 3).…”

High resolution spectroscopy of circumstellar material around A stars

“…The members of this small subgroup of A stars show solar abundances of lighter elements like C, N, and O whereas heavier elements are underabundant. The metal deficiency of the λ Bootis stars is attributed to accretion of depleted gas after separation of gas and dust (Venn & Lambert 1990) either from their circumstellar environment or from interaction with diffuse interstellar clouds (Kamp & Paunzen 2002). We observed HR 4881 in previous observing runs and detected a conspicuous narrow absorption feature near the core.…”

“…We observed the Ca K line of each of our program stars several times each night (see Table 2) in order to search for short-term variability. As in our previous work (see Kamp et al 2002 and references therein) we have reduced our spectra with MIDAS routines. We used Th -Ar spectra for wavelength calibration.…”

The heterogeneous class ofλBootis stars

“…For the HD 141 851 binary system the existence of a secondary separated by less than 0.1 arcsec has been known since 1987 (McAlister et al 1987); however, the companion has been considered too faint to affect the observed spectrum, which has always been interpreted as that of a single object (North et al 1994;Paunzen et al 1999;Kamp et al 2002;Andrievsky et al 2002). The AO observations confirm the presence of a companion star that cannot be separated at a spectrograph entrance.…”