Line emission from circumstellar disks around A stars*
Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
2 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
Corresponding author: I. Kamp, firstname.lastname@example.org
Accepted: 29 October 2002
The nature of the tenuous disks around A stars has raised considerable controversy in the literature during the past decade. The debate whether or not the disk around β Pictoris contains gaseous molecular hydrogen is only the most recent example. Since CO is in general a poor tracer for the gas content of these low mass disks, we discuss here detailed emission line calculations for alternative tracers like C and C+, based on recent optically thin disk models by Kamp & van Zadelhoff (2001). The  157.7 μm line was searched toward Vega and β Pictoris – the most prominent A stars with disks – using ISO LWS data, and a tentative detection is reported toward the latter object. From a comparison with emission line observations as well as absorption line studies of both stars, the gas-to-dust ratio is constrained to lie between 0.5 and 9 for β Pictoris. For Vega the  observations indicate an upper limit of 0.2 for the disk gas mass. Predicted line intensities of C+ and C are presented for a range of models and appear promising species to trace the gas content in the disks around A stars with future instrumental capabilities (SOFIA, Herschel, APEX and ALMA). Searches for CO emission should focus on the –2 line.
Key words: stars: circumstellar matter / stars: planetary systems: protoplanetary disks / stars: early-type / stars: individual: β Pictoris / stars: individual: Vega
© ESO, 2003