Study of an ISO-based sample of Vega stars: towards a better understanding of the evolutionary sequence

Details Study of an ISO-based sample of Vega stars: towards a better understanding of the evolutionary sequence Study of an ISO-based sample of Vega stars: towards a better understanding of the evolutionary sequence

Sep 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sptz.prop.3401a&link_type=abstract

Spitzer Proposal ID #3401

Computer Science

Scientific paper

One of the main discoveries of the IRAS mission was that main-sequence stars can be accompanied by circumstellar dust disks (Vega phenomenon). In this proposal we investigate a sample of 16 Vega candidate stars, whose far-infrared excess above the photosphere - indication for the presence of a disk - was already well measured (5-10 sigma) at 60 and 90 micrometer by ISO. All stars are in the spectral range of F0-F9, therefore, due to the narrow mass range, the stellar luminosities do not change much within the sample. The temporal evolution of the density and temperature structure of the disks, as derived from the proposed observations, can be compared with models which predict that 1) the debris dust production site propagates outwards with time; 2) the relative contributions from small and large grains (which can be deduced from the shape of the disks spectrum) is also evolving with time. There are a number of GTO programmes plus a Legacy programme which are devoted to the Vega phenomenon. However, these proposals focus either on intermediate mass A-type or late F-, G-, K- type stars. Our proposed sample of 16 F stars would fill the gap between these two major categories. Debris disks with fractional luminosity higher than 10^{-3} are in a very special and short state of disk evolution. The sample contains five stars belonging to this interesting category of stars with debris disks, providing an excellent opportunity to study in details these very important cases. We propose to observe 16 F-type main-sequence stars with Spitzer. We obtain MIPS photometry and IRS low resolution spectra for each target in order to measure Vega-type excess at MIPS wavelengths, and to measure the short wavelength cut-off of the excess as well as search for solid-state features at the mid-infrared wavelengths. MIPS SED is requested for five objects to determine detailed SEDs in the far-infrared for the most spectacular (high fractional luminosity) targets. The total programme takes 12.2 hours.

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