THE DUST DISK AROUND THE VEGA-EXCESS STAR SAO 26804

摘要

We present multiwaveband observations of the K2 Vega-excess star SAO 26804 ( = HD 233517). These include James Clerk Maxwell Telescope millimeter-wave photometry, plus spectra in the 8-13 μm and 18-24 μm atmospheric windows, an image at a wavelength of 10 μm through a broadband N filter and near-IR (JHKLL'M) photometry all taken at the United Kingdom Infrared Telescope. The source is resolved at 10 μm, and we can confirm with these observations that the IR excess seen in IRAS observations of this source is associated with the optical star. The image is consistent with the dust being confined to a disk with FWHM 1.5″ on the major axis, with an inclination angle of less than 30° away from edge-on. This represents the first confirmation that the dust in a Vega-excess star other than β Pic is confined to a disk geometry. We present models of the source which show that many of the properties of the disk and the dust in it are similar to those which we have previously derived for the disk around SAO 179815, but that there are some very small grains in the disk around the star which give rise to a very prominent and narrow silicate dust feature at 9.7 μm and to so-called unidentified infrared bands in the 10 μm region. The larger grains are composed of a mixture of amorphous carbon and silicate with an abundance ratio consistent with an interstellar origin. The total mass of dust in the disk is 3.0 x 10~ (-7) solar mass. Finally, our model suggests that there may be a substantial UV and/or soft X-ray flux from SAO 26804, consistent with it being a very young and rather active star.