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R. S. Fisher, C. M. Telesco, R. K. Pina (U. Florida - Infrared Astrophysics Group), R. F. Knacke (Penn State Erie, Behrend College)
We present new mid-IR (10 and 18 \micron) observations of two Vega-like sources, HD 169142 and HD 233517 (SAO 26804). Using OSCIR on Keck II, we have detected extended emission around HD 169142 in what appears to be a nearly face-on disk. The mid-IR-emitting region of the disk has a diameter of ~175 AU, comparable to HD 141569 and the Vega-like archetype \beta Pictoris. The position of HD 169142 in the H-R diagram implies that it is close to, but not yet on, the ZAMS. Comparison with PMS evolutionary tracks indicates that it is 3 - 10 Myr old, in transition between the Herbig Ae/Be and Vega-like classes. Assuming that the mid-IR-emitting dust particles are Mie spheres implies that their diameter is < 3 \micron. We also present new 10 and 18 \micron images of HD 233517 (SAO 26804) that show this source is unresolved at the highest resolution currently attainable in the mid-IR. Our imaging with OSCIR on Keck II places full-width at half maximum (FWHM) limits on the source size of 0\farcs31 at 10.8 \micron and 0\farcs inconsistent with previously published values. The fact that SAO 26804 is unresolved in the mid-IR has implications for the evolutionary status. We propose that the unresolved nature of SAO 26804 is strong circumstantial evidence that the source is not a main sequence (luminosity class V dwarf) Vega-like source, but a lithium-rich giant (luminosity class III). The giant classification for SAO 26804 is supported by its position in the H-R diagram.
This research was supported in part by NSF and NASA grants to the University of Florida and Pennsylvania State University at Erie.
The author(s) of this abstract have provided an email address for comments about the abstract: fisher@astro.ufl.edu