Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...185.4812h&link_type=abstract
American Astronomical Society, 185th AAS Meeting, #48.12; Bulletin of the American Astronomical Society, Vol. 26, p.1389
Astronomy and Astrophysics
Astronomy
Scientific paper
In September 1994, we obtained HST/GHRS spectra and maps of beta Pic (HD 39060) and its surrounding disk. In this paper, we report our preliminary findings concerning the star and circumstellar gas disk. Both Stromgren photometry and Geneva photometry (as listed by SIMBAD) yield the following parameters for the star: T_eff=8200 +/- 50 K log g = 4.25 +/- 0.05 [Fe/H] = -0.1 +/- 0.2 To refine the estimated metallicity, we have compared the GHRS ultraviolet spectra with model spectra. Our model of beta Pic incorporates both a LTE stellar atmosphere plus a circumstellar gas disk, treated in a first approximation as a homogeneous, absorbing slab at T=5,000 K with a column density, N_H=2x10(19) cm(-2) . We confirm that the star has a near-solar metallicity. We have compared the derived stellar parameters with evolutionary models for Z=0.017. For reference, a ZAMS star having a T_eff=8,200 K has a mass, M ~1.72 M_sun, and a gravity, log g= 4.37. The somewhat low surface gravity of beta Pic suggests that the star has evolved slightly off the ZAMS or is still in the pre-main sequence phase. In either case, it should be somewhat more luminous than a 1.72M_sun ZAMS star. However, its absolute magnitude, M_V= 2.70 (for a distance of 17 pc) is 0.21 mag fainter than a M=1.72 M_sun star on the ZAMS. We therefore conclude that (1) the dust disk must diminish light from the star, and (2) it is entirely possible that beta Pic is a very young star. Both conclusions raise problems for interpreting observations of the dust disk (c.f. Paresce, 1991, A&A, 247, L25).
Heap Sally R.
Hubeny Ivan
Lanz Thierry
Lindler Don
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