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Title:
LkHα 101 and the Young Cluster in NGC 1579
Authors:
Herbig, G. H.; Andrews, Sean M.; Dahm, S. E.
Affiliation:
AA(Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822), AB(Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822), AC(Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822)
Publication:
The Astronomical Journal, Volume 128, Issue 3, pp. 1233-1253. (AJ Homepage)
Publication Date:
09/2004
Origin:
UCP
AJ Keywords:
open clusters and associations: individual (NGC 1579), Stars: Emission-Line, Be, Stars: Formation, Stars: Individual: Alphanumeric: LkHα 101, Stars: Pre-Main-Sequence
DOI:
10.1086/423043
Bibliographic Code:
2004AJ....128.1233H

Abstract

The central region of the dark cloud L1482 is illuminated by LkHα 101, a heavily reddened (AV~10 mag) high-luminosity (>=8×103 Lsolar) star having an unusual emission-line spectrum plus a featureless continuum. About 35 much fainter (mostly between R=16 and >21) Hα emitters have been found in the cloud. Their color-magnitude distribution suggests a median age of about 0.5 Myr, with considerable dispersion. There are also at least five bright B-type stars in the cloud, presumably of about the same age; none show the peculiarities expected of HAeBe stars. Dereddened, their apparent V magnitudes lead to a distance of about 700 pc. Radio observations suggest that the optical object LkHα 101 is in fact a hot star surrounded by a small H II region, both inside an optically thick dust shell. The level of ionization inferred from the shape of the radio continuum corresponds to a Lyman continuum luminosity appropriate for an early B-type zero-age main-sequence star. The V-I color is consistent with a heavily reddened star of that type. However, the optical spectrum does not conform to this expectation: the absorption lines of an OB star are not detected. Also, the [O III] lines of an H II region are absent, possibly because those upper levels are collisionally deexcited at high densities. There are several distinct contributors to the optical spectrum of LkHα 101. The Hα emission line is very strong, with wings extending to about +/-1700 km s-1, which could be produced by a thin overlying layer of hot electron scatterers. There is no sign of P Cygni type mass ejection. Lines of Si II are narrower, while the many Fe II lines are still narrower and are double with a splitting of about 20 km s-1. Lines of [Fe II], [O I], and [S II] are similarly sharp but are single, at the same velocity as the Fe II average. Work by Tuthill et al. allowed the inference, from K-band interferometry, that the central source is actually a small horseshoe-shaped arc about 0.05" (35 AU) across. A tipped annulus of that size in rotation about a 15 Msolar star would produce double spectrum lines having about the splitting observed for Fe II. The totality of observational evidence encourages the belief that LkHα 101 is a massive star caught in an early evolutionary state.
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