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Massive Young Stellar Objects in high-mass star-forming regions

By SpaceRef Editor
August 16, 2005
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Astrophysics, abstract

From: Arjan Bik [view email]
Date: Tue, 14 Jun 2005 12:23:10 GMT (486kb)

Massive Young Stellar Objects in high-mass star-forming regions

Arjan Bik (ESO, Garching),
Lex Kaper (Univ Amsterdam),
Wing-Fai Thi (ESA, ESTEC),
Rens Waters (Univ Amsterdam)

Comments: 6 pages, 4 figures, to appear in "Massive Star Birth – A Crossroads
of Astrophysics" (CUP), eds. R. Cesaroni, E. Churchwell, M. Felli, and C.M.

High-quality K-band spectra of point sources, deeply embedded in massive
star-forming regions, have revealed a population of 20 young massive stars
showing no photospheric absorption lines, but only emission lines. The K-band
spectra exhibit one or more features commonly associated with massive Young
Stellar Objects surrounded by circumstellar material: a very red color (J-K) =
2, CO bandhead emission, hydrogen emission lines (sometimes doubly peaked), and
FeII and/or MgII emission lines. The CO emission comes from a relatively dense
(~10^10 cm^(-3)) and hot (T ~ 2000-5000 K) region, sufficiently shielded from
the intense UV radiation field of the young massive star. Modeling of the
CO-first overtone emission shows that the CO gas is located within 5 AU of the
star. The hydrogen emission is produced in an ionized medium exposed to UV
radiation. The best geometrical configuration is a dense and neutral
circumstellar disk causing the CO bandhead emission, and an ionized upper layer
where the hydrogen lines are produced. We argue that the circumstellar disk is
likely a remnant of the accretion via a circumstellar disk.

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