HII and hot dust emission around young massive stars in G9.62+0.19
by
L. Testi (1,2), M. Felli (3), P. Persi (4), M. Roth (5)
(1) Dipartimento di Astronomia e Scienza dello Spazio,
Università di Firenze, Largo E. Fermi, 5, I-50125 Firenze, Italy
(2) Division of Physics, Mathematics and Astronomy, Caltech,
MS 105-24, Pasadena, CA 91125, USA
(3) Osservatorio Astrofisico di Arcetri,
Largo Enrico Fermi 5, I-50125 Firenze, Italy
(4) Istituto di Astrofisica Spaziale, C.N.R., C.P. 67,
I-00044 Frascati, Italy
(5) Las Campanas Observatory, Casilla 601, La Serena, Chile
Abstract:
In this paper we present new near infrared (NIR) observations
(J, H, and K broadbands), of the G9.62+0.19 star forming complex.
Comparison of our observations with similar resolution centimetric continuum,
millimeter continuum and molecular emission show that
the mm continuum source F, not detected in the cm wavelength
free-free radio continuum
and associated with a high density molecular peak,
is detected at 2.2 um, while the ultracompact HII region
D, one of the youngest of the HII regions in the complex,
is not detected in the near infrared.
We propose a simple model that explains why, in the
first stages of evolution of a young massive star, the source
may be observable at K but not in the cm radio continuum. When the size of
the UC HII region is <<10^{-3} pc the hot dust present around
the YSO strongly emits at K band, but the radio emission will be strongly
self-absorbed. At later stages, when the size of the UC HII becomes greater
than <~10^{-3} pc, the dust temperature goes down and
the K band dust emission strongly decreases; at
the same time the cm radio continuum becomes detectable. As the UCHII expands
the extinction drops and the K band emission rises again due to the
stellar and ionized gas free-free and free-bound emission.
We propose an evolutionary sequence of the different sites of star formation
in the complex, based on the radio continuum--infrared morphology and on
the association with H2O masers.
Mantained by:
Leonardo Testi
lt@arcetri.astro.it