A massive disk/envelope in shocked H2 emission around an UCHII region
Por:
Kumar M.S.N., Fernandas A.J.L., Hunter T.R., Davis C.J., Kurtz S.
Publicada:
1 ene 2003
Resumen:
A multi-wavelength study of IRAS 07427-2400 in line and continuum emission was conducted to investigate the nature of a H2 v = 1-0 S(1) line emitting feature around this ultra-compact HII region. High resolution 3.6 cm continuum observations from the Very Large Array and 350?m continuum observations from the Caltech Submillimeter Observatory, combined with archival far-infrared data of IRAS 07427-2400 show a flux density distribution indicating a luminous (L = 5.6 × 104 L?) point source associated with an ultra-compact HII region. A Grey body model fit to the flux density distribution yields a dust emissivity index (? ? 0.66) indicative of a circumstellar disk/envelope. Our C18O map shows a dense core centered on the continuum source, with the major axis roughly aligned with the H2 feature. A position-velocity diagram of the C18O core obtained along the major axis shows rotation with a velocity gradient of ?0.1 km s-1 arcsec-1. New CO J = 3-2 maps of the region are presented which reveal a massive molecular outflow from the IRAS source. We argue that the H2 feature arises in a disk/envelope around IRAS 07427-2400 and not in an outflow. We present a near-infrared H K band spectrum of the H2 features that shows several ro-vibrational emission lines of H2 and [FeII]. Analysis of the line ratios indicates that the line emission is shock-excited and not due to fluorescence. We estimate an excitation temperature of ?1600 K and an average extinction of Av ? 11 mag to the H2 feature. The line fluxes yield a mass accretion rate of M ? 2.6 ± 0.9 × 10-2 M? yr-1 and a lifetime of ?5360 ± 1200 yr resulting in a disk/envelope mass of 140 ± 50 M?. The resulting Jeans Mass of 2420 M? indicates that the disk/ envelope will not undergo fragmentation. IRAS 07427-2400 represents one of the most massive YSOs known to date forming by means of accretion.
Filiaciones:
Kumar M.S.N.:
Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 7150-462 Porto, Portugal
Fernandas A.J.L.:
Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 7150-462 Porto, Portugal
Instituto Superior da Maia, Av. Carlos Oliveira Campos, 4475-690 Avioso S.Pedro, Portugal
Hunter T.R.:
Harvard Smithsonian Ctr. Astrophys., MS-78, 60 Garden Street, Cambridge, MA 02138, United States
Davis C.J.:
Joint Astronomy Center, 660 N. A'ohoku Place, University Park, Hilo, HI 96720, United States
Kurtz S.:
Instituto de Astronomia, UNAM-Morelia, Apartado postal 3-72, CP 58090 Morelia, Michoacan, Mexico
All Open Access; Bronze
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