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[71.15] A Survey Of High Mass Protostellar Objects for Evidence of Infall

G.A. Fuller, S.J. Williams (UMIST), T.K. Sridharan (CfA)

An important aspect of understanding star formation is identifying and studying the accretion flows which are adding mass to the protostars. Although spectroscopic evidence of gravitational infall has been detected in the envelopes of a number of low mass protostars, little is known about infall towards forming high mass stars. Here we report on the first results of a survey to search for evidence of infall towards a sample of high mass protostellar objects (HMPOs).

The sources being observed are IRAS point sources which are infrared bright with the same infrared colours and fluxes as UCHII regions. The sources are associated with hot, dense gas but have not yet produced their own UCHII regions. This list of 69 candidate isolated sources have luminosities ranging from 10³ to 10⁵L_\odot and have been shown by Sridharan et al. (2002) to be good candidate high mass protostellar objects, analogues of the low mass Class 0 sources, the youngest class of low mass protostars.

In an infalling envelope, the different extinction suffered by the red and blue shifted emission of an optically thick line leads to an asymmetric line profile, with stronger blue than red shifted emission (e.g. Zhou 1992). This is the so called infall asymmetry which has been detected towards a number of low mass protostars and also starless cores (Mardones et al. 1997;Lee et al. 1999; Williams et al 1999). We are using the IRAM 30m telescope and JCMT to search for this blue line asymmetry as evidence of gravitational infall of the massive circumstellar envelopes around these HMPOs. We are observing the J=4-3 transition of HCO⁺ and the J=3-2 transition of H¹³CO⁺ with JCMT and the HCO⁺ J=1-0, N₂H⁺ J=1-0 and H₂CO 2_1,2-1_1,1 transitions with the IRAM 30m.

Presenting our initial results for the incidence of blue asymmetry in the line profiles, we will discuss whether the observed asymmetries are tracing infall and the range of mass accretion rates consistent with the observations.

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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.