Informatica

It has been proposed that some hot molecular cores (HMCs) harbor a young embedded massive star, which heats an infalling envelope and accretes mass at a rate high enough to ``choke off'' an incipient HII region. This class of HMCs would mark the youngest phase known of massive star formation. In order to test this hypothesis, we model this type of object calculating the radiative transfer through a spherically symmetric dusty envelope infalling onto a central OB star, with accretion rates from 0.0006 to 0.001 solar masses per year. The dust thermal spectrum from infrared to radio wavelengths is derived and is compared with the observed fluxes of several hot cores which may be internally heated. We find that the data are best fitted using an envelope with the density distribution resulting from the collapse of a singular logatropic sphere, instead of that of a singular isothermal sphere. We conclude that several of these sources may be undergoing an intense accretion phase and find in all the cases that the accretion luminosity exceeds the stellar luminosity. We discuss the implications of this phase on the formation of massive stars.

We model the Class I source L1551 IRS 5, adopting a flattened infalling envelope surrounding a binary disk system and a circumbinary disk. With our composite model, we calculate self-consistently the spectral energy distribution of each component of the L1551 IRS 5 system, using additional constraints from recent observations by ISO, the water ice feature from observations with SpeX, the SCUBA extended spatial brightness distribution at sub-mm wavelengths, and the VLA spatial intensity distributions at 7 mm of the binary disks. We analyze the sensitivity of our results to the various parameters involved. Our results show that a flattened envelope collapse model is required to explain simultaneously the large scale fluxes and the water ice and silicate features. On the other hand, we find that the circumstellar disks are optically thick in the millimeter range and are inclined so that their outer parts hide the emission along the line of sight from their inner parts. We also find that these disks have lower mass accretion rates than the infall rate of the envelope.

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