ar X iv : a st ro - p h / 04 11 15 7 v 1 5 N ov 2 00 4 A Pre - Protostellar Core in L 1551
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چکیده
Large field surveys of NH3, C2S, CO and CO in the L1551 dark cloud have revealed a prolate, pre-protostellar molecular core (L1551-MC) in a relatively quiescent region to the northwest of the well-known IRS 5 source. The kinetic temperature is measured to be 9K, the total mass is ∼ 2M⊙, and the average particle density is 10 –10 cm . L1551-MC is 2 .25×1 .11 in projection oriented at a position angle of 133. The turbulent motions are on the order of the sound speed in the medium and contain 4% of the gravitational energy, Egrav, of the core. The angular momentum vector is projected along the major axis of L1551-MC corresponding to a rotational energy of 2.5× 10 sin i |Egrav|. The thermal energy constitutes about a third of |Egrav| and the virial mass is approximately equal to the total mass. L1551-MC is gravitationally bound and in the absence of strong, ∼ 160μG, magnetic fields will likely contract on a ∼ 0.3Myr time scale. The line profiles of many molecular species suggest that the cold quiescent interior is surrounded by a dynamic, perhaps infalling envelope which is embedded within the ambient molecular gas of L1551. Subject headings: ISM: clouds — ISM: individual(L1551) — stars: formation
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تاریخ انتشار 2004