Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...450..183n&link_type=abstract
Astrophysical Journal v.450, p.183
Astronomy and Astrophysics
Astronomy
101
Ism: Clouds, Ism: H Ii Regions, Ism: Jets And Outflows, Stars: Formation, Stars: Luminosity Function, Mass Function
Scientific paper
We have investigated the mechanisms of determining the stellar mass in the process of star formation. Because the stellar core grows by the inflow of matter from the parent cloud core, the mass of the growing star is fixed when the supply of matter from the cloud core is stopped. Because the cloud core matter falls onto the stellar core mostly through an accretion disk, a significant fraction of the mass outflow from the stellar vicinity and the stellar radiation escapes from the inner region without interacting with the infalling matter. A considerable fraction of the cloud core matter which has not yet contracted much is blown off by the mass outflow and the H II region developed by the stellar ultraviolet radiation. Although some cloud core matter may remain at this stage, it disperses soon because it is no longer gravitationally bound. Consequently, the supply of matter to the accretion disk and then to the stellar core stops. The stellar mass, M*, determined in this way is a function of the density of the cloud core, nc, the mass inflow rate from the cloud core, Mdot1, the mass outflow rate relative to the inflow rate, MdotO/Mdot1, and the cloud core mass relative to the generalized Jeans mass, Mc/MJ, and it can also be represented as a function of nc, Mc, MdotO/Mdot1, and Mc/MJ. When the mass outflow is dominant in blowing off the cloud core matter, we have M* ∝ Mc7/6nc1/12 with the proportionality coefficient dependent on Mdot0/Mdot1, and thus the stellar mass is almost independent of nc. The star formation efficiency M*/Mc is therefore mainly determined by Mdot0/M1 and is only weakly dependent on the core parameters Mc and nc; for a typical value Mdot0/Mdot1 = 0.1, we obtain M*/Mc ≍ 0.04 around Mc ˜ 100 Msun. Applying this method to the observed cloud cores in the Orion A molecular cloud by assuming that each core does not contain subclumps, we estimate the stellar mass and the initial mass function of stars (IMF) expected in this cloud. As long as Mdot0/Mdot1 > 0.02, the mass outflow is more efficient than the H II region in determining the stellar mass for all the Orion A cores. The IMF at M* ≳ 4 Msun can be approximated by a power law dN*/d log M* ∝ M*-1.7 for Mdot0/Mdot1 = 0.1, which is in reasonable agreement with the IMF of field stars ∝M*-1.5 at M* ≳ 3 Msun. We also discuss star formation in the cloud core which contains many subclumps
Hasegawa Tetsuo
Nakano Takenori
Norman Colin
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