CO outflows from young stars in the NGC2023 cluster
Astronomy & Astrophysics(2024)
摘要
Young early-type HAeBe stars are still embedded in the molecular clouds in
which they formed. They illuminate reflection nebulae, which shape the
surrounding molecular cloud and may trigger star formation. They are therefore
ideal places to search for ongoing star formation activity. NGC2023 is
illuminated by the Herbig Be star HD37903. It is the most massive member of a
small young cluster with about 30 PMS stars, several of which are Class I
objects that still heavily accrete. It might therefore be expected that they
might drive molecular outflows. We examined the whole region for outflows. We
analyzed previously published APEX data to search for and characterize the
outflows in the NGC2023 region. This is the first systematic search for
molecular outflows in this region. Since the outflows were mapped in several CO
transitions, we can determine their properties quite well. We have discovered
four molecular outflows in the vicinity of NGC2023, three of which are
associated with Class I objects. MIR-63, a bright mid-infrared and
submillimeter Class I source, is a binary with a separation of 2.4" and drives
two bipolar outflows orthogonal to each other. The large southeast-northwest
outflow excites the Herbig-Haro flow HH247. MIR-73, a Class I object, which is
also a far-infrared source, drives a pole-on outflow. MIR-62 is a Class II
object with strong infrared excess and a luminosity of 7 Lsun. It is not
detected in the far-infrared. The Class I sources have bolometric luminosities
of about 20 Lsun or lower, that is, they are all low-mass stars. One other
far-infrared source, MIR-75, may have powered an outflow in the past because it
now illuminates an egg-shaped cavity. The four outflow sources are at a similar
evolutionary stage, which suggests that their formation may have been triggered
by the expanding C II region.
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