613 research outputs found
Protoplanetary Disk Evolution around the Triggered Star Forming Region Cepheus B
The Cepheus B (CepB) molecular cloud and a portion of the nearby CepOB3b OB
association, one of the most active regions of star formation within 1 kpc,
have been observed with the IRAC detector on board the Spitzer Space Telescope.
The goals are to study protoplanetary disk evolution and processes of
sequential triggered star formation in the region. Out of ~400 pre-main
sequence (PMS) stars selected with an earlier Chandra X-ray Observatory
observation, 95% are identified with mid-infrared sources and most of these are
classified as diskless or disk-bearing stars. The discovery of the additional
>200 IR-excess low-mass members gives a combined Chandra+Spitzer PMS sample
complete down to 0.5 Mo outside of the cloud, and somewhat above 1 Mo in the
cloud. Analyses of the nearly disk-unbiased combined Chandra+Spitzer selected
stellar sample give several results. Our major finding is a spatio-temporal
gradient of young stars from the hot molecular core towards the primary
ionizing O star HD 217086. This strongly supports the radiation driven
implosion (RDI) model of triggered star formation in the region. The empirical
estimate for the shock velocity of 1 km/s is very similar to theoretical models
of RDI in shocked molecular clouds...ABRIDGED... Other results include: 1.
agreement of the disk fractions, their mass dependency, and fractions of
transition disks with other clusters; 2. confirmation of the youthfulness of
the embedded CepB cluster; 3. confirmation of the effect of suppression of
time-integrated X-ray emission in disk-bearing versus diskless systems.Comment: Accepted for publication in The Astrophysical Journal. 48 pages, 14
figures. For a version with high-quality figures, see
http://www.astro.psu.edu/users/gkosta/RESEARCH/cepb_spitzer_chandra.pd
Gaia Stellar Kinematics in the Head of the Orion A Cloud: Runaway Stellar Groups and Gravitational Infall
This work extends previous kinematic studies of young stars in the Head of
the Orion A cloud (OMC-1/2/3/4/5). It is based on large samples of infrared,
optical, and X-ray selected pre-main sequence stars with reliable radial
velocities and Gaia-derived parallaxes and proper motions. Stellar kinematic
groups are identified assuming they mimic the motion of their parental gas.
Several groups are found to have peculiar kinematics: the NGC 1977 cluster and
two stellar groups in the Extended Orion Nebula (EON) cavity are caught in the
act of departing their birthplaces. The abnormal motion of NGC 1977 may have
been caused by a global hierarchical cloud collapse, feedback by massive Ori
OB1ab stars, supersonic turbulence, cloud-cloud collision, and/or slingshot
effect; the former two models are favored by us. EON groups might have
inherited anomalous motions of their parental cloudlets due to small-scale
`rocket effects' from nearby OB stars. We also identify sparse stellar groups
to the east and west of Orion A that are drifting from the central region,
possibly a slowly expanding halo of the Orion Nebula Cluster. We confirm
previously reported findings of varying line-of-sight distances to different
parts of the cloud's Head with associated differences in gas velocity.
Three-dimensional movies of star kinematics show contraction of the groups of
stars in OMC-1 and global contraction of OMC-123 stars. Overall, the Head of
Orion A region exhibits complex motions consistent with theoretical models
involving hierarchical gravitational collapse in (possibly turbulent) clouds
with OB stellar feedback.Comment: Accepted for publication in MNRAS. 26 pages, 13 figures. The two 3-D
stellar kinematic movies, aimed as Supplementary Materials, can be found on
YouTube at: https://youtu.be/B4GHCVvCYfo (`restricted' sample) and
https://youtu.be/6fUu8sP0QFI (`full' sample
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