490 research outputs found
Cluster Formation in Protostellar Outflow-Driven Turbulence
Most, perhaps all, stars go through a phase of vigorous outflow during
formation. We examine, through 3D MHD simulation, the effects of protostellar
outflows on cluster formation. We find that the initial turbulence in the
cluster-forming region is quickly replaced by motions generated by outflows.
The protostellar outflow-driven turbulence (``protostellar turbulence'' for
short) can keep the region close to a virial equilibrium long after the initial
turbulence has decayed away. We argue that there exist two types of turbulence
in star-forming clouds: a primordial (or ``interstellar'') turbulence and a
protostellar turbulence, with the former transformed into the latter mostly in
embedded clusters such as NGC 1333. Since the majority of stars are thought to
form in clusters, an implication is that the stellar initial mass function is
determined to a large extent by the stars themselves, through outflows which
individually limit the mass accretion onto forming stars and collectively shape
the environments (density structure and velocity field) in which most cluster
members form. We speculate that massive cluster-forming clumps supported by
protostellar turbulence gradually evolve towards a highly centrally condensed
``pivotal'' state, culminating in rapid formation of massive stars in the
densest part through accretion.Comment: 11 pages (aastex format), 2 figures submitted to ApJ
Observations of Global and Local Infall in NGC 1333
We report ``infall asymmetry'' in the HCO (1--0) and (3--2) lines toward
NGC 1333, extended over , a larger extent than has been
reported be fore, for any star-forming region. The infall asymmetry extends
over a major portion of the star-forming complex, and is not limited to a
single protostar, or to a single dense core, or to a single spectral line. It
seems likely that the infall asymmetry represents inward motions, and that
these motions are physically associated with the complex. Both blue-asymmetric
and red-asymmetric lines are seen, but in both the (3--2) and (1--0) lines of
HCO the vast majority of the asymmetric lines are blue, indicating inward
motions. The (3--2) line, tracing denser gas, has the spectra with the
strongest asymmetry and these spectra are associated with the protostars IRAS
4A and 4B, which most likely indicates a warm central source is affecting the
line profiles. The (3--2) and (1--0) lines usually have the same sense of
asymmetry in common positions, but their profiles differ significantly, and the
(1--0) line appears to trace motions on much larger spatial scales than does
the (3--2) line. Line profile models fit the spectra well, but do not strongly
constrain their parameters. The mass accretion rate of the inward motions is of
order 10 M/yr, similar to the ratio of stellar mass to cluster
age.Comment: 28 pages, 11 figures, 1 colour figur
An S-shaped outflow from IRAS 03256+3055 in NGC 1333
The IRAS source 03256+3055 in the NGC 1333 star forming region is associated
with extended sub-millimeter emission of complex morphology, showing multiple
clumps. One of these is found to coincide with the driving source of a bipolar
jet of S-shaped morphology seen in the emission lines of H_alpha and [SII] as
well as in the H2 emission lines in the K-band. Detailed images of the driving
source at the wavelengths of H_alpha and [SII] and in the I, J, H, and K bands
as well as a K-band spectrum and polarimetry are discussed. The near-infrared
morphology is characterized by a combination of line emission from the jet and
scattered light from a source with a steep continuum spectrum. The morphology
and proper motion of the jet are discussed in the context of a binary system
with a precessing disk. We conclude that the molecular core associated with
IRAS 03256+3055 consists of several clumps, only one of which shows evidence of
recent star formation at optical and near-infrared wavelengths.We also briefly
discuss a second, newly found near-infrared source associated with a compact
sub-millimeter continuum source near IRAS 03256+3055, and conclude that this
source may be physically unrelated the cluster of molecular clumps.Comment: 25 pages, including 5 figures. Accepted for publication in The
Astronomical Journa
Infall, Outflow, Rotation, and Turbulent Motions of Dense Gas within NGC 1333 IRAS 4
Millimeter wavelength observations are presented of NGC 1333 IRAS 4, a group
of highly-embedded young stellar objects in Perseus, that reveal motions of
infall, outflow, rotation, and turbulence in the dense gas around its two
brightest continuum objects, 4A and 4B. These data have finest angular
resolution of approximately 2" (0.0034 pc) and finest velocity resolution of
0.13 km/s. Infall motions are seen from inverse P-Cygni profiles observed in
H2CO 3_12-2_11 toward both objects, but also in CS 3-2 and N2H+ 1-0 toward 4A,
providing the least ambiguous evidence for such motions toward low-mass
protostellar objects. Outflow motions are probed by bright line wings of H2CO
3_12-2_11 and CS 3-2 observed at positions offset from 4A and 4B, likely
tracing dense cavity walls. Rotational motions of dense gas are traced by a
systematic variation of the N2H+ line velocities, and such variations are found
around 4A but not around 4B. Turbulent motions appear reduced with scale, given
N2H+ line widths around both 4A and 4B that are narrower by factors of 2 or 3
than those seen from single-dish observations. Minimum observed line widths of
approximately 0.2 km/s provide a new low, upper bound to the velocity
dispersion of the parent core to IRAS 4, and demonstrate that turbulence within
regions of clustered star formation can be reduced significantly. A third
continuum object in the region, 4B', shows no detectable line emission in any
of the observed molecular species.Comment: LateX, 51 pages, 9 figures, accepted by Ap
Turbulence driven by outflow-blown cavities in the molecular cloud of NGC 1333
Outflows from young stellar objects have been identified as a possible source
of turbulence in molecular clouds. To investigate the relationship between
outflows, cloud dynamics and turbulence, we compare the kinematics of the
molecular gas associated with NGC 1333, traced in 13CO(1-0), with the
distribution of young stellar objects (YSOs) within. We find a velocity
dispersion of ~ 1-1.6 km/s in 13CO that does not significantly vary across the
cloud, and is uncorrelated with the number of nearby young stellar outflows
identified from optical and submillimeter observations. However, from velocity
channel maps we identify about 20 cavities or depressions in the 13CO intensity
of scales > 0.1-0.2 pc and velocity widths 1-3 km/s. The cavities exhibit limb
brightened rims in both individual velocity channel maps and position velocity
diagrams, suggesting that they are slowly expanding. We interpret these
cavities to be remnants of past YSO outflow activity: If these cavities are
presently empty, they would fill in on time scales of a million years. This can
exceed the lifetime of a YSO outflow phase, or the transit time of the central
star through the cavity, explaining the the absence of any clear correlation
between the cavities and YSO outflows. We find that the momentum and energy
deposition associated with the expansion of the cavities is sufficient to power
the turbulence in the cloud. In this way we conclude that the cavities are an
important intermediary step between the conversion of YSO outflow energy and
momentum into cloud turbulent motions.Comment: Accepted for publication in ApJ. Check out
http://astro.pas.rochester.edu/~aquillen/coolpics.html for channel map and
PosVel movies of N133
The origin of short-lived radionuclides and the astrophysical environment of solar system formation
Based on early solar system abundances of short-lived radionuclides (SRs),
such as Al (T Myr) and Fe (T Myr),
it is often asserted that the Sun was born in a large stellar cluster, where a
massive star contaminated the protoplanetary disk with freshly
nucleosynthesized isotopes from its supernova (SN) explosion. To account for
the inferred initial solar system abundances of short-lived radionuclides, this
supernova had to be close ( 0.3 pc) to the young ( 1 Myr)
protoplanetary disk.
Here we show that massive star evolution timescales are too long, compared to
typical timescales of star formation in embedded clusters, for them to explode
as supernovae within the lifetimes of nearby disks. This is especially true in
an Orion Nebular Cluster (ONC)-type of setting, where the most massive star
will explode as a supernova 5 Myr after the onset of star formation,
when nearby disks will have already suffered substantial photoevaporation
and/or formed large planetesimals.
We quantify the probability for {\it any} protoplanetary disk to receive SRs
from a nearby supernova at the level observed in the early solar system. Key
constraints on our estimate are: (1) SRs have to be injected into a newly
formed ( 1 Myr) disk, (2) the disk has to survive UV
photoevaporation, and (3) the protoplanetary disk must be situated in an
enrichment zone permitting SR injection at the solar system level without disk
disruption. The probability of protoplanetary disk contamination by a supernova
ejecta is, in the most favorable case, 3 10
Spitzer Observations of NGC 1333: A Study of Structure and Evolution in a Nearby Embedded Cluster
We present a comprehensive analysis of structure in the young, embedded
cluster, NGC 1333 using members identified with Spitzer and 2MASS photometry
based on their IR-excess emission. In total, 137 members are identified in this
way, composed of 39 protostars and 98 more evolved pre-main sequence stars with
disks. Of the latter class, four are transition/debris disk candidates. The
fraction of exposed pre-main sequence stars with disks is 83% +/- 11%, showing
that there is a measurable diskless pre-main sequence population. The sources
in each of the Class I and Class II evolutionary states are shown to have very
different spatial distributions relative to the distribution of the dense gas
in their natal cloud. However, the distribution of nearest neighbor spacings
among these two groups of sources are found to be quite similar, with a strong
peak at spacings of 0.045 pc. Radial and azimuthal density profiles and surface
density maps computed from the identified YSOs show that NGC 1333 is elongated
and not strongly centrally concentrated, confirming previous claims in the
literature. We interpret these new results as signs of a low velocity
dispersion, extremely young cluster that is not in virial equilibrium.Comment: 59 pages, 20 figures, accepted to ApJ, verion with full resolution
figures available at
http://www.cfa.harvard.edu/~rgutermuth/preprints/gutermuth_ngc1333.pdf .
Updated to fix astro-ph figure garblin
An Optical Study of BG Geminorum: An Ellipsoidal Binary with an Unseen Primar Star
We describe optical photometric and spectroscopic observations of the bright
variable BG Geminorum. Optical photometry shows a pronounced ellipsoidal
variation of the K0 I secondary, with amplitudes of ~0.5 mag at VRI and a
period of 91.645 days. A deep primary eclipse is visible for wavelengths <
4400A; a shallower secondary eclipse is present at longer wavelengths. Eclipse
timings and the radial velocity curve of the K0 secondary star indicate an
interacting binary where a lobe-filling secondary, M_2 ~ 0.5 Msun, transfers
material into a extended disk around a massive primary, M_1 ~ 4.5 Msun. The
primary star is either an early B-type star or a black hole. If it did contain
a black hole, BG Gem would be the longest period black hole binary known by a
factor of 10, as well as the only eclipsing black hole binary system.Comment: 27 pages, includes 8 figures and 5 tables, accepted to A
Protostellar Jets and Turbulence in Molecular Clouds: The Role of Interactions
We present a series of numerical studies of the interaction of colliding
radiative, hydrodynamic young stellar outflows. We study the effect of the
collision impact parameter on the acceleration of ambient material and the
degree to which the flow is isotropized by the collision as a mechanism for
driving turbulence in the parent molecular cloud. Our results indicate that the
high degrees of compression of outflow material, achieved through radiative
shocks near the vertex of the interaction, prevents the redirected outflow from
spraying over a large spatial region. Furthermore, the collision reduces the
redirected outflow's ability to entrain and impart momentum into the ambient
cloud. Consideration of the probabilities of outflow collisions leads us to
conclude that individual low velocity fossil outflows are the principle
coupling between outflows and the cloud.Comment: 21 pages, 10 figures, submitted to Ap
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