83 research outputs found
A 1000 AU Scale Molecular Outflow Driven by a Protostar with an age of <4000 Years
To shed light on the early phase of a low-mass protostar formation process,
we conducted interferometric observations towards a protostar GF9-2 using the
CARMA and SMA. The observations have been carried out in the CO J=3-2 line and
in the continuum emission at the wavelengths of 3 mm, 1 mm and 850 micron. All
the continuum images detected a single point-like source with a radius of
250+/-80 AU at the center of the previously known ~3 Msun molecular cloud core.
A compact emission is detected towards the object at the Spitzer MIPS and IRAC
bands as well as the four bands at the WISE. Our spectroscopic imaging of the
CO line revealed that the continuum source is driving a 1000 AU scale molecular
outflow, including a pair of lobes where a collimated "higher" velocity red
lobe exists inside a poorly collimated "lower" velocity red lobe. These lobes
are rather young and the least powerful ones so far detected. A protostellar
mass of M~<0.06 Msun was estimated using an upper limit of the protostellar age
of (4+/-1)x10^3 yrs and an inferred non-spherical steady mass accretion rate of
~10^{-5} Msun/yr. Together with results from an SED analysis, we discuss that
the outflow system is driven by a protostar whose surface temperature
of~3,000K, and that the natal cloud core is being dispersed by the outflow.Comment: 27 pages, 14 figures, accepted for publication in Astrophysical
Journa
The Initial Conditions for Gravitational Collapse of a Core: An Extremely Young Low-Mass Class 0 Protostar GF9-2
We present a study of the natal core harboring the class 0 protostar GF9-2 in
the filamentary dark cloud GF 9 (d = 200 pc). GF9-2 stands unique in the sense
that it shows H2O maser emission, a clear signpost of protostar formation,
whereas it does not have a high-velocity large-scale molecular outflow
evidenced by our deep search for CO wing emission. These facts indicate that
GF9-2 core is early enough after star formation so that it still retains some
information of initial conditions for collapse. Our 350 um dust continuum
emission image revealed the presence of a protostellar envelope in the center
of a molecular core. The mass of the envelope is ~0.6 Msun from the 350 um flux
density, while LTE mass of the core is ~3 Msun from moleuclar line
observations. Combining visibility data from the OVRO mm-array and the 45m
telescope, we found that the core has a radial density profile of
for 0.003 < r/pc < 0.08 region. Molecular line data
analysis revealed that the velocity width of the core gas increases
inward,while the outermost region maintains a velocity dispersion of a few
times of the ambient sound speed. The broadened velocity width can be
interpreted as infall. Thus, the collapse in GF9-2 is likely to be described by
an extension of the Larson-Penston solution for the period after formation of a
central star. We derived the current mass accretion rate of ~3E-05 Msun/year
from infall velocity of ~ 0.3 km/s at r~ 7000 AU. All results suggest that
GF9-2 core has been undergoing gravitational collapse for ~ 5000 years since
the formation of central protostar(s), and that the unstable state initiated
the collapse ~2E+05 years (the free-fall time) ago.Comment: ApJ Accepted. The preprint including figures with the original
quality is available at http://subarutelescope.org/staff/rsf/publication.htm
High-velocity Molecular Outflow in CO J = 7-6 Emission from the Orion Hot Core
Using the Caltech Submillimeter Observatory 10.4 m telescope, we performed sensitive mapping observations of ^(12)CO J = 7-6 emission at 807 GHz toward Orion IRc2. The image has an angular resolution of 10", which is the highest angular resolution data toward the Orion Hot Core published for this transition. In addition, thanks to the on-the-fly mapping technique, the fidelity of the new image is rather high, particularly in comparison with previous images. We have succeeded in mapping the northwest-southeast high-velocity molecular outflow, whose terminal velocity is shifted by ~70-85 km s^(â1) with respect to the systemic velocity of the cloud. This yields an extremely short dynamical time scale of ~900 years. The estimated outflow mass loss rate shows an extraordinarily high value, on the order of 10^(â3) M_â yr^(â1). Assuming that the outflow is driven by Orion IRc2, our result agrees with the picture so far obtained for a 20 M_â (proto)star in the process of formation
Helicity proxy for edge-on galaxies
We study the prospects of detecting magnetic helicity in galaxies by observing the dust polarization of the edge-on galaxy NGC 891. Our numerical results of mean-field dynamo calculations show that there should be a large-scale component of the rotationally invariant parity-odd B polarization that we predict to be negative in the first and third quadrants, and positive in the second and fourth quadrants. The large-scale parity-even E polarization is predicted to be negative near the axis and positive further away in the outskirts. These properties are shown to be mostly a consequence of the magnetic field being azimuthal and the polarized intensity being maximum at the centre of the galaxy and are not a signature of magnetic helicity
Low-Mass Star Forming Cores in the GF9 Filament
We carried out an unbiased mapping survey of dense molecular cloud cores
traced by the NH3 (1,1) and (2,2) inversion lines in the GF9 filament which
contains an extremely young low-mass protostar GF9-2 (Furuya et al. 2006, ApJ,
653, 1369). The survey was conducted using the Nobeyama 45m telescope over a
region of ~1.5 deg with an angular resolution of 73". The large-scale map
revealed that the filament contains at least 7 dense cores, as well as 3
possible ones, located at regular intervals of ~0.9 pc. Our analysis shows that
these cores have kinetic temperatures of 10 K and LTE-masses of 1.8
-- 8.2 Msun, making them typical sites of low-mass star formation. All the
identified cores are likely to be gravitationally unstable because their
LTE-masses are larger than their virial masses. Since the LTE-masses and
separations of the cores are consistent with the Jeans masses and lengths,
respectively, for the low-density ambient gas, we argue that the identified
cores have formed via the gravitational fragmentation of the natal filamentary
cloud.Comment: accepted by pas
Warm Extended Dense Gas Lurking At The Heart Of A Cold Collapsing Dense Core
In order to investigate when and how the birth of a protostellar core occurs,
we made survey observations of four well-studied dense cores in the Taurus
molecular cloud using CO transitions in submillimeter bands. We report here the
detection of unexpectedly warm (~ 30 - 70 K), extended (radius of ~ 2400 AU),
dense (a few times 10^{5} cm^{-3}) gas at the heart of one of the dense cores,
L1521F (MC27), within the cold dynamically collapsing components. We argue that
the detected warm, extended, dense gas may originate from shock regions caused
by collisions between the dynamically collapsing components and
outflowing/rotating components within the dense core. We propose a new stage of
star formation, "warm-in-cold core stage (WICCS)", i.e., the cold collapsing
envelope encases the warm extended dense gas at the center due to the formation
of a protostellar core. WICCS would constitutes a missing link in evolution
between a cold quiescent starless core and a young protostar in class 0 stage
that has a large-scale bipolar outflow.Comment: Accepted for publication in The Astrophysical Journal Letter
Spectroscopic Evidence for Gas Infall in GF9-2
We present spectroscopic evidence for infall motion of gas in the natal cloud
core harboring an extremely young low-mass protostar GF9-2. We previously
discussed that the ongoing collapse of the GF9-2 core has agreement with the
Larson-Penston-Hunter (LPH) theoretical solution for the gravitational collapse
of a core (Furuya et al.; paper I). To discuss the gas infall on firmer ground,
we have carried out On-The-Fly mapping observations of the HCO+ (1--0) line
using the Nobeyama 45m telescope equipped with the 25 Beam Array Receiver
System. Furthermore, we observed the HCN (1--0) line with the 45m telescope,
and the HCO+ (3--2) line with the Caltech Submillimeter Observatory 10.4 m
telescope. The optically thick HCO+ and HCN lines show blueskewed profiles
whose deepest absorptions are seen at the peak velocity of optically thin
lines, i.e., the systemic velocity of the cloud (paper I), indicating the
presence of gas infall toward the central protostar. We compared the observed
HCO+ line profiles with model ones by solving the radiative transfer in the
core under LTE assumption.We found that the core gas has a constant infall
velocity of ~0.5 km/s in the central region, leading to a mass accretion rate
of 2.5x10^{-5} Msun/yr. Consequently, we confirm that the gas infall in the
GF9-2 core is consistent with the LPH solution.Comment: 13 pages, 5 figure, full resolution version of the figures are
available at http://subarutelescope.org/staff/rsf/publication.htm
Water Maser Survey toward LowâMass Young Stellar Objects in the Northern Sky with the Nobeyama 45 Meter Telescope and the Very Large Array
n/
- âŠ