16 research outputs found
First measurement of the 14N/15N ratio in the analogue of the Sun progenitor OMC-2 FIR4
We present a complete census of the 14N/15N isotopic ratio in the most
abundant N-bearing molecules towards the cold envelope of the protocluster
OMC-2 FIR4, the best known Sun progenitor. To this scope, we analysed the
unbiased spectral survey obtained with the IRAM-30m telescope at 3mm, 2mm and
1mm. We detected several lines of CN, HCN, HNC, HC3N, N2H+, and their
respective 13C and 15N isotopologues. The lines relative fluxes are compatible
with LTE conditions and moderate line opacities have been corrected via a
Population Diagram method or theoretical relative intensity ratios of the
hyperfine structures. The five species lead to very similar 14N/15N isotopic
ratios, without any systematic difference between amine and nitrile bearing
species as previously found in other protostellar sources. The weighted average
of the 14N/15N isotopic ratio is 270 +/- 30. This 14N/15N value is remarkably
consistent with the [250-350] range measured for the local galactic ratio but
significantly differs from the ratio measured in comets (around 140).
High-angular resolution observations are needed to examine whether this
discrepancy is maintained at smaller scales. In addition, using the CN, HCN and
HC3N lines, we derived a 12C/13C isotopic ratio of 50 +/- 5.Comment: Accepted for publication in ApJ ; 19 pages, 5 tables, 12 figure
Rotation in the NGC 1333 IRAS 4C Outflow
We report molecular line observations of the NGC 1333 IRAS 4C outflow in the
Perseus Molecular Cloud with the Atacama Large Millimeter/Submillimeter Array.
The CCH and CS emission reveal an outflow cavity structure with clear
signatures of rotation with respect to the outflow axis. The rotation is
detected from about 120 au up to about 1400 au above the envelope/disk
mid-plane. As the distance to the central source increases, the rotation
velocity of the outflow decreases while the outflow radius increases, which
gives a flat specific angular momentum distribution along the outflow. The mean
specific angular momentum of the outflow is about 100 au km/s. Based on
reasonable assumptions on the outward velocity of the outflow and the protostar
mass, we estimate the range of outflow launching radii to be 5-15 au. Such a
launching radius rules out that this outflow is launched as an X-wind, but
rather, it is more consistent to be a slow disk wind launched from relatively
large radii on the disk. The radius of the centrifugal barrier is roughly
estimated, and the role of the centrifugal barrier in the outflow launching is
discussed.Comment: Accepted to ApJ. 29 pages, 8 figure
Sub-arcsecond Kinematic Structure of the Outflow in the Vicinity of the Protostar in L483
The bipolar outflow associated with the Class 0 low-mass protostellar source
(IRAS 18148-0440) in L483 has been studied in the CCH and CS line emission at
245 and 262 GHz, respectively. Sub-arcsecond resolution observations of these
lines have been conducted with ALMA. Structures and kinematics of the outflow
cavity wall are investigated in the CS line, and are analyzed by using a
parabolic model of an outflow. We constrain the inclination angle of the
outflow to be from 75 degree to 90 degree, i.e. the outflow is blowing almost
perpendicular to the line of sight. Comparing the outflow parameters derived
from the model analysis with those of other sources, we confirm that the
opening angle of the outflow and the gas velocity on its cavity wall correlate
with the dynamical timescale of the outflows. Moreover, a hint of a rotating
motion of the outflow cavity wall is found. Although the rotation motion is
marginal, the specific angular momentum of the gas on the outflow cavity wall
is evaluated to be comparable to or twice that of the infalling-rotating
envelope of L483
Chemical survey toward young stellar objects in the Perseus molecular cloud complex
Chemical diversity of the gas in low-mass protostellar cores is widely
recognized. In order to explore its origin, a survey of chemical composition
toward 36 Class 0/I protostars in the Perseus molecular cloud complex, which
are selected in an unbiased way under certain physical conditions, has been
conducted with IRAM 30 m and NRO 45 m telescope. Multiple lines of C2H, c-C3H2
and CH3OH have been observed to characterize the chemical composition averaged
over a 1000 au scale around the protostar. The derived beam-averaged column
densities show significant chemical diversity among the sources, where the
column density ratios of C2H/CH3OH are spread out by 2 orders of magnitude.
From previous studies, the hot corino sources have abundant CH3OH but deficient
C2H, their C2H/CH3OH column density ratios being relatively low. In contrast,
the warm-carbon-chain chemistry (WCCC) sources are found to reveal the high
C2H/CH3OH column density ratios. We find that the majority of the sources have
intermediate characters between these two distinct chemistry types. A possible
trend is seen between the C2H/CH3OH ratio and the distance of the source from
the edge of a molecular cloud. The sources located near cloud edges or in
isolated clouds tend to have a high C2H/CH3OH ratio. On the other hand, the
sources having a low C2H/CH3OH ratio tend to be located in inner regions of the
molecular cloud complex. This result gives an important clue to an
understanding of the origin of the chemical diversity of protostellar cores in
terms of environmental effects.Comment: Accepted for publication in ApJ
Seeds of Life in Space (SOLIS). IX. Chemical Segregation of SO 2 and SO toward the Low-mass Protostellar Shocked Region of L1157
International audienceWe present observations of SO and SO 2 lines toward the shocked regions along the L1157 chemically rich outflow, taken in the context of the Seeds of Life in Space IRAM Northern Extended Millimeter Array Large Program, and supported by data from the Submillimeter Array and IRAM-30 m telescope at 1.1-3.6 mm wavelengths. We simultaneously analyze, for the first time, all of the brightest shocks in the blueshifted lobe, namely, B0, B1, and B2. We found the following. (1) SO and SO 2 may trace different gas, given that the large(-scale) velocity gradient analysis indicates for SO 2 a volume density (-10 10 cm 5 6 3) denser than that of the gas emitting in SO by a factor up to an order of magnitude. (2) Investigating the 0.1 pc scale field of view, we note a tentative gradient along the path of the precessing jet. More specifically, () c SO SO 2 decreases from the B0-B1 shocks to the older B2. (3) At a linear resolution of 500-1400 au, a tentative spatial displacement between the two emitting molecules is detected, with the SO peak closer (with respect to SO 2) to the position where the recent jet is impinging on the B1 cavity wall. Our astrochemical modeling shows that the SO and SO 2 abundances evolve on timescales less than about 1000 years. Furthermore, the modeling requires high abundances (2Ă10 â6) of both H S H 2 and S/H injected in the gas phase due to the shock occurrence, so prefrozen OCS only is not enough to reproduce our new observations
Sulfur-bearing Species Tracing the Disk/Envelope System in the Class I Protostellar Source Elias 29
International audienc