5,723 research outputs found
Dust emission from young outflows: the case of L1157
We present new high-sensitivity 1.3 mm bolometer observations of the young
outflow L1157. These data show that the continuum emission arises from four
distinct components: a circumstellar disk, a protostellar envelope, an extended
flattened envelope --the dense remnant of the molecular cloud in which the
protostar was formed--, and the outflow itself, which represents ~20% of the
total flux. The outflow emission exhibits two peaks that are coincident with
the two strong shocks in the southern lobe of L1157. We show that the mm
continuum is dominated by thermal dust emission arising in the high velocity
material. The spectral index derived from the new 1.3 mm data and 850 mu
observations from Shirley et al. (2000), is ~5 in the outflow, significantly
higher than in the protostellar envelope (~3.5). This can be explained by an
important line contamination of the 850 mu map, and/or by different dust
characteristics in the two regions, possibly smaller grains in the post-shocks
regions of the outflow. Our observations show that bipolar outflows can present
compact emission peaks which must not be misinterpreted as protostellar
condensations when mapping star forming regions
A Mid-Infrared Study of the Class 0 Cluster in LDN 1448
We present ground-based mid-infrared observations of Class 0 protostars in
LDN 1448. Of the five known protostars in this cloud, we detected two, L1448N:A
and L1448C, at 12.5, 17.9, 20.8, and 24.5 microns, and a third, L1448 IRS 2, at
24.5 microns. We present high-resolution images of the detected sources, and
photometry or upper limits for all five Class 0 sources in this cloud. With
these data, we are able to augment existing spectral energy distributions
(SEDs) for all five objects and place them on an evolutionary status diagram.Comment: Accepted by the Astronomical Journal; 26 pages, 9 figure
Two Bipolar Outflows and Magnetic Fields in a Multiple Protostar System, L1448 IRS 3
We performed spectral line observations of CO J=2-1, 13CO J=1-0, and C18O
J=1-0 and polarimetric observations in the 1.3 mm continuum and CO J=2-1 toward
a multiple protostar system, L1448 IRS 3, in the Perseus molecular complex at a
distance of ~250 pc, using the BIMA array. In the 1.3 mm continuum, two sources
(IRS 3A and 3B) were clearly detected with estimated envelope masses of 0.21
and 1.15 solar masses, and one source (IRS 3C) was marginally detected with an
upper mass limit of 0.03 solar masses. In CO J=2-1, we revealed two outflows
originating from IRS 3A and 3B. The masses, mean number densities, momentums,
and kinetic energies of outflow lobes were estimated. Based on those estimates
and outflow features, we concluded that the two outflows are interacting and
that the IRS 3A outflow is nearly perpendicular to the line of sight. In
addition, we estimated the velocity, inclination, and opening of the IRS 3B
outflow using Bayesian statistics. When the opening angle is ~20 arcdeg, we
constrain the velocity to ~45 km/s and the inclination angle to ~57 arcdeg.
Linear polarization was detected in both the 1.3 mm continuum and CO J=2-1. The
linear polarization in the continuum shows a magnetic field at the central
source (IRS 3B) perpendicular to the outflow direction, and the linear
polarization in the CO J=2-1 was detected in the outflow regions, parallel or
perpendicular to the outflow direction. Moreover, we comprehensively discuss
whether the binary system of IRS 3A and 3B is gravitationally bound, based on
the velocity differences detected in 13CO J=1-0 and C18O J=1-0 observations and
on the outflow features. The specific angular momentum of the system was
estimated as ~3e20 cm^2/s, comparable to the values obtained from previous
studies on binaries and molecular clouds in Taurus.Comment: ApJ accepted, 20 pages, 2 tables, 10 figure
Molecules in Bipolar Outflows
Bipolar outflows constitute some of the best laboratories to study shock
chemistry in the interstellar medium. A number of molecular species have their
abundance enhanced by several orders of magnitude in the outflow gas, likely as
a combined result of dust mantle disruption and high temperature gas chemistry,
and therefore become sensitive indicators of the physical changes taking place
in the shock. Identifying these species and understanding their chemical
behavior is therefore of high interest both to chemical studies and to our
understanding of the star-formation process. Here we review some of the recent
progress in the study of the molecular composition of bipolar outflows, with
emphasis in the tracers most relevant for shock chemistry. As we discuss, there
has been rapid progress both in characterizing the molecular composition of
certain outflows as well as in modeling the chemical processes likely involved.
However, a number of limitations still affect our understanding of outflow
chemistry. These include a very limited statistical approach in the
observations and a dependence of the models on plane-parallel shocks, which
cannot reproduce the observed wing morphology of the lines. We finish our
contribution by discussing the chemistry of the so-called extremely high
velocity component, which seems different from the rest of the outflow and may
originate in the wind from the very vicinity of the protostar.Comment: 15 pages, 7 figures. Contribution to the IAU Conference "The
Molecular Universe" held in Toledo in June 201
The radio continuum spectrum of Mira A and Mira B up to submillimeter wavelengths
We present new measurements of the flux densities at submillimeter
wavelengths based on ALMA band 7 (338 GHz) and band 9 (679 GHz) observations to
better constrain the origin of the continuum emission of the Mira AB binary
system and to check its orbit. We have measured the Mira A and Mira B continuum
in ALMA band 7, with a resolution of ~0"31, and for the first time in ALMA band
9, with a resolution of ~0"18. We resolved the binary system at both bands, and
derived the continuum spectral index of the stars and their relative position.
We also analyzed ALMA SciVer data obtained in bands 6 and 3. Measurements at
centimeter wavelengths obtained by other authors have been included in our
study of the spectral energy distribution of the Mira components. The Mira A
continuum emission has a spectral index of 1.98+-0.04 extending from
submillimeter down to centimeter wavelengths. The spectral index of the Mira B
continuum emission is 1.93+-0.06 at wavelengths ranging from submillimeter to
~3.1 mm, and a shallower spectral index of 1.22+-0.09 at longer wavelengths.
The Mira A continuum emission up to submillimeter wavelengths is consistent
with that of a radio photosphere surrounding the evolved star for which models
predict a spectral index close to 2. The Mira B continuum emission cannot be
described with a single ionized component. An extremely compact and dense
region around the star can produce the nearly thermal continuum measured in the
0.4-3.1 mm wavelength range, and an inhomogeneous, less dense, and slightly
larger ionized envelope could be responsible for the emission at longer
wavelengths. Our results illustrate the potential of ALMA for high precision
astrometry of binary systems. We have found a significant discrepancy of ~14
milliarcsec between the ALMA measurements and the predicted orbit positions.Comment: 6 pages, 3 figures, 2 tables, accepted for publication in Astronomy
and Astrophysic
Star formation in the vicinity of the IC 348 cluster
Aims. We present molecular line observations of the southwestern part of the
IC 348 young cluster, and we use them together with NIR and mm continuum data
to determine the distribution of dense gas, search for molecular outflows, and
analyze the ongoing star formation activity in the region. Methods. Our
molecular line data consists of C18O(1--0) and N2H+(1--0) maps obtained with
the FCRAO telescope at a resolution of about 50'' and CO(2--1) data obtained
with the IRAM 30m telescope at a resolution of 11''. Results. The dense gas
southwest of IC 348 is concentrated in two groups of dense cores, each of them
with a few solar masses of material and indications of CO depletion at high
density. One of the core groups is actively forming stars, while the other
seems starless. There is evidence for at least three bipolar molecular outflows
in the region, two of them powered by previously identified Class 0 sources,
while the other one is powered by a still not well characterized low-luminosity
object. The ongoing star formation activity is producing a small stellar
subgroup in the cluster. Using the observed core characteristics and the star
formation rate in the cluster we propose that that similar episodes of stellar
birth may have produced the subclustering observed in the halo of IC 348.Comment: 10 pages, 6 figures, A&A accepte
- …