74 research outputs found
Discovery of A Binary System in IRAM 04191+1522
We present high angular resolution observations of the Class 0 protostar
IRAM04191+1522, using the Submillimeter Array (SMA). The SMA 1.3 mm continuum
images reveal within IRAM04191+1522 two distinct sources with an angular
separation of 7.8\,\,0.2. The two continuum sources are located in the
southeast-northwest direction, with total gas masses of about 0.011 M_sun and
about 0.005 M_sun, respectively. The southeastern source, associated with an
infrared source seen in the Spitzer images, is the well-known Class 0 protostar
with a bolometric luminosity of about 0.08 L_sun. The newly-discovered
northwestern continuum source is not visible in the Spitzer images at
wavelengths from 3.6 to 70 micron, and has an extremely low bolometric
luminosity (< 0.03 L_sun). Complementary IRAM N2H+(1-0) data that probe the
dense gas in the common envelope suggest that the two sources were formed
through the rotational fragmentation of an elongated dense core. Furthermore,
comparisons between IRAM04191+1522 and other protostars suggest that most cores
with binary systems formed therein have ratios of rotational energy to
gravitational energy > 1%. This is consistent with
theoretical simulations and indicates that the level of rotational energy in a
dense core plays an important role in the fragmentation process.Comment: 15 pages, 4 figures, to be published by ApJ Letter
Morphokinematic properties of the 21 micron source IRAS 22272+5435
We obtained a high-resolution CO map of IRAS 22272+5435 in the CO J=2-1 line using CARMA. The target exhibits a second biggest angular size of the circumstellar molecular envelope among known 21 μm sources. In the preliminary results, we found that the CO properties of IRAS 22272+5435 is clearly different from those of IRAS 07134+1005, which is another well-investigated 21 μm source. For example, elongations seen in the mid-infrared and CO images are extended in mutually perpendicular directions, although in case of IRAS 07134+1005 the CO feature coincides well with the mid-infrared structure. © 2012 International Astronomical Union.published_or_final_versio
Magnetic Field Structure around Low-Mass Class 0 Protostars: B335, L1527 and IC348-SMM2
We report new 350 micron polarization observations of the thermal dust
emission from the cores surrounding the low-mass, Class 0 YSOs L1527,
IC348-SMM2 and B335. We have inferred magnetic field directions from these
observations, and have used them together with results in the literature to
determine whether magnetically regulated core-collapse and star-formation
models are consistent with the observations. These models predict a pseudo-disk
with its symmetry axis aligned with the core magnetic field. The models also
predict a magnetic field pinch structure on a scale less than or comparable to
the infall radii for these sources. In addition, if the core magnetic field
aligns (or nearly aligns) the core rotation axis with the magnetic field before
core collapse, then the models predict the alignment (or near alignment) of the
overall pinch field structure with the bipolar outflows in these sources. We
show that if one includes the distorting effects of bipolar outflows on
magnetic fields, then in general the observational results for L1527 and
IC348-SMM2 are consistent with these magnetically regulated models. We can say
the same for B335 only if we assume the distorting effects of the bipolar
outflow on the magnetic fields within the B335 core are much greater than for
L1527 and IC348-SMM2. We show that the energy densities of the outflows in all
three sources are large enough to distort the magnetic fields predicted by
magnetically regulated models.Comment: Accepted for publication in The Astrophysical Journa
L1448 IRS2E: A candidate first hydrostatic core
Intermediate between the prestellar and Class 0 protostellar phases, the
first core is a quasi-equilibrium hydrostatic object with a short lifetime and
an extremely low luminosity. Recent MHD simulations suggest that the first core
can even drive a molecular outflow before the formation of the second core
(i.e., protostar). Using the Submillimeter Array and the Spitzer Space
Telescope, we present high angular resolution observations towards the embedded
dense core IRS2E in L1448. We find that source L1448 IRS2E is not visible in
the sensitive Spitzer infrared images (at wavelengths from 3.6 to 70 um), and
has weak (sub-)millimeter dust continuum emission. Consequently, this source
has an extremely low bolometric luminosity (< 0.1 L_sun). Infrared and
(sub-)millimeter observations clearly show an outflow emanating from this
source; L1448 IRS2E represents thus far the lowest luminosity source known to
be driving a molecular outflow. Comparisons with prestellar cores and Class 0
protostars suggest that L1448 IRS2E is more evolved than prestellar cores but
less evolved than Class 0 protostars, i.e., at a stage intermediate between
prestellar cores and Class 0 protostars. All these results are consistent with
the theoretical predictions of the radiative/magneto hydrodynamical
simulations, making L1448 IRS2E the most promising candidate of the first
hydrostatic core revealed so far.Comment: 20 pages, 4 figures, to be published by Ap
CO Structure of the 21 μm Source IRAS 22272+5435: A Sign of a Jet Launch?
We report the results of radio interferometric observations of the 21 μm source IRAS 22272+5435 in the CO J = 2-1 line. 21 μm sources are carbon-rich objects in the post-asymptotic-giant-branch phase of evolution, which show an unidentified emission feature at 21 μm. Since 21 μm sources usually also have circumstellar molecular envelopes, the mapping of CO emission from the envelope will be useful in tracing the nebular structure. From observations made with the Combined Array for Research in Millimeter-wave Astronomy, we find that a torus and spherical wind model can explain only part of the CO structure. An additional axisymmetric region created by the interaction between an invisible jet and ambient material is suggested
R CrA SMM1A: Fragmentation in A Prestellar Core
We report the discovery of multiple condensations in the prestellar core
candidate SMM1A in the R~CrA cloud, which may represent the earliest phase of
core fragmentation observed thus far. The separation between the condensations
is between 1000 and 2100 AU, and their masses range from about 0.1 to 0.2
M_sun. We find that the three condensations have extremely low bolometric
luminosities (< 0.1 L_sun) and temperatures (< 20 K), indicating that these are
young sources that have yet to form protostars. We suggest that these sources
were formed through the fragmentation of an elongated prestellar core. Our
results, in concert with other observed protostellar binary systems with
separations in the scale of 1000 AU, support the scenario that prompt
fragmentation in the isothermal collapse phase is an efficient mechanism for
wide binary star formation, while the fragmentation in the subsequent adiabatic
phase may be an additional mechanism for close (< 100 AU) binary star
formation.Comment: 13 pages, 3 figures, to be published by ApJ Letter
The N2D+/N2H+ ratio as an evolutionary tracer of Class 0 protostars
Deuterated ions are abundant in cold (T=10 K), dense (n=10^5 cm^-3) regions,
in which CO is frozen out onto dust grains. In such environments, the deuterium
fractionation of such ions can exceed the elemental abundance ratio of D/H by a
factor of 10^4. In this paper we use the deuterium fractionation to investigate
the evolutionary state of Class 0 protostars. In a sample of 20 protostellar
objects, we found a clear correlation between the N2D+/N2H+ ratio and
evolutionary tracers. As expected, the coolest, i.e. the youngest, objects show
the largest deuterium fractionation. Furthermore, we find that sources with a
high N2D+/N2H+ ratio show clear indication for infall.Comment: 19 pages, 12 figures, accepted by A&
Complex Structure in Class 0 Protostellar Envelopes III: Velocity Gradients in Non-Axisymmetric Envelopes, Infall or Rotation?
We present an interferometric kinematic study of morphologically complex
protostellar envelopes based on observations of the dense gas tracers N2H+ and
NH3. The strong asymmetric nature of most envelopes in our sample leads us to
question the common interpretation of velocity gradients as rotation, given the
possibility of projection effects in the observed velocities. Several
"idealized" sources with well-ordered velocity fields and envelope structures
are now analyzed in more detail. We compare the interferometric data to
position-velocity diagrams of kinematic models for spherical rotating collapse
and filamentary rotating collapse. For this purpose, we developed a filamentary
parametrization of the rotating collapse model to explore the effects of
geometric projection on the observed velocity structures. We find that most
envelopes in our sample have PV structures that can be reproduced by an
infalling filamentary envelope projected at different angles within the plane
of the sky. The infalling filament produces velocity shifts across the envelope
that can mimic rotation, especially when viewed at single-dish resolutions and
the axisymmetric rotating collapse model does not uniquely describe any
dataset. Furthermore, if the velocities are assumed to reflect rotation, then
the inferred centrifugal radii are quite large in most cases, indicating
significant fragmentation potential or more likely another component to the
line-center velocity. We conclude that ordered velocity gradients cannot be
interpreted as rotation alone when envelopes are non-axisymmetric and that
projected infall velocities likely dominate the velocity field on scales larger
than 1000 AU.Comment: 37 pages, 15 Figures, 2 Tables, Accepted to Ap
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