347 research outputs found
ATCA and Spitzer Observations of the Binary Protostellar Systems CG30 and BHR71
We present interferometric observations with resolution of ~3 arcsecs of the
isolated, low-mass protostellar double cores CG30 and BHR71 in the N2M_\odotSpitzerSpitzer$ observations, we construct spectral
energy distributions (SEDs) and derive temperatures and luminosities for all
cores. Based on the morphology and velocity structure, we suggest that the
sub-cores in CG30 were formed by initial fragmentation of a filamentary
prestellar core, while those in BHR71 could originate from rotational
fragmentation of a single collapsing protostellar core.Comment: 31 pages, 10 figures, to be published by ApJ in Sep. 200
A close view on the protoplanetary disk in the Bok globule CB26
We present new sub-arcsecond-resolution near-infrared polarimetric imaging
and millimetre interferometry data on the circumstellar disk system in the Bok
globule CB26. The data imply the presence of a M > 0.01 M_sun edge-on disk of
>400 AU in diameter, being in Keplerian rotation around a young ~0.35 M_sun
star. The mm dust emission from the inner 200 AU is highly optically thick, but
the outer parts are optically thin and made of small dust grains. Planetesimal
growth in the inner disk could neither be comfirmed nor excluded. The outer
optically thin part of the disk is strongly warped. We argue that the CB 26
disk is a very young protoplanetary disk and show that it is comparable to the
early solar system.Comment: Conference proceeding "Origins of stars and planets: The VLT view",
ESO, Garching, April 24-27 200
Search for Binary Protostars
In an effort to shed more light on the formation process of binary stars, we
have started a program to study multiplicity among nearby low- and
intermediate-mass protostars using the OVRO Millimeter Array. Here, we describe
the project and present the first results on the protostellar core in the Bok
globule CB230 (L1177). At 10 arcsec resolution, the molecular core is resolved
into two components separated by 5000 AU. The morphology and kinematics of the
double core suggest that it formed from a single cloud core due to rotational
fragmentation.Comment: 4 pages, 2 figures, ALMA conference proceeding
OVRO N2H+ Observations of Class 0 Protostars: Constraints on the Formation of Binary Stars
We present the results of an interferometric study of the N2H+(1--0) emission
from nine nearby, isolated, low-mass protostellar cores, using the OVRO
millimeter array. The main goal of this study is the kinematic characterization
of the cores in terms of rotation, turbulence, and fragmentation. Eight of the
nine objects have compact N2H+ cores with FWHM radii of 1200 -- 3500 AU,
spatially coinciding with the thermal dust continuum emission. The only more
evolved (Class I) object in the sample (CB 188) shows only faint and extended
N2H+ emission. The mean N2H+ line width was found to be 0.37 km/s. Estimated
virial masses range from 0.3 to 1.2 M_sun. We find that thermal and turbulent
energy support are about equally important in these cores, while rotational
support is negligible. The measured velocity gradients across the cores range
from 6 to 24 km/s/pc. Assuming these gradients are produced by bulk rotation,
we find that the specific angular momenta of the observed Class 0 protostellar
cores are intermediate between those of dense (prestellar) molecular cloud
cores and the orbital angular momenta of wide PMS binary systems. There appears
to be no evolution (decrease) of angular momentum from the smallest prestellar
cores via protostellar cores to wide PMS binary systems. In the context that
most protostellar cores are assumed to fragment and form binary stars, this
means that most of the angular momentum contained in the collapse region is
transformed into orbital angular momentum of the resulting stellar binary
systems.Comment: 35 pages, 9 figures (one in color), 6 tables. Accepted by ApJ (to
appear in Nov. 2007
A young protoplanetary disk in the Bok globule CB26?
We present sub-arcsecond resolution millimeter-wave images of a circumstellar
disk in the Bok globule CB26. The presence of an edge-on disk is confirmed by
the dust continuum morphology and the velocity field of 13CO emission, which
displays a Keplerian rotation pattern about an axis perpendicular to the long
axis of the dust emission. We deduce a mass ~0.3 Msun for the obscured central
star. The disk is optically thick at mm wavelengths inside 120 AU, has a
symmetric 20 degree warp beyond 120 AU, an outer radius of ~200 AU, and a mass
of at least 0.1 Msun. We suggest that the CB26 system is in an intermediate
stage between deeply embedded protostellar accretion disks and the more
evolved, perhaps protoplanetary, disks around T Tauri stars.Comment: 4 pages, 3 figures. Accepted by ApJ Letter
Looking into the hearts of Bok globules: MM and submm continuum images of isolated star-forming cores
We present the results of a comprehensive infrared, submillimetre, and
millimetre continuum emission study of isolated low-mass star-forming cores in
32 Bok globules, with the aim to investigate the process of star formation in
these regions. The submillimetre and millimetre dust continuum emission maps
together with the spectral energy distributions are used to model and derive
the physical properties of the star-forming cores, such as luminosities, sizes,
masses, densities, etc. Comparisons with ground-based near-infrared and
space-based mid and far-infrared images from Spitzer are used to reveal the
stellar content of the Bok globules, association of embedded young stellar
objects with the submm dust cores, and the evolutionary stages of the
individual sources. Submm dust continuum emission was detected in 26 out of the
32 globule cores observed. For 18 globules with detected (sub)mm cores we
derive evolutionary stages and physical parameters of the embedded sources. We
identify nine starless cores, most of which are presumably prestellar, nine
Class 0 protostars, and twelve Class I YSOs. Specific source properties like
bolometric temperature, core size, and central densities are discussed as
function of evolutionary stage. We find that at least two thirds (16 out of 24)
of the star-forming globules studied here show evidence of forming multiple
stars on scales between 1,000 and 50,000 AU. However, we also find that most of
these small prototstar and star groups are comprised of sources with different
evolutionary stages, suggesting a picture of slow and sequential star formation
in isolated globulesComment: 60 pages, 28 figures, accepted by The Astrophysical Journal
Supplement Serie
High-Resolution NIR Observations of the Circumstellar Disk System in the Bok Globule CB 26
We report on results of near-infrared and optical observations of the mm disk
embedded in the Bok globule CB 26 (Launhardt & Sargent 2001). The near-infrared
images show a bipolar reflection nebula with a central extinction lane which
coincides with the mm disk. Imaging polarimetry of this object yielded a
polarization pattern which is typical for a young stellar object surrounded by
a large circumstellar disk and an envelope, seen almost edge-on. The strong
linear polarization in the bipolar lobes is caused by single scattering at dust
grains and allowed to locate the illuminating source which coincides with the
center of the mm disk. The spectral energy distribution of the YSO embedded in
CB 26 resembles that of a ClassI source with a luminosity of 0.5 L_sun.Using
the pre-main-sequence evolutionary tracks and the stellar mass inferred from
the rotation curve of the disk, we derive an age of the system of <10^6 yr.
H_alpha and [SII] narrow-band imaging as well as optical spectroscopy revealed
an Herbig-Haro object 6.15 arcmin northwest of CB 26 YSO 1, perfectly aligned
with the symmetry axis of the bipolar nebula. This Herbig-Haro object (HH 494)
indicates ongoing accretion and outflow activity in CB 26 YSO 1. Its excitation
characteristics indicate that the Herbig-Haro flow is propagating into a
low-density environment. We suggest that CB 26 YSO 1 represents the transition
stage between embedded protostellar accretion disks and more evolved
protoplanetary disks around T Tauri stars in an undisturbed environment.Comment: 21 pages, 6 figures (reduced resolution), ApJ accepte
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