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 N2$H+(1-0) line and at 3mm dust continuum, using the Australian Telescope Compact Array (ATCA). The results are complemented by infrared data from the Spitzer Space Telescope. In CG30, the 3mm dust continuum images resolve two compact sources with a separation of ~21.7 arcsecs (~8700 AU). In BHR71, strong dust continuum emission is detected at the position of the mid-infrared source IRS1, while only weak emission is detected from the secondary mid-infrared source IRS2. Assuming optically thin 3mm dust continuum emission, we derive hydrogen gas masses of 0.05--2.1$M_\odot$for the four sub-cores. N2H+(1-0) line emission is detected in both CG30 and BHR71, and is spatially associated with the thermal dust continuum emission. We derive the velocity fields and find symmetric velocity gradients in both sources. Assuming that these gradients are due to core rotation, we estimate the specific angular momenta and ratios of rotational energy to gravitational energy for all cores. We also find that the N2H+ emission is strongly affected by the outflows, both in terms of entrainment and molecule destruction.$Spitzer$images show the mid-infrared emission from all four sub-cores. All four sources appear to drive their own outflows. Based on the ATCA and$Spitzer$ 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

IRAM-PdBI Observations of Binary Protostars I: The Hierarchical System SVS13 in NGC1333

We present millimeter interferometric observations of the young stellar object SVS13 in NCG1333 in the N2H+(1-0) line and at 1.4 and 3mm dust continuum, using the IRAM Plateau de Bure interferometer. The results are complemented by infrared data from the Spitzer Space Telescope. The millimeter dust continuum images resolve four sources (A, B, C, and VLA3) in SVS13. With the dust continuum images, we derive gas masses of 0.2-1.1 M_sun for the sources. N2H+(1-0) line emission is detected and spatially associated with the dust continuum sources B and VLA3. The observed mean line width is ~0.48 km/s and the estimated virial mass is ~0.7 M_sun. By simultaneously fitting the seven hyperfine line components of N2H+, we derive the velocity field and find a symmetric velocity gradient of about 28 km/s/pc across sources B and VLA3, which could be explained by core rotation. The velocity field suggests that sources B and VLA3 are forming a physically bound protobinary system embedded in a common N2H+ core. Spitzer images show mid-infrared emission from sources A and C, which is spatially associated with the mm dust continuum emission. No infrared emission is detected from source B, implying that the source is deeply embedded. Based on the morphologies and velocity structure, we propose a hierarchical fragmentation picture for SVS13 where the three sources (A, B, and C) were formed by initial fragmentation of a filamentary prestellar core, while the protobinary system (sources B and VLA3) was formed by rotational fragmentation of a single collapsing sub-core.Comment: 26 pages, 9 figures, accepted by Ap

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

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

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

SMA CO(2-1) Observations of CG30: A Protostellar Binary System with a High-Velocity Quadrupolar Molecular Outflow

We present interferometric observations in the 12CO (2-1) line and at 1.3 mm dust continuum of the low-mass protostellar binary system in the cometary globule CG30, using the Submillimeter Array. The dust continuum images resolve two compact sources (CG30N and CG30S), with a linear separation of ~8700 AU and total gas masses of ~1.4 and ~0.6 M_sun, respectively. With the CO images, we discover two high-velocity bipolar molecular outflows, driven by the two sources. The two outflows are nearly perpendicular to each other, showing a quadrupolar morphology. The northern bipolar outflow extends along the southeast (redshifted, with a velocity up to ~23 km/s) and northwest (blueshifted, velocity up to ~30 km/s) directions, while the southern pair has an orientation from southwest (blueshifted, velocity up to 13 km/s) to northeast (redshifted, velocity up to ~41 km/s). The outflow mass of the northern pair, driven by the higher mass source CG30N, is ~9 times larger than that of the southern pair. The discovery of the quadrupolar molecular outflow in the CG30 protobinary system, as well as the presence of other quadrupolar outflows associated with binary systems, demonstrate that the disks in (wide) binary systems are not necessarily co-aligned after fragmentation.Comment: 12 pages, 3 figures, to be published by ApJL in October 200