arXiv subjects

Josep M. Girart

Publications and source records attributed to Josep M. Girart.

78 records · Page 5Linked to original sources

arXiv2009

The molecular emission of the irradiated star forming core ahead of HH 80N

We present a Berkeley-Illinois-Maryland Association (BIMA) Array molecular survey of the star forming core ahead of HH 80N, the optically obscured northern counterpart of the Herbig-Haro objects HH 80/81. Continuum emission at 1.4 mm and 8 micron is detected at the center of the core, which confirms the presence of an embedded very young stellar object in the core. All detected molecular species arise in a ring-like structure, which is most clearly traced by CS(2-1) emission. This molecular ring suggests that strong molecular depletion occurs in the inner part of the core (at a radius of ~0.1 pc and densities higher than ~5 x 10^4 cm^{-3}). Despite of the overall morphology and kinematic similarity between the different species, there is significant molecular differentiation along the ring-like structure. The analysis of the chemistry along the core shows that part of this differentiation may be caused by the UV irradiation of the nearby HH 80N object, that illuminates the part of the core facing HH 80N, which results in an abundance enhancement of some of the detected species.

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arXiv2008

Modeling the magnetic field in the protostellar source NGC 1333 IRAS 4A

Magnetic fields are believed to play a crucial role in the process of star formation. We compare high-angular resolution observations of the submillimeter polarized emission of NGC 1333 IRAS 4A, tracing the magnetic field around a low-mass protostar, with models of the collapse of magnetized molecular cloud cores. Assuming a uniform dust alignment efficiency, we computed the Stokes parameters and synthetic polarization maps from the model density and magnetic field distribution by integrations along the line-of-sight and convolution with the interferometric response. The synthetic maps are in good agreement with the data. The best-fitting models were obtained for a protostellar mass of 0.8 solar masses, of age 9e4 yr, formed in a cloud with an initial mass-to-flux ratio ~2 times the critical value. The magnetic field morphology in NGC 1333 IRAS 4A is consistent with the standard theoretical scenario for the formation of solar-type stars, where well-ordered, large-scale, rather than turbulent, magnetic fields control the evolution and collapse of the molecular cloud cores from which stars form.

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arXiv2006

Magnetic Fields in the Formation of Sun-Like Stars

We report high-angular-resolution measurements of polarized dust emission toward the low-mass protostellar system NGC 1333 IRAS 4A. We show that in this system the observed magnetic field morphology is in agreement with the standard theoretical models of the formation of Sun-like stars in magnetized molecular clouds at scales of a few hundred astronomical units; gravity has overcome magnetic support, and the magnetic field traces a clear hourglass shape. The magnetic field is substantially more important than turbulence in the evolution of the system, and the initial misalignment of the magnetic and spin axes may have been important in the formation of the binary system.

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arXiv2006

Who Is Eating the Outflow?: High-Angular Resolution Study of an Intermediate-Mass Protostar in L1206

Up to now only a few intermediate-mass molecular outflows have been studied with enough high-angular resolution. The aim of this work is to study in detail the intermediate-mass YSO IRAS 22272+6358A, which is embedded in L1206, and its molecular outflow, in order to investigate the interaction of the outflow with the dense protostellar material, and to compare their properties with those of lower mas counterparts. We carried out OVRO observations of the 2.7 mm continuum emission, CO(1-0), C18O(1-0), and HC3N(12-11) in order to map with high-angular resolution the core of L1206, and to derive the properties of the dust emission, the molecular outflow and the dense protostellar envelope. The 2.7 mm continuum emission has been resolved into four sources, labeled OVRO~1, 2, 3, and 4. The intermediate-mass Class~0/I object OVRO 2, with a mass traced by the dust emission of 14.2 Msun, is the source associated with IRAS 22272+6358A. The CO(1-0) observations have revealed a very collimated outflow driven by OVRO 2, at a PA ~140 degr, that has a very weak southeastern red lobe and a much stronger northwestern blue lobe. Photodissociation toward the red lobe produced by the ionization front coming from the bright-rimmed diffuse HII region could be responsible of the morphology of the outflow. The spatial correlation between the outflow and the elongated dense protostellar material traced by HC3N(12-11) suggests an interaction between the molecular outflow and the protostellar envelope. Shocks produced by the molecular outflow, and possibly by the shock front preceding the ionization front could account for the southern enhancement of HC3N. The properties of the intermediate-mass protostar OVRO 2 and the molecular outflow are consistent with those of lower mass counterparts.

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arXiv2004

The Dense Molecular Cores in the IRAS 21391+5802 region

We present a detailed kinematical study and modeling of the emission of the molecular cores at ambient velocities surrounding IRAS 21391+5802, an intermediate-mass protostar embedded in IC 1396N. The high-density gas emission is found in association with three dense cores associated with the YSOs BIMA 1, BIMA 2, and BIMA 3. The CS (5-4) and CH3OH (5-4) emission around BIMA 1 has been modeled by considering a spatially infinitely thin ring seen edge-on by the observer. From the model we find that CS is detected over a wider radii range than CH3OH. A bipolar outflow is detected in the CS (2-1) line centered near BIMA 1. This outflow could be powered by a yet undetected YSO, BIMA 1W, or alternatively could be part of the BIMA 1 molecular outflow. The CS and CH3OH emission associated with the intermediate-mass protostar BIMA 2 is highly perturbed by the bipolar outflow even at cloud velocities, confirming that the protostar is in a very active stage of mass loss. For YSO BIMA 3 the lack of outflow and of clear evidence of infall suggests that both outflow and infall are weaker than in BIMA 1, and that BIMA 3 is probably a more evolved object.

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arXiv2003

Interferometric Mapping of Magnetic Fields in Star-forming Regions III. Dust and CO polarization in DR21(OH)

We present the polarization detections in DR21(OH) from both the thermal dust emission at 1.3 mm and the CO J=2-1 line obtained with the Berkeley-Illinois-Maryland Association (BIMA) array. Our results are consistent with the prediction of the Goldreich-Kylafis effect that the CO polarization is either parallel or perpendicular to the magnetic field direction. The detection of the polarized CO emission is over a more extended region than the dust polarization, while the dust polarization provides an aide in resolving the ambiguity of the CO polarization. The combined results suggest that the magnetic field direction in DR21(OH) is parallel to the CO polarization and therefore parallel to the major axis of DR21(OH). The strong correlation between the CO and dust polarization suggests that magnetic fields are remarkably uniform throughout the envelope and the cores. The dispersion in polarization position angles implies a magnetic field strength in the plane of the sky of about 1 mG, compared with about 0.5 mG inferred for the line-of-sight field from previous CN Zeeman observations. Our CO data also show that both MM1 and MM2 power high-velocity outflows with $v\gtrsim$25 km/s relative to the systematic velocity.

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