Aina Palau

THE OUTBURST DECAY OF THE LOW MAGNETIC FIELD MAGNETAR SGR 0418+5729

N.R. is supported by a Ramon y Cajal Research Fellowship, and by grants AYA2009-07391, AYA2012-39303, SGR2009-811, TW2010005, and iLINK 2011-0303. J.A.P. and D.V. acknowledge support from the grants AYA 2010-21097-C03-02 and Prometeo/2009/103. R.T. and S.M. are partially funded through an INAF 2011 PRIN grant. A.P. is supported by a JAE-Doc CSIC fellowship co-funded with the European Social Fund under the program “Junta para la Ampliacion de Estudios,” by the Spanish MICINN grant AYA2011-30228-C03-02 (co-funded with FEDER funds), and by the AGAUR grant 2009SGR1172 (Catalonia).

Submillimeter Arcsecond-Resolution Mapping of the Highly Collimated Protostellar Jet HH 211

We have mapped the protostellar jet HH 211 in 342 GHz continuum, SiO (J = 8-7), and CO (J = 3-2) emission at ~1 resolution with the Submillimeter Array. Thermal dust emission is seen in continuum at the center of the jet, tracing an envelope and a possible optically thick compact disk (with a size <130 AU) around the protostar. A knotty jet is seen in CO and SiO as in H2, but extending closer to the protostar. It consists of a chain of knots on each side of the protostar, with an interknot spacing of ~2-3 or 600-900 AU and the innermost pair of knots at only ~1.7 or 535 AU from the protostar. These knots likely trace unresolved internal (bow) shocks (i.e., working surfaces) in the jet, with a velocity range up to ~25 km s-1. The two-sided mass-loss rate of the jet is estimated to be ~(0.7-2.8) × 10-6 M☉ yr-1. The jet is episodic, precessing, and bending. A velocity gradient is seen consistently across two bright SiO knots (BK3 and RK2) perpendicular to the jet axis, with ~1.5 ± 0.8 km s-1 at ~30 ± 15 AU, suggesting the presence of jet rotation. The launching radius of the jet, derived from the potential jet rotation, is ~0.15-0.06 AU in the inner disk.

ROTATION AND OUTFLOW MOTIONS IN THE VERY LOW-MASS CLASS 0 PROTOSTELLAR SYSTEM HH 211 AT SUBARCSECOND RESOLUTION

HH 211 is a nearby young protostellar system with a highly collimated jet. We have mapped it in 352 GHz continuum, SiO (J = 8 – 7), and HCO+ (J = 4 – 3) emission at up to ~02 resolution with the Submillimeter Array (SMA). The continuum source is now resolved into two sources, SMM1 and SMM2, with a separation of ~ 84 AU. SMM1 is seen at the center of the jet, probably tracing a (inner) dusty disk around the protostar driving the jet. SMM2 is seen to the southwest of SMM1 and may trace an envelope-disk around a small binary companion. A flattened envelope-disk is seen in HCO+ around SMM1 with a radius of ~ 80 AU perpendicular to the jet axis. Its velocity structure is consistent with a rotation motion and can be fitted with a Keplerian law that yields a mass of ~50 ± 15 M Jup (a mass of a brown dwarf) for the protostar. Thus, the protostar could be the lowest mass source known to have a collimated jet and a rotating flattened envelope-disk. A small-scale (~200 AU) low-speed (~2 km s–1) outflow is seen in HCO+ around the jet axis extending from the envelope-disk. It seems to rotate in the same direction as the envelope-disk and may carry away part of the angular momentum from the envelope-disk. The jet is seen in SiO close to ~100 AU from SMM1. It is seen with a C-shaped bending. It has a transverse width of 40 AU and a velocity of ~ 170 ± 60 km s–1. A possible velocity gradient is seen consistently across its innermost pair of knots, ~0.5 km s–1 at ~10 AU, consistent with the sense of rotation of the envelope-disk. If this gradient is an upper limit of the true rotational gradient of the jet, then the jet carries away a very small amount of angular momentum of 5 AU km s–1 and thus must be launched from the very inner edge of the disk near the corotation radius.

Deuteration as an evolutionary tracer in massive-star formation

Context. Theory predicts, and observations confirm, that the column density ratio of a molecule containing D to its counterpart containing H can be used as an evolutionary tracer in the low-mass star formation process. Aims. Since it remains unclear if the high-mass star formation process is a scaled-up version of the low-mass one, we investigated whether the relation between deuteration and evolution can be applied to the high-mass regime. Methods. With the IRAM-30 m telescope, we observed rotational transitions of N 2 D + and N 2 H + and derived the deuterated fraction in 27 cores within massive star-forming regions understood to represent different evolutionary stages of the massive-star formation process. Results. The abundance of N 2 D + is higher at the pre-stellar/cluster stage, then drops during the formation of the protostellar object(s) as in the low-mass regime, remaining relatively constant during the ultra-compact HII region phase. The objects with the highest fractional abundance of N 2 D + are starless cores with properties very similar to typical pre-stellar cores of lower mass. The abundance of N 2 D + is lower in objects with higher gas temperatures as in the low-mass case but does not seem to depend on gas turbulence. Conclusions. Our results indicate that the N 2 D + -to-N 2 H + column density ratio can be used as an evolutionary indicator in both low-and high-mass star formation, and that the physical conditions influencing the abundance of deuterated species likely evolve similarly during the processes that lead to the formation of both low- and high-mass stars.

UNVEILING A NETWORK OF PARALLEL FILAMENTS IN THE INFRARED DARK CLOUD G14.225–0.506

We present the results of combined NH_3 (1,1) and (2,2) line emission observed with the Very Large Array and the Effelsberg 100 m telescope of the infrared dark cloud G14.225–0.506. The NH3 emission reveals a network of filaments constituting two hub-filament systems. Hubs are associated with gas of rotational temperature T_(rot) ~ 15 K, non-thermal velocity dispersion σ_(NT) ~ 1 km s^(–1), and exhibit signs of star formation, while filaments appear to be more quiescent (T_(rot) ~ 11 K and σ_(NT) ~ 0.6 km s^(–1)). Filaments are parallel in projection and distributed mainly along two directions, at P.A. ~ 10° and 60°, and appear to be coherent in velocity. The averaged projected separation between adjacent filaments is between 0.5 pc and 1 pc, and the mean width of filaments is 0.12 pc. Cores within filaments are separated by ~0.33 ± 0.09 pc, which is consistent with the predicted fragmentation of an isothermal gas cylinder due to the sausage-type instability. The network of parallel filaments observed in G14.225–0.506 is consistent with the gravitational instability of a thin gas layer threaded by magnetic fields. Overall, our data suggest that magnetic fields might play an important role in the alignment of filaments, and polarization measurements in the entire cloud would lend further support to this scenario.

A RING/DISK/OUTFLOW SYSTEM ASSOCIATED WITH W51 NORTH: A VERY MASSIVE STAR IN THE MAKING

Sensitive and high angular resolution (~04) SO2[222,20 → 221,21] and SiO[5 → 4] line and 1.3 and 7 mm continuum observations made with the Submillimeter Array (SMA) and the Very Large Array (VLA) toward the young massive cluster W51 IRS2 are presented. We report the presence of a large (of about 3000 AU) and massive (40 M ☉) dusty circumstellar disk and a hot gas molecular ring around a high-mass protostar or a compact small stellar system associated with W51 North. The simultaneous observations of the silicon monoxide molecule, an outflow gas tracer, further revealed a massive (200 M ☉) and collimated (~14°) outflow nearly perpendicular to the dusty and molecular structures suggesting thus the presence of a single very massive protostar with a bolometric luminosity on the order of 105 L ☉. A molecular hybrid local thermodynamic equilibrium model of a Keplerian and infalling disk with an inner cavity and a central stellar mass of more than 60 M ☉ agrees well with the SO2[222,20 → 221,21] line observations. Finally, these results suggest that mechanisms, such as mergers of low- and intermediate-mass stars, might not be necessary for forming very massive stars.

EARLY STAGES OF CLUSTER FORMATION: FRAGMENTATION OF MASSIVE DENSE CORES DOWN TO ≲ 1000 AU*

In order to study the fragmentation of massive dense cores, which constitute the cluster cradles, we observed the continuum at 1.3xa0mm and the COxa0(2-1) emission of four massive cores with the Plateau de Bure Interferometer in the most extended configuration. We detected dust condensations down to ~0.3 M ☉ and separate millimeter sources down to 0.4 or 1000 AU, comparable to the sensitivities and separations reached in optical/infrared studies of clusters. The COxa0(2-1) high angular resolution images reveal high-velocity knots usually aligned with previously known outflow directions. This, in combination with additional cores from the literature observed at similar mass sensitivity and spatial resolution, allowed us to build a sample of 18 protoclusters with luminosities spanning three orders of magnitude. Among the 18 regions, ~30% show no signs of fragmentation, while 50% split up into 4 millimeter sources. We compiled a list of properties for the 18 massive dense cores, such as bolometric luminosity, total mass, and mean density, and found no correlation of any of these parameters with the fragmentation level. In order to investigate the combined effects of the magnetic field, radiative feedback, and turbulence in the fragmentation process, we compared our observations to radiation magnetohydrodynamic simulations and found that the low-fragmented regions are reproduced well in the magnetized core case, while the highly fragmented regions are consistent with cores where turbulence dominates over the magnetic field. Overall, our study suggests that the fragmentation in massive dense cores could be determined by the initial magnetic field/turbulence balance in each particular core.

SUBMILLIMETER EMISSION FROM THE HOT MOLECULAR JET HH 211

We observed the HH 211 jet in the submillimeter continuum and the CO (3-2) and SiO (8-7) transitions with the Submillimeter Array. The continuum source detected at the center of the outflow shows an elongated morphology, perpendicular to the direction of the outflow axis. The high-velocity emission of both molecules shows a knotty and highly collimated structure. The SiO (8-7) emission at the base of the outflow, close to the driving source, spans a wide range of velocities, from -20 up to 40 km s-1. This suggests that a wide-angle wind may be the driving mechanism of the HH 211 outflow. For distances ≥5 (~1500 AU) from the driving source, emission from both transitions follows a Hubble-law behavior, with SiO (8-7) reaching higher velocities than CO (3-2) and being located upstream of the CO (3-2) knots. This indicates that the SiO (8-7) emission is likely tracing entrained gas very close to the primary jet, while the CO (3-2) is tracing less dense entrained gas. From the SiO (5-4) data of Hirano et al., we find that the SiO (8-7)/SiO (5-4) brightness temperature ratio along the jet decreases for knots far from the driving source. This is consistent with the density decreasing along the jet, from (3-10) × 106 cm-3 at 500 AU to (0.8-4) × 106 cm-3 at 5000 AU from the driving source.

IRAS 21391+5802: The Molecular Outflow and Its Exciting Source

We present centimeter and millimeter observations of gas and dust around IRAS 21391+5802, an intermediate-mass source embedded in the core of IC 1396N. Continuum observations from 3.6 cm to 1.2 mm are used to study the embedded objects and overall distribution of the dust, while molecular line observations of CO, CS, and CH3OH are used to probe the structure and chemistry of the outflows in the region. The continuum emission at centimeter and millimeter wavelengths has been resolved into three sources separated ~15 from each other, and with one of them, BIMA 2, associated with IRAS 21391+5802. The dust emission around this source shows a very extended envelope, which accounts for most of the circumstellar mass of 5.1 M☉. This source is powering a strong molecular outflow, elongated in the east-west direction, which presents a complex structure and kinematics. While at high outflow velocities the outflow is clearly bipolar, at low outflow velocities the blueshifted and redshifted emission are highly overlapping and the strongest emission shows a V-shaped morphology. The outflow as traced by CS and CH3OH exhibits two well-differentiated and clumpy lobes, with two prominent northern blueshifted and redshifted clumps. The curved shape of the clumps and the spectral shape at these positions are consistent with shocked material. In addition, CS and CH3OH are strongly enhanced toward these positions with respect to typical quiescent material abundances in other star-forming regions. This kinematical and chemical evidence suggests that the clumps are tracing gas entrained within the surface of interaction between the molecular outflow and the dense ambient quiescent core and that the morphology of the molecular outflow is a result of this interaction. The circumstellar mass together with the power-law index of the dust emissivity measured, β = 1.1 ± 0.3, and the fact that the source is driving a molecular outflow are consistent with the source BIMA 2 being an embedded intermediate-mass protostar. In addition, the source fits very well correlations between source and outflow properties found for low-mass Class 0 objects. The other two sources in the region, BIMA 1 and BIMA 3, have a mass of 0.07 M☉ each, and their dust emissivity index, β < 0.3 and β = 0.1 ± 0.3, respectively, is consistent with more evolved objects. BIMA 1 is also driving a very collimated and small bipolar outflow elongated in the north-south direction.

Forming an early O-type star through gas accretion?

We present high angular resolution (~3 ) and sensitive 1.3xa0mm continuum, cyanogen (CN) and vinyl cyanidexa0(C 2 H 3 CN) line observations made with the Submillimeter Array (SMA) toward one of most highly obscured objects of the W51xa0IRS2 region, W51xa0North. We find that the CNxa0line exhibits a pronounced inverse P-Cygni profile indicating that the molecular gas is falling into this object with a mass accretion rate between 4 and 7xa0