Disentangling the jet emission from protostellar systems. The ALMA view of VLA1623

Context: High-resolution studies of class 0 protostars represent the key to constraining protostar formation models. VLA16234-2417 represents the prototype of class 0 protostars, and it has been recently identified as a triple non-coeval system. Aim: We aim at deriving the physical properties of the jets in VLA16234-2417 using tracers of shocked gas. Methods: ALMA Cycle 0 Early Science observations of CO(2-1) in the extended configuration are presented in comparison with previous SMA CO(3-2) and Herschel-PACS [OI}] 63 micron observations. Gas morphology and kinematics were analysed to constrain the physical structure and origin of the protostellar outflows. Results: We reveal a collimated jet component associated with the [OI] 63 micron emission at about 8'' (about 960 AU) from source B. This newly detected jet component is inversely oriented with respect to the large-scale outflow driven by source A, and it is aligned with compact and fast jet emission very close to source B (about 0.3'') rather than with the direction perpendicular to the A disk. We also detect a cavity-like structure at low projected velocities, which surrounds the [OI] 63 micron emission and is possibly associated with the outflow driven by source A. Finally, no compact outflow emission is associated with source W. Conclusions: Our high-resolution ALMA observations seem to suggest there is a fast and collimated jet component associated with source B. This scenario would confirm that source B is younger than A, that it is in a very early stage of evolution, and that it drives a faster, more collimated, and more compact jet with respect to the large-scale slower outflow driven by A. However, a different scenario of a precessing jet driven by A cannot be firmly excluded from the present observations.Comment: Accepted for publication in Astronomy & Astrophysic

Fast molecular jet from L1157-mm

L1157-mm powers a molecular outflow that is well-known for its shock-induced chemical activity in several hot-spots. We have studied the molecular emission toward L1157-mm searching for a jet component responsible for these spots. We used the IRAM 30m telescope to observe the vicinity of L1157-mm in several lines of SiO. The SiO(5-4) and SiO(6-5) spectra toward L1157-mm present blue and red detached components about 45 km/s away from the ambient cloud. These extremely high-velocity (EHV) components are similar to those found in the L1448 and IRAS 04166+2706 outflows, and probably arise from a molecular jet driven by L1157-mm. Observations of off-center positions indicate that the jet is unresolved in SiO(5-4) (<11"). The EHV jet seen in SiO probably excites L1157-B1 and the other chemically active spots of the L1157 outflow.Comment: 6 pages, 8 figures. Accepted for publication in Astronomy & Astrophysic

The census of interstellar complex organic molecules in the Class I hot corino of SVS13-A

We present the first census of the interstellar Complex Organic Molecules (iCOMs) in the low-mass Class I protostar SVS13-A, obtained by analysing data from the IRAM-30m Large Project ASAI (Astrochemical Surveys At IRAM). They consist of an high-sensitivity unbiased spectral survey at the 1mm, 2mm and 3mm IRAM bands. We detected five iCOMs: acetaldehyde (CH$_3$CHO), methyl formate (HCOOCH$_3$), dimethyl ether (CH$_3$OCH$_3$), ethanol (CH$_3$CH$_2$OH) and formamide (NH$_2$CHO). In addition we searched for other iCOMs and ketene (H$_2$CCO), formic acid (HCOOH) and methoxy (CH$_3$O), whose only ketene was detected. The numerous detected lines, from 5 to 37 depending on the species, cover a large upper level energy range, between 15 and 254 K. This allowed us to carry out a rotational diagram analysis and derive rotational temperatures between 35 and 110 K, and column densities between $3\times 10^{15}$ and $1\times 10^{17}$ cm$^{-2}$ on the 0."3 size previously determined by interferometric observations of glycolaldehyde. These new observations clearly demonstrate the presence of a rich chemistry in the hot corino towards SVS13-A. The measured iCOMs abundances were compared to other Class 0 and I hot corinos, as well as comets, previously published in the literature. We find evidence that (i) SVS13-A is as chemically rich as younger Class 0 protostars, and (ii) the iCOMs relative abundances do not substantially evolve during the protostellar phase.Comment: 24 pages, MNRAS in pres

Molecular outflows towards O-type young stellar objects

We have searched for massive molecular outflows in a sample of high-mass star forming regions, and we have characterised both the outflow properties and those of their associated molecular clumps. With a sample composed largely of more luminous objects than previous ones, this work complements analogous surveys performed by other authors by adding the missing highest luminosity sources. The sample under study has been selected so as to favour the earliest evolutionary phases of star formation, and is composed of very luminous objects (L_bol > 2x10^4 L_sun and up to ~10^6 L_sun), possibly containing O-type stars. Each source has been mapped in 13CO(2-1) and C18O(2-1) with the IRAM-30m telescope on Pico Veleta (Spain). The whole sample shows high-velocity wings in the 13CO(2-1) spectra, indicative of outflowing motions. In addition, we have obtained outflow maps in 9 of our 11 sources, which display well-defined blue and/or red lobes. For these sources, the outflow parameters have been derived from the line wing 13CO(2-1) emission. An estimate of the clump masses from the C18O(2-1) emission is also provided and found to be comparable to the virial masses. From a comparison between our results and those found by other authors at lower masses, it is clear that the outflow mechanical force increases with the bolometric luminosity of the clump and with the ionising photon rate of the associated HII regions, indicating that high-mass stars drive more powerful outflows. A tight correlation between outflow mass and clump mass is also found. Molecular outflows are found to be as common in massive star forming regions as in low-mass star forming regions. This, added to the detection of a few tentative large-scale rotating structures suggests that high-mass stars may generally form via accretion, as low-mass stars.Comment: 16 pages, 10 figures, accepted by Astronomy and Astrophysic

Abundances of Molecular Species in Barnard 68

Abundances for 5 molecules (C18O, CS, NH3, H2CO, and C3H2) and 1 molecular ion (N2H+) and upper limits for the abundances of 1 molecule (13CO) and 1 molecular ion (HCO+) are derived for gas within the Bok globule Barnard 68 (B68). The abundances were determined using our own BIMA millimeter interferometer data and single-dish data gathered from the literature, in conjunction with a Monte Carlo radiative transfer model. Since B68 is the only starless core to have its density structure strongly constrained via extinction mapping, a major uncertainty has been removed from these determinations. All abundances for B68 are lower than those derived for translucent and cold dense clouds, but perhaps only significantly for N2H+, NH3, and C3H2. Depletion of CS toward the extinction peak of B68 is hinted at by the large offset between the extinction peak and the position of maximum CS line brightness. Abundances derived here for C18O and N2H+ are consistent with other, recently determined values at positions observed in common.Comment: 16 pages, 1 figure, accepted by AJ, typo corrected, reference removed in Section 4.

Infall of gas as the formation mechanism of stars up to 20 times more massive than the Sun

Theory predicts and observations confirm that low-mass stars (like the Sun) in their early life grow by accreting gas from the surrounding material. But for stars ~ 10 times more massive than the Sun (~10 M_sun), the powerful stellar radiation is expected to inhibit accretion and thus limit the growth of their mass. Clearly, stars with masses >10 M_sun exist, so there must be a way for them to form. The problem may be solved by non-spherical accretion, which allows some of the stellar photons to escape along the symmetry axis where the density is lower. The recent detection of rotating disks and toroids around very young massive stars has lent support to the idea that high-mass (> 8 M_sun) stars could form in this way. Here we report observations of an ammonia line towards a high-mass star forming region. We conclude from the data that the gas is falling inwards towards a very young star of ~20 M_sun, in line with theoretical predictions of non-spherical accretion.Comment: 11 pages, 2 figure

Radio Continuum and Recombination Line Study of UC HII Regions with Extended Envelopes

We have carried out 21 cm radio continuum observations of 16 UC HII regions using the VLA (D-array) in search of associated extended emission. We have also observed H76$_\alpha$ recombination line towards all the sources and He76$_\alpha$ line at the positions with strong H76$_\alpha$ line emission. The UC HII regions have simple morphologies and large (>10) ratios of single-dish to VLA fluxes. Extended emission was detected towards all the sources. The extended emission consists of one to several compact components and a diffuse extended envelope. All the UC HII regions but two are located in the compact components, where the UC HII regions always correspond to their peaks. The compact components with UC HII regions are usually smaller and denser than those without UC HII regions. Our recombination line observations indicate that the ultracompact, compact, and extended components are physically associated. The UC HII regions and their associated compact components are likely to be ionized by the same sources on the basis of the morphological relations mentioned above. This suggests that almost all of the observed UC HII regions are not `real' UC HII regions and that their actual ages are much greater than their dynamical age (<10000 yr). We find that most of simple UC HII regions previously known have large ratios of single-dish to VLA fluxes, similar to our sources. Therefore, the `age problem' of UC HII regions does not seem to be as serious as earlier studies argued. We present a simple model that explains extended emission around UC HII regions. Some individual sources are discussed.Comment: 29 pages, 28 postscript figures, Accepted for publication in Ap

Far and mid infrared observations of two ultracompact H II regions and one compact CO clump

Two ultracompact H II regions (IRAS 19181+1349 and 20178+4046) and one compact molecular clump (20286+4105) have been observed at far infrared wavelengths using the TIFR 1 m balloon-borne telescope and at mid infrared wavelengths using ISO. Far infrared observations have been made simultaneously in two bands with effective wavelengths of ~ 150 and ~ 210 micron, using liquid 3He cooled bolometer arrays. ISO observations have been made in seven spectral bands using the ISOCAM instrument; four of these bands cover the emission from Polycyclic Aromatic Hydrocarbon (PAH) molecules. In addition, IRAS survey data for these sources in the four IRAS bands have been processed using the HIRES routine. In the high resolution mid infrared maps as well as far infrared maps multiple embedded energy sources have been resolved. There are structural similarities between the images in the mid infrared and the large scale maps in the far infrared bands, despite very different angular resolutions of the two. Dust temperature and optical depth (tau_150 um) maps have also been generated using the data from balloon-borne observations. Spectral energy distributions (SEDs) for these sources have been constructed by combining the data from all these observations. Radiation transfer calculations have been made to understand these SEDs. Parameters for the dust envelopes in these sources have been derived by fitting the observed SEDs. In particular, it has been found that radial density distribution for three sources is diffrent. Whereas in the case of IRAS 20178+4046, a steep distribution of the form r^-2 is favoured, for IRAS 20286+4105 it is r^-1 and for IRAS 19181+1349 it the uniform distribution (r^0). Line ratios for PAH bands have generally been found to be similar to those for other compact H II regions but different from general H II regions.Comment: To appear in Astronomy & Astrophysics; (19 pages including 14 Figures and 6 Tables

SOLIS: XII. SVS13-A Class i chemical complexity as revealed by S-bearing species

Context. Recent results in astrochemistry have revealed that some molecules, such as interstellar complex organic species and deuterated species, can serve as valuable tools in the investigation of star-forming regions. Sulphuretted species can also be used to follow the chemical evolution of the early stages of a Sun-like star formation process. Aims. The goal is to obtain a census of S-bearing species using interferometric images towards SVS13-A, a Class I object associated with a hot corino that is rich in interstellar complex organic molecules. Methods. To this end, we used the NGC 1333 SVS13-A data at 3 mm and 1.4 mm obtained with the IRAM-NOEMA interferometer in the framework of the SOLIS (Seeds of Life in Space) Large Program. The line emission of S-bearing species was imaged and analyzed using local thermodynamic equilibrium (LTE) and large velocity gradient (LVG) approaches. Results. We imaged the spatial distribution on =300 au scale of the line emission of 32SO, 34SO, C32S, C34S, C33S, OCS, H2C32S, H2C34S, and NS. The low excitation (9 K) 32SO line traces: (i) the low-velocity SVS13-A outflow and (ii) the fast (up to 100 km s-1 away from the systemic velocity) collimated jet driven by the nearby SVS13-B Class 0 object. Conversely, the rest of the lines are confined in the inner SVS13-A region, where complex organics were previously imaged. More specifically, the non-LTE LVG analysis of SO, SO2, and H2CS indicates a hot corino origin (size in the 60 120 au range). Temperatures between 50 K and 300 K, as well as volume densities larger than 105 cm-3 have been derived. The abundances of the sulphuretted are in the following ranges: 0.3 6 ± 10-6 (CS), 7 ± 10-9 1 ± 10-7 (SO), 1 10 ± 10-7 (SO2), a few 10-10 (H2CS and OCS), and 10-10 10-9 (NS). The N(NS)/N(NS+) ratio is larger than 10, supporting the assessment that the NS+ ion is mainly formed in the extended envelope. Conclusions. The [H2CS]/[H2CO] ratio, once measured at high-spatial resolutions, increases with time (from Class 0 to Class II objects) by more than one order of magnitude (from =10-2 to a few 10-1). This suggests that [S]/[O] changes along the process of Sunlike star formation. Finally, the estimate of the [S]/[H] budget in SVS13-A is 2 17% of the Solar System value (1.8 ± 10-5), which is consistent with what was previously measured towards Class 0 objects (1 8%). This finding supports the notion that the enrichment of the sulphuretted species with respect to dark clouds remains constant from the Class 0 to the Class I stages of low-mass star formation. The present findings stress the importance of investigating the chemistry of star-forming regions using large observational surveys as well as sampling regions on the scale of the Solar System

Massive Stars: Their Environment and Formation

Cloud environment is thought to play a critical role in determining the mechanism of formation of massive stars. In this contribution we review the physical characteristics of the environment around recently formed massive stars. Particular emphasis is given to recent high angular resolution observations which have improved our knowledge of the physical conditions and kinematics of compact regions of ionized gas and of dense and hot molecular cores associated with luminous O and B stars. We will show that this large body of data, gathered during the last decade, has allowed significant progress in the understanding of the physical processes that take place during the formation and early evolution of massive stars.Comment: Pub. Astron. Soc. of Pacific (Invited Review), 95 pages (Latex), 5 pages (tables, Latex), 11 postscript or gif figure