P. Schilke

Methanol as a diagnostic tool of interstellar clouds - II. Modelling high-mass protostellar objects

Context. Fundamental properties of interstellar clouds must be known to investigate the initial conditions of star formation within them and the interaction of newly formed stars with their environment. Methanol has proven to be useful to probe densities and temperatures of various environments within interstellar clouds. Aims. We aim to explore the potential of methanol as a tracer molecule for regions in which high-mass stars are forming or have recently formed, in particular so-called high-mass protostellar objects (HMPOs) and infrared dark clouds (IRDCs). Methods. We present and analyse multi-frequency centimetre and (sub)millimetre single-dish observations of methanol toward a sample of 13 sources that are in the poorly understood earliest phases of evolution of high-mass stars (HMPOs and IRDCs). For each source in our sample, we derive physical parameters such as the kinetic temperature, the spatial density. and the methanol column density. We apply our large velocity gradient modelling and fitting technique that involves fitting a synthetic spectrum to all the measured lines simultaneously. Results. In several sources, we find that more than one physical component is necessary to fit the spectra; moreover, broad non-Gaussian linewidths suggest outflows in many sources from both the IRDC and the HMPO subsamples. Kinetic temperatures are found to be between 10 and 60 K and spatial densities in the range 10 5 -10 6 cm -3 . Hotter, denser cores are found in a few HMPOs, indicating that these sources already harbour hot cores heated by protostars.

Detection of the interstellar NH2 radical

The NH 2 radical has been detected for the first time in interstellar clouds. Using the Caltech Submillimeter Observatory, five features containing 15 lines of NH 2 have been observed in absorption toward Sgr B2(N) and Sgr B2(M). The NH 2 is located in a low-density envelope in front of the dense, hot cores seen in emission lines of other molecules. It is not detected in the hot cores themselves. We infer a NH 2 column density of 5×10 15 cm −2 , a fractional abundance relative to H 2 of (1-3)×10 −8 , and a total NH 2 /NH 3 column density ratio in the envelope of 0.5

The James Clerk Maxwell Telescope Spectral Legacy Survey

Stars form in the densest, coldest, most quiescent regions of molecular clouds. Molecules provide the only probes which can reveal the dynamics, physics, chemistry and evolution of these regions, but our understanding of the molecular inventory of sources and how this is related to their physical state and evolution is rudimentary and incomplete. The Spectral Legacy Survey (SLS) is one of seven surveys recently approved by the JCMT Board. Starting in 2007, the SLS will produce a spectral imaging survey of the content and distribution of all the molecules detected in the 345 GHz atmospheric window (between 332 GHz and 373 GHz) towards a sample of 5 sources. Our intended targets are: a low mass core (NGC1333 IRAS4), 3 high mass cores spanning a range of star forming environments and evolutionary states (W49, AFGL2591, and IRAS20126), and a PDR (the Orion Bar). The SLS will use the unique spectral imaging capabilities of HARP-B/ACSIS to study the molecular inventory and the physical structure of these objects, which span different evolutionary stages and physical environments, to probe their evolution during the star formation process. As its name suggests, the SLS will provide a lasting data legacy from the JCMT that is intended to benefit the entire astronomical community. As such, the entire data set (including calibrated spectral datacubes, maps of molecular emission, line identifications, and calculations of the gas temperature and column density) will be publicly available. Subject headings: Astronomical Data Bases: Surveys — Stars: Formation — ISM: Abundances — ISM: Molecules — ISM: EvolutionStars form in the densest, coldest, most quiescent regions of molecular clouds. Molecules provide the only probes that can reveal the dynamics, physics, chemistry, and evolution of these regions, but our understanding of the molecular inventory of sources and how this is related to their physical state and evolution is rudimentary and incomplete. The Spectral Legacy Survey (SLS) is one of seven surveys recently approved by the James Clerk Maxwell Telescope (JCMT) Board of Directors. Beginning in 2007, the SLS will produce a spectral imaging survey of the content and distribution of all the molecules detected in the 345 GHz atmospheric window (between 332 and 373 GHz) toward a sample of five sources. Our intended targets are a low-mass core (NGC 1333 IRAS 4), three high-mass cores spanning a range of star-forming environments and evolutionary states (W49, AFGL 2591, and IRAS 20126), and a photodissociation region (the Orion Bar). The SLS will use the unique spectral imaging capabilities of HARP-B/ACSIS (Heterodyne Array Receiver Programme B/Auto-Correlation Spectrometer and Imaging System) to study the molecular inventory and the physical structure of these objects, which span different evolutionary stages and physical environments and to probe their evolution during the star formation process. As its name suggests, the SLS will provide a lasting data legacy from the JCMT that is intended to benefit the entire astronomical community. As such, the entire data set (including calibrated spectral data cubes, maps of molecular emission, line identifications, and calculations of the gas temperature and column density) will be publicly available.

High-mass star formation at high luminosities: W31 at >10 6 L ,

Context. High-mass star formation has been a very active field over the past decade; however, most studies have targeted regions of luminosities between 10 4 and 10 5 L� . In contrast to that, the highest mass stars reside in clusters exceeding 10 5 or even 10 6 L� . Aims. We want to study the physical conditions associated with the formation of the highest mass stars. Methods. To do this, we selected the W31 star-forming complex with a total luminosity of ∼6 × 10 6 L� (comprised of at least two subregions) for a multiwavelength spectral line and continuum study covering wavelengths from the near- and midinfrared via (sub)mm wavelength observations to radio data in the cm regime. Results. While the overall structure is similar among the multiwavelength continuum data, there are several intriguing differences. The 24 μm emission stemming largely from small dust grains tightly follows the spatial structure of the cm emission tracing the ionized free-free emission. As a result, warm dust resides in regions that are spatially associated with the ionized hot gas (∼10 4 K) of the Hii regions. Furthermore, we find several evolutionary stages within the same complexes, ranging from infrared-observable clusters, via deeply embedded regions associated with active star formation traced by 24 μm and cm emission, to at least one highmass gas clump devoid of any such signature. The 13 CO(2–1) and C 18 O(2–1) spectral line observations reveal kinematic breadth in the entire region with a total velocity range of approximately 90 km s −1 . Kinematic and turbulent structures are set into context. While the average virial mass ratio for W31 is close to unity, the line width analysis indicates large-scale evolutionary differences between the southern and northern subregions (G10.2-0.3 and G10.3-0.1) of the whole W31 complex. A color−color analysis of the IRAC data also shows that the class II sources are broadly distributed throughout the entire complex, whereas the Class 0/I sources are more tightly associated with the active high-mass star-forming regions. The clump mass function – tracing cluster scales and not scales of individual stars – derived from the 875 μm continuum data has a slope of 1.5 ± 0.3, consistent with previous cloud mass functions. Conclusions. The highest mass and luminous stars form in highly structured and complex regions with multiple events of star formation that do not always occur simultaneously but in a sequential fashion. Warm dust and ionized gas can spatially coexist, and high-mass starless cores with low-turbulence gas components can reside in the direct neighborhood of active star-forming clumps with broad linewidths.

Circumbinary molecular rings around young stars in Orion

We present high angular resolution 1.3 mm continuum, methyl cyanide molecular line, and 7 mm continuum observations made with the Submillimeter Array and the Very Large Array, toward the most highly obscured and southern part of the massive star forming region OMC1S located behind the Orion Nebula. We find two flattened and rotating molecular structures with sizes of a few hundred astronomical units suggestive of circumbinary molecular rings produced by the presence of two stars with very compact circumstellar disks with sizes and separations of about 50 AU, associated with the young stellar objects 139-409 and 134-411. Furthermore, these two circumbinary rotating rings are related to two compact and bright hot molecular cores. The dynamic mass of the binary systems

CO and CH3OH observations of the BHR71 outflows with APEX [Letter]

Context.Highly-collimated outflows are believed to be the earliest stage in outflow evolution, so their study is essential for understanding the processes driving outflows. The BHR71 Bok globule is known to harbour such a highly-collimated outflow, which is powered by a protostar belonging to a protobinary system. Aims.We aimed at investigating the interaction of collimated outflows with the ambient molecular cloud by using molecular tracers. Methods.We mapped the BHR71 highly-collimated outflow in CO(3-2) with the APEX telescope, and observed several bright points of the outflow in the molecular transitions CO(4-3), 13CO(3-2), C18O(3-2), and CH3OH(7-6). We use an LVG code to characterise the temperature enhancements in these regions. Results.In our CO(3-2) map, the second outflow driven by IRS2, which is the second source of the binary system, is completely revealed and shown to be bipolar. We also measure temperature enhancements in the lobes. The CO and methanol LVG modelling points to temperatures between 30 and 50 K in the IRS1 outflow, while the IRS2 outflow seems to be warmer (up to 300 K).

The evolutionary state of the southern dense core Chamaeleon-MMS1 [Letter]

Aims.Our goal is to set constraints on the evolutionary state of the dense core Cha-MMS1 in the Chamaeleon I molecular cloud. Methods: .We analyze molecular line observations carried out with the new submillimeter telescope APEX. We look for outflow signatures around the dense core and probe its chemical structure, which we compare to predictions of models of gas-phase chemistry. We also use the public database of the Spitzer Space Telescope (SST) to compare Cha-MMS1 with the two Class 0 protostars IRAM 04191 and L1521F, which are at the same distance. Results: .We measure a large deuterium fractionation for N2H+ (11 ± 3 %), intermediate between the prestellar core L1544 and the very young Class 0 protostar L1521F. It is larger than for HCO+ (2.5 ± 0.9 %), which is probably the result of depletion removing HCO+ from the high-density inner region. Our CO(3-2) map reveals the presence of a bipolar outflow driven by the Class I protostar Ced 110 IRS 4 but we do not find evidence for an outflow powered by Cha-MMS1. We also report the detection of Cha-MMS1 at 24, 70 and 160 μm by the instrument MIPS of the SST, at a level nearly an order of magnitude lower than IRAM 04191 and L1521F. Conclusions: .Cha-MMS1 appears to have already formed a compact object, either the first hydrostatic core at the very end of the prestellar phase, or an extremely young protostar that has not yet powered any outflow, at the very beginning of the Class 0 accretion phase.

Survey for High-Mass Protostars in Cygnus X

The process of the formation of high-mass stars is still largely unknown and poorly constrained by observations. Both theoretical and observational approaches are paved with serious difficulties. The models face the same limitations as for the low-mass regime but in an even more extreme case in terms of short timescales, large infall rates and large central masses (e.g. Stahler et al. [11]). The rare occurence of massive stars renders observations and surveys for proto-OB stars difficult. The search for and the studies of collapsing high-mass protostellar objects (HMPOs) are therefore of prime importance (e.g. Kurtz et al. [5]).