N. F. H. Tothill

The spatial distribution of star formation in the solar neighbourhood: do all stars form in dense clusters?

We present a global study of low mass, young stellar object (YSO) surface densities (�) in nearby (< 500 pc) star forming regions based on a comprehensive collection of Spitzer Space Telescope surveys. We show that the distribution of YSO surface densities in the solar neighbourhood is a smooth distribution, being adequately described by a lognormal function from a few to 10 3 YSOs per pc 2 , with a peak at � 22 stars pc

Low upper limits on the O2 abundance from the Odin satellite

For the first time, a search has been conducted in our Galaxy for the 119 GHz transition connecting to the ground state of O2, using the Odin satellite. Equipped with a sensitive 3 mm receiver (Tsy ...

Detection of the 205 μm [N II] line from the Carina Nebula

We report the first detection of the 205 μm 3P1 P0 [N II] line from a ground-based observatory using a direct detection spectrometer. The line was detected from the Carina star formation region using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) on the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at the South Pole. The [N II] 205 μm line strength indicates a low-density (n ~ 32 cm-3) ionized medium, similar to the low-density ionized halo previously reported in its [O III] 52 and 88 μm line emission. When compared with the Infrared Space Observatory [C II] observations of this region, we find that 27% of the [C II] line emission arises from this low-density ionized gas, but the large majority (~73%) of the observed [C II] line emission arises from the neutral interstellar medium. This result supports and underpins prior conclusions that most of the observed [C II] 158 μm line emission from Galactic and extragalactic sources arises from the warm, dense photodissociated surfaces of molecular clouds. The detection of the [N II] line demonstrates the utility of Antarctic sites for THz spectroscopy.

The Herschel and JCMT Gould Belt Surveys: Constraining Dust Properties in the Perseus B1 Clump with PACS, SPIRE, and SCUBA-2

We present Herschel observations from the Herschel Gould Belt Survey and SCUBA-2 science verification observations from the JCMT Gould Belt Survey of the B1 clump in the Perseus molecular cloud. We determined the dust emissivity index using four different techniques to combine the Herschel PACS+SPIRE data at 160 - 500 microns with the SCUBA-2 data at 450 microns and 850 microns. Of our four techniques, we found the most robust method was to filter-out the large-scale emission in the Herschel bands to match the spatial scales recovered by the SCUBA-2 reduction pipeline. Using this method, we find beta ~ 2 towards the filament region and moderately dense material and lower beta values (beta > 1.6) towards the dense protostellar cores, possibly due to dust grain growth. We find that beta and temperature are more robust with the inclusion of the SCUBA-2 data, improving estimates from Herschel data alone by factors of ~ 2 for beta and by ~ 40% for temperature. Furthermore, we find core mass differences of < 30% compared to Herschel-only estimates with an adopted beta = 2, highlighting the necessity of long wavelength submillimeter data for deriving accurate masses of prestellar and protostellar cores.

The JCMT Legacy Survey of the Gould Belt: a first look at Orion B with HARP

The Gould Belt Legacy Survey will survey nearby star-forming regions (within 500 pc), using HARP (Heterodyne Array Receiver Programme), SCUBA-2 (Submillimetre CommonUser Bolometer Array 2) and POL-2 (Polarimeter 2) on the James Clerk Maxwell Telescope (JCMT). This paper describes the initial data obtained using HARP to observe 12 CO, 13 CO and C 18 O J = 3! 2 towards two regions in Orion B, NGC 2024 and NGC 2071. We describe the physical characteristics of the two clouds, calculating temperatures and opacities utilizing all three isotopologues. We find good agreement between temperatures calculated from CO and from dust emission in the dense, energetic regions. We determine the mass and energetics of the clouds, and of the high-velocity material seen in 12 CO emission, and compare the relative energetics of the high- and low-velocity material in the two clouds. We present a CLUMPFIND analysis of the 13 CO condensations. The slope of the condensation mass functions, at the high-mass ends, is similar to the slope of the initial mass function.

The JCMT Gould Belt Survey: first results from the SCUBA-2 observations of the Ophiuchus molecular cloud and a virial analysis of its prestellar core population

In this paper, we present the first observations of the Ophiuchus molecular cloud performed as part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey (GBS) with the SCUBA-2 instrument. We demonstrate methods for combining these data with previous HARP CO, Herschel, and IRAM N2H+ observations in order to accurately quantify the properties of the SCUBA-2 sources in Ophiuchus. We produce a catalogue of all of the sources found by SCUBA-2. We separate these into protostars and starless cores. We list all of the starless cores and perform a full virial analysis, including external pressure. This is the first time that external pressure has been included in this level of detail. We find that the majority of our cores are either bound or virialized. Gravitational energy and external pressure are on average of a similar order of magnitude, but with some variation from region to region. We find that cores in the Oph A region are gravitationally bound prestellar cores, while cores in the Oph C and E regions are pressure-confined. We determine that N2H+ is a good tracer of the bound material of prestellar cores, although we find some evidence for N2H+ freeze-out at the very highest core densities. We find that non-thermal linewidths decrease substantially between the gas traced by C18O and that traced by N2H+, indicating the dissipation of turbulence at higher densities. We find that the critical Bonnor–Ebert stability criterion is not a good indicator of the boundedness of our cores. We detect the pre-brown dwarf candidate Oph B-11 and find a flux density and mass consistent with previous work. We discuss regional variations in the nature of the cores and find further support for our previous hypothesis of a global evolutionary gradient across the cloud from south-west to north-east, indicating sequential star formation across the region.

Exceptional terahertz transparency and stability above Dome A, Antarctica

We present the first direct measurements of the terahertz atmospheric transmission above Dome A, the highest point on the Antarctic plateau at an elevation of 4.1 km. The best-quartile atmospheric transmission during the Austral winter is 80% at a frequency of 661 GHz (453 μm), corresponding to a precipitable water vapor column of 0.1 mm. Daily averages as low as 0.025 mm were observed. The Antarctic atmosphere is very stable, and excellent observing conditions generally persist for many days at a time. The exceptional conditions over the high Antarctic plateau open new far-infrared spectral windows to ground-based observation. These windows contain important spectral-line diagnostics of star formation and the interstellar medium which would otherwise only be accessible to airborne or space telescopes. Online material: color figures

The PLATO Dome A Site-Testing Observatory : instrumentation and first results

The PLATeau Observatory (PLATO) is an automated self-powered astrophysical observatory that was deployed to Dome A, the highest point on the Antarctic plateau, in 2008 January. PLATO consists of a suite of site-testing instruments designed to quantify the benefits of the Dome A site for astronomy, and science instruments designed to take advantage of the unique observing conditions. Instruments include CSTAR, an array of optical telescopes for transient astronomy; Gattini, an instrument to measure the optical sky brightness and cloud cover statistics; DASLE, an experiment to measure the statistics of the meteorological conditions within the near-surface layer; Pre-HEAT, a submillimeter tipping radiometer measuring the atmospheric transmission and water vapor content and performing spectral line imaging of the Galactic plane; and Snodar, an acoustic radar designed to measure turbulence within the near-surface layer. PLATO has run completely unattended and collected data throughout the winter 2008 season. Here we present a detailed description of the PLATO instrument suite and preliminary results obtained from the first season of operation.

THE STRUCTURE AND EVOLUTION OF THE LAGOON NEBULA. I. SUBMILLIMETER CONTINUUM AND CO LINE MAPPING

We present submillimeter- and millimeter-wave maps tracing the molecular gas and dust around the edge of the H ii region M8. The molecular material is clumped into cores on the scale of the beam (about 0.1 pc) whose temperatures can be estimated from CO observations. The masses of the clumps, estimated from their continuum fluxes, are consistent with a power-law mass function with index � 1:7 � 0:6, which agrees with determinations for other molecular clouds at similar resolutions, using molecular lines as tracers. The submillimeter clumps are sited at the interface between the H ii region and the background molecular cloud, where they are exposed to the ultraviolet flux of OB stars. The physical parameters of the clumps are compared to published models of molecular clouds undergoing photoevaporation, suggesting that the pressure of the ionized gas exceeds the internal pressure of the clumps and, therefore, that a shock front will be driven into the clumps. The clumps themselves currently appear to be gravitationally unbound, but the compression may be sufficient to induce collapse. Subject headings: H ii regions — ISM: individual (M8) — ISM: structure — stars: formation — submillimeter

The JCMT Legacy Survey of the Gould Belt: a first look at Serpens with HARP: GBS: first look at Serpens

The Gould Belt Legacy Survey will survey nearby star-forming regions (within 500 pc), using HARP (Heterodyne Array Receiver Programme), SCUBA-2 (Submillimetre Common- User Bolometer Array 2) and POL-2 (Polarimeter 2) on the James Clerk Maxwell Telescope (JCMT). This paper describes the initial data obtained using HARP to observe 12CO, 13CO and C18O J = 3 - 2 towards two regions in Orion B, NGC 2024 and NGC 2071. We describe the physical characteristics of the two clouds, calculating temperatures and opacities utilizing all three isotopologues. We find good agreement between temperatures calculated from CO and from dust emission in the dense, energetic regions. We determine the mass and energetics of the clouds, and of the high-velocity material seen in 12CO emission, and compare the relative energetics of the high- and low-velocity material in the two clouds. We present a CLUMPFIND analysis of the 13CO condensations. The slope of the condensation mass functions, at the high-mass ends, is similar to the slope of the initial mass function.