The JCMT Gould Belt survey: Dense core clusters in Orion B

The James Clerk Maxwell Telescope Gould Belt Legacy Survey obtained SCUBA-2 observations of dense cores within three sub-regions of OrionB: LDN1622, NGC2023/2024, and NGC2068/2071, all of which contain clusters of cores. We present an analysis of the clustering properties of these cores, including the two-point correlation function and Cartwright’s Q parameter. We identify individual clusters of dense cores across all three regions using a minimal spanning tree technique, and find that in each cluster, the most massive cores tend to be centrally located. We also apply the independent M–Σ technique and find a strong correlation between core mass and the local surface density of cores. These two lines of evidence jointly suggest that some amount of mass segregation in clusters has happened already at the dense core stage

Insects Inhabiting the Burrows of the Ozark Pocket Gopher in Arkansas

Pocket gopher burrows provide a stable environment for a variety of inquilines; hence this mammal is regarded as a keystone species. Most of the arthropods inhabiting pocket gopher burrows are restricted to this microhabitat. As part of a planned state-wide biotic survey of insects inhabiting this unusual microhabitat, we have focused our initial sampling efforts on the Ozark pocket gopher (Geomys bursarius ozarkensis; Geomyidae). In 2004 and 2005, pitfall traps were established in pocket gopher burrows and in 2007 and 2008, nests and associated chambers were excavated. Retrieved samples contained scarab, histerid, and rove beetles, cave crickets and anthomyiid flies. The histerids consisted of five species, one of which is undescribed, and all of which are new state records. A total of five species of scarab beetles were collected and all of these represent new state records. Two species of cave crickets were collected; one appears to be undescribed, and the other is essentially a Great Plains species and represents a considerable range extension. Both crickets are new to Arkansas

The debris disk around gamma Doradus resolved with Herschel

We present observations of the debris disk around gamma Doradus, an F1V star, from the Herschel Key Programme DEBRIS (Disc Emission via Bias-free Reconnaissance in the Infrared/Submillimetre). The disk is well-resolved at 70, 100 and 160 micron, resolved along its major axis at 250 micron, detected but not resolved at 350 micron, and confused with a background source at 500 micron. It is one of our best resolved targets and we find it to have a radially broad dust distribution. The modelling of the resolved images cannot distinguish between two configurations: an arrangement of a warm inner ring at several AU (best-fit 4 AU) and a cool outer belt extending from ~55 to 400 AU or an arrangement of two cool, narrow rings at ~70 AU and ~190 AU. This suggests that any configuration between these two is also possible. Both models have a total fractional luminosity of ~10^{-5} and are consistent with the disk being aligned with the stellar equator. The inner edge of either possible configuration suggests that the most likely region to find planets in this system would be within ~55 AU of the star. A transient event is not needed to explain the warm dust's fractional luminosity.Comment: 12 pages, 6 figures, accepted for publication in Ap

Young Stellar Objects in the Gould Belt

We present the full catalog of Young Stellar Objects (YSOs) identified in the 18 molecular clouds surveyed by the Spitzer Space Telescope "cores to disks" (c2d) and "Gould Belt" (GB) Legacy surveys. Using standard techniques developed by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of which survive visual inspection and form our final catalog of YSOs in the Gould Belt. We compile extinction corrected SEDs for all 2966 YSOs and calculate and tabulate the infrared spectral index, bolometric luminosity, and bolometric temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and 1182 (40%) are classified as Class 0+I, Flat-spectrum, Class II, and Class III, respectively, and show that the Class III sample suffers from an overall contamination rate by background AGB stars between 25% and 90%. Adopting standard assumptions, we derive durations of 0.40-0.78 Myr for Class 0+I YSOs and 0.26-0.50 Myr for Flat-spectrum YSOs, where the ranges encompass uncertainties in the adopted assumptions. Including information from (sub)millimeter wavelengths, one-third of the Class 0+I sample is classified as Class 0, leading to durations of 0.13-0.26 Myr (Class 0) and 0.27-0.52 Myr (Class I). We revisit infrared color-color diagrams used in the literature to classify YSOs and propose minor revisions to classification boundaries in these diagrams. Finally, we show that the bolometric temperature is a poor discriminator between Class II and Class III YSOs.Comment: Accepted for publication in ApJS. 29 pages, 11 figures, 14 tables, 4 appendices. Full versions of data tables (to be published in machine-readable format by ApJS) available at the end of the latex source cod

The Luminosities of Protostars in the Spitzer c2d and Gould Belt Legacy Clouds

Motivated by the long-standing "luminosity problem" in low-mass star formation whereby protostars are underluminous compared to theoretical expectations, we identify 230 protostars in 18 molecular clouds observed by two Spitzer Space Telescope Legacy surveys of nearby star-forming regions. We compile complete spectral energy distributions, calculate Lbol for each source, and study the protostellar luminosity distribution. This distribution extends over three orders of magnitude, from 0.01 Lsun - 69 Lsun, and has a mean and median of 4.3 Lsun and 1.3 Lsun, respectively. The distributions are very similar for Class 0 and Class I sources except for an excess of low luminosity (Lbol < 0.5 Lsun) Class I sources compared to Class 0. 100 out of the 230 protostars (43%) lack any available data in the far-infrared and submillimeter (70 um < wavelength < 850 um) and have Lbol underestimated by factors of 2.5 on average, and up to factors of 8-10 in extreme cases. Correcting these underestimates for each source individually once additional data becomes available will likely increase both the mean and median of the sample by 35% - 40%. We discuss and compare our results to several recent theoretical studies of protostellar luminosities and show that our new results do not invalidate the conclusions of any of these studies. As these studies demonstrate that there is more than one plausible accretion scenario that can match observations, future attention is clearly needed. The better statistics provided by our increased dataset should aid such future work.Comment: Accepted for publication in AJ. 21 pages, 10 figures, 4 table

The JCMT Gould Belt Survey: A First Look at the Auriga–California Molecular Cloud with SCUBA-2

We present 850 and 450 μm observations of the dense regions within the Auriga–California molecular cloud using SCUBA-2 as part of the JCMT Gould Belt Legacy Survey to identify candidate protostellar objects, measure the masses of their circumstellar material (disk and envelope), and compare the star formation to that in the Orion A molecular cloud. We identify 59 candidate protostars based on the presence of compact submillimeter emission, complementing these observations with existing Herschel/SPIRE maps. Of our candidate protostars, 24 are associated with young stellar objects (YSOs) in the Spitzer and Herschel/PACS catalogs of 166 and 60 YSOs, respectively (177 unique), confirming their protostellar nature. The remaining 35 candidate protostars are in regions, particularly around LkHα 101, where the background cloud emission is too bright to verify or rule out the presence of the compact 70 μm emission that is expected for a protostellar source. We keep these candidate protostars in our sample but note that they may indeed be prestellar in nature. Our observations are sensitive to the high end of the mass distribution in Auriga–Cal. We find that the disparity between the richness of infrared star-forming objects in Orion A and the sparsity in Auriga–Cal extends to the submillimeter, suggesting that the relative star formation rates have not varied over the Class II lifetime and that Auriga–Cal will maintain a lower star formation efficiency

The Spitzer Survey of Interstellar Clouds in the Gould Belt. VI. The Auriga-California Molecular Cloud observed with IRAC and MIPS

We present observations of the Auriga-California Molecular Cloud (AMC) at 3.6, 4.5, 5.8, 8.0, 24, 70 and 160 micron observed with the IRAC and MIPS detectors as part of the Spitzer Gould Belt Legacy Survey. The total mapped areas are 2.5 sq-deg with IRAC and 10.47 sq-deg with MIPS. This giant molecular cloud is one of two in the nearby Gould Belt of star-forming regions, the other being the Orion A Molecular Cloud (OMC). We compare source counts, colors and magnitudes in our observed region to a subset of the SWIRE data that was processed through our pipeline. Using color-magnitude and color-color diagrams, we find evidence for a substantial population of 166 young stellar objects (YSOs) in the cloud, many of which were previously unknown. Most of this population is concentrated around the LkHalpha 101 cluster and the filament extending from it. We present a quantitative description of the degree of clustering and discuss the fraction of YSOs in the region with disks relative to an estimate of the diskless YSO population. Although the AMC is similar in mass, size and distance to the OMC, it is forming about 15 - 20 times fewer stars.Comment: (30 pages, 17 figures (2 multipage figures), accepted for publication in ApJ

The JCMT Gould Belt Survey: a quantitative comparison between SCUBA-2 data reduction methods

Performing ground-based submillimetre observations is a difficult task as the measurements are subject to absorption and emission from water vapour in the Earth's atmosphere and time variation in weather and instrument stability. Removing these features and other artefacts from the data is a vital process which affects the characteristics of the recovered astronomical structure we seek to study. In this paper, we explore two data reduction methods for data taken with the Submillimetre Common-User Bolometer Array-2 (SCUBA-2) at the James Clerk Maxwell Telescope (JCMT). The JCMT Legacy Reduction 1 (JCMT LR1) and The Gould Belt Legacy Survey Legacy Release 1 (GBS LR1) reduction both use the same software (starlink) but differ in their choice of data reduction parameters. We find that the JCMT LR1 reduction is suitable for determining whether or not compact emission is present in a given region and the GBS LR1 reduction is tuned in a robust way to uncover more extended emission, which better serves more in-depth physical analyses of star-forming regions. Using the GBS LR1 method, we find that compact sources are recovered well, even at a peak brightness of only three times the noise, whereas the reconstruction of larger objects requires much care when drawing boundaries around the expected astronomical signal in the data reduction process. Incorrect boundaries can lead to false structure identification or it can cause structure to be missed. In the JCMT LR1 reduction, the extent of the true structure of objects larger than a point source is never fully recovered

The JCMT Gould Belt Survey: Evidence for radiative heating in Serpens MWC 297 and its influence on local star formation

We present SCUBA-2 450micron and 850micron observations of the Serpens MWC 297 region, part of the JCMT Gould Belt Survey of nearby star-forming regions. Simulations suggest that radiative feedback influences the star-formation process and we investigate observational evidence for this by constructing temperature maps. Maps are derived from the ratio of SCUBA-2 fluxes and a two component model of the JCMT beam for a fixed dust opacity spectral index of beta = 1.8. Within 40 of the B1.5Ve Herbig star MWC 297, the submillimetre fluxes are contaminated by free-free emission with a spectral index of 1.03+-0.02, consistent with an ultra-compact HII region and polar winds/jets. Contamination accounts for 73+-5 per cent and 82+-4 per cent of peak flux at 450micron and 850micron respectively. The residual thermal disk of the star is almost undetectable at these wavelengths. Young Stellar Objects are confirmed where SCUBA-2 850micron clumps identified by the fellwalker algorithm coincide with Spitzer Gould Belt Survey detections. We identify 23 objects and use Tbol to classify nine YSOs with masses 0.09 to 5.1 Msun. We find two Class 0, one Class 0/I, three Class I and three Class II sources. The mean temperature is 15+-2K for the nine YSOs and 32+-4K for the 14 starless clumps. We observe a starless clump with an abnormally high mean temperature of 46+-2K and conclude that it is radiatively heated by the star MWC 297. Jeans stability provides evidence that radiative heating by the star MWC 297 may be suppressing clump collapse.Comment: 24 pages, 13 figures, 7 table

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 regio