The 362.156 GHz absorption spectrum of H2O2 in the Mars atmosphere was observed on September 4 of 2003, employing the James Clerk Maxwell Telescope (JCMT) sub-millimeter facility on Mauna Kea, ...Hawaii. Radiative transfer analysis of this line absorption yields an average volume mixing ratio of 18 +/-0.4 ppbv within the lower (0-30 km) Mars atmosphere, in general accordance with standard photochemical models (e.g. Nair et al. 1994, Icarus 111, 124-150). Our derived H2O2 abundance is roughly three times greater than the upper limit retrieved by Encrenaz et al. (2002, Astron. Astrophys. 396, 1037-1044) from infrared spectroscopy, although part of this discrepancy may result from the different solar longitudes (L(s)) of observation. Aphelion-to-perihelion thermal forcing of the global Mars hygropause generates substantial ( > 200 percent) increases in HO(x) abundances above about 10 km altitudes between the L(s) = 112 period of the Encrenaz et al. upper limit measurement and the current L(s) = 250 period of detection (Clancy and Nair, 1996, J. Geophys. Res. 101, 12785-12590). The observed H2O2 line absorption weakens arguments for non-standard homogeneous (Encrenaz et al. 2002, Astron. Astrophys. 396, 1037-1044) or heterogeneous (Krasnopolsky, 2003a, J. Geophys. Res. 108; 2003b, Icarus 165, 315-325) chemistry, which have been advocated partly on the basis of infrared (8-micron) non-detections for Mars H2O2. Observation of Mars H2O2 also represents the first measurement of a key catalytic specie in a planetary atmosphere other than our own.
We present the JCMT Gould Belt Survey's first look results of the southern extent of the Orion A Molecular Cloud (δ ≤ −5:31:27.5). Employing a two-step structure identification process, we construct ...individual catalogues for large-scale regions of significant emission labelled as islands and smaller-scale subregions called fragments using the 850 μm continuum maps obtained using SCUBA-2. We calculate object masses, sizes, column densities, and concentrations. We discuss fragmentation in terms of a Jeans instability analysis and highlight interesting structures as candidates for follow-up studies. Furthermore, we associate the detected emission with young stellar objects (YSOs) identified by Spitzer and Herschel. We find that although the population of active star-forming regions contains a wide variety of sizes and morphologies, there is a strong positive correlation between the concentration of an emission region and its calculated Jeans instability. There are, however, a number of highly unstable subregions in dense areas of the map that show no evidence of star formation. We find that only ∼72 per cent of the YSOs defined as Class 0+I and flat-spectrum protostars coincide with dense 850 μm emission structures (column densities >3.7 × 1021 cm−2). The remaining 28 per cent of these objects, which are expected to be embedded in dust and gas, may be misclassified. Finally, we suggest that there is an evolution in the velocity dispersion of YSOs such that sources which are more evolved are associated with higher velocities.
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.
ABSTRACT We present results of an infrared study of the molecular cloud Lynds 1340, forming three groups of low- and intermediate-mass stars. Our goals are to identify and characterize the young ...stellar population of the cloud, study the relationships between the properties of the cloud and the emergent stellar groups, and integrate L1340 into the picture of the star-forming activity of our Galactic environment. We selected candidate young stellar objects (YSOs) from the Spitzer and WISE databases using various published color criteria and classified them based on the slope of the spectral energy distribution (SED). We identified 170 Class II, 27 flat SED, and 45 Class 0/I sources. High angular resolution near-infrared observations of the RNO 7 cluster, embedded in L1340, revealed eight new young stars of near-infrared excess. The surface density distribution of YSOs shows three groups, associated with the three major molecular clumps of L1340, each consisting of 100 members, including both pre-main-sequence stars and embedded protostars. New Herbig-Haro objects were identified in the Spitzer images. Our results demonstrate that L1340 is a prolific star-forming region of our Galactic environment in which several specific properties of the intermediate-mass mode of star formation can be studied in detail.
We present SCUBA-2 450 and 850 μm observations of the Serpens MWC 297 region, part of the James Clerk Maxwell Telescope (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 β = 1.8. Within 40 arcsec 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 ultracompact H ii region and polar winds/jets. Contamination accounts for 73 ± 5 per cent and 82 ± 4 per cent of peak flux at 450 μm and 850 μm, respectively. The residual thermal disc of the star is almost undetectable at these wavelengths. Young stellar objects (YSOs) are confirmed where SCUBA-2 850 μm clumps identified by the fellwalker algorithm coincide with Spitzer Gould Belt Survey detections. We identify 23 objects and use T
bol to classify nine YSOs with masses 0.09 to 5.1 M⊙. We find two Class 0, one Class 0/I, three Class I and three Class II sources. The mean temperature is 15 ± 2 K for the nine YSOs and 32 ± 4 K for the 14 starless clumps. We observe a starless clump with an abnormally high mean temperature of 46 ± 2 K 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.
We present 850 and 450 m 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 LkH 101, where the background cloud emission is too bright to verify or rule out the presence of the compact 70 m 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.
We present 850 and 450 μm data from the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey obtained with Submillimetre Common-User Bolometer Array 2 (SCUBA-2) and characterize the dust attributes ...of Class I, Class II and Class III disc sources in L 1495. We detect 23 per cent of the sample at both wavelengths, with the detection rate decreasing through the Classes from I to III. The median disc mask is 1.6 × 10−3 M⊙, and only 7 per cent of Class II sources have disc masses larger than 20 Jupiter masses. We detect a higher proportion of discs towards sources with stellar hosts of spectral type K than spectral type M. Class II discs with single stellar hosts of spectral type K have higher masses than those of spectral type M, supporting the hypothesis that higher mass stars have more massive discs. Variations in disc masses calculated at the two wavelengths suggest that there may be differences in dust opacity and/or dust temperature between discs with hosts of spectral types K to those with spectral type M.
The Venus mesosphere constitutes a highly variable transition region between the zonal rotation of the lower atmosphere and the diurnal circulation of the upper atmosphere. It further serves as the ...primary photochemical region of the Venus atmosphere. We obtained James Clerk Maxwell Telescope (JCMT, Mauna Kea Hawaii) sub-millimeter line observations of mesospheric
12CO and
13CO during coordinated space (MESSENGER and Venus Express) and ground-based observations of Venus in June of 2007. Such CO spectra line measurements support temperature, CO mixing ratio, and wind retrievals over the 80–110
km altitude range, encompassing the upper mesosphere and lower thermosphere of Venus. Five-point beam integrations were obtained across the observed Venus disk, allowing distinction of afternoon (noon to 6
p.m.) versus evening (6
p.m. to midnight) local times and northern (0–60N) versus southern (0–60S) latitudes. Distinctive diurnal variations (noon to midnight) are retrieved for both temperatures above 95
km and CO mixing ratios above 85
km altitudes. Separate CO line maps obtained on (UT) June 2, 3, 6, and 11 indicate moderate daily variability in afternoon and evening CO mixing ratios (20–50%) and temperatures (5–10
K). Average Venus mesospheric temperatures over this period were 10
K warmer than returned from 1978 to 1979 Pioneer Venus or 2000–01 sub-millimeter measurements, without evidence for the very large temperature inversions indicated by Venus Express SPICAV measurements at 90–100
km altitudes (Bertaux, J.L., Vandaele, A.-C., Korablev, O., Villard, E., Fedorova, A., Fussen, D., Quémerais, E., Belyaev, D., Mahieux, A., Montmessin, F., Muller, C., Neefs, E., Nevejans, D., Wilquet, V., Dubois, J.P. Hauchecorne, A., Stepanov, A., Vinogradov, I., Rodin, A., Bertaux, J.-L., Nevejans, D., Korablev, O., Montmessin, F., Vandaele, A.-C., Fedorova, A., Cabane, M., Chassefière, E., Chaufray, J.Y., Dimarellis, E., Dubois, J.P., Hauchecorne, A., Leblanc, F., Lefèvre, F., Rannou, P., Quémerais, E., Villard, E., Fussen, D., Muller, C., Neefs, E., Van Ransbeeck, E., Wilquet, V., Rodin, A., Stepanov, A., Vinogradov, I., Zasova, L., Forget, F., Lebonnois, S., Titov, D., Rafkin, S., Durry, G., Gérard, J.C., Sandel, B., 2007. A warm layer in Venus’ cryosphere and high-altitude measurements of HF, HCl, H
2O and HDO. Nature 450, 646–649). Measured Doppler shifts associated with June 2 and 11
12CO line center absorptions indicate nearly supersonic (200
m/s, Mach 1) afternoon-to-evening (retrograde) circulation; composed of additive subsolar-to-antisolar (SSAS) and zonal retrograde wind components, which are not separable due to the particular observational geometry.
We present SCUBA-2 450 μm and 850 μm observations of the W40 complex in the Serpens-Aquila region as part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey (GBS) of nearby star-forming ...regions. We investigate radiative heating by constructing temperature maps from the ratio of SCUBA-2 fluxes using a fixed dust opacity spectral index, β = 1.8, and a beam convolution kernel to achieve a common 14.8 arcsec resolution. We identify 82 clumps ranging between 10 and 36 K with a mean temperature of 20 ± 3 K. Clump temperature is strongly correlated with proximity to the external OB association and there is no evidence that the embedded protostars significantly heat the dust. We identify 31 clumps that have cores with densities greater than 105cm−3. 13 of these cores contain embedded Class 0/I protostars. Many cores are associated with bright-rimmed clouds seen in Herschel 70 μm images. From JCMT HARP observations of the 12CO 3–2 line, we find contamination of the 850 μm band of up to 20 per cent. We investigate the free–free contribution to SCUBA-2 bands from large-scale and ultracompact H ii regions using archival VLA data and find the contribution is limited to individual stars, accounting for 9 per cent of flux per beam at 450 μm or 12 per cent at 850 μm in these cases. We conclude that radiative heating has potentially influenced the formation of stars in the Dust Arc sub-region, favouring Jeans stable clouds in the warm east and fragmentation in the cool west.
PDF
