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31. Extinction map of OMC-1
ID:
ivo://CDS.VizieR/J/A+A/533/A38
Title:
Extinction map of OMC-1
Short Name:
J/A+A/533/A38
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Orion Nebula and its associated young stellar cluster are located at the front-side of the optically thick OMC-1 molecular cloud. In order to disentangle the cluster members from background contamination, it is important to know the extinction provided by the OMC-1, which is poorly known, the available measurements yielding contradictory results. Our main goal is to derive a new extinction map of the OMC-1, obtaining information about the structure of the OMC-1 and the Orion Nebula Cluster. The most recent near-infrared catalog of stars is used to study the distribution of reddening across a 0.3deg^2^ area covering the Orion Nebula Cluster. On the basis of the observed (H,H-Ks) diagram, we establish a criterion for disentangling contaminants from bona-fide cluster members. For contaminant stars, interstellar reddenings are estimated by comparison with a synthetic galactic model. A statistical analysis is then performed to consistently account for local extinction, reddening and star-counts analysis. We derive the extinction map of the OMC-1 with angular resolution <5'. We also assemble a sample of candidate cluster members, for which we measure the extinction provided by the nebular environment. These extinction measurements are analyzed similarly to the contaminant sample, and an extinction map of the Orion Nebula is derived. The extinction provided by the OMC-1 is variable on spatial scales of a few arcminutes, while showing a general increase from the outskirts (A_V_~6) to the direction of the Trapezium asterism (A_V_>30). The Orion Nebula extinction map is more irregular and optically thinner, with Av of the order of a few magnitudes. Both maps are consistent with the optical morphology, in particular the Dark Bay to the north-east of the Trapezium. Both maps also show the presence of a north-south high-density ridge, which confirms the filamentary structure of the Orion molecular complex inside which star formation is still taking place.
32. Faint Object Camera
ID:
ivo://archive.stsci.edu/hst/foc
Title:
Faint Object Camera
Short Name:
HST.FOC
Date:
23 Jul 2020 19:48:27
Publisher:
Space Telescope Science Institute Archive
Description:
The Faint Object Camera (FOC) was one of the 4 original axial instruments on the Hubble Space Telescope (HST). FOC is used to make high-resolution observations of faint sources at UV and visible wavel
33. Faint Object Spectrograph
ID:
ivo://archive.stsci.edu/hst/fos
Title:
Faint Object Spectrograph
Short Name:
HST.FOS
Date:
23 Jul 2020 19:48:53
Publisher:
Space Telescope Science Institute Archive
Description:
The Faint Object Spectrograph (FOS) was one of the 4 original axial instruments aboard the Hubble Space Telescope (HST). The FOS was designed to make spectroscopic observations of astrophysical sources from the near ultraviolet to the near infrared (1150 - 8000 Angstroms). The instrument was removed from HST during the Second Servicing Mission in February 1997.
34. Fluctuations of UV background from GALEX
ID:
ivo://CDS.VizieR/J/A+A/631/A59
Title:
Fluctuations of UV background from GALEX
Short Name:
J/A+A/631/A59
Date:
21 Oct 2021
Publisher:
CDS
Description:
The all sky survey run by the Galaxy Evolution Explorer (GALEX AIS) mapped about 85 % of the Galaxy at ultraviolet (UV) wavelengths and detected the diffuse UV background produced by the scattering of the radiation from OBA stars by interstellar dust grains. Against this background, diffuse weak structures are detected as well as the UV counterparts to nebulae and molecular clouds. To make full profit of the survey, unsupervised and semi-supervised procedures need to be implemented. The main objective of this work is to implement and analyze the results of the method developed by us for the blind detection of ISM features in the GALEX AIS. Most ISM features are detected at very low signal levels (dark filaments, globules) against the already faint UV background. We have defined an index the UV background fluctuations index (or UBF index) to identify areas of the sky where these fluctuations are detected. The algorithm is applied to the images obtained in the FUV (1344-1786{AA}) band since this is less polluted by stellar sources, facilitating the automated detection. The UBF index is shown to be sensitive to the main star forming regions within the Gould's Belt, as well as to some prominent loops like Loop I or the Eridanus and Monogem areas. The catalogue with the UBF index values is made available on-line to the community.
35. Galactic cold cores. V. Dust opacity
ID:
ivo://CDS.VizieR/J/A+A/584/A93
Title:
Galactic cold cores. V. Dust opacity
Short Name:
J/A+A/584/A93
Date:
21 Oct 2021
Publisher:
CDS
Description:
The project Galactic Cold Cores has carried out Herschel photometric observations of interstellar clouds where Planck satellite survey has located cold and compact clumps. The sources represent different stages of cloud evolution from starless clumps to protostellar cores and are located in different Galactic environments. We examine this sample of 116 Herschel fields to estimate the submillimetre dust opacity and to look for variations that could be attributed to the evolutionary stage of the sources or to environmental factors, including the location within the Galaxy. The submillimetre dust opacity is derived from Herschel data and near-infrared observations of the reddening of background stars are converted to near-infrared optical depth. We investigate the systematic errors affecting these parameters and use modelling to make corrections for the expected biases. The ratio of 250{mu}m and J band opacities is correlated with the Galactic location and the star formation activity. Local variations in the ratio {tau}(250{mu}m)/{tau}(J) are searched using the correlation plots and maps of the opacity ratio. We find a median ratio of {tau}(250{mu}m)/{mu}(J)=(1.6+/-0.2)*10^-3^, which is more than three times the mean value reported for the diffuse medium. Assuming an opacity spectral index {beta}=1.8 instead of {beta}=2.0, the value would be smaller by ~30%. No significant systematic variation is detected with Galactocentric distance or with Galactic height. Examination of the {tau}(250{mu}m)/{tau}(J) maps reveals half a dozen fields with clear indications of local increase of submillimetre opacity, up to {tau}(250{mu}m)/{tau}(J)~4*10^-3^, towards the densest clumps. These are all nearby fields with spatially resolved clumps of high column density. We interpret the increase in the far-infrared opacity as a sign of grain growth in the densest and coldest regions of interstellar clouds.
36. Galactic cold cores. VI. List of Herschel fields
ID:
ivo://CDS.VizieR/J/A+A/584/A94
Title:
Galactic cold cores. VI. List of Herschel fields
Short Name:
J/A+A/584/A94
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Galactic Cold Cores project has carried out Herschel photometric observations of 116 fields where the Planck survey has found signs of cold dust emission. The fields contain sources in different environments and different phases of star formation. Previous studies have revealed variations in their dust submillimetre opacity. The aim is to measure the value of dust opacity spectral index and to understand its variations spatially and with respect to other parameters, such as temperature, column density, and Galactic location. The dust opacity spectral index {beta} and the dust colour temperature T are derived using Herschel and Planck data. The relation between {beta} and T is examined for the whole sample and inside individual fields.
37. Galactic distribution of IRDCs
ID:
ivo://CDS.VizieR/J/ApJ/680/349
Title:
Galactic distribution of IRDCs
Short Name:
J/ApJ/680/349
Date:
21 Oct 2021
Publisher:
CDS
Description:
CS(2-1) measurements toward a large sample of fourth Galactic quadrant infrared dark clouds (IRDCs) were made with the Australia Telescope National Facility Mopra telescope in order to establish their kinematic distances and Galactic distribution. Due to its large critical density, CS unambiguously separates the dense IRDCs from more diffuse giant molecular clouds. The fourth-quadrant IRDCs show a pronounced peak in their radial galactocentric distribution at R=6kpc. The first-quadrant IRDC distribution (traced by ^13^CO emission) also shows a peak, but at a galactocentric radius of R=5kpc rather than 6kpc. The reliability of the MSX IRDC catalog by Simon and coworkers is estimated by using the CS detection rate of IRDC candidates. The overall reliability is at least 58%, and increases to near 100% for high contrasts, Galactic longitudes within ~30{deg} of the Galactic center, and large mid-IR backgrounds. A significant fraction of our IRDC sample (14%) showed two CS velocity components, which probably represent two distinct IRDCs along the same line of sight.
38. Galactic HII regions. I. Stellar distances
ID:
ivo://CDS.VizieR/J/AJ/150/147
Title:
Galactic HII regions. I. Stellar distances
Short Name:
J/AJ/150/147
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a new catalog of spectrophotometric distances and line of sight systemic velocities to 103 HII regions between 90{deg}{<=}l<=195{deg} (longitude quadrants II and part of III). Two new velocities for each region are independently measured using 1 arcmin resolution 21cm HI and 2.6mm^12^CO line maps (from the Canadian Galactic Plane Survey and Five College Radio Astronomy Observatory Outer Galaxy Surveys) that show where gaseous shells are observed around the periphery of the ionized gas. Known and neighboring O- and B-type stars with published UBV photometry and MK classifications are overlaid onto 21cm continuum maps, and those stars observed within the boundary of the HII emission (and whose distance is not more than three times the standard deviation of the others) are used to calculate new mean stellar distances to each of the 103 nebulae. Using this approach of excluding distance outliers from the mean distance to a group of many stars in each HII region lessens the impact of anomalous reddening for certain individuals. The standard deviation of individual stellar distances in a cluster is typically 20% per stellar distance, and the error in the mean distance to the cluster is typically +/-10%. Final mean distances of nine common objects with very long baseline interferometry parallax distances show a 1:1 correspondence. Further, comparison with previous catalogs of HII regions in these quadrants shows a 50% reduction in scatter for the distance to Perseus spiral arm objects in the same region, and a reduction by ~1/2^0.5^ in scatter around a common angular velocity relative to the Sun {Omega}-{Omega}_0_(km/s/kpc). The purpose of the catalog is to provide a foundation for more detailed large-scale Galactic spiral structure and dynamics (rotation curve, density wave streaming) studies in the 2nd and 3rd quadrants, which from the Sun's location is the most favorably viewed section of the Galaxy.
39. Gas and dust in star-forming region rho OphA
ID:
ivo://CDS.VizieR/J/A+A/608/A133
Title:
Gas and dust in star-forming region rho OphA
Short Name:
J/A+A/608/A133
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate to what degree local physical and chemical conditions are related to the evolutionary status of various objects in star-forming media. rho Oph A displays the entire sequence of low-mass star formation in a small volume of space. Using spectrophotometric line maps of H_2_, H_2_O, NH_3_, N_2_H^+^, O_2_, OI, CO, and CS, we examine the distribution of the atomic and molecular gas in this dense molecular core. The physical parameters of these species are derived, as are their relative abundances in rho Oph A. Using radiative transfer models, we examine the infall status of the cold dense cores from their resolved line profiles of the ground state lines of H_2_O and NH_3_, where for the latter no contamination from the VLA 1623 outflow is observed and line overlap of the hyperfine components is explicitly taken into account. The stratified structure of this photon dominated region (PDR), seen edge-on, is clearly displayed. Polycyclic aromatic hydrocarbons (PAHs) and OI are seen throughout the region around the exciting star S1. At the interface to the molecular core 0.05pc away, atomic hydrogen is rapidly converted into H_2_, whereas OI protrudes further into the molecular core. This provides oxygen atoms for the gas-phase formation of O_2_ in the core SM1, where X(O_2_)~5x10^-8^. There, the ratio of the O_2_ to H_2_O abundance [X(H_2_O)~5x10^-9^] is significantly higher than unity. Away from the core, O_2_ experiences a dramatic decrease due to increasing H_2_O formation. Outside the molecular core, on the far side as seen from S1, the intense radiation from the 0.5pc distant early B-type star HD147889 destroys the molecules. Towards the dark core SM1, the observed abundance ratio X(O_2_)/X(H_2_O)>1, which suggests that this object is extremely young, which would explain why O_2_ is such an elusive molecule outside the solar system.
40. Gas and dust in the star-forming region rho OphA
ID:
ivo://CDS.VizieR/J/A+A/578/A131
Title:
Gas and dust in the star-forming region rho OphA
Short Name:
J/A+A/578/A131
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using mapping observations of the very dense rho Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimeter continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N_2_H^+^, which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N_2_H^+^(J=3-2) and (J=6-5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H2), hence the surface density distribution of the gas. The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM1. The global average, =88, is not far from the canonical value of 100, however. In rho Oph A, the exponent beta of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class-1 sources to low values close to 0 for the disk-dominated emission in ClassIII objects. beta assumes intermediate values for evolutionary classes in between. Since beta is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like C^18^O, also N_2_H^+^ is frozen onto the grains.