- ID:
- ivo://CDS.VizieR/J/ApJS/136/631
- Title:
- IUE absorption toward 164 early-type stars
- Short Name:
- J/ApJS/136/631
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present measurements of Galactic interstellar AlIII, SiIV, and CIV absorption recorded in high-resolution archival ultraviolet spectra of 164 hot early-type stars observed by the International Ultraviolet Explorer (IUE) satellite. The objects studied were drawn from the list of hot stars scheduled to be observed with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite as part of observing programs designed to investigate absorption by OVI in the Galactic disk and halo. Multiple IUE echelle-mode integrations have been combined to produce a single ultraviolet (1150-1900{AA}) spectrum of each star with a spectral resolution of ~25km/s (FWHM). Selected absorption-line profiles are presented for each star along with plots of the apparent column density per unit velocity for each line of the AlIII, SiIV, and CIV doublets. We report absorption-line equivalent widths, absorption velocities, and integrated column densities based on the apparent optical depth method of examining interstellar absorption lines. We also determine column densities and Doppler parameters from single-component curve-of-growth analyses. The scientific analysis of these observations will be undertaken after the FUSE satellite produces similar measurements for absorption by interstellar OIV, FeIII, SIII, and other ions.
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- ID:
- ivo://CDS.VizieR/J/A+A/648/A38
- Title:
- J1717-3342 and J1744-3116 CO spectra
- Short Name:
- J/A+A/648/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemistry of the diffuse interstellar medium is driven by the combined influences of cosmic rays, ultraviolet (UV) radiation, and turbulence. Previously detected at the outer edges of photodissociation regions (PDRs) and formed from the reaction of C^+^ and OH, CO^+^ is the main chemical precursor of HCO^+^ and CO in a thermal, cosmic-ray, and UV-driven chemistry. Our aim was to test whether the thermal cosmic-ray and UV-driven chemistry is producing CO in diffuse interstellar molecular gas through the intermediate formation of CO^+^ We searched for CO^+^ absorption with the Atacama Large Millimeter Array (ALMA) toward two quasars with known Galactic foreground absorption from diffuse interstellar gas, J1717-3342 and J1744-3116, targeting the two strongest hyperfine components of the J=2-1 transition near 236GHz. We could not detect CO^+^ but obtained sensitive upper limits toward both targets. The derived upper limits on the CO^+^ column densities represent about 4% of the HCO^+^ column densities. The corresponding upper limit on the CO^+^ abundance relative to H_2_ is <1.2x10^-10^. The non-detection of CO^+^ confirms that HCO^+^ is mainly produced in the reaction between oxygen and carbon hydrides, CH2^+^ or CH3^+^, induced by suprathermal processes, while CO^+^ and HOC^+^ result from reactions of C^+^ with OH and H_2_O. The densities r equired to form CO molecules at low extinction are consistent with this scheme.
- ID:
- ivo://CDS.VizieR/J/ApJ/838/80
- Title:
- JHK polarimetry of stars behind bubble N4
- Short Name:
- J/ApJ/838/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of a curved magnetic field in the ring-like shell of the bubble N4, derived from near-infrared polarization of reddened diskless stars located behind this bubble. The magnetic field in the shell is curved and parallel to the ring-like shell, and its strength is estimated to be ~120{mu}G in the plane of the sky. The magnetic field strength in the shell is significantly enhanced compared to the local field strength. We calculate the mass-to-flux ratio for the submillimeter clumps in the shell and find that they are all magnetically subcritical. Our results demonstrate that the magnetic field strengthens as the interstellar medium is compressed into a shell, and suggest that the magnetic field has the potential to hinder star formation triggered by H II region expansion.
- ID:
- ivo://CDS.VizieR/J/ApJS/234/42
- Title:
- JHKs polarimetry in Circinus Molecular Cloud
- Short Name:
- J/ApJS/234/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of near-infrared (NIR) linear imaging polarimetry in the J, H, and Ks bands of the low-mass star cluster-forming region in the Circinus Molecular Cloud Complex. Using aperture polarimetry of point-like sources, positive detection of 314, 421, and 164 sources in the J, H, and Ks bands, respectively, was determined from among 749 sources whose photometric magnitudes were measured. For the source classification of the 133 point-like sources whose polarization could be measured in all 3 bands, a color-color diagram was used. While most of the NIR polarizations of point-like sources are well-aligned and can be explained by dichroic polarization produced by aligned interstellar dust grains in the cloud, 123 highly polarized sources have also been identified with some criteria. The projected direction on the sky of the magnetic field in the Cir-MMS region is indicated by the mean polarization position angles (70{deg}) of the point-like sources in the observed region, corresponding to approximately 1.6x1.6pc^2^. In addition, the magnetic field direction is compared with the outflow orientations associated with Infrared Astronomy Satellite sources, in which two sources were found to be aligned with each other and one source was not. We also show prominent polarization nebulosities over the Cir-MMS region for the first time. Our polarization data have revealed one clear infrared reflection nebula (IRN) and several candidate IRNe in the Cir-MMS field. In addition, the illuminating sources of the IRNe are identified with near- and mid-infrared sources.
- ID:
- ivo://CDS.VizieR/J/ApJS/221/2
- Title:
- Keck+Magellan survey for LLSs. III.
- Short Name:
- J/ApJS/221/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an absorption-line survey of optically thick gas clouds --Lyman Limit Systems (LLSs)-- observed at high dispersion with spectrometers on the Keck and Magellan telescopes. We measure column densities of neutral hydrogen N_H1_ and associated metal-line transitions for 157 LLSs at z_LLS_=1.76-4.39 restricted to 10^17.3^cm^-2^<=N_HI_<10^20.3^cm^-2^. An empirical analysis of ionic ratios indicates an increasing ionization state of the gas with decreasing N_H1_ and that the majority of LLSs are highly ionized, confirming previous expectations. The Si^+^/H^0^ ratio spans nearly four orders of magnitude, implying a large dispersion in the gas metallicity. Fewer than 5% of these LLSs have no positive detection of a metal transition; by z~3 nearly all gas that is dense enough to exhibit a very high Lyman limit opacity has previously been polluted by heavy elements. We add new measurements to the small subset of LLS (~5%-10%) that may have super-solar abundances. High Si^+^/Fe^+^ ratios suggest an {alpha}-enhanced medium, whereas the Si^+^/C^+^ ratios do not exhibit the super-solar enhancement inferred previously for the Ly{alpha} forest.
- ID:
- ivo://CDS.VizieR/J/MNRAS/338/253
- Title:
- K extinction near the Galactic Centre
- Short Name:
- J/MNRAS/338/253
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We extract J and Ks magnitudes from the 2MASS Point Source Catalog for approximately 6 million stars with 8<Ks<13 in order to build an A_K_ extinction map within 10 degrees of the Galactic centre. The extinction was determined by fitting the upper giant branch of (Ks, J-Ks) colour-magnitude diagrams to a dereddened upper giant branch mean locus built from previously studied Bulge fields. The extinction values vary from A_K=0.05 in the edges of the map up to A_K=3.2 close to the Galactic centre. The resulting extinction map is given in the file 'extmap.dat'.
- ID:
- ivo://CDS.VizieR/J/ApJ/884/4
- Title:
- KEYSTONE: ammonia structures in Galactic GMCs
- Short Name:
- J/ApJ/884/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present initial results from the K-band Focal Plane Array Examinations of Young STellar Object Natal Environments survey (KEYSTONE), a large project on the 100m Green Bank Telescope mapping ammonia emission across 11 giant molecular clouds at distances of 0.9-3.0kpc (Cygnus X North, Cygnus X South, M16, M17, Mon R1, Mon R2, NGC 2264, NGC 7538, Rosette, W3, and W48). This data release includes the NH_3_ (1,1) and (2,2) maps for each cloud, which are modeled to produce maps of kinetic temperature, centroid velocity, velocity dispersion, and ammonia column density. Median cloud kinetic temperatures range from 11.4+/-2.2K in the coldest cloud (Mon R1) to 23.0+/-6.5K in the warmest cloud (M17). Using dendrograms on the NH_3_ (1,1) integrated intensity maps, we identify 856 dense gas clumps across the 11 clouds. Depending on the cloud observed, 40%-100% of the clumps are aligned spatially with filaments identified in H2 column density maps derived from spectral energy distribution fitting of dust continuum emission. A virial analysis reveals that 523 of the 835 clumps (~63%) with mass estimates are bound by gravity alone. We find no significant difference between the virial parameter distributions for clumps aligned with the dust-continuum filaments and those unaligned with filaments. In some clouds, however, hubs or ridges of dense gas with unusually high mass and low virial parameters are located within a single filament or at the intersection of multiple filaments. These hubs and ridges tend to host water maser emission, multiple 70{mu}m detected protostars, and have masses and radii above an empirical threshold for forming massive stars.
- ID:
- ivo://CDS.VizieR/J/A+A/579/A51
- Title:
- Kinematic and thermal structure of IRDCs
- Short Name:
- J/A+A/579/A51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We studied the kinematic and thermal structure of the early phases of high- mass and intermediate mass star formation using ammonia observations from the Very Large Array (VLA) and the Effelsberg 100m telescope.
- ID:
- ivo://CDS.VizieR/J/ApJ/699/1153
- Title:
- Kinematic distances to GRS molecular clouds
- Short Name:
- J/ApJ/699/1153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Kinematic distances to 750 molecular clouds identified in the ^13^COJ=1-0 Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey (GRS) are derived assuming the Clemens rotation curve of the Galaxy. The kinematic distance ambiguity is resolved by examining the presence of HI self-absorption toward the ^13^CO emission peak of each cloud using the Very Large Array Galactic Plane Survey. We also identify 21cm continuum sources embedded in the GRS clouds in order to use absorption features in the HI 21cm continuum to distinguish between near and far kinematic distances. The Galactic distribution of GRS clouds is consistent with a four-arm model of the Milky Way. The locations of the Scutum-Crux and Perseus arms traced by GRS clouds match star-count data from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire star-count data. We conclude that molecular clouds must form in spiral arms and be short-lived (lifetimes <10^7^yr) in order to explain the absence of massive, ^13^CO bright molecular clouds in the interarm space.
- ID:
- ivo://CDS.VizieR/J/A+A/617/A27
- Title:
- Kinematics of dense gas in L1495 filament
- Short Name:
- J/A+A/617/A27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Nitrogen bearing species, such as NH_3_, N_2_H^+^, and their deuterated isotopolo- gues show enhanced abundances in CO-depleted gas, and thus are perfect tracers of dense and cold gas in star-forming regions. The Taurus molecular cloud contains the long L1495 filament providing an excellent opportunity to study the process of star formation in filamentary environments. We study the kinematics of the dense gas of starless and protostellar cores traced by the N_2_D^+^(2-1), N_2_H^+^(1-0), DCO^+^(2-1), and H^13^CO^+^(1-0) transitions along the L1495 filament and the kinematic links between the cores and surrounding molecular cloud. We measured velocity dispersions, local and total velocity gradients, and estimate the specific angular momenta of 13 dense cores in the four transitions using on-the-fly observations with the IRAM 30-m antenna. To study a possible connection to the filament gas, we used the C^18^O(1-0) observations.
