- ID:
- ivo://CDS.VizieR/J/A+A/574/A127
- Title:
- Photodissociation with mechanical heating
- Short Name:
- J/A+A/574/A127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- CO observations in active galactic nuclei and starbursts reveal high kinetic temperatures. Those environments are thought to be very turbulent due to dynamic phenomena, such as outflows and high supernova rates. We investigate the effect of mechanical heating on atomic fine-structure and molecular lines and on their ratios. We try to use those ratios as a diagnostic to constrain the amount of mechanical heating in an object and also study its significance on estimating the H_2_ mass. Equilibrium photodissociation models (PDRs hereafter) were used to compute the thermal and chemical balance for the clouds. The equilibria were solved for numerically using the optimized version of the Leiden PDR-XDR code. Large velocity-gradient calculations were done as post-processing on the output of the PDR models using RADEX. High-J CO line ratios are very sensitive to mechanical heating ({GAMMA}mech hereafter). Emission becomes at least one order of magnitude brighter in clouds with n~10^5^cm^-3^ and a star formation rate of 1M_{sun}/yr (corresponding to {GAMMA}mech=2x10^-19^erg/cm^3^/s). The Emission of low-J CO lines is not as sensitive to {GAMMA}mech, but they do become brighter in response to {GAMMA}mech. Generally, for all of the lines we considered, {GAMMA}mech increases excitation temperatures and decreases the optical depth at the line centre. Hence line ratios are also effected, strongly in some cases. Ratios involving HCN are a good diagnostic for {GAMMA}mech , where the HCN(1-0)/CO(1-0) increases from 0.06 to 0.25, and the HCN(1-0)/HCO^+^ (1-0) increase from 0.15 to 0.5 for amounts of {GAMMA}mech that are equivalent to 5% of the surface heating rate. Both ratios increase to more than 1 for higher {GAMMA}mech , as opposed to being much less than unity in pure PDRs. The first major conclusion is that low-J to high-J intensity ratios will yield a good estimate of the mechanical heating rate (as opposed to only low-J ratios). The second one is that the mechanical heating rate should be taken into account when determining AV or, equivalently, NH, and consequently the cloud mass. Ignoring {GAMMA}mech will also lead to large errors in density and radiation field estimates.
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- ID:
- ivo://CDS.VizieR/J/A+A/654/A172
- Title:
- Photoionization of the CH radical
- Short Name:
- J/A+A/654/A172
- Date:
- 07 Mar 2022 07:12:57
- Publisher:
- CDS
- Description:
- The primary motivation of this paper is to provide accurate data for the photoionization of the CH radical, including absolute total photoionization cross section, partial cross sections and photo electron angular distribution. In addition,the near threshold features in the photoionization curve (which are absent in previous studies) are produced with high precision. A multichannel wavefunction based on R-matrix approach, which uses the configuration interaction (CI) method to describe electronic correlation, is carried out in the present calculations. A set of B-spline orbitals is employed to represent the accurate continuum. The distinctive feature of the present calculations allows us to generate a more accurate description of the bound and continuum states than those employed before. Total photoionization cross sections from the ground state of CH radicals and partial cross sections corresponding to 1{pi}, 3{sigma}, and 2{sigma} states of CH+ ions are presented for photon energies ranging from threshold to 80eV. Extensive resonance structures, which are absent in previous studies, near the ionization threshold, are observed for the first time. The cross-section dataset obtained from the present calculations is expected to be sufficiently accurate and comprehensive for most current modeling applications involving the photon and CH radicals scattering system.
- ID:
- ivo://CDS.VizieR/J/ApJ/706/896
- Title:
- Photometry in the cometary globule Ori I-2
- Short Name:
- J/ApJ/706/896
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the young stellar population in and near the cometary globule Ori I-2. The analysis is based on deep Nordic Optical Telescope R-band and H{alpha} images, JCMT SCUBA 450 and 850um images combined with near-infrared Two Micron All Sky Survey (2MASS) photometry and mid-infrared archival Spitzer images obtained with the Infrared Array Camera (IRAC; 3.6, 4.5, 5.8, and 8um), and MIPS (24 and 70um) instruments. We identify a total of 125 sources within the 5'x5' region imaged by the IRAC. Of these sources, 87 are detected in the R-band image and 51 are detected in the 2MASS. Ori I-2 shows clear evidence of triggered star formation with four young low-luminosity pre-main-sequence (PMS) stars embedded in the globule. At least two, possibly as many as four, additional low-mass PMS objects were discovered in the field which are probably part of the young {sigma} Orionis cluster. Among the PMS stars which have formed in the globule, MIR-54 is a young, deeply embedded Class 0/I object; MIR-51 and 52 are young Class II sources, while MIR-89 is a more evolved, heavily extincted Class II object with its apparent colors mimicking a Class 0/I object. The Class 0/I object MIR-54 coincides with a previously known IRAS source and is a strong submillimeter source. It is most likely the source for the molecular outflow and the large parsec-scale Herbig-Haro (HH) flow. However, the nearby Class II source, MIR-52, which is strong a H{alpha} emission line star, also appears to drive an outflow approximately aligned with the outflow from MIR-54, and because of the proximity of the two outflows, either star could contribute. MIR-89 appears to excite a low-excitation HH object, HH 992, discovered for the first time in this study.
- ID:
- ivo://CDS.VizieR/J/BaltA/18/33
- Title:
- Photometry of stars around NGC 7023
- Short Name:
- J/BaltA/18/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Interstellar extinction is investigated in a 1.5 square degree area in the direction of the reflection nebula NGC7023 at l=104.1{deg}, b=+14.2{deg}. The study is based on photometric classification and the determination of interstellar extinctions and distances of 480 stars down to V=16.5mag from photometry in the Vilnius seven-color system published in Paper I (2008BaltA..17..161Z). The investigated area is divided into five smaller subareas with slightly different dependence of the extinction on distance. The distribution of reddened stars is in accordance with the presence of two dust clouds at 282pc and 715pc, however in some directions the dust distribution can be continuous or more clouds can be present.
- ID:
- ivo://CDS.VizieR/J/A+A/628/A110
- Title:
- Photometry of submm cores in Vela C
- Short Name:
- J/A+A/628/A110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a study of the population of compact submm cores in Vela C, one of the molecular clouds making up the Vela Molecular Ridge, a nearby (~700pc) star forming region in the Galactic plane. A large scale map of dust emission at 345GHz was obtained with LABOCA at the APEX telescope. Core retrieval and photometry were performed with the algorithms CuTEx and CLUMPFIND. Table 1 lists the sources retrieved by CuTEx. Table 2 lists the sources retrieved by CLUMPFIND.
- ID:
- ivo://CDS.VizieR/J/AJ/145/15
- Title:
- Photometry of YSOs in BRC 27 and BRC 34
- Short Name:
- J/AJ/145/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used archival Spitzer Space Telescope mid-infrared data to search for young stellar objects (YSOs) in the immediate vicinity of two bright-rimmed clouds, BRC 27 (part of CMa R1) and BRC 34 (part of the IC 1396 complex). These regions both appear to be actively forming young stars, perhaps triggered by the proximate OB stars. In BRC 27, we find clear infrared excesses around 22 of the 26 YSOs or YSO candidates identified in the literature, and identify 16 new YSO candidates that appear to have IR excesses. In BRC 34, the one literature-identified YSO has an IR excess, and we suggest 13 new YSO candidates in this region, including a new Class I object. Considering the entire ensemble, both BRCs are likely of comparable ages, within the uncertainties of small number statistics and without spectroscopy to confirm or refute the YSO candidates. Similarly, no clear conclusions can yet be drawn about any possible age gradients that may be present across the BRCs.
- ID:
- ivo://CDS.VizieR/J/ApJ/665/369
- Title:
- Photopolarimetry of Southern Coalsack stars
- Short Name:
- J/ApJ/665/369
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new multicolor photopolarimetry of stars behind the Southern Coalsack. Analyzed together with multiband polarization data from the literature, probing the Chamaeleon I, Musca, rho Opiuchus, R CrA, and Taurus clouds, we show that the wavelength of maximum polarization ({lambda}_max_) is linearly correlated with the radiation environment of the grains. Using far-infrared emission data, we show that the large scatter seen in previous studies of {lambda}_max_ as a function of Av is primarily due to line-of-sight effects causing some Av measurements to not be a good tracer of the extinction (radiation field strength) seen by the grains being probed.
- ID:
- ivo://CDS.VizieR/J/A+A/632/A58
- Title:
- Physical properties of CHIMPS clumps
- Short Name:
- J/A+A/632/A58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The latest generation of high-angular-resolution unbiased Galactic plane surveys in molecular-gas tracers are enabling the interiors of molecular clouds to be studied across a range of environments. The CO Heterodyne Inner Milky Way Plane Survey (CHIMPS) simultaneously mapped a sector of the inner Galactic plane, within 27.8<l<46.2{deg} and |b|<0.5{deg}, in ^13^CO (3-2) and C^18^O (3-2) at an angular resolution of 15 arcsec. The combination of the CHIMPS data with ^12^CO (3-2) data from the CO High Resolution Survey (COHRS) has enabled us to perform a voxel-by-voxel local-thermodynamic-equilibrium (LTE) analysis, determining the excitation temperature, optical depth, and column density of ^13^CO at each l,b,v position. Distances to discrete sources identified by FellWalker in the ^13^CO (3-2) emission maps were determined, allowing the calculation of numerous physical properties of the sources, and we present the first source catalogues in this paper. We find that, in terms of size and density, the CHIMPS sources represent an intermediate population between large-scale molecular clouds identified by CO and dense clumps seen in thermal dust continuum emission, and therefore represent the bulk transition from the diffuse to the dense phase of molecular gas. We do not find any significant systematic variations in the masses, column densities, virial parameters, mean excitation temperature, or the turbulent pressure over the range of Galactocentric distance probed, but we do find a shallow increase in the mean volume density with increasing Galactocentric distance. We find that inter-arm clumps have significantly narrower linewidths, and lower virial parameters and excitation temperatures than clumps located in spiral arms. When considering the most reliable distance-limited subsamples, the largest variations occur on the clump-to-clump scale, echoing similar recent studies that suggest that the star-forming process is largely insensitive to the Galactic-scale environment, at least within the inner disc.
- ID:
- ivo://CDS.VizieR/J/ApJ/723/492
- Title:
- Physical properties of GRS molecular clouds
- Short Name:
- J/ApJ/723/492
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive the physical properties of 580 molecular clouds based on their ^12^CO and ^13^CO line emission detected in the University of Massachusetts-Stony Brook (UMSB) and Galactic Ring surveys (GRS). We provide a range of values of the physical properties of molecular clouds, and find a power-law correlation between their radii and masses, suggesting that the fractal dimension of the interstellar medium is around 2.36. This relation, M=(228+/-18)R^2.36+/-0.04^, allows us to derive masses for an additional 170 Galactic Ring Survey (GRS) molecular clouds not covered by the UMSB survey. We derive the Galactic surface mass density of molecular gas and examine its spatial variations throughout the Galaxy. We find that the azimuthally averaged Galactic surface density of molecular gas peaks between Galactocentric radii of 4 and 5kpc. Although the Perseus arm is not detected in molecular gas, the Galactic surface density of molecular gas is enhanced along the positions of the Scutum-Crux and Sagittarius arms.
- ID:
- ivo://CDS.VizieR/J/A+A/620/A24
- Title:
- Pipe nebula optical-depth, column-density maps
- Short Name:
- J/A+A/620/A24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multi-wavelength observations in the sub-mm regime provide information on the distribution of both the dust column density and the effective dust temperature in molecular clouds. In this study, we created high-resolution and high-dynamic-range maps of the Pipe nebula region and explored the value of dust-temperature measurements in particular towards the dense cores embedded in the cloud. The maps are based on data from the Herschel and Planck satellites, and calibrated with a near-infrared extinction map based on 2MASS observations. We have considered a sample of previously defined cores and found that the majority of core regions contain at least one local temperature minimum. Moreover, we observed an anti-correlation between column density and temperature. The slope of this anti-correlation is dependent on the region boundaries and can be used as a metric to distinguish dense from diffuse areas in the cloud if systematic effects are addressed appropriately. Employing dust-temperature data thus allows us to draw conclusions on the thermodynamically dominant processes in this sample of cores: external heating by the interstellar radiation field and shielding by the surrounding medium. In addition, we have taken a first step towards a physically motivated core definition by recognising that the column-density-temperature anti-correlation is sensitive to the core boundaries. Dust-temperature maps therefore clearly contain valuable information about the physical state of the observed medium.
