Photoelectric magnitudes and color indices in the Vilnius seven-color system for 152 stars are used to investigate the interstellar extinction in the area of the Aries molecular cloud MBM 12, coinciding with the L1454 and L1457 dust clouds. Spectral types, absolute magnitudes, color excesses, interstellar extinctions and distances of the stars are determined. The plot of interstellar extinction A_v_ versus distance shows that the dust cloud is situated at a distance of 325pc, at 180pc from the Galactic plane, and its true diameter is about 11pc. The interstellar extinction law in the area is found to be normal, typical for the diffuse dust. Ten peculiar or unresolved binary stars and some heavily reddened stars are detected.
Using Spitzer Infrared Spectrograph observations of G0-M4III stars behind dark clouds, I construct 5-20um empirical extinction curves for 0.3<=A_K_<7, which is equivalent to A_V_ between ~3 and 50. For A_K_<1, the curve appears similar to the Mathis diffuse interstellar medium extinction curve, but with a greater degree of extinction. For A_K_>1, the curve exhibits lower contrast between the silicate and absorption continuum, develops ice absorption, and lies closer to the Weingartner and Draine R_V_=5.5 Case B curve, a result which is consistent with that of Flaherty et al. (2007ApJ...663.1069F) and Chiar et al. (2007ApJ...666L..73C). Recently, work using Spitzer Infrared Array Camera data by Chapman et al. independently reaches a similar conclusion that the shape of the extinction curve changes as a function of increasing A_K_. By calculating the optical depths of the 9.7um silicate and 6.0, 6.8, and 15.2um ice features, I determine that a process involving ice is responsible for the changing shape of the extinction curve and speculate that this process is a coagulation of ice-mantled grains rather than ice-mantled grains alone.
The relationships between atomic and molecular hydrogen and dust of various sizes in extragalactic star-forming regions are considered, based on observational data from the Spitzer and Herschel infrared space telescopes, the Very Large Array (atomic hydrogen emission) and IRAM (CO emission). The source sample consists of approximately 300 star-forming regions in 11 nearby galaxies. Aperture photometry has been applied to measure the fluxes in eight infrared bands (3.6, 4.5, 5.8, 8, 24, 70, 100, and 160um), the atomic hydrogen 21 cm line, and CO (2-1) line. The parameters of the dust in the starforming regions were determined via synthetic-spectra fitting, such as the total dust mass, the fraction of polycyclic aromatic hydrocarbons (PAHs), etc. Comparison of the observed fluxes with the measured parameters shows that the relationships between atomic hydrogen, molecular hydrogen, and dust are different in low- and high-metallicity regions. Low-metallicity regions contain more atomic gas, but less molecular gas and dust, including PAHs. The mass of dust constitutes about 1% of the mass of molecular gas in all regions considered. Fluxes produced by atomic and molecular gas do not correlate with the parameters of the stellar radiation, whereas the dust fluxes grow with increasing mean intensity of stellar radiation and the fraction of enhanced stellar radiation. The ratio of the fluxes at 8 and 24um, which characterizes the PAH content, decreases with increasing intensity of the stellar radiation, possibly indicating evolutionary variations of the PAH content. The results confirm that the contribution of the 24um emission to the total IR luminosity of extragalactic star-forming regions does not depend on the metallicity.
We have conducted near-infrared spectroscopy of 26 faint objects around young stellar objects in the Taurus molecular cloud. These objects were detected during a course of near-infrared coronagraphic searches for companions around 72 young stellar objects with the Subaru Telescope and the near-infrared coronagraph CIAO (coronagraphic imager with adaptive optics). A comparison of the Subaru and HST archive images revealed that three central stars and faint companions share common proper motions, suggesting that they are physically associated with each other. None of the 26 sources show deep water absorption bands at near-infrared, except for DH Tau B. This result indicates that all of them, but DH Tau B, have a high photospheric temperature or a large amount of excess from circumstellar materials.
A summary of global properties and an evaluation of the equilibrium state of molecular regions in the outer Galaxy are presented from the decomposition of the Five College Radio Astronomy Observatory (FCRAO, see 1998ApJS..115..241H) Outer Galaxy Survey and targeted ^12^CO and ^13^CO observations (at 115GHz) of four giant molecular cloud complexes. The ensemble of identified objects includes both small, isolated clouds and clumps within larger cloud complexes.
The Vela complex is a region of the sky that gathers several stellar and interstellar structures in a few hundred square degrees. Gaia data now allows us to obtain a 3D view of the Vela interstellar structures through the dust extinction. We used the FEDReD (Field Extinction-Distance Relation Deconvolver) algorithm on near-infrared 2MASS data, cross-matched with the Gaia DR2 catalogue, to obtain a 3D cube of extinction density. We applied the FellWalker algorithm on this cube to locate clumps and dense structures. We analysed 18 million stars on 450 deg 2 to obtain the extinction density of the Vela complex from 0.5 to 8kpc at l in [250, 280] and b in [-10, 5].This cube reveals the complete morphology of known structures and relations between them. In particular, we show that the Vela Molecular Ridge is more likely composed by three substructures instead of four, as suggested by the 2D densities. These substructures form the shell of a large cavity. This cavity is visually aligned with the Vela supernova remnant but located at a larger distance. We provide a catalogue of location, distance, size and total dust content of ISM clumps that we extracted.
Pre-stellar cores within molecular clouds provide the very initial conditions in which stars are formed. FeSt 1-457 is a prototypical starless core and the most chemically evolved among those isolated, embedded in the most pristine part of the Pipe nebula, the bowl. We use the IRAM 30m telescope and the PdBI to study the chemical and physical properties of the starless core FeSt 1-457 (Core 109) in the Pipe nebula. We fit the hyperfine structure of the N_2_H^+^ (1-0) IRAM 30m data. This allowed us to measure with high precision the velocity field, line widths and opacity and derive the excitation temperature and column density in the core. We used a modified Bonnor-Ebert sphere model adding a temperature gradient towards the center to fit the 1.2mm continuum emission and visual extinction maps. Using this model, we have estimated the abundances of the N_2_H^+^ and the rest of molecular lines detected in the 30GHz wide line survey performed at 3mm with IRAM 30m using ARTIST software.
We present observations of three active sites of star formation in the Taurus molecular cloud complex taken at 323 and 608MHz (90 and 50cm, respectively) with the Giant Metrewave Radio Telescope (GMRT). Three pointings were observed as part of a pathfinder project, targeted at the young stellar objects (YSOs) L1551 IRS 5, T Tau and DG Tau (the results for these target sources were presented in a previous paper). In this paper, we search for other YSOs and present a survey comprising of all three fields; a by-product of the large instantaneous field of view of the GMRT. The resolution of the survey is of order 10 arcsec and the best rms noise at the centre of each pointing is of order 100{mu}Jy/beam at 323MHz and 50{mu}Jy/beam at 608MHz. We present a catalogue of 1815 and 687 field sources detected above 5{sigma}_rms_ at 323 and 608MHz, respectively. A total of 440 sources were detected at both frequencies, corresponding to a total unique source count of 2062 sources. We compare the results with previous surveys and showcase a sample of extended extragalactic objects. Although no further YSOs were detected in addition to the target YSOs based on our source-finding criteria, these data can be useful for targeted manual searches, studies of radio galaxies or to assist in the calibration of future observations with the Low-Frequency Array towards these regions.
We present 850{mu}m imaging polarimetry data of the {rho} Oph-A core taken with the Submillimeter Common-User Bolometer Array-2 (SCUBA-2) and its polarimeter (POL-2) as part of our ongoing survey project, B-fields In STar forming RegiOns (BISTRO). The polarization vectors are used to identify the orientation of the magnetic field projected on the plane of the sky at a resolution of 0.01pc. We identify 10 subregions with distinct polarization fractions and angles in the 0.2pc {rho} Oph-A core; some of them can be part of a coherent magnetic field structure in the {rho} Oph region. The results are consistent with previous observations of the brightest regions of {rho} Oph-A, where the degrees of polarization are at a level of a few percent, but our data reveal for the first time the magnetic field structures in the fainter regions surrounding the core where the degree of polarization is much higher (>5%). A comparison with previous near-infrared polarimetric data shows that there are several magnetic field components that are consistent at near-infrared and submillimeter wavelengths. Using the Davis-Chandrasekhar-Fermi method, we also derive magnetic field strengths in several subcore regions, which range from approximately 0.2 to 5mG. We also find a correlation between the magnetic field orientations projected on the sky and the core centroid velocity components.
Infrared dark clouds (IRDCs) are believed to host the earliest stages of high-mass star and cluster formation. Because O stars typically travel short distances over their lifetimes, if IRDCs host the earliest stages of high-mass star formation then these cold, dense molecular clouds should be located in or near the spiral arms in the Galaxy. The Galactic distribution of a large sample of IRDCs should therefore provide information on Galactic structure. Moreover, determination of distances enables mass and luminosity calculations. We have observed a large sample of IRDC candidates in the first Galactic quadrant in the dense gas tracer CS(2-1) using the Mopra telescope in order to determine kinematic distances from the molecular line velocities. We find that the IRDCs are concentrated around a Galactocentric distance of ~4.5kpc, agreeing with the results of Simon et al. (2006, J/ApJ/653/1325). This distribution is consistent with the location of the Scutum-Centaurus spiral arm. The group of IRDCs near the Sun in the first quadrant detected in ^13^CO(1-0) in Simon et al. is not detected in the CS data. This discrepancy arises from the differences in the critical densities between the ^13^CO(1-0) and CS(2-1) lines. We determine that the Midcourse Space Experiment selected IRDCs are not a homogeneous population, and ^13^CO(1-0) traces a population of IRDCs with lower column densities and lower 1.1 mm flux densities in addition to more dense IRDCs detected in CS. Masses of the first quadrant IRDCs are calculated from ^13^CO(1-0) maps. We find a strong peak in the Galactocentric IRDC mass surface density distribution at R_Gal_~4.5kpc.
