We present results of deep polarization imaging at 1.4GHz with the Dominion Radio Astrophysical Observatory as part of the DRAO Planck Deep Fields project. This deep extragalactic field covers 15.16deg^2^ centered at RA(J2000)=16:14 and DE(J2000)=54:56, has an angular resolution of 42"x62" at the field center, and reaches a sensitivity of 55uJy/beam in Stokes I and 45uJy/beam in Stokes Q and U. We detect 958 radio sources in Stokes I of which 136 are detected in polarization. We present the Euclidean-normalized polarized differential source counts down to 400uJy. These counts indicate that sources have a higher degree of fractional polarization at fainter Stokes I flux density levels than for brighter sources, confirming an earlier result. We find that the majority of our polarized sources are steep-spectrum objects with a mean spectral index of -0.77, and there is no correlation between fractional polarization and spectral index. We also matched deep field sources to counterparts in the Faint Images of the Radio Sky at Twenty Centimeters catalog. Of the polarized sources, 77% show structure at the arcsecond scale whereas only 38% of the sources with no detectable polarization show such structure. The median fractional polarization for resolved sources is 6.8%, while it is 4.4% for compact objects. The polarized radio sources in our deep field are predominantly those sources which are resolved and show the highest degrees of fractional polarization, indicating that the lobe dominated structure may be the source of the highly polarized sources. These resolved radio galaxies dominate the polarized source counts at P_0_=(Q^2^+U^2^)^0.5^<3mJy.
This catalog contains 1692 radio sources observed with the Penticton synthesis telescope at 408 MHz and at 1420 MHz. The catalog is comprised of sources detected in the P-surveys 1P through 9P, 12P through 15P, and 20P through 27P (see the "References" section below). The database was provided by R.Roger & C.R.Purton in May 1990 and an update of the data with further P-surveys is currently in progress.
We have studied the young low-mass pre-main sequence (PMS) stellar population associated with the massive star-forming region DR 21 by using archival X-ray Chandra observations and by complementing them with existing optical and infrared (IR) surveys. The Chandra observations have revealed for the first time a new highly extincted population of PMS low-mass stars previously missed in observations at other wavelengths. The X-ray population exhibits three main stellar density peaks, coincident with the massive star-forming regions, being the DR 21 core the main peak. The cross-correlated X-ray/IR sample exhibits a radial 'Spokes-like' stellar filamentary structure that extends from the DR 21 core towards the northeast. The near-IR data reveal a centrally peaked structure for the extinction, which exhibits its maximum in the DR 21 core and gradually decreases with the distance to the N-S cloud axis and to the cluster centre. We find evidence of a global mass segregation in the full low-mass stellar cluster, and of a stellar age segregation, with the youngest stars still embedded in the N-S cloud, and more evolved stars more spatially distributed. The results are consistent with the scenario where an elongated overall potential well created by the full low-mass stellar cluster funnels gas through filaments feeding stellar formation. Besides the full gravitational well, smaller scale local potential wells created by dense stellar sub-clusters of low-mass stars are privileged in the competition for the gas of the common reservoir, allowing the formation of massive stars. We also discuss the possibility that a stellar collision in the very dense stellar cluster revealed by Chandra in the DR 21 core is the origin of the large-scale and highly energetic outflow arising from this region.
A three-dimensional reddening map for stars within 1100pc of the Sun are presented. Analysis of the distribution of 70 million stars from the 2MASS catalog with the most accurate photometry on the (J-Ks)-Ks diagram supplemented with Monte Carlo simulations has shown that one of the maxima of this distribution corresponds to F-type dwarfs and subgiants with a mean absolute magnitude M_Ks_=2.5m. The shift of this maximum toward large (J-Ks) with increasing Ks reflects the reddening of these stars with increasing heliocentric distance. The distribution of the sample of stars over Ks, l, and b cells with a statistically significant number of stars in each cell corresponds to their distribution over three-dimensional spatial cells. As a result, the reddening E(J-Ks) has been determined with an accuracy of 0.03m for spatial cells with a side of 100pc. All of the known large absorbing clouds within 1100pc of the Sun have manifested themselves in the results obtained. The absorbing matter of the Gould Belt is shown to manifest itself at latitudes up to 40{deg} and within 600pc of the Sun. The size and influence of the Gould Belt may have been underestimated thus far. The absorbing matter at latitudes up to 60{deg} and within 1100pc of the Sun has been found to be distributed predominantly in the first and second quadrants in the southern hemisphere and in the third and fourth quadrants in the northern hemisphere. The E(B-V) should be used together with Rv from Gontcharov (2012AstL...38...12G, Cat. J/PAZh/38/15) and Av from Gontcharov (2012AstL...38...87G, Cat. J/PAZh/38/108).
We present an updated version of the spectroscopic catalogue of white dwarf-main-sequence (WDMS) binaries from the Sloan Digital Sky Survey (SDSS). We identify 938 WDMS binaries within the data releases (DR) 9-12 of SDSS plus 40 objects from DR 1-8 that we missed in our previous works, 646 of which are new. The total number of spectroscopic SDSS WDMS binaries increases to 3294. This is by far the largest and most homogeneous sample of compact binaries currently available. We use a decomposition/fitting routine to derive the stellar parameters of all systems identified here (white dwarf effective temperatures, surface gravities and masses, and secondary star spectral types). The analysis of the corresponding stellar parameter distributions shows that the SDSS WDMS binary population is seriously affected by selection effects. We also measure the Na I {lambda}{lambda} 8183.27, 8194.81 absorption doublet and H {alpha} emission radial velocities (RV) from all SDSS WDMS binary spectra identified in this work. 98 objects are found to display RV variations, 62 of which are new. The RV data are sufficient enough to estimate the orbital periods of three close binaries.
Protoplanetary disks around young stars often contain substructures like rings, gaps, and spirals that could be caused by interactions between the disk and forming planets. We aim to study the young (1-3Myr) star DR Tau in the near-infrared and characterize its disk, which was previously resolved through sub-millimeter interferometry with ALMA, and to search for possible sub-stellar companions embedded into it. We observed DR Tau with VLT/SPHERE both in polarized light (H broad band) and total intensity (in Y, J, H, and K spectral bands). We also performed L' band observations with LBTI/LMIRCam on the Large Binocular Telescope (LBT). We applied differential imaging techniques to analyze the polarized data, using dual beam polarization imaging (DPI), and total intensity data, using both angular and spectral differential imaging (ADI, SDI). We found two previously undetected spirals extending north-east and south of the star, respectively. We further detected an arc-like structure north of the star. Finally a bright, compact and elongated structure was detected at separation of 303+/-10 mas and position angle 21.2+/-3.7 degrees, just at the root of the north-east spiral arm. Since this feature is visible both in polarized light and in total intensity and has a flat spectrum it is likely caused by stellar light scattered by dust. The two spiral arms are at different separation from the star, have very different pitch angles, and are separated by an apparent discontinuity, suggesting they might have a different origin. The very open southern spiral arm might be caused by infalling material from late encounters with cloudlets into the formation environment of the star itself. The compact feature could be caused by interaction with a planet in formation still embedded in its dust envelope and it could be responsible for launching the north-east spiral. We estimate a mass of the putative embedded object of the order of few M Jup .
The Wilson-Devinney program has been used to analyze well-calibrated photometric and new radial velocity data to determine the properties and distance of DS Andromedae, a 1.01 day period, double-lined, totally eclipsing binary system of early-F spectral type and a likely member of the intermediate-age open cluster NGC 752. The determinations of many of the system elements including the distance are robust against modest changes in model assumptions. Third light is present in all passbands at the 10% level. The weighted means of the best-fitting model yield a distance of 477+/-4+/-12 pc, equivalent to (m-M)_0_=8.390+/-0.018+/-0.060 mag, and masses of 1.655+/-0.003+/-0.030 M_Sun_ and 1.087+/-0.005+/-0.040 M_Sun_, radii of 2.086+/-0.003+/-0.013 and 1.255+/-0.005+/-0.012 R_Sun_, and effective temperatures 7056+/-21+/-140 R_Sun_ and 5971+/-33+/-130 K, for components 1 and 2, respectively, where the formal internal uncertainties are followed by conservatively estimated systematic errors. Possible but less satisfactory semidetached models produce more parameter variations and larger mean residuals. The primary star is seen to be at or very close to the main-sequence turnoff at an age of 1.55+/-0.05 Gyr but appears to be too small for its mass, whereas the secondary appears to be too luminous for its temperature and too large for its mass compared to models of single stars.
We use the Gaia DR2 distances of about 700 mid-infrared selected young stellar objects in the benchmark giant molecular cloud Orion A to infer its 3D shape and orientation. We find that Orion A is not the fairly straight filamentary cloud that we see in (2D) projection, but instead a cometary-like cloud oriented toward the Galactic plane, with two distinct components: a denser and enhanced star-forming (bent) Head, and a lower density and star-formation quieter ~75pc long Tail. The true extent of Orion A is not the projected ~40pc but ~90pc, making it by far the largest molecular cloud in the local neighborhood. Its aspect ratio (~30:1) and high column-density fraction (~45%) make it similar to large-scale Milky Way filaments ("bones"), despite its distance to the galactic mid-plane being an order of magnitude larger than typically found for these structures.
The three-dimensional (3D) shape of a galaxy inevitably is tied to how it has formed and evolved and to its dark matter halo. Local extremely metal-poor galaxies (XMPs; defined as having an average gas-phase metallicity <0.1 solar) are important objects for understanding galaxy evolution largely because they appear to be caught in the act of accreting gas from the cosmic web, and their 3D shape may reflect this. Here, we report on the 3D shape of XMPs as inferred from their observed projected minor-to-major axial ratios using a hierarchical Bayesian inference model, which determines the likely shape and orientation of each galaxy, while simultaneously inferring the average shape and dispersion. We selected a sample of 149 XMPs and divided it into three subsamples according to physical size and found that (1) the stellar component of XMPs of all sizes tends to be triaxial, with an intermediate axis ~0.7 times the longest axis and that (2) smaller XMPs tend to be relatively thicker, with the shortest axis going from ~0.15 times the longest axis for the large galaxies to ~0.4 for the small galaxies. We provide the inferred 3D shape and inclination of the individual XMPs in electronic format. We show that our results for the intermediate axis are not clouded by a selection effect against face-on XMPs. We discuss how an intermediate axis significantly smaller than the longest axis may be produced by several mechanisms, including lopsided gas accretion, non-axisymmetric star formation, or coupling with an elongated dark matter halo. Large relative thickness may reflect slow rotation, stellar feedback, or recent gas accretion.
The Disk Substructures at High Angular Resolution Project (DSHARP) used the Atacama Large Millimeter/submillimeter Array (ALMA) to map the 1.25mm continuum of protoplanetary disks at a spatial resolution of ~5au. We present a systematic analysis of annular substructures in the 18 single-disk systems targeted in this survey. No dominant architecture emerges from this sample; instead, remarkably diverse morphologies are observed. Annular substructures can occur at virtually any radius where millimeter continuum emission is detected and range in widths from a few astronomical units to tens of astronomical units. Intensity ratios between gaps and adjacent rings range from near-unity to just a few percent. In a minority of cases, annular substructures coexist with other types of substructures, including spiral arms (3/18) and crescent-like azimuthal asymmetries (2/18). No clear trend is observed between the positions of the substructures and stellar host properties. In particular, the absence of an obvious association with stellar host luminosity (and hence the disk thermal structure) suggests that substructures do not occur preferentially near major molecular snowlines. Annular substructures like those observed in DSHARP have long been hypothesized to be due to planet-disk interactions. A few disks exhibit characteristics particularly suggestive of this scenario, including substructures in possible mean-motion resonance and "double gap" features reminiscent of hydrodynamical simulations of multiple gaps opened by a planet in a low-viscosity disk.