Massive star-formation toward G28.87+0.07 (IRAS 18411-0338) investigated by means of maser kinematics and radio to infrared, continuum observations

We used the Very Long Baseline Array (VLBA) and the European VLBI Network (EVN) to perform phase-referenced VLBI observations of the three most powerful maser transitions associated with the high-mass star-forming region G28.87+0.07: the 22.2 GHz H$_{2}$O, 6.7 GHz CH$_{3}$OH, and 1.665 GHz OH lines. We also performed VLA observations of the radio continuum emission at 1.3 and 3.6 cm and Subaru observations of the continuum emission at 24.5 $\mu$m. Two centimeter continuum sources are detected and one of them (named "HMC") is compact and placed at the center of the observed distribution of H$_{2}$O, CH$_{3}$OH and OH masers. The bipolar distribution of line-of-sight (l.o.s) velocities and the pattern of the proper motions suggest that the water masers are driven by a (proto)stellar jet interacting with the dense circumstellar gas. The same jet could both excite the centimeter continuum source named "HMC" (interpreted as free-free emission from shocked gas) and power the molecular outflow observed at larger scales -- although one cannot exclude that the free-free continuum is rather originating from a hypercompact \ion{H}{2} region. At 24.5 $\mu$m, we identify two objects separated along the north-south direction, whose absolute positions agree with those of the two VLA continuum sources. We establish that $\sim$90% of the luminosity of the region ($\sim$\times10^{5} L_\sun$) is coming from the radio source "HMC", which confirms the existence of an embedded massive young stellar object (MYSO) exciting the masers and possibly still undergoing heavy accretion from the surrounding envelope.Comment: Accepted for publication in Ap

Studies of Diffuse Interstellar Bands. V. Pairwise Correlations of Eight Strong DIBs and Neutral Hydrogen, Molecular Hydrogen, and Color Excess

We establish correlations between equivalent widths of eight diffuse interstellar bands (DIBs), and examine their correlations with atomic hydrogen, molecular hydrogen, and EB-V . The DIBs are centered at \lambda\lambda 5780.5, 6204.5, 6283.8, 6196.0, 6613.6, 5705.1, 5797.1, and 5487.7, in decreasing order of Pearson\^as correlation coefficient with N(H) (here defined as the column density of neutral hydrogen), ranging from 0.96 to 0.82. We find the equivalent width of \lambda 5780.5 is better correlated with column densities of H than with E(B-V) or H2, confirming earlier results based on smaller datasets. We show the same is true for six of the seven other DIBs presented here. Despite this similarity, the eight strong DIBs chosen are not well enough correlated with each other to suggest they come from the same carrier. We further conclude that these eight DIBs are more likely to be associated with H than with H2, and hence are not preferentially located in the densest, most UV shielded parts of interstellar clouds. We suggest they arise from different molecules found in diffuse H regions with very little H (molecular fraction f<0.01). Of the 133 stars with available data in our study, there are three with significantly weaker \lambda 5780.5 than our mean H-5780.5 relationship, all of which are in regions of high radiation fields, as previously noted by Herbig. The correlations will be useful in deriving interstellar parameters when direct methods are not available. For instance, with care, the value of N(H) can be derived from W{\lambda}(5780.5).Comment: Accepted for publication in The Astrophysical Journal; 37 pages, 11 figures, 6 table

The Bolocam Galactic Plane Survey: Survey Description and Data Reduction

We present the Bolocam Galactic Plane Survey (BGPS), a 1.1 mm continuum survey at 33" effective resolution of 170 square degrees of the Galactic Plane visible from the northern hemisphere. The survey is contiguous over the range -10.5 < l < 90.5, |b| < 0.5 and encompasses 133 square degrees, including some extended regions |b| < 1.5. In addition to the contiguous region, four targeted regions in the outer Galaxy were observed: IC1396, a region towards the Perseus Arm, W3/4/5, and Gem OB1. The BGPS has detected approximately 8400 clumps over the entire area to a limiting non-uniform 1-sigma noise level in the range 11 to 53 mJy/beam in the inner Galaxy. The BGPS source catalog is presented in a companion paper (Rosolowsky et al. 2010). This paper details the survey observations and data reduction methods for the images. We discuss in detail the determination of astrometric and flux density calibration uncertainties and compare our results to the literature. Data processing algorithms that separate astronomical signals from time-variable atmospheric fluctuations in the data time-stream are presented. These algorithms reproduce the structure of the astronomical sky over a limited range of angular scales and produce artifacts in the vicinity of bright sources. Based on simulations, we find that extended emission on scales larger than about 5.9' is nearly completely attenuated (> 90%) and the linear scale at which the attenuation reaches 50% is 3.8'. Comparison with other millimeter-wave data sets implies a possible systematic offset in flux calibration, for which no cause has been discovered. This presentation serves as a companion and guide to the public data release through NASA's Infrared Processing and Analysis Center (IPAC) Infrared Science Archive (IRSA). New data releases will be provided through IPAC IRSA with any future improvements in the reduction.Comment: Accepted for publication in Astrophysical Journal Supplemen

A New FUSE Survey of Interstellar HD

We have used archival FUSE data to complete a survey of interstellar HD in 41 lines of sight with a wide range of extinctions. This follow up to an earlier survey was made to further assess the utility of HD as a cosmological probe; to analyze the HD formation process; and to see what trends with other interstellar properties were present in the data. We employed the curve-of-growth method, supported by line profile fitting, to derive accurate column densities of HD. We find that the N(HD)/2N(H2) ratio is substantially lower than the atomic D/H ratio and conclude that the molecular ratio has no bearing on cosmology, because local processes are responsible for the formation of HD. Based on correlations with E(B-V), H2, CO, and iron depletion, we find that HD is formed in the densest portion of the clouds; the slope of the logN(HD)/log(H2) correlation is greater than 1.0, caused by the destruction rate of HD declining more slowly than that of H2; and, as a sidelight, that the depletions are density dependent.Comment: 30 pages, 13 figures; Accepted for publication in Ap

The Bolocam Galactic Plane Survey: II. Catalog of The Image Data

We present a catalog of 8358 sources extracted from images produced by the Bolocam Galactic Plane Survey (BGPS). The BGPS is a survey of the millimeter dust continuum emission from the northern Galactic plane. The catalog sources are extracted using a custom algorithm, Bolocat, which was designed specifically to identify and characterize objects in the large-area maps generated from the Bolocam instrument. The catalog products are designed to facilitate follow-up observations of these relatively unstudied objects. The catalog is 98% complete from 0.4 Jy to 60 Jy over all object sizes for which the survey is sensitive ( \u3c 3\u27.5). We find that the sources extracted can best be described as molecular clumps-large dense regions in molecular clouds linked to cluster formation. We find that the flux density distribution of sources follows a power law with dN/dS alpha S(-2.4+/-0.1) and that the mean Galactic latitude for sources is significantly below the midplane: \u3c b \u3e = (-0 degrees.095 +/- 0 degrees.001)

The Bolocam Galactic Plane Survey IV: 1.1 and 0.35 mm Dust Continuum Emission in the Galactic Center Region

The Bolocam Galactic Plane Survey (BGPS) data for a six square degree region of the Galactic plane containing the Galactic center is analyzed and compared to infrared and radio continuum data. The BGPS 1.1 mm emission consists of clumps interconnected by a network of fainter filaments surrounding cavities, a few of which are filled with diffuse near-IR emission indicating the presence of warm dust or with radio continuum characteristic of HII regions or supernova remnants. New 350 {\mu}m images of the environments of the two brightest regions, Sgr A and B, are presented. Sgr B2 is the brightest mm-emitting clump in the Central Molecular Zone and may be forming the closest analog to a super star cluster in the Galaxy. The Central Molecular Zone (CMZ) contains the highest concentration of mm and sub-mm emitting dense clumps in the Galaxy. Most 1.1 mm features at positive longitudes are seen in silhouette against the 3.6 to 24 {\mu}m background observed by the Spitzer Space Telescope. However, only a few clumps at negative longitudes are seen in absorption, confirming the hypothesis that positive longitude clumps in the CMZ tend to be on the near-side of the Galactic center, consistent with the suspected orientation of the central bar in our Galaxy. Some 1.1 mm cloud surfaces are seen in emission at 8 {\mu}m, presumably due to polycyclic aromatic hydrocarbons (PAHs). A ~0.2\degree (~30 pc) diameter cavity and infrared bubble between l \approx 0.0\degree and 0.2\degree surrounds the Arches and Quintuplet clusters and Sgr A. The bubble contains several clumpy dust filaments that point toward Sgr A\ast; its potential role in their formation is explored. [abstract truncated]Comment: 76 pages, 22 figures, published in ApJ: http://iopscience.iop.org/0004-637X/721/1/137

THE CHEMISTRY OF CANDIDATE MOLECULAR ION CARRIERS OF THE DIFFUSE INTERSTELLAR BANDS

Author Institution: Center for Astrophysics and Space Astronomy, University of Colorado,; 389 UCB, Boulder, CO 80309; Department of Chemistry and Biochemistry,; University of Colorado, 215 UCB, Boulder, CO 80309; Center for Astrophysics and Space Astronomy, University of Colorado,; 389 UCB, Boulder, CO 80309; Department of Chemistry and Biochemistry,; University of Colorado, 215 UCB, Boulder, CO 80309Our group at Colorado has been exploring the diffuse interstellar band (DIB) problem by conducting laboratory experiments to measure chemical reaction rates of molecular ions that have been proposed as DIBs carriers. Our facility consists of a Flowing Afterglow Selected Ion Flow Tube (FA-SIFT), into which we inject ions selected by a quadrupole mass spectrometer which are then allowed to react in the flow tube with neutral species expected to be abundant in the diffuse interstellar environments where the DIBs form. The reaction products are then measured using a second quadrupole mass spectrometer. To date we have focused our attention on PAH cations and carbon chain anions, both of which have been proposed as DIBs carriers. In general we find that PAH cations become hydrogenated by the addition of one or two hydrogen atoms when reacting with atomic or molecular hydrogen, while reaction rates with neutral oxygen and nitrogen typically yield CO and HCN or adducts, again with high reaction rates. We conclude that in the diffuse ISM PAH cations will generally be hydrogenated, so that the protonated forms are the species one should consider as DIBs candidates if PAH cations are viable at all. We find that carbon chain anions, up to C$_9$$^-$, are very quickly destroyed by reactions with H atoms and are not chemically viable candidates as the DIBs carriers. Current work, which will be emphasized in this talk, is aimed at measurements of larger PAH cations than previously studied, to see whether the trends already observed continue as we progress to larger species

VELOCITY STRUCTURE IN THE DIFFUSE INTERSTELLAR BANDS

Author Institution: Center for Astrophysics and Space Astronomy, University of Colorado; Department of Astronomy and Astrophysics, The University of Chicago; Departments of Chemistry and Astronomy, University of; Illinois at Urbana-Champaign; Department of Physics and Astronomy, Johns Hopkins University; Space Telescope Science Institute; Department of Physics, Embry-Riddle Aeronautical UniversityWe present results of a search for velocity structure in the Diffuse Interstellar Bands (DIBs) using data from a four-year survey using the Astrophysics Research Consortium Echelle Spectrograph (ARCES) at the 3.5-m telescope at Apache Point Observatory. This high resolution, high signal-to-noise (S/N $\sim$ 1000) database contains spectra of nearly 200 sight lines. A handful of these sight lines shows evidence of clear velocity structure in the atomic optical absorption lines in the spectrum. We use these observed velocity components as a template to look for the same component structure in the DIBs. Several DIBs in the lines of sight to be presented show possible evidence of velocity structure. The complete results of our analysis will be presented and discussed in the context of the implications this study may have for furthering our understanding of the nature of the diffuse interstellar bands

THE NEARLY PERFECT CORRELATION BETWEEN THE DIFFUSE INTERSTELLAR BANDS λλ\lambda\lambda6196.0 AND 6613.6

Author Institution: University of Illinois at Urbana-Champaign, Urbana, IL 61801; Univeristy of Virginia, Charlottesville, VA 22904; Carthage College, Kenosha, WI 53140; University of Chicago, Chicago, IL 60637; Space Telescope Science Institute, Baltimore, MD 21218; University of Chicago, Yerkes Observatory, Williams Bay, WI 53191; Embry-Riddle Aeronautical University, Prescott, AZ 86301; University of Colorado, Boulder, CO 80309; Johns Hopkins University, Baltimore, MD 21218; University of Illinois at Urbana-Champaign, Urbana, IL 61801As part of our long-term survey of the diffuse interstellar bands (DIBs) at the Apache Point Observatory, we found that the equivalent widths of $\lambda\lambda$6196.0 and 6613.6 are extremely well correlated, with a correlation coefficient of 0.986 in a diverse sample of 114 diffuse cloud sightlines. The observations are statistically consistent with a perfect correlation if the observational errors have been underestimated by a factor of two. The quality of this correlation far exceeds other previously studied correlations, for example those between the $\lambda$5780.5 DIB and quantities such as the color excess or atomic hydrogen column density. The very tight correlation between these two DIBs strongly suggests that they may represent the first pair of DIBs known to be caused by the same molecular carrier. However, an explanation of how a single carrier can produce bands with such different linewidths and band shapes is still needed