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

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

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

LINE PROFILES IN THE DIFFUSE INTERSTELLAR BANDS

Author Institution: University of Colorado, Center for Astrophysics and Space; Astronomy,; 389 UCB, Boulder CO 80309-0389; Department of Astronomy and Astrophysics, The University of; Chicago; Department of Chemistry and Department of Astronomy, University; of; Illinois at Urbana-Champaign; Department of Physics and Astronomy, Johns Hopkins University; Space Telescope Science Institute; Department of Physics and Astronomy, Carleton CollegeWe present results of an ongoing study of the line profiles of the Diffuse Interstellar Bands (DIBs) using data from a long-term survey with the Astrophysics Research Consortium Echelle Spectrograph (ARCES) on the 3.5-m telescope at Apache Point Observatory. This high resolution, high signal-to-noise (S/N $\approx$ 1000) dataset contains spectra of nearly 200 sightlines, allowing us to compare profiles of the diffuse bands extracted from a large sample of stars with a wide range of interstellar physical properties. We fit three profiles for comparison to each of the DIBs: a Gaussian, a Lorentzian, and a Drude function. Each profile is characteristic of a different physical origin for the observed absorption lines. Results currently indicate that some of the broadest DIBs exhibit Lorentzian profiles, suggesting rapid internal conversion within a molecule is the type of transition producing these features. The narrower DIBs, however, may have a fundamentally different lineshape from their broad counterparts, suggesting an entirely separate formation mechanism for these lines such as a blend of rotational lines within an electronic transition. Our goal is to characterize and understand the physics of the transition mechanisms in the hopes of placing constraints on the carriers of each of the DIBs in the study

THE APACHE POINT DIFFUSE BANDS SURVEY: EMISSION FROM THE RED RECTANGLE

Author Institution: CASA - University of Colorado; Center for Astronomy \& Physics, University of Chicago; Department of Astronomy, University of California; Department of Astronomy, Space Telescope Science Institute; Department of Physics \& Astronomy, Johns Hopkins UniversityAs an extension of our ongoing observational survey of the diffuse interstellar bands (DIBs), described in a series of talks at this meeting a year ago, we have carried out intensive spectroscopic observations at different positions within the Red Rectangle, a unique emission/reflection nebula associated with the star HD 44179. Emission lines from the Red Rectangle have been tentatively identified with DIBs, suggesting that the analysis of the emission bands might shed light on the nature and the identity of the DIBs carriers. Our new data, which have better spectral resolving power and S/N than previous observations, provide emission band profiles from various locations within the nebula, including the ``whiskers'' or bright arms of the cross-shaped pattern of the biconical nebula, and also selected locations within the nebula but between the whiskers. We will discuss the relationship between the DIBs and the emission bands in the Red Rectangle, in terms of both the general spectral distribution of DIBs as compared to the continuous emission (the so-called extended red emission, or ERE) and the specific matches of Red Rectangle emission bands and interstellar DIBs in absorption. We note a general coincidence between the ERE from the Red Rectangle and the overall distribution of DIBs with wavelength; and we critically evaluate earlier reports that some of the observed emission bands appear to coincide with known DIBs, with progressive wavelength shifts that may be attributed to varying rotational excitation in a moleculer carrier. We also examine the hypothesis that some of the DIB carriers are contributing to both the ERE and the emission bands in the Red Rectangle