The Production of HI in Photodissociation Regions and A Comparison with CO(1-0) Emission

The gas at the surfaces of molecular clouds in galaxies is heated and dissociated by photons from young stars both near and far. HI resulting from the dissociation of molecular hydrogen H2 emits hyperfine line emission at 21 cm, and warmed CO emits dipole rotational lines such as the 2.6 mm line of CO(1-0). We use previously developed models for photodissociation regions (PDRs) to compute the intensities of these HI and CO(1-0) lines as a function of the total volume density n in the cloud and the far ultraviolet flux G0 incident upon it and present the results in units familiar to observers. The intensities of these two lines behave differently with changing physical conditions in the PDR, and, taken together, the two lines can provide a ground-based radio astronomy diagnostic for determining n and G0 separately in distant molecular clouds. This diagnostic is particularly useful in the range Gzero <~ 100, 10 cm^{-3} <~ n <~ 10^5 cm^{-3}, which applies to a large fraction of the volume of the interstellar medium in galaxies. If the molecular cloud is located near discrete sources of far-UV (FUV) emission, the PDR-generated HI and CO(1-0) emission on the cloud surface can be more easily identified, appearing as layered ``blankets'' or ``blisters'' on the side of the cloud nearest to the FUV source. As an illustration, we consider the Galactic object G216 -2.5, i.e. ``Maddalena's Cloud'', which has been previously identified as a large PDR in the Galaxy. We determine that this cloud has n ~ 200 cm^{-3}, G0 ~ 0.8, consistent with other data.Comment: 13 Pages, 3 Figures. Accepted for publication in the Astrophysical Journa

SPECTRAL PARAMETERS FROM BLENDED HCl DOUBLETS

Author Institution: Astronomy Research Facility, University of Massachusetts AmherstHere experimental tests of the selection theory for isolated strong spectral lines (Appl. Opt. 11, 2664, Nov. 1972), made with HCl gas in a 3.5 meter absorption path, are reported. At pressures between 1 and 760 torr, measured equivalent widths of sequentially pressure blended isotopic doublets are intercompared with widths predicted from published line parameters. Prior measurements of S and $\gamma$ for lines in the HCl fundamental band agree only in the upper R branch. These lines test the procedure. Resolution of the disagreement in the lower R branch and in the entire P branch --- a further purpose of this study --- is then discussed. With this long path at room temperature, absorption lines from high rotational transitions become evident at the greatest pressures. Their parameters and frequency residences are evaluated. The conformity of these observations to the assumed Lorentz profile, and thereby the validity of parameters faithful to such contours, will then be scrutinized

The Benefits from Marriage and Religion in the United States: A Comparative Analysis

In the United States, married people have better outcomes on a variety of measures of wellbeing than do single persons. People who participate in religious activities show similar advantages relative to those who have no religious involvement. This article présents a comparative analysis of these two social institutions: marriage and religion. A critical review of the literature on how religious involvement and being married affect a range of child and adult outcomes provides evidence of generally positive effects. Religion and marriage have an impact on many of the same domains of life, and there are remarkable similarities in the mechanisms through which they exert an influence. Copyright 2003 by The Population Council, Inc..