12 research outputs found
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 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..