Ultraviolet HST Spectroscopy of Planck Cold Clumps. (arXiv:1901.05012v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Dirks_C/0/1/0/all/0/1">Cody Dirks</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Meyer_D/0/1/0/all/0/1">David M. Meyer</a>
We report results of the first study utilizing the ultraviolet capabilities
of the Hubble Space Telescope to investigate a sample of Planck Galactic Cold
Clump (PGCC) sources. We have selected high-resolution spectra toward 25 stars
that contain a multitude of interstellar absorption lines associated with the
interstellar medium (ISM) gas within these PGCC sources, including carbon
monoxide (CO), C I and O I. By building cloud-component models of the
individual absorption components present in these spectra, we can identify and
isolate components associated with the PGCC sources, allowing for a more
accurate investigation of the ISM behavior within these sources. Despite
probing a broad range of overall sightline properties, we detect CO along each
sightline. Sightlines with CO column density N(CO)$~>~$10$^{15}~$cm$^{-2}$
exhibit spatial dependence in N(CO) and CO/C I, while sightlines with
N(CO)$~<~$10$^{15}~$cm$^{-2}$ show no such spatial dependence. Differences
between N(H$_2$) values derived from UV absorption and dust emission suggest
structure in the spatial distribution of N(H$_2$), where "CO-bright" sightlines
are associated with PGCC sources embedded within smooth translucent envelopes,
and "CO-dark" sightlines are associated with PGCC sources embedded in patchier
environments containing more diffuse gas.
We report results of the first study utilizing the ultraviolet capabilities
of the Hubble Space Telescope to investigate a sample of Planck Galactic Cold
Clump (PGCC) sources. We have selected high-resolution spectra toward 25 stars
that contain a multitude of interstellar absorption lines associated with the
interstellar medium (ISM) gas within these PGCC sources, including carbon
monoxide (CO), C I and O I. By building cloud-component models of the
individual absorption components present in these spectra, we can identify and
isolate components associated with the PGCC sources, allowing for a more
accurate investigation of the ISM behavior within these sources. Despite
probing a broad range of overall sightline properties, we detect CO along each
sightline. Sightlines with CO column density N(CO)$~>~$10$^{15}~$cm$^{-2}$
exhibit spatial dependence in N(CO) and CO/C I, while sightlines with
N(CO)$~<~$10$^{15}~$cm$^{-2}$ show no such spatial dependence. Differences
between N(H$_2$) values derived from UV absorption and dust emission suggest
structure in the spatial distribution of N(H$_2$), where “CO-bright” sightlines
are associated with PGCC sources embedded within smooth translucent envelopes,
and “CO-dark” sightlines are associated with PGCC sources embedded in patchier
environments containing more diffuse gas.
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