384 research outputs found
Line Ratios Reveal N2H+ Emission Originates Above the Midplane in TW Hydrae
Line ratios for different transitions of the same molecule have long been
used as a probe of gas temperature. Here we use ALMA observations of the N2H+
J~=~1-0 and J~=~4-3 lines in the protoplanetary disk around TW Hya to derive
the temperature at which these lines emit. We find an averaged temperature of
39~K with a one sigma uncertainty of 2~K for the radial range 0.8-2'',
significantly warmer than the expected midplane temperature beyond 0.5'' in
this disk. We conclude that the N2H+ emission in TW Hya is not emitting from
near the midplane, but rather from higher in the disk, in a region likely
bounded by processes such as photodissociation or chemical reprocessing of CO
and N2 rather than freeze out.Comment: Accepted for publication in ApJ Letters, 5 pages, 1 figur
Richard Bergin reflects on the impact of John Steward’s CHDS thesis, “Applying Technology Acceptance Research to Information Systems Implementation in Fire Service”
The article record may be found at https://www.hsaj.org/articles/17516Sponsored the U. S. Department of Homeland Security’s National Preparedness Directorate, FEMA, CHDS is part of the Naval Postgraduate School (NPS)
Structure and Composition of Molecular Clouds with CN Zeeman Detections I: W3OH
We have carried out a multi-species study of a region which has had previous
measurements of strong magnetic fields through the CN Zeeman effect in order to
to explore the relationship between CN and NH, both of which have
evidence that they remain in the gas phase at densities of 10 - 10
cm. To achieve this we map the 1 arcmin region around the UCHII
region of W3(OH) using the Combined Array for Millimeter-wave Astronomy
(CARMA). Approximately 105 hours of data were collected in multiple array
configurations to produce maps with an effective resolution of
2.5\arcsec at high signal-to-noise in CN, CO, HCN, HCO, NH,
and two continuum bands (91.2 GHz and 112 GHz). These data allow us to compare
tracer molecules associated with both low and high density regions to infer gas
properties. We determine that CARMA resolves out approximately 35% of the CN
emission around W3(OH) when compared with spectra obtained from the IRAM-30
meter telescope. The presence of strong absorption lines towards the continuum
source in three of the molecular transitions infers the presence of a cold,
dark, optically thick region in front of the continuum source. In addition, the
presence of high-velocity emission lines near the continuum source shows the
presence of hot clumpy emission behind the continuum source. These data
determine that future high-resolution interferometric CN Zeeman measurements
which cannot currently be performed (due to technical limitations of current
telescopes) are feasible. We confirm that CN is indeed a good tracer for high
density regions; with certain objects such as W3(OH) it appears to be a more
accurate tracer than NH.Comment: 33 pages, 16 figures. Accepted by Ap
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