arXiv subjects

S. K. Ramsay Howat

Publications and source records attributed to S. K. Ramsay Howat.

4 recordsLinked to original sources

arXiv2005

Imaging and integral field spectroscopy of shocked H2 around G25.65+1.05

Near-infrared imaging of the emission from molecular hydrogen is a powerful method for discovering outflows in star-forming regions. We present new near-infrared images, long slit and integral field spectroscopy of the ultra-compact HII region G25.65+1.05. These new observations reveal shocked H2 emission associated with a bipolar outflow from a young high mass star at the centre of the source. The physical parameters of the outflow are discussed and compared with outflows from lower mass stars.

astro-ph↗

arXiv2003

A search for H2 around pre-main-sequence stars

We present the results of a search for pure rotational molecular hydrogen emission from two pre-main-sequence stars, AB Aur and CQ Tau. Observations were made using MICHELLE, the mid-IR echelle spectrometer at the UK Infrared Telescope. We found some evidence for emission in the J = 4 --> 2 line in AB Aur, but no J = 3 --> 1 line from either star. We derive upper limits on line flux which are significantly smaller than previous line flux estimates based on ISO observations. This suggests that the emission detected by ISO is extended on scales of at least 6 arcsec, and does not come from the disk as previously thought.

astro-ph↗

arXiv2002

Ground-based detection of a vibration-rotation line of HD in Orion

The v =1-0 R(5) line of HD at 2.46um has been detected at the position of brightest line emission of shocked H2 in the Orion Molecular Cloud. The flux in this HD line, when compared to that of the previously detected HD 0--0 R(5) line at 19.43um, suggests that, like the v=1 levels of H2, the v=1 levels of HD are populated in LTE, despite their much higher rates of spontaneous emission compared to H2. The higher than expected population of vibrationally excited HD may be due to chemical coupling of HD to H2 via the reactive collisions HD + H <--> H2 + D in the shocked gas. The deuterium abundance implied by the strengths of these lines relative to those of H2 is (5.1 pm 1.9 x 10^-6.

astro-ph↗

arXiv2000

Excitation of H_2 and HD in shocks and PDRs

Photodissociation regions (PDRs) and shocks give rise to conspicuous emission from rotationally and vibrationally excited molecular hydrogen. This line emission has now been studied with ISO and from the ground in great detail. A remarkable discovery has been that toward the Orion outflow and other shock-excited regions, the H_2 level populations show a very high excitation component. We suggest that these high-excitation populations may arise from non-thermal pumping processes, such as H_2 formation and high-velocity ion-molecule collision in partially dissociative shocks. In PDRs such as NGC 7023 however, formation pumping is always less important than fluorescent pumping. We furthermore present two HD emission line detections toward Orion Peak 1. This enables the first comparison of the H_2 and the HD excitation, which surprisingly turn out to be identical.

astro-ph↗