arXiv subjects

P. G. Martin

Publications and source records attributed to P. G. Martin.

111 records · Page 7Linked to original sources

arXiv1999

Interstellar Dust in the WIRE to Planck Era

Interstellar dust appears in a number of roles in the interstellar medium. Historically, the most familiar one is as a source of extinction in the optical. Absorbed optical and ultraviolet light heats the dust, whence infrared (including near-infrared to submillimeter) emission, the particular theme of this review. In some distant galaxies, most of the luminosity of the galaxy is thus converted into the infrared, though in the Milky Way the situation is not generally as extreme, except in localized regions of star formation. I briefly review the range of physical conditions in which the dust emits in the interstellar medium and the various sizes of dust probed. Of interest astrophysically are observations of both the spectrum and the spatial distribution of the emission, preferably in combination. In the past fifteen year probes of dust emission have advanced significantly: through IRAS, KAO, COBE experiments, IRTS, ISO, and MSX. Satellite and stratospheric observations of dust emission are complemented by ground-based studies, such as imaging and polarimetry in the submillimeter with the JCMT or imaging of reflected light from dust in the near infrared with 2MASS. Looking ahead, the next decade promises to be equally exciting. I give an overview of some of the distinctive features of facilities anticipated in the near term (WIRE), early in the new millennium (SOFIA, SIRTF), and somewhat further out (IRIS, FIRST, Planck).

astro-ph↗

arXiv1998

Dynamical Evolution and Ionization Structure of an Expanding Superbubble: Application to W4

Recent observations have revealed a superbubble associated with the young stellar cluster OCl 352 near the W4 H II region: a void in H I emission (Normandeau, Taylor, and Dewdney), and a bright shell in H alpha emission (Dennison, Topasna, and Simonetti). We investigate the hypothesis that the bubble is blown by stellar winds from the O-type stars in the association. The Kompaneets approximation is adapted to model a wind-blown bubble in a stratified interstellar medium. We describe some general principles necessary for understanding the dynamics of an expanding bubble and the associated ionization structure in a stratified atmosphere. The Kompaneets model can be used to determine the mean scale height of the ambient medium as well as the age of the bubble. The ionization structure also places constraints on the ambient density near the cluster. We also estimate the surface brightness of the shell and the fraction of ionizing photons which escape the bubble. The prescription we use can be applied to any observed bubble that is blown by the effectively continuous energy output of stellar winds or multiple supernovae. Application to the W4 superbubble shows that the mean scale height of the ambient gas around the cluster is remarkably small, 25 pc for a cluster distance of 2.35 kpc. The age of the bubble is estimated to be about 2.5 Myr, consistent with the notion that the bubble is blown by stellar winds from a very young cluster in which no supernovae have yet occurred.

astro-ph↗

arXiv1996

Physical Conditions in Low Ionization Regions of the Orion Nebula

We reexamine the spectroscopic underpinnings of recent suggestions that [O I] and [Fe II] lines from the Orion H II region are produced in gas where the iron-carrying grains have been destroyed and the electron density is surprisingly high. Our new observations show that previous detections of [O I] 5577 were dominated by telluric emission. Our limits are consistent with a moderate density (10^4 cm^{-3}) photoionized gas. We show that a previously proposed model of the Orion H II region reproduces the observed [O I] and [Fe II] spectrum. These lines are fully consistent with formation in a dusty region of moderate density.

astro-ph↗