Fluctuations in ISM Thermal Pressures Measured from C I Observations

Details Fluctuations in ISM Thermal Pressures Measured from C I Observations Fluctuations in ISM Thermal Pressures Measured from C I Observations

Jul 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aspc..365...51j&link_type=abstract

SINS - Small Ionized and Neutral Structures in the Diffuse Interstellar Medium ASP Conference Series, Vol. 365, Proceedings of t

Astronomy and Astrophysics

Astronomy

9

Scientific paper

The ground electronic state of the neutral carbon atom is split into three fine-structure levels whose relative populations are determined by the balance between collisional excitations (and de-excitations) and radiative decay. High resolution absorption-line spectroscopy of stars in the ultraviolet reveal how much these populations vary with radial velocity and from one location to the next, which in turn indicate the magnitude of changes in thermal pressures and how they relate to the gas kinematics. We now report on our analysis of nearly all of the suitable high-resolution spectra in the HST archive, which represents a five-fold increase in coverage beyond that of our original survey of 21 stars published in 2001 (ApJS, 137, 297). We conclude that converging and diverging flows within a turbulent medium are responsible for the pressure changes, and that the barytropic index of the gas is higher than that based on predictions for thermal equilibrium. This near adiabatic behavior suggests that most of the pressure changes occur on scales as small as about 50 AU, where the characteristic times for such changes are much shorter than the thermal equilibration times. The raw results for measured pressures are weighted by the C I densities, which in turn are influenced by ionization equilibria. We correct for this effect when we derive an H I mass-weighted pressure distribution. This distribution is centered at p/k=2700 {cm}-3 K, and there is evidence that very small amounts of gas at pressures greater than p/k=105 cm-3 K may also be present.

Affiliated with

Also associated with

No associations

Rating

Fluctuations in ISM Thermal Pressures Measured from C I Observations does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Fluctuations in ISM Thermal Pressures Measured from C I Observations, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fluctuations in ISM Thermal Pressures Measured from C I Observations will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1660699