Ionization--induced star formation V: Triggering in partially unbound clusters

We present the fourth in a series of papers detailing our SPH study of the effects of ionizing feedback from O--type stars on turbulent star forming clouds. Here, we study the effects of photoionization on a series of initially partially unbound clouds with masses ranging from $10^{4}$--$10^{6}$M$_{\odot}$ and initial sizes from 2.5-45pc. We find that ionizing feedback profoundly affects the structure of the gas in most of our model clouds, creating large and often well-cleared bubble structures and pillars. However, changes in the structures of the embedded clusters produced are much weaker and not well correlated to the evolution of the gas. We find that in all cases, star formation efficiencies and rates are reduced by feedback and numbers of objects increased, relative to control simulations. We find that local triggered star formation does occur and that there is a good correlation between triggered objects and pillars or bubble walls, but that triggered objects are often spatially-mixed with those formed spontaneously. Some triggered objects acquire large enough masses to become ionizing sources themselves, lending support to the concept of propagating star formation. We find scant evidence for spatial age gradients in most simulations, and where we do see them, they are not a good indicator of triggering, as they apply equally to spontaneously-formed objects as triggered ones. Overall, we conclude that inferring the global or local effects of feedback on stellar populations from observing a system at a single epoch is very problematic.Comment: 17 pages, 11 figures (mostly degraded to get under the submission size limit), accepted by MNRA

Ionizing feedback from massive stars in massive clusters III: Disruption of partially unbound clouds

We extend our previous SPH parameter study of the effects of photoionization from O-stars on star-forming clouds to include initially unbound clouds. We generate a set of model clouds in the mass range $10^{4}-10^{6}$M$_{\odot}$ with initial virial ratios $E_{\rm kin}/E_{\rm pot}$=2.3, allow them to form stars, and study the impact of the photoionizing radiation produced by the massive stars. We find that, on the 3Myr timescale before supernovae are expected to begin detonating, the fractions of mass expelled by ionizing feedback is a very strong function of the cloud escape velocities. High-mass clouds are largely unaffected dynamically, while lower-mass clouds have large fractions of their gas reserves expelled on this timescale. However, the fractions of stellar mass unbound are modest and significant portions of the unbound stars are so only because the clouds themselves are initially partially unbound. We find that ionization is much more able to create well-cleared bubbles in the unbound clouds, owing to their intrinsic expansion, but that the presence of such bubbles does not necessarily indicate that a given cloud has been strongly influenced by feedback. We also find, in common with the bound clouds from our earlier work, that many of the systems simulated here are highly porous to photons and supernova ejecta, and that most of them will likely survive their first supernova explosions.Comment: 14 pages, 13 figures (some degraded and greyscaled), accepted by MNRA

Ionisation-induced star formation II: External irradiation of a turbulent molecular cloud

In this paper, we examine numerically the difference between triggered and revealed star formation. We present Smoothed Particle Hydrodynamics (SPH) simulations of the impact on a turbulent 10^4 solar-mass molecular cloud of irradiation by an external source of ionising photons. In particular, using a control model, we investigate the triggering of star formation within the cloud. We find that, although feedback has a dramatic effect on the morphology of our model cloud, its impact on star formation is relatively minor. We show that external irradiation has both positive and negative effects, accelerating the formation of some objects, delaying the formation of others, and inducing the formation of some that would not otherwise have formed. Overall, the calculation in which feedback is included forms nearly twice as many objects over a period of \sim0.5 freefall times (\sim2.4 Myr), resulting in a star--formation efficiency approximately one third higher (\sim4% as opposed to \sim3% at this epoch) as in the control run in which feedback is absent. Unfortunately, there appear to be no observable characteristics which could be used to differentiate objects whose formation was triggered from those which were forming anyway and which were simply revealed by the effects of radiation, although this could be an effect of poor statistics.Comment: 12 pages, 9 figures, accepted by MNRA

The prompt energy release of gamma-ray bursts using a cosmological k-correction

The fluences of gamma-ray bursts (GRBs) are measured with a variety of instruments in different detector energy ranges. A detailed comparison of the implied energy releases of the GRB sample requires, then, an accurate accounting of this diversity in fluence measurements which properly corrects for the redshifting of GRB spectra. Here, we develop a methodology to ``k-correct'' the implied prompt energy release of a GRB to a fixed co-moving bandpass. This allows us to homogenize the prompt energy release of 17 cosmological GRBs (using published redshifts, fluences, and spectra) to two common co-moving bandpasses: 20-2000 keV and 0.1 keV-10 MeV (``bolometric''). While the overall distribution of GRB energy releases does not change significantly by using a k-correction, we show that uncorrected energy estimates systematically undercounts the bolometric energy by ~5% to 600%, depending on the particular GRB. We find that the median bolometric isotropic-equivalent prompt energy release is 2.2 x 10^{53} erg with an r.m.s. scatter of 0.80 dex. The typical estimated uncertainty on a given k-corrected energy measurement is ~20%.Comment: Accepted to the Astronomical Journal. 21 pages (LaTeX) and 4 figure

Morgali, Jim Oral History Interview

Professor of Civil Engineering, Chair of Management Engineering, assistant dean of School of Engineering (1961-1999). Topics include:Served with Henderson McGee, and Robert Heyborne, aided with growth of School of Engineering, and Engineering Co-op Program, assisted with accreditation with engineering program. [Interviewed simultaneously with Robert Hamernik]https://scholarlycommons.pacific.edu/esohc/1094/thumbnail.jp

Hamernik, Robert Oral History Interview

Professor of Civil Engineering, Associate Dean of School of Engineering (1962-1998). Topics include:Assisted with growth of School of Engineering, aided growth of Engineering Co-op Program, assisted with Engineering Council of Professional Development 1970-71, Served with Henderson McGee and Robert Heyborne, specialized in structural design and construction techniques. Interview conducted with Jim Morgali. Only answers to Hamernik are included in transcription.https://scholarlycommons.pacific.edu/esohc/1095/thumbnail.jp

Are the Needs of Industry for Data Processing Programmers Being Adequately Supported by Technical Training Programs in Oklahoma

In 1970 over 40,000 computers were in use in the United States and 1,000 more on order from manufacturers. Every major newspaper had published at least one news article or editorial about computers during 1970. These articles reported how computers function, the speed at which they function, their limitations and how they have, and are continuing to become, a complex part of the business world and social affairs of man