astro-ph/0209077 [abs, ps, pdf, other] : Title: Confirmation of SBS 1150+599A As An Extremely Metal-Poor Planetary Nebula Authors: George Jacoby (1), John Feldmeier (2), Charles F. Claver (3), Peter M. Garnavich (4), Alberto Noriega-Crespo (5), Howard E. Bond (6), Jason Quinn (4) ((1) WIYN, (2) CWRU, (3) NOAO, (4) U. Notre Dame, (5) SIRTF Science Center, (6) STScI) Comments: 19 pages, 6 figures. Accepted for publication in the Astronomical Journal SBS 1150+599A is a blue stellar object at high galactic latitude discovered in the Second Byurakan Survey. New high-resolution images of SBS 1150+599A are presented, demonstrating that it is very likely to be an old planetary nebula in the galactic halo, as suggested by Tovmassian et al (2001). An H-alpha image taken with the WIYN 3.5-m telescope and its "tip/tilt" module reveals the diameter of the nebula to be 9.2", comparable to that estimated from spectra by Tovmassian et al. Lower limits to the central star temperature were derived using the Zanstra hydrogen and helium methods to determine that the star's effective temperature must be > 68,000K and that the nebula is optically thin. New spectra from the MMT and FLWO telescopes are presented, revealing the presence of strong [Ne V] lambda 3425, indicating that the central star temperature must be > 100,000K. With the revised diameter, new central star temperature, and an improved central star luminosity, we can constrain photoionization models for the nebula significantly better than before. Because the emission-line data set is sparse, the models are still not conclusive. Nevertheless, we confirm that this nebula is an extremely metal-poor planetary nebula, having a value for O/H that is less than 1/100 solar, and possibly as low as 1/500 solar. (253kb) astro-ph/0209080 [abs, ps, pdf, other] : Title: Solar Models: An Historical Overview Authors: John N. Bahcall Comments: Invited talk, Neutrino 2002, Munich, May 2002 I summarize in four slides the 40 years of development of the standard solar model that is used to predict solar neutrino fluxes and then describe the current uncertainties in the predictions. I next dispel the misconception that the p-p neutrino flux is determined by the solar luminosity and present a related formula that gives, in terms of the p-p and 7Be neutrino fluxes, the ratio of the rates of the two primary ways of terminating the p-p fusion chain. I will also attempt to explain why it took so long, about three and a half decades, to reach a consensus view that new physics is being learned from solar neutrino experiments. Finally, I close with a personal confession. (350kb) http://arxiv.org/abs/0804.4473 The Dartmouth Stellar Evolution Database Aaron Dotter, Brian Chaboyer, Darko Jevremovic, Veselin Kostov, E. Baron, J. W. Ferguson (Submitted on 28 Apr 2008) The ever-expanding depth and quality of photometric and spectroscopic observations of stellar populations increase the need for theoretical models in regions of age-composition parameter space that are largely unexplored at present. Stellar evolution models that employ the most advanced physics and cover a wide range of compositions are needed to extract the most information from current observations of both resolved and unresolved stellar populations. The Dartmouth Stellar Evolution Database is a collection of stellar evolution tracks and isochrones that spans a range of [Fe/H] from -2.5 to +0.5, [alpha/Fe] from -0.2 to +0.8 (for [Fe/H] <=0) or +0.2 (for [Fe/H] >0), and initial He mass fractions from Y=0.245 to 0.40. Stellar evolution tracks were computed for masses between 0.1 and 4 Msun, allowing isochrones to be generated for ages as young as 250 Myr. For the range in masses where the core He flash occurs, separate He-burning tracks were computed starting from the zero age horizontal branch. The tracks and isochrones have been transformed to the observational plane in a variety of photometric systems including standard UBV(RI)c, Stromgren uvby, SDSS ugriz, 2MASS JHKs, and HST ACS-WFC and WFPC2. The Dartmouth Stellar Evolution Database is accessible through a website at this http URL where all tracks, isochrones, and additional files can be downloaded. http://stellar.dartmouth.edu/~models/
Copyright © Michael Richmond. This work is licensed under a Creative Commons License.