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Record 15 of 51355
Hot HB Stars in Globular Clusters: Physical Parameters and Consequences for Theory. VI; The Second Parameter Pair M 3 and M 13
Availability: Go to Request Form
Author and Affiliation:
Moehler, S.(Institut fuer Theoretische Astrophysik, Kiel, Germany)
Landsman, W. B.(Science Systems and Applications, Inc., Greenbelt, MD, United States)
Sweigart, A. V.(NASA Goddard Space Flight Center, Greenbelt, MD, United States)
Grundahl, F.(Aarhus Univ., Inst. of Physics and Astronomy, Denmark)
Abstract: We present the results of spectroscopic analyses of hot horizontal branch (HB) stars in M 13 and M 3, which form a famous "second parameter" pair. F rom the spectra and Stromgren photometry we derived - for the first time in M 13 - atmospheric parameters (effective temperature and surface gravity). For stars with Stromgren temperatures between 10,000 and 12,000 K we found excellent agreement between the atmospheric parameters derived from Stromgren photometry and those derived from Balmer line profile fits. However, for cooler stars there is a disagreement in the parameters derived by the two methods, for which we have no satisfactory explanation. Stars hotter than 12,000 K show evidence for helium depletion and iron enrichment, both in M 3 and M 13. Accounting for the iron enrichment substantially improves the agreement with canonical evolutionary models, although the derived gravities and masses are still somewhat too low. This remaining discrepancy may be an indication that scaled-solar metal-rich model atmospheres do not adequately represent the highly non-solar abundance ratios found in blue HB stars affected by diffusion. We discuss the effects of an enhancement in the envelope helium abundance on the atmospheric parameters of the blue HB stars, as might be caused by deep mixing on the red giant branch or primordial pollution from an earlier generation of intermediate mass asymptotic giant branch stars. Key words. Stars: atmospheres - Stars: evolution - Stars: horizontal branch - Globular clusters: individual: M 3 - Globular clusters: individual: M 13
Publication Date: Jan 01, 2003
Document ID:
(Acquired Mar 23, 2004)
Subject Category: ASTROPHYSICS
Report/Patent Number: astro-ph/0304475v1
Document Type: Preprint
Contract/Grant/Task Num: DLR-50-OR-96029-ZA
Financial Sponsor: NASA Goddard Space Flight Center; Greenbelt, MD, United States
Deutsche Forschungsanstalt fuer Luft- und Raumfahrt; Germany
Organization Source: NASA Goddard Space Flight Center; Greenbelt, MD, United States
Description: 15p; In English; Original contains black and white illustrations
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright; Distribution as joint owner in the copyright
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