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F Grundahl - One of the best experts on this subject based on the ideXlab platform.

  • hot hb stars in globular clusters physical Parameters and consequences for theory vi the second Parameter Pair m 3 and m 13
    arXiv: Astrophysics, 2003
    Co-Authors: S Moehler, W B Landsman, Allen V Sweigart, F Grundahl
    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. From the spectra and Stroemgren photometry we derived -- for the first time in M 13 -- atmospheric Parameters (effective temperature and surface gravity). For stars with Stroemgren temperatures between 10,000 and 12,000 K we found excellent agreement between the atmospheric Parameters derived from Stroemgren 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.

  • hot hb stars in globular clusters physical Parameters and consequences for theory vi the second Parameter Pair m 3 and m 13
    Astronomy and Astrophysics, 2003
    Co-Authors: S Moehler, W B Landsman, Allen V Sweigart, F Grundahl
    Abstract:

    We present the results of spectroscopic analyses of hot horizontal branch (HB) stars in M13 and M3, which form a famous second Parameter Pair. From the spectra we derived - for the first time in M13 - atmospheric Parameters (effective temperature and surface gravity) as well as abundances of helium, magnesium, and iron. Consistent with analyses of hot HB stars in other globular clusters we find evidence for helium depletion and iron enrichment in stars hotter than about 12,000 K in both M3 and M13. 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 with radiative levitation. 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.

S Moehler - One of the best experts on this subject based on the ideXlab platform.

  • hot hb stars in globular clusters physical Parameters and consequences for theory vi the second Parameter Pair m 3 and m 13
    arXiv: Astrophysics, 2003
    Co-Authors: S Moehler, W B Landsman, Allen V Sweigart, F Grundahl
    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. From the spectra and Stroemgren photometry we derived -- for the first time in M 13 -- atmospheric Parameters (effective temperature and surface gravity). For stars with Stroemgren temperatures between 10,000 and 12,000 K we found excellent agreement between the atmospheric Parameters derived from Stroemgren 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.

  • hot hb stars in globular clusters physical Parameters and consequences for theory vi the second Parameter Pair m 3 and m 13
    Astronomy and Astrophysics, 2003
    Co-Authors: S Moehler, W B Landsman, Allen V Sweigart, F Grundahl
    Abstract:

    We present the results of spectroscopic analyses of hot horizontal branch (HB) stars in M13 and M3, which form a famous second Parameter Pair. From the spectra we derived - for the first time in M13 - atmospheric Parameters (effective temperature and surface gravity) as well as abundances of helium, magnesium, and iron. Consistent with analyses of hot HB stars in other globular clusters we find evidence for helium depletion and iron enrichment in stars hotter than about 12,000 K in both M3 and M13. 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 with radiative levitation. 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.

Allen V Sweigart - One of the best experts on this subject based on the ideXlab platform.

  • hot hb stars in globular clusters physical Parameters and consequences for theory vi the second Parameter Pair m 3 and m 13
    arXiv: Astrophysics, 2003
    Co-Authors: S Moehler, W B Landsman, Allen V Sweigart, F Grundahl
    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. From the spectra and Stroemgren photometry we derived -- for the first time in M 13 -- atmospheric Parameters (effective temperature and surface gravity). For stars with Stroemgren temperatures between 10,000 and 12,000 K we found excellent agreement between the atmospheric Parameters derived from Stroemgren 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.

  • hot hb stars in globular clusters physical Parameters and consequences for theory vi the second Parameter Pair m 3 and m 13
    Astronomy and Astrophysics, 2003
    Co-Authors: S Moehler, W B Landsman, Allen V Sweigart, F Grundahl
    Abstract:

    We present the results of spectroscopic analyses of hot horizontal branch (HB) stars in M13 and M3, which form a famous second Parameter Pair. From the spectra we derived - for the first time in M13 - atmospheric Parameters (effective temperature and surface gravity) as well as abundances of helium, magnesium, and iron. Consistent with analyses of hot HB stars in other globular clusters we find evidence for helium depletion and iron enrichment in stars hotter than about 12,000 K in both M3 and M13. 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 with radiative levitation. 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.

W B Landsman - One of the best experts on this subject based on the ideXlab platform.

  • hot hb stars in globular clusters physical Parameters and consequences for theory vi the second Parameter Pair m 3 and m 13
    arXiv: Astrophysics, 2003
    Co-Authors: S Moehler, W B Landsman, Allen V Sweigart, F Grundahl
    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. From the spectra and Stroemgren photometry we derived -- for the first time in M 13 -- atmospheric Parameters (effective temperature and surface gravity). For stars with Stroemgren temperatures between 10,000 and 12,000 K we found excellent agreement between the atmospheric Parameters derived from Stroemgren 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.

  • hot hb stars in globular clusters physical Parameters and consequences for theory vi the second Parameter Pair m 3 and m 13
    Astronomy and Astrophysics, 2003
    Co-Authors: S Moehler, W B Landsman, Allen V Sweigart, F Grundahl
    Abstract:

    We present the results of spectroscopic analyses of hot horizontal branch (HB) stars in M13 and M3, which form a famous second Parameter Pair. From the spectra we derived - for the first time in M13 - atmospheric Parameters (effective temperature and surface gravity) as well as abundances of helium, magnesium, and iron. Consistent with analyses of hot HB stars in other globular clusters we find evidence for helium depletion and iron enrichment in stars hotter than about 12,000 K in both M3 and M13. 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 with radiative levitation. 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.

R A Schommer - One of the best experts on this subject based on the ideXlab platform.

  • hubble space telescope wfpc2 color magnitude diagrams of halo globular clusters in m33 implications for the early formation history of the local group
    The Astrophysical Journal, 1998
    Co-Authors: Ata Sarajedini, D Geisler, Paul Harding, R A Schommer
    Abstract:

    We have constructed color-magnitude diagrams for 10 globular clusters in the halo of the nearby spiral galaxy M33 based on Hubble Space Telescope Wide Field Planetary Camera 2 observations in the F555W (~V) and F814W (~I) filters. These data reveal the morphology of the horizontal branch (HB) and allow us to estimate the cluster metallicity using the shape and color of the red giant branch. The principal result we report herein is that eight of the 10 clusters possess exclusively red HB morphologies and yet their metallicities are as metal poor as [Fe/H]=-1.6. Indeed, these eight clusters basically present only giant branch clumps reminiscent of intermediate-age star clusters in the Magellanic Clouds. In addition, two of the clusters form a second Parameter Pair that have similar metallicities but very disparate HB types. Under the assumption that cluster age is the global second Parameter, the average age of halo globular clusters in M33 appears to be a few gigayears younger than halo clusters in the Milky Way. Using the observed properties of HB stars in M31 and M33, along with published main-sequence turnoff ages for the globular clusters in the Milky Way, LMC, SMC, and the Sagittarius dwarf spheroidal (Sgr), we attempt to sketch the early formation history of these galaxies. This indicates that the Milky Way, M31, M33, the LMC, and Sgr all experienced their first epoch of cluster formation soon after the big bang. And 3-4 Gyr later, the SMC began to form its first generation of clusters; the bulk of the M33 clusters formed later still. We note that the halo clusters in M33 formed over a much larger time period than those in the Milky Way and M31.