White dwarf observations with the ultraviolet imaging telescope

Landsman, W. B.; Hintzen, P.; Stecher, T. P.

doi:10.1007/3-540-59157-5_207

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(2 citation statements)

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“…Since hot HB stars are important UV emitters (e.g., ; see also Catelan 2008b for a recent review), this is expected to translate into a far UV (integrated) color-HB type correlation, especially when the contribution of bright, individual far-UV sources (such as post-AGB stars), which are present in clusters in non-statistically significant numbers, is removed from estimates of the integrated far UV colors. Landsman et al (2001) and Landsman and Catelan (2009, in preparation) tested this prediction, using integrated far UV fluxes for Galactic globular clusters as summarized by , and including revisions to the far UV photometry based on images taken with the Ultraviolet Imaging Telescope (UIT). The result is shown in Fig.…”

Section: Far-uv Observationsmentioning

confidence: 99%

“…The lines indicate theoretical predictions based on solar-scaled (continuous lines) and α-enhanced (dotted gray lines) abundances. From Landsman et al (2001) and Landsman and Catelan (2009, in preparation) (B2 − R)/(B + V + R) (as well as several other HB morphology parameters, including some of those defined by Fusi Catelan et al 2001a) are better suited for the task. Indeed, Fig.…”

Section: Far-uv Observationsmentioning

confidence: 99%

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Horizontal branch stars: the interplay between observations and theory, and insights into the formation of the Galaxy

Catelan

2009

Astrophys Space Sci

351

430

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We review and discuss horizontal branch (HB) stars in a broad astrophysical context, including both variable and non-variable stars. A reassessment of the Oosterhoff dichotomy is presented, which provides unprecedented detail regarding its origin and systematics. We show that the Oosterhoff dichotomy and the distribution of globular clusters in the HB morphology-metallicity plane both exclude, with high statistical significance, the possibility that the Galactic halo may have formed from the accretion of dwarf galaxies resembling present-day Milky Way satellites such as Fornax, Sagittarius, and the LMC-an argument which, due to its strong reliance on the ancient RR Lyrae stars, is essentially independent of the chemical evolution of these systems after the very earliest epochs in the Galaxy's history. Convenient analytical fits to isochrones in the HB type-[Fe/H] plane are also provided. In this sense, a rediscussion of the second-parameter problem is also presented, focusing on the cases of NGC 288/NGC 362, M13/M3, the extreme outer-halo globular clusters with predominantly red HBs, and the metal-rich globular clusters NGC 6388 and NGC 6441. The recently revived possibility that the helium abundance may play an important role as a second parameter is also addressed, and possible constraints on this scenario discussed. We critically discuss the possibility that the observed properties of HB stars in NGC 6388 and NGC 6441 might be accounted for if these clusters possess a relatively minor population of helium-enriched stars. A technique is M. Catelan is John Simon Guggenheim Memorial Foundation Fellow.M. Catelan ( ) proposed to estimate the HB types of extragalactic globular clusters on the basis of integrated far-UV photometry. The importance of bright type II Cepheids as tracers of faint blue HB stars in distant systems is also emphasized. The relationship between the absolute V magnitude of the HB at the RR Lyrae level and metallicity, as obtained on the basis of trigonometric parallax measurements for the star RR Lyr, is also revisited. Taking into due account the evolutionary status of RR Lyr, the derived relation implies a true distance modulus to the LMC of (m-M) 0 = 18.44 ± 0.11. Techniques providing discrepant slopes and zero points for the M V (RRL)-[Fe/H] relation are briefly discussed. We provide a convenient analytical fit to theoretical model predictions for the period change rates of RR Lyrae stars in globular clusters, and compare the model results with the available data. Finally, the conductive opacities used in evolutionary calculations of low-mass stars are also investigated.

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Section: Far-uv Observationsmentioning

confidence: 99%

Section: Far-uv Observationsmentioning

confidence: 99%