Why hot horizontal branch stars can appear redder than red giants
نویسندگان
چکیده
منابع مشابه
Why Hot Horizontal Branch Stars Can Appear Redder Than Red Giants ⋆
In this paper we report on a curious feature in the V , (U − B) color-magnitude diagrams of globular clusters. In our database, we find that a considerable fraction of blue horizontal branch stars, hotter than the instability strip and cooler than the Grundahl et al. (1999) jump (i.e., 6000 ≤ Teff(K)≤ 10000), have (U − B) colors redder than their red giant progenitors. This red incursion is not...
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There is now considerable evidence that horizontal branch (HB) stars hotter than about 11,500 K experience an enormous enhancement of their photospheric iron abundance due to radiative levitation. In globular clusters, the photospheric iron abundance can reach values of [Fe/H] ∼ +0.3, or up to two orders of magnitude higher than the cluster iron abundance. Model atmospheres which take into acco...
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We revisit the problem of why stars become red giants. We modify the physics of a standard stellar evolution code in order to determine what does and what does not contribute to a star becoming a red giant. In particular, we have run tests to try to separate the effects of changes in the mean molecular weight and in the energy generation. The implications for why stars become red giants are dis...
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We present high resolution UVES+VLT spectroscopic observations of 61 stars in the extended blue horizontal branches of the Galactic globular clusters NGC 1904 (M79), NGC 2808, NGC 6093 (M80), and NGC 7078 M15). Our data reveal for the first time the presence in NGC 1904 of a sizable population of fast (vsini ≥ 20 km/s) horizontal branch (HB) rotators, confined to the cool end of the EHB, simila...
متن کاملRotation Velocities of Red and Blue Field Horizontal-Branch Stars
We present measurements of the projected stellar rotation velocities (v sin i) of a sample of 45 candidate field horizontal-branch (HB) stars spanning a wide range of effective temperature, from red HB stars with Teff ' 5000 K to blue HB stars with Teff of 17000 K. Among the cooler blue HB stars (Teff = 7500– 11500 K), we confirm prior studies showing that although a majority of stars rotate at...
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ژورنال
عنوان ژورنال: Astronomy & Astrophysics
سال: 2003
ISSN: 0004-6361,1432-0746
DOI: 10.1051/0004-6361:20030827