Horizontal-Branch Stars as Sources of the UV Upturn in Early-Type Galaxies

2004 ◽  
Vol 291 (3) ◽  
pp. 223-230 ◽  
Author(s):  
Suk-Jin Yoon ◽  
Young-Wook Lee ◽  
Soo-Chang Rey ◽  
Chang H. Ree ◽  
Sukyoung Ken Yi
Keyword(s):  
Horizontal Branch ◽  
Early Type ◽  
Horizontal Branch Stars ◽  
Uv Upturn

scholarly journals Early-Type Stars

1995 ◽  
Vol 164 ◽  
pp. 119-127
Author(s):  
K.C. Freeman
Keyword(s):  
Main Sequence ◽  
Velocity Dispersion ◽  
Galactic Rotation ◽  
Horizontal Branch ◽  
Early Type ◽  
Horizontal Branch Stars ◽  
The Galaxy ◽  
Stellar Halo ◽  
Early Type Stars ◽  
Insight Into

Away from the young disk, several classes of early type stars are found. They include (i) the old, metal-poor blue horizontal branch stars of the halo and the metal-poor tail of the thick disk; (ii) metal-rich young A stars in a rapidly rotating subsystem but with a much higher velocity dispersion than the A stars of the young disk, and (iii) a newly discovered class of metal-poor young main sequence A stars in a subsystem of intermediate galactic rotation (Vrot ≈ 120 km s−1). The existence and kinematics of these various classes of early type stars provide insight into the formation of the metal-poor stellar halo of the Galaxy and into the continuing accretion events suffered by our Galaxy.

scholarly journals The current status on the UV upturn

2009 ◽  
Vol 5 (S262) ◽  
pp. 147-149
Author(s):  
Sukyoung K. Yi
Keyword(s):  
Elliptical Galaxies ◽  
Current Status ◽  
Horizontal Branch ◽  
Horizontal Branch Stars ◽  
Theoretical Predictions ◽  
Uv Upturn ◽  
Space Observations

AbstractThe UV upturn phenomenon found in giant elliptical galaxies through space observations has been a mystery. Recent GALEX observations have revealed new facts. The most notable is the rarity of UV upturn galaxies. Unlike previous beliefs, UV upturn is found only in less than 10 percent of giant ellitpical galaxies. Another notable finding is that the UV flux has been increasing for the last couple of billion years. This is consistent with the theoretical predictions that suggest hot horizontal branch stars are the main UV sources. Remaining theoretical and observational issues on this topic can be found in another recent review of mine (Yi 2008).

scholarly journals UV color-color relation of early-type galaxies

2012 ◽  
Vol 10 (H16) ◽  
pp. 130-130
Author(s):  
Chang H. Ree ◽  
Hyunjin Jeong ◽  
Kyuseok Oh ◽  
Chul Chung ◽  
Joon Hyeop Lee ◽  
...  
Keyword(s):  
Spectral Shape ◽  
Minority Population ◽  
Horizontal Branch ◽  
Early Type ◽  
Spectral Slope ◽  
Canonical Models ◽  
Data Support ◽  
Uv Excess ◽  
Uv Upturn ◽  
Red Sequence

AbstractThe ultraviolet (UV) color-color relation of early-type galaxies (ETGs) in the nearby universe (0.05 < z < 0.12) is re-examined with the latest GALEX GR6 and SDSS DR7 data. By drawing the FUV – NUV (as a measure of UV temperature) versus FUV – r (as a measure of UV amplitude) color-color diagram for the morphologically-cleaned, spectroscopically-cleaned sample of ~3700 quiescent ETGs, we find that the “old and dead“ ETGs consist of a well-defined sequence in UV colors, the “UV red sequence”, so that the stronger UV excess galaxies should have a harder UV spectral shape systematically. However, the observed UV spectral slope is too steep to be reproduced by the canonical models in which the UV flux is mainly controlled by age or metallicity parameters. The observed data support the helium enhancement scenario in which the UV spectral shape of UV upturn (FUV – NUV < 0.9; FUV – r ~ 6) galaxies may be governed by the minority population of helium-enhanced horizontal-branch (HB) stars.

scholarly journals Extreme Horizontal Branch Stars in Passively Evolving Early Type Galaxies

2012 ◽  
Vol 10 (H16) ◽  
pp. 120-120
Author(s):  
Fabiola Hernández-Pérez ◽  
Gustavo Bruzual
Keyword(s):  
Binary Star ◽  
Horizontal Branch ◽  
Population Synthesis ◽  
Early Type ◽  
Star Evolution ◽  
Horizontal Branch Stars ◽  
Uv Excess ◽  
Ehb Stars

AbstractWe study the effects of including binary star evolution in population synthesis models. We use the Hurley et al. (2002) code to compute binary star evolutionary tracks, and follow the procedure by Han et al. (2002), in particular, the two 2HeWD merger channel, to form EHB stars from a binary pair. We apply the resulting models to study UV excess ETGs.

scholarly journals Non-variable horizontal-branch stars

1997 ◽  
Vol 189 ◽  
pp. 363-368
Author(s):  
Robert T. Rood
Keyword(s):  
Mass Loss ◽  
Physical Basis ◽  
Horizontal Branch ◽  
Loss Process ◽  
Horizontal Branch Stars ◽  
Theoretical Results ◽  
Branch Morphology

For 25 years our ignorance of the physical basis of this mass loss process has been the barrier to progress in understanding horizontal branch morphology. I review some recent observational and theoretical results which may be giving us clues about the nature of the mass loss process.

scholarly journals Rotational broadening and conservation of angular momentum in post-extreme horizontal branch stars

2018 ◽  
Vol 613 ◽  
pp. A66
Author(s):  
G. Fontaine ◽  
M. Latour
Keyword(s):  
Angular Momentum ◽  
Rotation Speed ◽  
Momentum Conservation ◽  
Evolutionary Models ◽  
Horizontal Branch ◽  
Natural Consequence ◽  
Average Value ◽  
Horizontal Branch Stars ◽  
The Moment ◽  
Ehb Stars

We show that the recent realization that isolated post-extreme horizontal branch (post-EHB) stars are generally characterized by rotational broadening with values of V rot sini between 25 and 30 km s−1 can be explained as a natural consequence of the conservation of angular momentum from the previous He-core burning phase on the EHB. The progenitors of these evolved objects, the EHB stars, are known to be slow rotators with an average value of V rot sini of ~7.7 km s−1. This implies significant spin-up between the EHB and post-EHB phases. Using representative evolutionary models of hot subdwarf stars, we demonstrate that angular momentum conservation in uniformly rotating structures (rigid-body rotation) boosts that value of the projected equatorial rotation speed by a factor ~3.6 by the time the model has reached the region of the surface gravity-effective temperature plane where the newly-studied post-EHB objects are found. This is exactly what is needed to account for their observed atmospheric broadening. We note that the decrease of the moment of inertia causing the spin-up is mostly due to the redistribution of matter that produces more centrally-condensed structures in the post-EHB phase of evolution, not to the decrease of the radius per se.

Super-Helium-rich Populations and the Origin of Extreme Horizontal-Branch Stars in Globular Clusters

2005 ◽  
Vol 621 (1) ◽  
pp. L57-L60 ◽  
Author(s):  
Young-Wook Lee ◽  
Seok-Joo Joo ◽  
Sang-Il Han ◽  
Chul Chung ◽  
Chang H. Ree ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Horizontal Branch ◽  
Horizontal Branch Stars

scholarly journals Abundances anomalies and meridional circulation in horizontal branch stars

2009 ◽  
Vol 500 (3) ◽  
pp. 1163-1171 ◽  
Author(s):  
D. Quievy ◽  
P. Charbonneau ◽  
G. Michaud ◽  
J. Richer
Keyword(s):  
Meridional Circulation ◽  
Horizontal Branch ◽  
Horizontal Branch Stars

scholarly journals Study of the Helium Enrichment in Globular Clusters

2009 ◽  
Vol 5 (S262) ◽  
pp. 27-30
Author(s):  
Aldo A. R. Valcarce ◽  
Márcio Catelan
Keyword(s):  
High Precision ◽  
Globular Clusters ◽  
Stellar Populations ◽  
Horizontal Branch ◽  
Previous Generation ◽  
Horizontal Branch Stars

AbstractGlobular clusters (GCs) are spheroidal concentrations typically containing of the order of 105 to 106, predominantly old, stars. Historically, they have been considered as the closest counterparts of the idealized concept of “simple stellar populations.” However, some recent observations suggest than, at least in some GCs, some stars are present that have been formed with material processed by a previous generation of stars. In this sense, it has also been suggested that such material might be enriched in helium, and that blue horizontal branch stars in some GCs should accordingly be the natural progeny of such helium-enhanced stars. In this contribution we show that, at least in the case of M3 (NGC 5272), the suggested level of helium enrichment is not supported by the available, high-precision observations.

scholarly journals The Origin of Extreme Horizontal Branch Stars

1996 ◽  
Vol 466 ◽  
pp. 359 ◽  
Author(s):  
Noella L. D'Cruz ◽  
Ben Dorman ◽  
Robert T. Rood ◽  
Robert W. O'Connell
Keyword(s):  
Horizontal Branch ◽  
Horizontal Branch Stars
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