Issue |
A&A
Volume 420, Number 2, June III 2004
|
|
---|---|---|
Page(s) | 605 - 617 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20035699 | |
Published online | 28 May 2004 |
The ubiquitous nature of the horizontal branch second U-jump*
A link with the Blue Hook scenario?
1
Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy e-mail: [piotto,bedin,ortolani,recio,deangeli]@pd.astro.it
2
INAF - Osservatorio Astronomico di Collurania, Via M. Maggini, 64100 Teramo, Italy e-mail: cassisi@te.astro.it
3
INAF - Osservatorio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy e-mail: castelli@ts.astro.it
Corresponding author: Y. Momany, momany@pd.astro.it
Received:
17
November
2003
Accepted:
19
February
2004
In a previous paper we reported on a discontinuity in the extreme
horizontal branch (EHB) of the Galactic globular cluster NGC 6752,
which we called the second U-jump. This feature was attributed to a
combination of post zero-age horizontal branch evolution and diffusion
effects. In this follow-up study we analyze other EHB clusters and
show that the second U-jump is a common feature among EHB clusters
reaching K, and that its onset in different
clusters converges around
± 3000 K.
We also present near-ultraviolet diagrams of ωCen and NGC 2808,
the only two objects with spectroscopically confirmed “blue hook”
stars (
K).
We confirm predictions of a photometric discontinuity
separating late from early-helium flashers. Moreover, we present
empirical evidence that the second U-jump population might be
mainly composed of early-helium flashers.
Lastly, we revisit the discussion on the ubiquitous nature of the gaps
and jumps so far identified in the blue HB tails, suggesting a
possible discrete nature of the distribution in temperature of the HB stars.
Key words: stars: horizontal-branch / stars: Hertzsprung-Russell (HR) and C-M diagrams / stars: Population II / Galaxy: globular clusters: general / ultraviolet: stars
© ESO, 2004
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