Volume 420, Number 2, June III 2004
|Page(s)||605 - 617|
|Section||Stellar structure and evolution|
|Published online||28 May 2004|
The ubiquitous nature of the horizontal branch second U-jump*
A link with the Blue Hook scenario?
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: email@example.com
3 INAF - Osservatorio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy e-mail: firstname.lastname@example.org
Corresponding author: Y. Momany, email@example.com
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
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.