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 Teff≥23 000 K, and that its onset in different clusters converges around Teff˜ 21 000 ± 3000 K. We also present near-ultraviolet diagrams of ωCen and NGC 2808, the only two objects with spectroscopically confirmed ``blue hook'' stars (Teff≥35 000 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. Based on observations with the ESO/MPI 2.2 m and ESO/NTT telescopes, located at La Silla Observatory (Chile) and on observations with the NASA/ESA Hubble Space Telescope.

The ubiquitous nature of the horizontal branch second U-jump. A link with the Blue Hook scenario?

AL MOMANY, YAZAN;BEDIN, LUIGI;PIOTTO, GIAMPAOLO;ORTOLANI, SERGIO;RECIO BLANCO, ALEJANDRA;
2004

Abstract

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 Teff≥23 000 K, and that its onset in different clusters converges around Teff˜ 21 000 ± 3000 K. We also present near-ultraviolet diagrams of ωCen and NGC 2808, the only two objects with spectroscopically confirmed ``blue hook'' stars (Teff≥35 000 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. Based on observations with the ESO/MPI 2.2 m and ESO/NTT telescopes, located at La Silla Observatory (Chile) and on observations with the NASA/ESA Hubble Space Telescope.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/2439343
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