Chemical composition of UV-bright star ZNG 4 in the globular cluster M 13

Ambika, S.; Parthasarathy, M.; Aoki, Wako; Fujii, Takeshi; Nakada, Y.; Ita, Yoshifusa; Izumiura, Hideyuki

doi:10.1051/0004-6361:20031759

Cited by 9 publications

(7 citation statements)

References 37 publications

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“…The star NGC 7078 K 1082 shows possible signatures of diffusion and radiative levitation of elements in its spectra similar to those found in the post-HB star ZNG4 in M 13 (Ambika et al 2004), and in the BHB stars in M 13 (Behr et al 1999) and in NGC 6752 (Moehler et al 1999). …”

Section: Discussionsupporting

confidence: 59%

“…Only five UV-bright stars have detailed chemical composition determinations based on high resolution spectra: Barnard 29 in M 13 (Conlon et al 1994;Moehler et al 1998), ZNG 4 in M 13 (Ambika et al 2004), ROA 24 in ω Cen (Gonzalez & Wallerstein 1994), ROA 5701 in ω Cen (Moehler et al 1998), and ZNG 1 in M 10 (Mooney et al 2001). To this list we can add the young planetary nebula K 648 in M 15 (Bianchi et al 2001).…”

Section: Introductionmentioning

confidence: 99%

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Chemical composition and evolutionary status of nine UV-bright stars in five globular clusters from VLT/UVES spectra

Jasniewicz¹,

Laverny

Parthasarathy

et al. 2004

A&A

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Abstract.We have derived the chemical composition of nine UV-bright stars belonging to five Galactic globular clusters of various metallicities ([Fe/H] from −1.0 to −2.4 dex). The analyses are based on high resolution spectra obtained with the UV-Visual Echelle Spectrograph (UVES) at VLT-UT2. The evolutionary status of the stars is assessed from the chemical analysis and location in the H-R diagram. The star ID7 in NGC 5986 is confirmed as a bona fide post-asymptotic giant branch star (post-AGB) whereas the highluminosity star ID6 has probably left the AGB before the third dredge-up. ZNG 1 in NGC 6712 shows an overabundance of sodium, oxygen, and silicon similar to overabundances we find in the UV-bright star ID6 in NGC 5986; both stars could be in a post-early-AGB (PEAGB) phase of evolution. The UV-bright star ZNG 7 in NGC 6218 seems to be an AGB star. The stars V-4 and ZNG 5 in NGC 6656 are in a post-horizontal-branch phase of evolution, with V-4 being significantly overabundant in heavy elements. The origin of these overabundances is discussed in the context of the evolutionary versus primordial scenario. The three UV-bright stars K 260, K 996 and K 1082 observed in the very metal-deficient globular cluster NGC 7078 are post-horizontal-branch stars, one of them being slightly enriched in s-elements but with a luminosity too low for third dredge-up to have occured. The abundance patterns of K 1082 in NGC 7078 seem to indicate the presence of mild diffusion and a radiative levitation process, already reported in the blue HB stars of M 13 (Behr et al. 1999, ApJ, 517, L135) and NGC 6752 (Moehler et al. 1999, A&A, 339, 537).

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Section: Discussionsupporting

confidence: 59%

Section: Introductionmentioning

confidence: 99%

Chemical composition and evolutionary status of nine UV-bright stars in five globular clusters from VLT/UVES spectra

Jasniewicz¹,

Laverny

Parthasarathy

et al. 2004

A&A

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“…The stars they considered have effective temperatures and metal abundances similar to those of the stars we are analysing in M 22, and they adopted similar values for the microturbulent velocities. An even lower abundance of [Sr/Fe]=-0.7 was obtained by Ambika et al (2004) for a supra-BHB star in M 13. This might suggest a trend toward underestimating Sr abundances in LTE analysis of low-gravity hot stars that might represent an extrapolation of the small trend observed in cooler stars by Andrievsky et al (2013).…”

Section: Metal Abundancesmentioning

confidence: 81%

The Na-O anticorrelation in horizontal branch stars

Gratton

Lucatello

Sollima

et al. 2014

A&A

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We used FLAMES+GIRAFFE (Medusa mode) at the VLT to obtain moderately high resolution spectra for 30 red horizontal branch (RHB) stars, 4 RR Lyrae variables, and 17 blue horizontal branch (BHB) stars in the low-concentration, moderately metal-rich globular cluster NGC 6723 ([Fe/H] = −1.22 ± 0.08 from our present sample). The spectra were optimized to derive O and Na abundances. In addition, we obtained abundances for other elements, including N, Fe, Mg, Ca, Ni, and Ba. We used these data to discuss the evidence of a connection between the distribution of stars along the horizontal branch (HB) and the multiple populations that are typically present in globular clusters. We found that all RHB and most (13 out of 17) BHB stars are O-rich, Na-poor, and N-poor; these stars probably belong to the first stellar generation in this cluster. Only the four warmest observed stars are (moderately) O-poor, Na-rich, and N-rich, and they probably belong to the second generation. While our sample is not fully representative of the whole HB population in NGC 6723, our data suggest that in this cluster only HB stars warmer than ∼9000 K, that is one fourth of the total, belong to the second generation, if at all. Since in many other clusters this fraction is about two thirds, we conclude that the fraction of first/second generation in globular clusters may be strongly variable. In addition, the wide range in colour of chemically homogeneous first-generation HB stars requires a considerable spread in mass loss (>0.10 M ). The reason for this spread is yet to be understood. Finally, we found a high Ba abundance, with a statistically significant radial abundance gradient.

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“…9). ZNG4 was observed spectroscopically by Ambika et al (2004), who identified chemical signatures of diffusion, which only shows up among blue HB stars with T eff 11000 K. A likely explanation is that ZNG 4 (T eff = 8500 K) was once a hot blue HB star that evolved, and the chemical signature is leftover from the earlier phase. A significant convective envelope is not likely to appear until the star reaches lower T eff .…”

Section: Ultraviolet Bright Starsmentioning

confidence: 99%

A Re-Evaluation of the Evolved Stars in the Globular Cluster M13

Sandquist

Gordon

Levine

et al. 2010

The Astronomical Journal

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We have analyzed photometry from space-and ground-based cameras to identify all bright red giant branch (RGB), horizontal branch (HB), and asymptotic giant branch (AGB) stars within 10 ′ of the center of the globular cluster M13.We identify a modest (7%) population of HB stars redder than the primary peak (including RR Lyrae variables at the blue end of the instability strip) that is somewhat more concentrated to the cluster core than the rest of the evolved stars. We find support for the idea that they are noticeably evolved and in the late stages of depleting helium in their cores. This resolves a disagreement between distance moduli derived from the tip of the red giant branch and from stars in or near the RR Lyrae instability strip. We identified disagreements between HB model sets on whether stars with T eff 10000 K (near the "knee" of the horizontal branch in optical CMDs) should evolve redward or blueward, and the differences may depend on the inclusion of diffusion in the stellar interior. The sharp cut at the red end of M13's HB provides strong evidence that stars from the dominant HB group must still be undergoing blue loops, which implies that diffusion is being inhibited. We argue that M13's HB is a somewhat pathological casethe dominant HB population occurs very near the "knee" in optical CMDs, and evolved stars exclusively appear redward of that peak, leading to the incorrect appearance of a continuation of the unevolved HB.We identify two stars as "blue hook" star candidates -the faintest stars in optical bands that remain significantly subluminous in the shortest ultraviolet wavelength photometry available. M13 also has a distinct group of stars previously identified with the "second U jump". Based on far UV photometry, we find that these stars have genuinely high temperatures (probably 26000 K T eff 31000 K), and are not produced by a jump in brightness at lower temperature (T eff ≈ 22000 K) as previously suggested. These stars are brighter Subject headings: stars: AGB and post-AGB -stars: evolution -Hertzsprung-Russell and C-M diagrams -stars: horizontal branch -globular clusters: individual (M13) -ultraviolet: stars

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Chemical composition of UV-bright star ZNG 4 in the globular cluster M 13

Cited by 9 publications

References 37 publications

Chemical composition and evolutionary status of nine UV-bright stars in five globular clusters from VLT/UVES spectra

Chemical composition and evolutionary status of nine UV-bright stars in five globular clusters from VLT/UVES spectra

The Na-O anticorrelation in horizontal branch stars

A Re-Evaluation of the Evolved Stars in the Globular Cluster M13

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