Is Dust Forming on the Red Giant Branch in 47 Tuc?
M. L. Boyer, J. Th. van Loon, I. McDonald, K. D. Gordon, B. Babler, M. Block, S. Bracker, C. Engelbracht, J. Hora, R. Indebetouw, M. Meade, M. Meixner, K. Misse… 展开作者
M. L. Boyer, J. Th. van Loon, I. McDonald, K. D. Gordon, B. Babler, M. Block, S. Bracker, C. Engelbracht, J. Hora, R. Indebetouw, M. Meade, M. Meixner, K. Misselt, M. Sewilo, B. Shiao, B. Whitney
Using Spitzer IRAC observations from the SAGE-SMC Legacy program and archived Spitzer IRAC data, we investigate dust production in 47 Tuc, a nearby massive Galactic globular cluster. A previous study detected infrared excess, indicative of circumstellar dust, in a large population of stars in 47 Tuc, spanning the entire Red Giant Branch (RGB). We show that those results suffered from effects caused by stellar blending and imaging artifacts and that it is likely that no stars below about 1 mag from the tip of the RGB are producing dust. The only stars that appear to harbor dust are variable stars, which are also the coolest and most luminous stars in the cluster.
We report a new star formation history for the Tucana dwarf spheroidal galaxy, obtained from a new look at a deep HST/ACS colour-magnitude diagram. We combined information from the main sequence turn-off and the horizontal branch to resolve the ancient star formation rates on a finer temporal scale than previously possible. We show that Tucana experienced three major phases of star formation, two very close together at ancient times and the last one ending between 6 and 8 Gyr ago. We show that the three discrete clumps of stars on the horizontal branch are linked to the distinct episodes of st…
The Gradients in the 47 Tuc Red Giant Branch Bump and Horizontal Branch are Consistent With a Centrally-Concentrated, Helium-Enriched Second Stellar Generation
Light element abundances in the Galactic globular cluster 47 Tuc
大多数(也许是所有)银河系球状星团(GGC)很可能经历了两次甚至更多的恒星形成事件。这是特别表明,由特殊的化学组成的星团的恒星,显示大的变化,轻元素,如Li,C,N,O,Na,Mg,和Al的丰度。我们研究了Na,Mg,和Al的丰度在103红巨星支星位于下方(49颗恒星)和上方(54颗恒星)的RGB凸点在GGC 47 Tuc的大气。我们的结果表明,[Na/Fe]丰度比的扩展约为[Mg/Fe]的三倍。我们的数据也证实了弱Na-Al相关性的存在,类似于在其他GGC中观察到的。与此同时,我们没有发现Carretta et al.(2013)最近报道的三种具有不同铝丰度特征的恒星群存在的证据。
We determined zirconium abundance in the atmospheres of 327 red giant branch (RGB) stars in the globular cluster 47 Tuc. The 1D LTE abundances were obtained from the archival VLT GIRAFFE spectra, using 1D hydrostatic ATLAS9 stellar model atmospheres and synthetic Zr I line profiles computed with the SYNTHE package. The average zirconium abundance determined in the sample of RGB stars, [Zr/Fe] = +0.38 +/- 0.12, agrees well with zirconium abundances obtained at this metallicity in the Galactic field stars, as well as with those observed in other Galactic globular clusters.
We present new large field-of-view ($\sim$1°$\times$1°) Ca-CN photometry of the prototypical metal-rich globular cluster 47 Tucanae (NGC 104). Our results are the following. (1) The populational number ratios of the red giant branch (RGB) and red horizontal branch (RHB) are in excellent agreement: n(CN-w):n(CN-s) = 30:70 ($\pm$1--2), where the CN-w and CN-s stand for the CN-weak and CN-strong populations, respectively. Both the CN-s RGB and RHB populations are more centrally concentrated than those of CN-w populations are. (2) Our photometric metallicities of individual RGB stars in each popul…
High-resolution Hubble Space Telescope optical observations have been used to analyze the stellar population and the structure of the poorly investigated bulge globular cluster NGC 6316. We constructed the first high-resolution reddening map in the cluster direction, which allowed us to correct the evolutionary sequences in the color magnitude diagram (CMD) for the effects of differential reddening. A comparison between the CMDs of NGC 6316 and 47 Tucanae revealed strikingly similar stellar populations, with the two systems basically sharing the same turn-off, sub-giant branch, and horizontal …
Stellar models for -2.5 <= [Fe/H] <= -0.5 that have been computed for variations in the C:N:O abundance ratio (for two different values of [CNO/Fe]) are compared with HST Wide Field Camera 3 (WFC3) observations of the globular clusters (GCs) 47 Tuc, NGC 6362, M5, M5, M55, and M92. The bolometric corrections used to transpose the models to the observed planes are based on new MARCS synthetic spectra that incorporate improved treatments of molecules that involve atoms of C, N, and O. On the assumption of well-supported distance moduli and reddenings, isochrones for [O/Fe] = 0.6 and [m/Fe] = 0.4 …
Carbon measurements in two ultra-faint dwarf galaxies: Grus II and Tucana IV
Università degli Studi di Firenze(佛罗伦萨大学);INAF/Osservatorio Astrofisico di Arcetri(意大利国家天体物理研究所阿切特里天文台);Alma Mater Studiorum, Università di Bologna(博洛尼亚大学);INAF, Osservatorio di Astrofisica e Scienza dello Spazio(意大利国家天体物理研究所空间科学天文台);Instituto de Astrofísica de Canarias(加那利天体物理学研究所);Universidad de La Laguna(拉古纳大学)
Context. While most (if not all) Type I Galactic globular clusters (GGCs) are characterised by spreads in the abundances of light chemical elements (e.g. Li, N, O, Na, Mg, Al), it is not yet well established whether similar spreads may exist in s-process elements as well. Aims. We investigated the possible difference in Ba abundance between the primordial (1P) and polluted (2P) stars in the Galactic globular cluster (GGC) 47 Tuc (NGC 104). For this, we obtained homogeneous abundances of Fe, Na, and Ba in a sample of 261 red giant branch (RGB) stars which is the largest sample used for Na and B…
The variable mass-loss in low-mass red giant stars: Chromospheric motion across stellar evolution in 47 Tuc
Universidad Andrés Bello(安德烈斯贝略大学);European Southern Observatory(欧洲南方天文台);Osservatorio Astronomico di Padova-INAF(帕多瓦天文台-意大利国家天体物理研究所);Università degli Studi di Bologna(博洛尼亚大学);INAF – Osservatorio di astrofisica e scienza dello spazio di Bologna(意大利国家天体物理研究所-博洛尼亚天文与空间科学观测站)
Stars in globular clusters formed and evolved in the most extreme environment: high density and low metallicity. If the formation of stars and planets are at all sensitive to environmental conditions, this should therefore be evident in globular clusters. Observations have indicated that hot Jupiters are at least an order of magnitude less prevalent in the central region of the globular cluster 47 Tucanae than in the field. In this work, we explore the claims in the literature for additional consequences for the low mass stellar initial mass function. Tidal capture, the mechanism that produces…
The TESS mission will survey ~85 % of the sky, giving us the opportunity of extracting high-precision light curves of millions of stars, including stellar cluster members. In this work, we present our project "A PSF-based Approach to TESS High quality data Of Stellar clusters" (PATHOS), aimed at searching and characterise candidate exoplanets and variable stars in stellar clusters using our innovative method for the extraction of high-precision light curves of stars located in crowded environments. Our technique of light-curve extraction involves the use of empirical Point Spread Functions (PS…