Infrared photometry of Sakurai’s object (V4334 Sgr) in 1996–1999

The infrared photometric observations of V4334 Sgr in 1996–1999 are presented. Together with optical data, they have allowed us to accurately estimate the bolometric flux from this star and to investigate the structure of its dust envelope over the above period. The star is shown to have passed through four well-defined stages in these four years as it moved backward along the post-AGB track, and it now appears to have started moving forward after a halt. At the first stage (1996), there was no dust in the star’s envelope. Its visual brightness slightly increased, and it reddened in the entire observed spectral range. The bolometric flux also gradually rose. At the second stage (1997), an optically thick dust envelope condensed around the star, which, however, essentially did not manifest itself at optical wavelengths. The bolometric flux continued to rise through an increase in the star’s infrared brightness alone; the rate of its rise also increased. At the third stage (1998–March 1999), V4334 Sgr entered the R CrB phase. First two shallow minima and then two deep minima were observed at optical wavelengths. The star appreciably reddened during the deep minima. The bolometric flux ceased to rise and began to gradually fall in the second half of 1998. At the fourth stage (since March 1999 up until now), V4334 Sgr has been at a protracted deep minimum, which is atypical of the R CrB stars. The bolometric flux between March and October underwent no significant variations. We describe the structure of the dust envelope around V4334 Sgr since its formation. From June 1997 until July 1998, the optical depth of the dust shell, its inner and outer radii, and its mass increased by factors of ～2.2, ～2.0, 2.3, and ～10, respectively. In July 1998, τ(V)≈2.3, R _{d, in}≈7.4×10¹⁴ cm, R _{d, in}/R _{d, out}≈0.7(R _{d, in}/R _*≈47), and M _dust≈1.6×10^?7 M _⊙.     

Analysis of HST ultraviolet spectra for T Tauri stars: RU Lup

The ultraviolet spectra of the star RU Lup obtained with the Hubble Space Telescope are analyzed. Emission lines are identified. The presence of absorption components with a nearly zero residual intensity in the Mg II resonance doublet lines is indicative of mass outflow with a velocity V _∞?300 km s^?1. These lines also exhibit a broad (?1400 km s^?1 at the base) component originating in the star itself. The profiles of the (optically thin) Si II] and Si III]1892 Å lines for the first time unequivocally prove that these lines originate in an accretion shock wave rather than in the chromosphere, with the gas infall velocity being V ₀?400 km s^?1. The intensity ratio of the C IV 1550 Å and Si IV 1400 Å resonance doublet components was found to be close to unity, suggesting a high accreted-gas density, logN ₀>12.5. Molecular H₂ Lyman lines formed in the stellar wind were detected. The H I Lα luminosity of RU Lup was found from their intensities to exceed 10% of L _bol. Radiation pressure in the Lα line on atomic hydrogen may play a significant role in the initial acceleration of stellar-wind matter, but the effect of Lα emission on the dynamics of molecular gas is negligible.     

Elemental abundance analyses with DAO spectrograms – XXII. The B9–A3 stars λ Ursae Majoris, 59 Herculis, 14 Cygni and 29 Cygni

Elemental abundances of the moderately rotating B9–A3 stars λ UMa, 59 Her, 14 Cyg and 29 Cyg have been derived in a consistent manner with previous studies of this series from spectrograms obtained with Reticon and CCD detectors. The derived elemental abundances show that λ UMa is a mild Am star, while 59 Her is slightly metal-rich. Although 14 Cyg has values closer to solar than these stars, its subsolar Ca and Sc abundances indicate that it might be the hottest known hot-Am star. 29 Cyg is a metal-poor λ Boo star.     

On‐line database of photometric observations of magnetic chemically peculiar stars

We present our extensive project of the On‐line database of photometric observations of magnetic chemically peculiar stars to collect published data of photometric observations of magnetic chemically peculiar (mCP) stars in the optical and near IR regions. Now the nascent database contains more than 107 000 photometric measurements of 102 mCP stars and will be continually supplemented with published or new photometric data on these and about 150 additional mCP stars. This report describes the structure and organization of the database. Moreover, for the all included data we estimated the error of measurements and the effective amplitudes of the light curves. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Variability of the HeIλ5876 Å line in early type chemically peculiar stars. II

To try to understand the behavior of helium variability in Chemically Peculiar stars, we continued our on‐going observational campaign started by Catanzaro, Leone & Catalano (1999). In this paper we present a new set of time resolved spectroscopic observations of the HeI5876 Å line for a sample of 10 stars in the spectral range B3 ‐ A2 and characterized by different overabundances. This line does not show variability in two stars: HD77350 and HD175156. It shows instead an equivalent width variation in phase with the Hipparcos light curve for two stars: HD79158 and HD196502. Antiphase variations have been found in 4 stars of our sample, namely: HD35502, HD124224, HD129174 and HD142990. Nothing we can say about HD115735 because of the constancy of Hipparcos photometric data, while no phase relation has been observed for HD90044. In the text we discuss the case of HD175156, according to photometric calibration and our spectroscopic observations we rule out the membership of this star to the main sequence chemically peculiar stars. We confirm the results obtained in the previous paper for which phase relations between light, spectral and magnetic variations are not dependent on stellar spectral type or peculiarity subclass.     

CEMP星HE1005-1439中子俘获元素天体物理来源的研究

HE1005-1439是一颗金属丰度极低([Fe/H] ~ - 3.0)的碳增丰贫金属星(Carbon Enhanced Metal-Poor,CEMP), 该星的s-过程元素显著超丰([Ba/Fe] = 1.16±0.31, [Pb/Fe] = 1.98±0.19), 而r-过程元素温和超丰([Eu/Fe] = 0.46±0.22), 使用单一的s-过程模型和i-过程模型均不能拟合该星中子俘获丰度分布. 采用丰度分解的方法探究该星化学元素的天体物理来源可有助于理解CEMP星的形成和化学演化. 利用s-过程和r-过程的混合模型对其中子俘获元素的丰度分布进行拟合, 发现该星的中子俘获元素主要来源于低质量低金属丰度AGB伴星的s-过程核合成, 而r-过程核合成也有贡献.     

LAMOST-Kepler视场中富锂巨星表面转动研究

Kepler卫星提供的长时序、高精度的光度观测和郭守敬望远镜(LAMOST)提供的大规模光谱观测为研究恒星表面转动周期与富锂巨星锂丰度关系提供了良好的数据.将LAMOST搜寻到的富锂巨星与Kepler观测交叉,获得了619颗共同源,研究了其中295颗有良好观测数据的富锂巨星的表面转动.在205颗有星震学参数的恒星中提取出14颗恒星的转动周期,其中氦核燃烧星(HeB) 11颗,红巨星支(RGB) 2颗, 1颗演化阶段未确定.本样本中的极富锂巨星(A(Li) 3.3 dex)皆为HeB;对于90颗没有星震学参数的样本因而没有依靠星震学手段确定演化阶段的恒星中,有22颗提取出了自转周期.前者的自转探测率为6.8%,显著高于之前工作中大样本巨星2.08%的探测率.同时,此研究首次从自转周期的角度确认了恒星转动与巨星锂增丰存在相关性,在增丰程度较弱时,自转周期分布比较弥散;强锂增丰的星倾向于快速转动.富锂巨星与极富锂巨星在转动速度随锂丰度的演化上展现了两个序列,在转动-锂丰度图上的A(Li)≈3.3 dex处产生第2个下降序列,或许暗示了两者在形成机制上的不同.极富锂巨星的样本中,随巨星锂增丰程度增强,恒星转速加快.这种相关性为由转动引起的额外混合作为富锂巨星形成的机制提供了支持.     

两颗CEMP-s视单星化学元素的天体物理来源研究

CS30301–015和HE1045+0226是两颗C元素和s-过程元素均超丰的贫金属(CEMP-s)星.视向速度观测发现这两颗星可能为单星.采用叠加与分解的方法探究这两颗星化学元素的天体物理来源能够为更好地理解银河系早期化学演化提供线索.计算结果表明:这两颗星的轻元素和Fe族元素主要产生于大质量星的primary过程.对于CS 30301–015,中子俘获元素主要来自AGB (Asymptotic Giant Branch)星中的主要s-过程. Pb的显著超丰主要归因于主要s-过程的贡献(约占Pb观测丰度的99.8%).需要更多的视向速度观测来确定这两颗星的轨道特征.对于HE 1045+0226, 56Z (质子数)62的重中子俘获元素主要来源于主要s-过程; Eu主要来源于主要r-过程.而轻中子俘获元素Y和Zr主要来自快速自转大质量星的primary弱s-过程,这一核合成过程对HE 1045+0226的Y和Zr丰度的贡献分别约为69.8%和67.6%.这从观测的角度证明弱s-过程能够在贫金属环境下发生.