GALEX J184559.8-413827: a new extreme helium star identified using SALT

在SALT巡天中利用{\it TESS}搜索贫氢恒星中的密近双星系统

A search for close binary systems in the SALT survey of hydrogen-deficient stars using {\it TESS}

利用TESS数据在SALT巡天贫氢恒星中搜索密近双星，发现16颗变星中6颗为真变星，其中1颗为已知密近双星，密近双星比例在中性氦热亚矮星中约3.5%，在极端氦亚矮星中为0%。

利用SALT发现三颗富氦磁性热亚矮星

Discovery of three magnetic helium-rich hot subdwarfs with SALT

本文利用SALT发现了三颗大气参数相似但磁场较弱（约200kG）的富氦磁性热亚矮星，提出双白矮星合并触发磁发电机产生磁场的起源机制，并探讨了4630Å宽吸收线与氦丰度及氢原子碰撞扰动的关联。

SALT巡天中的氦丰富热亚矮星：无监督分类与运动学分析

The SALT survey of helium-rich hot subdwarfs: unsupervised classification and kinematic analysis

SALT巡天通过PCA和SC对氦丰富热亚矮星进行无监督分类，揭示了新的光谱序列和运动学特征。

Hot white dwarfs and pre-white dwarfs discovered with SALT

The Southern African Large Telescope (SALT) survey of helium-rich hot subdwarfs aims to explore evolutionary pathways amongst groups of highly-evolved stars. The selection criteria mean that several hot white dwarfs and related objects have also been included. This paper reports the discovery and analysis of eight new very hot white dwarf and pre-white dwarf stars with effective temperatures exceeding 100,000 K. They include two PG1159 stars, one DO white dwarf, three O(He) and two O(H) stars. One of the O(H) stars is the central star of a newly-discovered planetary nebula, the other is the ho…

An Ultraviolet-Optical Color-Metallicity relation for Red Clump Stars using GALEX and Gaia

Although core helium-burning red clump (RC) stars are faint at ultraviolet wavelengths, their ultraviolet-optical color is a unique and accessible probe of their physical properties. Using data from the GALEX All Sky Imaging Survey, Gaia Data Release 2 and the SDSS APOGEE DR14 survey, we find that spectroscopic metallicity is strongly correlated with the location of an RC star in the UV-optical color magnitude diagram. The RC has a wide spread in (NUV - G)$_0$ color, over 4 magnitudes, compared to a 0.7-magnitude range in (G$_{BP}$ - G$_{RP}$)$_0$. We propose a photometric, dust-corrected, ult…

Spectroscopic analysis of BPS CS 22940-0009: connecting evolved helium stars

BPS CS 22940-0009 is a helium-rich B-star that shares characteristics with both helium-rich B subdwarfs and extreme helium stars. The optical spectrum of BPS CS 22940-0009 has been analysed from SALT observations. The atmospheric parameters were found to be $T_{\rm eff} = 34970 \pm 370$ K, $\log g/{\rm cm \, s^{-2}} = 4.79 \pm 0.17$, $n_{\rm H}/n_{\rm He} \simeq 0.007$, $n_{\rm C}/n_{\rm He} \simeq 0.007$, $n_{\rm N}/n_{\rm He} \simeq 0.002$, although further improvement to the helium line fits would be desirable. This places the star as a link between the He-sdB and EHe populations in $g$-$T$…

Optical spectroscopy of the blue supergiant Sk-69 279 and its circumstellar shell with SALT

We report the results of optical spectroscopy of the blue supergiant Sk-69 279 and its circular shell in the Large Magellanic Cloud (LMC) with the Southern African Large Telescope (SALT). We classify Sk-69 279 as an O9.2 Iaf star and analyse its spectrum by using the stellar atmosphere code CMFGEN, obtaining a stellar temperature of \approx 30 kK, a luminosity of log(L_*/Lsun)=5.54, a mass-loss rate of log(\dot{M}/(Msun/yr))=-5.26, and a wind velocity of 800 km/s. We found also that Sk-69 279 possesses an extended atmosphere with an effective temperature of \approx 24 kK and that its surface h…

Wray 15-906: a candidate luminous blue variable discovered with WISE, Herschel and SALT

We present the results of study of the Galactic candidate luminous blue variable Wray 15-906, revealed via detection of its infrared circumstellar shell (of \approx2 pc in diameter) with the Wide-field Infrared Survey Explorer and the Herschel Space Observatory. Using the stellar atmosphere code CMFGEN and the Gaia parallax, we found that Wray 15-906 is a relatively low-luminosity, log(L/Lsun)\approx5.4, star of temperature of 25\pm2 kK, with a mass-loss rate of \approx3\times10^{-5} Msun/yr, a wind velocity of 280\pm50 km/s, and a surface helium abundance of 65\pm2 per cent (by mass). In the …

Helium Enhancement in the Metal Rich Red Giants of Omega Centauri

The helium-enriched (He-enriched) metal-rich red giants of Omega Centauri, discovered by Hema and Pandey using the low-resolution spectra from the Vainu Bappu Telescope (VBT) and confirmed by the analyses of the high-resolution spectra obtained from the HRS-South African Large Telescope (SALT) for LEID 34225 and LEID 39048, are reanalysed here to determine their degree of He-enhancement/hydrogen-deficiency (H-deficiency). The observed MgH band combined with model atmospheres with differing He/H ratios are used for the analyses. The He/H ratios of these two giants are determined by enforcing th…

[HP99] 159 -- 与氦星供体相关的第一颗超软X射线源的性质

[HP99] 159 -- Properties of the first Supersoft X-ray Source with a Helium star donor

[HP99] 159 是首个与氦星供体相关的超软X射线源，通过长期光谱和光度学数据确定其轨道周期和低倾角系统特征，揭示其作为单个衰减Ia型超新星前身的独特性质。

EC 22536-5304: a lead-rich and metal-poor long-period binary

Helium-burning hot subdwarf stars of spectral types O and B (sdO/B) are thought to be produced through various types of binary interaction. The helium-rich hot subdwarf star EC22536-5304 was recently found to be extremely enriched in lead. Here, we show that EC22536-5304 is a binary star with a metal-poor subdwarf F-type (sdF) companion. We have performed a detailed analysis of high-resolution SALT/HRS and VLT/UVES spectra, deriving metal abundances for the hot subdwarf, as well as atmospheric parameters for both components. Because we consider the contribution of the sdF star, the derived lea…