Chemical spots on the surface of the strongly magnetic Herbig Ae star HD 101412

Due to the knowledge of the rotation period and the presence of a rather strong surface magnetic field, the sharp‐lined young Herbig Ae star HD 101412 with a rotation period of 42 d has become one of the most well‐studied targets among the Herbig Ae stars. High‐resolution HARPS polarimetric spectra of HD 101412 were recently obtained on seven different epochs. Our study of the spectral variability over the part of the rotation cycle covered by HARPS observations reveals that the line profiles of the elements Mg, Si, Ca, Ti, Cr, Mn, Fe, and Sr are clearly variable while He exhibits variability that is opposite to the behaviour of the other elements studied. Since classical Ap stars usually show a relationship between the magnetic field geometry and the distribution of element spots, we used in our magnetic field measurements different line samples belonging to the three elements with the most numerous spectral lines, Ti, Cr, and Fe. Over the time interval covered by the available spectra, the longitudinal magnetic field changes sign from negative to positive polarity. The distribution of field values obtained using Ti, Cr, and Fe lines is, however, completely different compared to the magnetic field values determined in previous low‐resolution FORS 2 measurements, where hydrogen Balmer lines are the main contributors to the magnetic field measurements, indicating the presence of concentration of the studied iron‐peak elements in the region of the magnetic equator. Further, we discuss the potential role of contamination by the surrounding warm circumstellar matter in the appearance of Zeeman features obtained using Ti lines. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The stellar mass spectrum of the open cluster NGC 3293

We have obtained and analyzed UBVRI CCD frames of the young, 4–10 Myr, open cluster NGC 3293 and the surrounding field in order to study its stellar content and determine the cluster’s IMF. We found significantly fewer lower mass stars, M≤2.5M _⊙, than expected. This is particularly so if a single age for the cluster of 4.6 Myr is adopted as derived from fitting evolutionary models to the upper main sequence. Some intermediate-mass stars near the main sequence in the HR diagram imply an age for the cluster of about 10 Myr. When compared with the Scalo (The stellar initial mass function. ASP conference series, vol. 24, p. 201, 1998) IMF scaled to the cluster IMF in the intermediate mass range, 2.5≤M/M _⊙≤8.0 where there is good agreement, the high mass stars have a distinctly flatter IMF, indicating an over abundance of these stars, and there is a sharp turnover in the distribution at lower masses. The radial density distribution of cluster stars in the massive and intermediate mass regimes indicate that these stars are more concentrated to the cluster core whereas the lower-mass stars show little concentration. We suggest that this is evidence supporting the formation of massive stars through accretion and/or coagulation processes in denser cluster cores at the expense of the lower mass proto-stars. R.W. Slawson and E.P. Horch are guest investigators at the University of Toronto Southern Observatory, Las Campanas, Chile.     

红团簇巨星的光谱分析及其作为I、K波段标准烛光的研究

基于高分辨率、高信噪比光谱观测资料，确定了19颗贫金属红团簇巨星的恒星大气参数，得到样本星4种α族元素(O、Mg、Ca、Si)的化学丰度．讨论了铁丰度与恒星大气参数的相关性以及α族元素丰度随金属丰度的变化，计算了共58颗红团簇巨星在I、K波段的绝对星等，讨论了它们与恒星铁丰度之间的关系．结果表明，在分析铁丰度范围内相对于I波段，K波段的绝对星等与铁丰度的相关性更弱，并且与利用理论模型得到的红团簇巨星I、K波段绝对星等与铁丰度的关系进行了比较与验证。     

Observations of pulsating Ap stars in South Africa

The rapidly oscillating Ap (roAp) stars currently represent the only main sequence stars other than the Sun which exhibit non-radial acoustic pulsations of high overtone. This makes them excellent subjects for asteroseismology, an approach which promises to yield accurate knowledge of the interior structures of stars. Of the 27 known roAp stars, 24 were discovered in Sutherland despite extensive searches conducted elsewhere. This paper reviews the discovery of the roAp phenomenon and describes the factors that contribute to the high discovery rate for these stars at Sutherland. Two long-term observational projects in progress at Sutherland are discussed,viz. the Cape roAp Star Survey and long-term monitoring of frequency variations in roAp stars.     

Preliminary Photometric Evidence of Starspot Umbrae and Penumbrae on Late-Type Active Stars

We constrain the properties of the spotted regions on the photosphere of the active late-type star DX Leonis by comparing the observed amplitudes of light and color variations with synthetic amplitudes obtained by means of Dorren's spot model and computed for a grid of values of spot temperatures, areas and latitudes.     

Infrared photometry of AGB stars

The goal of this article is to show that, if one avoids star forming regions, mass-losing AGB stars can generally be selected from the data that will be provided by the near-infrared surveys which are presently considered. Also, if IRAS data are available, the separation between carbon-rich and oxygen-rich stars can be operated by their positions in infrared colour diagrams. In extragalactic systems, red supergiants can be discriminated from AGB stars by their luminosities.based on observations obtained with the ESO 1-m telescope     

密近双星自转的测量和研究（Ⅰ）观测和处理结果

用相同的仪器条件在美国ＫｉｔｔＰｅａｋ国立天文台观测了一批密近双星，并用两种方法得出其自转速度，最后给出了７５个双星系统的９９个子星的自转速度，其中５４个子星是首次进行自转测量。这批高精度的自转值为研究双星的同步性和检验各种同步机制提供了可靠的观测资料。     

A near-infrared survey of IRAS sources in the South Galactic Cap

The paper describes the JHK colours of late-type stars which were investigated as part of a survey of South Galactic Cap (b < -30°) IRAS sources selected on the basis of their 12/25µm flux ratios as high mass-loss candidates. Near-infrared two-colour diagrams provide an effective technique for distinguishing between various groups of late-type stars. Such diagrams are also useful in indicating which stars are likely to be peculiar and worthy of more detailed study. The late-type stars isolated by this survey comprise: 61 Mira variables (3 of which are carbon stars with very thick shells), 3 young stellar objects, 4 interacting binaries, 2 semi-regular carbon variables and 154 oxygen-rich giants.