We present NLTE abundances and atmospheric parameters for three metal-poor stars ([Fe/H]<-2) in Coma Berenices ultra-faint dwarf galaxy (UFD). The derived results are based on new photometric observations obtained with the 2.5-m telescope of the SAI MSU Caucasian observatory and spectra from the archive of the 10-m Keck telescope. Effective temperatures were determined from V-I, V-K, V-J colours. For each star, Teffs derived from different colours agree within 20K. Surface gravities (log g) were calculated using a relation between log g, MV, BC, distance, Teff, and mass, adopted as 0.8MSun. The NLTE abundances for Na, Mg, Ca, Ti, Fe, Ni, Sr, and Ba were determined. A revision of atmospheric parameters and abundances, based on new photometric observations and accurate modelling of spectral line formation resulted in reinterpretation of the star formation history in Coma Berenices UFD. The derived chemical abundance patterns for three stars differ from each other and from that, which is typical for the MW halo stars of similar [Fe/H]. The S1 star shows solar [alpha/Fe] and unprecedentedly low [Na/Mg] of -1.46, which is the lowest value among metal-poor stars known to date. Abundance pattern of the S1 star is well reproduced by nucleosynthesis model in metal-free massive stars explosion. The stars S2 and S3, in contrast to S1, show high [alpha/Fe] ratios, for example, [Mg/Fe]=0.8 in S2, while stars with -3.5<[Fe/H]<-2 in the other dwarf galaxies and the MW show a typical ratio [Ca,Mg/Fe] of 0.3 dex. All the three stars show low Sr and Ba abundances. These peculiarities in chemical composition argue for a small number of nucleosynthesis events contributed to chemical abundances of these stars. A wide range of metallicity, 0.65 dex, observed in Coma Berenices is likely produced by inhomogeneous mixing of the interstellar medium, but not an increase in [Fe/H] during a prolonged star formation.
Searching for short-period variable stars in the direction of Coma Berenices and Upgren 1 open clusters: Melotte 111 AV 1224 a new eclipsing binary star
本文报道了在后发座Berenices和Upgren 1疏散星团方向进行的CCD测光观测结果，目的是寻找新的短周期变星。总共检查了35颗恒星的变异性。经过这次搜索，在SIMBAD数据库中被命名为Melotte 111 AV 1224的恒星被发现是一颗新的食双星。后续的斯特伦格伦测光和光谱观测使我们能够推导出恒星的光谱类型，距离，红化和有效温度。对双星的光变曲线进行了初步分析，并导出了轨道系统的参数。从导出的物理参数，我们得出结论，Melotte 111 AV 1224是最有可能的W UMA食双星，是不是后发座疏散星团的成员。另一方面，在后发座疏散星团中，我们没有发现先前被编目为变星的NSV 5612和NSV 5615的亮度变化的证据。
Crowning the Queen: Membership, Age, Rotation, and Activity for the Open Cluster Coma Berenices
Columbia University（哥伦比亚大学）；Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS（波尔多天体物理实验室，波尔多大学，法国国家科学研究中心）；Rutgers, the State University of New Jersey（新泽西州立罗格斯大学）
后发座FK是一颗快速旋转的磁活性恒星，其光变曲线受到其表面冷斑的调制。它是第一颗发现“翻转”现象的恒星。从那时起，在许多其他恒星中，也报道了黑子活动的变化。因此，对FK Com中的斑点活动的演变进行更彻底的研究是有意义的。在这项研究中，我们用两种不同的时间序列分析方法分析了15年的测光观测，特别强调从数据中检测触发器类型的事件。我们应用连续周期搜索和载波拟合方法对1995- 2010年的长期标准Johnson-Ruminins V观测值进行了分析。这些观测是用两台自动测光望远镜进行的，凤凰-10和Amadeus T7位于亚利桑那州。我们在15个分析数据段中的6个中识别出复杂的相位行为。我们确定了五个触发事件和两个相位跳变的情况，其中相移为Δ << 0.4. In addition we see two mergers of spot regions and two cases where the apparent phase shifts are caused by spot regions drifting with respect to each other. Furthermore we detect variations in the rotation period corresponding to a differential rotation coefficien…
