天琴RR型变星的绝对星等与运动学参数

对天琴ＲＲ型变星绝对星等运动学参数的测定及其对确定距离、球状星团年龄估计的影响,并对它们和其他距离指示器求得的结果的比较作了评述。由于不同作者采用的方法和资料不同,结果的不确定性较大。例如由直接和间接测定方法决定的天琴ＲＲ型变星的绝对星等分成较暗和较亮两类,由天琴ＲＲ型变星和其他距离批示器决定大麦哲伦云（ＬＭＣ）的距离模数和球状星团年龄估计并不完全一致。这表明还有一些天体测量和天体物理问题需要深入     

天琴RR型变星的速度椭球和空间速度

本文使用上海天文台编制的“天琴RR型变星自行星表”并利用空间速度的方法，确定天琴RR型变星的速度椭球，计算表明是三轴速度椭球，分析认为，子样中还包含着圆盘星族和中介星族Ⅱ的成员。本文还同时给出了在银心柱面坐标系中变星的柱面坐标和空间速度，为进一步作银河系动力学提供精确的资料。     

天琴RR型变星的绝对星等与运动学参数须同祺

对天琴RR型变星绝对星等与运动学参数的测定及其对确定距离、球状星团年龄估计的影响,并对它们和其他距离指示器求得的结果的比较作了评述.由于不同作者采用的方法和资料不同,结果的不确定性较大.例如由直接和间接测定方法决定的天琴RR型变星的绝对星等分成较暗和较亮两类,由天琴RR型变星和其他距离指示器决定的大麦哲伦云(LMC) 的距离模数和球状星团年龄估计并不完全一致.这表明还有一些天体测量和天体物理问题需要深入研究.新的空间视差卫星和地基干涉测定计划将可能有助这些问题的解决.     

天琴座RR型变星的自行和强度平均星等

本给出使用上海天台的40cm双筒折射望远镜拍摄的历元差平均18年的底片对测定的30颗天琴座RR型变星场星的自行，给出了它们的平均目视星等统一到Barnes的强度平均星等标度的强度平均星等，还列出了它们的金融丰度[Fc/H]。     

贫金属富碳天琴RR变星的形成

贫金属富碳恒星(Carbon-Enhanced Metal-Poor, CEMP)是研究宇宙早期恒星性质和化学演化的极佳样本,通常认为来自双星.目前发现的贫金属富碳星中有9颗天琴RR变星(RR Lyrae star, RRL),其中至少7颗未表现出任何双星特征.传统双星物质转移模型不足以充分解释贫金属富碳天琴RR变星(CEMP-RR Lyrae)单星的形成.之前研究表明氦白矮星和赫氏空隙星(HG)的并合模型可以解释部分富碳红巨星单星的碳增丰现象,因此贫金属富碳星单星也可能来自氦白矮星和赫氏空隙星的并合模型渠道.通过详细计算的氦白矮星和赫氏空隙星并合模型来检验这一演化渠道,结果表明:该并合模型在后续的演化过程中,其重力加速度、温度、表面碳丰度均能与观测符合较好.由此,氦白矮星和赫氏空隙星并合模型极有可能是贫金属富碳天琴RR变星的形成渠道之一.     

银河场天琴RR型星的绝对自行测定：方法和一个实例（SW Aqr）

利用Lick天文台的NPM昨表作为参考架，高精度地测定银河场天琴RR型星的绝对自行，可以使得对于这些恒星空间运动的研究建立在更加可靠的基础上，一个使用上海天文台佘山40cm折射望远镜拍摄的底片进行这项工作的计划已经开始执行。本文详细描述了这一计划所要用的归算方法，并用SW Aqr作为实例，对不同方法得出的结果作了比较。这一这产例表明，即使仅用几颗NPM星作参考，也可获得较好的结果。当NPM星过少时，可在局部天区内把PPM星表的自行改正到NPM系统，然后用PPM星补充作为参考星，同们可以得到很好的结果。     

星系金属丰度的研究进展（I）：定标方法

金属丰度是表征星系特征的重要参量，对于理解星系的形成与演化具有重要意义．随着观测设备的不断完善与发展，已经获得越来越多的星系（包括近邻星系、中等红移及高红移星系）金属丰度的观测资料。在光致电离模型方面也取得了很大进展．这些对于理解星系中金属及恒星成分的累积历史有非常重要的作用．有多种方法可以用来估计星系的金属丰度（主要是星际介质中气相的O丰度），介绍和评述了估计星系的O丰度的多种方法，包括电子温度的方法、R23方法以及其他一些“强线”比值的方法，并给出了相应的解析公式，同时介绍了电离星云的物理本质及由光致电高模型估计星系金属丰度的方法．还给出了估计星系的C和N元素丰度的方法．     

星系金属丰度的研究进展(Ⅱ):光度-金属丰度关系

金属丰度与星系光度是星系的重要特征参量,研究它们之间的关系有助于理解星系中恒星质量与金属成分的累积过程。评述了星系的光度-金属丰度关系的最新研究进展,包括对近邻星系、中等红移星系(0．42)的研究结果．由于观测样本跨越较宽的宇宙学时标,可以由此来探讨这一关系的演化过程,从而帮助理解星系演化的整体图景。     

7颗银河场天琴RR型星绝对自行的测定

给出了RY Psc,XX And,R Cet,XX Hya,TV Leo,U Com,SW Aqr等7颗银河场天琴RR型星基于NPM星表的河外参考架的绝对自行的测定结果,并与万籁等人、NPM和Hipparcos的结果作了比较。测量和归算的方法已在本年刊第18期（1997年）第49机上发表的一篇论中叙述。本工作的结果的内部精密度明显比NPM星表好。比较表明,这些结果与由Hipparcos星表从光学方面所代表的ICRS符合得非常好。     

Formation of Carbon-Enhanced Metal-Poor RR Lyrae Stars

Carbon-enhanced metal-poor (CEMP) stars are considered to be related to the first generation of stars, and responsible for the chemical evolution of the early Galaxy. More than half of them are in binaries, and could be explained by the binary evolution, but the formation channel of them is still not fully understood. Among the hundreds of CEMP stars, there are nine CEMP RR Lyrae stars identified, and at least seven of which are very likely not binaries. The usual binary star evolution channel is difficult to produce such a single star, particularly that of carbon enrichment. One way in which such a single star might be produced is the merger of a helium white dwarf with a Hertzsprung gap (HG) star. We use a stellar evolution program to calculate the models of the merger remnants, and find that the models can reproduce the observed distribution of these CEMP single RR Lyrae stars in terms of surface temperature, gravity, and carbon abundance. Hence, it is extremely possible that the helium white dwarf and HG star merger model is one of the formation channels of the metal-poor carbon-rich RR Lyrae stars.     

[Fe/H] relations for c-type RR Lyrae variables based upon Fourier coefficients

[Fe/H]–φ₃₁– P relations are found for c-type RR Lyrae stars in globular clusters. The relations are analogous to that found by Jurcsik & Kovács for field ab-type RR Lyrae stars, where a longer period correlates with lower metallicity values for similar values of the Fourier coefficient φ₃₁. The relations obtained here are used to determine the metallicity of field c-type RR Lyrae stars, those within ω Cen, the Large Magellanic Cloud and toward the galactic bulge. The results are found to compare favourably to metallicity values obtained elsewhere.     

The double‐mode RR Lyrae variable BS Com

We present the frequency analysis of the multicolour time series photometry of the field RRd variable BS Comae. The large number of data points in each of the BV (RI)_C bands and the ∼0.01 magnitude accuracy of the individual measurements allow us a high precision analysis of the properties of the combination frequencies due to nonlinear coupling. Through the combination of the frequency spectra in different colors we show that except for the components corresponding to the linear combinations of the two pulsation modes, there are no other components present above the millimagnitude amplitude level. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the period changes of RR Lyrae variables in the globular cluster M3

O – C diagrams of 78 RR Lyrae variables of the years 1963 to 1978 were used to investigate their comparability with the diagrams of 1895 to 1963. Only 5% have been proved to show a fundamentally deviating trend of the period change.     

The slope of the RR Lyrae MV–[Fe/H] relation

We review the available observational data to show that the slope of the RR Lyrae M_V –[Fe/H] relation is 0.18±0.03. The recent claim by Feast that, because of biases, the true slope is much steeper is not justified.     

Pulsational MV versus [Fe/H] relation(s) for globular cluster RR Lyrae variables

We use the results from recent computations of updated non-linear convective pulsating models to constrain the distance modulus of Galactic globular clusters through the observed periods of first-overtone (RR _c ) pulsators. The resulting relation between the mean absolute magnitude of RR Lyrae stars 〈 M _V (RR)〉 and the heavy element content [Fe/H] appears well in the range of several previous empirical calibrations, but with a non-linear dependence on [Fe/H] so that the slope of the relation increases when moving towards larger metallicities. On this ground, our results suggest that metal-poor ([Fe/H]<−1.5) and metal-rich ([Fe/H]>−1.5) variables follow two different linear 〈 M _V (RR)〉−[Fe/H] relations. Application to RR Lyrae stars in the metal-poor globular clusters of the Large Magellanic Cloud (LMC) provides an LMC distance modulus of the order of 18.6 mag, thus supporting the 'long' distance scale. The comparison with recent predictions based on updated stellar evolution theory is briefly presented and discussed.     

Studying Blazhko RR Lyrae stars with the 24‐inch telescope of the Konkoly Observatory

About a dozen field RR Lyrae stars have been observed with the 24‐inch Heyde‐Zeiss telescope of the Konkoly Observatory at Svábhegy, Budapest, since its refurbishment in 2003. Most of the observing time is allocated for the investigation of the Blazhko modulation, a phenomenon that still does not have a satisfactory explanation. The obtained multicolour CCD observations are unique in extent. The accuracy of the measurements makes it possible to detect low amplitude modulation of the light curve as well. The discovery of Blazhko stars with low modulation amplitudes warns that the incidence rate of the Blazhko modulation is, in fact, much larger than it was previously expected. This makes the efforts exploring the cause of the modulation even more important. A summary of our measurements and results achieved during the last 3 years is presented. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)