摘要
1976年《天文学报》报道了初毓华的新发现:球状星团M15中的紫外亮星K1082是一颗变幅约0.~m2,周期为0.~d087004的热超短周期造父变星.国外的反应表明,他们基本上对这点持怀疑态度.由于潜在的演化意义,我们用PDS对初氏所用的库卡金等人所拍底片重新处理,结果是,我们能够以90%的概率说,K1082在当时的确是一颗变幅约0.~m2的新变星.但对所说的0.~d087004周期,我们认为有误.分析表明,变光至少由两个周期合成,其中主周期P_1～0.~d1683,次周期或者为P_2～0.~d0985,或者为0.~d0437,难以区分优劣.无论如何,这是一颗值得注意的新型变星.
It is now generally realized that the uv-bright stars in globular clusters are of particular interest concerning the rapid stage of advanced evolution in low mass population Ⅱ stars. Chu (1976) reported that the uv-bright star K1082 in the globular cluster M15 is a 0~d.087004 variable with a peak-to-peak amplitude of 0.2 mag. He proposed that it may be the prototype of a new class of hot ultrashort-period population Ⅱ cepheids. Hesser and Nemec (1979) gave K 1082 the spectral type A3, their radial velocity measurements and the proper motion studies (Cudworth 1976) show that K1082 is a cluster member. However, the reported period of O^d. 087004 has not been confirmed by other observers yet. Smith et al. (1979) measured the blue plates taken at Yale in 1967-68 and 1972. They were unable to show definitely the O^d. 087004 variation of this star, but from a new series of ten-minute plates taken in rapid succesion over a O^d. 09 interval in late 1978 they did find that the star was apparently not varying during that time. They also measured 31 plates taken between 1896 and 1908 with the 33-cm Boyden refractor of the Harvard College Observatory and found no magnitude change in K1082 (nor K1073) during this period. Smith et al. (1979) pointed out that the average magnitude of the star on the 1978 plates was 0.1 mag fainter than that from the Yale plates, but later obser-vations with the same telescope placed the star still about 0.1 mag fainter than other photoelectric measurements so it was due to a kind of systematic effect (Liller and Schommer 1980). However, from their photoelectric observations Liller and Schommer suggested 'that there is currently no short-period variation of K1082, but variations over periods longer than several hours remain a distinct possibility' becaues both their B and V magnitudes never deviated from the corresponding average values within each night by more than ±0.015 mag, but the differences among the average magnitudes of different nights were as large as 0.1 mag in V and 0.05 mag in B. In summary, just as Hesser and Nemer(1979) said 'that the object is of potential interest needs no further emphasis, but additional speculation on its evolutionary status or nature is best postponed until better observational data concerning its suspected variability become available'. While investigating new variable stars in MIS, we happened to include K1082 in our CCD frames for three nights in November 1987. (Yao et al. 1990) This star did not show evidence of any light variation larger than ±0.005 mag on each night. However, there is little doubt that a period P=0~d.027898 with the peak to peak amplitude of about 0.004 mag exists in the curve. People have already known that there are a few stars which pulsate during some time and cease pulsating during another time. Now that K1082 pulsated in 1956 and 1957 with an amplitude of 0.2 mag, but it has not shown var ations with similar amplitude and period since then. Maybe K1082 belongs to this kind of rare varaible stars. Due to the potential evolutional importance, we have scanned the original plates used by Chu again with the PDS. we use the Stetson's (1979, 1980) method to get the magnitudes of K1082. Scargle's (1982) modified periodogram was used to analyse the data. In order to answer: if the peak in the periodogram has arisen from chance (noise) fluctuations? we determined the false alarm probability and did the Fisher's randomization test. (Nemec et al. 1985) Our results have shown that: 1. With the probability P= 90% we can say that K1082 is a new type variable star indeed. Its amplitude was about 0.15 mag in 1957. 2. The reported period P=0~d.087004 is wrong. We determined P=0~d.1683. A second period P=0~d.0985 or P=0~d.0437 maybe exists, but it is less certain. 3. We will continue to observe K1082 in order to monitor its variation.
出处
《天文学报》
CSCD
北大核心
1992年第4期383-394,共12页
Acta Astronomica Sinica
基金
国家自然科学基金
关键词
变星
紫外亮星
球状星团
Variable star—UV bright star—Globular cluster
