Cygnus X-2 is one of the brightest and longest known X-ray sources. We present high-resolution optical spectroscopy of Cyg X-2 obtained over 4 yr, which gives an improved mass function of 0.69 (cid:53) 0.03 M (cid:44) (1 (cid:106) ). In addition, we resolve the rotationally broadened absorption features of the secondary star for the first time, deriving a rotation speed of km s (cid:50) 1 (1 (cid:106) ), which leads to a mass ratio of (cid:118) sin i (cid:53) 34.2 (cid:53) 2.5 q (cid:53) M / M (cid:53) c X (cid:53) 0.04 (1 (cid:106) , assuming a tidally locked and Roche lobe-filling secondary). Hence, with the lack of X-ray 0.34eclipses (i.e., ) we can set firm 95% confidence lower limits to the neutron star mass of M (cid:44) (cid:67) i (cid:38) 73 M (cid:49) 1.27 X and to the companion star mass of M (cid:44) . However, by additionally requiring that the companion must M (cid:49) 0.39 c exceed 0.75 M (cid:44) (as required theoretically to produce a steady low-mass X-ray binary), then M (cid:44) and M (cid:49) 1.88 X (95% confidence lower and upper limit, respectively), thereby making Cyg X-2 the highest mass neutron (cid:67) i (cid:33) 61 star measured to date. If confirmed, this would set significant constraints on the equation of state of nuclear matter.
天鹅座X-2是已知最亮和最长的x射线源之一。我们展示了Cyg X-2在4年内获得的高分辨率光学光谱，其质量函数改进为0.69 (cid:53) 0.03 M (cid:44) (1 (cid:106))。此外，我们首次解析了该副恒星的旋转加宽吸收特征，推导出其旋转速度为km s (cid:50) 1 (1 (cid:106))，由此得出质量比为(cid:118) sini (cid:53) 34.2 (cid:53) 2.5 q (cid:53) M / M (cid:53) c X (cid:53) 0.04 (1 (cid:106)，假设这是一颗潮汐锁定且罗氏叶填充的副恒星)。因此，由于缺少X射线0.34日食(即)，我们可以为中子星质量M (cid:44) (cid:67) i (cid:38) 73 M (cid:49) 1.27 X和伴星质量M (cid:44)设置95%置信下限。然而，通过额外要求伴星M (cid:49) 0.39 c必须超过0.75 M (cid:44)(理论上需要产生稳定的低质量X射线双星)，那么M (cid:44)和M (cid:49) 1.88 X(分别为95%置信下限和上限)，从而使Cyg X-2成为迄今测量到的质量最高的中子(cid:67) i (cid:33) 61恒星。如果得到证实，这将对核物质的状态方程设置重大限制。
{"title":"[ Star ]","authors":"M. Cuntz","doi":"10.2307/j.ctv18b5cjk.29","DOIUrl":"https://doi.org/10.2307/j.ctv18b5cjk.29","url":null,"abstract":"Cygnus X-2 is one of the brightest and longest known X-ray sources. We present high-resolution optical spectroscopy of Cyg X-2 obtained over 4 yr, which gives an improved mass function of 0.69 (cid:53) 0.03 M (cid:44) (1 (cid:106) ). In addition, we resolve the rotationally broadened absorption features of the secondary star for the first time, deriving a rotation speed of km s (cid:50) 1 (1 (cid:106) ), which leads to a mass ratio of (cid:118) sin i (cid:53) 34.2 (cid:53) 2.5 q (cid:53) M / M (cid:53) c X (cid:53) 0.04 (1 (cid:106) , assuming a tidally locked and Roche lobe-filling secondary). Hence, with the lack of X-ray 0.34eclipses (i.e., ) we can set firm 95% confidence lower limits to the neutron star mass of M (cid:44) (cid:67) i (cid:38) 73 M (cid:49) 1.27 X and to the companion star mass of M (cid:44) . However, by additionally requiring that the companion must M (cid:49) 0.39 c exceed 0.75 M (cid:44) (as required theoretically to produce a steady low-mass X-ray binary), then M (cid:44) and M (cid:49) 1.88 X (95% confidence lower and upper limit, respectively), thereby making Cyg X-2 the highest mass neutron (cid:67) i (cid:33) 61 star measured to date. If confirmed, this would set significant constraints on the equation of state of nuclear matter.","PeriodicalId":326028,"journal":{"name":"Gesichter des Films","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125011162","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-12-31DOI: 10.1515/9783839404164-009
F. Meyer
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