发表机构
Pennsylvania State University; Space Telescope Science Institute; Rocket Girls Ranch Observatory; Eklund Smurf Observatory; Deep Space Imaging Network; INAF National Institute of Astrophysics, Astronomical Observatory of Padova; Stark Bayou Observatory; Hobby-Eberly Telescope, University of Texas at Austin（宾夕法尼亚州立大学; 太空望远镜科学研究所; 火箭女孩牧场天文台; 埃克伦德史密夫天文台; 深空成像网络; 意大利国家天体物理研究所帕多瓦天文台; 斯塔克湾天文台; 霍比-埃伯利望远镜，得克萨斯大学奥斯汀分校）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究偶然发现两颗新共生双星GR Cygni与[D75]141，通过光谱与图像观测揭示其星云形态、中心星性质及星云形成机制，表明存在大量未发现的共生星。
AI 中文摘要
在为一项暗淡行星状星云核的光谱巡天挑选目标时，我们遇到了两例异常的晚型变星，其周围存在由业余天文学家发现的星云。我们对这两个星云获取了后续的深窄带图像：StDr Objet 14（直径1.5角分）和StDr 4（直径2.5角分）。StDr Objet 14是低激发星云，仅在Hα+[N II]波段明亮，呈现独特的双环“靶心”形态；StDr 4则表现出弓形激波结构，在Hα和[S II]波段明亮，嵌入在延展发射星云中。两颗中心星分别为GR Cygni和[D75]141，均为脉动半规则变星。我们的光谱观测显示，GR Cyg是C9,2型冷碳星，具有巴耳末系、[O II]、[O III]、[Ne III]、[S II]及Fe II的发射线；GR Cyg的合成窄带图像显示，其强[O II]3727埃发射线的源头是一个距恒星约1.6角秒的 knot，表明存在近期的准直抛射事件。[D75]141是M6 III型红巨星，巴耳末系发射线微弱。两颗恒星均呈现蓝过量，GR Cyg被GALEX空间望远镜在近紫外波段探测到。这些数据证实两颗恒星为新的共生双星，包含一颗晚型红巨星和一颗从其恒星风吸积物质的热伴星。我们推测GR Cyg周围的双环是氦壳热脉冲期间抛射的（或可能来自反复新星爆发），而[D75]141周围的星云可能是共生星抛射物与星际云碰撞的结果。我们因两颗恒星周围存在暗淡星云而偶然发现它们，支持仍有大量“缺失”的共生星有待发现的观点。
英文摘要
In the course of selecting targets for a spectroscopic survey of faint planetary-nebula nuclei, we encountered two anomalous cases of late-type variable stars surrounded by nebulosities discovered by amateur astronomers. We obtained follow-up deep narrow-band images of the two nebulae: StDr Objet 14 (diameter 1.5 arcmin) and StDr 4 (diameter 2.5 arcmin). StDr Objet 14 is found to be a low-excitation nebula, bright only in Ha+[N II], and showing a unique double-ring "bull's-eye" morphology. StDr 4 exhibits a bow-shock structure, bright in Halpha and [S II], embedded in an extended emission nebula. Both central stars, respectively GR Cygni and [D75] 141, are found to be pulsating semiregular variable stars. Our spectroscopic observations show GR Cyg to be a cool carbon star of type C9,2, with emission lines of the Balmer series, [O II] and [O III], [Ne III], [S II], and Fe II. A synthetic narrow-band image of GR Cyg shows that the source of its strong [O II] 3727 A emission line is a knot displaced from the star by about 1.6 arcsec, indicative of a recent collimated ejection event. [D75] 141 is a M6 III red giant, with weak Balmer-series emission. Both stars show a blue excess, and GR Cyg was detected in the near-UV by the GALEX spacecraft. These data establish both stars as new symbiotic binaries, containing a late-type red giant and a hot companion accreting from its stellar wind. We speculate that the double rings surrounding GR Cyg were ejected during helium-shell thermal pulses (or conceivably from recurring nova outbursts), while the nebula around [D75] 141 may be the result of a collision of the symbiotic star's ejecta with an interstellar cloud. Our accidental discoveries of these two binaries because they are surrounded by faint nebulae supports the view that there is a significant population of "missing" symbiotic stars yet to be discovered.
CommentsAccepted by PASP
