Werner K, Rauch T, Kruk J W
Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Sand 1, 72076 Tübingen, Germany.
NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
Astron Astrophys. 2018 Jan 25;609. doi: 10.1051/0004-6361/201731740.
About a dozen hot white dwarfs with effective temperatures = 65 000 K - 120 000 K exhibit unusual absorption features in their optical spectra. These objects were tentatively identified as Rydberg lines of ultra-high excited metals in ionization stages v-x, indicating line formation in a dense environment with temperatures near 10 K. Since some features show blueward extensions, it was argued that they stem from a superionized wind. A unique assignment of the lines to particular elements is not possible, although they probably stem from C, N, O, and Ne. To further investigate this phenomenon, we analyzed the ultraviolet spectra available from only three stars of this group; that is, two helium-rich white dwarfs, HE 0504-2408 and HS 0713+3958 with spectral type DO, and a hydrogen-rich white dwarf, HS 2115+1148 with spectral type DAO. We identified light metals (C, N, O, Si, P, and S) with generally subsolar abundances and heavy elements from the iron group (Cr, Mn, Fe, Co, Ni) with solar or oversolar abundance. The abundance patterns are not unusual for hot WDs and can be interpreted as the result of gravitational settling and radiative levitation of elements. As to the origin of the ultra-high ionized metals lines, we discuss the possible presence of a multicomponent radiatively driven wind that is frictionally heated.
大约一打有效温度在65000K至120000K之间的热白矮星在其光学光谱中呈现出异常的吸收特征。这些天体被初步认定为处于电离阶段v - x的超高激发态金属的里德伯线，这表明谱线形成于温度接近10K的致密环境中。由于一些特征呈现出向蓝端的延伸，有人认为它们源自超电离风。尽管这些谱线可能源自碳、氮、氧和氖，但无法将它们唯一地归属于特定元素。为了进一步研究这一现象，我们分析了该组中仅有三颗恒星的紫外光谱；即两颗富氦白矮星，光谱类型为DO的HE 0504 - 2408和HS 0713 + 3958，以及一颗富氢白矮星，光谱类型为DAO的HS 2115 + 1148。我们识别出了轻金属（碳、氮、氧、硅、磷和硫），其丰度普遍低于太阳丰度，以及铁族重元素（铬、锰、铁、钴、镍），其丰度与太阳丰度相当或高于太阳丰度。这种丰度模式对于热白矮星来说并不罕见，可以解释为元素引力沉降和辐射悬浮的结果。关于超高电离态金属谱线的起源，我们讨论了可能存在的由辐射驱动的多组分风，这种风会因摩擦而加热。
