最慢共生新星AG静止期间Peg的FUSE光谱分析
FUSE Spectroscopic Analysis of the Slowest Symbiotic Nova AG Peg During Quiescence
摘要：
我们提出了一个远紫外光谱分析已知最慢的共生新星AG Peg（M3/4 III巨星+热白矮星; P = 818.4天），经历了一个新星爆炸在1850年，随后是一个非常缓慢的下降，直到1996年才结束，标志着开始的平静。这19年的静止期在2015年6月结束，当时AG Peg展示了一个光学振幅为1.5等的Z And型爆发。我们已经进行了吸积盘和WD光球合成光谱建模的远紫外光谱探测器（FUSE）光谱在2003年6月5.618日获得的平静间隔12年前的2015年爆发。光谱受ISM吸收和强发射线的影响很大。假设E（B-V）= 0.10，这是AG Peg方向上银河系红化的最大值。我们讨论我们采用前盖亚距离超过盖亚视差。对于一系列的白矮星表面重力和表面温度，我们发现最适合的光球是温度T = 150，000 K，低重力log（g）~6.0-6.5的热WD。对于800 pc的距离，比例WD半径约为0.06 Rsun，对于0.65 Msun WD质量，log（g）= 6.67。我们从这个模型中得到的亮度是1729 Lsun。热光球模型提供了更好的拟合比吸积盘模型，FUV通量赤字对较短的波长的FUSE，下降到莱曼极限。考虑到真正的共生吸积盘的性质的不确定性，并且，虽然一个非常热的低重力简并恒星主导FUV通量，但不能简单地排除稳态（标准）吸积盘的存在。
英文摘要：
We present a far ultraviolet spectroscopic analysis of the slowest known symbiotic nova AG Peg (M3/4III giant + hot white dwarf; P = 818.4 days) which underwent a nova explosion in 1850 followed by a very slow decline that did not end until 1996, marking the beginning of quiescence. The 19 years of quiescence ended in June 2015, when AG Peg exhibited a Z And-type outburst with an optical amplitude of 1.5 magnitudes. We have carried out accretion disk and WD photosphere synthetic spectral modeling of a Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum obtained on June 5.618, 2003 during the quiescence interval 12 years before the 2015 outburst. The spectrum is heavily affected by ISM absorption as well as strong emission lines. We de-reddened the FUSE fluxes assuming E(B-V) = 0.10, which is the maximum galactic reddening in the direction of AG Peg. We discuss our adoption of the pre-Gaia distance over the Gaia parallax. For a range of white dwarf surface gravities and surface temperatures we find that the best-fitting photosphere is a hot WD with a temperature T = 150,000 K, and a low gravity log(g)~6.0-6.5. For a distance of 800 pc, the scaled WD radius is about 0.06 Rsun, giving log(g) = 6.67 for a 0.65 Msun WD mass. The Luminosity we obtain from this model is 1729 Lsun. The hot photosphere models provide better fits than the accretion disk models which have FUV flux deficits toward the shorter wavelengths of FUSE, down to the Lyman Limit. Given the uncertainty of the nature of a true symbiotic accretion disk, and, while a very hot low gravity degenerate star dominates the FUV flux, the presence of a steady-state (standard) accretion disk cannot be summarily ruled out.
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