ULTRACAM photometry of the ultracompact binaries V407 Vul and HM Cnc
ULTRACAM photometry of the ultracompact binaries V407 Vul and HM Cnc
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DOI：
10.1111/j.1365-2966.2006.11244.x
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发表时间：
2006-11
影响因子：
4.8
通讯作者：
S. Barros;T. Marsh;V. Dhillon;P. Groot;S. Littlefair;G. Nelemans;G. Roelofs;D. Steeghs;P. Wheat
中科院分区：
文献类型：
--
作者：
S. Barros;T. Marsh;V. Dhillon;P. Groot;S. Littlefair;G. Nelemans;G. Roelofs;D. Steeghs;P. Wheat
V407 Vul (RXJ1914.4+2456) 和 HM Cnc (RXJ0806.3+1527) 是 X 射线发射恒星，其 X 射线光变曲线分别在 569 秒和 321 秒的周期上 100% 调制。这些周期被认为可能代表了靠近的白矮星对的轨道周期。在本文中，我们展示了 2003 年 5 月和 2005 年 8 月在 4.2 米威廉赫歇尔望远镜上使用高速 CCD 相机 ULTRACAM 以及 2005 年 11 月使用 VLT 拍摄的光学光变曲线。据报道，HM Cnc 的光学和 X 射线光曲线是反相的，但我们发现实际上 X 射线在光学光最大值后约 0.2 个周期达到峰值，正如在 V407 Vul 中所见。如果大部分光学调制来自质量供体的加热面，并且如果 X 射线发射点位于质量供体之前（正如考虑到吸积材料的角动量所预期的那样），则 X 射线/光学相移可以在系统的吸积模型下得到很好的解释。一些光学发射也可能来自 X 射线点附近，我们进一步表明这可以解释 HM Cnc 的非正弦光曲线。在此模型的基础上，我们约束伴星加热面的温度，发现测辐射热光度 > 10(33) erg s(-1) 和距离 d > 1.1 kpc。我们无法对系统的中间极性和单极性电感器模型下的 X 射线/光学相移进行解释。两颗恒星之间唯一显着的区别是 V407 Vul 被观察到具有 G 星的光谱。变星和恒星混合体在天空中位置的变化可以用来衡量它们的分离，并且对远低于通过观察设定的极限的值很敏感。我们应用这种“脉动天体测量学”来推断 G 星与变星相距约 0.027 角秒，因此在 V407 Vul 的变化中不起任何作用。我们表明，如果 V407 Vul 与 G 星形成三重系统，光走时的变化可能会影响 V407 Vul 的周期变化。
V407 Vul (RXJ1914.4+2456) and HM Cnc (RXJ0806.3+1527) are X-ray emitting stars with X-ray light curves that are 100 per cent modulated on periods of 569 and 321 s, respectively. These periods are thought possibly to represent the orbital periods of close pairs of white dwarfs. In this paper we present optical light curves taken with the high-speed CCD camera ULTRACAM on the 4.2-m William Hershel Telescope in 2003 May and 2005 August and with the VLT in 2005 November. The optical and X-ray light curves of HM Cnc have been reported as being in antiphase, but we find that in fact the X-rays peak around 0.2 cycles after the maximum of the optical light, as seen also in V407 Vul. The X-ray/optical phase shifts are well explained under the accreting models of the systems if most of the optical modulation comes from the heated faces of the mass donors and if the X-ray emitting spots are positioned in advance of the mass donors, as is expected given the angular momentum of the accreting material. Some optical emission may also come from the vicinity of the X-ray spot, and we further show that this can explain the non-sinusoidal light curves of HM Cnc. On the basis of this model we constrain the temperature of the heated face of the companion star finding a bolometric luminosity > 10(33) erg s(-1) and a distance, d > 1.1 kpc. We can identify no explanation for the X-ray/optical phase shifts under the intermediate polar and unipolar inductor models of the systems. The only significant difference between the two stars is that V407 Vul is observed to have the spectrum of a G star. The variation in position on the sky of a blend of a variable and a constant star can be used as a measure of their separation, and is sensitive to values well below the limit set by seeing. We apply this 'pulsation astrometry' to deduce that the G star is separated from the variable by about 0.027 arcsec and hence plays no role in the variability of V407 Vul. We show that light traveltime variations could influence the period change in V407 Vul if it forms a triple system with the G star.