Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-11-03
Mon.Not.Roy.Astron.Soc.374:1334-1346,2007
Astronomy and Astrophysics
Astrophysics
15 pages, 10 figures, accepted for publication in MNRAS
Scientific paper
10.1111/j.1365-2966.2006.11244.x
V407 Vul (RXJ1914.4+2456) and HM Cnc (RXJ0806.3+1527) are X-ray emitting stars with X-ray light curves that are 100% modulated on periods of 569 and 321 seconds 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 4.2m WHT in May 2003 and August 2005 and with the VLT in November 2005. The optical and X-ray light curves of HM Cnc have been reported as being in anti-phase, 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 lightcurves of HM Cnc. 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 "pulsation astrometry" to deduce that the G star is separated from the variable by about 0.027'' and hence plays no role in the variability of V407 Vul. We show that light travel time variations could influence the period change in V407 Vul if it forms a triple system with the G star.
Barros S. C. C.
Dhillon Vik S.
Groot Paul J.
Littlefair Stuart
Marsh Thomas R.
No associations
LandOfFree
ULTRACAM Photometry of the ultracompact binaries V407 Vul and HM Cnc does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with ULTRACAM Photometry of the ultracompact binaries V407 Vul and HM Cnc, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and ULTRACAM Photometry of the ultracompact binaries V407 Vul and HM Cnc will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-163340