Observations: several sessions between July and Sept 2004
Updated: 12 Nov 2004
Revised: 18 January 2005
V2400 Oph is an IP, discless cataclysmic star. It is observed (the data are not very good)
to flicker and that the color is V-R=0.3+/-0.1.
V2400 Oph is a cataclysmic binary star with an orbital period of 3.43
hours (from sidebands). It is an Intermediate Polar with the accreting
white dwarf having a magnetic field of about 10^7 gauss. The spin period
is 927.66 s (from polarimetry). The X-ray emission is pulsed but with
the synodic period (1006 s) and not the spin period, therefore it is inferred
that there is no accretion disk. (Hellier, Beardmore (2002))
V2400 Oph was observed very low over the horizon (air mass >3) with a small telescope,
therefore the data are not very good. The observations show flickering, apparently random,
and allow for an estimate of V-R.
V2400 Oph was observed with a 203 mm SC telescope and a SBIG ST7E camera (KAF401E CCD).
The comparison star is GSC 6812-00397 (RA=258.18135° DEC=-24.22438°) with a
magnitude of 10.71. There are 2 check stars K and K1:K: GSC 6812-00389 (RA=258.12531° DEC=-24.24844°). It is observed to have an average
magnitude of 10.293 with a standard deviation of 0.084;
K1: an anonymous star at RA=17h12mn39.32s DEC=-24°14'18.7".
It is observed to have an average
magnitude of 14.089 with a standard deviation of 0.129. It is about one magnitude
fainter than V2400 Oph.
The error bars are the +/- one-sigma statistical uncertainties on the
magnitudes. There is an uncertainty of 80 seconds on the HJD. The lines
are smoothed with a 5 mn-hernel. Red: the light
curves for V2400 Oph; Green: the K star +5
magnitudes; Brown: the K1 star.
There is a short time scale variability or flickering.
However there is no obvious periodicity and no obvious relation to the spin and
to the synodic periods.
V and Rc observations
V2400 Oph was observed on 14 July 2004 with a V filter and a Rc filter in a filter wheel.
The exposures are all one-minute long and the filter sequence is RcVVRc. The LONEOS
catalog is used to calibrate the images. There are 22 usable Rc images that are
stacked to yield the magnitude Rc=13.870+/-0.057 (1-sigma statistical uncertainty).
There are 30 V images that give V=14.167+/-0.088.
The color is then V-Rc=0.297+/-0.105.
The object was also observed on 15 July 2004 with the same setup and the RcVRcV filter
sequence. The stack of 51 images gives Rc=13.860+/-0.073 and the one of 32 images gives
V=14.256+/-0.068. Then V-Rc=0.396+/-0.100.
There may be color variations on a time scale of a few minutes
but the data do not allow for firm conclusions.
C. Hellier, A.P. Beardmore (2002) MNRAS and arXiv astro-ph/0201473.