BT Mon: no more hump
Observed: 13, 15 Dec 2006
16 Dec 2006
At the end of 2005, I observed this eclipsing cataclysmic system with a hump.
This hump is no longer present.
BT Mon is a cataclysmic variable, that is a binary with an accreting
white dwarf. The orbital period is 8h.
In Oct 2005 - Jan 2006 I observed it
with a large hump on the ingress side of the
eclipse. These new observations are then a follow up.
The observations were carried out with the same setup as in 2005:
203mm SC telescope, f/6.3, ST7E Camera (KAF401E CCD);
327 images, 60s exposures;
the comparison star is GSC 4803-00206 with an assumed unfiltered
magnitude of 13.5 and the check star is GSC 4803-00332. The aperture circle
for BT Mon encompasses both the variable and a nearby star, therefore the origin
of the observed magnitudes is arbitrary.
The resulting light curves:
Red: BT Mon, arbitrary origin for the magnitudes. Blue: the check star
shifted by +2 magnitudes. The error bars are +/- the 1 sigma statistical
The peak for the check star at 85.485 is due to a hot pixel.
Conditions: intermitent clouds.
The data may be folded with the ephemeris from Smith et al (1998)
to obtain the phase plot:
Comparison with previous observations
A large hump was observed at the end of 2005:
It is no longer present.
Between the eclipses, the light curve is actually rather flat. This suggests
that there is very little reflection from the secondary.
BT Mon: an eclipser with a hump.
Smith D.A., Dhillon V.S., Marsh T.R. (1998) MNRAS 296 465.
Telescope and camera configuration.
Computer and software configuration.