V1118 Ori eruption: RVB observations
Observed 10 Jan 2005
7 Feb 2005
Revised: 31 March, 24 April, 5 May 2005
The eruptive star V1118 Ori was observed during an outburst as
fading down and cooling down.
The eruptive variable V1118 Ori was reported in outburst on 10 Jan 2005,
for the first time since 1997 (Williams 2005). I observed it from 19h
TU to 01h TU with Rc, V, B filters.
Time-series observations were carried out with a 203 mm SC telescope,
a SBIG ST7E camera (KAF401E CCD chip) and Johnson-Cousins Rc, V, B filters
in a filter wheel. 31 images were obtained with the Rc filter, 29 with
the V filter and also 29 with the B filter. Each exposure is 200-second
The differential photometry is somewhat challenging: nebulosities from
the Orion Nebula M42 are present and nearly all the stars in the field
are known variables.
The comparison star is UCAC2 29776568 with a R magnitude of 11.73.
The check star is GSC 4774-00825. It is observed to have the average
relative magnitudes Rc=0.242+/-0.023, V=0.081+/-0.022, B=-0.272+/-0.045
where the errors are the standard deviations.
With the Rc filter. The comparison star has the yellow symbol. The
apertures are also shown. The ring of the comparison star aperture is
large so as not to include a nearby star.
The light curves are:
The error bars are the +/- 1 sigma statistical uncertainties. The dot
lines are best fits.
The light curves for the check star and the air mass variation are here.
The variable is observed as decaying. The decay slopes are not the same
for the different bands, with the B light curve being steeper than the
V, itself steeper than the Rc:
R band: 0.74 mag/day
V band: 0.97 mag/day
B band: 1.25 mag/day
The uncertainty is about 0.06. This reddening is not observed for the
check star, therefore it is intrinsic to the variable star and not due
to the air mass increase during the session. This suggests that V1118
is cooling down as it is fading down.
Williams P.(2005) IAU Circular 8460.
Telescope and camera configuration.
Computer and software configuration.