MBCAA Observatory

V1432 Aql time keeping

Observed: 28 June, 22 July, 6, 30 August 2008

Michel Bonnardeau
2 Sept 2008
Revised 19 Feb 2012 (new comparison star and photometry)

Abstract

Light curves for this asynchronous polar are presented. They show the eclipses and the spin modulation. They are compared with ephemerides.

Introduction

V1432 Aql is a cataclysmic system, that is a binary with an accreting white dwarf. It shows eclipses and the orbital period is Porb=3.37h. It is a bright X-ray source and the white dwarf is strongly magnetized.

According to Mukai et al (2003), the white dwarf spin period is almost equal to the orbital period (an asynchronous polar). The spin period is slightly larger than the orbital period, and decreasing with dPspin/dt=-10^-8, so the two periods should equalize in a century.

I already observed this system in 2007.

A CBA target in 2008.

Observations

The observations were carried out with the same setup as in 2007:

203mm SC telescope, a Clear filter, and a SBIG ST7E camera (KAF401E CCD);

202 usable images were obtained, each with an exposure of 200s;

for the differential photometry, the comparison star is GSC5728-00410 with an assumed unfiltered magnitude of 11.950;

the check star is GSC5728-01558 with a measured magnitude of 15.027+/-0.021+/-0.037 where the first +/- is the average 1-sigma statistical uncertainty and the second one is the standard deviation.

An example of a light curve:

Red: V1432 Aql, Blue: the check star. The error bars are +/- the 1 sigma statistical uncertainties.

Comparison with the orbital ephemeris

According to Mukai et al (2003), an ephemeris for the orbital motion is:
t(E) = To + Po*E
with To = 2,449,199.693 HJD
Po = 0.14023475 d

My data are in good agreement with this ephemeris:

Another ephemeris from Andronov et al (2006) is:
To = 2,451,492.09876 HJD
Po = 0.140235812 d
This is not compatible with Mukai et al (2003) and this gives a shift with my data.

Comparison with the spin ephemeris

Andronov et al (2006) gives the ephemeris for the spin modulation (the minimum):
t(E) = Ts + Ps*E +b*E^2
with Ts = 2,449,638.327427 HJD
Ps = 0.14062831 d
b = -7.81*10^-10

My data are in good agreement with this ephemeris:

Mukai et (2003) also gives an ephemeris, with a lesser spin up (b=-6.5*10^-10) , and my observations do not fit it.

The spin minimum I observe is then at:
Ts8 =2,454,679.1297 HJD
and in 2007 I observed it at:
Ts7 = 2,454,313.629 HJD

The O-C diagram of my minima versus the Andronos et al (2006)'s ephemeris, along with the minima of Mukai et al (2003) is:

Red squares: my 2007 and 2008 observations, Blue circles: Mukai et al (2003)'s observations, Green dots: Andronov et al (2006)'s ephemeris.

Modelling

The orbital modulation may be described with the function:

with Aorb = 15.8
and Borb = 1

and the spin modulation with:

with Aspin =15.05
and Bspin = 0.6.