COMMISSIONS 27 AND 42 OF THE IAU
           INFORMATION BULLETIN ON VARIABLE STARS
                        Number 4100

                                                Konkoly Observatory
                                                Budapest
                                                12 October 1994                      
                                                HU ISSN 0374 - 0676





          CIRCULAR POLARIMETRIC OBSERVATIONS OF THE
                   MAGNETIC CV 1H1752+081




1H1752+081 was discovered using the HEAO-1 satellite and identified with
an eclipsing CV whose period was 113 mins (Silber et al. 1994, Barwig, Ritter
& Barnbantner 1994). The eclipse is unusual in that the ingress to eclipse
is more variable and twice as long as the egress. Silber et al. (1994) claim
that the system has a small accretion disk with the possibility that it is an
intermediate-polar (a close binary in which the primary is a mass accreting
white dwarf with a magnetic field strength B=1-10MG). On the other hand,
Barwig et al., (1994) suggest that their observations are consistent with the
object being an AM Her system (a close binary in which the primary is a mass
accreting white dwarf whose spin period is coupled with the orbital period and
has  a magnetic field strength B=10-70MG; sufficiently strong to prevent the
formation of an accretion disc). The AM Her systems show strongly variable
circular polarisation while the intermediate-polars have generally undetectable
levels of circular polarisation, with the exception of BG CMi (Penning, Schmidt
& Liebert, 1986) and RE0751+14 (Rosen, Mittaz  Hakala, 1993). These have
detectable but lower values of circular polarisation than found in AM Her 
systems and inferred magnetic field strengths at the lower end of the  range
found for AM Hers. 1H1752+081 was observed spectroscopically during a low
intensity state and was found to have a magnetic field strength B~7MG
(Ferrario et al., 1994). Such a low magnetic field strength
suggests that the object would exhibit low levels of circular polarisation. To
confirm this we obtained circular polarimetry of 1H1752+081 covering two
orbital cycles.


We made observations of 1H1752+081 at two separate epochs  using  the Anglo
Australian Telescope. The Faint Object Polarimeter was used with a   Tektronix
CCD as the detector and an OG570 filter (~5500-9500A). Both photometry
and circular polarisation data were obtained on 1994 July 3 for 113 mins and
133 mins the following day. The exposures were 30 sec in duration. The data
were reduced as described by Cropper et al. (1990).


Figures 1 & 2 show the photometric and polarimetric data folded on the
ephemeris of Barwig et al. (1994). The photometric light curve is similar in
shape to that reported by Barwig et al. (1994) and Silber et al. (1994).
However, the main point of interest is the very low level of circular
polarisation. Although a positive level of circular polarisation was recorded
on each night, the observations of unpolarised standard stars using the same
instrumental configuration are inadequate for ruling out the possibility that
this low level of polarisation is instrumental in origin. This view is
strengthened by the fact that the phased  circular polarisation is different on
the two nights. We therefore  conclude that any circular polarisation in
1H1752+081 is <=1%. 

These results coupled with the low magnetic field strength determined by
Ferrario et al. (1994) suggest that 1H1752+081 is not in fact an AM Her star
but is more likely to be an intermediate-polar.


                           [FIGURE 1]

 Figure 1. Circular polarisation and photometric data (folded on the ephemeris
 of Barwig et al., 1994) taken on 1994 July 3 with the OG570 filter.

                           [FIGURE 2]

 Figure 2. Circular polarisation and photometric data (folded on the ephemeris 
 of Barwig et al., 1994) taken on 1994 July 4 with the OG570 filter.




Gavin RAMSAY 
Mark CROPPER
Mullard Space Science Lab., 
University College London, 
Dorking, Surrey, RH5 6NT,
U.K.



References:

Barwig, H., Ritter, H. & Barnbantner, O., 1994, A&A, 288, 204 [BIBCODE 1994A&A...288..204B ]

Cropper, M., Bailey, J., Wickramasinghe, D. T., Ferrario, L., 1990, 
MNRAS, 224, 34P [BIBCODE 1990MNRAS.244P..34C ]

Ferrario, L., Wickramasinghe, D., Bailey, J. & Buckley, D., 1994, in press

Penning, W. R., Schmidt, G. D.  Liebert, J., 1986, ApJ, 301, 881 [BIBCODE 1986ApJ...301..881P ]

Rosen, S. R., Mittaz, J. P. D.  Hakala, P. J., 1993, MNRAS, 264, 171 [BIBCODE 1993MNRAS.264..171R ]

Silber, A. D., Remillard, R. A., Horne, K. & Bradt, H. V., 1994, ApJ, 424,
955 [BIBCODE 1994ApJ...424..955S ]