, R. VANSCHEIDT. CVs HQ And, RX And and FO Per. The target objects were selected from the CV catalogue

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1 COMMISSIONS 7 AND 4 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 4779 Konkoly Observatory Budapest 5 October 999 HU ISSN 374 { 676 DIFFERENTIAL PHOTOMETRY OF SUSPECTED CATACLYSMIC VARIABLES N. BENNERT, I. KONIG, E. MANTHEY, H. BLEUL, K. FIEGER, M. HESS, A. HOVEST 5, ; W. HOVEST, T. JUR GES, J. KLEIMANN, D. MUNSTERMANN ;4, D. REYMANN, K. ROSLER C. KRIEGESKORTE, E. KRUSCH,, M. NIELBOCK, M. POHLEN, ; 3 SCHMIDTOBREICK, ; 3 L. C. TAPPERT, R. VANSCHEIDT Astronomisches Institut, Ruhr{Universitat Bochum, Universitatsstrae 5, D{4478 Bochum, hlist users@astro.ruhr-uni-bochum.de Universit at Dortmund, Otto{Hahn{Strae 4, D{447 Dortmund, Osservatorio Astronomico di Padova, Viccolo dell'osservatorio 5, I{35 Padova, Italy Universitat Heidelberg, Albert{ Ub erle{strae, D{69 Heidelberg, Sudring 3, D{483 Warendorf, We here present dierential photometry of the four suspected cataclysmic variables (CVs) HM Aur, FBS , FBS 64+7 and NSV 7956, and of the three known CVs HQ And, RX And and FO Per. The target objects were selected from the CV catalogue of Downes et al. (997) (hereafter DWS 97), searching for not yet conrmed CVs and poorly observed systems with unknown orbital periods. Therefore the list of Ritter & Kolb (998) was used to exclude objects with known periods. To evaluate the signicance of our results, we included three systems with a certain CV classication. The data were taken at Hoher List Observatory on March 9,, and, on October 8, 998, and on March, 999 in the framework of the Astronomisches Beobachtungsprak- tikum of the Ruhr{Universitat Bochum. We used an astrograph (D = 3 m, f = :5 m) and a Cassegrain reector (D = :6 m, f = 3:68 m) equipped with Ford Loral FA48 CCDs and Johnson V-lters. In order to resolve the CV-typical short-term variation (ickering), the integration time was limited to sec., thus constraining the accessible V-magnitude to 7.. Table lists the details of the observations. Standard reduction was performed with IRAF packages using overscan and domeor skyats for the.6 m telescope, biasframes and skyats for the astrograph data. Aperture photometry was done with the DAOPHOT package. On each image frame we chose all non-saturated comparison stars comprising a S/N-ratio greater or equal to the S/N-ratio of the target object. For j = ; : : : ; n let I j (t) denote the instrumental intensity of comparison star j at time t. For t begin t t end all dierential lightcurves I j (t) := I j (t) I k (t); j; k f; : : : ; ng; j 6= k were calculated. For t begin t t end the a k verage lightcurve I av (t) was computed as the arithmetic mean of all comparison star intensities. j Then, dierential magnitudes were calculated according to I av (t) := I j (t) I av (t). All comparison stars with brightness variations above the noise level were easily discriminated IRAF is distributed by the National Optical Astronomy Observatories.

2 IBVS 4779 Table : List of observations. The coordinates in columns and 3 have been taken from DWS 97. Column 4 shows the instrument used, while columns 6 and 7 give the number of data points (lightcurves of observations marked with a * have been omitted in this paper) and the total time coverage per night, respectively. Object RA DEC Instrument Date n data HM Aur astrograph.3.98 * *3.7 FBS m telescope * FBS m telescope NSV astrograph *5.8 HQ And m telescope RX And astrograph FO Per m telescope t obs [h] and subsequently excluded from the average lightcurve. In an iterative process only comparison stars with constant brightness within the noise level contributed to the average lightcurve. HM Aur: This system has been discovered by Geyer et al. (955) who described it as a long-period variable showing irregular waves spanning over 5{ days with an amplitude of.5{. mag. However, Vogt (989) suspected a quiescent nova, while DWS 97 list it as nova-like with photographic magnitudes.3{.4. To our knowledge, no spectrum has been published. FBS and FBS 64+7: Both objects have been reported as possible CVs by Abramyan & Mikaelyan (994, 995) as discoveries of the First Byurakan Objec- tive Prism Survey. The authors do not present nding charts. Therefore, charts published by DWS 97 are based on the published coordinates only. The reported magnitudes are V = 5:9 for FBS and B = 6:4 for FBS 64+7, respectively. While for FBS , a spectrum is not available, FBS 64+7 has recently been studied by Liu et al. (999) who classied it as a DAB type white dwarf. NSV 7956: NSV 7956 is listed in the NSV catalogue of Kholopov (98) as a possible dwarf nova. No spectrum has been published so far and therefore this classication remains uncertain. DWS 97 give a magnitude range of V = 9{:5. HQ And: HQ And is listed as a CV in DWS 97 with a magnitude range of mphot = 5: {6:. Meinunger (975) rst classied HQ And as a rapid irregular star and revised it later (98) in favour of a CV classication. She already suspected a possible polar nature which was subsequently strengthened by the polarimetry of Andronov & Meinunger (987). RX And: RX And is a well-known dwarf nova of subtype Z Cam with a magnitude range of V = 9{:6 (DWS 97). Spectroscopic studies were conducted e.g. by Kaitchuck et al. (988) and Smith et al. (995), while Verbunt et al. (984) present a lightcurve. The orbital period has been determined to P = 5:4 hours by Kaitchuck (989). FO Per: According to Howarth (976) and Gessner (978) FO Per is a dwarf nova with a mean outburst cycle length of roughly days. The spectrum published by Bruch (989) shows the typical strong emission lines of such a system and thus supports this classication. DWS 97 give a maximum visual magnitude of.8 and a photographically

3 IBVS Table : Results of the dierential photometry are given in this table. Column 3 shows the average magnitude of the dierential lightcurve for the target and the comparison stars (CS{CS7). Comparison stars marked with a * are used to calculate the average lightcurve. HJD 4588 Object HM Aur : HM Aur : 4548 HM Aur : FBS FBS FBS 64+7 CS : 954 : 87 : 883 : 937 : 78 : Vdi HJD Object Vdi NSV { NSV { HJD Object V di : { 4594 HQ And : CS CS7 45 { 4594 RX And : CS : : FO Per 77 4 { : : CS CS7 57 determined minimum value of 6.. In Table we give the mean dierential magnitudes together with their standard deviation over the night. Figure shows the lightcurves of the program stars as plots of the dierential magnitude (except for FO Per and RX And, where the calibrated V- magnitude was available) against time in units of the Heliocentric Julian Date (HJD). All magnitude-axes cover a range of.7 mag, while all HJD-axes cover a time of.7 d, thus rendering all lightcurves directly comparable. The nding charts on the left side of Figure give the location of the objects as well as of all comparison stars referred to in Table for which dierential lightcurves were computed. Known CVs: HQ And, RX And and FO Per It is evident from Table that the standard deviation of the dierential lightcurve is much higher than those of the comparison stars. The dierential lightcurves of HQ And and RX And show the characteristic ickering while the lightcurve of FO Per shows a slow descent. Furthermore, we can derive a calibrated magnitude for FO Per and RX And, as several comparison stars have been measured as secondary standards by Misselt (996).

4 4 IBVS 4779 HQ And And RX FO Per Figure. On the left side, we present the nding charts for the analyzed stars. On the right side, the corresponding lightcurves (Magnitude vs. HJD) are displayed. Scales were chosen to be directly comparable. 3 3 ), Finding charts: HM Aur (dimensions: FBS (7 7 ), FBS 64 (6 6 ), NSV 7956 (3 3 ), HQ And (6 6 ), RX And (7 7 ), and FO Per (7 7 ). North is up, East is to the left. Numbers correspond to the comparison stars.

5 IBVS Aur HM FBS FBS 64+7 Figure NSV (cont.)

6 6 IBVS 4779 For RX And, we thus obtain a V = 4: 35(){4:5(6). The mentioned magnitude range. We place shortly after an outburst visual latter magnitude of V = 3:9(6){4:48() and for FO Per value lies almost exactly in the middle of the above therefore conclude that our observation must have taken while the CV was still in its decline. Candidate CVs: HM Aur, FBS , FBS 64+7, and NSV 7956 In the cases of HM Aur, FBS , and NSV7956 the resulting lightcurves show a straight line at a constant magnitude. None of the targets shows a standard deviation signicantly higher than those of the comparison stars. Furthermore, all objects which could be observedin morethan one night always show the same average magnitudes within the errors. We therefore conclude that a CV nature seems unlikely for these objects. As for FBS 64+7, due to the large uncertainties and the short time interval we do not consider our lightcurve to provide sucient information to speak in favour or against a CV classication. However, the very recently published spectrum by Liu et al. (999) clearly lacks any CV characteristic. We thus take the fact that the most doubtful lightcurve was obtained from an object which was proven afterwards not to be a CV to strengthen our conclusions on the other three candidates, although spectroscopic observations will be required to nally clarify their status. Acknowledgements. We thank the director of the Hoher List Observatory, Prof. Dr. W. Seggewiss, for generous allocation of observing time. References: Abramyan, H.V., Mikaelyan, A.M., 994, Astrophys., 37, 4 Abramyan, H.V., Mikaelyan, A.M., 995, Astrophys., 38, 8 Andronov, I.L., Meinunger, L., 987, IBVS, 35, Bruch, A., 989, A&AS, 78, 45 Downes, R., Webbink, R.F., Shara, M.M., 997, PASP, 9, 345 (DWS 97) Gessner, H., 978, Mitt. Verand. Sterne, 8, 66 Geyer, E., Kippenhahn, R., Strohmeier, W., 955, Kleine Ver o. Bamberg 9 Howarth, I.D., 976, Mitt. Verand. Sterne, 7, 47 Kaitchuck, R.H., Mansperger, C.S., Hantzios, P.A., 988, ApJ, 33, 35 Kaitchuck, R.H., 989, PASP,, 9 Kholopov, P. (ed.), 98, New catalogue of variable stars, Moscow: Publ. Oce Nauk a Liu, W., Hu, J.Y., Li, Z.Y., Cao, L., 999, ApJS,, 57 Meinunger, L., 975, Mitt. Verand. Sterne, 7, Meinunger, L., 98, IBVS, 795, Misselt, K.A., 996, PASP, 8, 46 Ritter, H., Kolb, U., 998, A&AS, 9, 83 Smith, D., Mateo, M. Szkody, P., 995, Astrophys. Space Sci., 5, 6 Verbunt, F., Pringle, J.E., Wade, R.A., et al., 984, MNRAS,, 97 Vogt, N., 989, in: Classical Novae, Bode, M.F., Evans, A. (eds.), Wiley & Sons, p. 5