IBVS 5596

Downes R. A., Shara M. M., 1993, PASP, 105, 127 (1993PASP..105..127D)

Misselt K. A., 1996, PASP, 108, 146 (1996PASP..108..146M)

Ritter H., Kolb U. 2003, A&A, 404, 301 (2003A&A...404..301R)

Spogli C., Fiorucci M., Tosti G., 1998, A&AS, 130, 485 (1998A&AS..130..485S)

Spogli C., Fiorucci M., Raimondo G., 2003, IBVS, 5365 (IBVS N°.5365)

Tosti G., Pascolini S., Fiorucci M., 1996, PASP, 108, 706 (1996PASP..108..706T)

V light curve of EM Cyg from June 1st to October 27th 2003. Circles represent the data here reported, while small crosses are visual estimates available from AFOEV (http://cdsweb.u-strasbg.fr/afoev/).

Color-Magnitude diagram for the dwarf nova EM Cygni. The diagram contains the data here reported and the previous results (Spogli et al. 2003).

References:

21/08/2004

3239.444

13.89±0.12

13.19±0.07

12.74±0.04

12.22±0.05

22/08/2004

3239.571

13.93±0.09

13.26±0.04

12.78±0.04

12.24±0.05

08/10/2004

3287.418

12.91±0.05

12.16±0.05

23/10/2004

3302.404

13.57±0.05

12.35±0.04

Table 3 Photometric characteristics of EM Cyg from our 1997-2004 observations.

Maximum Outburst

12.25

12.20

11.98

11.62

Minimum of Light

14.51

13.83

13.24

12.65

Outburst Amplitude

2.2

1.5

1.1

0.9

Decay Rates(mag/day)

0.18±0.06

0.14±0.04

0.12±0.04

0.09±0.04

(B-V)

(V-Rc)

(V-Ic)

Averages during the outburst

0.2

0.3

0.7

Averages during quiescence

0.7

0.5

1.1

Table 1 2003 BVRcIc data of EM Cyg

15/07/2003

2836.496

14.51±0.05

13.61±0.04

13.09±0.04

12.47±0.04

18/07/2003

2839.475

14.49±0.10

13.62±0.05

13.13±0.04

12.46±0.04

19/07/2003

2840.495

13.99±0.11

13.53±0.04

13.04±0.04

12.41±0.04

22/07/2003

2842.536

14.01±0.09

13.42±0.06

13.12±0.03

12.48±0.04

23/07/2003

2843.526

14.47±0.11

13.53±0.03

13.04±0.04

03/08/2003

2854.509

13.44±0.06

12.88±0.05

12.54±0.04

12.07±0.04

05/08/2003

2857.334

12.86±0.05

06/08/2003

2858.428

14.33±0.05

10/08/2003

2862.461

14.12±0.11

12/08/2003

2864.487

14.23±0.07

13.49±0.04

13.15±0.04

12.47±0.04

13/08/2003

2865.404

13.68±0.05

13.18±0.04

12.54±0.04

18/08/2003

2870.321

13.57±0.05

13.08±0.05

19/08/2003

2871.441

14.03±0.05

13.51±0.04

13.01±0.04

20/08/2003

2872.392

14.32±0.12

13.83±0.04

13.21±0.05

22/08/2003

2874.394

14.09±0.08

13.51±0.04

13.02±0.05

12.43±0.04

10/09/2003

2893.389

12.25±0.12

15/09/2003

2898.346

12.51±0.09

12.32±0.05

17/09/2003

2900.405

12.85±0.05

12.53±0.03

12.25±0.04

11.81±0.04

18/09/2003

2901.368

12.94±0.07

12.68±0.05

12.35±0.05

11.92±0.04

19/09/2003

2902.377

13.23±0.09

12.84±0.05

12.54±0.05

12.12±0.04

21/09/2003

2904.317

13.71±0.06

13.20±0.08

12.86±0.05

12.35±0.04

22/09/2003

2905.341

14.01±0.05

13.31±0.04

25/09/2003

2908.355

13.98±0.05

13.28±0.07

12.85±0.07

12.37±0.05

26/09/2003

2909.363

13.96±0.07

13.41±0.06

12.92±0.06

12.34±0.05

03/10/2003

2916.336

13.26±0.08

12.76±0.05

12.44±0.05

12.03±0.04

06/10/2003

2919.321

13.67±0.08

13.21±0.05

12.72±0.05

10/10/2003

2923.331

14.04±0.08

13.44±0.05

12.98±0.05

12.43±0.04

12/10/2003

2925.307

13.91±0.04

13.39±0.05

16/10/2003

2929.396

13.23±0.12

12.86±0.05

12.51±0.05

12.09±0.04

27/10/2003

2940.271

13.56±0.13

13.07±0.05

12.76±0.03

12.21±0.04

Table 2 2004 BVRcIc data of EM Cyg

UT Date

(2450000+)

25/05/2004

3150.599

13.08±0.09

12.74±0.05

12.45±0.04

12.01±0.03

31/05/2004

3156.609

13.69±0.08

13.31±0.05

12.91±0.05

12.37±0.04

12/06/2004

3168.612

13.82±0.08

19/06/2004

3175.557

13.75±0.08

13.24±0.04

12.84±0.04

06/07/2004

3193.394

12.67±0.07

11.94±0.06

15/07/2004

3202.384

13.40±0.05

12.33±0.04

16/07/2004

3203.379

13.31±0.05

12.37±0.05

17/07/2004

3204.379

13.49±0.05

12.36±0.05

22/07/2004

3209.487

14.04±0.09

23/07/2004

3210.395

13.45±0.05

12.34±0.04

30/07/2004

3217.413

13.45±0.05

12.31±0.04

01/08/2004

3219.498

14.09±0.07

17/08/2004

3235.441

14.45±0.11

13.58±0.05

13.05±0.05

12.42±0.04

18/08/2004

3235.514

14.38±0.09

13.62±0.05

13.10±0.04

12.50±0.04

UT Date

(2450000+)

02/06/2003

2792.528

13.02±0.05

12.82±0.04

12.49±0.04

12.01±0.04

05/06/2003

2795.549

13.29±0.13

12.97±0.05

12.65±0.04

12.14±0.03

06/06/2003

2796.556

13.61±0.12

13.21±0.05

12.79±0.04

12.21±0.03

11/06/2003

2801.581

14.08±0.05

13.38±0.05

12.93±0.04

12.33±0.03

12/06/2003

2802.574

13.96±0.05

13.43±0.05

13.02±0.04

12.37±0.03

20/06/2003

2810.554

13.11±0.05

12.86±0.05

12.58±0.04

12.14±0.03

21/06/2003

2811.546

13.38±0.07

13.01±0.05

12.65±0.04

12.12±0.03

22/06/2003

2812.558

13.57±0.08

13.15±0.04

12.74±0.04

25/06/2003

2815.542

14.31±0.07

13.64±0.04

13.08±0.04

12.46±0.04

26/06/2003

2816.592

14.43±0.08

13.57±0.05

13.04±0.03

08/07/2003

2828.501

12.78±0.09

12.43±0.04

12.13±0.04

11.66±0.04

12/07/2003

2832.521

13.35±0.07

13.12±0.05

12.77±0.04

12.22±0.04

The dwarf nova EM Cyg is an eclipsing and spectroscopic binary that belongs to the Z Cam class (Downes & Shara 1993). From the catalogue of Ritter and Kolb (2003), we know that EM Cyg has V =~ 13m.3 mag during the regular minimum, V =~ 14m.4 at minimum during the eclipse, V =~ 12m.5 during the maximum, and V =~ 12m.9 in standstill. We observed EM Cyg since 1997 with the aim to study its variability using broad band photometry (Spogli et al. 2003). Here we improve our previous analysis using new BVRcIc data obtained during the Summer-Autumn 2003 and 2004, for a total of 57 new nights. All photometric new data are reported in Tables 1 and 2.

The observations of EM Cyg were made at the Perugia Astronomical Observatory with 0.40 m Automatic Imaging Telescope (Tosti et al. 1996), and at Porziano Astronomical Observatory (Assisi) with the 0.35 m Schmidt-Cassegrain telescope equipped with an HiSIS 23 CCD camera (Kodak Kaf 401E of 762×512 pixel). The instruments used and the photometric techniques have been already described in Spogli et al. (1998). Both telescopes are endowed with standard BVRcIc Johnson-Cousins broad-band filters. An inter-comparison between results obtained during the same nights shows no relevant systematic difference, within the typical standard deviation of each instrument. All data are obtained in differential photometry using the calibration stars reported by Misselt (1996) and Spogli et al. (2003).

Figure 1 shows the V light curve during 2003, and the visual estimates available from AFOEV (http://cdsweb.u-strasbg.fr/afoev/). A similar comparison can be done with all our database (including Spogli et al. 2003), with the conclusion that our multi-band photometry samples very well the outburst, the decline and the minimum phases, while there are few data about the rising phase. The typical time interval between two outbursts is 23 days, with a range of 15-40 days. The general trend is well characterized, with the emission dominated by the secondary star during the minimum (V-I =~ 1m.1, see Figure 2) and by the accretion disk during the outburst (V-I =~ 0m.6). The main photometric informations are summarized in Table 3, taking into account the new data and the 1997-2000 data (Spogli et al. 2003).

Konkoly Observatory

Budapest

17 January 2005

HU ISSN 0374 - 0676 (print)

HU ISSN 1587 - 2440 (on-line)

BVRI observations of EM Cygni in the Years 2003-2004

Spogli, Corrado (1); Fiorucci, Massimo (1); Capezzali, Daniele (1); Mancinelli, Vannio (2); Nucciarelli, Giuliano (1); Brunozzi, Paolo (2); Fagotti, Paolo (2); Rocchi, Gianni (2)

(1) Osservatorio Astronomico, Università di Perugia, Via A. Pascoli I-06100 Perugia, Italy

(2) Gruppo Astrofili Monte Subasio, Piazza Santa Maria 2, Assisi, Italy

SIMBAD object(s): EM Cyg

Type(s): UG

Keyword(s): photometry

Abstract: In this paper we report BVRI observations of the dwarf nova EM Cyg obtained in the years 2003 and 2004. A preliminary statistical analysis is reported.

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