Phase-diagram of DX And in quiescence considering an hypothetical period of 10.645 days. Dotted line is the sinusoidal best fit. This variation is superimposed to an ellipsoidal variation well defined by Hilditch (1995).

Table 1

UT Date

HJD

Rc

UT Date

HJD

Rc

(2452000+)

(2452000+)

18/07/2003

839.387

14.67±0.05

11/08/2003

863.346

14.90±0.05

19/07/2003

840.339

14.53±0.04

12/08/2003

864.391

14.70±0.10

20/07/2003

841.329

14.82±0.03

13/08/2003

865.373

14.45±0.03

21/07/2003

842.326

14.82±0.04

14/08/2003

866.320

14.50±0.03

22/07/2003

843.329

14.73±0.03

15/08/2003

867.311

14.37±0.03

23/07/2003

844.322

14.40±0.05

16/08/2003

868.316

14.74±0.03

24/07/2003

845.326

14.62±0.03

17/08/2003

869.366

14.55±0.03

25/07/2003

846.388

14.59±0.03

18/08/2003

870.299

14.54±0.03

26/07/2003

847.322

14.63±0.04

19/08/2003

871.293

14.48±0.04

27/07/2003

848.323

14.71±0.04

20/08/2003

872.294

14.47±0.03

28/07/2003

849.333

14.50±0.03

21/08/2003

873.297

14.89±0.04

01/08/2003

853.381

14.64±0.03

22/08/2003

874.349

14.63±0.03

03/08/2003

855.349

14.78±0.05

23/08/2003

875.293

14.68±0.03

05/08/2003

857.453

14.49±0.03

13/09/2003

896.265

14.51±0.03

06/08/2003

858.381

14.46±0.04

15/09/2003

898.248

14.48±0.04

07/08/2003

859.361

14.66±0.04

16/09/2003

899.301

14.59±0.03

08/08/2003

860.312

14.59±0.03

17/09/2003

900.274

14.46±0.03

09/08/2003

861.319

14.78±0.03

18/09/2003

901.295

14.44±0.03

10/08/2003

862.323

14.73±0.05

19/09/2003

902.261

14.57±0.05

11/08/2003

863.342

14.97±0.03

20/09/2003

903.258

14.61±0.03

Table 2

UT Date

HJD

B

V

Rc

Ic

(2453000+)

26/09/2005

640.414

12.48±0.04

12.38±0.04

12.21±0.03

12.12±0.02

03/10/2005

647.386

12.09±0.08

12.03±0.02

11.86±0.04

11.71±0.02

09/10/2005

653.393

13.29±0.05

13.11±0.02

12.87±0.02

12.65±0.02

11/10/2005

655.341

14.26±0.07

13.89±0.02

13.52±0.02

13.22±0.02

12/10/2005

656.342

14.55±0.05

14.05±0.05

13.61±0.03

14/10/2005

658.324

15.78±0.05

14.99±0.04

14.37±0.02

14.01±0.02

15/10/2005

659.399

16.18±0.05

15.09±0.02

14.38±0.02

13.96±0.03

18/10/2005

662.351

16.21±0.07

15.07±0.02

14.34±0.02

13.87±0.02

22/10/2005

666.344

15.77±0.08

15.07±0.02

14.39±0.02

13.84±0.02

24/10/2005

668.325

15.93±0.05

15.02±0.02

14.38±0.02

13.91±0.02

25/10/2005

669.365

15.70±0.06

15.01±0.02

14.44±0.04

13.94±0.03

26/10/2005

670.364

15.99±0.05

15.16±0.02

14.47±0.02

14.02±0.02

29/10/2005

673.333

16.10±0.05

15.04±0.02

14.53±0.03

13.99±0.02

30/10/2005

674.349

16.20±0.05

15.15±0.03

14.52±0.03

14.01±0.02

31/10/2005

675.263

16.07±0.05

15.13±0.03

14.51±0.02

13.97±0.03

02/11/2005

677.435

16.15±0.05

15.24±0.03

14.57±0.02

14.06±0.03

27/11/2005

702.361

16.11±0.05

15.20±0.02

14.56±0.02

14.04±0.02

V light curve of DX And during Autumn 2005 (left panel), filled circles represent our data, while small crosses are visual estimates available from AFOEV (cdsweb.u-strasbg.fr/afoev/). The right panel shows our BVRI data only: it is evident the different color indices from the outburst to the minimum, and the internal variability during quiescence.

During the year 2003, DX And was observed for a total of 40 photometric nights only with the Rc filter and it was always in quiescence (Table 1). The variable oscillates between Rc =~ 14.4 and Rc =~15.0, with an average of Rc =~14.63. In quiescence and at these wavelengths the system is dominated by the late-type secondary and its ellipsoidal variations: this is a familiar pattern for long-period cataclysmic binaries. Hilditch (1995) studied R and I variations of DX And during five consecutive nights, ten orbital cycles, and he found an ellipsoidal variation of amplitude 0.13 mag, superimposed to additional variability. We have already analyzed intra-night data to verify the ellipsoidal variation (Spogli, Fiorucci & Tosti 1998), so we collected data with a longer time-scale with the aim to obtain information about the additional variability. However, periodograms and other statistical tools are not able to find evidence of strict periodicity with the data reported in Table 1. The analysis is seriously biased by the data sampling (±1, ±2 c/d alias frequencies) that makes correct identification of the frequency components ambiguous. The most probable results are obtained for P=10.645 days (65 %, Fig. 1), P=0.912 day (58 %), P=0.47625 day (55 %), and P=0.4482 day (50 %). Probably the latter can be identified with the actual value of the orbital period, while the additional variability showed by DX And during quiescence is of an unknown origin.

In the year 2005, DX And was monitored from September 26 to November 11 with the B V Rc Ic photometric bands, for a total of 17 photometric nights (see Table 2). It was in outburst and we followed part of the rise and the decline (Fig. 2). The profile and the time-scales confirm the results obtained by Simon (2000). Also the color indices are in substantial agreement with our previous BVRcIc observations (Spogli et al. 1998). However, these new data increase the historical database on this variable source and they can help to constrain theoretical models.

References:

Bruch, A., 1989, A&AS, 78, 145 (1989A&AS...78..145B)

Bruch, A., Vrielmann, S., Hessman, F.V., et al., 1997, A&A, 327, 1107 (1997A&A...327.1107B)

Hilditch, R.W., 1995, MNRAS, 273, 675 (1995MNRAS.273..675H)

Ritter H., & Kolb U., 1998, A&AS, 129, 83 (1998A&AS..129...83R)

Simon, V., 2000, A&A, 364, 694 (2000A&A...364..694S)

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

In this brief paper we present the results of our observations made in the years 2003 and 2005 at the Porziano Astronomical Observatory, Monte Subasio Astronomical Association. We used the 0.30-m Schmidt-Cassegrain f/6.5 telescope, equipped with an AP-32ME CCD camera (Kodak 3200-ME, 2184×1470 pixels) and Johnson-Cousins B V Rc Ic photometric filters. The exposure time was 60-300 s depending on the brightness of the object. The frames were first corrected for standard de-biasing and flat-fielding, and then processed by a PC-based aperture photometry package developed by one of the authors. The magnitudes were determined relative to the calibration stars reported by Spogli et al. (1998). Calibrations done with standard Landolt stars show negligible color effects in the V, Rc and Ic bands, while B data have been corrected and the reported standard deviations take into account this effect. Heliocentric corrections to observed times were applied before the following analysis.

SIMBAD object(s):    DX And

Type(s):    UG

Keyword(s):    photometry

Abstract:   In this paper we report BVRI observations of the dwarf nova DX And during the 2005 September-October Outburst. Moreover, optical variability of DX And in quiescence has been observed and studied.

DX And is a well-known dwarf nova with a long outburst recurrence time (270-330 days, Simon 2000) and a long orbital period (P = 10.6 hours, Bruch et al. 1997). Only few known cataclysmic variables have similar characteristics, and for this reason it has been extensively studied by many astronomers. Spectroscopic observation were made by Bruch (1989) who reports that DX And exhibits a considerable contribution of the secondary star to the continuum energy distribution as well as the line spectrum. During the years 1981-1999, the brightest outbursts reach up to about 11.5 magvis from a typical quiescent level of 14-14.7 magvis (Simon 2000). Ritter and Kolb (1998) report a wider range: DX And varies from V=16.5 at minimum to V=10.9 at the maximum of brightness.

COMMISSIONS 27 AND 42 OF THE IAU

INFORMATION BULLETIN ON VARIABLE STARS

Number 5716

Konkoly Observatory

Budapest

18 July 2006

HU ISSN 0374 - 0676  (print)

HU ISSN 1587 - 2440  (on-line)

BVRI photometry of DX And: the Autumn 2005 Outburst

Spogli, C. (1),(2); Fiorucci, M. (1); Capezzali, D. (1),(2); Rocchi, G. (2); Mancinelli, V. (2);

Brunozzi, P. (2); Fagotti, P. (2)

(1) Physics Department, University of Perugia, Via A. Pascoli, 06123 Perugia, Italy

(2) Porziano Astronomical Observatory, Via Santa Chiara 2, Assisi, Italy

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