RC light curve of DX And in July-October 2006. The maximum occurred in Sept.23

Spectral flux distribution of DX And during the rise to the outburst. The data have been obtained during the nights of September 19 (circle), 20 (diamond), 21 (triangle), 22 (cross) and 23 (box). The dotted line represents a generic power-law function f({lambda}){proportional to}{lambda}-7/3.

Magnitudes and their errors for the stars in the photometric sequence.

Id

GSC id

RA

DEC

U

B

V

RC

IC

03242-

(J2000)

C1

00510

23 29 42.7

+43 45 42

13.65±0.07

13.42±0.04

12.72±0.03

12.26±0.03

11.90±0.03

C2

00216

23 29 50.5

+43 44 49

13.98±0.07

13.90±0.04

13.33±0.03

12.95±0.03

12.64±0.03

C3

00856

23 30 01.2

+43 48 41

13.4±0.1

12.71±0.05

11.68±0.04

11.10±0.04

10.58±0.04

C4

00562

23 29 40.2

+43 50 04

13.2±0.1

12.21±0.05

11.03±0.04

10.36±0.04

 9.84±0.04

C5

00990

23 29 24.5

+43 43 27

12.6±0.1

12.58±0.05

12.12±0.04

11.80±0.04

11.55±0.04

UBVRCIC magnitudes of DX And during the 2006 outburst

UT date

J.D.

U

B

V

RC

IC

2453000+

23/07/2006

939.534

14.60±0.02

27/07/2006

944.401

14.58±0.02

30/07/2006

947.378

14.48±0.03

04/08/2006

952.359

14.63±0.02

05/08/2006

953.391

14.52±0.02

15/08/2006

963.369

14.67±0.03

18/08/2006

966.354

14.45±0.02

21/08/2006

969.335

14.47±0.02

24/08/2006

972.353

14.55±0.01

27/08/2006

975.329

14.51±0.01

02/09/2006

981.325

14.43±0.02

03/09/2006

982.327

14.62±0.02

05/09/2006

984.352

14.45±0.05

06/09/2006

985.375

14.67±0.03

07/09/2006

986.343

14.58±0.03

10/09/2006

989.316

14.55±0.02

11/09/2006

990.335

14.50±0.02

13/09/2006

992.342

14.39±0.02

15/09/2006

994.345

14.38±0.03

19/09/2006

998.371

12.70±0.10

13.31±0.03

13.12±0.03

12.91±0.02

12.80±0.06

20/09/2006

999.305

12.38±0.08

12.94±0.03

12.79±0.02

12.62±0.02

12.49±0.03

21/09/2006

1000.304

12.05±0.03

12.60±0.08

12.53±0.03

12.33±0.03

12.23±0.02

22/09/2006

1001.309

11.75±0.05

12.28±0.04

12.21±0.02

12.05±0.02

11.97±0.03

23/09/2006

1002.309

11.58±0.10

12.23±0.03

12.14±0.03

11.95±0.03

11.85±0.02

24/09/2006

1003.336

12.40±0.04

12.21±0.04

12.05±0.03

11.92±0.02

29/09/2006

1008.306

12.54±0.03

12.39±0.02

12.19±0.02

12.00±0.03

30/09/2006

1009.284

12.66±0.05

12.45±0.02

12.23±0.03

12.09±0.03

06/10/2006

1015.376

14.73±0.03

14.33±0.02

14.03±0.02

13.68±0.01

08/10/2006

1017.288

15.59±0.03

14.77±0.02

14.29±0.02

13.77±0.03

13/10/2006

1022.321

14.45±0.02

14/10/2006

1023.278

14.54±0.02

15/10/2006

1024.298

14.53±0.03

27/10/2006

1036.305

14.52±0.03

28/10/2006

1037.391

14.60±0.03

29/10/2006

1038.227

14.52±0.02

02/11/2006

1042.337

14.51±0.03

03/11/2006

1043.267

14.49±0.02

10/11/2006

1050.383

14.54±0.03

14/11/2006

1054.302

14.51±0.01

15/11/2006

1055.295

14.52±0.04

References:

Bessell, M., 2000, Magnitude Scales and Photometric Systems, in ``Encyclopedia of Astronomy and Astrophysics'', P. Murdin (Ed.), Bristol Inst. of Physics Publishing

Echevarria, J., 1984, Rev. Mex. Astron. Astrofis., 9, 99 (1984RMxAA...9...99E)

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

Landolt, A.U., 1983, AJ, 88, 439 (1983AJ.....88..439L)

Landolt, A.U., 1992, AJ, 104, 340 (1992AJ....104..340L)

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

In the contest of a long-term variability study of a sample of dwarf novae, we are monitoring DX And since 1994 and we have already obtained photometric data in the BVRCIC bands during two outbursts, in 1994 and 2005 (Spogli et al., 1998, 2006). In this brief paper we present the results of our observations done in 2006, that includes also the U broad band together with the usual BVRCIc Johnson-Cousins filters. These are the firsts U data during the rise and the maximum of the outburst, since we know only two other data reported in literature obtained during the descending phase (Echevarria, 1984). The telescope we used was a 0.30-m f/6.5 Schmidt-Cassegrain reflector, equipped with an AP-32ME CCD camera (Kodak 3200-ME, 2184×1470 pixels) and Schuler UBVRCIC filters, located on Mt. Subasio, Assisi (PG), Italy. The exposure time was 120-600 s depending on the brightness of the object and the filter used. The frames were first corrected for bias and flat-field, and then processed by a PC-based aperture photometry package developed by one of the authors using DAOPHOT routines (Stetson, 1987).

All the data here reported were obtained in differential photometry using the photometric comparison sequence around DX And tabulated in Table 1. The UBVRCIC magnitudes have been calibrated with CCD observations obtained in July-August 2006 during three different photometric nights with respect to a selected sample of standard stars (Landolt 1983, 1992). Color transformation equations were characterized by slopes always within the margins 0.9-1.1. The photometric stability of the comparison stars can be guaranteed for C1 and C2 because they have been checked by repeated observations since 1994 (Spogli et al., 1998), while for the other stars we can only say that they were stable during the four months reported in this paper.

DX And has been monitored from July 23 to November 15, for a total of 40 different nights (Table 2). During the minimum we used only the RC broad-band, because we already knew that in quiescence the emission of DX And is dominated by the secondary star (Spogli et al., 2006). Our data confirm that in this phase of activity the RC magnitude oscillate between 14.4 and 14.6, probably ellipsoidal variations superimposed to additional variability, a typical pattern for long-period cataclysmic binaries (Hilditch, 1995). The precedent outburst occurred at the end of September 2005 (Spogli et al., 2006), so our aim was to observe the rise to the new outburst with the UBVRCIC filters, and the outburst effectively went up at the middle of September 2006 (Fig. 1). We obtained data in all the photometric range during the rise up to the maximum, observed in the night of September 23. Unfortunately, soon after the outburst we were not able to use the U filter for technical problems, so we followed the decline with the BVRCIC bands.

Fig. 2 shows the spectral flux distribution of DX And during the rise. The magnitudes have been converted in f({lambda}) using the flux calibrations reported by Bessell (2000). The increasing rate is more or less the same in all the filters, with the remarkable exception in the U, where the brightness continues to increase when in the other bands the maximum is already reached. This feature is quite common in outside-in outbursts, i.e. when the thermal instability (that gives rise to the outburst) starts in the outer part of the accretion disk and propagates inwards, producing an asymmetric light curve with a rapid rise and slow decay. The figure shows the progressive increase of the disk emission, theoretically represented - in a first approximation - as a power-law f({lambda}){proportional to}{lambda}-7/3, during the final steps of the outburst.

IBVS - KONKOLY OBSERVATORY, BUDAPEST, HUNGARY - ABOUT THIS DOCUMENT - ToC ENTRY - META-INFORMATION - THIS ISSUE IN   [PS]   [PDF]   FORMAT

COMMISSIONS 27 AND 42 OF THE IAU

INFORMATION BULLETIN ON VARIABLE STARS

Number 5792

Konkoly Observatory

Budapest

28 August 2007

HU ISSN 0374 - 0676  (print)

HU ISSN 1587 - 2440  (on-line)

UBVRI Photometry of DX And: the 2006 Outburst

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

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

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

SIMBAD object(s):    DX And   

Type(s):    UG

Keyword(s):    photometry

Abstract:   A new UBV(RI)c photometric sequence around DX And is presented, together with the photometric data obtained during the 2006 Outburst of this cataclysmic variable.

The dwarf nova DX And is one of the few cataclysmic variables with the orbital period length near the upper limit of the range (10.6 hours), together with an exceptional long cycle length (270-330 days), a secondary star probably evolved off the main sequence, and a very low mass-transfer rate (Simon, 2000). For all these reasons, DX And can be considered representative of the upper limit of the distribution of dwarf novae, and a detailed study of its activity can help to constrain theoretical models. Nevertheless, only a few outbursts have been studied in detail, and rarely with multi-colors photometry (see Simon 2000 for an overview of the scarce database available in literature).

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

Spogli, C., Fiorucci, M., Capezzali, D., et al., 2006, IBVS, 5716 (IBVS N°.5716)

Stetson, P.B., 1987, PASP, 99, 191 (1987PASP...99..191S)