IBVS 5749

Table 2: Photometric data of VW Vulpeculae

06/07/2004

193.417

14.84±0.03

14.54±0.04

14.24±0.05

07/07/2004

194.437

14.97±0.03

14.70±0.04

14.37±0.04

09/07/2004

196.475

15.19±0.04

14.85±0.02

14.50±0.03

10/07/2004

197.473

15.38±0.08

14.96±0.02

14.64±0.02

14.38±0.03

13/07/2004

200.437

15.30±0.10

14.98±0.04

14.55±0.04

15/07/2004

202.406

15.28±0.10

14.79±0.02

14.52±0.02

14.18±0.02

17/07/2004

204.471

13.93±0.07

13.71±0.02

13.57±0.02

13.44±0.02

21/07/2004

208.426

14.88±0.08

14.53±0.02

14.30±0.02

14.08±0.02

23/07/2004

210.443

14.68±0.08

14.47±0.05

14.34±0.05

13.99±0.04

14/08/2005

596.525

15.77±0.03

15.39±0.03

15.02±0.04

15/08/2005

597.534

15.77±0.10

15.40±0.04

15.01±0.04

14.61±0.04

16/08/2005

599.441

15.63±0.10

15.15±0.02

14.86±0.02

14.64±0.03

09/09/2005

623.420

15.84±0.05

15.32±0.02

15.03±0.03

14.66±0.03

10/09/2005

624.428

15.65±0.05

15.22±0.03

15.06±0.02

14.71±0.04

23/09/2005

637.415

15.36±0.05

15.06±0.05

14.75±0.04

26/09/2005

640.398

14.61±0.05

14.24±0.04

29/10/2005

673.379

15.17±0.03

14.92±0.02

14.57±0.05

19/11/2005

694.261

14.68±0.07

14.34±0.02

14.16±0.03

13.97±0.03

10/11/2005

695.230

14.95±0.05

14.57±0.02

14.30±0.02

14.10±0.04

New comparison stars to be added to the Misselt (1996) sequence. North is up and East to the left. The frame is 11'×8'

V light curve of VW Vul in summer 2004. Filled circles are our data, while small crosses are visual estimates available from AFOEV (cdsweb.u-strsbg.fr/afoev). The variable was observed during the rise to a low-amplitude outburst, the successive decline and the following fast burst. Error bars show the standard deviations

All the data of VW Vul here reported were obtained in differential photometry using the calibration stars given by Misselt (1996) with the numbers M2, M3, M6, M7. Moreover, we calibrated these comparison stars with the Ic filter by observing, on different photometric nights, several standard stars (Landolt, 1992) having B-V from -0.2 to 1.4, over a wide range of airmass. The weighted averages are: Ic(M2)=12.33±0.05, Ic(M3) = 13.61±0.05, Ic(M6)=13.82±0.05, Ic(M7)=12.01±0.05. All these stars are placed in the East direction of VW Vul, so we included more comparison objects to the sequence. Figure 1 shows the finding chart for the new reference stars that we have found near VW Vul, numbered from C1 to C6. Table 1 gives the V, Rc, Ic data of these new reference stars. The first column gives the number (see Fig. 1), the second and the third columns are the J2000.0 coordinates of the objects, the last column is the number of different nights each new reference star has been calibrated to give the average values reported in columns 4-6. All the stars have been observed for a minimum of 15 months to a maximum of 19 months, so they can be considered stable.

In 2004, VW Vul has been monitored from June 25 to July 23, for a total of 16 nights (see Figure 2). More observations have been collected in 2005, from August 14 to November 10, so the overall database consists of 26 nights for a total of 95 photometric measurements (Table 2). From these data we can see that VW Vul varies between V=13.71±0.02 and 15.77±0.03.

We know that the UV emission of VW Vul during quiescence is dominated by the accretion disk, plus the white dwarf contribution (Henry & Sion, 2001; Urban & Sion, 2006). The strong emission of the disk is evident also in the optical B band, with a relatively low difference in the average B-V color-index: it varies between 0m.30 during the outburst and 0m.45 in quiescence. On the other side, in the infrared part of the spectrum, the emission is usually dominated by the late-type secondary star. The average value of V-Ic varies between 0m.39 and 0m.65, but the complete variation goes from V-Ic=0m.27 to 0m.79.

References:

Bruch, A., Engel, A., 1994, A&AS, 104, 79 (1994A&AS..104...79B)

Henry, C.K., Sion, E.M., 2001, PASP, 113, 970 (2001PASP..113..970H)

Kato, T., 1999, IBVS, No. 4769 (IBVS N°.4769)

Kholopov, P.N., et al., 1985-1990, General Catalogue of Variable Stars, 4th ed., Nauka, Moscow

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

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

Shafter, A.W., 1985, AJ, 90, 643 (1985AJ.....90..643S)

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

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

Thorstensen, J.R., Taylor, C.J., Kemp, J., 1998, PASP, 110, 1405 (1998PASP..110.1405T)

Urban, J.A., Sion, E.M., 2006, ApJ, 642, 1029 (2006ApJ...642.1029U)

Wenzel W, 1985, IBVS, No. 2757 (IBVS N°.2757)

Keyword(s): photometry

Abstract: In this paper we report BVRI observations of the dwarf nova VW Vulpeculae. Moreover, new comparison stars are calibrated in the VRI bands and included in the text with the finding chart.

The dwarf nova VW Vulpeculae is classified as Z Cam (UGZ) in the GCVS (Kholopov et al., 1985-1990), with B magnitudes ranging from 13.1 to 16.27. Shafter (1985) published a spectroscopic study and reported a period of 0.0731 day. However, Thorstensen et al. (1998) computed an orbital period of 0.1687 day from the measurement of H{alpha} radial velocities in quiescence. Only a few photometric data are available for this source. Wenzel (1985) found a 19±5 days cycle length on 40 years of archival plates. Bruch & Engel (1994) report B-V=0.12 during the outburst, and B-V=0.35 in quiescence. More recently, Kato (1999) gives the light curve of VW Vul during the 1995 standstill.

With the aim to increase the multi-band photometric database of VW Vul, we observed this source at the Porziano Astronomical Observatory during the summers of 2004 and 2005. The photometric system consists of an 0.35-m Schmidt-Cassegrain telescope, equipped with an HiSIS 23 CCD camera (Kodak Kaf 401E of 762×512 pixels) and B, V, Rc, Ic Johnson-Cousins broad-band filters. The exposure time was 120-300 s depending on the brightness of the object. 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).

Few other observations were obtained with the AIT at the Perugia University Observatory (see Spogli et al., 1998 for a description of instruments and data-reduction). There is no evaluable difference between the reduced data obtained with the two different telescopes.

Table 1: New comparison stars of VW Vul

No.

J2000.0 coord.

Obs.

{alpha}

{delta}

[mag]

nights

20h57m32s.82

+25°30'20".3

14.26±0.02

13.86±0.02

13.44±0.03

20h57m28s.48

+25°33'27".8

15.17±0.05

14.59±0.02

14.03±0.04

20h57m18s.30

+25°29'49".0

15.39±0.03

14.92±0.01

14.44±0.03

20h57m20s.95

+25°28'52".5

13.53±0.03

12.49±0.02

11.58±0.03

20h57m14s.35

+25°29'36".3

16.02±0.05

15.64±0.02

15.27±0.03

20h57m21s.35

+25°26'34".6

15.41±0.04

14.90±0.03

14.41±0.03

UT Date

(2453000+)

25/06/2004

181.526

15.19±0.08

14.77±0.02

14.49±0.02

14.33±0.03

26/06/2004

182.556

15.08±0.08

14.72±0.04

14.48±0.03

14.24±0.03

27/06/2004

184.421

14.79±0.08

14.50±0.02

14.28±0.02

14.10±0.03

28/06/2004

185.413

14.64±0.09

14.28±0.03

14.11±0.02

13.90±0.03

01/07/2004

188.485

14.34±0.07

13.99±0.03

13.85±0.03

13.59±0.04

02/07/2004

189.457

14.56±0.07

14.25±0.05

14.05±0.03

13.81±0.04

05/07/2004

192.411

15.11±0.08

14.76±0.03

14.48±0.02

14.27±0.04

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 5749

Konkoly Observatory

Budapest

22 January 2007

HU ISSN 0374 - 0676 (print)

HU ISSN 1587 - 2440 (on-line)

BVRI Photometry of VW Vul and New Comparison Stars

Capezzali, D. (1),(2); Spogli, C. (1),(2); Fiorucci, M. (1); Ciprini, S. (1); Nucciarelli, G. (1);

Mancinelli, V. (2); Brunozzi, P. (2); Fagotti, P. (2); Brandoni, L. (2); Rocchi, G. (2)

(1) Physics Department and Astronomical Observatory, University of Perugia, Perugia, Italy

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

SIMBAD object(s): VW Vul

Type(s): UGZ