Peremennye Zvezdy (Variable Stars) 32, No. 1, 2012 Received 1 January; accepted 8 February.

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Photometric Activity of the Herbig Ae star WW Vul

S. N. Udovichenko

Astronomical observatory of Odessa National University, Marazliyevskaya 1v, Odessa 65014, Ukraine, e-mail: udovich222@ukr.net

The star WW Vul (HD 344361, Sp A3ea), its maximum amplitude of brightness variations being 27 (GCVS database, Samus et al. 2011) belong to pre-main-sequence (PMS) Herbig Ae/Be stars with unusual photometric activity due to variable circumstellar extinction caused by gas-and-dust disks surrounding them. To learn what dust fragments rotate about the star, attempts to determine rotation periods were undertaken. From the photoelectric observations by Zajtseva (1983), a period of 404 exists. Fourier analysis by Volchkova (1993) of photoelectric observations by various authors in a 22-year range did not confirm it, but found two quasi-periods: 274 and 1100. However, the star does not always quite follow these periods. Bernabei et al. (2004) report that the star might pulsate at low frequencies, , but only one night of observations was available for the star. During their evolution towards the main sequence (MS), Herbig Ae/Be stars of intermediate mass ( ) cross the pulsation instability region of more evolved Scuti stars (Ripepi et al. 2011). At least a part of activity of such PMS stars is due to stellar pulsation. Up to now, several candidates were detected from precise observations (Bernabei et al. 2004, Marconi et al. 2010).

Our CCD photometry of WW Vul was performed at the astronomical station near Odessa in 2007-2011. The 48-cm AZT-3 reflector, with the Newtonian focus and a CCD photometer equipped with an UAI CCD (Sony ICX429ALL, Peltier-cooled) and a  filter, was used. Three stars were chosen as the comparison and check stars (comp=GSC 1612-393, ; check=GSC 1612-527, or GSC 1612-151, ).

Reductions of the CCD frames were carried out with the MUNIPACK (http://c-munipack.sourceforge.net/) software. Our procedures for aperture photometry consisted of dark-level and flat-field corrections, followed with the determination of the instrumental magnitude and uncertainty. Relative magnitudes of WW Vul were measured with respect of the comparison star. Table 1 summarizes the log of the photometric data.

All our observations are shown in Fig. 1. Individual measurements are accessible in the html version of this paper as data.txt.

WW Vul has the following observed and model characteristics: , (Krivova and Il'in 1997), (Montesinos et al. 2009), confirming the star's location in the instability region of  Scuti stars (Rodriguez and Breger 2001). Taking into account this fact, an attempt to search for periodicity of light variations was made. The frequency analysis for short periodicity was carried out with the Period04 package (Lenz & Breger 2005), which applies both the Fourier and least-squares algorithms and permits simultaneous fitting of multiple sinusoidal variations. Only the data of 2009 and 2011 were analyzed for periodicity, they being more precise and suited for calculations. The data were de-trended with the aid of polynomial fitting (Fig. 2b). The first two frequencies and the signal-to-noise ratio (in the amplitude) for each frequency are presented in Table 2.

Analytical uncertainties were calculated as a results of the least-squares fit and Monte Carlo simulation in the Period04 package. Unfortunately, the signal-to-noise ratio is too small for reliable determination of the significance of the detected frequencies because of the influence of circumstellar clouds and gas that obscure the star from the observer and cause light variations or to other reasons. However, Fig. 2c exhibits the low-amplitude phase curve for the season of 2011 with the first frequency, 9.34 d. Very detailed light curves and account of the envelope influence are needed for reliable confirmation of the short periodicity for WW Vul.

References:

Bernabei S., Ripepi V., Marconi M. et al. 2004, Proc. IAU Symposium No. 224, p.812

Krivova N.A., Il'in V.B. 1997, Astronomy Letters, 23, 791

Lenz P., Breger M. 2004, Comm. in Asteroseismology, No. 144, 41

Marconi M., Ripepi V., Bernabei S. et al. 2010, Astrophys.& Sp. Sci., 328, 109

Montesinos B., Eiroa C., Mora A., Merin B. 2009, Astron.& Astrophys., 495, 901

Ripepi V., Cusano F., Di Criscienzo M. et al. 2011, Mon. Not. R. Astron. Soc., 416, 1535

Rodriguez E., Breger M. 2001, Astron.& Astrophys., 366, 178

Samus N.N., Durlevich O.V., Kazarovets E V., Kireeva N.N., Pastukhova E.N., Zharova A.V. et al. 2011, General Catalogue of Variable Stars (GCVS database, Version 2011Jan)

Volchkova N.A. 1993, Astrofizika, 36, 61

Zajtseva G.V. 1983, Perem. Zvezdy, 22, 1

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