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Peremennye Zvezdy (Variable Stars) 32, No. 1, 2012 Received 1 January; accepted 8 February.
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Article in PDF |
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
Photometric CCD observations of the pre-main-sequence
Herbig Ae star WW Vul on separate nights during 2007-2011 are
presented. The star exhibited long-term non-periodic variability
in the range of 0 8; rapid variations with a small amplitude
were superimposed. The results of a search for periodicity in the
light variations are reported.
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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.
Table 1. Photometric observations of WW Vul
| Year | JD | No. of nights | Typical uncertainty, mag |
| 2007 | 2454262-2454303 | 12 | 0.01-0.02 |
| 2008 | 2454650-2454651 | 2 | 0.01-0.02 |
| 2009 | 2455033-2455095 | 8 | 0.005 |
| 2011 | 2455795-2455803 | 4 | 0.005 |
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.
Table 2. The frequencies and amplitudes of WW Vul
| N | Frequency | Signal- | Amplitude | Frequency, d | Signal- | Amplitude |
2011, d |
to-noise | mag | 2009, d |
to-noise | mag | |
| F1 |
 |
2.1 |
 |
 |
2.4 |
 |
| F2 |  |
2.2 |
 |
 |
2.5 |
 |
 |
Fig. 2.
From top to bottom:
(a) one night of observations of WW Vul: differences variable - comparison
star and comparison star - check star; (b) de-trended light
curve; (c) phase curve for the season 2011 with the first
frequency, 9.34 d |
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