6 Conclusions

In this paper, we presented an analysis of photometric and spectroscopic observations of the recently discovered $\delta$ Scuti variable V784 Cas. The UBV photometry was carried out at Szeged Observatory (Hungary), while the simultaneous uvby data were obtained at Sierra Nevada Observatory (Spain) in three consecutive years (1999-2001). Medium-resolution spectroscopy in the H$\alpha$ region was carried out at the David Dunlap Observatory (Canada) in 1999 and 2001. These data were used to determine the frequency content and to estimate physical parameters of the star. The main results can be summarized as follows:

1. Multicolor data consisting of more than 3000 individual points were analyzed with the standard Fourier-analysis. The multiperiodic nature of the star is revealed unambiguously. Besides the dominant period listed also in the Hipparcos catalog, we could detect three more frequencies in the 9.46-15.9 d^-1 range. There is a suggestion for more, unresolved frequency components.

2. We have obtained almost 100 radial velocity measurements using the H$\alpha$ line. The measured radial velocity curves also show the multiperiodic nature and a close correlation with the four-component light curve fit. Spectra obtained in 1999 covered a few weak metallic lines and the varying asymmetric line profiles suggest the presence of non-radial pulsation, too.

3. Physical parameters of the star are determined from the mean Strömgren indices and synthetic colour grids. The resulting parameters give a consistent picture of an evolved $\delta$ Scuti star. Evolutionary mass ( $1.89\pm0.11~M_\odot$) and age ($1.3\pm0.3$ Gyr) is derived.

4. Possible mode identification was discussed based on the Strömgren photometric behaviour (amplitude and phase relations). We identify f₁ with the radial fundamental mode, while the remaining frequencies correspond to low-order (l=1 or 2) non-radial modes, although some ambiguity may arise from the moderate rotation of the star.

 

 

Table 4: Pulsational constants and amplitude and phase relations for the adopted set of frequencies. Note, that ordinal numbers are the same as in Table 2.

i	$f_{\rm i}$ (c/d)	$P_{\rm i}$ (d)	$Q_{\rm i}$	v/y	$\phi_v-\phi_y$	b/y	$\phi_b-\phi_y$
1	9.1565	0.10921	0.030 $\pm$ 0.006	1.61 $\pm$ 0.03	+5 $.\!\!^\circ$6 $\pm$ 0 $.\!\!^\circ$5	1.29 $\pm$ 0.02	+3 $.\!\!^\circ$2 $\pm$ 0 $.\!\!^\circ$5
2	9.4649	0.10565	0.029 $\pm$ 0.006	1.58 $\pm$ 0.07	-1 $.\!\!^\circ$1 $\pm$ 1 $.\!\!^\circ$4	1.27 $\pm$ 0.06	-1 $.\!\!^\circ$0 $\pm$ 1 $.\!\!^\circ$4
3	15.4036	0.06492	0.018 $\pm$ 0.003	1.46 $\pm$ 0.09	+1 $.\!\!^\circ$5 $\pm$ 2 $.\!\!^\circ$0	1.20 $\pm$ 0.08	+1 $.\!\!^\circ$2 $\pm$ 2 $.\!\!^\circ$0
5	15.9013	0.06289	0.017 $\pm$ 0.003	1.55 $\pm$ 0.13	-8 $.\!\!^\circ$2 $\pm$ 3 $.\!\!^\circ$1	1.25 $\pm$ 0.13	-5 $.\!\!^\circ$0 $\pm$ 3 $.\!\!^\circ$1

Further observations (photometric, as well as spectroscopic) of this variable star are expected to extend the data baseline yielding to a better resolution of the pulsational pattern, mode identification and detection of time-dependent phenomena (e.g. amplitude and/or frequency modulation).

Acknowledgements

This work has been supported by the MTA-CSIC Joint Project No. 15/1998, OTKA Grants #T032258, #T030743 and #T034615, the "Bolyai János'' Research Scholarship to LLK from the Hungarian Academy of Sciences, the Hungarian Eötvös Fellowship to LLK, FKFP Grant 0010/2001, Pro Renovanda Cultura Hungariae Grant DCS 2001/ápr/6. and Szeged Observatory Foundation. Fruitful discussions with J. Vinkó are acknowledged. The NASA ADS Abstract Service was used to access data and references. This research has made use of the SIMBAD database, operated at CDS-Strasbourg, France.