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\IBVShead{4686}{17 March 1999}

\IBVStitle{HD~130484: A NEW $\delta$~Sct VARIABLE IN VIRGO}

\IBVSauth{E. RODRIGUEZ$^1$, S.F. GONZALEZ-BEDOLLA$^{2,}$\IBVSfm, M.J. LOPEZ-GONZALEZ$^1$, A. ROLLAND$^1$, V. COSTA$^1$}

\IBVSinst{Instituto de Astrof\'{\i}sica de Andaluc\'{\i}a, CSIC, P.O. Box 3004, 
E-18080 Granada, Spain}
\IBVSinst{Instituto de Astronom\'{\i}a, UNAM, P.O. Box 70-264, CP-4510 
M\'{e}xico D.F., Mexico}

\IBVSfoot{Deceased}

\SIMBADobj{HD 130484}

\begintext

During an observational program on the $\delta$~Sct-type pulsating star
IP~Vir, HD~129727 (V = 9\fmm 5) was used as main comparison star and
HD~130484 (V = 8\fmm8) as a check star. These two comparison stars
have not been reported as variable before in any catalogue, however our
observations showed that while HD~129727 kept a constant brightness
HD~130484 presents a slight $\delta$~Sct-type photometric variability
every night with a luminosity amplitude of about 0\fmm01 and a period
of about 3~hours. Figure~1 shows the light curves in the {\it v} filter
corresponding to six nights of observations as magnitude differences
HD~130484$-$HD~129727 versus the Heliocentric Julian Day.

The observations were collected through the springs of 1995 and 1996 at
the observatories of San Pedro M\'{a}rtir, M\'{e}xico (1.5~m telescope)
and Sierra Nevada, Spain (0.9~m telescope). These observations
consisted of simultaneous {\it uvby} data into the Str\"omgren
photometric system. Additionally, some H$\beta$ data were collected
in order to derive the physical parameters of these stars. Both
telescopes are equipped with identical six-channel {\it uvby$\beta$}
spectrograph photometers for simultaneous measurements in {\it uvby} or
in the narrow and wide H$\beta$ channels, respectively, using
uncooled EMI 9789~QA photomultipliers. To transform our data into
the standard system we have used the same procedure described in
Rodr\'{\i}guez et al. (1997). This way, we have derived for HD~130484
the following values: V = 8\fmm786, $b-y = 0\fmm188$, m$_1$ = 0\fmm172,
c$_1$ = 0\fmm946 and $\beta$ = 2\fmm771.

An analysis of frequencies was carried out on our data using the method
described in Rodr\'{\i}guez et al. (1998) where single-frequency and
multiple-frequency techniques are combined using both Fourier and
multiple least squares algorithms. The analysis was made on all the
four {\it uvby} filters and the results show that there is a main peak
at $\nu$ = 7.804~cd$^{-1}$, that is, a period of P = 0\fday1281. After
prewhitening for this frequency, the resulting periodograms suggest
that other periodicities may be present in the light curves of this
star, however the noise level is too high and the possible secondary
frequencies cannot be confirmed. The multiperiodicity is also suggested
from the light curves shown in Figure~1. The corresponding amplitudes
(as determined by means of the Fourier analysis, i.e., semiamplitudes)
obtained for the main frequency $\nu$ = 7.804~cd$^{-1}$ are of
0\fmm0045~($\pm$0.0008), 0\fmm0040~($\pm$0.0003),
0\fmm0037~($\pm$0.0003) and 0\fmm0031~($\pm$0.0004) for {\it u}, {\it
v}, {\it b} and {\it y}, respectively, which agree well with a
$\delta$~Sct type pulsation. Figure~2 shows the power spectra in the
filter {\it b} before and after prewhitening the frequency $\nu$.

In order to derive the physical parameters of this star, the
photometric Str\"omgren indices obtained before were used. Intrinsic
indices were derived using the reference lines of Philip \& Egret
(1980) with the appropriate corrections for gravity and metallicity
(Crawford 1975a,b; Philip et al.\ 1976).  Thus, colour excess of
0\fmm036, 0\fmm012 and 0\fmm007 were found for $b-y$, m$_1$ and c$_1$,
respectively. Then, deviations from the ZAMS's values of $\delta$m$_1$
= 0\fmm009 and $\delta$c$_1$ = 0\fmm217 are obtained. This means this
star is a normal $\delta$~Sct star with nearly solar abundance. In
fact, a value of [Me/H] = $-$0.01 is obtained using the Smalley's (1993)
calibration for metal abundance. In addition, using the relations by
Crawford (1975b) for luminosity, Code et al. (1976) for bolometric
correction and the grids by Lester et al. (1986) with [Me/H] = 0.0 for
temperature and gravity, we obtain the following values for M$_{\rm bol}$ =
1\fmm07, T$_e$ = 7560\,K and $\log g = 3.62$.  These results place
HD~130484 in the middle part of the instability strip corresponding to
the $\delta$~Sct region as can be seen in Figure~3. This figure shows
the sample of $\delta$~Sct stars and the observational edges of the
instability strip in the $\delta$~Sct region from Rodr\'{\i}guez et
al.\ (1994). Finally, using the relation by Petersen \& J{\o}rgensen
(1972), a value of Q = 0\fday028 ($\pm$0.005) is found for the
pulsation constant. This suggests that HD~130484 is pulsating in the
fundamental mode or first overtone radial order.

Acknowledgements. This research was supported by the Junta de
Andaluc\'{\i}a and the Direcci\'{o}n General de Ense\~{n}anza Superior
(DGES) under project PB96-0840.


\IBVSfig{12cm}{4686-f1.ps}{Differential light curves HD~130484$-$HD~129727 in the {\it v} filter versus Heliocentric Julian Day}

\vfill \eject

\IBVSfig{10.0cm}{4686-f2.ps}{Power spectra of HD~130484 in the filter
{\it b} before and after prewhitening the frequency $\nu$ =
7.804~cd$^{-1}$ to our data}

\IBVSfig{8.5cm}{4686-f3.ps}{Position of the $\delta$~Sct stars in the
H--R diagram.  HD~130484 is shown with the symbol O}

\vfill\eject

\references

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