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\begin{document}

\IBVShead{5331}{5 November 2002}

\IBVStitle{HIP 60725 and CU CV\lowercase{n}: Two New {\boldmath $\delta$} S\lowercase{ct} Stars}

\IBVSauth{Vidal-S\'{a}inz, J.$^{1}$; Gomez-Forrellad, J. M.$^{1,2}$; Garc\'{i}a-Melendo, E.$^2$; Wils, P.$^3$; \break Lampens, P.$^4$}

\IBVSinst{Grup d'Estudis Astronomics, Apartado 9481, 08080 Barcelona, Spain, email: jmgomez@astrogea.org}
\IBVSinst{Esteve Duran Observatory Foundation, Montseny 46, El Montanya, 08553 Seva, Barcelona, Spain, \\email: duranobs@astrogea.org}
\IBVSinst{Vereniging Voor Sterrenkunde, Belgium, email: patrick.wils@cronos.be}
\IBVSinst{Koninklijke Sterrenwacht van Belgi\"e, Ringlaan 3, B-1180 Brussel, Belgium, email: patricia.lampens@oma.be}

\SIMBADobj{HIP 60725}
\SIMBADobjAlias{CU CVn}{HIP 67357}
\IBVSkey{photometry - Delta Scuti stars}
\IBVSabs{CCD photometry shows that HIP 60725 and CU CVn are}
\IBVSabs{delta Scuti variables.} 

\begintext

In the period from 1996 to 1998, a few $\delta$ Sct stars were observed
from Monegrillo and Mollet del Valles Observatories in Spain while monitoring
a small set of selected HIPPARCOS variable stars. In both cases a 40cm
Newtonian telescope was used. The telescopes were also equipped with a 
Johnson $V$ filter and a SX Starlight CCD camera with a Sony ICX027BL chip cooled
by a Peltier system to about $-$25\deg C. Dark frames and flat fields were
obtained and used to perform image cleaning. Photometric reductions were
carried out using a synthetic aperture differential magnitude extraction
method and the software package LAIA (Laboratory for Astronomical Image Analysis).

The HIPPARCOS variables, discovered by the satellite mission, 
were selected on the basis of a reanalysis of the
satellite data, which suggested that the actual variable type for some
objects could be different from the one assigned in the HIPPARCOS
and TYCHO catalogues (ESA, 1997). This new analysis was based on a search for
periodicities in the satellite photometric data and on inspection of the
light-curve morphology. We present here our observations and results for two
of these HIPPARCOS variables HIP 60725, and CU CVn (HIP 67357), which are shown to be new
$\delta$ Sct stars. {\tt Period98} (Sperl, 1998) was used to analyse our photometric
and the Hipparcos Epoch Photometry data series. Table 1 shows the
observational log, and Table 2 gives some additional basic information on
these objects.  The spectral types were retrieved from the HIC (Turon et al., 1993), 
and equatorial coordinates from the Hipparcos Catalogue (ESA, 1997).

\begin{center}
{\normalsize Table 1. Observational log} \vskip2mm
\begin{tabular}{llcccc}
\hline
Star & Observation period & Comp. star & Check star & Data points & Remarks \\
\hline
HIP 60725 & 13 Mar-11 Jul 1998 & SAO 002046 & GSC 4556-800 & 607 & 1 \\
HIP 67357 & 16 Feb-27 Feb 1998 & HIP 67327 & $-$ & 467 & 2 \\
\hline
\end{tabular}
\end{center}
$^1$ {\small Monegrillo Observatory, 40-cm telescope} \\
$^2$ {\small Mollet del Valles Observatory, 40-cm telescope} \\

\begin{center}
{\normalsize Table 2. Basic data} \vskip2mm
\begin{tabular}{lccl}
\hline
Star & GCVS Name & Spectral type & Equatorial coordinates (epoch 2000)\\
\hline
HIP 60725 & $-$ & F0 & $\alpha=12\hr26\mm43\fsec735$ $\delta=+81\deg28\arcm26\farcs27$ \\
HIP 67357 & CU CVn & F0 & $\alpha=13\hr48\mm20\fsec117$ $\delta=+31\deg24\arcm03\farcs80$ \\
\hline
\end{tabular}
\end{center}


HIP 60725 (= SAO 2041 = GSC 04557-09079) is listed in the HIPPARCOS catalogue
as an unsolved variable (ESA, 1997). Our analysis of the Hipparcos data shows a main
frequency at $7.5306 \pm 0.0004$~c/d, or a 0.13279 day period. The new photometric data 
show that HIP 60725 is actually a small amplitude variable (maximum amplitude of 0.1~mag 
in the $V$ band), which displays strong amplitude changes from night to night. Its F0
spectral type as well as the short period and the multiperiodic character of the 
light-curve are good indicators of light variations due to $\delta$ Sct pulsations.\\

A Fourier analysis of the ground-based data indicates that there are two
pairs of strong frequencies at 7.512 and 7.530 c/d, and at 7.655 and
7.673 c/d, with a typical error for all of them of $\pm 0.003$~c/d.
As there is a strong 7-day feature in the spectral window, these pairs are
clearly 7-day aliases of each other. Among the detected frequencies in these data, 
the frequency at 7.530 c/d corresponds to the main frequency detected 
in the satellite photometry with a semi-amplitude of 27 mmag (25 mmag in the
ground based data). 
As an additional test, our photometric data and the HIPPARCOS
data were merged after removing their respective average values. A subsequent
frequency analysis revealed that all the data could be folded on a 
$0.132792 \pm 0.000001$~day period, showing that this period is real and stable within
the given errors since the HIPPARCOS era (mean epoch of 1991.25) until our 1998 observations
(Fig. 1). The 7.673 c/d frequency is then its 7-day alias.


\IBVSfig{6cm}{5331-f1.eps}{HIP 60725 satellite (crosses) and new photometric data (points) folded on the 0.132792 day period. Phase zero is assigned arbitrarily.}
%\IBVSfigKey5331-f1.eps}{HIP 60725}{light curve}

Since the light-curve of HIP 60725 shows a strong amplitude modulation, a second
period was searched for. The satellite and ground-based data sets were
prewhitened to remove the 0.13279 day period component and its alias forest.
The ground-based prewhitened data showed two strong peaks at 7.656 c/d
and 7.798 c/d in the frequency domain, which again are two 7-day aliases of
the same frequency (the abovementioned 7.512 c/d alias also appears but with a
lower amplitude). The frequency at 7.798 c/d can also be identified in the
HIPPARCOS data. If both prewhitened data sets are merged, the 7.798 c/d
frequency becomes the dominant one with a semi-amplitude of 16 mmag and all 
observations can be folded on a $0.128233 \pm 0.000001$~day period (Fig. 2). 
Its presence in the two independent data sets suggests that is a genuine frequency.
Table~3 summarizes our results of the frequency analysis.

 
\begin{center}
{\normalsize Table 3. Results of detected frequencies in the satellite data} \vskip2mm
\begin{tabular}{lcrrrrc}
\hline
Data set & Name & Frequency & Semi-ampl. & Period & S/N & Ground-based  \\
 &  & (c/d) & (mag) & (days) &  & detection?  \\
\hline
HIP 60725 & $f_1$ & 7.530 & 0.027 & 0.1328 & 5.5 & y  \\
          & $f_2$ & 7.798 & 0.020 & 0.1282 & 5.5 & y \\
\\
CU CVn & $f_1$ & 14.742 & 0.023 & 0.0678 & 10.3 & y \\
       & $f_2$ & 12.561 & 0.009 & 0.0821 & 4.8 & n \\
\hline
\end{tabular}
\end{center}


\IBVSfig{6cm}{5331-f2.eps}{HIP 60725 satellite (crosses) and new photometric data (points) folded on the 0.128233 day period after removing the main 0.132792 day component.}
%\IBVSfigKey5331-f2.eps}{HIP 60725}{light curve}


CU CVn (HIP 67357) is listed as a periodic variable in the HIPPARCOS
catalogue with a mean period of 0.1356670 days (ESA, 1997) and was 
classified as an EW: in the 74th Special Name-List (Kazarovets et al. 1999). 
A period analysis of the Hipparcos Epoch Photometry data shows a dominant 
frequency at $14.7419 \pm 0.0004$~c/d (period of $0.067834 \pm 0.000002$~days).
Our photometric observations in the $V$ band show that this object is a small-amplitude 
variable star with a maximum total amplitude of 0.06~mag, and rapid as well as irregular
light-curve changes (Fig.~3). As for HIP 60725, its F0 spectral type, the short period 
as well as the rapid modulation probably caused by multiperiodicity are indicators of 
pulsation of the $\delta$ Sct type.


\IBVSfig{7cm}{5331-f3.eps}{Ground-based light-curve in $V$ light of CU CVn.}
%\IBVSfigKey5331-f3.eps}{CU CVn}{light curve}


Although the small number of observed nights, only six, makes it difficult 
to obtain a reliable Fourier analysis of the new data for CU CVn, the 
frequency at 14.742 c/d is present, but only as part of a forest of 1 day 
aliases and not as the strongest component. As a matter of fact, even a satisfactory 
folded light-curve based on the 0.067834~day period could not be achieved after 
merging all available (ground-based and satellite) photometric data. 
The rapid modulation of the light-curve indicates that this object is a probable
multiperiodic variable. Prewhitening of the satellite data suggests the
presence of at least another frequency at $12.5606 \pm 0.0004$ c/d, which is
very close to the frequency at $12.5869 \pm 0.0004$ detected in the prewhitened
ground-based data. However, both cannot be unambiguously identified as corresponding 
to the exact same frequency. Table~3 illustrates the results for the HIPPARCOS data
only. It is obvious that larger data sets spread over many nights are needed - 
especially in the case of CU CVn - to have a better knowledge of all the frequencies 
that are excited in these new $\delta$ Sct variables.\\


{\bf Acknowledgements:} This research is based on data obtained by the Hipparcos astrometry satellite.
Use has been made of the SIMBAD data
base operated at the {\it Centre de Donn\'ees Astronomiques (Strasbourg)}
in France. 



\references

ESA, 1997, {\it The Hipparcos and Tycho Catalogues}, ESA SP-1200

Kazarovets, A. V., Samus, N. N., Durlevich, O. V., Frolov, S. V., Antipin, S. V., Kireeva, N. N., Pastukhova, E. E., 1999, {\it IBVS}, No.\,4659

Sperl, M., 1998, Manual for Period98 (V1.0.4). A period search-program for Windows and Unix, http://dsn.astro.univie.ac.at/\~{}period98

Turon, C., Creze, M., Egret, D., Gomez, A., Grenon, M., Jahrei\ss, H.,
  Requieme, Y., Argue, A. N., Bec-Borsenberger, A., Dommanget, J., 
  Mennessier, M. O., Arenou, F., Chareton, M., Crifo, F., Mermilliod, J. C., 
  Morin, D., Nicolet, B., Nys, O., Prevot, L., Rousseau, M., Perryman, 
  M. A. C., 1993, Version 2 of the Hipparcos Input Catalogue, 
  {\it Bull. Inf. Centre Donnees Stellaires}, {\bf 43}, 5

\endreferences

\end{document}

