Searching for short-period variable stars in the direction of Coma Berenices and Upgren 1 open clusters: Melotte 111 AV 1224 a new eclipsing binary star

We report the results of CCD photometric observations in the direction of the Coma Berenices and Upgren 1 open clusters with the aim at searching for new short-period variable stars. A total of 35 stars were checked for variability. As a result of this search the star designated in the SIMBAD database as Melotte 111 AV 1224 was found to be a new eclipsing binary star. Follow-up Stromgren photometric and spectroscopic observations allowed us to derive the spectral type, distance, reddening and effective temperature of the star. A preliminary analysis of the binary light curve was performed and the parameters of the orbital system were derived. From the derived physical parameters we conclude that Melotte 111 AV 1224 is most likely a W UMa eclipsing binary that is not a member of the Coma Berenices open cluster. On other hand, we did not find evidence of brightness variations in the stars NSV 5612 and NSV 5615 previously catalogued as variable stars in Coma Berenices open cluster.

Stromgren photometry and medium-resolution spectroscopy of some $delta$ Scuti and $gamma$ Doradus in the Kepler field

We have obtained CCD photometry and medium-resolution spectroscopy of a number of $delta$ Scuti and $gamma$ Doradus stars in the Kepler field-of-view as part of the ground-based observational efforts to support the textit{Kepler} space mission. In this work we present the preliminary results of these observations.

Characterizing the variability of Melotte 111 AV 1224: a new variable star in the Coma Berenices open cluster

A search for new pulsating stars in the Coma Berenices open cluster was carried out. As a result of this search the cluster member Melotte 111 AV 1224 presented clear indications of photometric variability. In order to determine its physical parameters Stromgren standard indices and low-resolution spectra were acquired. In this work we present the preliminary results of these observations.

Solar like oscillations in the stars KIC 5390438 and KIC 5701829 observed by Kepler

The preliminary results of an analysis of the KIC 5390438 and KIC 5701829 light curves are presented. The variations of these stars were detected by Baran et al. (2011a) in a search for pulsating M dwarfs in the Kepler public database. The objects have been observed by the Kepler spacecraft during the Q2 and Q3 runs in a short-candence mode (integration time of $sim$ 1 min). A Fourier analysis of the time series data has been performed by using the PERIOD04 package. The resulting power spectrum of each star shows a clear excess of power in the frequency range 100 and 350 $mu$Hz with a sequence of spaced peaks typical of solar-like oscillations. A rough estimation of the large and small separations has been obtained. Spectroscopic observations secured at the Observatorio Astronomico Nacional in San Pedro Martir allowed us to derive a spectral classification K2III and K0III for KIC 5390438 and KIC 5701829, respectively. Thus, KIC 5390438 and KIC 5701829 have been identified as solar-like oscillating red giant stars.

Determination of the physical characteristics of the variable stars in the direction of the open cluster NGC 6811 through $uvbybeta$ photoelectric photometry

The study of open clusters and their short period variable stars is fundamental in stellar evolution. Because the cluster members are formed in almost the same physical conditions, they share similar stellar properties such age and chemical composition. The assumption of common age, metallicity and distance impose strong constraints when modeling an ensemble of short period pulsators belonging to open clusters (e.g. Fox Machado et al., 2006). Very recently, Luo et al. (2009) carried out a search for variable stars in the direction of NGC 6811 with CCD photometry in B and V bands. They detected a total of sixteen variable stars. Among these variables, twelve were catalogued as $delta$ {it Scuti} stars, while no variability type was assigned to the remaining stars. In this paper we present $uvbybeta$ photoelectric photometry for the variable stars in the direction of NGC 6811.

Mt. Suhora M dwarf survey - Detection of eight short-period variable stars

The Mt. Suhora M,dwarf survey searching for pulsations in low mass main sequence stars has acquired CCD photometry of 46 M,dwarf stars during the first year of the project (Baran et al 2011). As a by-product of this search hundreds field stars have been checked for variability. This paper presents our initial result of a search for periodic variables in field stars observed in the course of the survey. On the basis of the periodicity and the shape of the light curves, eight new variables has been detected, among which five are $delta$ Scuti stars and three likely RR Lyrae stars. Although variation in one of the stars has been previously detected, it was classified incorrectly. To support our classification, in August 2010, we performed spectroscopic observations to derive spectral types and luminosity classes for all eight variable stars.

$uvby-beta$ photoelectric photometry of the open clusters NGC 6811 and NGC 6830

From $uvby-beta$ photometry of the open clusters NGC 6811 (75 stars), and NGC 6830 (19 stars) we were able to determine membership of the stars to each cluster, and fix the age and reddening for each. Since several short period stars have recently been found, we have carried out a study of these variables.

Asterosesimology of the Delta Scuti Star V650 Tauri

The preliminary results of a multisite photometric campaign on the Pleiades Delta Scuti variable V650 Tauri are reported. The star was observed photometrically for 14 days during 2008 November from three observatories distributed in Longitude around the Earth. As a result of the preliminary analysis we have detected in V650 Tauri at least nine oscillation frequencies above a 99% confidence level.

HD 207331 a new $delta$ Scuti star in the Cygnus field: discovery and follow-up observations

Preliminary results on the discovery and follow-up observations of a new $delta$ Scuti pulsator in the Cygnus field are presented. The variability of the star HD 207331 was detected while testing a Stromgren spectrophotometer attached to the H.L. Johnson 1.5-m telescope at the San Pedro Martir observatory, Mexico. CCD photometric data acquired soon after confirmed its variability. A few hours of $uvby$ differential photoelectric photometry during three nights revealed at least two beating periods. A two-site observational campaign carried out during one week in 2009 confirms the multi-periodic nature of this new $delta$ Scuti pulsator.

On the nature of HD 207331: a new Delta Scuti variable

While testing a Stromgren spectrophotometer attached to the 1.5-m telescope at the San Pedro Martir observatory, Mexico, a number of A-type stars were observed, one of which, HD 207331, presented clear indications of photometric variability. CCD photometric data acquired soon after, confirmed its variability. In order to determine its pulsation behaviour more accurately, uvby differential photoelectric photometry was carried out for three nights. As a result of the period analysis of the light curves we have found a dominant pulsation mode at 21.1 c/d with an amplitude of 6 mmag. This strongly suggests that HD 207331 is a new Delta Scuti-type pulsating star.