Search

We present the analysis of the variability of HD 170699, a COROT star showing the characteristics of a non evolutionary Delta Scuti star with high rotational velocity. There is a clear period of 10.45 c/d with 5.29 mmag amplitude in the y filter. From the data, it can be seen that the star shows multi-periodicity and it is necessary to add more frequencies to adjust the observations, Comment: To appear in RevMexAA(SC) in Proceedings of XII Reunion Regional Latinoamericana de la UAI held in Isla Margarita, Venezuela, October 22-26, 2007

Context: We present the results of an extensive ground-based photometric and spectroscopic campaign on the gamma Dor CoRoT target HD49434. This campaign was preparatory to the CoRoT satellite observations, which took place from October 2007 to March 2008. Results: The frequency analysis clearly shows the presence of four frequencies in the 0.2-1.7 c/d interval, as well as six frequencies in the 5-12 c/d domain. The low frequencies are typical for gamma Dor variables while the high frequencies are common for delta Sct pulsators. We propose the frequency 2.666 c/d as a possible rotational frequency. All modes, for which an identification was possible, seem to be high-degree modes (3 <= l <= 8). We did not find evidence for a possible binary nature of HD49434. The element abundances we derived are consistent with the values obtained in previous analyses. Conclusions: We classify the gamma Dor star HD49434 as a hybrid pulsator, which pulsates simultaneously in p- and g-modes. This finding makes HD49434 an extremely interesting target for asteroseismic modelling. Observations: Based on observations made with the 2.2m ESO/MPI telescope at the La Silla Observatory under the ESO Large Programme: LP178.D-0361. Also based on observations obtained at Observatorio de Sierra Nevada (Spain), at the Centro Astronomico Hispano Aleman at Calar Alto (Spain), at Observatorio Astronomico Nacional San Pedro Martir (Mexico), at the Piszkesteto Mountain Station of Konkoly Observatory (Hungary), at Observatoire de Haute Provence (France) and at Mount John University Observatory (New Zealand)., Comment: 15 pages, 10 figures, 9 tables accepted for publication in Astronomy and Astrophysics

We have carried out an intensive survey of the northern region of the Fornax dwarf spheroidal galaxy with the aim of detecting the galaxy's short--period pulsating stars (P<0.25 days). Observations collected over three consecutive nights with the Wide Field Imager of the 2.2m MPI telescope at ESO allowed us to detect 85 high-amplitude (0.20-1.00 mag in B-light) variable stars with periods in the range from 0.046 to 0.126 days, similar to SX Phoenicis stars in Galactic metal-poor stellar populations. The plots of the observed periods vs. the B and V magnitudes show a dispersion largely exceeding the observational errors. To disentangle the matter, we separated the first-overtone from the fundamental-mode pulsators and tentatively identified a group of subluminous variables, about 0.35 mag fainter than the others. Their nature as either metal-poor intermediate-age stars or stars formed by the merging of close binary systems is discussed. The rich sample of the Fornax variables also led us to reconstruct the Period-Luminosity relation for short-period pulsating stars. An excellent linear fit, M(V)=-1.83(+/-0.08)-3.65(+/-0.07) log P(fund), was obtained using 153 Delta Scuti and SX Phoenicis stars in a number of different stellar systems., Comment: 11 pages plus 1 on-line figure and 1 on-line table; accepted for publication in ApJ. Part of this work has been the subject of the Laurea thesis of LDA. His supervisor and our colleague, Prof. Laura E. Pasinetti, suddendly passed away on September 13, 2006. Several astronomers have been trained under her tutelage and we gratefully honor her memory

The times of maximum brightness collected in the GEOS RR Lyr database allowed us to trace the period variations of a sample of 123 galactic RRab variables. These data span a time baseline exceeding 100 years. Clear evidence of period increases or decreases at constant rates has been found, suggesting evolutionary effects. The observed rates are slightly larger than those predicted by theoretical models; moreover, there is an unexpected large percentage of RRab stars showing a period decrease. The new possibilities offered by the use of robotic telecopes (TAROTs, REM) and of data from satellite (CoRoT) are expected to speed up the project to measure stellar evolution in real time. It is noteworthy that the outlines of this project have been sketched during several GEOS meetings, where the different knowledge of amateur and professional astronomers found a very profitable synthesis., Comment: 5 pages, 4 figures; to appear in Mem. Soc. Astr. Italiana, (proceeding Cefalu' Workshop "XXI Century Challenges for Stellar Evolution", eds. S. Cassisi & M. Salaris)

To optimise the science results of the asteroseismic part of the CoRoT satellite mission a complementary simultaneous ground-based observational campaign is organised for selected CoRoT targets. The observations include both high-resolution spectroscopic and multi-colour photometric data. We present the preliminary results of the analysis of the ground-based observations of three targets. A line-profile analysis of 216 high-resolution FEROS spectra of the delta Sct star HD 50844 reveals more than ten pulsation frequencies in the frequency range 5-18 c/d, including possibly one radial fundamental mode (6.92 c/d). Based on more than 600 multi-colour photometric datapoints of the beta Cep star HD180642, spanning about three years and obtained with different telescopes and different instruments, we confirm the presence of a dominant radial mode nu1=5.48695 c/d, and detect also its first two harmonics. We find evidence for a second mode nu2=0.3017 c/d, possibly a g-mode, and indications for two more frequencies in the 7-8 c/d domain. From Stromgren photometry we find evidence for the hybrid delta Sct/gamma Dor character of the F0 star HD 44195, as frequencies near 3 c/d and 21 c/d are detected simultaneously in the different filters., Comment: 7 pages, 6 figures, HELAS II International Conference "Helioseismology, Asteroseismology and MHD Connections", 2008, J.Phys.: Conf. Ser. 118, 012077

The theory of stellar evolution can be more closely tested if we have the opportunity to measure new quantities. Nowadays, observations of galactic RR Lyr stars are available on a time baseline exceeding 100 years. Therefore, we can exploit the possibility of investigating period changes, continuing the pioneering work started by V. P. Tsesevich in 1969. We collected the available times of maximum brightness of the galactic RR Lyr stars in the GEOS RR Lyr database. Moreover, we also started new observational projects, including surveys with automated telescopes, to characterise the O-C diagrams better. The database we built has proved to be a very powerful tool for tracing the period variations through the ages. We analyzed 123 stars showing a clear O-C pattern (constant, parabolic or erratic) by means of different least-squares methods. Clear evidence of period increases or decreases at constant rates has been found, suggesting evolutionary effects. The median values are beta=+0.14 day/Myr for the 27 stars showing a period increase and beta=-0.20 day/Myr for the 21 stars showing a period decrease. The large number of RR Lyr stars showing a period decrease (i.e., blueward evolution) is a new and intriguing result. There is an excess of RR Lyr stars showing large, positive $\beta$ values. Moreover, the observed beta values are slightly larger than those predicted by theoretical models., Comment: 15 pages, 9 figures; to be published in Astronomy and Astrophysics; full resolution version available at http://dbrr.ast.obs-mip.fr/tarot/publis/publis.html

Variable stars have been identified for the first time in Fornax 4, the globular cluster located near the center of the Fornax dwarf spheroidal galaxy. By applying the image subtraction technique to B,V time series photometry obtained with the MagIC camera of the 6.5-m Magellan/Clay telescope and with the wide field imager of the 4-m Blanco/CTIO telescope, we detected 27 RR Lyrae stars (22 fundamental mode, 3 first overtone, and 2 double-mode pulsators) in a 2.4'x2.4' area centered on Fornax 4. The average and minimum periods of the ab-type RR Lyrae stars, = 0.594 d and P(ab,min)=0.5191 d, respectively, as well as the revised position of the cluster in the horizontal branch type--metallicity plane, all consistently point to an Oosterhoff-intermediate status for the cluster, unlike what is seen for the vast majority of Galactic globular clusters, but in agreement with previous indications for the other globular clusters in Fornax. The average apparent magnitude of the RR Lyrae stars located within 30 arcsec from the cluster center is =21.43 +/- 0.03 mag (sigma=0.10 mag, average on 12 stars), leading to a true distance modulus of (m-M)o=20.64 +/- 0.09 mag or (m-M)o=20.53 +/- 0.09 mag, depending on whether a low ([Fe/H]=-2.0) or a moderately high ([Fe/H]=-1.5) metallicity is adopted., Comment: Apj, in press

Aims: We define the relationship between the double-mode pulsation of Cepheids and metallicity in a more accurate way, determine the empirical metallicities of double-mode Cepheids from homogeneous, high-resolution spectroscopic data, and study of the period-ratio -- metallicity dependence. Methods: The high S/N echelle spectra obtained with the FEROS spectrograph were analyzed using a self-developed IRAF script, and the iron abundances were determined by comparing with synthetic spectra assuming LTE. Results: Accurate [Fe/H] values of 17 galactic beat Cepheids were determined. All these stars have solar or slightly subsolar metallicity. Their period ratio P1/P0 shows strong correlation with their derived [Fe/H] values. The corresponding period ratio -- metallicity relation has been evaluated., Comment: 10 pages, 7 figures, accepted in A&A

Aims: This work presents a high--precision variability survey in the field of the old, super metal-rich open cluster NGC 6791. Methods: The data sample consists of more than 75,000 high-precision CCD time series measurements in the V band obtained mainly at the Canada-France-Hawaii Telescope, with additional data from S. Pedro Martir and Loiano observatories, over a time span of ten nights. The field covers an area of 42x28 arcmin^2. Results: We have discovered 260 new variables and re-determined periods and amplitudes of 70 known variable stars. By means of a photometric evaluation of the membership in NGC 6791, and a preliminary membership based on the proper motions, we give a full description of the variable content of the cluster and surrounding field in the range 16

The successful launch of the CoRoT (COnvection, ROtation and planetary Transits) satellite opens a new era in asteroseismology. The space photometry is complemented by high-resolution spectroscopy and multicolour photometry from ground, to disclose the pulsational content of the asteroseismic targets in the most complete way. Some preliminary results obtained with both types of data are presented. The paper is based on observations collected at S. Pedro Martir, Serra La Nave, La Silla, and Telescopio Nazionale Galileo Observatories., Comment: Contributed talk at the " 51 Congresso Societa' Astronomica Italiana", Firenze (Italy), April 17-20, 2007

We obtained the first long, homogenous time-series of V2104Cyg, consisting of 679 datapoints, with the uvbybeta photometers of Sierra Nevada and San Pedro Martir Observatories with the aim to detect and subsequently interpret the intrinsic frequencies of this previously unstudied variable star, which turned out to be a Be star. We try to figure out its place among the variable B stars on the upper Main Sequence. In order to obtain additional information on physical parameters we collected a few spectra with the ELODIE and FIES instruments. We searched for frequencies in the uvby passbands using 2 different frequency analysis methods and used the S/N>4 criterion to select the significant periodicities. We obtained an estimate of the physical parameters of the underlying B star of spectral type between B5 and B7, by correcting for the presence of a circumstellar disk, using a formalism based on the strenght of the Halpha line emission. We detected 3 independent frequencies with amplitudes below 0.01mag, f1 = 4.7126 c/d, f2 = 2.2342 c/d and f3 = 4.671 c/d, and discovered that V2104Cyg is a Be star. The fast rotation (vsini=290+/-10 km/s, and 27

Context. Searching for planets in open clusters allows us to study the effects of dynamical environment on planet formation and evolution. Aims. Considering the strong dependence of planet frequency on stellar metallicity, we studied the metal rich old open cluster NGC 6791 and searched for close-in planets using the transit technique. Methods. A ten-night observational campaign was performed using the Canada-France-Hawaii Telescope (3.6m), the San Pedro M\'artir telescope (2.1m), and the Loiano telescope (1.5m). To increase the transit detection probability we also made use of the Bruntt et al. (2003) eight-nights observational campaign. Adequate photometric precision for the detection of planetary transits was achieved. Results. Should the frequency and properties of close-in planets in NGC 6791 be similar to those orbiting field stars of similar metallicity, then detailed simulations foresee the presence of 2-3 transiting planets. Instead, we do not confirm the transit candidates proposed by Bruntt et al. (2003). The probability that the null detection is simply due to chance coincidence is estimated to be 3%-10%, depending on the metallicity assumed for the cluster. Conclusions. Possible explanations of the null-detection of transits include: (i) a lower frequency of close-in planets in star clusters; (ii) a smaller planetary radius for planets orbiting super metal rich stars; or (iii) limitations in the basic assumptions. More extensive photometry with 3-4m class telescopes is required to allow conclusive inferences about the frequency of planets in NGC 6791., Comment: 23 pages, 23 figures, A&A accepted

The space mission CoRoT (COnvection, ROtation and planetary Transits) will offer the possibility to detect extrasolar planets by means of the transit method. The satellite will observe about 60000 targets in the range 11.0

We report the results of CCD V and R photometry of the RR Lyrae stars in M2. The periodicities of most variables are revised and new ephemerides are calculated. Light curve decomposition of the RR Lyrae stars was carried out and the corresponding mean physical parameters [Fe/H] = -1.47, Teff = 6276 K, log L = 1.63 Lsun and Mv = 0.71 from nine RRab and [Fe/H] = -1.61, M = 0.54 Msun, Teff = 7215 K, log L = 1.74 Lsun and Mv = 0.71 from two RRc stars were calculated. A comparison of the radii obtained from the above luminosity and temperature with predicted radii from nonlinear convective models is discussed. The estimated mean distance to the cluster is 10.49 +- 0.15 kpc. These results place M2 correctly in the general globular cluster sequences Oosterhoff type, mass, luminosity and temperature, all as a function of the metallicity. Mean relationships for M, log L/Lsun, Teff and Mv as a function of [Fe/H] for a family of globular clusters are offered. These trends are consistent with evolutionary and structural notions on the horizontal branch. Eight new variables are reported., Comment: 13 Pages, 10 Figures, Accepted for publication in MNRAS

We present a mode identification based on new high-resolution time-series spectra of the non-radially pulsating Delta Scuti star FG~Vir (HD 106384, V = 6.57, A5V). From 2002 February to June a global Delta Scuti Network (DSN) campaign, utilizing high-resolution spectroscopy and simultaneous photometry has been conducted for FG~Vir in order to provide a theoretical pulsation model. In this campaign we have acquired 969 Echelle spectra covering 147 hours at six observatories. The mode identification was carried out by analyzing line profile variations by means of the Fourier parameter fit method, where the observational Fourier parameters across the line are fitted with theoretical values. This method is especially well suited for determining the azimuthal order m of non-radial pulsation modes and thus complementary with the method of Daszynska-Daszkiewicz (2002) which does best at identifying the degree l. 15 frequencies between 9.2 and 33.5 c/d were detected spectroscopically. We determined the azimuthal order m of 12 modes and constrained their harmonic degree l. Only modes of low degree (l <= 4) were detected, most of them having axisymmetric character mainly due to the relatively low projected rotational velocity of FG Vir. The detected non-axisymmetric modes have azimuthal orders between -2 and 1. We derived an inclination of 19 degrees, which implies an equatorial rotational rate of 66 km/s., Comment: 14 pages, 26 figures

gamma Dor-type oscillations have been discovered in the star HD218427 through simultaneous uvby photometric observations carried out in the year 2003. A few Hbeta-Crawford measurements were also collected for calibration purposes which place this star well-located inside the gamma Dor instability region. Deficiency in metal content, similar to other well-defined gamma Dor stars, is found in HD218427 and the possibility of a lambda Boo nature is discussed. Frequency analysis was carried out for different filters, the combined "vby" filter was also used and five frequencies were found as significant with periods ranging between 0.3 and 0.8 days. The recently developed Frequency Ratio Method is used in order to perform an identification of the excited modes. The results are consistent with an l=2 identification for all the modes and high radial quantum numbers (n~40) for the three main observed periodicities. The possibility of multiplet structures is also discussed. However, no consistency is found when the Time-Dependent Convection treatment is used for modes discrimination. The disagreement can be due to the large rotation velocity taking place in HD218427 and, consequently, the significant coupling between the modes., Comment: 10 pages, 3 figures. Accepted by A&A

We report a multisite photometric campaign for the Beta Cephei star 12 Lacertae. 750 hours of high-quality differential photoelectric Stromgren, Johnson and Geneva time-series photometry were obtained with 9 telescopes during 190 nights. Our frequency analysis results in the detection of 23 sinusoidal signals in the light curves. Eleven of those correspond to independent pulsation modes, and the remainder are combination frequencies. We find some slow aperiodic variability such as that seemingly present in several Beta Cephei stars. We perform mode identification from our colour photometry, derive the spherical degree l for the five strongest modes unambiguously and provide constraints on l for the weaker modes. We find a mixture of modes of 0 <= l <= 4. In particular, we prove that the previously suspected rotationally split triplet within the modes of 12 Lac consists of modes of different l; their equal frequency splitting must thus be accidental. One of the periodic signals we detected in the light curves is argued to be a linearly stable mode excited to visible amplitude by nonlinear mode coupling via a 2:1 resonance. We also find a low-frequency signal in the light variations whose physical nature is unclear; it could be a parent or daughter mode resonantly coupled. The remaining combination frequencies are consistent with simple light-curve distortions. The range of excited pulsation frequencies of 12 Lac may be sufficiently large that it cannot be reproduced by standard models. We suspect that the star has a larger metal abundance in the pulsational driving zone, a hypothesis also capable of explaining the presence of Beta Cephei stars in the LMC., Comment: 12 pages, 7 figures, MNRAS, in press

We present the first results of a variable star search in the field and in the globular clusters of the Fornax dwarf spheroidal galaxy. Variable stars were identified using the Image Subtraction Technique (Alard 2000) on time-series data obtained with the ESO 2.2 m and the Magellan 6.5 m telescopes. The variable star sample includes RR Lyrae stars, Dwarf Cepheids and Anomalous Cepheids. The pulsation properties (namely: periods, light curves, period-amplitude relations and classification in Oosterhoff types) of Fornax variables from the present study are discussed in some detail., Comment: 10 pages, 9 figures, to appear in the Proceedings of "Resolved Stellar Populations", 2005, Cancun, Mexico

The double--mode pulsation of GSC 00144-03031 has been detected when searching for COROT targets. A very large dataset composed of 4722 photometric measurements was collected at six observatories in Europe and America. There is no hint of the excitation of additional modes (down to 0.6 mmag) and therefore GSC 00144-03031 seems to be a pure double--mode pulsator, with a very short fundamental radial mode (P=84 min). From Stromgren photometry and evolutionary tracks it appears to be a Pop. I star with M=1.75 solar masses, located in the middle of the instability strip, close to the Zero--Age Main Sequence. We also discovered other new double--mode pulsators in the databases of large--scale projects: OGLE BW2_V142, OGLE BW1_V207, ASAS3 094303-1707.3, ASAS3 000116-6037.0, NSVS 3234596 and NSVS 3324715. An observational Petersen diagram is presented and explained by means of new models. A common sequence connecting Pop. I stars from the shortest to the longest periods is proposed and the spreads in the period ratios are ascribed to different metallicities (at the shortest periods) and to different masses (at the longest ones). The paper is based on data collected at S. Pedro Martir and Sierra Nevada Observatories and on the contributions from several amateur astronomers., Comment: 9 pages, 5 pages, accepted for publication in Astronomy and Astrophysics

We present a study based on more than 2500 uvby-measurements collected on HD 172189, a new eclipsing binary system with a Delta Sct-type pulsating component that belongs to the open cluster IC 4756. The great interest of this object lies in that three important characteristics coexist: cluster membership, binarity and pulsation. Its binarity and the Delta Sct-type pulsations of one component were detected in the course of several Stromgren photometric campaigns. The frequency analysis of all the uvby out-of-eclipse data reveals a clear frequency of 19.5974 c/d as well as the existence of other high values in the range 18-20 c/d. We have also carried out a first evaluation of the binary parameters and determined a value of 5.702 d for the orbital period. An additional potential interest of HD 172189 resides in its location in the field of view of the COROT mission and, therefore, this star is an excellent candidate for becoming a target for asteroseismology., Comment: 4 pages, 3 figures, accepted by A&A

The activities related to the preparation of the asteroseismic, photometric space mission COROT are described. Photoelectric observations, wide--field CCD photometry, uvbyB calibrations and further time--series have been obtained at different observatories and telescopes. They have been planned to complete the COROT programme in the direction of the galactic Anticenter. In addition to suitable asteroseismic targets covering the different evolutionary stages between ZAMS and TAMS, we discovered several other variable stars, both pulsating and geometrical. We compared results on the incidence of variability in the galactic Center and Anticenter directions. Physical parameters have been obtained and evolutionary tracks fitting them have been calculated. The peculiarities of some individual stars alre pointed out. Paper based on observations collected at the San Pedro Martir, Sierra Nevada, Teide, La Silla, Haute-Provence and Roque de Los Muchachos (Telescopio Nazionale Galileo and Mercator telescopes) observatories., Comment: 13 pages, 9 figures. Accepted for The Astronomical Journal (2005 May volume)

The GAUDI database (Ground-based Asteroseismology Uniform Database Interface, http://sdc.laeff.esa.es/gaudi/) is a preparatory archive for the COROT (COnvection, ROtation and planetary Transits, http://www.astrsp-mrs.fr/projets/corot/) mission developed at LAEFF (Laboratory for Space Astrophysics and Theoretical Physics, http://www.laeff.esa.es). Its intention is to make the ground-based observations obtained in the preparation of the asteroseismology programme available in a simple and efficient way. It contains spectroscopic and photometric data together with inferred physical parameters for more than 1500 objects gathered since January 1998 in 6 years of observational campaigns. In this paper, the main functionalities and characteristics of the system are described. The observations have been collected at ESO-La Silla, Telescopio Nazionale Galileo, Observatoire de Haute-Provence, South African Astronomical Observatory, Tautenberg Observatory and Sierra Nevada Observatory., Comment: 12 pages, 3 figures (quality degraded). Accepted for publication in The Astronomical Journal

A high-accuracy multisite campaign was carried out from 2002 January to May with a photometric coverage of 398 hours at five observatories. The concentration on a few selected sites gives better consistency and accuracy than collecting smaller amounts from a larger number of sites. 23 frequencies were detected with a high statistical significance. 6 of these are new. The 17 frequencies found in common with the 1992-1995 data are the modes with highest amplitudes. This indicates that the pulsation spectrum of FG Vir is relatively stable over the ten-year period. Two frequencies have variable amplitudes and phases from year to year as well as during 2002. These were both found to be double modes with close frequencies. For the mode at 12.15 c/d this leads to an apparent modulation with a time scale of about 129d. The close frequencies at 12.15 c/d are composed of a radial and a nonradial mode, suggesting a similarity with the Blazhko Effect seen in RR Lyrae stars., Comment: 8 pages, 4 figures, 2 tables

We present the first results of a 2-year high-resolution spectroscopy campaign of 59 candidate Gamma Doradus stars which were mainly discovered from the HIPPARCOS astrometric mission. More than 60 % of the stars present line profile variations which can be interpreted as due to pulsation related to Gamma Doradus stars. For all stars we also derived the projected rotation velocity (up to more than 200 km\s). The amplitude ratios 2K/Delta m for the main HIPPARCOS frequency are in the range 35 - 96 (km\s)\mag. Less than 50 % of the candidates are possible members of binary systems, with 20 stars being confirmed Gamma Doradus. At least 6 stars present composite spectra, and in all but one case (for which only one spectrum could be obtained), the narrow component shows line profile variations, pointing towards an uncomfortable situation if this narrow component originates from a shell surrounding the star. This paper is the first of a series concerning mode identification using both photometric and spectroscopic methods for the confirmed Gamma Doradus stars of the present sample., Comment: 11 pages, 8 figures, Accepted for Astronomy & Astrophysics

The aspects of the analysis of photometric time-series obtained on double-mode or multiperiodic pulsating stars are briefly reviewed. In particular, the ratios between frequencies are used to pin cases revealing peculiarities. In addition to the Petersen diagrams, we also demonstrated that the period ratios can detect interesting objects. In particular, new results are obtained on High--Amplitude Delta Scuti contained in the OGLE-II database., Comment: Invited review presented at the MinySymposium ``Asteroseeismology and Stellar Evolution", JENAM, Budapest, 25-30 August 2003 -- To be published in Communications in Asteroseismology Series, 2004

The different research teams involved in the study of delta Sct stars have slightly changed their strategy in the past years. The observational effort to secure worldwide coverage of case studies is continued, but the specifications become more severe, especially about target characterization and frequency resolution., Comment: 4 pages, 2 figures. IAU Colloquium 193 held in Christchurch, New Zealand in 2003

The CNES/European space mission COROT will monitor asteroseismic targets located in selected fields to probe stellar interiors. Therefore, suitable candidate targets have to be searched for in order to optimize the scientific return of the mission. However, to be able to use the asteroseismic tools on the stars, their physical parameters must be known in advance. In this work, we detail the process of building a photometric database of all the stars brighter than V=8.0 mag in the field of view of COROT and the process of selecting suitable delta Scuti and gamma Dor-type stars for the mission.

We illustrate the approach to the use of asteroseismology to sound stellar interiors. We also present the spectroscopic and photometric observations carried out to give the complete characterisation of the potential targets of the space mission COROT. The Italian contribution plays an important role in the preparation of the observational basis of this space mission. The use of the TNG/SARG high-resolution spectra is described., Comment: 4 pages, 1 figure, Contributed talk to "Stars in Galaxies", La Palma, Canary Islands, March 2003, Mem. S.A.It., in press

The analysis of a dense time-series on V974 Oph disclosed the rich pulsational content (at least five independent terms) of this high-amplitude (0.60 mag in B-light) Delta Sct star. A mode with a frequency very close to the main one (probably the fundamental radial mode) has been detected: such a doublet is not a common feature in stars of the same class. Also another term can be considered a radial one, but the high ratio (0.786) raises some problems that can be solved only by admitting very low metallicity. It is quite evident that some undetectable terms are again hidden in the noise, as the least--squares fit leaves a rms residual much higher than the observational noise. All that considered, nonradial modes seem to play a key role in the light variability of V974 Oph. Revealing an unsuspected asteroseismic interest, V974 Oph provides a link between low- and high-amplitude Delta Sct stars. By discussing other high-amplitude Delta Sct stars showing unusual period ratios, it is evident that the asteroseismic approach is possible also for this class of pulsators., Comment: 6 pages, 5 figures. Accepted for publication in Astronomy & Astrophysics

By pursuing the goal to find new variables in the COROT field-of-view we characterised a sample of stars located in the lower part of the instability strip. Our sample is composed of stars belonging to the disk population in the solar neighbourhood. We found that 23% of the stars display multiperiodic light variability up to few mmag of amplitude. uvbyBeta photometry fixed most of the variables in the middle of the instability strip and high-resolution spectroscopy established that they have vsin i>100 km/s. The comparison with delta Sct stars in the whole Galaxy shows slightly different features, i.e., most delta Sct stars have a 0.05-mag redder (b-y)_0 index and lower vsin i values. Additional investigation in the open cluster NGC 6633 confirms the same incidence of variability, i.e., around 20%. The wide variety of pulsational behaviours of delta Sct stars (including unusual objects such as a variable beyond the blue edge or a rapidly rotating high-amplitude pulsator) makes them very powerful asteroseismic tools to be used by COROT. Being quite common among bright stars, delta Sct stars are suitable targets for optical observations from space., Comment: 9 pages, 9 figures Accepted for publication in Astronomy & Astrophysics, Main Journal

We briefly review our photometric and spectroscopic study of RR Lyrae variable stars in the bar of the Large Magellanic Cloud (LMC), that allowed us to reconcile the so-called "short" and "long" distance moduli of the LMC on the value mod_LMC=18.51 +/- 0.085 mag. Then we present preliminary results from the photometric study of a 33' x 34' area in the Fornax dwarf spheroidal galaxy containing the stellar clusters Fornax 3 (NGC 1049) and 6. We identified about 1000 candidate variables in this field of Fornax, and report the first detection and measure of about 60 RR Lyrae variable stars in the globular cluster Fornax 3., Comment: 4 pages, 2 figures, uses mem.cls, in Stars in Galaxies, La Palma, March 2003

We present the results of a systematic search for multiperiodic pulsators among the Galactic Bulge RR Lyrae stars of the OGLE-1 sample. We identify one "canonical" double-mode variable (RRd star) pulsating in two radial modes. In 38 stars we detect secondary periodicities very close to the primary pulsation frequency. This type of multiperiodic variables constitute ~23% of RRab and ~5% of RRc population of the Bulge. With the observed period ratios of 0.95-1.02 the secondary periods must correspond to nonradial modes of oscillation. Their beating with the primary (radial) pulsation leads to a long-term amplitude and phase modulation, known as the Blazhko effect. The Blazhko RRab variables occur more frequently in the Galactic Bulge than in the LMC. The opposite tendency is seen in case of the RRd stars. The differences of incidence rates are most likely caused by different metallicity of the two populations. We discuss pulsation properties of the OGLE-1 Blazhko stars and compare them with predictions of theoretical models. We argue, that the oblique magnetic pulsator model of Shibahashi (2000) cannot account for the observations and should be ruled out., Comment: 11 pages, 8 figures, accepted for publication in Astronomy & Astrophysics

We report on the discovery of the second case of a galactic Cepheid, ASAS112843-5925.7=HD 304373, pulsating in the the first (1O) and second (2O) radial overtones. The ratio between the periods (0.8058), the short value of the 1O period (0.922405 d) and the shape of the 1O light curve makes HD 304373 very similar to the 1O/2O Cepheids in the Magellanic Clouds. The implications of a so close similarity between a galactic 1O/2O pulsator and LMC ones are discussed in terms of importance of the metallicity effects., Comment: 4 pages (in A&A style), 3 eps figures. Accepted for A&A Letters

We discuss new photometric data collected on the gamma Dor variables HD 224945 and HD 224638. Multiperiodicity was detected in both stars, thanks to the clear spectral window of a multisite campaign that involved five observatories. HD 224945 shows the shortest period among the gamma Dor stars, i.e., 0.3330 d. The pulsation behaviour is very different: HD 224945 displays a set of frequencies spread over an interval much wider than that of HD 224638. We clearly found evidence for amplitude variations in the excited modes by comparing data from different years. HD 224945 and HD 224638 are among the best examples of $\gamma$ Dor stars that show multimode pulsations, which make them very interesting from an asteroseismological point of view., Comment: 8 pages (in A&A style), 3 eps figures. Accepted for A&A Main Journal

The first intensive photometric time-series of a Delta Scuti star was obtained from space. Theta2 Tau was monitored with the star camera on the Wide-Field Infrared Explorer (WIRE) satellite. Twelve independent frequencies were detected down to the 0.5 mmag amplitude level. Their reality was investigated by searching for them using two different algorithms and by some internal checks. All the frequencies are in the range 10.8-14.6 c\d. The histogram of the frequency spacings shows that 81% are below 1.8 c\d; rotation may thus play a role in the mode excitation. The fundamental radial mode is not observed, although it is expected to occur in a region where the noise level is very low (55 micromag). The rms residual is about two times lower than that usually obtained from successful ground--based multisite campaigns. The comparison of the results of previous campaigns with the new ones establishes the amplitude variability of some modes., Comment: 7 pages (in A&A style), 7 eps figures. Accepted for A&A Main Journal

We discuss the results of a systematic search for multiperiodic pulsations in Galactic Bulge Delta Scuti and RR Lyrae stars. Six "normal" double-mode variables pulsating in two radial modes have been identified (5 Delta Scuti-type and 1 RR Lyrae-type). In 37 RR Lyrae stars secondary periodicities very close to the primary pulsation frequency have been detected. These periodicities correspond to nonradial modes of oscillation. They are found in \~23% of RRab and in ~3% of RRc variables of our sample., Comment: 4 pages, 2 figures, to appear in proceedings of IAU Coll. 185 "Radial and Nonradial Pulsations as Probes of Stellar Physics"

Optical polarization of seven selected BL Lac objects in UBVRI bands was studied with the Nordic Optical Telescope from December 10-14, 1999. Two of them, 3C 66A and PKS 0735+178, were monitored for 4 nights for a total integration time of 4.75 and 5.5 hours, respectively. Other objects (1Jy 0138-097, H 0414+009, PKS 0823-223, OJ287 and BL Lac) were observed sparsely during the run. Apart from PKS 0823-223 (more polarized than observed in the past), the sources show levels of flux and polarization consistent with results at previous epochs. 3C 66A and PKS 0735+178 were intensively observed during December 11 and 12 and exhibited variability of polarization, both on internight and intranight time scales. Wavelength dependence of polarization has been investigated, as well as circular polarization. The results are discussed within the standard model for BL Lacs., Comment: 11 pages, 7 figures, accepted to Astronomy & Astrophysics

The OGLE database is revisited to investigate in more detail the properties of the Fourier parameters. Methodological improvements led us to identify a clear separation among High-Amplitude Delta Scuti (HADS), RRc and RRab stars. The bimodal distribution of the R21 parameter in HADS stars is explained as a contamination effect from RRc stars: there is evidence that all stars with 0.200.55 d; evolutionary phases or the combination of different physical conditions (not only metallicity) are suggested to explain this separation, observed also in the cluster RRab stars. The stellar parameters of RRc stars in a given globular cluster show different tendencies than those of RRc stars from different clusters., Comment: 12 pages (in A&A style), 14 eps figures. Accepted for A&A Main Journal. Table 3, 4 and 5 are also included as ascii files. The atlas of the light curves and least-squares fits can be requested from the author

We discuss here the pulsation properties of the $\delta$ Scuti star BV Circini on the basis of data obtained during a simultaneous photometric and spectroscopic campaign in 1996 and a spectroscopic one in 1998, and taking also advantage of the previous photometric observations by Kurtz (1981). Nine pulsation modes were detected from photometry and thirteen from spectroscopy; five of them are in common to both techniques. The spectroscopic data give ample evidence of dramatic amplitude variations in some modes, in particular the strongest spectroscopic mode in 1998 was not detectable in 1996 data. The two dominant photometric modes (6.33 and 7.89 c\d) are observed on both seasons. The typing of the modes was performed by means of a simultaneous model fit of line profile and light variations. The 6.33 c\d photometric term is probably the fundamental radial mode, while the 7.89 c\d is a nonradial mode with mi different than 0. There are six high-degree prograde modes with an azimuthal order m ranging from -12 to -14, and also a retrograde mode with m~7. These modes combined with the identification of the 6.33 c\d mode allowed us to estimate i~60 deg for the value of the inclination of the rotation axis. An accurate evaluation of the main stellar physical parameters is also proposed as a result of the pulsational analysis., Comment: 12 pages (in A&A style), 9 ps figures (Fig. 7 in colour) Accepted for A&A Main Journal

The polarized and total flux of the BL Lac object PKS 2155-304 were monitored intensively and simultaneously in the optical UBVRI bands with the Turin photopolarimeter at the CASLEO 2.15 m telescope during 4 campaigns in June, August, November 1998 and August 1999. The effective observation time amounted to ~47 hours. PKS 2155-304 showed a linear polarization percentage (P) usually ranging between 3% and 7% and a polarization position angle (PA) mainly between 70 and 120 deg. The highest temporal resolution of our observations, 15 minutes, is unprecedented for polarimetric monitoring of this source, and has allowed us to detect amplitude variations of the linear polarization percentage from 6 to 7.5% in time scales of hours. In some nights the polarization percentage seems to increase toward shorter wavelengths, however the polarized spectrum does not vary significantly with time. The most remarkable variability event occurred on 1998 June 18, when the degree of linear polarization decreased by more than a factor 2 in one day in all bands, while the PA rotated by 90 deg. This is consistent with the presence of two emission components, of different polarization degree and position angle. Intranight variability of P and PA can be interpreted with small amplitude physical or geometrical changes within the jet. Measurements of the circular polarization over time intervals of days set upper limits of 0.2%. Simultaneous photometry taken with the Turin Photopolarimeter and with a CCD camera at Cordoba Astronomical Observatory did not show light variations correlated with those of the linearly polarized flux., Comment: 21 pages, 6 eps figures. Accepted for The Astrophysical Journal Supplement Series

The MONS space experiment will be able to verify some of the most important topics in the asteroseismologic studies of Delta Sct and Gamma Dor stars. We discuss how the $\gamma$ Doradus can be considered possible "bridges" between the opacity driven overstable pulsation and the stochastically excited solar like oscillation. For this reason the possible inclusion of a Gamma Dor representative in the MONS main target list is presented and discussed. To study Delta Sct stars, an appropriate frequency resolution, comparable to or better than what is currently achieved by ground-based observations, is necessary and hence two runs are recommended. To avoid over-scheduling of the Main Camera, a possible combination of observations from the Main Camera and from the Star Trackers is proposed. As a result, key-objects could be adequately monitored, affording the possibility to enter into details of amplitude variations. Simultaneously, the same results could be obtained on two Gamma Dor stars., Comment: 2 contributions, 6 pages each. To appear in "MONS Science Preparation and Target Selection", Eds. T.Teixeira and T. Beddings Eds

The results obtained by means of the photometric approach to the study of Delta Sct stars are extensively discussed. The different frequency contents of the three best candidates for asteroseismological studies (FG Vir, 4 CVn and XX Pyx) are presented and compared; the importance of the amplitude variations and of the combination terms is emphasized. The analysis of other multiperiodic variables shows how a large variety of nonradial modes are excited; in some cases, modifications of the power spectrum can be observed over a few years and new modes can be seen to grow. Among monoperiodic pulsators, constant as well as variable amplitudes can be observed. The difficulty of identifying an oscillation yielding quantum numbers is emphasized; the possibilities offered by $\delta$ Sct stars belonging to binary systems and open clusters are discussed. In this respect, combining the photometric and the spectroscopic approaches could lead to a solution. A comparison is also made between low- and high-amplitude pulsators, finding similarities. The use of a reliable Period-Luminosity-Colour relationships toward the shortest periods can greatly help mode identification in the galactic stars; moreover, it could provide an independent verification of extragalactic distances., Comment: 22 pages, 9 eps figures. Invited review at "Delta Scuti and Related Stars", (Vienna, August 1999). To be published in ASP Conference Series, M. Breger and M.H. Montgomery Eds

IIPeg is an ideal target to study stellar activity and flares, since intense and long lasting flares have been frequently detected from this system at all wavelengths. We report here about a BeppoSAX observation of IIPeg. We followed the system for ~19 hours on December 5 and 6 1997 with BeppoSAX and the X-ray light curve resembles the typical behavior of a decay phase of a long-lasting flare. The spectral analysis shows that the IIPeg X-ray spectrum is described by a two-temperature components, with the two dominant temperatures centered in the range of 9-11 and 24-26 MK. The derived coronal metal abundance is low Z~0.2 Zo compared to recent determinations of the photospheric abundance (Z~0.6 Zo). Some possible explanations for this phenomenology are reviewed. As for most other stellar coronal sources observed with BeppoSAX, we find that in order to fit the BeppoSAX spectra an interstellar column density about a factor ten higher than previously determined is required., Comment: 3 figures, accepted for publication in A&A Main Journal

In this contribution two papers on the BL Lac object PKS 2155-304 are presented. They are based on our program of systematic intensive optical monitoring in search of fast variability events. In the first paper the results of a CCD photometric campaign conducted at ESO (La Silla, Chile) on 6-14 July 1998, for a total time on the source of ~30 hours. Some peculiarities in the light and colour cutves were evidenced. In the second paper we report on linear polarization, as observed in the UBVRI bands in June and August 1998 for a total of ~45 hours. Between the two epochs, the linear polarization in the V band increased from ~3.5% to ~5.5%, and the position angle decreased from 100 deg to 70 deg. Significant day-to-day variations of both quantities are also observed. An isolated "dip" of the polarization percentage occurred between 17 and 19 June in all bands: a decrease and subsequent rise of a factor of 2 is seen in the linear polarization, accompanied by a variation of the position angle by 90 deg., Comment: 8 pages, 6 ps figures. Two papers to be published in the Proceedings of the OJ-94 meeting "Blazar monitoring towards the third millenium", Torino (Italy), May 19-21, 1999

The line profile variations of the Delta Scuti star HD 2724=BB Phe were studied on the basis of new 189 high-resolution spectrograms covering 52 hours of observations on a baseline of 8.3 days. By combining these results with those of a previous campaign 13 pulsation modes were identified: 5 of them are both photometric and spectroscopic, 3 are purely spectroscopic and 5 purely photometric. For the first time it was possible to compare spectroscopic data taken in two different seasons: 6 modes were found to be common to both datasets and furthermore strong amplitude variations of the excited modes were detected. The fit of the line profile variations with a model of non-radial pulsating star allowed us to obtain a reasonable estimate of the inclination of the rotational axis and to propose the l,m typing of the spectroscopic modes. The frequency content resembles that of 4 CVn, a delta Sct star with similar physical parameters., Comment: 7 pages (in A&A style), 5 ps figures (Fig. 4 in colour) Accepted for A&A Main Journal

In this paper we describe a new class of pulsating stars, the prototype of which is the bright, early, F-type dwarf, Gamma Doradus. These stars typically have between 1 and 5 periods ranging from 0.4 to 3 days with photometric amplitudes up to 0.1 in Johnson V. The mechanism for these observed variations is high-order, low-degree, non-radial, gravity-mode pulsation. Gamma Doradus stars exhibit variability on a time scale that is an order of magnitude slower than Delta Scuti stars. They may offer additional insight into stellar physics when they are better understood (e.g., they may represent the cool portion of an "iron opacity instability strip" currently formed by the Beta Cephei stars, the SPB stars, and the subdwarf B stars; they may also offer insight into the presence of g-modes in solar-like stars)., Comment: 15 pages, 1 ps figure. Accepted for publication in PASP

The lower part of the classical instability strip and the surrounding main sequence are populated by a large variety of pulsating variable stars. In the past years a great effort was made by the stellar group of Brera Observatory to collect a large amount of photometric and spectroscopic data on Delta Sct stars, the more numerous class. In this paper I will describe our approach to this study. In Sect. 2.1 I show as the light curves of high-amplitude Delta Sct stars can be described in a synthetic and powerful way by using the Fourier decomposition. In Sect. 2.2 some interesting cases are presented, i.e. the peculiar light curves of some double-mode pulsators and the multiperiodicity of V974 Oph. As regards the small amplitude Delta Sct stars, the results which can be extracted from the photometry and (high-resolution) spectroscopy are discussed in Sect. 3; the importance of combining the two techniques into the synergic approach is stressed. As a final step, an excursus on the Gamma Dor stars is presented in Sect.4; the rich pulsational content makes these stars very similar to Delta Sct variables., Comment: 15 pages, 7 ps figures To be published in the Proceedings of "Variable Stars as Important Astrophysical Tools" (Invited talk), NATO ASI - Izmir, 31 Aug - 11 Sep 1998

The Fourier decomposition was applied to the light curves of the short period variable stars discovered by the OGLE team in Omega Cen. The phi_21 parameters are confined in a narrow strip for periods between 0.042 d and 0.07 d. Toward longer periods, there is an overlapping with the values obtained in the case of galactic stars. Toward shorter periods, the tendency to decreasing phi_21 values is also verified. A careful analysis should take more details in consideration: 1) Attention should be paid to the scatter in the distribution of the phi_21 parameters around 0.050 d. By analogy to Cepheid light curves, such a change can be the signature of a resonance between the fundamental mode and a higher overtone. 2) The small bunch of points above the progression at 0.038 d suggests a different light curve family. Since this group of stars shows a very small amplitude, it is possible that they are nonradial pulsators, not necessarily radial pulsators in a higher overtone. 3) The very low phi_21 value emphasizes the anomalous light curve of OGLEGC 26. The fact that such a light curve is observed in a Pop.II object is quite surprising, since V1719 Cyg and V798 Cyg (whose light curves are similar) are very probably Pop.I stars. In many cases, it seems that the phenomenon at the origin of the anomalous brightness increase should be carefully evaluated when dealing with pulsating star models., Comment: 4 pages, 3 ps figures Accepted for publication in Astronomy & Astrophysics, Main Journal

The importance of Cepheids is well known in many fields of astronomy. Section 2 introduces the Fourier decomposition, a tool to describe quantitatively the light curves of pulsating stars. Sect. 3 shows how an observational result was progressively built on the basis of old and new data; the latter were collected on selected targets just to clarify some controversial points. Since different pulsation modes were suspected among Cepheids, an independent confirmation was searched for. To do that we applied the least-squares technique to Double Mode Cepheids. By obtaining a very satisfactory description of their pulsational content (Sect.4), we could confirm that between Cepheids with P<8d they are both fundamental and first overtone pulsators (Sect.5). The detection of small amplitude cross-coupling terms and higher harmonics in the light curves of Double Mode Cepheids allowed us to quantify the properties of the high-order terms and hence to discover other peculiarities (Sect.6), very useful to complete the scenario of the resonance effects and to test some theoretical models (Sect.7). Therefore, we can study the Cepheids from the point of view of asteroseismology since to find resonance effects is as to sound their interiors., Comment: 16 pages, 11 ps figures To be published in the Proceedings of "Variable Stars as Important Astrophysical Tools" (Invited talk), NATO ASI - Izmir, 31 Aug - 11 Sep 1998

The re-analysis of the data reported by Mateo et al. (1998) allowed us to obtain a partially different set of frequencies for the 20 short period variable stars discovered in the Carina dSph galaxy. They are subdivided into 6 overtone-pulsators, 13 fundamental-pulsators; 1 case remains uncertain. The analysis of the light curves was conducted star by star and the first Fourier parameters were obtained for 17 variables. No clear separation between pulsation modes is discernible in the F21-P plot, but the very narrow range of the observed periods hampered us to consider that statement as a definitive one. A more extensive observational study is recommended, since a preliminary comparison with galactic variable stars displays small differences in the F21 values. Owing to the high standard deviation of the fit, the possibility that some stars are double-mode pulsators is also suggested., Comment: 4 pages, 3 ps figures. Submitted to Astronomy and Astrophysics as a Research Note