Nonradial Modes in Classical Cepheids

Systematic search for multiperiodicity in the LMC Cepheids (Moskalik, Kolaczkowski & Mizerski 2004) has led to discovery of low amplitude nonradial modes in a substantial fraction of overtone pulsators. We present detailed discussion of this new type of multimode Cepheid pulsators and compare them to similar nonradial pulsators discovered among RR Lyrae stars. Finally, we show first detections of secondary nonradial modes in FU/FO double-mode Cepheids.Comment: 7 pages, 4 figures. Poster presented at Wroclaw HELAS Workshop "Interpretation of Asteroseismic Data", 23-27 June 2008, Wroclaw, Poland. Shortened version will be published in Communications in Asteroseismolog

Unveiling the phenomenon of Double Periodic Variables

In this paper we give a brief report of our recent research on Double Periodic Variables (DPVs), including the discovery of DPVs in the Galaxy and some insights on the nature of their long-cycle variability.Comment: To appear in "Proceedings of the XII Reunion Latinoamericana de la UIA", Revista Mexicana de Astronomia y Astrofisica, in pres

The class of interacting binaries Double Periodic Variables

We introduce the class of intermediate mass binaries named Double Periodic Variables (DPVs), characterized by orbital photometric variability (ellipsoidal or eclipsing) in time scales of few days and a long photometric cycle lasting roughly 33 times the orbital period. After a search conducted in the OGLE and ASAS catalogues, we identified 114 of these systems in the Magellanic Clouds and 11 in the Galaxy. We present results of our photometric and spectroscopic campaigns on DPVs conducted during the last years, outlining their main observational characteristics. We present convincing evidence supporting the view that DPVs are semidetached interacting binaries with optically thick discs around the gainer, that experience regular cycles of mass loss into the interstellar medium. The mechanism regulating this long-term process still is unknown but probably is related to relaxation cycles of the circumprimary disc. A key observational fact is the modulation of the FWHM of HeI 5875 with the long cycle in V393 Sco. The DPV evolution stage is investigated along with their relationship to Algols and W Serpentid stars. We conclude that DPVs can be used to test models of non-conservative binary evolution including the formation of circumbinary discs.Comment: To appear in ASP Conference Series special issue: "Binaries: Key to Comprehension of the Universe

Double Mode Cepheids with Amplitude Modulation

Recent search for multiperiodicity in LMC Cepheids (Moskalik, Kolaczkowski & Mizerski 2004) has led to discovery of periodic modulation of amplitudes and phases in many of the first/second overtone (FO/SO) double mode pulsators. We discuss observational characteristics and possible mechanisms responsible for this behaviour.Comment: 2 pages, 2 figures, presented at conference "Stellar Pulsation and Evolution", Monte Porzio Catone, 19-24 June 200

Variable Stars in the Open Cluster NGC 7044

We present results of a search for variable stars in the intermediate-age open cluster NGC 7044. We found 23 variable stars in the observed field. One star turned out to be of the delta Sct type with two pulsational modes excited. From the position in the color-magnitude diagram we conclude that this star is a member of the cluster. Moreover, we found 13 eclipsing systems, of which five are W UMa stars, one is a beta Lyr variable, six are beta Per binaries showing detached configuration, and the last one is another probable beta Per system. Using the period-luminosity-color relation for W UMa stars we established the membership of the contact binaries, finding four of them to be very probable cluster members. We estimated from these four stars an apparent distance modulus (m-M)_V of NGC 7044 to be 14.2 +/- 0.4 mag, which is smaller than previous determinations of this parameter. We were able to derive orbital period for only four beta Per systems. For the remaining ones we observed only two or three eclipses. Finally, nine stars we found to show irregular light changes. Most of them are red stars not belonging to the cluster. For the cluster core we determined a reddening map, which allowed us to construct a dereddened color-magnitude diagram of NGC 7044 with a narrow main-sequence. By fitting a theoretical isochrone to this diagram we derived E(V-I_C) = 0.92 mag, (m-M)_V = 14.45 mag and log(age/yr) = 9.2.Comment: 17 pages, 12 figures, published in Acta Astronomica (2008

High-amplitude Delta Scuti stars in the Galactic bulge from the OGLE-II and MACHO data

Searching for main-sequence pulsators, we analyzed photometry of ~200,000 variable star candidates from the OGLE-II Galactic fields, finding 193 high-amplitude Delta Scuti stars. This doubles the number of known stars of this type. The MACHO data, available for half of stars, were also analyzed. In our sample of the HADS stars, we found 50 multiperiodic objects, including 39 that have period ratios in the range of 0.76-0.80, an indication of the radial fundamental and first-overtone pulsation. We discuss the resulting Petersen diagram for these stars in view of the period ratios predicted by models. Except for stars showing pulsations in the radial fundamental mode and first overtone, we find the evidence for higher radial overtones and non-radial modes in the analyzed sample of multiperiodic HADS stars.Comment: 4 pages, 3 figues, to appear in the proceedings of the "Stellar Pulsation and Evolution" conference, Monte Porzio Catone, June 200

Beta Cephei stars in the inner part of the Galaxy

From the Fourier analysis of the catalogue of ~200,000 variable candidates in the OGLE-II Galactic fields, we found a sample of about 230 short-period low-amplitude variable stars. From their position in the colour-magnitude diagram and the observed periods (multiple in most cases), we identify the stars as a mixture of Beta Cephei and Delta Scuti stars. Beta Cephei stars from this sample are located in the Galactic disk at distances from 3 to 6 kpc. Many of them shows large range of the excited periods, an indication of high metallicity. We estimate that even a half of the sample of 230 short-period variables we found, can be Beta Cephei stars. The periods alone, however, are rarely sufficient to distinguish between both types of pulsators. We point out, how this can be done observationally.Comment: 2 pages, 2 figures, to appear in the proceedings of the "Stellar Pulsation and Evolution" conference, Monte Porzio Catone, June 200

Interacting Binary Star Environments and the W Ser - DPV - Algol Connection

Recent work on some kinds of interacting binaries is summarized, with emphasis on Cataclysmic Variables, Algol-like variables and the recently discovered Double Periodic Variables (DPVs). The sequence W Serpentids (very massive with irregular variability and large mass loss) $\to$ DPVs (less massive with regular variability and ciclic mass loss) $\to$ Algols (even less massive with small mass loss) could correspond to an evolutionary sequence, and illustrate the importance of the mass transfer rate in shaping observable and mass loss properties for these systems.Comment: Invited talk to the ESO workshop "The Interferometric view on Hot Stars", March 2-6, 2009, Vina del Mar, Chile, to be published in Revista Mexicana de Astronomia y Astrofisic

Reanalysis of the OGLE-I observations with the Image Subtraction Method. I. Galactic bar fields MM1-A, MM1-B, MM7-A, and MM7-B

As a result of the reanalysis of the OGLE-I observations by means of the image subtraction method, we present the first part of a catalog, consisting of the data for variable stars in four Galactic fields observed by the OGLE-I, viz. MM1-A, MM1-B, MM7-A, and MM7-B. In total, 2016 variable stars have been found. This increased the number of known variable in these fields stars more than twofold. We comment on the detectability of the variable stars in previous studies. Some interesting findings are also discussed. Among others, we found 45 Delta Scuti stars (38 are new) including several multiperiodic objects. Detailed analysis of the light curves of 47 RR Lyrae stars (24 are new detections) allowed us to find five stars which exhibit nonradial pulsations and one RRd star. Three RRab stars are members of the Sagittarius dwarf galaxy (Sgr dSph). We also find four objects which are probably galactic RV Tauri stars and one W Virginis star which seems to belong to Sgr dSph. This is the first Population II Cepheid found in this satellite galaxy and dSph other than the Fornax one. For eclipsing EW-type binaries, which are the most abundant variables in our catalog, we investigate the amplitude and period distributions. A comparison with the previous OGLE-I catalogs indicates that we found more stars with smaller amplitudes. Finally, in addition to the two microlensing events discovered previously in these fields, we find five more.Comment: 19 pages, 9 figures, accepted by the Acta Astronomic

Two Be stars in the Small Magellanic Cloud with B[e]-like properties

We present an analysis of UVES and MIKE (ground based) high resolution and Far Ultraviolet Spectroscopic Explorer spectra of two novel and photometrically variable bright blue stars in the SMC; OGLE004336.91-732637.7 and the periodically occulted star OGLE004633.76-731204.3. The light curves of these stars exhibit multiple frequencies, and their spectra are similar. The latter are dominated by absorption/emission features produced in a circumstellar (CS) envelope whereas photospheric features are barely visible and forbidden emission lines are not visible. Modeling of spectral features indicates similar physical conditions for the CS envelope in both stars. An optically thick, slowly and thermally stratified disk. OGLE004633.76-731204.3 is noteworthy in showing blue discrete absorption components ("BACs") in their spectra possibly indicating the shock interaction between high velocity and low velocity material. Optical spectra from two spectra separated by 5 years show little change in the radial velocity over this period. However because these observations happen to be made in roughly similar phases over their long period, these suggest only that the stars are not in close binaries. We interpret the occultations and additional photometric nearly periodic variability in OGLE004633.76-731204.3 as due to covering of the star by a density modulation in a sector of a quasi-Keplerian circumstellar disk. Altogether, we suggest that these stars are prototypes of a larger group of stars, which we dub the "bgBe's" and discuss their similarities and differences with respect to the well known sgB[e] variables. Although OGLE004336.91-732637.7 appears to be a member the open cluster NGC 242, the evolutionary context of these stars is unclear.Comment: 26 pages, 10 figure