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Wils P.,Vereniging voor Sterrenkunde | Henden A.A.,American Association of Variable Star Observers | Kleidis S.,Zagori Observatory | Schmidt E.G.,University of Nebraska - Lincoln | Welch D.L.,McMaster University
Monthly Notices of the Royal Astronomical Society | Year: 2010

V371 Per was found to be a double-mode Cepheid with a fundamental mode period of 1.738 days, the shortest among Galactic beat Cepheids, and an unusually high period ratio of 0.731, while the other Galactic beat Cepheids have period ratios between 0.697 and 0.713. The latter suggests that the star has a metallicity [Fe/H] between -1 and -0.7. The derived distance from the Galactic plane places it in the thick disc or the Halo, while all other Galactic beat Cepheids belong to the thin disc. There are indications from historical data that both the fundamental and first overtone periods have lengthened. © 2009 The Authors. Journal compilation © 2009 RAS. Source

Broens E.,Vereniging voor Sterrenkunde
Monthly Notices of the Royal Astronomical Society | Year: 2013

Extreme mass-ratio contact binaries with a high degree of overcontact may be in the late evolutionary stages of the contact phase. Detailed photometric analyses and orbital period studies of those systems can provide invaluable information for the coalescence scenario of close binary systems, as recently observed in V1309 Sco. In this paper the first light-curve analysis and period study for the totally eclipsing contact binary AW CrB is presented. The VRcIc CCD photometric light curves are analysed by means of the WD code. The asymmetry of the light curves is modelled by a cool star spot on the primary component. It is shown that AW CrB has a high degree of overcontact f = 75 per cent and an extreme mass-ratio of q = 0.10, placing it among the few contact binaries with the lowest known mass-ratios. The mean density of the primary component suggests that it has evolved away from the zero age main sequence (ZAMS). Eighty-four times of minimum light are reported, derived from observations available in public archives, the literature and the observations presented in this paper. The orbital period study shows a continuously increasing period, at a rate of dP/dt = 3.58 × 10-7 d yr-1, suggesting a mass transfer from the secondary component to the primary one, implying a further decreasing mass-ratio. © 2013 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Pastorello A.,National institute for astrophysics | Cappellaro E.,National institute for astrophysics | Inserra C.,Queens University of Belfast | Smartt S.J.,Queens University of Belfast | And 42 more authors.
Astrophysical Journal | Year: 2013

We report the results of a three-year-long dedicated monitoring campaign of a restless luminous blue variable (LBV) in NGC 7259. The object, named SN 2009ip, was observed photometrically and spectroscopically in the optical and near-infrared domains. We monitored a number of erupting episodes in the past few years, and increased the density of our observations during eruptive episodes. In this paper, we present the full historical data set from 2009 to 2012 with multi-wavelength dense coverage of the two high-luminosity events between 2012 August and September. We construct bolometric light curves and measure the total luminosities of these eruptive or explosive events. We label them the 2012a event (lasting ∼50 days) with a peak of 3 × 10 41 erg s-1, and the 2012b event (14 day rise time, still ongoing) with a peak of 8 × 1042 erg s-1. The latter event reached an absolute R-band magnitude of about -18, comparable to that of a core-collapse supernova (SN). Our historical monitoring has detected high-velocity spectral features (∼13,000 km s-1) in 2011 September, one year before the current SN-like event. This implies that the detection of such high-velocity outflows cannot, conclusively, point to a core-collapse SN origin. We suggest that the initial peak in the 2012a event was unlikely to be due to a faint core-collapse SN. We propose that the high intrinsic luminosity of the latest peak, the variability history of SN 2009ip, and the detection of broad spectral lines indicative of high-velocity ejecta are consistent with a pulsational pair-instability event, and that the star may have survived the last outburst. The question of the survival of the LBV progenitor star and its future fate remain open issues, only to be answered with future monitoring of this historically unique explosion. © 2013. The American Astronomical Society. All rights reserved.. Source

Schaffenroth V.,University of Bamberg | Schaffenroth V.,University of Innsbruck | Geier S.,University of Bamberg | Geier S.,European Southern Observatory | And 6 more authors.
Astronomy and Astrophysics | Year: 2013

We report the discovery of a bright (mV = 11.6 mag), eclipsing, hot subdwarf binary of spectral type B with a late main sequence companion from the All Sky Automated Survey (ASAS 102322-3737.0). Such systems are called HW Vir stars after the prototype. The lightcurve shows a grazing eclipse and a strong reflection effect. An orbital period of P = 0.13927 d, an inclination of i = 65.86, a mass ratio q = 0.34, a radial velocity semiamplitude K1 = 81.0 km s-1, and other parameters were derived from a combined spectroscopic and photometric analysis. The short period can only be explained by a common envelope origin of the system. The atmospheric parameters (T eff = 28 400 K, log g = 5.60) are consistent with a core helium-burning star located on the extreme horizontal branch. In agreement with that we derived the most likely sdB mass to be MsdB = 0.46 M ⊙, close to the canonical mass of such objects. The companion is a late M-dwarf with a mass of Mcomp = 0.16 M⊙. ASAS 102322-3737.0 is the third brightest of only 12 known HW Virginis systems, which makes it an ideal target for detailed spectroscopic studies and long-term photometric monitoring to search for period variations, e.g., those caused by a substellar companion. © 2013 ESO. Source

Wils P.,Vereniging voor Sterrenkunde | Panagiotopoulos K.,Helliniki Astronomiki Enosi | Van Wassenhove J.,Vereniging voor Sterrenkunde | Ayiomamitis A.,Helliniki Astronomiki Enosi | And 11 more authors.
Information Bulletin on Variable Stars | Year: 2012

432 maxima of 64 High-Amplitude Delta Scuti Stars (HADS) obtained from CCD observations, are presented. Observations of the newly discovered HADS GSC 3004-0870 are included. The object GSC 1924-1134 was found to be a double-mode HADS, while GSC 1621-1643, GSC 2847-586 and GSC 3490-814 were found to be multiperiodic pulsators. GSC 4556-1113 is showing cyclical variations of the pulsation frequency with a period of 164 days. Source

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