Vereniging voor Sterrenkunde


Vereniging voor Sterrenkunde

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Neustroev V.V.,University of Turku | Neustroev V.V.,University of Oulu | Marsh T.R.,University of Warwick | Zharikov S.V.,National Autonomous University of Mexico | And 24 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2017

We report extensive 3-yr multiwavelength observations of the WZ Sge-type dwarf nova SSS J122221.7-311525 during its unusual double superoutburst, the following decline and in quiescence. The second segment of the superoutburst had a long duration of 33 d and a very gentle decline with a rate of 0.02 mag d-1, and it displayed an extended post-outburst decline lasting at least 500 d. Simultaneously with the start of the rapid fading from the superoutburst plateau, the system showed the appearance of a strong near-infrared excess resulting in very red colours, which reached extreme values (B - I ≃ 1.4) about 20 d later. The colours then became bluer again, but it took at least 250 d to acquire a stable level. Superhumps were clearly visible in the light curve from our very first time-resolved observations until at least 420 d after the rapid fading from the superoutburst. The spectroscopic and photometric data revealed an orbital period of 109.80 min and a fractional superhump period excess ≲0.8 per cent, indicating a very low mass ratio q ≲ 0.045. With such a small mass ratio the donor mass should be below the hydrogen-burning minimum mass limit. The observed infrared flux in quiescence is indeed much lower than is expected from a cataclysmic variable with a nearmain- sequence donor star. This strongly suggests a brown-dwarf-like nature for the donor and that SSS J122221.7-311525 has already evolved away from the period minimum towards longer periods, with the donor now extremely dim. © 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Drake A.J.,California Institute of Technology | Gansicke B.T.,University of Warwick | Djorgovski S.G.,California Institute of Technology | Wils P.,Vereniging voor Sterrenkunde | And 10 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present 855 cataclysmic variable candidates detected by the Catalina Real-time Transient Survey (CRTS) of which at least 137 have been spectroscopically confirmed and 705 are new discoveries. The sources were identified from the analysis of five years of data, and come from an area covering three quarters of the sky. We study the amplitude distribution of the dwarf novae cataclysmic variables (CVs) discovered by CRTS during outburst, and find that in quiescence they are typically 2 mag fainter compared to the spectroscopic CVsample identified by the Sloan Digital Sky Survey. However, almost all CRTS CVs in the SDSS footprint have ugriz photometry. We analyse the spatial distribution of the CVs and find evidence that many of the systems lie at scale heights beyond those expected for a Galactic thin disc population. We compare the outburst rates of newly discovered CRTS CVs with the previously known CV population, and find no evidence for a difference between them. However, we find significant evidence for a systematic difference in orbital period distribution. We discuss the CVs found below the orbital period minimum and argue that many more are yet to be identified among the full CRTS CV sample. We cross-match the CVs with archival X-ray catalogues and find that most of the systems are dwarf novae rather than magnetic CVs. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

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.

Wils P.,Vereniging voor Sterrenkunde | Gansicke B.T.,University of Warwick | Drake A.J.,California Institute of Technology | Southworth J.,University of Warwick
Monthly Notices of the Royal Astronomical Society | Year: 2010

By cross-matching blue objects from the Sloan Digital Sky Survey with Galaxy Evolution Explorer and the astrometric catalogues USNO-B1.0, GSC2.3 and CMC14, 64 new dwarf nova candidates with one or more observed outbursts have been identified. 14 of these systems are confirmed as cataclysmic variables through existing and follow-up spectroscopy. A study of the amplitude distribution and an estimate of the outburst frequency of these new dwarf novae and those discovered by the Catalina Real-time Transient Survey indicate that besides systems that are faint because they are farther away, there also exists a population of intrinsically faint dwarf novae with rare outbursts. © 2009 The Authors. Journal compilation © 2009 RAS.

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.

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.

Pastorello A.,National institute for astrophysics | Cappellaro E.,National institute for astrophysics | Inserra C.,Queen's University of Belfast | Smartt S.J.,Queen's 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..

Wils P.,Vereniging Voor Sterrenkunde | Panagiotopoulos K.,Helliniki Astronomiki Enosi | Panagiotopoulos K.,Pouda Observatory | Van Wassenhove J.,Vereniging Voor Sterrenkunde | And 16 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.

Odell A.P.,Astronomy Box | Wils P.,Vereniging Voor Sterrenkunde | Dirks C.,Evergreen State College | Guvenen B.,University of Arizona | And 3 more authors.
Information Bulletin on Variable Stars | Year: 2012

We present new light curves for V963 Per and derive a new ephemeris. An abrupt change in the depth of secondary minimum of about 4 % occurred during the observations.

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