Publications by Year: 2001

2001
Gazeas KD, Niarchos PG, Manimanis VN. A new CCD photometric study of V1162 Orionis. In: ; 2001. pp. 83.1. Website
Harlaftis ET, Steeghs D, Sokoloski J, Rutten RGM, Niarchos P, Gazeas K, Papadimitriou C, Manimanis V. The accretion Disc evolution of the eclipsing cataclysmic variable EX Draconis. In: ; 2001. pp. 61.1. WebsiteAbstract
The dwarf nova EX Draconis shows deep and wide eclipses, in addition to its frequent outburst activity (every 2-3 weeks), which makes it the ideal target for monitoring a complete outburst cycle. We observed EX Draconis in BVI colours with the 1.2m telescope at Kryonerion Korinthias (Greece) between 1 July-20 August 2000 covering 3 outburst events (1-5 July, 20-30 July and 6-12 August). Here, we present a preliminary eclipse mapping study of the light curves obtained in August 2000.
Arentoft T, Sterken C, Handler G, Freyhammer LM, Bruch A, Niarchos P, Gazeas K, Manimanis V, van Cauteren P, Poretti E, et al. V 1162 Ori: A multiperiodic delta Scuti star with variable period and amplitude. [Internet]. 2001;374:1056 - 1070. WebsiteAbstract
We present the results of multisite observations of the delta Scuti star V 1162 Ori. The observations were done in the period October 1999-May 2000, when 18 telescopes at 15 observatories were used to collect 253 light extrema during a total of 290 hours of time-series observations. The purpose of the observations was to investigate amplitude and period variability previously observed in this star, and to search for low-amplitude frequencies. We detect, apart from the main frequency and its two first harmonics, four additional frequencies in the light curves, all with low amplitudes (1-3 mmag). Combining the present data set with data obtained in 1998-99 at ESO confirms the new frequencies and reveals the probable presence of yet another pulsational frequency. All five low-amplitude frequencies are statistically significant in the data, but at least one of them (f5) suffers from uncertainty due to aliasing. Using colour photometry we find evidence for a radial main frequency (f1), while most or all low-amplitude frequencies are likely non-radial. We show that the main frequency of V 1162 Ori has variable amplitude and period/phase, the latter is also displayed in the O-C diagram from light extrema. The amplitude variability in our data is cyclic with a period of 282 d and a range of nearly 20 mmag, but earlier amplitude values quoted in the literature cannot be explained by this cyclic variation. O-C analysis including data from the literature show that the period of V 1162 Ori displays a linear period change as well as sudden or cyclic variations on a time scale similar to that of the amplitude variations. Based on observations obtained at the South African Astronomical Observatory (SAAO), Athens University and Kryonerion Observatories, European Southern Observatories (ESO: applications ESO 62H-0110, 64H-0065 and 64L-0182), Laboratório Nacional de Astrofísica (Brazil), Xinglong, Beersel Hills, Ege University, San Pedro Martir, Merate, Mt. Laguna, Siding Spring, Sierra Nevada, Braeside and Lick Observatories. Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/374/1056
Arentoft T, Sterken C, Handler G, Freyhammer LM, Bruch A, Niarchos P, Gazeas K, Manimanis V, van Cauteren P, Poretti E, et al. VizieR Online Data Catalog: V1162 Ori variations (Arentoft+, 2001). [Internet]. 2001:J/A+A/374/1056. WebsiteAbstract
V1162 Ori is a delta Scuti star with variable period and amplitude. To analyse data acquired in the years 1998-2000, the data were subdivided in smaller subsets to take the amplitude and period variability into account. Four different ways of subdividing the data discussed in the paper are outlined in this table 2. A database containing the observations of V1162 Ori is in preparation; it will be published in the Journal of Astronomical data (http://www.vub.ac.be/STER/JAD/jad.htm). (2 data files).
Gazeas K, Manimanis VN, Niarchos PG. Observing variable stars at the University of Athens Observatory. In: ; 2001. pp. 127 - 135. WebsiteAbstract
In 1999 the University of Athens installed a 0.4-m Cassegrain telescope (CCT-16, by DFM Engineering) on the roof of the Department of Astrophysics, Astronomy and Mechanics, equipped with a ST-8 CCD camera and Bessel UBVRI filters. Although the telescope was built for educational purposes, we found it can be a perfect research instrument, as we can obtain fine quality light curves of bright variable stars, even from a place close to the city center. Light curves of the δ Scuti star V1162 Ori and of the sdB star PG 1336-018 are presented, showing the ability of a 40-cm telescope to detect negligible luminosity fluctuations of relatively bright variable stars. To date, we succeed in making photometry of stars down to 15th magnitude with satisfactory results. We expect to achieve even better results in the future, as our methods still improve, and as the large number of relatively bright stars gives us the chance to study various fields of CCD photometry of variables.
Andronov IL, Yushchenko AV, Niarchos PG, Gazeas K. Early Superhumps in the "King of the Superoutbursts" System WZ Sge. [Internet]. 2001;14:17 - 20. WebsiteAbstract
Time series analysis of 6 nights of CCD observations of WZ Sge after it's unexpected superoutburst on July 23, 2001 has shown highly asymmetric periodic variations with a period 0.0566513(22)deg, full amplitude 0.218(4)m and a very high asymmetry M-m=0.670(9), a secondary minimum 0.38P after the main one. The initial epochs are Tmax=BJD 2452118.7483(3) and Tmin=BJD 52118.7670(2). The characteristics of the phase light curve are listed. In addition, we have found superhumps with a semi-amplitude of 0.021(2)m and an ephemeris Tmax,sh=BJD 2452117.6830(8)+0.057435(45)d E. Other peaks at 21 and 25 minutes possibly correspond to quasi-periodic oscillations with an effective semi-amplitude of 0.014m.
Arentoft T, Sterken C, Knudsen MR, Handler G, Niarchos P, Gazeas K, Manimanis V, Moalusi MB, Vuthela FF, van Cauteren P. Irregular amplitude variations and another abrupt period change in the δ Scuti star V 1162 Ori. [Internet]. 2001;378:L33 - L36. WebsiteAbstract
We report that the intermediate amplitude delta Scuti star V 1162 Ori has changed its main pulsational period in the course of the year 2000. This new period change falls in a sequence of period changes observed during the last 5 years. While the average amplitude value of all our new data, 63 mmag, fits a cyclic amplitude variation suggested by Arentoft et al. (2001), splitting the data up in smaller subsets discloses significant deviations from regularity, with stretches of constant amplitude during short intervals of time. The new data show that the amplitude of one of the secondary frequencies, f2, has in 3 years dropped from more than 3 mmag to now about 1 mmag, and that the previously obtained f5 probably is a 1 d-1 alias of the real frequency. We present the newly acquired times of minimum and maximum light as support for subsequent observing campaigns. Based on observations obtained at the South African Astronomical Observatory (SAAO), Athens University Observatory, the Danish 1.5 m telescope at ESO, La Silla, Chile, and Beersel Hills Observatory.
Boffin H, Harlaftis E, Papadimitriou C, Gazeas K, Brinias A. Photometric monitoring of WZ Sge. In: ; 2001. pp. 89.1. WebsiteAbstract
The cataclysmic variable, WZ Sge, and one of prototype of of the SU Uma-type dwarf nova sub-class, went into outburst on July 23 of this year. This is its first outburst since 23 years. The brightness and rarety of the event has perhaps made it the most observed object of the year. From July 29 on, we have started a photometric monitoring of this system, mainly with B-band time series with the 1.2m telescope at Kryoneri Korinthias (Greece). Here, we will present the first preliminary light curves obtained, covering the first two and a half weeks of the outburst, from July 29 to August 9, when the star was in steady decline up to when it started to show superhumps. Our on-going monitoring will continue until December 2001.
Gazeas KD, Manimanis VN, Niarchos PG. BVR CCD photometry and light curve analysis of the eclipsing binary BF Virginis. In: ; 2001. pp. 86.1. Website
Manimanis VN, Gazeas KD, Niarchos PG. The first photometric study of the near-contact system GW Tauri. In: ; 2001. pp. 85.1. Website