C. Sterken

Vrije Universiteit Brussel, Bruxelles, Brussels Capital Region, Belgium

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Publications (350)640.78 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In 1871, the Belgian astronomer Jean-Charles Houzeau developed a new approach to determine the solar parallax. His ``heliometer with unequal focal lengths" produces a large and a small solar image, as well as a large and small image of Venus. Making the small solar and the large Venus image coincide yields a measure of the distance of the centers of both objects. Two such instruments were build. After being appointed director of the Royal Observatory of Belgium in 1876, Houzeau obtained support to organize two Belgian expeditions to observe the Venus transit of December 6, 1882: one to San Antonio, Texas, and another one to Santiago de Chile. That enterprise was the first major expedition in the history of Belgian science. This paper describes the expeditions, gives some biographical information about the team members, and clarifies the principal instrument and its present-day whereabouts.
    Journal of Astronomical Data. 05/2013;
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    ABSTRACT: CCD photometry of GSC04778-00152 was carried out on 54 nights during 9 observing runs. In January 2006 the observations were made with the 41-cm Meade telescope at Observatorio Cerro Armazones (OCA), Chile, using an SBIG STL-6303E CCD camera (3072x2048 pixels, FOV 23.0'x15.4') and Johnson V filter. On 3 nights in December 2006 and on 2 nights in October 2007 we used the 2.4-m Hiltner telescope at the MDM Observatory, Arizona, USA, equipped with the 8kx8k Mosaic imager (FOV 23.6'x23.6'). In December 2006 and January 2007, we also used the 41-cm Meade telescope at OCA, using an SBIG ST-7XME CCD camera (FOV 5.9'x3.9') with no filter. Figure 3 shows all OCA light curves obtained with this configuration. At Tartu Observatory the observations were carried out in December 2006 and January 2007, using the 60-cm telescope with a SpectraSource Instruments HPC-1 camera (1024x1024 pixels, FOV 11.2'x11.2') and V filter. >From January to March 2007 the system was observed using the 1.0-m telescope at SAAO, Sutherland, South Africa with an STE4 CCD camera (1024x1024 pixels, FOV 5.3'x5.3') and UBVRI filters. Spectroscopic observations were carried out at the Tartu Observatory, Estonia, using the 1.5-m telescope with the Cassegrain spectrograph ASP-32 and an Andor Newton CCD camera. (3 data files).
    VizieR Online Data Catalog. 04/2012;
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    ABSTRACT: Based on more than a dozen partial nights of filterless CCD photometry combined with Strömgren uvby photomultiplier photometry, we derive 29 new times of maximum light of the SX Phoenicis star CY Aquarii. These times support a linear ephemeris for 2003-2011. In addition, we present uvby light curves for this star. Our dataset displays the smallest residual spread compared to any other substantial dataset published during the last decade.
    Journal of Astronomical Data. 02/2012;
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    ABSTRACT: The differential magnitudes of V* CY Aqr are presented in rgb2011.dat and sat.2011.dat. The times of maximum light of V* CY Aqr are given in tmax2011.dat. (3 data files).
    VizieR Online Data Catalog. 02/2012;
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    ABSTRACT: We present a collection of 102 new times of maximum of the SX Phoenicis star CY Aquarii. These times, together with 20 times of maximum taken from the literature, lead to a new local linear ephemeris for 2003-2009 with a formally slightly shorter period than the one for 1996-2002. It will require at least another half decade of additional monitoring before any significant update to any model can be considered. Such monitoring should preferably occur at regular intervals, be done in a consistent photometric band, and at high time resolution. A set of 114 new times of maximum obtained since 2002 leads to a new local linear ephemeris for 2003-2009: Tmax=2426159.512(+/-0.001)+0.061038349E(+/-0.000000002). (6 data files).
    VizieR Online Data Catalog. 11/2011;
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    ABSTRACT: All the data discussed in this paper were obtained through CCD imaging at one single observing site during 12 partial nights in September-December 2010 from a rooftop location at Realgymnasium Bruneck (Sudtirol, Italy). (1 data file).
    VizieR Online Data Catalog. 11/2011;
  • C. Sterken
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    ABSTRACT: This paper gives an account of the origin and evolution of the Long-Term Phoiometry of Variables (LTPV) project that, for more than a decade, has been running at the European Southern Observatory in Chile. The LTPV project is the scientific pacemaker for this meeting. KeywordsHD 160529–LTPV–Long-Term Monitoring
    07/2011: pages 1-18;
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    ABSTRACT: We describe our on-going project of photometric monitoring of Wolf-Rayet stars. Our strategy is based on the complementarity between data issued from the Long-Term Photometry of Variables project and data issued from dedicated observing runs. This method is illustrated by a few concrete examples. KeywordsWR stars– uvby photometry
    07/2011: pages 101-116;
  • N. Vogt, R. Mennickent, C. Sterken
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    ABSTRACT: A brief description of the brightness and colour variations of 15 southern Be stars, observed between 1982 and 1991 by means of differential photoelectric Strömgren photometry, is given. Seven stars of the sample revealed pronounced long-term variations on time scales of years to decades with amplitudes larger than 0.m2. In two of them, relatively sudden fadings by up to 1 mag in a few weeks were detected; they are interpreted as possible obscuration events by circumstellar dust clouds. Six other stars are characterized by variations on shorter timescales with periods between 4.6 and 88 days, among them one massive eclipsing binary and one newly-detected ellipsoidal variable. Most stars of our sample show only marginal variations—or no variations at all—in the b — y colour index; the UV dominated c 1 index is redder when the star is faint, and bluer when the star is bright. This implies that the amplitude of photometric variability is usually largest in the u band. The amplitudes of short-term and long-term variations are correlated: stars with stronger surface activities (“short-term”) tend to display also major changes in their circumstellar envelopes (“long-term”). KeywordsBe stars–variable stars–photoelectric photometry
    07/2011: pages 41-54;
  • T. Tuvikene, C. Sterken
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    ABSTRACT: The differential magnitudes of GSC 08613-02122 are presented in oca.dat, and saao.dat. eso.dat gives the uvby photometry of GSC 08613-02122 and NGC 3293-20. (3 data files).
    VizieR Online Data Catalog. 05/2011;
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    M. Weiler, H Rauer, C Sterken
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    ABSTRACT: The determination of the nuclear magnitudes of comets, and with it nuclear size frequency distributions, is strongly complicated by cometary activity. By now, only nuclear size frequency distributions for Jupiter Family comets are available, and they are still subject of uncertainties. For comets of other dynamical classes, nuclear magnitudes are known for only a few comets. The size frequency distributions are thus not well constrained.In this work we study whether nuclear magnitudes of comets can be constrained from sky survey observations as published by the Minor Planet Center. Observations from sky survey programs in which the comet was classified as a point-like source are analyzed in this respect.From the available published observations from 1998 to 2008, we derive nuclear magnitudes, as well as nuclear radii, for 84 comets. Among these are comets of the Jupiter Family, dynamically old and new isotropic comets, Halley-type comets and Centaurs. For Jupiter Family comets and for isotropic comets, the size frequency distributions are presented.Uncertainties of derived nuclear magnitudes arise from photometry and from potentially undetected activity. However, a comparison with objects with well known nuclear parameters shows that, despite substantial observational uncertainties, nuclear magnitudes are constrained to ±0.6 mag, thereby providing first indications for nuclear sizes. This is particularly relevant for isotropic comets with so far ill-constrained size distributions. Exponents of the differential size frequency distributions of 2.01-0.17+0.21 for Jupiter Family comets and 1.56-0.12+0.15 for isotropic comets are presented. The values derived here form a basis for future, dedicated observational studies which provide higher measurement accuracy.
    Icarus 03/2011; 212(2011):351-366. · 3.16 Impact Factor
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    ABSTRACT: We present 24 new times of maximum of the SX Phoenicis star CY Aquarii. These times lead to a slightly more precise local linear ephemeris for 2003--2010.
    Journal of Astronomical Data. 03/2011;
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    ABSTRACT: We present a brief overview of the history of attempts to obtain a clear detection of solar-like oscillations in cluster stars, and discuss the results on the first clear detection, which was made by the Kepler Asteroseismic Science Consortium (KASC) Working Group 2. Comment: 4 pages, 7 figures, accepted by Astronomische Nachrichten
    Astronomische Nachrichten 06/2010; · 1.40 Impact Factor
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    [Show abstract] [Hide abstract]
    ABSTRACT: We present a collection of 102 new times of maximum of the SX Phoenicis star CY Aquarii. These times, together with 20 times of maximum taken from the literature, lead to a new local linear ephemeris for 2003--2009 with a formally slightly shorter period than the one for 1996--2002. It will require at least another half decade of additional monitoring before any significant update to any model can be considered. Such monitoring should preferably occur at regular intervals, be done in a consistent photometric band, and at high time resolution.
    Journal of Astronomical Data. 04/2010;
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    T. Tuvikene, C. Sterken
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    ABSTRACT: We present a collection of more than 4000 UBVRI and uvby differential photometric measurements of the newly-discovered 12th-magnitude southern delta Scuti star GSC08613-02122. The star has a main pulsation period of about 4 hours with an amplitude of 0.05 mag in the V band. The pulsation amplitude is variable, and the O-C diagram reveals the existence of a long P~29.5-day cycle, which possibly results from the beating of the main pulsation frequency with a nearby frequency.
    Journal of Astronomical Data. 02/2010;
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    ABSTRACT: Asteroseismology of stars in clusters has been a long-sought goal because the assumption of a common age, distance and initial chemical composition allows strong tests of the theory of stellar evolution. We report results from the first 34 days of science data from the Kepler Mission for the open cluster NGC 6819 -- one of four clusters in the field of view. We obtain the first clear detections of solar-like oscillations in the cluster red giants and are able to measure the large frequency separation and the frequency of maximum oscillation power. We find that the asteroseismic parameters allow us to test cluster-membership of the stars, and even with the limited seismic data in hand, we can already identify four possible non-members despite their having a better than 80% membership probability from radial velocity measurements. We are also able to determine the oscillation amplitudes for stars that span about two orders of magnitude in luminosity and find good agreement with the prediction that oscillation amplitudes scale as the luminosity to the power of 0.7. These early results demonstrate the unique potential of asteroseismology of the stellar clusters observed by Kepler. Comment: 5 pages, 4 figures, accepted by ApJ (Lett.)
    The Astrophysical Journal Letters 12/2009; · 6.35 Impact Factor
  • C. Sterken
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    ABSTRACT: This paper focuses on one particular type of telescope – the heliometer – designed for solving one specific basic problem in astronomy: the scale factor of the solar system. One very special instrument of this type was the “heliometer with unequal focal lengths” designed by the Belgian astronomer Jean-Charles Houzeau for the 1882 transit of Venus. We also draw attention to the most interesting personality of Houzeau, and to his social engagement that went much beyond his work as a scientist (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Astronomische Nachrichten 06/2009; 330(6):582 - 585. · 1.40 Impact Factor
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    ABSTRACT: We present time-series photometry of nine cataclysmic variables: EI UMa, V844 Her, V751 Cyg, V516 Cyg, GZ Cnc, TY Psc, V1315 Aql, ASAS J002511+1217.2, V1315 Aql and LN UMa. The observations were conducted at various observatories, covering 170 hours and comprising 7850 data points in total. For the majority of targets we confirm previously reported periodicities and for some of them we give, for the first time through photometry, their underlying spectroscopic orbital period. For those dwarf-nova systems which we observed during both quiescence and outburst, the increase in brightness was accompanied by a decrease in the level of flickering. For the eclipsing system V1315 Aql we have covered 9 eclipses, and obtained a refined orbital ephemeris. We find that, during its long baseline of observations, no change in the orbital period of this system has occurred. V1315 Aql also shows eclipses of variable depth. (22 data files).
    VizieR Online Data Catalog. 05/2009;
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    ABSTRACT: Historical optical data are combined with more recent optical, extreme ultraviolet, and X-ray data to update the spin ephemeris of the cataclysmic variable EX Hya.
    03/2009;
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    ABSTRACT: The encounter of Deep Impact with comet 9P/Tempel 1 led to an unprecedented coordinated observational ground-based observing campaign which attracted many non-specialists. This paper discusses aspects of observational accuracy achieved by untrained observers using standard CCD cameras at 0.5 and 1-m class telescopes in South Africa and Chile. Our experience illustrates that calibrated photometry of comets cannot be accomplished without dedicated observing.
    Deep Impact as a World Observatory Event: Synergies in Space, Time, and Wavelength; 01/2009

Publication Stats

702 Citations
640.78 Total Impact Points

Institutions

  • 1970–2012
    • Vrije Universiteit Brussel
      Bruxelles, Brussels Capital Region, Belgium
  • 1998–2011
    • University Hospital Brussels
      Bruxelles, Brussels Capital Region, Belgium
    • Ege University
      Ismir, İzmir, Turkey
    • University of Concepción
      • Departamento de Física
      Concepción, Region del Biobio, Chile
  • 2006
    • Leiden University
      Leyden, South Holland, Netherlands
  • 2005
    • University of Hawaiʻi at Mānoa
      • Institute of Astronomy
      Honolulu, HI, United States
  • 2001
    • Royal Observatory of Belgium
      Bruxelles, Brussels Capital Region, Belgium
  • 1999
    • University of Groningen
      Groningen, Groningen, Netherlands
  • 1994–1995
    • Pontifical Catholic University of Chile
      • Instituto de Astrofísica
      CiudadSantiago, Santiago, Chile
  • 1987–1992
    • University of Liège
      • Department of Astrophysics, Geophysics and Oceanography
      Luik, Walloon Region, Belgium