Now showing items 1-12 of 12

    • The analysis of indexed astronomical time series – X. Significance testing of O − C data 

      Koen, Chris (Oxford University Press, 2006)
      It is assumed that O − C (‘observed minus calculated’) values of periodic variable stars are determined by three processes, namely measurement errors, random cycle-to-cycle jitter in the period, and possibly long-term ...
    • Evidence for rapid evolution of periodic variations in an ultracool dwarf 

      Koen, Chris (Oxford University Press, 2006)
      The results of three short photometric monitoring runs on the L0 dwarf 2MASS J06050196−2342270, during three consecutive nights, are presented. The observations show the persistent presence of a 2.4-h period, with an IC ...
    • HE 0230−4323 revisited: a new rapidly pulsating sdB star 

      Kilkenny, David; Koen, Chris; Worters, H. (Oxford University Press, 2010)
      HE 0230−4323 is a hot sdB star in a binary system. An earlier work demonstrated that the light curve of the system shows a strong (∼4 per cent) reflection effect and also appears to exhibit photometric variations of the ...
    • HE0230–4323: an unusual pulsating hot subdwarf star 

      Koen, Chris (Oxford University Press, 2007)
      HE 0230−4323 is a known binary, consisting of a subdwarf star and a companion which is not observable in the optical. Photometric measurements reported in this paper have shown it to be both a reflection-effect and a ...
    • IC and RC band time-series observations of some bright ultracool dwarfs 

      Koen, Chris (Oxford University Press, 2005)
      The results of more than 100 h of CCD photometric monitoring of 10 L dwarfs and two T dwarfs are presented. Reasonable evidence is shown for IC band variability in DENIS 0255−4700, DENIS 1705−0516 and 2M 2104−1037. ...
    • JHKs time-series observations of a few ultracool dwarfs 

      Koen, Chris; Tanabe, T.; Tamura, M.; Kusakabe, N. (Oxford University Press, 2005)
      The M8.5 object SSSPM J0109−5101 has recently been shown to be both a periodic and a flaring variable, based on optical observations in the extreme red. More than 16 h of monitoring in the near-infrared (NIR) reported ...
    • JL 82: a slowly pulsating hot subdwarf star in a close binary system 

      Koen, Chris (Oxford University Press, 2009)
      JL 82 is a known binary, consisting of an sdB star and a companion which is not directly observable in the optical. Photometric measurements reported in this paper show it to variable with both the binary period (∼0.75 ...
    • KPD 0629–0016, a slowly pulsating hot subdwarf star 

      Koen, Chris; Green, E.M. (Oxford University Press, 2007)
      The results of nine CCD photometric observing runs on KPD 0629–0016 are presented. During six of the runs measurements were obtained alternately through B and V filters. Four periodicities, for which there is good agreement ...
    • Multicolour time series photometry of 2MASS 1207−3932 

      Koen, Chris (Oxford University Press, 2008)
      Time series photometry in VRI of the young brown dwarf Two-Micron All-Sky Survey (2MASS) J1207334−393254 is presented. Variability in I is insignificant, but amplitudes up to ∼0.2 mag in R, and ∼0.55 mag in V, are seen ...
    • Near-infrared time-series photometry of six fields in the young open cluster IC 2391 

      Koen, Chris; Ishihara, Akika (Oxford University Press, 2006)
      Fields containing targets of spectral types later than M5 were monitored in JHKs for about 7 h each. None of the targets showed variability at levels exceeding 0.02 (or smaller, in some cases). Seven new variable stars ...
    • Photometry of the magnetic white dwarf SDSS 121209.31+013627.7 

      Koen, Chris; Maxted, P.F.L. (Oxford University Press, 2006)
      The results of 27 h of time series photometry of SDSS 121209.31+013627.7 are presented. The binary period established from spectroscopy is confirmed and refined to 0.061 412 d (88.43 min). The photometric variations are ...
    • Two new variable sdB stars, HE 0218−3437 and LB 1516 

      Koen, Chris; Kilkenny, David; Pretorius, M.L.; Frew, D.J. (Oxford University Press, 2010)
      We present photometry which shows that two known hot subdwarf stars, HE 0218−3437 and LB 1516, are variable. LB 1516 exhibits several frequencies in the range 12–25 cycles d−1 (periods of about 1–2 h) with amplitudes ...