Now showing items 1-7 of 7

    • 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 ...
    • 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 ...
    • 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 ...
    • Multicolour time series photometry of three periodic ultracool dwarfs 

      Koen, Chris (Oxford University Press, 2013)
      Photometry in I, or contemporaneously in I and R, of the known variable ultracool dwarfs Kelu-1 and 2MASS J11553952−3727350 is presented. The nature of the variability of Kelu-1 appears to evolve on time-scales of a day ...
    • 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 ...