Now showing items 1-6 of 6

  • Correcting CCD photometry of stars for seeing effects 

    Koen, Chris (Oxford Univeristy Press, 2009)
    Systematic variability in stellarmagnitudes, as derived from profile fitting to CCD images,may in some instances be due to variable seeing. It is suggested that this happens in cases where the stars are unresolved pairs, ...
  • An extensive search for rapid optical variability in ultracool dwarfs 

    Koen, Chris (Oxford University Press, 2013)
    In this paper, a summary of optical time-series photometry of 125 ultracool dwarfs is given. The observing strategy was to monitor each object continuously for 2–3 h in order to ascertain whether itwas rapidly variable. ...
  • Improved SAAO–2MASS photometry transformations 

    Koen, Chris; Marang, F.; Kilkenny, David; Jacobs, C. (Oxford University Press, 2007)
    Near-infrared photometry of 599 stars is used to calculate transformations from the South African Astronomical Observatory (SAAO) JHK system to the Two-Micron All-Sky Survey (2MASS) JHKS system. Both several-term formal ...
  • 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 ...
  • Linking multi-epoch CCD photometry of partially overlapping fields 

    Koen, Chris (Oxford University Press, 2013)
    A common problem in CCD photometry is to combine measurements obtained at different epochs. This is especially challenging if the fields only overlap partially, and are sparse, so that not all calibrating stars are ...
  • UBV(RI)C photometry of transiting planet hosting stars 

    Maxted, P.F.L.; Koen, Chris; Smalley, B. (Oxford University Press, 2011)
    We present new UBV(RI)C photometry of 22 stars that host transiting planets, 19 of which were discovered by the Wide Angle Search for Planets (WASP) survey. We use these data together with Two Micron All Sky Survey (2MASS) ...