Now showing items 21-40 of 55

    • The “four sigma” limit for significant periodicities 

      Koen, Chris (Springer Verlag, 2010)
      Most of the pulsations which have been observed in sdB stars have very low amplitudes. Detection of modes from photometric observations is usually performed by noting the most prominent peaks in a periodogram or, ...
    • Simulation of Y-chromosomal haplotype data 

      Koen, Chris; D’Amato, M.E. (Elsevier, 2010)
      The non-recombining nature of the Y-chromosome determines the non-independence of alleles between loci. The evolution of short tandem repeat (STR) loci in the Y-chromosome is the result of different factors such as ...
    • 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) ...
    • A re-assessment of the nearest neighbour alignment of the X-ray isophotes of galaxy clusters 

      Koen, Chris; Lombard, Fred (Oxford University Press, 2006)
      Alignment is defined as the tendency of the distribution of pointing angles between the major axes of clusters and their nearest neighbours to be more concentrated towards small values for small nearest neighbour distances, ...
    • 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 ...
    • 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 ...
    • 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 ...
    • Multiple regression of GRB luminosity on light-curve properties 

      Koen, Chris (Oxford University Press, 2009)
      Statistical relations between the luminosity L of gamma-ray burster (GRBs) and several of their other observable properties have been discovered. Four of these properties are considered here: the spectral lag; a measure ...
    • More on the nature of the variable star UNSW-V-760 

      Koen, Chris (Oxford University Press, 2012)
      The results of two multicolour time-series photometric observing runs, separated by about two months, are presented. The same periodicities previously detected in photometry of UNSWV- 760 are still present, albeit at ...
    • 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. ...
    • Time series models of three sets of RXTE Observations of 4U 1543-47 

      Koen, Chris (Oxford University Press, 2013)
      The X-ray nova 4U 1543−47 was in a different physical state (low/hard, high/soft, and very high) during the acquisition of each of the three time series analyzed in this paper. Standard time series models of the ...
    • UBV(RI)C JHK observations of Hipparcos-selected nearby stars 

      Koen, Chris; Kilkenny, David; van Wyk, F.; Marang, F. (Oxford University Press, 2010)
      We present homogeneous, standardized UBV(RI)C photometry for over 700 nearby stars selected on the basis of Hipparcos parallaxes. Additionally, we list JHK photometry for about half of these stars, as well as L photometry ...
    • Is there evolution in the infrared Tully–Fisher relation? Comparing two linear regressions 

      Koen, Chris; Lombard, Fred (Oxford University Press, 2009)
      In a recent paper, Puech and co-workers compared K-band Tully–Fisher relations derived for nearby and distant galaxies, respectively. They concluded that the two relations differ, and deduced that there is evolution in ...
    • Time series photometry of the nearby brown dwarf DENIS-P J0041353-562112 

      Koen, Chris (Oxford University Press, 2011)
      DENIS-P J0041353−562112 is a brown dwarf, with a spectral type of M7.5, which may be younger than 20 Myr. On the basis of its Hα emission-line asymmetry, it has been suggested that the object is accreting material. If ...
    • The detailed forms of the LMC Cepheid PL and PLC relations 

      Koen, Chris; Kanbur, S; Ngeow, C (Oxford University Press, 2007)
      Possible deviations from linearity of the Large Magellanic Cloud Cepheid period–luminosity (PL) and period–luminosity–colour (PLC) relations are investigated. Two data sets are studied, respectively from the Optical ...
    • 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. ...
    • Fitting sinusoids to observations of rotating spotted stars 

      Koen, Chris (Oxford University Press, 2007)
      It is assumed that K blocks (e.g. seasons) of observations are available, and the parameters characterizing a fixed-frequency sinusoidal variability (mean light level, amplitude, phase) are constant within each of the ...
    • 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 ...
    • Confidence intervals for the correlation between the gamma-ray burst peak energy and the associated supernova peak brightness 

      Koen, Chris (Oxford University Press, 2009)
      A strong correlation between the gamma-ray burster peak energy and the peak luminosity of the associated supernova was discovered by Li for four GRBs. Despite the fact that the formal significance level of the correlation ...
    • PG 0907+123 and JL 194: slowly pulsating hot subdwarf stars 

      Koen, Chris; Green, E.M. (Oxford University Press, 2010)
      Multicolour time-series photometry of two newly discovered slowly pulsating sdB stars (V1093 Her stars, also known as PG 1716 stars) is described. Both stars are fairly bright and appear, from the limited amount of data, ...