Now showing items 21-40 of 55

    • Fitting power-law distributions to data with measurement errors 

      Koen, Chris; Kondlo, L (Oxford University Press, 2009)
      If X, which follows a power-law distribution, is observed subject to Gaussian measurement error e, thenX+e is distributed as the convolution of the power-lawand Gaussian distributions. Maximum-likelihood estimation of ...
    • Statistical tests for changes in the amplitude, frequency or phase of a sinusoidal variation 

      Koen, Chris (Oxford University Press, 2009)
      The problem considered is that of testing for small changes over time in the properties of a sinusoidal signal contaminated by noise. Two test statistics are proposed. The first is a frequency domain statistic based on ...
    • 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, ...
    • 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 ...
    • 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 ...
    • The Nyquist frequency for time series with slight deviations from regular spacing 

      Koen, Chris (Oxford University Press, 2009)
      The paper is based on the notion that the Nyquist frequency νN is a symmetry point of the periodogram of a time series: the power spectrum at frequencies above νN is a mirror image of that below νN. Koen showed that the ...
    • 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 ...
    • Predicting gamma-ray burster redshifts from their prompt emission properties 

      Koen, Chris (Oxford University Press, 2010)
      This paper presents a study of the relation between gamma-ray burster redshift and several of its prompt emission properties (spectral lag, light curve variability, peak energy, rise time and the peak bolometric flux ...
    • 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 ...
    • 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 ...
    • 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 ...
    • 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 ...
    • 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, ...
    • 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, ...
    • On the nature of the variable star UNSW-V-760 

      Koen, Chris (Oxford University Press, 2011)
      The results of multicolour photometric monitoring over several nights of the probable X-ray source UNSW-V-760 are presented. Drawing on both present and past observations, it is shown that the star is multiperiodic and ...
    • Two large amplitude slowly pulsating hot subdwarf stars 

      Koen, Chris (Oxford University Press, 2011)
      The discovery observations of two new slowly pulsating subdwarf B stars (V1093 Her stars), BPS CS22890−74 and PB 7032, are presented. Both stars are highly multiperiodic, and have – for V1093 Her stars – large amplitudes. ...
    • 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 ...
    • 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) ...
    • On multiple classes of gamma-ray bursts, as deduced from autocorrelation functions or bivariate duration/hardness ratio distributions 

      Koen, Chris; Bere, A. (Oxford University Press, 2012)
      Autocorrelation functions (ACFs) of 119 gamma-ray bursts (GRBs) monitored by the Burst Alert Telescope (BAT) on Swift are calculated. Contrasting with previous results for smaller numbers of bursts from other missions, ...
    • Estimation of the coherence time of stochastic oscillations from modest samples 

      Koen, Chris (Oxford University Press, 2012)
      ‘Quasi-periodic’ or ‘solar-like’ oscillations can be described by three parameters – a characteristic frequency, a coherence time (or ‘quality factor’) and the variance of the random driving process. This paper is concerned ...