Now showing items 21-40 of 112

  • 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 ...
  • 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 ...
  • Work participation and disabilities in India 

    Appunni, Sathiya Susuman; Deshpande, A.P. (Kamla-Raj Enterprises, 2009)
    United Nations General Assembly in 1976 proclaimed 1981 as the International Year of the Disable Persons. Persons with disabilities are enthusiastic to overcome the social and economic barriers. In the present paper an ...
  • 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 ...
  • 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 ...
  • 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 ...
  • Two new pulsating hot subdwarf stars from the Edinburgh-Cape survey 

    Kilkenny, David; O'Donoghue, D.; Crause, L.; Engelbrecht, C.; Hambly, N.; MacGillivray, H. (Oxford University Press, 2009)
    We report the discovery of very rapid pulsations in two hot subdwarf stars from the Edinburgh- Cape blue object survey. The short periods, small amplitudes and multiperiodicity establish these stars as members of the ...
  • 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 ...
  • 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, ...
  • 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 ...
  • 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 ...
  • 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 ...
  • Correlates of infant and child mortality in Ethiopia 2005 

    Appunni, Sathiya Susuman (University of the Western Cape, 2010)
    INTRODUCTION: Risk of mortality prevails for children with shorter birth interval since their mothers are likely to have poor health. AIM: The aim of the study is to determine the indirect estimation of infant and child ...
  • 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) ...