scholarly journals Upper limit for Poisson variable incorporating systematic uncertainty by Bayesian approach

2009 ◽  
Author(s):  
Yongsheng Zhu
Keyword(s):  
Systematic Uncertainty ◽  
Bayesian Approach ◽  
Upper Limit ◽  
Poisson Variable

scholarly journals X-ray Emission from Hot DA White Dwarfs; EXOSAT Results, and Implications for Atmospheric Models

1989 ◽  
Vol 114 ◽  
pp. 198-201
Author(s):  
Frits Paerels ◽  
John Heise
Keyword(s):  
Systematic Uncertainty ◽  
Effective Temperature ◽  
White Dwarfs ◽  
Current Model ◽  
Broad Band ◽  
Model Calculations ◽  
X Ray ◽  
Transmission Grating ◽  
Upper Limit ◽  
Optical Flux

AbstractWe present the observations of the photospheric X-ray spectra of hot DA white dwarfs, obtained with the 500 lines mm−1 Transmission Grating Spectrometer on EXOSAT. These spectra cover the full soft X-ray band, at high wavelength resolution and statistical quality. They allow us to do an accurate measurement of the photospheric parameters, particularly of effective temperature and chemical composition of the atmosphere.We consider the case of HZ 43 in some detail. Model atmospheric spectra that satisfy all measured absolute optical, UV and X-ray fluxes turn out not to fit the shape of the measured X-ray spectrum. However, from a comparison of model spectra calculated with different model atmospheres codes we infer the existence of a 15% systematic uncertainty in the model fluxes at the shortest wavelengths (λ < 100 Å) in current model calculations. This can explain the fitting problem. Since the systematic uncertainty in the models is larger than the statistical uncertainty in the shape of the measured X-ray spectrum of HZ 43, we cannot at present use this measured shape to derive the effective temperature and gravity. We revert to broad band photometry, using the measured integrated soft X-ray flux and the optical flux, to determine Te = 45,000 – 54,000K, R/R⊙ = 0.0140 – 0.0165. From the absence of the He II Ly edge at 227 Å in the measured spectrum, we set a upper limit on the photospheric helium abundance of He/H = 1.0 × 10−5; this upper limit is independent of the uncertainties in the model calculations mentioned above.

scholarly journals Limits on a stochastic background of gravitational waves

1996 ◽  
Vol 160 ◽  
pp. 129-130
Author(s):  
M. P. McHugh ◽  
G. Zalamansky ◽  
F. Vernotte ◽  
E. Lantz
Keyword(s):  
Energy Density ◽  
Bayesian Approach ◽  
Measurement Noise ◽  
Frequency Interval ◽  
Previous Knowledge ◽  
Upper Limit ◽  
Stochastic Background ◽  
Logarithmic Frequency ◽  
Gravitational Wave Background ◽  
Sufficient Strength

A gravitational wave background (GWB) of sufficient strength, characterized by Ω, the energy density per logarithmic frequency interval in units of the closure density, would introduce timing residuals in the most stable millisecond pulsars. For a description pertaining to the observations of PSR’s 1937+21 and 1855+09 see Kaspi, Taylor and Ryba (1994), hereafter KTR, and references therein. Thorsett and Dewey (1996, see also this volume) present a method for placing a statistical upper limit on Ω. Their method however, cannot correctly account for the presence of a known level of white measurement noise in the timing residuals. We use a Bayesian approach which can best account for this white noise along with our lack of previous knowledge on the parameter Ω (McHugh, Zalamansky, Vernotte and Lantz, submitted).

Uncertainties in the Galactic Cepheid Distance Scale

1995 ◽  
Vol 155 ◽  
pp. 363-364
Author(s):  
Thomas G. Barnes ◽  
Thomas J. Moffett
Keyword(s):  
Systematic Uncertainty ◽  
Random Error ◽  
Surface Brightness ◽  
Distance Measurement ◽  
Distance Scale ◽  
Upper Limit ◽  
Cepheid Variables

AbstractWe have examined the uncertainties involved in using the visual surface brightness technique on Galactic Cepheid variables. The random error in a single Cepheid distance measurement is well determined to be ±8%. An upper limit to the systematic uncertainty is shown to be ±6% in distance. These combine for a single Cepheid to a typical uncertainty of ±10% and, for samples larger than ten Cepheids, to a typical uncertainty of less than ±6% in distance.

scholarly journals On the red supergiant problem

2020 ◽  
Vol 493 (4) ◽  
pp. 4945-4949 ◽  
Author(s):  
C S Kochanek
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Bayesian Approach ◽  
Mass Range ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Maximum Mass ◽  
Upper Limit

ABSTRACT We examine the problem of estimating the mass range corresponding to the observed red supergiant (RSG) progenitors of Type IIP supernovae. Using Monte Carlo simulations designed to reproduce the properties of the observations, we find that the approach of Davies & Beasor significantly overestimates the maximum mass, yielding an upper limit of Mh/M⊙ = 20.5 ± 2.6 for an input population with Mh/M⊙ = 18. Our preferred Bayesian approach does better, with Mh/M⊙ = 18.6 ± 2.1 for the same input populations, but also tends to overestimate Mh. For the actual progenitor sample and a Salpeter initial mass function, we find $M_{\rm h}/\mathrm{M}_\odot = 19.01_{-2.04}^{+4.04}$ for the Eldridge & Tout mass–luminosity relation used by Smartt and Davies & Beasor, and $M_{\rm h}/\mathrm{M}_\odot = 21.28_{-2.28}^{+4.52}$ for the Sukhbold, Woosley & Heger mass–luminosity relation. Based on the Monte Carlo simulations, we estimate that these are overestimated by $(3.3\pm 0.8)\, \mathrm{M}_\odot$. The red supergiant problem remains.

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