Archive for September 2007

[ArXiv] CMB statistics, Sept. 7, 2007

From arxiv/astro-ph:0709.1144v1:
Cosmic Microwave Background Statistics for a Direction-Dependent Primordial Power Spectrum by A. R. Pullen and M. Kamionkowski

The authors developed cosmic microwave background statistics for a primordial power spectrum, motivated from the needs of testing the cosmological common assumption, i.e. the statistical isotropy of primordial perturbations. This statistics is for a primordial power spectrum, depending on the direction and the magnitude of the Fourier wavevector. Statistically speaking, the most interesting part is their construction of the minimum-variance estimators for the coefficients of a spherical-harmonic expansion of the direction-dependence of the primordial power spectrum.

[ArXiv] Swift and XMM measurement errors, Sep. 8, 2007

From arxiv/astro-ph:0708.1208v1:
The measurement errors in the Swift-UVOT and XMM-OM by N.P.M. Kuin and S.R. Rosen

The probability distribution of photon counts from the Optical Monitor on XMM Newton satellite (XMM-OM) and the UVOT on the Swift satellite follows a binomial distribution due to detector characteristics. Incident count rate was derived as a function of the measured count rate, which was shown to follow a binomial distribution.
Continue reading ‘[ArXiv] Swift and XMM measurement errors, Sep. 8, 2007’ »

Wrong Priors?

arXiv:0709.1067v1 : Wrong Priors (Carlos C. Rodriguez)

This came through today on astro-ph, suggesting that we could be choosing priors better than we do, and in fact that we generally do a very bad job of it. I have been brought up to believe that, like points in Whose Line Is It Anyway, priors don’t matter (unless you have very little data), so I am somewhat confused. What is going on here?

Beyond Google Sky

Google Sky is good for a quick look “what’s that you just saw over there?”, but not for anything more than that. Not yet anyway. Mind you, I think it is a good thing. It is easy to use, and definitely worth a look as an astronomy popularization tool. But there are a number of astro visualization programs that can (so to speak) beat the pants off Google Sky with one hand tied behind the back. Check these out (all open source): Continue reading ‘Beyond Google Sky’ »

BEHR update

BEHR (Bayesian Estimation of Hardness Ratios) is a C program designed to compute hardness ratios – summary statistics of a spectrum for faint X-ray sources – while explicitly modeling the arrival of photons as an inhomogeneous Poisson process and properly accounting for background contamination.

In the previous versions of BEHR, users are allowed to choose only the gamma prior distribution that is parametrized in terms of an index (shape) parameter and a scale parameter. But there was need for using a tabulated prior distribution that does not necessarily look like a gamma distribution. The use of a tabulated prior distribution gives us two advantages:
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[ArXiv] Identifiability and mixtures of distributions, Aug. 3, 2007

From arxiv/ 0708.0499v1
Inference for mixtures of symmetric distributions by Hunter, Wang, and Hettmansperger, Annals of Statistics, 2007, Vol.35(1), pp.224-251.
Continue reading ‘[ArXiv] Identifiability and mixtures of distributions, Aug. 3, 2007’ »

[ArXiv] Google Sky, Sept. 05, 2007

Ah..Sky in Google Earth made an arxiv appearance [arxiv/astro-ph:0709.0752], Sky in Google Earth: The Next Frontier in Astronomical Data Discovery and Visualization by R. Scranton et al.


I once talked about the relationship between astronomers and statisticians in the slog posting Data Doctors. To astronomers, statisticians are assistants. Statisticians are just helping astronomical data analysis with statistically limited eyes. Less frequently statistical improvements and modification occurred in the astronomical society through collaborations with statisticians compared to other fields.
Continue reading ‘Arrogant?’ »

2 Stats papers on astro-ph today

There are two statistics papers on astro-ph. Check them out:


Title: Bayesian Inversion of Stokes Profiles

Authors: A. Asensio Ramos (1), M. J. Martinez Gonzalez (2), J. A. Rubino-Martin (1) ((1) IAC, (2) LERMA)

Comments: 15 pages, 12 figures, accepted for publication in A&A


Title: Bayesian posterior classification of planetary nebulae according to the Peimbert types

Authors: C. Quireza (1), H.J. Rocha-Pinto (2), W.J. Maciel (3) ((1) Observatorio Nacional/MCT, (2) Observatorio do Valongo/UFRJ, (3) Instituto de Astronomia, Geofisica e Ciencias Atmosfericas/USP)

Comments: 26 pages, 4 figures, 6 tables. Accepted for publication in Astronomy and Astrophysics.

[ArXiv] NGC 6397 Deep ACS Imaging, Aug. 29, 2007

From arxiv/astro-ph:0708.4030v1
Deep ACS Imaging in the Globular Cluster NGC 6397: The Cluster Color Magnitude Diagram and Luminosity Function by H.B. Richer

This paper presented an observational study of a globular cluster, named NGC 6397, enhanced and more informative compared to previous observations in a sense that 1) a truncation in the white dwarf cooling sequence occurs at 28 magnitude, 2) the cluster main sequence seems to terminate approximately at the hydrogen-burning limit predicted by two independent stellar evolution models, and 3) luminosity functions (LFs) or mass functions (MFs) are well defined. Nothing statistical, but the idea of defining color magnitude diagrams (CMDs) and LFs described in the paper, will assist developing suitable statistics on CMD and LF fitting problems in addition to the improved measurements (ACS imaging) of stars in NGC 6397.
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[ArXiv] Decision Tree, Aug. 31, 2007

From arxiv/astro-ph:0708.4274v1
Comparison of decision tree methods for finding active objects by Y. Zhao and Y. Zhang

The authors (astronomers) introduced and summarized various decision three methods (REPTree, Random Tree, Decision Stump, Random Forest, J48, NBTree, and AdTree) to the astronomical community.
Continue reading ‘[ArXiv] Decision Tree, Aug. 31, 2007’ »