The AstroStat Slog

From arxiv/astro-ph:0708.1510v1
Connecting GRBs and galaxies: the probability of chance coincidence by Cobb and Bailyn

Without an optical afterglow, a galaxy within the 2 arc second error region of a GRB x-ray afterglow is identified as a host galaxy; however confusion can rise due to the facts that 1. the edge of a galaxy is diffused, 2. multiple sources could exist within 2 arc second error region, 3.the distance between the galaxy and the x-ray afterglow is measured by projection, and 4. lensing causes increase of brightness and position shifts. In this paper, the authors “investigated the fields of 72 GRBs in order to examine the general issue of associations between GRBs and host galaxies.”
Continue reading ‘[ArXiv] GRB host galaxies, Aug. 10, 2007’ »

From IMS Bulletin Vol. 36(7) p.10, Terence’s Stuff: Changing my mind (again)
Continue reading ‘[Quote] Changing my mind (again)’ »

From IMS Bulletin Vol. 36(3), p.11, Terence’s Stuff: Model skeptics

[Once I quoted an article by Prof. Terry Speed in IMS Bulletin: Data-Doctors. Reading his columns in the IMS Bulletin provides me an opportunity to reflect who I am as a statistician and some guidance for treating data. Although his ideas were not from astronomy or astronomical data analysis, I often find his thoughts and words can be shared with astronomers.]
Continue reading ‘[Quote] Model Skeptics’ »

X-ray summer school is on going. Numerous interesting topics were presented but not much about statistics (Only advice so far, “use implemented statistics in x-ray data reduction/analysis tools” and “it’s just a tool”). Nevertheless, I happened to talk two students extensively on their research topics, finding features from light curves. One was very empirical from comparing gamma ray burst trigger time to 24kHz observations and the other was statistical and algorithmic by using Bayesian Block. Sadly, I could not give them answers but the latter one dragged my attention.
Continue reading ‘Change Point Problem’ »

From arxiv/astro-ph:0707.1891v1
The Geneva-Copenhagen Survey of the Solar neighborhood II. New uvby calibrations and rediscussion of stellar ages, the G dwarf problem, age-metalicity diagram, and heating mechanisms of the disk by Holmberg, Nordstrom, and Andersen

Researchers, including scientists from CHASC, working on color magnitude diagrams to infer ages, metalicities, temperatures, and other physical quantities of stars and stellar clusters may find this paper useful.
Continue reading ‘[ArXiv] Geneva-Copenhagen Survey, July 13, 2007’ »

From arxiv/astro-ph:0707.3413
The Sixth Data Release of the Sloan Digital Sky Survey by … many people …

The sixth data release of the Sloan Digital Sky Survey (SDSS DR6) is available at http://www.sdss.org/dr6. Additionally, Catalog Archive Service (CAS) and
SQL interface to access the catalog would be useful to data searching statisticians. Simple SQL commends, which are well documented, could narrow down the size of data and the spatial coverage.
Continue reading ‘[ArXiv] SDSS DR6, July 23, 2007’ »

From arxiv/astro-ph:0705.4020v2
Statistical Evidence for Three classes of Gamma-ray Bursts by T. Chattopadhyay et. al.

In general, gamma-ray bursts (GRBs) are classified into two groups: long (>2 sec) and short (<2 sec) duration bursts. Nonetheless, there have been some studies including arxiv/astro-ph:0705.4020v2 that statistically proved the optimal existence of 3 clusters. The pioneer work of GRB clusterings was based on hierarchical clustering methods by Mukerjee et. al.(Three Types of Gamma-Ray Bursts)
Continue reading ‘[ArXiv] Three Classes of GRBs, July 21, 2007’ »

Since I began to subscribe arxiv/astro-ph abstracts, from an astrostatistical point of view, one of the most frequent topics has been photometric redshifts. This photometric redshift has been a popular topic as the catalog of remote photometric object observation multiplies its volume and sky survey projects in multiple bands lead to virtual observatories (VO – will discuss in the later posting). Just searching by photometric redshifts in google scholar and arxiv.org provides more than 2000 articles since 2000.
Continue reading ‘Photometric Redshifts’ »

From arxiv/astro-ph:0707.2474,
Visualization, Exploration and Data Analysis of Complex Astrophysical Data by Comparato, Becciani, Costa, Larsson, Garilli, Gheller, and Taylor

This paper introduces a novel advanced visualization tool VisIVO,^[1] its advantages from combining a protocol called PLASTIC (Platform for Astronomy Tool Interconnection) for displaying and extracting information from astrophysical data, its enhanced connection to VO (Virtual Observatory), and its usage in several scientific cases. Continue reading ‘[ArXiv] Data Visualization, July 17, 2007’ »

1. Available at http://visivo.cineca.it[↩]

From arxiv/astro-ph:0707.2064v1
Star Formation via the Little Guy: A Bayesian Study of Ultracool Dwarf Imaging Surveys for Companions by P. R. Allen.

I rather skip all technical details on ultracool dwarfs and binary stars, reviews on star formation studies, like initial mass function (IMF), astronomical survey studies, which Allen gave a fair explanation in arxiv/astro-ph:0707.2064v1 but want to emphasize that based on simple Bayes’ rule and careful set-ups for likelihoods and priors according to data (ultracool dwarfs), quite informative conclusions were drawn:
Continue reading ‘[ArXiv] Bayesian Star Formation Study, July 13, 2007’ »

From arxiv/astro-ph:0707.1982v1,
Nflation: observable predictions from the random matrix mass spectrum by Kim and Liddle

To my knowledge, random matrix received statisticians’ interests fairly recently and SAMSI (Statistical and Applied Mathematical Sciences Institute) offered a semester long program on High Dimensional Inference and Random Matrices (tutorials and lecture notes can be found) during Fall 2006 . However, my knowledge is very limited to make a comment or critic on Kim and Liddle’s paper. Clearly, nonetheless, this paper is not about random matrix theory but about its straightforward application to the cosmological model viability.
Continue reading ‘[ArXiv] Random Matrix, July 13, 2007’ »

From arxiv/astro-ph:0707.1900v1
The complete catalogue of gamma-ray bursts observed by the Wide Field Cameras on board BeppoSAX by Vetere, et.al.

This paper intend to publicize the largest data set of Gamma Ray Burst (GRB) X-ray afterglows (right curves after the event), which is available from http://www.asdc.asi.it. It is claimed to be a complete on-line catalog of GRB observed by two wide-Field Cameras on board BeppoSAX (Click for its Wiki) in the period of 1996-2002. It is comprised with 77 bursts and 56 GRBs with Xray light curves, covering the energy range 40-700keV. A brief introduction to the instrument, data reduction, and catalog description is given.

From arxiv/astro-ph: 0707.1611 Probabilistic Cross-Identification of Astronomical Sources by Budavari and Szalay

As multi-wave length studies become more popular, various source matching methodologies have been discussed. One of such methods particularly focused on Bayesian idea was introduced by Budavari and Szalay with a demand for symmetric algorithms in a unified framework.
Continue reading ‘[ArXiv] Matching Sources, July 11, 2007’ »

Since I start reading arxiv/astro-ph abstracts and a few relevant papers about a month ago, so often I see chi-square something as an optimization or statistical inference tool. Chi-square function, chi-square statistics, chi-square goodness-of-fit test are the words that serve different data analysis purposes but under the same prefix. As a newbie to statistics, although I learned chi-square distribution and chi-square test, doing statistics with chi-square are somewhat considered to be obsolete in terms of robust applications to modern data. These are introduced as one of many distributions and statistical tests. Nothing special. However, in astronomy, chi-square becomes the almost only method for statistical data analysis. I wonder how such strong bond between chi-square tactics and astronomer’s keen mind to data analysis has happened?
Continue reading ‘What is so special about chi square in astronomy?’ »

This is the cover article in the science section of New York Times (July 10, 2007) and talks about Digital Access to a Sky Century at Harvard.

*Click the link to see the article. You may need to sign-up for an access but it’s free.