model vs model
As Alanna pointed out, astronomers and statisticians mean different things when they say “model”. To complicate matters, we have also started to use another term called “data model”. Continue reading ‘model vs model’ »
Archive for the ‘Astro’ Category.
Virtual Observatory
Another talk in the Visualizing Astronomy series organized by the CXC/CfA folks: Pepi Fabbiano is scheduled to speak on NVO efforts on Thursday, Oct 4, at 1pm at Phillips:
Continue reading ‘Virtual Observatory’ »
P Values: What They Are and How to Use Them
After observing the recent discussion among CHASC, the following paper
P Values: What They Are and How to Use Them by Luc Demortier emerged from my mind.
Continue reading ‘P Values: What They Are and How to Use Them’ »
Betraying your heritage
[arXiv:0709.3093v1] Short Timescale Coronal Variability in Capella (Kashyap & Posson-Brown)
We recently submitted that paper to AJ, and rather ironically, I did the analysis during the same time frame as this discussion was going on, about how astronomers cannot rely on repeating observations. Ironic because the result reported there hinges on the existence of small, but persistent signal that is found in repeated observations of the same source. Doubly ironic in fact, in that just as we were backing and forthing about cultural differences I seemed to have gone and done something completely contrary to my heritage! Continue reading ‘Betraying your heritage’ »
Spurious Sources
[arXiv:0709.2358] Cleaning the USNO-B Catalog through automatic detection of optical artifacts, by Barron et al.
Statistically speaking, “false sources” are generally in the domain of Type II Type I errors, defined by the probability of detecting a signal where there is none. But what if there is a clear signal, but it is not real? Continue reading ‘Spurious Sources’ »
VOConvert (ConVOT)
VOConvert or ConVOT is a small java script which does file format conversion from fits to ascii or the other way around. These tools might be useful for statisticians who want to convert astronomers’ data format called fits into ascii quickly for a statistical analysis. Additionally, VOConvert creates an interim output for VOStat, designed for statistical data analysis from Virtual Observatory. The softwares and the list of Virtual Observatories around the world can be found at Virtual Observatory India. Please, check a link in VOstat (http://hea-www.harvard.edu/AstroStat/slog/2007/vostat) for more information about VOstat.
[ArXiv] 2nd week, Sept. 2007
In addition to preprints discussed in [ArXiv] Swift and XMM measurement errors, [ArXiv] SVM and galaxy morphological classification, Sept. 10, 2007, and [ArXiv] Recent bayesian studies from astro-ph, I wish to point a few more out from this week.
Continue reading ‘[ArXiv] 2nd week, Sept. 2007’ »
Visualizing Astronomy
The CXC Education & Outreach Program at the CfA hosts a series of lectures on Visualizing Astronomy, and the first of this season’s is scheduled for Sep 18 at 1:30pm at Phillips:
Date & Time: Tuesday, September 18, 1:30pm
Location: Phillips Auditorium
Speaker: Alyssa Goodman (Harvard)
Title: Amazing New Tools for Exploring Astronomical Data
[ArXiv] SVM and galaxy morphological classification, Sept. 10, 2007
From arxiv/astro-ph:0709.1359,
A robust morphological classification of high-redshift galaxies using support vector machines on seeing limited images. I Method description by M. Huertas-Company et al.
Machine learning and statistical learning become more and more popular in astronomy. Artificial Neural Network (ANN) and Support Vector Machine (SVM) are hardly missed when classifying on massive survey data is the objective. The authors provide a gentle tutorial on SVM for galactic morphological classification. Their source code GALSVM is linked for the interested readers.
Continue reading ‘[ArXiv] SVM and galaxy morphological classification, Sept. 10, 2007’ »
[ArXiv] Bimodal Color Distribution in GCS, Sept. 7, 2007
From arxiv/astro-ph:0709.1073v1
On the Metallicity-Color Relations and Bimodal Color Distributions in Extragalactic Globular Cluster Systems by M. Cantiello and J. P. Blakeslee
Many observations on globular cluster systems (GCS) show bimodal distributions in color and metallicity space. The authors discussed the complication of non-linear metalicity and color relations and presented their careful study to suggest the optimal color(s) for revealing the presence of real bimodal GC metallicity distributions. Based on their simulation study, (V-H) and (V-K) are confirmed to be good colors for revealing unbiased bimodal metallicity distributions in GCS.
Continue reading ‘[ArXiv] Bimodal Color Distribution in GCS, Sept. 7, 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’ »
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’ »
[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 et.al
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.
Continue reading ‘[ArXiv] NGC 6397 Deep ACS Imaging, Aug. 29, 2007’ »
[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’ »