Confidence Intervals and Upper Bounds for Small Signals in the Presence of Background Noise

We discuss a new method for setting limits on small signals in the presence of background noise. The method is based on a combination of a two dimensional confidence region and the large sample approximation to the likelihood ratio test statistic. It automatically quotes upper limits for small signals and two-sided confidence intervals for larger samples. We show that this method gives the correct coverage and also has good power.Comment: Document was created by Sciword V3.0, it consists of one main document (lrt.tex), eight figures (figure1.eps - figure8.eps) and one table (table.tex). Paper was revised after being accepted for publication in NIM A Paper was revised after being accepted for publication in NIM

Limits and Confidence Intervals in the Presence of Nuisance Parameters

We study the frequentist properties of confidence intervals computed by the method known to statisticians as the Profile Likelihood. It is seen that the coverage of these intervals is surprisingly good over a wide range of possible parameter values for important classes of problems, in particular whenever there are additional nuisance parameters with statistical or systematic errors. Programs are available for calculating these intervals.Comment: 6 figure

Spectrophotometry of nearby field galaxies: the data

We have obtained integrated and nuclear spectra, as well as U, B, R surface photometry, for a representative sample of 196 nearby galaxies. These galaxies span the entire Hubble sequence in morphological type, as well as a wide range of luminosities (M_B=-14 to -22). Here we present the spectrophotometry for these galaxies. The selection of the sample and the U, B, R surface photometry is described in a companion paper (Paper I). Our goals for the project include measuring the current star formation rates and metallicities of these galaxies, and elucidating their star formation histories, as a function of luminosity and morphology. We thereby extend the work of Kennicutt (1992a) to lower luminosity systems. We anticipate that our study will be useful as a benchmark for studies of galaxies at high redshift. We describe the observing, data reduction and calibration techniques, and demonstrate that our spectrophotometry agrees well with that of Kennicutt. The spectra span the range 3550--7250 A at a resolution (FWHM) of ~6 A, and have an overall relative spectrophotometric accuracy of +/- 6 per cent. We present a spectrophotometric atlas of integrated and nuclear rest-frame spectra, as well as tables of equivalent widths and synthetic colors. We study the correlations of galaxy properties determined from the spectra and images. Our findings include: (1) galaxies of a given morphological class display a wide range of continuum shapes and emission line strengths if a broad range of luminosities are considered, (2) emission line strengths tend to in- crease and continua tend to get bluer as the luminosity decreases, and (3) the scatter on the general correlation between nuclear and integrated H_alpha emission line strengths is large.Comment: Accepted for publication in ApJS (scheduled for Vol.127, 2000 March); 63 pages, LateX, 9 figures and 6 tables included, a spectrophotometric atlas is provided as GIF images, fig 1 as a JPEG image, in a single tar-file; a full 600 dpi version is available at http://www.astro.rug.nl/~nfgs

Practices of Historicism in Times of Change: Chaucer, Pope, Barron Field, A. D. Hope and the Idea of the Culture Hero

The article's abstract is no available

Correcting the Minimization Bias in Searches for Small Signals

We discuss a method for correcting the bias in the limits for small signals if those limits were found based on cuts that were chosen by minimizing a criterion such as sensitivity. Such a bias is commonly present when a "minimization" and an "evaluation" are done at the same time. We propose to use a variant of the bootstrap to adjust the limits. A Monte Carlo study shows that these new limits have correct coverage.Comment: 14 pages, 5 figue

Relations of Mercury to other Metals

n/

A Photometric Technique to Search for Be Stars in Open Clusters

We describe a technique to identify Be stars in open clusters using Stromgren b, y, and narrow-band Halpha photometry. We first identify the B-type stars of the cluster using a theoretical isochrone fit to the (b-y, y) color-magnitude diagram. The strongest Be stars are easily identified in a (b-y, y-Halpha) color-color diagram, but those with weaker Halpha emission (classified as possible Be star detections) may be confused with evolved or foreground stars. Here we present such photometry plus Halpha spectroscopy of members of the cluster NGC 3766 to demonstrate the accuracy of our technique. Statistical results on the relative numbers of Be and B-type stars in additional clusters will be presented in a future paper.Comment: 15 pages, 6 figures, 1 table. Accepted by Ap

Including Systematic Uncertainties in Confidence Interval Construction for Poisson Statistics

One way to incorporate systematic uncertainties into the calculation of confidence intervals is by integrating over probability density functions parametrizing the uncertainties. In this note we present a development of this method which takes into account uncertainties in the prediction of background processes, uncertainties in the signal detection efficiency and background efficiency and allows for a correlation between the signal and background detection efficiencies. We implement this method with the Feldman & Cousins unified approach with and without conditioning. We present studies of coverage for the Feldman & Cousins and Neyman ordering schemes. In particular, we present two different types of coverage tests for the case where systematic uncertainties are included. To illustrate the method we show the relative effect of including systematic uncertainties the case of dark matter search as performed by modern neutrino tel escopes.Comment: 23 pages, 10 figures, replaced to match published versio