Testing one hypothesis multiple times

In applied settings, tests of hypothesis where a nuisance parameter is only identifiable under the alternative often reduces into one of Testing One Hypothesis Multiple times (TOHM). Specifically, a fine discretization of the space of the non-identifiable parameter is specified, and the null hypothesis is tested against a set of sub-alternative hypothesis, one for each point of the discretization. The resulting sub-test statistics are then combined to obtain a global p-value. In this paper, we discuss a computationally efficient inferential tool to perform TOHM under stringent significance requirements, such as those typically required in the physical sciences, (e.g., p-value < 10−7 ). The resulting procedure leads to a generalized approach to perform inference under non-standard conditions, including non-nested models comparisons

A Tale of Two Impostors: SN2002kg and SN1954J in NGC 2403

We describe new results on two supernova impostors in NGC 2403, SN 1954J(V12) and SN 2002kg(V37). For the famous object SN 1954J we combine four critical observations: its current SED, its Halpha emission line profile, the Ca II triplet in absorption in its red spectrum, and the brightness compared to its pre-event state. Together these strongly suggest that the survivor is now a hot supergiant with T ~ 20000 K, a dense wind, substantial circumstellar extinction, and a G-type supergiant companion. The hot star progenitor of V12's giant eruption was likely in the post-red supergiant stage and had already shed a lot of mass. V37 is a classical LBV/S Dor variable. Our photometry and spectra observed during and after its eruption show that its outburst was an apparent transit on the HR Diagram due to enhanced mass loss and the formation of a cooler, dense wind. V37 is an evolved hot supergiant at ~10^6 Lsun with a probable initial mass of 60 -80 Msun.Comment: To appear in the Astrophysical Journa

The Progenitors of Recent Core-Collapse Supernovae

We present the results of our analysis of Hubble Space Telescope (HST) and deep ground-based images to isolate the massive progenitor stars of the two recent core-collapse supernovae 2008 bk and 2008 cn. The identification of the progenitors is facilitated in one of these two cases by high-precision astrometry based on our HST imaging of SNe at late times

On The Progenitor of the Type II-Plateau Supernova 2003gd in Messier 74

HST WFPC2 archival F606W and F300W images obtained within one year prior to the explosion of the nearby Type II supernova (SN) 2003gd in Messier 74 (NGC 628) have been analyzed to isolate the progenitor star. The SN site was located using precise astrometry applied to the HST images. Two plausible candidates are identified within 0.6" of the SN position in the F606W image. Neither candidate was detected in the F300W image. SN 2003gd appears to be of Type II-plateau (II-P), with age ~87 d on June 17 UT and with low reddening [E(B-V) = 0.13 mag]. The most likely of the two progenitor candidates has M_V_0 ~ -3.5 mag (for an extinction-corrected distance modulus of 29.3 mag) and, based on additional color information derived from a high-quality, archival ground-based I-band image, we estimate that this star was a red supergiant with initial mass M_ZAMS ~ 8 -- 9 Msun. This mass estimate is somewhat lower than, but relatively consistent with, recent limits placed on the progenitor masses of other SNe II-P, using HST data. Future HST imaging with the Advanced Camera for Surveys, when the SN has faded considerably, will be extremely useful in pinpointing the exact SN location and securing identification of the progenitor. If our proposed candidate is confirmed, it will be only the sixth SN progenitor ever directly identified.Comment: 10 pages, 6 figures, to appear now in PASP, 2003 Nov. This update includes more detailed light and color curves for the S

Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud (SAGE-SMC). I. Overview

The Small Magellanic Cloud (SMC) provides a unique laboratory for the study of the lifecycle of dust given its low metallicity (~1/5 solar) and relative proximity (~60 kpc). This motivated the SAGE-SMC (Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud) Spitzer Legacy program with the specific goals of studying the amount and type of dust in the present interstellar medium, the sources of dust in the winds of evolved stars, and how much dust is consumed in star formation. This program mapped the full SMC (30 deg^2) including the body, wing, and tail in seven bands from 3.6 to 160 μm using IRAC and MIPS on the Spitzer Space Telescope. The data were reduced and mosaicked, and the point sources were measured using customized routines specific for large surveys. We have made the resulting mosaics and point-source catalogs available to the community. The infrared colors of the SMC are compared to those of other nearby galaxies and the 8 μm/24 μm ratio is somewhat lower than the average and the 70 μm/160 μm ratio is somewhat higher than the average. The global infrared spectral energy distribution (SED) shows that the SMC has approximately 1/3 the aromatic emission/polycyclic aromatic hydrocarbon abundance of most nearby galaxies. Infrared color-magnitude diagrams are given illustrating the distribution of different asymptotic giant branch stars and the locations of young stellar objects. Finally, the average SED of H II/star formation regions is compared to the equivalent Large Magellanic Cloud average H II/star formation region SED. These preliminary results will be expanded in detail in subsequent papers

Propensity-score based methods for causal inference in observational studies with non-binary treatments

Propensity score methods are a part of the standard toolkit for applied researchers who wish to ascertain causaleffects from observational data. While they were originally developed for binary treatments, several researchershave proposed generalizations of the propensity score methodology for non-binary treatment regimes. Suchextensions have widened the applicability of propensity score methods and are indeed becoming increasinglypopular themselves. In this article, we closely examine two methods that generalize propensity scores in thisdirection, namely, the propensity function (pf), and the generalized propensity score (gps), along with twoextensions of thegpsthat aim to improve its robustness. We compare the assumptions, theoretical properties,and empirical performance of these methods. On a theoretical level, thegpsand its extensions are advantageousin that they are designed to estimate the full dose response function rather than the average treatment effectthat is estimated with thepf. We comparegpswith a newpfmethod, both of which estimate the doseresponse function. We illustrate our findings and proposals through simulation studies, including one based onan empirical study about the effect of smoking on healthcare costs. While our proposedpf-based estimatorpreforms well, we generally advise caution in that all available methods can be biased by model misspecificationand extrapolation

The importance of including toxicity assays when screening plant extracts for antimalarial activity

Identifying plant extracts as sources of antimalarial compounds needs to be addressed as numerous studies screen extracts without the means of eliminating extracts that are merely cytotoxic. Fifty-nine organic solvent extracts from South African plants were screened for antiplasmodial activity using the [3H]-hypoxanthine incorporation assay against the chloroquine-resistant Plasmodium falciparum. Variable antiplasmodial activity and toxicity was observed. Extracts form Combretum erythrophyllumand Crinum bulbispermum, had IC50 values 1 mg/ml with the ethyl acetate extracts of C. bulbispermum roots and bulbs having values comparable to chloroquine (0.04 mg/ml). Nine extracts hadtoxicity indexes 100. Lycorine, isolated from C. bulbispermum was as active as chloroquine (IC50 of 0.03 mg/ml) and had a favourable security index