Detections of massive stars in the cluster MCM2005b77, in the star-forming regions GRS G331.34−-00.36 (S62) and GRS G337.92−-00.48 (S36)

Large infrared and millimeter wavelength surveys of the Galactic plane have unveiled more than 600 new bubble HII regions and more than 3000 candidate star clusters. We present a study of the candidate clusters MCM2005b72, DBS2003-157, DBS2003-172, and MCM2005b77, based on near-infrared spectroscopy taken with SofI on the NTT and infrared photometry from the 2MASS, VVV, and GLIMPSE surveys. We find that (1) MCM2005b72 and DBS2003-157 are subregions of the same star-forming region, HII GRS G331.34-00.36 (bubble S62). MCM2005b72 coincides with the central part of this HII region, while DBS2003-157 is a bright mid-infrared knot of the S62 shell. We detected two O-type stars at extinction \Aks=1.0-1.3 mag. Their spectrophotometric properties are consistent with the near-kinematic distance to GRS G331.34-00.36 of 3.9pm0.3 kpc. (2) DBS2003-172 coincides with a bright mid-infrared knot in the S36 shell (GRS G337.92-00.48), where we detected a pair of candidate He I stars embedded in a small cometary nebula. (3) The stellar cluster MCM2005b77 is rich in B-type stars, has an average Aks of 0.91 mag, and is adjacent to the HII region IRAS 16137-5025. The average spectrophotometric distance of $\sim 5.0$ kpc matches the near-kinematic distance to IRAS 16137-5025 of 5.2pm0.1 kpc.Comment: 22 pages, 11 Figures, ApJ accepte

Solution of Orthopositronium lifetime Puzzle

The intrinsic decay rate of orthopositronium formed in ${\rm SiO_2}$ powder is measured using the direct $2\gamma$ correction method such that the time dependence of the pick-off annihilation rate is precisely determined. The decay rate of orthopositronium is found to be $7.0396\pm0.0012 (stat.)\pm0.0011 (sys.)\mu s^{-1}$, which is consistent with our previous measurements with about twice the accuracy. Results agree well with the $O(\alpha^2)$ QED prediction, and also with a result reported very recently using nanoporous film

Deep near-IR observations of the Globular Cluster M4: Hunting for Brown Dwarfs

We present an analysis of deep HST/WFC3 near-IR (NIR) imaging data of the globular cluster M4. The best-photometry NIR colour-magnitude diagram (CMD) clearly shows the main sequence extending towards the expected end of the Hydrogen-burning limit and going beyond this point towards fainter sources. The white dwarf sequence can be identified. As such, this is the deepest NIR CMD of a globular cluster to date. Archival HST optical data were used for proper-motion cleaning of the CMD and for distinguishing the white dwarfs (WDs) from brown dwarf (BD) candidates. Detection limits in the NIR are around F110W approx 26.5 mag and F160W approx27 mag, and in the optical around F775W approx 28 mag. Comparing our observed CMDs with theoretical models, we conclude that we have reached beyond the H-burning limit in our NIR CMD and are probably just above or around this limit in our optical-NIR CMDs. Thus, any faint NIR sources that have no optical counterpart are potential BD candidates, since the optical data are not deep enough to detect them. We visually inspected the positions of NIR sources which are fainter than the H-burning limit in F110W and for which the optical photometry did not return a counterpart. We found in total five sources for which we did not get an optical measurement. For four of these five sources, a faint optical counterpart could be visually identified, and an upper optical magnitude was estimated. Based on these upper optical magnitude limits, we conclude that one source is likely a WD, one source could either be a WD or BD candidate, and the remaining two sources agree with being BD candidates. For only one source no optical counterpart could be detected, which makes this source a good BD candidate. We conclude that we found in total four good BD candidates.Comment: ApJ accepted, 28 pages including 16 figure

Fabrication and characterization of a lithium-glass-based composite neutron detector

A novel composite, scintillating material intended for neutron detection and composed of small (1.5 mm) cubes of KG2-type lithium glass embedded in a matrix of scintillating plastic has been developed in the form of a 2.2 in.-diameter, 3.1 in.-tall cylindrical prototype loaded with $\left( 5.82 \pm 0.02 \right)\%$ lithium glass by mass. The response of the material when exposed to ${}^{252}$Cf fission neutrons and various $\gamma$-ray sources has been studied; using the charge-integration method for pulse shape discrimination, good separation between neutron and $\gamma$-ray events is observed and intrinsic efficiencies of $\left( 1.15 \pm 0.16 \right)\times 10^{-2}$ and $\left( 2.28 \pm 0.21 \right)\times 10^{-4}$ for ${}^{252}$Cf fission neutrons and ${}^{60}$Co $\gamma$ rays are obtained; an upper limit for the sensitivity to ${}^{137}$Cs $\gamma$ rays is determined to be $< 3.70 \times 10^{-8}$. The neutron/$\gamma$ discrimination capabilities are improved in circumstances when a neutron capture signal in the lithium glass can be detected in coincidence with a preceding elastic scattering event in the plastic scintillator; with this coincidence requirement, the intrinsic efficiency of the prototype detector for ${}^{60}$Co $\gamma$ rays is $\left( 2.42 \pm 0.61 \right)\times 10^{-6}$ while its intrinsic efficiency for unmoderated ${}^{252}$Cf fission neutrons is $\left( 4.31 \pm 0.59 \right)\times 10^{-3}$. Through use of subregion-integration ratios in addition to the coincidence requirement, the efficiency for $\gamma$ rays from ${}^{60}$Co is reduced to $\left( 7.15 \pm 4.10 \right) \times 10^{-7}$ while the ${}^{252}$Cf fission neutron efficiency becomes $\left( 2.78 \pm 0.38 \right) \times 10^{-3}$.Comment: Final results, figures, and text; published in Nuclear Instruments and Methods in Physics Research Section

Chronic arsenic exposure and risk of infant mortality in two areas of Chile.

Chronic arsenic exposure has been associated with a range of neurologic, vascular, dermatologic, and carcinogenic effects. However, limited research has been directed at the association of arsenic exposure and human reproductive health outcomes. The principal aim of this study was to investigate the trends in infant mortality between two geographic locations in Chile: Antofagasta, which has a well-documented history of arsenic exposure from naturally contaminated water, and Valparaíso, a comparable low-exposure city. The arsenic concentration in Antofagasta's public drinking water supply rose substantially in 1958 with the introduction of a new water source, and remained elevated until 1970. We used a retrospective study design to examine time and location patterns in infant mortality between 1950 and 1996, using univariate statistics, graphical techniques, and Poisson regression analysis. Results of the study document the general declines in late fetal and infant mortality over the study period in both locations. The data also indicate an elevation of the late fetal, neonatal, and postneonatal mortality rates for Antofagasta, relative to Valparaíso, for specific time periods, which generally coincide with the period of highest arsenic concentration in the drinking water of Antofagasta. Poisson regression analysis yielded an elevated and significant association between arsenic exposure and late fetal mortality [rate ratio (RR) = 1.7; 95% confidence interval (CI), 1.5-1.9], neonatal mortality (RR = 1.53; CI, 1.4-1.7), and postneonatal mortality (RR = 1.26; CI, 1.2-1.3) after adjustment for location and calendar time. The findings from this investigation may support a role for arsenic exposure in increasing the risk of late fetal and infant mortality

Nova Sagittarii 1994 #1 (V4332 Sagittarii): The Discovery and Evolution of an Unusual Luminous Red Variable Star

We report photometry and spectroscopy of the evolution of Nova Sagittarii 1994 #1 (V4332 Sagittarii) during outburst. We compare the photometric and spectral evolution of this outburst to known classes of outbursts -- including classical novae and outbursts occurring on symbiotic stars -- and find this object does NOT conform to any known class of outburst. The closest match to the behavior of this unusual object is M31 RV, an extremely luminous and red variable object discovered in the bulge of M31 in 1988. However, the temporal behavior and maximum luminosity of the two events differ by several orders of magnitude, requiring substantial intrinsic variation if these two events are members the same type of outburst. Our model of the spectroscopic evolution of this outburst shows that the effective temperature cooled from 4400 K to 2300 K over the three month span of our observations. In combination with line diagnostics in our later spectra, including [OI] lambda 5577 and the dramatic increase in the Halpha to Hbeta ratio, we infer the existence of a cool, dense (N_e ~ 10^{8-9} cm^{-3}) envelope that is optically thick in the Hydrogen Balmer recombination lines (case C). We suggest that a nuclear event in a single star, in which a slow shock drove the photosphere outwards, can power the observed luminosity evolution and the emission spectrum.Comment: Accepted for publication in AJ. 24 pages including 8 embedded postscript figures. Also available at http://www.astronomy.ohio-state.edu/~martini/pub