Magellan/M2FS Spectroscopy of Galaxy Clusters: Stellar Population Model and Application to Abell 267

We report the results of a pilot program to use the Magellan/M2FS spectrograph to survey the galactic populations and internal kinematics of galaxy clusters. For this initial study, we present spectroscopic measurements for $223$ quiescent galaxies observed along the line of sight to the galaxy cluster Abell 267 ($z\sim0.23$). We develop a Bayesian method for modeling the integrated light from each galaxy as a simple stellar population, with free parameters that specify redshift ($v_\mathrm{los}/c$) and characteristic age, metallicity ($\mathrm{[Fe/H]}$), alpha-abundance ($[\alpha/\mathrm{Fe}]$), and internal velocity dispersion ($\sigma_\mathrm{int}$) for individual galaxies. Parameter estimates derived from our 1.5-hour observation of A267 have median random errors of $\sigma_{v_\mathrm{los}}=20\ \mathrm{km\ s^{-1}}$, $\sigma_{\mathrm{Age}}=1.2\ \mathrm{Gyr}$, $\sigma_{\mathrm{[Fe/H]}}=0.11\ \mathrm{dex}$,$\sigma_{[\alpha/\mathrm{Fe}]}=0.07\ \mathrm{dex}$, and$\sigma_{\sigma_\mathrm{int}}=20\ \mathrm{km\ s^{-1}}$. In a companion paper, we use these results to model the structure and internal kinematics of A267.Comment: 16 pages, 11 figures, accepted for publication in The Astronomical Journa

NGC 1866: First Spectroscopic Detection of Fast Rotating Stars in a Young LMC Cluster

High-resolution spectroscopic observations were taken of 29 extended main sequence turn-off (eMSTO) stars in the young ($\sim$200 Myr) LMC cluster, NGC 1866 using the Michigan/Magellan Fiber System and MSpec spectrograph on the Magellan-Clay 6.5-m telescope. These spectra reveal the first direct detection of rapidly rotating stars whose presence has only been inferred from photometric studies. The eMSTO stars exhibit H-alpha emission (indicative of Be-star decretion disks), others have shallow broad H-alpha absorption (consistent with rotation $\gtrsim$150 km s$^{-1}$), or deep H-alpha core absorption signaling lower rotation velocities ($\lesssim$150 km s$^{-1}$ ). The spectra appear consistent with two populations of stars - one rapidly rotating, and the other, younger and slowly rotating.Comment: 9 pages, 4 figures, Accepted for publication in ApJ Letter

Predictive value of respiratory symptoms and bronchial hyperresponsiveness to diagnose asthma in New Zealand

SummaryRespiratory symptoms are often used as the only diagnostic criteria for asthma in epidemiological surveys and the clinical diagnosis of asthma relies primarily on a detailed history. The aim of this study is to predict the diagnostic value of 11 different respiratory symptoms to diagnose asthma, and to determine if bronchial hyperresponsiveness (BHR) improves the predictive value of these respiratory symptoms.A random sample of 1257 subjects aged 20–44 years old in 3 different areas of New Zealand were selected between March 1991 and December 1992 to answer the European Community Respiratory Health Survey questionnaire on respiratory symptoms. Of these, 784 underwent bronchial challenge with methacholine. The prevalence of current doctor diagnosed asthma (DDA) defined as asthma confirmed by a physician and an asthma attack in the last 12 months was 8.3%. Wheezing with dyspnoea is the single best predictor of diagnosed asthma with a sensitivity of 82%, a specificity of 90% and a Youden's index of 0.72. Wheezing alone is more sensitive (94%) but less specific (76%), with a Youden's index of 0.70. The addition of BHR to asthma symptoms decreases sensitivity and increases specificity with a small increase in Youden's index to 0.75. In New Zealand adults, a history of wheezing with BHR best predicts a diagnosis of asthma but wheezing alone or with dyspnoea are the two best symptoms for predicting asthma

AGB Sodium Abundances in the Globular Cluster 47 Tucanae (NGC 104)

A recent analysis comparing the [Na/Fe] distributions of red giant branch (RGB) and asymptotic giant branch (AGB) stars in the Galactic globular cluster NGC 6752 found that the ratio of Na-poor to Na-rich stars changes from 30:70 on the RGB to 100:0 on the AGB. The surprising paucity of Na-rich stars on the AGB in NGC 6752 warrants additional investigations to determine if the failure of a significant fraction of stars to ascend the AGB is an attribute common to all globular clusters. Therefore, we present radial velocities, [Fe/H], and [Na/Fe] abundances for 35 AGB stars in the Galactic globular cluster 47 Tucanae (47 Tuc; NGC 104), and compare the AGB [Na/Fe] distribution with a similar RGB sample published previously. The abundances and velocities were derived from high resolution spectra obtained with the Michigan/Magellan Fiber System (M2FS) and MSpec spectrograph on the Magellan-Clay 6.5m telescope. We find the average heliocentric radial velocity and [Fe/H] values to be =-18.56 km s^-1 (sigma=10.21 km s^-1) and =-0.68 (sigma=0.08), respectively, in agreement with previous literature estimates. The average [Na/Fe] abundance is 0.12 dex lower in the 47 Tuc AGB sample compared to the RGB sample, and the ratio of Na-poor to Na-rich stars is 63:37 on the AGB and 45:55 on the RGB. However, in contrast to NGC 6752, the two 47 Tuc populations have nearly identical [Na/Fe] dispersion and interquartile range values. The data presented here suggest that only a small fraction <20% of Na-rich stars in 47 Tuc may fail to ascend the AGB. Regardless of the cause for the lower average [Na/Fe] abundance in AGB stars, we find that Na-poor stars and at least some Na-rich stars in 47 Tuc evolve through the early AGB phase. [abridged]Comment: Accepted for publication in the Astronomical Journal; 15 pages; 8 figures; 4 table

A detailed analysis of the HD 73526 2:1 resonant planetary system

We present six years of new radial velocity data from the Anglo-Australian and Magellan Telescopes on the HD 73526 2:1 resonant planetary system. We investigate both Keplerian and dynamical ( interacting) fits to these data, yielding four possible configurations for the system. The new data now show that both resonance angles are librating, with amplitudes of 40 degrees and 60 degrees, respectively. We then perform long-term dynamical stability tests to differentiate these solutions, which only differ significantly in the masses of the planets. We show that while there is no clearly preferred system inclination, the dynamical fit with i = 90 degrees provides the best combination of goodness-of-fit and long-term dynamical stability.Peer reviewe

How Lyman Alpha Emission Depends On Galaxy Stellar Mass

In this work, we show how the stellar mass (M) of galaxies affects the 3<z<4.6 Ly-alpha equivalent width (EW) distribution. To this end, we design a sample of 629 galaxies in the M range 7.6 < logM/Msun < 10.6 from the 3D-HST/CANDELS survey. We perform spectroscopic observations of this sample using the Michigan/Magellan Fiber System, allowing us to measure Ly-alpha fluxes and use 3D-HST/CANDELS ancillary data. In order to study the Ly-alpha EW distribution dependence on M, we split the whole sample in three stellar mass bins. We find that, in all bins, the distribution is best represented by an exponential profile of the form dN(M)/dEW= A(M)exp(-EW/W0(M))/W0(M). Through a Bayesian analysis, we confirm that lower M galaxies have higher Ly-alpha EWs. We also find that the fraction A of galaxies featuring emission and the e-folding scale W0 of the distribution anti- correlate with M, recovering expressions of the forms A(M)= -0.26(.13) logM/Msun+3.01(1.2) and W0(M)= -15.6(3.5) logM/Msun +166(34). These results are crucial for proper interpretation of Ly-alpha emission trends reported in the literature that may be affected by strong M selection biases.Comment: 4 pages, 5 figure

Exploring Halo Substructure with Giant Stars: Spectroscopy of Stars in the Galactic Anticenter Stellar Structure

To determine the nature of the recently discovered, ring-like stellar structure at the Galactic anticenter, we have collected spectra of a set of presumed constituent M giants selected from the 2MASS point source catalog. Radial velocities have been obtained for stars spanning ~100 degrees, exhibiting a trend in velocity with Galactic longitude and an estimated dispersion of 20 +/- 4 km/sec. A mean metallicity [Fe/H] = -0.4 +/- 0.3 measured for these stars combines with previous evidence from the literature to suggest a population with a significant metallicity spread. In addition, a curious alignment of at least four globular clusters of lower mean metallicity is noted to be spatially and kinematically consistent with this stellar distribution. We interpret the M giant sample position and velocity variation with Galactic longitude as suggestive of a satellite galaxy currently undergoing tidal disruption in a non-circular, prograde orbit about the Milky Way.Comment: (1) University of Virginia, 4 pages, 3 figures, accepted for publication in The Astrophysical Journal Letter