Results from the GMT Ground-Layer Experiment at the Magellan Telescopes

We present results from our two year study of ground-layer turbulence as seen through the 6.5-meter Magellan Telescopes at Las Campanas Observatory. The experiment consists of multiple, moderate resolution, Shack-Hartmann wavefront sensors deployed over a large 16 arcminute field. Over the two years of the experiment, the ground-layer turbulence has been sampled on eleven nights in a variety of seeing and wind conditions. On most nights the ground-layer turbulence contributes 10% to the total visible-band seeing, although a few nights exhibit ground-layer contributions up to 30%. We present the ground-layer turbulence on the sampled nights as well as a demonstration of its strength as a function of field size. This information is combined with data from a MASS-DIMM seeing monitor adjacent to the Magellan Telescopes to infer the annual ground-layer contribution to seeing at Las Campanas.Comment: To appear in Proc. SPIE 627

An Update on the 0Z Project

We give an update on our 0Z Survey to find more extremely metal poor (EMP) stars with [Fe/H] < -3 dex through mining the database of the Hamburg/ESO Survey. We present the most extreme such stars we have found from ~1550 moderate resolution follow up spectra. One of these, HE1424-0241, has highly anomalous abundance ratios not seen in any previously known halo giant, with very deficient Si, moderately deficient Ca and Ti, highly enhanced Mn and Co, and low C, all with respect to Fe. We suggest a SNII where the nucleosynthetic yield for explosive alpha-burning nuclei was very low compared to that for the hydrostatic alpha-burning element Mg, which is normal in this star relative to Fe. A second, less extreme, outlier star with high [Sc/Fe] has also been found. We examine the extremely metal-poor tail of the HES metallicity distribution function (MDF). We suggest on the basis of comparison of our high resolution detailed abundance analyses with [Fe/H](HES) for stars in our sample that the MDF inferred from follow up spectra of the HES sample of candidate EMP stars is heavily contaminated for [Fe/H](HES) < -3 dex; many of the supposed EMP stars below that metallicity are of substantially higher Fe-metallicity, including most of the very C-rich stars, or are spurious objects.Comment: to appear in conference proceedings "First Stars III", ed. B. O'Shea, A. Heger & T.Abel, 4 pages, 2 figure

A Detailed Study of Giants and Horizontal Branch Stars in M68: Atmospheric Parameters and Chemical Abundances

In this paper, we present a detailed high-resolution spectroscopic study of post main sequence stars in the Globular Cluster M68. Our sample, which covers a range of 4000 K in $T_{eff}$, and 3.5 dex in $log(g)$, is comprised of members from the red giant, red horizontal, and blue horizontal branch, making this the first high-resolution globular cluster study covering such a large evolutionary and parameter space. Initially, atmospheric parameters were determined using photometric as well as spectroscopic methods, both of which resulted in unphysical and unexpected $T_{eff}$, $log(g)$, $\xi_{t}$, and [Fe/H] combinations. We therefore developed a hybrid approach that addresses most of these problems, and yields atmospheric parameters that agree well with other measurements in the literature. Furthermore, our derived stellar metallicities are consistent across all evolutionary stages, with $\langle$[Fe/H]$\rangle$ = $-$2.42 ($\sigma$ = 0.14) from 25 stars. Chemical abundances obtained using our methodology also agree with previous studies and bear all the hallmarks of globular clusters, such as a Na-O anti-correlation, constant Ca abundances, and mild $r$-process enrichment.Comment: Accepted to the Astronomical Journa

PANIC: A Near-infrared Camera for the Magellan Telescopes

PANIC (Persson's Auxiliary Nasmyth Infrared Camera) is a near-infrared camera designed to operate at any one of the f/11 folded ports of the 6.5m Magellan telescopes at Las Campanas Observatory, Chile. The instrument is built around a simple, all-refractive design that reimages the Magellan focal plane to a plate scale of 0.125'' pixel^{-1} onto a Rockwell 1024x1024 HgCdTe detector. The design goals for PANIC included excellent image quality to sample the superb seeing measured with the Magellan telescopes, high throughput, a relatively short construction time, and low cost. PANIC has now been in regular operation for over one year and has proved to be highly reliable and produce excellent images. The best recorded image quality has been ~0.2'' FWHM.Comment: 8 pages, 5 figures. To appear in "Astronomical Telescopes and Instrumentation," Proc SPIE (Glasgow), June 2004. Version with higher resolution figures is available at http://cfa-www.harvard.edu/~pmartini/professional/publications/panic.pd

Deriving Iodine-free spectra for high-resolution echelle spectrographs

We describe a new method to derive clean, iodine-free spectra directly from observations acquired using high-resolution echelle spectrographs equipped with iodine cells. The main motivation to obtain iodine-free spectra is to use portions of the spectrum that are superimposed with the dense forest of iodine absorption lines, in order to retrieve lines that can be used to monitor the magnetic activity of the star, helping to validate candidate planets. In short, we provide a straight-forward methodology to clean the spectra by using the forward model used to derive radial velocities, the Line Spread Function information plus the stellar spectrum without iodine to reconstruct and subtract the iodine spectrum from the observations. We show our results using observations of the star $\tau$ Ceti acquired with the PFS, HIRES and UCLES spectrographs, reaching an iodine-free spectrum correction at the $\sim$1% RMS level. We additionally discuss the limitations and further applications of the method.Comment: 15 pages, 7 figures. Accepted for publication in A

The Environment of ``E+A'' Galaxies

The violent star formation history of ``E+A'' galaxies and their detection almost exclusively in distant clusters is frequently used to link them to the ``Butcher-Oemler effect'' and to argue that cluster environment influences galaxy evolution. From 11113 spectra in the Las Campanas Redshift Survey, we have obtained a unique sample of 21 nearby ``E+A" galaxies. Surprisingly, a large fraction (about 75%) of these ``E+A''s lie in the field. Therefore, interactions with the cluster environment, in the form of the ICM or cluster potential, are not essential for ``E+A'' formation. If one mechanism is responsible for ``E+A''s, their existence in the field and the tidal features in at least 5 of the 21 argue that galaxy-galaxy interactions and mergers are that mechanism. The most likely environments for such interactions are poor groups, which have lower velocity dispersions than clusters and higher galaxy densities than the field. In hierarchical models, groups fall into clusters in greater numbers at intermediate redshifts than they do today. Thus, the Butcher-Oemler effect may reflect the typical evolution of galaxies in groups and in the field rather than the influence of clusters on star formation in galaxies. This abstract is abridged.Comment: 39 uuencoded, compressed pages (except Fig 1), complete preprint at ftp://ociw.edu/pub/aiz/eplusa.ps, ApJ, submitte

Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. III. Power spectrum analysis and excess isotropic component of fluctuations

The cosmic infrared background (CIB) radiation is the cosmic repository for energy release throughout the history of the universe. Using the all-sky data from the COBE DIRBE instrument at wavelengths 1.25 - 100 mic we attempt to measure the CIB fluctuations. In the near-IR, foreground emission is dominated by small scale structure due to stars in the Galaxy. There we find a strong correlation between the amplitude of the fluctuations and Galactic latitude after removing bright foreground stars. Using data outside the Galactic plane ($|b| > 20\deg$) and away from the center ($90\deg< l <270\deg$) we extrapolate the amplitude of the fluctuations to cosec$|b|=0$. We find a positive intercept of $\delta F_{\rm rms} = 15.5^{+3.7}_{-7.0},5.9^{+1.6}_{-3.7}, 2.4^{+0.5}_{-0.9}, 2.0^{+0.25}_{-0.5}$ nW/m2/sr at 1.25, 2.2,3.5 and 4.9 mic respectively, where the errors are the range of 92% confidence limits. For color subtracted maps between band 1 and 2 we find the isotropic part of the fluctuations at $7.6^{+1.2}_{-2.4}$ nW/m2/sr. Based on detailed numerical and analytic models, this residual is not likely to originate from the Galaxy, our clipping algorithm, or instrumental noise. We demonstrate that the residuals from the fit used in the extrapolation are distributed isotropically and suggest that this extra variance may result from structure in the CIB. For 2\deg< \theta < 15^\deg, a power-spectrum analysis yields firm upper limits of (\theta/5^\deg) \times\delta F_{\rm rms} (\theta) < 6, 2.5, 0.8, 0.5 nW/m2/sr at 1.25, 2.2, 3.5 and 4.9 mic respectively. From 10-100 mic, the upper limits <1 nW/m2/sr.Comment: Ap.J., in press. 69 pages including 24 fig

Redshifts in the Southern Abell Redshift Survey Clusters. I. The Data

The Southern Abell Redshift Survey contains 39 clusters of galaxies with redshifts in the range 0.0 < z < 0.31 and a median redshift depth of z = 0.0845. SARS covers the region 0 21h (while avoiding the LMC and SMC) with b > 40. Cluster locations were chosen from the Abell and Abell-Corwin-Olowin catalogs while galaxy positions were selected from the Automatic Plate Measuring Facility galaxy catalog with extinction-corrected magnitudes in the range 15 <= b_j < 19. SARS utilized the Las Campanas 2.5 m duPont telescope, observing either 65 or 128 objects concurrently over a 1.5 sq deg field. New redshifts for 3440 galaxies are reported in the fields of these 39 clusters of galaxies.Comment: 20 pages, 5 figures, accepted for publication in the Astronomical Journal, Table 2 can be downloaded in its entirety from http://trotsky.arc.nasa.gov/~mway/SARS1/sars1-table2.cs