EAGLE ISS - A modular twin-channel integral-field near-IR spectrograph

The ISS (Integral-field Spectrograph System) has been designed as part of the EAGLE Phase A Instrument Study for the E-ELT. It consists of two input channels of 1.65x1.65 arcsec field-of-view, each reconfigured spatially by an image-slicing integral-field unit to feed a single near-IR spectrograph using cryogenic volume-phase-holographic (VPH) gratings to disperse the image spectrally. A 4k x 4k array detector array records the dispersed images. The optical design employs anamorphic magnification, image slicing, VPH gratings scanned with a novel cryo-mechanism and a three-lens camera. The mechanical implementation features IFU optics in Zerodur, a modular bench structure and a number of high-precision cryo-mechanisms.Comment: 12 pages, to be published in Proc SPIE 7735: Ground-based & Airborne Instrumentation for Astronomy II

NICMOS Imaging of the Nuclei of Arp 220

We report high resolution imaging of the ultraluminous infrared galaxy Arp 220 at 1.1, 1.6, and 2.22 microns with NICMOS on the HST. The diffraction-limited images at 0.1--0.2 arcsecond resolution clearly resolve both nuclei of the merging galaxy system and reveal for the first time a number of luminous star clusters in the circumnuclear envelope. The morphologies of both nuclei are strongly affected by dust obscuration, even at 2.2 microns : the primary nucleus (west) presents a crescent shape, concave to the south and the secondary (eastern) nucleus is bifurcated by a dust lane with the southern component being very reddened. In the western nucleus, the morphology of the 2.2 micron emission is most likely the result of obscuration by an opaque disk embedded within the nuclear star cluster. The morphology of the central starburst-cluster in the western nucleus is consistent with either a circumnuclear ring of star formation or a spherical cluster with the bottom half obscured by the embedded dust disk. Comparison of cm-wave radio continuum maps with the near-infrared images suggests that the radio nuclei lie in the dust disk on the west and near the highly reddened southern component of the eastern complex. The radio nuclei are separated by 0.98 arcseconds (corresponding to 364 pc at 77 Mpc) and the half-widths of the infrared nuclei are approximately 0.2-0.5 arcseconds. At least 8, unresolved infrared sources -- probably globular clusters -- are also seen in the circumnuclear envelope at radii 2-7 arcseconds . Their near-infrared colors do not significantly constrain their ages.Comment: LaTex, 15 pages with 1 gif figure and 5 postscript figures. ApJL accepte

High Mass Triple Systems: The Classical Cepheid Y Car

We have obtained an HST STIS ultraviolet high dispersion Echelle mode spectrum the binary companion of the double mode classical Cepheid Y Car. The velocity measured for the hot companion from this spectrum is very different from reasonable predictions for binary motion, implying that the companion is itself a short period binary. The measured velocity changed by 7 km/ s during the 4 days between two segments of the observation confirming this interpretation. We summarize "binary" Cepheids which are in fact members of triple system and find at least 44% are triples. The summary of information on Cepheids with orbits makes it likely that the fraction is under-estimated.Comment: accepted by A

The MACHO Project LMC Variable Star Inventory. VI. The Second-overtone Mode of Cepheid Pulsation From First/Second Overtone (FO/SO) Beat Cepheids

MACHO Project photometry of 45 LMC FO/SO beat Cepheids which pulsate in the first and second overtone (FO and SOo, respectively) has been analysed to determine the lightcurve characteristics for the SO mode of Cepheid pulsation. We predict that singly-periodic SO Cepheids will have nearly sinusoidal lightcurves; that we will only be able to discern SO Cepheids from fundamental (F) and (FO) Cepheids for P <= 1.4 days; and that the SO distribution will overlap the short-period edge of the LMC FO Cepheid period-luminosity relation (when both are plotted as a function of photometric period). We also report the discovery of one SO Cepheid candidate, MACHO*05:03:39.6$-$70:04:32, with a photometric period of 0.775961 +/- 0.000019 days and an instrumental amplitude of 0.047 +/- 0.009 mag in V.Comment: 23 pages, 7 Encapsulated PostScript figures. Accepted for publication in the Astrophysical Journa

The DA+dMe eclipsing binary EC13471-1258: its cup runneth over...just

EC13471-1258 is a detached eclipsing binary with Porb = 3h37m, comprising a DA white dwarf and a dMe dwarf. Total eclipses of the white dwarf lasting 14 min, and a large amplitude ellipsoidal variation are seen in the light curve. Flares from the dMe star occur regularly. Each star contributes roughly equal amounts of light at 5500 Ang. HST STIS spectra show strong Ly alpha with weak metal lines, and yield Teff = 14220 K, log g = 8.34, Z = 1/30th solar, K = 138 km/s and V sin i = 400 km/s for the white dwarf. Optical spectra yield the spectral type (M3.5-4.0), Teff = 3100 K, Z = solar, K = 266 km/s and V sin i = 140 km/s for the dMe star. The H alpha emission line comprises 2 or more components and implies that very weak mass transfer is occurring. The dynamical solution also implies that the dMe star just fills its Roche lobe. Accurate masses and radii for each star were derived: the dMe values favour the Clemens et al. (1998) mass-radius relation. The large rotational velocity of the white dwarf (400 km/s) suggests that the system has transferred mass in the past so that it is presently a hibernating cataclysmic variable. The metallicity contrast between the component stars provides an opportunity for tests of diffusion theory.Comment: 25 pages, 18 figures, accepted for publication in MNRA

The NOAO Data Lab virtual storage system

Collaborative research/computing environments are essential for working with the next generations of large astronomical data sets. A key component of them is a distributed storage system to enable data hosting, sharing, and publication. VOSpace is a lightweight interface providing network access to arbitrary backend storage solutions and endorsed by the International Virtual Observatory Alliance (IVOA). Although similar APIs exist, such as Amazon S3, WebDav, and Dropbox, VOSpace is designed to be protocol agnostic, focusing on data control operations, and supports asynchronous and third-party data transfers, thereby minimizing unnecessary data transfers. It also allows arbitrary computations to be triggered as a result of a transfer operation: for example, a file can be automatically ingested into a database when put into an active directory or a data reduction task, such as Sextractor, can be run on it. In this paper, we shall describe the VOSpace implementations that we have developed for the NOAO Data Lab. These offer both dedicated remote storage, accessible as a local file system via FUSE, and a local VOSpace service to easily enable data synchronization

Ensemble Characteristics of the ZZ Ceti stars

We present the observed pulsation spectra of all known non-interacting ZZ Ceti stars (hydrogen atmosphere white dwarf variables; DAVs) and examine changes in their pulsation properties across the instability strip. We confirm the well established trend of increasing pulsation period with decreasing effective temperature across the ZZ Ceti instability strip. We do not find a dramatic order of magnitude increase in the number of observed independent modes in ZZ Ceti stars, traversing from the hot to the cool edge of the instability strip; we find that the cool DAVs have one more mode on average compared to the hot DAVs. We confirm the initial increase in pulsation amplitude at the blue edge, and find strong evidence of a decline in amplitude prior to the red edge. We present the first observational evidence that ZZ Ceti stars lose pulsation energy just before pulsations shut down at the empirical red edge of the instability strip.Comment: ApJ, in press. (26 pages, 3 figures

The NOAO Data Lab: Science-Driven Development

The NOAO Data Lab aims to provide infrastructure to maximize community use of the high-value survey datasets now being collected with NOAO telescopes and instruments. As a science exploration framework, the Data Lab allow users to access and search databases containing large (i.e. terabyte-scale) catalogs, visualize, analyze, and store the results of these searches, combine search results with data from other archives or facilities, and share these results with collaborators using a shared workspace and/or data publication service. In the process of implementing the needed tools and services, specific science cases are used to guide development of the system framework and tools. The result is a Year-1 capability demonstration that (fully or partially) implements each of the major architecture components in the context of a real-world science use-case. In this paper, we discuss how this model of science-driven development helped us to build a fully functional system capable of executing the chosen science case, and how we plan to scale this system to support general use in the next phase of the project

Chemical data assimilation estimates of continental U.S. ozone and nitrogen budgets during the Intercontinental Chemical Transport Experiment-North America

Global ozone analyses, based on assimilation of stratospheric profile and ozone column measurements, and NOy predictions from the Real-time Air Quality Modeling System (RAQMS) are used to estimate the ozone and NOy budget over the continental United States during the July-August 2004 Intercontinental Chemical Transport Experiment-North America (INTEX-A). Comparison with aircraft, satellite, surface, and ozonesonde measurements collected during INTEX-A show that RAQMS captures the main features of the global and continental U.S. distribution of tropospheric ozone, carbon monoxide, and NOy with reasonable fidelity. Assimilation of stratospheric profile and column ozone measurements is shown to have a positive impact on the RAQMS upper tropospheric/lower stratosphere ozone analyses, particularly during the period when SAGE III limb scattering measurements were available. Eulerian ozone and NOy budgets during INTEX-A show that the majority of the continental U.S. export occurs in the upper troposphere/lower stratosphere poleward of the tropopause break, a consequence of convergence of tropospheric and stratospheric air in this region. Continental U.S. photochemically produced ozone was found to be a minor component of the total ozone export, which was dominated by stratospheric ozone during INTEX-A. The unusually low photochemical ozone export is attributed to anomalously cold surface temperatures during the latter half of the INTEX-A mission, which resulted in net ozone loss during the first 2 weeks of August. Eulerian NOy budgets are shown to be very consistent with previously published estimates. The NOy export efficiency was estimated to be 24%, with NOx + PAN accounting for 54% of the total NOy export during INTEX-A. Copyright 2007 by the American Geophysical Union