871 research outputs found
CCAT
Star formation, which drives the evolution of baryonic matter in the universe, occurs in the densest regions of the interstellar medium. As a result much of the emergent short wavelength radiation, UV to near IR, is absorbed by intervening dust and reradiated at longer wavelengths, far IR and subillimeter. Indeed the energy density of post primordial extragalactic light is divided equally between these short and long wavelengths, indicating equal amounts of radiation have passed through dusty and optically transparent environments over cosmic time. Comprehensive understanding of the processes of galaxy, star, and planetary formation requires, therefore, high sensitivity and high angular resolution observations, particularly surveys, in the far IR and submillimeter. A consortium led by Cornell and Caltech with JPL is now jointly planning the construction of a 25 m diameter telescope for submillimeter astronomy on a high mountain in northern Chile. This CCAT will combine high sensitivity, a wide field of view, and a broad wavelength range to provide an unprecedented capability for deep, large area, multi-color submillimeter surveys to complement narrow field, high resolution studies with ALMA. CCAT observations will address fundamental themes in contemporary astronomy, notably the formation and evolution of galaxies, the nature of the dark matter and dark energy that comprise most of the content of the universe, the formation of stars and planets, the conditions in circumstellar disks, and the conditions during the early history of the Solar system. The candidate CCAT site, at 5600m in northern Chile, enjoys superb observing conditions. To accommodate large format bolometer cameras, CCAT is designed with a 20 arcmin field of view. CCAT will incorporate closed loop active control of its segmented primary mirror to maintain a half wavefront error of 10 μm rms or less for the entire telescope. Instrumentation under consideration includes both short (650 μm–200 μm) and long (2 mm–750 μm) wavelength bolometer cameras, direct detection spectrometers, and heterodyne receiver arrays. In addition to Cornell and Caltech with JPL, the University of Colorado, the Universities of British Columbia and of Waterloo, the UK Astronomy Technology Centre on behalf of the UK community, and the Universities of Cologne and of Bonn have joined the CCAT consortium. When complete, CCAT will be the largest and most sensitive facility of its class as well as the highest altitude astronomical facility on Earth
Seeking the Local Convergence Depth. I. TF Observations of the Clusters A168, A397, A569, A1139, A1228, and A1983
We present first results of an all-sky observing program designed to improve
the quality of the I band Tully-Fisher (TF) template and to obtain the reflex
motion of the Local Group with respect to clusters to z = 0.06. We are
obtaining between 5 and 15 TF measurements per cluster on a sample of 50
clusters at intermediate redshifts (0.02 < z < 0.06). Presentation of the data
for seven Abell clusters of galaxies is given here. This data incorporates
methods for estimating the true inclination of a spiral disk, an observational
parameter undervalued for small angular-sized galaxies or for galaxies observed
in poor seeing conditions.Comment: 21 pages, uses AAS LaTeX, 3 tables and 8 postscript figures (only
first page of fig. 6 included in this version); to appear in the Astronomical
Journa
Seeking the Local Convergence Depth. The Abell Cluster Dipole Flow to 200 Mpc/h
We have obtained new Tully-Fisher (TF) peculiar velocity measurements for 52
Abell galaxy clusters distributed throughout the sky between ~ 50 and 200
Mpc/h.The measurements are based on I band photometry and optical rotation
curves for a sample of 522 spiral galaxies, from which an accurate TF template
relation has been constructed. Individual cluster TF relations are referred to
the template to compute cluster peculiar motions.
The reflex motion of the Local Group of galaxies is measured with respect to
the reference frame defined by our cluster sample and the distant portion of
the Giovanelli et al. (1998) cluster set. We find the Local Group motion in
this frame to be 565+/-113 km/s in the direction (l,b)=(267,26)+/-10 when
peculiar velocities are weighted according to their errors. After optimizing
the dipole calculation to sample equal volumes equally, the vector is 509+/-195
km/s towards (255,33)+/-22. Both solutions agree, to within 1-sigma or better,
with the Local Group motion as inferred from the cosmic microwave background
(CMB) dipole. Thus, the cluster sample as a whole moves slowly in the CMB
reference frame, its bulk flow being at most 200 km/s.Comment: 11 pages, uses AAS LaTeX; to appear in the Astrophysical Journal
Letter
Un inedito del Lyre Player Group da Tarquinia : alcune considerazioni
This brief note focuses on an unpublished seal of the Lyre Player Group found in Tarquinia. This particular class of seals, widespread in the basin of the Mediterranean and reaching the Italian Peninsula during the Orientalizing period, represents a good indicator for the study of the circulation of craftsmen and traders. In particular, this paper presents some considerations about the development of glyptic in Etruria during the Orientalizing period
A proposito di uno scarabeo da Colle del Forno : alcune considerazioni sulla produzione di stile globulare
L’esemplare di scarabeo dalla necropoli di Colle del Forno presentato in questa sede fornisce lo spunto per alcune brevissime considerazioni in merito alla produzione di stile globulare anche a fronte del recente lavoro di sintesi di U. Hannson sul tema che costituisce ad oggi un utilissimo aggiornamento sulle questioni stilistiche, formali, iconografiche, sugli aspetti produttivi nonché una discreta integrazione del corpus che era già stato apprestato da Peter Zazoff
Evolution of physicochemical, morphological and aromatic characteristics of Italian PDO dry-cured hams during processing
The aim of this work was to follow the evolution of physicochemical (dry matter, NaCl concentration, pH, water activity), morphological (image analysis) and aromatic (e-nose) characteristics of the three main Italian PDOs during processing, from slaughtering to end of ripening. Main phenomena distinguishing the PDOs are NaCl concentration increase, which is higher in Toscano than in Parma and San Daniele hams, starting from the salting phase. Water activity values decrease during processing, and the lowest values are detected in Toscano ham. Changes in morphological parameters (area, shape) and in color progressively occur during processing and are more pronounced in Toscano ham. A clear evolution of aroma of the three PDOs has been observed by e-nose, and the complexity of the aromatic profile of the ripened hams is clearly highlighted
No Hubble Bubble in the Local Universe
Zehavi et al. (1998) have suggested that the Hubble flow within 70/h Mpc may
be accelerated by the existence of a void centered on the Local Group. Its
underdensity would be ~20 %, which would result in a local Hubble distortion of
about 6.5 %. We have combined the peculiar velocity data of two samples of
clusters of galaxies, SCI and SCII, to investigate the amplitude of Hubble
distortions to 200/h Mpc. Our results are not supportive of that conclusion.
The amplitude of a possible distortion in the Hubble flow within 70/h Mpc in
the SCI+SCII merged data is 0.010\pm0.022. The largest, and still quite
marginal, geocentric deviation from smooth Hubble flow consistent with that
data set is a shell with (Delta H)/H =0.027\pm0.023, centered at hd = 101 Mpc
and extending over some 30/h Mpc. Our results are thus consistent with a Hubble
flow that, on distances in excess of about 50/h Mpc, is remarkably smooth.Comment: 11 pages, 1 tables, 1 figure; uses AAS LaTex; to appear in ApJ Nov 9
Statistical Tests for CHDM and \LambdaCDM Cosmologies
We apply several statistical estimators to high-resolution N-body simulations
of two currently viable cosmological models: a mixed dark matter model, having
contributed by two massive neutrinos (C+2\nuDM), and a Cold
Dark Matter model with Cosmological Constant (\LambdaCDM) with
and h=0.7. Our aim is to compare simulated galaxy samples with the
Perseus-Pisces redshift survey (PPS). We consider the n-point correlation
functions (n=2-4), the N-count probability functions P_N, including the void
probability function P_0, and the underdensity probability function U_\epsilon
(where \epsilon fixes the underdensity threshold in percentage of the average).
We find that P_0 (for which PPS and CfA2 data agree) and P_1 distinguish
efficiently between the models, while U_\epsilon is only marginally
discriminatory. On the contrary, the reduced skewness and kurtosis are,
respectively, S_3\simeq 2.2 and S_4\simeq 6-7 in all cases, quite independent
of the scale, in agreement with hierarchical scaling predictions and estimates
based on redshift surveys. Among our results, we emphasize the remarkable
agreement between PPS data and C+2\nuDM in all the tests performed. In
contrast, the above \LambdaCDM model has serious difficulties in reproducing
observational data if galaxies and matter overdensities are related in a simple
way.Comment: 12 pages, 10 figures, LaTeX (aaspp4 macro), in press on ApJ, Vol.
479, April 199
Submillimeter observing conditions on Cerro Chajnantor
Consistently superb observing conditions are crucial for achieving the scientific objectives of a ground based telescope. For observations at submillimeter wavelengths, choosing a site with very little atmospheric water vapor is paramount. In northern Chile, the high Andes near San Pedro de Atacama are among the highest and driest places on Earth. At the 5000 m Chajnantor plateau, long term measurements have demonstrated observing conditions are excellent for submillimeter astronomy. Even better conditions prevail on higher mountain peaks in the vicinity. For the CCAT, we have selected a candidate site at 5612 m near the summit of Cerro Chajnantor. Radiosonde measurements, meteorological data, and measurements of the 350 Consistently superb observing conditions are crucial for achieving the scientific objectives of a ground based telescope. For observations at submillimeter wavelengths, choosing a site with very little atmospheric water vapor is paramount. In northern Chile, the high Andes near San Pedro de Atacama are among the highest and driest places on Earth. At the 5000 m Chajnantor plateau, long term measurements have demonstrated observing conditions are excellent for submillimeter astronomy. Even better conditions prevail on higher mountain peaks in the vicinity. For the CCAT, we have selected a candidate site at 5612 m near the summit of Cerro Chajnantor. Radiosonde measurements, meteorological data, and measurements of the 350 ÎĽm transparency all indicate submillimeter observing conditions are consistently better at the CCAT site than at the plateau. transparency all indicate submillimeter observing conditions are consistently better at the CCAT site than at the plateau
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