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Unprecedented Accuracy (unprecedented + accuracy)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

The SAURON project , IV.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
The mass-to-light ratio, lenticular galaxies, the Fundamental Plane of elliptical, the virial mass estimator
ABSTRACT We investigate the well-known correlations between the dynamical mass-to-light ratio (M/L) and other global observables of elliptical (E) and lenticular (S0) galaxies. We construct two-integral Jeans and three-integral Schwarzschild dynamical models for a sample of 25 E/S0 galaxies with SAURON integral-field stellar kinematics to about one effective (half-light) radius Re. They have well-calibrated I -band Hubble Space Telescope WFPC2 and large-field ground-based photometry, accurate surface brightness fluctuation distances, and their observed kinematics is consistent with an axisymmetric intrinsic shape. All these factors result in an unprecedented accuracy in the M/L measurements. We find a tight correlation of the form (M/L) = (3.80 ± 0.14) × (,e/200 km s,1)0.84±0.07 between the M/L (in the I band) measured from the dynamical models and the luminosity-weighted second moment ,e of the LOSVD within Re. The observed rms scatter in M/L for our sample is 18 per cent, while the inferred intrinsic scatter is ,13 per cent. The (M/L),,e relation can be included in the remarkable series of tight correlations between ,e and other galaxy global observables. The comparison of the observed correlations with the predictions of the Fundamental Plane (FP), and with simple virial estimates, shows that the ,tilt' of the FP of early-type galaxies, describing the deviation of the FP from the virial relation, is almost exclusively due to a real M/L variation, while structural and orbital non-homology have a negligible effect. When the photometric parameters are determined in the ,classic' way, using growth curves, and the ,e is measured in a large aperture, the virial mass appears to be a reliable estimator of the mass in the central regions of galaxies, and can be safely used where more ,expensive' models are not feasible (e.g. in high-redshift studies). In this case the best-fitting virial relation has the form (M/L)vir= (5.0 ± 0.1) ×Re,2e/(LG), in reasonable agreement with simple theoretical predictions. We find no difference between the M/L of the galaxies in clusters and in the field. The comparison of the dynamical M/L with the (M/L)pop inferred from the analysis of the stellar population, indicates a median dark matter fraction in early-type galaxies of ,30 per cent of the total mass inside one Re, in broad agreement with previous studies, and it also shows that the stellar initial mass function varies little among different galaxies. Our results suggest a variation in M/L at constant (M/L)pop, which seems to be linked to the galaxy dynamics. We speculate that fast-rotating galaxies have lower dark matter fractions than the slow-rotating and generally more-massive ones. If correct, this would suggest a connection between the galaxy assembly history and the dark matter halo structure. The tightness of our correlation provides some evidence against cuspy nuclear dark matter profiles in galaxies. [source]

Extreme-ultraviolet laser metrology of O i transitions

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2008
T. I. Ivanov
ABSTRACT Some 16 transitions in atomic oxygen originating from its 3P ground state were measured using a tunable narrow-band extreme-ultraviolet laser source, with an unprecedented accuracy of ,,/,= 8 × 10,8. The results are relevant for comparisons with spectral absorption features observed in the line of sight of quasars, in order to test a possible variation of the fine-structure constant , on a cosmological time-scale. [source]

A synoptic program for large solar telescopes: Cyclic variation of turbulent magnetic fields

ASTRONOMISCHE NACHRICHTEN, Issue 6 2010
L. Kleint
Abstract Upcoming large solar telescopes will offer the possibility of unprecedented high resolution observations. However, during periods of non-ideal seeing such measurements are impossible and alternative programs should be considered to best use the available observing time. We present a synoptic program, currently carried out at the Istituto Ricerche Solari Locarno (IRSOL), to monitor turbulent magnetic fields employing the differential Hanle effect in atomic and molecular lines. This program can be easily adapted for the use at large telescopes exploring new science goals, nowadays impossible to achieve with smaller telescopes. The current, interesting scientific results prove that such programs are worthwhile to be continued and expanded in the future. We calculate the approximately achievable spatial resolution at a large telescope like ATST for polarimetric measurements with a noise level below 5 × 10 -5 and a temporal resolution which is sufficient to explore variations on the granular scale. We show that it would be important to optimize the system for maximal photon throughput and to install a high-speed camera system to be able to study turbulent magnetic fields with unprecedented accuracy (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The Gaia project: Technique, performance and status

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2008
S. Jordan
Abstract Gaia is a satellite mission of the ESA, aiming at absolute astrometric measurements of about one billion stars (all stars down to 20th magnitude, with unprecedented accuracy. Additionally, magnitudes and colors will be obtained for all these stars, while radial-velocities and spectral properties will be determined only for bright objects (V < 17.5). At 15th magnitude Gaia aims at an angular accuracy of 20 microarcseconds (, as). This goal can only be reached if the geometry of the telescopes, the detectors, and the pointing of Gaia at each moment ("attitude") can be inferred from the Gaia measurements itself with , as accuracy. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]