491 research outputs found
VLT/UVES shows no cosmological variability of alpha
The cosmological variability of alpha is probed from individual observations
of pairs of FeII lines. This procedure allows a better control of the
systematics and avoids the influence of the spectral shifts due to ionization
inhomogeneities in the absorbers and/or non-zero offsets between different
exposures. Applied to the FeII lines of the metal absorption systems at zabs =
1.839 in Q1101--264 and at zabs = 1.15 in HE0515--4414 observed by means of
UVES at the ESO-VLT, it provides da/a = 0.4 (+/- 1.5 stat)x10^{-6}. The result
is shifted with respect to the Keck/HIRES mean da/a = -5.7(+/- 1.1
stat})x10^{-6} (Murphy et al. 2004) at a high confidence level (95%). Full
details of this work are given in Levshakov et al (2005)Comment: 3 pages, 1 postscript figur
The lithium isotope ratio in the metal-poor halo star G271-162 from VLT/UVES observations
A high resolution (R = 110.000), very high S/N (>600) spectrum of the
metal-poor turnoff star G271-162 has been obtained in connection with the
commissioning of UVES at VLT/Kueyen. Using both 1D hydrostatic and 3D
hydrodynamical model atmospheres, the lithium isotope ratio has been estimated
from the LiI 670.8 nm line by means of spectral synthesis. The necessary
stellar line broadening (1D: macroturbulence + rotation, 3D: rotation) has been
determined from unblended KI, CaI and FeI lines. The 3D line profiles agree
very well with the observed profiles, including the characteristic line
asymmetries. Both the 1D and 3D analyses reveal a possible detection of 6Li in
G271-162, 6Li/7Li = 0.02 +-0.01 (one sigma). It is discussed if the smaller
amount of 6Li in G271-162 than in the similar halo star HD84937 could be due to
differences in stellar mass and/or metallicity or whether it may reflect an
intrinsic scatter of the Li isotope ratio in the ISM at a given metallicity.Comment: 5 pages with 6 figures. Accepted as a letter in A&
Connecting European snow cover variability with large scale atmospheric patterns
Abstract. Winter snowfall and its temporal variability are important factors in the development of water management strategies for snow-dominated regions. For example, mountain regions of Europe rely on snow for recreation, and on snowmelt for water supply and hydropower. It is still unclear whether in these regions the snow regime is undergoing any major significant change. Moreover, snow interannual variability depends on different climatic variables, such as precipitation and temperature, and their interplay with atmospheric and pressure conditions. This paper uses the EASE Grid weekly snow cover and Ice Extent database from the National Snow and Ice Data Center to assess the possible existence of trends in snow cover across Europe. This database provides a representation of snow cover fields in Europe for the period 1972–2006 and is used here to construct snow cover indices, both in time and space. These indices allow us to investigate the historical spatial and temporal variability of European snow cover fields, and to relate them to the modes of climate variability that are known to affect the European climate. We find that both the spatial and temporal variability of snow cover are strongly related to the Arctic Oscillation during wintertime. In the other seasons, weaker correlation appears between snow cover and the other patterns of climate variability, such as the East Atlantic, the East Atlantic West Russia, the North Atlantic Oscillation, the Polar Pattern and the Scandinavian Pattern
UVES radial velocity accuracy from asteroid observations. Implications for the fine structure constant variability
High resolution observations of the asteroids Iris and Juno have been
performed by means of the UVES spectrograph at the ESO VLT to obtain the
effective accurac y of the spectrograph's radial velocity. The knowledge of
this quantity has impo rtant bearings on studies searching for a variability of
the fine structure cons tant carried on with this instrument. Asteroids provide
a precise radial velocit y reference at the level of 1 m/s which allows
instrumental calibration and the recognition of small instrumental drifts and
calibration systematics. In particu lar, radial velocity drifts due to non
uniform slit illumination and slit optica l misalignment in the two UVES
spectrograph arms can be investigated. The positi on of the solar spectrum
reflected by the asteroids are compared with the solar wavelength positions or
with that of asteroid observations at other epochs or wi th the twilight to
asses UVES instrumental accuracy . Radial velocities offsets in the range
10--50 m/s are generally observed likely due to a non uniform slit
illumination. However, no radial velocity patterns with wavelength are detected
and the two UVES arms provide consistent radial velocities. These results
suggest that the detected alpha variability by Levshakov et al. (2007) deduced
from a drift of -180 (+/- 85) m/s at z =1.84, between two sets of FeII lines
falling in the two UVES arms may be real or induced by other kinds of
systematics than those investigated here. The proposed technique allows real
time quality check of the spectrograph and should be followed for very accurate
measurements.Comment: Accepted A&
The cosmic microwave background radiation temperature at z = 3.025 toward QSO 0347--3819
From the analysis of the CII fine-structure population ratio in the damped
Ly_alpha system at z = 3.025 toward the quasar Q0347--3819 we derive an upper
bound of 14.6 (+/- 0.2) K on the cosmic microwave background temperature
regardless the presence of other different excitation mechanisms. The analysis
of the ground state rotational level populations of H_2 detected in the system
reveals a Galactic-type UV radiation field ruling out UV pumping as an
important excitation mechanism for CII. The low dust content estimated from the
Cr/Zn ratio indicates that the IR dust emission can also be neglected. When the
collisional excitation is considered, we measure a temperature for the cosmic
background radiation of T = 12.1 (+1.7, -3.2) K. The results are in agreement
with the T = 10.968 (+/-) 0.004 K predicted by the hot Big Bang cosmology at z
= 3.025.Comment: Accepte
IR Colors and Sizes of Faint Galaxies
We present J and Ks band galaxy counts down to J=24 and Ks=22.5 obtained with
the new infrared imager/spectrometer, SOFI, at the ESO New Technology
Telescope. The co-addition of short, dithered, images led to a total exposure
time of 256 and 624 minutes respectively, over an area of arcmin
centered on the NTT Deep Field. The total number of sources with S/N is
1569 in the J sample and 1025 in the Ks-selected sample. These are the largest
samples currently available at these depths. A d/d relation with slope
of in J and in Ks is found with no evident sign of a
decline at the magnitude limit. The observed surface density of ``small''
sources is much lower than ``large'' ones at bright magnitudes and rises more
steeply than the large sources to fainter magnitudes. Fainter than
and Ks, small sources dominate the number counts. Galaxies get redder
in J-K down to
J and Ks. At fainter magnitudes, the median color becomes
bluer with an accompanying increase in the compactness of the galaxies. We show
that the blue, small sources which dominate the faint IR counts are not
compatible with a high redshift () population. On the contrary, the
observed color and compactness trends, together with the absence of a turnover
at faint magnitudes and the dominance of small sources, can be naturally
explained by an increasing contribution of sub- galaxies when going to
fainter apparent magnitudes. Such evidence strongly supports the existence of a
steeply rising () faint end of the local infrared luminosity
function of galaxies - at least for luminosities .Comment: Accepted for publication on A&A; 15 pages, 13 figure
- …