610 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
Pre-MS depletion, accretion and primordial 7Li
We reconsider the role of pre-main sequence (pre-MS) Li depletion on the
basis of new observational and theoretical evidence: i) new observations of
Halpha emissions in young clusters show that mass accretion could be continuing
till the first stages of the MS, ii) theoretical implications from
helioseismology suggest large overshooting values below the bottom of the
convective envelopes. We argue here that a significant pre-MS 7Li destruction,
caused by efficient overshoot mixing, could be followed by a matter accretion
after 7Li depletion has ceased on MS thus restoring Li almost to the pristine
value. As a test case we show that a halo dwarf of 0.85 Msun with an extended
overshooting envelope starting with an initial abundance of A(Li) = 2.74 would
burn Li completely, but an accretion rate of the type 1e-8xe^{-t/3e6} Msun
yr would restore Li to end with an A(Li) = 2.31. A self-regulating
process is required to produce similar final values in a range of different
stellar masses to explain the PopII Spite plateau. However, this framework
could explain why open cluster stars have lower Li abundances than the
pre-solar nebula, the absence of Li in the most metal poor dwarfs and a number
of other features which lack of a satisfactory explanation.Comment: To be published in Memorie della Societ\`a Astronomica Italiana
Supplementi Vol. 22, Proceedings of Lithium in the cosmos, Iocco F.,
Bonifacio P., Vangioni E., ed
QSO 0347-383 and the invariance of m_p/m_e in the course of cosmic time
The variation of the dimensionless fundamental physical constant mu = m_p/m_e
(the proton to electron mass ratio) can be constrained via observation of Lyman
and Werner lines of molecular hydrogen in the spectra of damped Lyman alpha
systems (DLAs) in the line of sight to distant QSOs. Drawing on VLT-UVES high
resolution data sets of QSO 0347-383 and its DLA obtained in 2009 our analysis
yields dmu/mu = (4.3 +/- 7.2) * 10^-6 at z_abs =3.025. We apply corrections for
the observed offsets between discrete spectra and for the first time we find
indications for inter-order distortions. Current analyses tend to underestimate
the impact of systematic errors. Based on the scatter of the measured redshifts
and the corresponding low significance of the redshift-sensitivity correlation
we estimate the limit of accuracy of line position measurements to about 220
m/s, consisting of roughly 150 m/s due to the uncertainty of the absorption
line fit and about 150 m/s allocated to systematics related to instrumentation
and calibration.Comment: 9 pages, 9 figures, accepted for publication in A&
The Spectra of Main Sequence Stars in Galactic Globular Clusters II. CH and CN Bands in M71
Spectra with a high signal-to-noise ratio of 79 stars which are just below
the main sequence turnoff of M71 are presented. They yield indices for the
strength of the G band of CH and the ultraviolet CN band at 3885 \AA. These
indices are each to first order bimodal and they are anti-correlated. There are
approximately equal numbers of CN weak/CH strong and CN strong/CH weak main
sequence stars in M71. It is not yet clear whether these star-to-star
variations arise from primordial variations or from mixing within a fraction of
individual stars as they evolve.Comment: Accepted for publication in the AJ to appear back to back with paper
I. 14 pages with 5 figure
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&
Daily variability of Ceres' Albedo detected by means of radial velocities changes of the reflected sunlight
Bright features have been recently discovered by Dawn on Ceres, which extend
previous photometric and Space Telescope observations. These features should
produce distortions of the line profiles of the reflected solar spectrum and
therefore an apparent radial velocity variation modulated by the rotation of
the dwarf planet. Here we report on two sequences of observations of Ceres
performed in the nights of 31 July, 26-27 August 2015 by means of the
high-precision HARPS spectrograph at the 3.6-m La Silla ESO telescope. The
observations revealed a quite complex behaviour which likely combines a radial
velocity modulation due to the rotation with an amplitude of approx +/- 6 m/s
and an unexpected diurnal effect. The latter changes imply changes in the
albedo of Occator's bright features due to the blaze produced by the exposure
to solar radiation. The short-term variability of Ceres' albedo is on
timescales ranging from hours to months and can both be confirmed and followed
by means of dedicated radial velocity observations.Comment: 5 pag, 1fig, two tables, MNRAS Letters 201
UVES observations of QSO 0000-2620: oxygen and zinc abundances in the Damped Ly-alpha galaxy at z_abs=3.3901
Observations of the QSO 0000-2620 with UVES spectrograph at the 8.2m ESO
KUEYEN telescope are used for abundance analysis of the damped Ly-alpha system
at z_{abs}=3.3901. Several Oxygen lines are identified in the Ly_alpha forest
and a measure for the oxygen abundance is obtained at [O/H]=-1.85 +/- 0.1 by
means of the unsaturated OI 925 A and OI 950 A lines. This represents the most
accurate O measurement in a damped Ly_alpha galaxy so far. We have also
detected ZnII 2026 A and CrII 2056, 2062 A redshifted at about 8900 A and found
abundances [Zn/H] = -2.07 +/- 0.1 and [Cr/H]=-1.99 +/- 0.1. Furthermore,
previous measurements of Fe, Si, Ni and N have been refined yielding
[Fe/H]=-2.04 +/- 0.1, [Si/H]=-1.90 +/- 0.1, [Ni/H]=-2.27 +/- 0.1, and
[N/H]=-2.68 +/- 0.1. The abundance of the non-refractory element zinc is the
lowest among the damped Ly-alpha systems showing that the associated
intervening galaxy is indeed in the early stages of its chemical evolution. The
fact that the Zn abundance is identical to that of the refractory elements Fe
and Cr suggests that dust grains have not formed yet. In this Damped Ly-alpha
system the observed [O,S,Si/Zn,Fe,Cr] ratios, in whatever combination are
taken, are close to solar (i.e 0.1-0.2 dex) and do not show the
[alpha-element/Fe] enhancement observed in Milky Way stars of comparable
metallicity. The observed behavior supports a galaxy evolution model
characterized by either episodic or low star formation rate rather than a
Milky-Way-type evolutionary model.Comment: Accepted by Ap
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