21 research outputs found
First measurement of Mg isotope abundances at high redshifts and accurate estimate of Delta alpha/alpha
(Abridged) We use a high-resolution spectrum of the quasar HE0001-2340
observed with the UVES/VLT to measure Mg isotope abundances in the intervening
absorption-line systems at high redshifts. Line profiles are prepared
accounting for possible shifts between the individual exposures. Due to unique
composition of the selected systems - the presence of several transitions of
the same ion - we can test the local accuracy of the wavelength scale
calibration which is the main source of errors in the sub-pixel line position
measurements. In the system at zabs = 0.45 which is probably a fragment of the
outflow caused by SN Ia explosion of high-metallicity white dwarf(s) we
measured velocity shifts of MgII and MgI lines relative to other lines (FeI,
FeII, CaI, CaII): Delta V(MgII) = -0.44 +/- 0.05 km/s and Delta V(MgI) = -0.17
+/- 0.17$ km/s. This translates into the isotopic ratio 24Mg:25Mg:26Mg = (19
+/- 11):(22 +/- 13):(59 +/- 6) with a strong relative overabundance of heavy Mg
isotopes, (25Mg+26Mg)/24Mg = 4, as compared to the solar ratio 24Mg:25Mg:26Mg =
79:10:11, and (25Mg+26Mg)/24Mg = 0.3. At zabs = 1.58, we put a strong
constraint on a putative variation of alpha: Delta alpha/alpha = (-1.5 +/-
2.6)x10^{-6} which is one of the most stringent limits obtained from optical
spectra of QSOs. We reveal that the wavelength calibration in the range above
7500 A is subject to systematic wavelength-dependent drifts.Comment: 20 pages, 13 figures, 7 tables. Accepted for publication in Astronomy
and Astrophysic
Detailed Abundances for 28 Metal-poor Stars: Stellar Relics in the Milky Way
We present the results of an abundance analysis for a sample of stars with
[Fe/H]. The data were obtained with the HIRES spectrograph at Keck
Observatory. The set includes 28 stars, with effective temperature ranging from
4800 to 6600 K. For 13 stars with [Fe/H], including nine with
[Fe/H] and one with [Fe/H], these are the first reported detailed
abundances. For the most metal-poor star in our sample, CS 30336-049, we
measure an abundance pattern that is very similar to stars in the range
[Fe/H], including a normal C+N abundance. We also find that it has
very low but measurable Sr and Ba, indicating some neutron-capture activity
even at this low of a metallicity. We explore this issue further by examining
other very neutron-capture-deficient stars, and find that at the lowest levels,
[Ba/Sr] exhibits the ratio of the main r-process. We also report on a new
r-process-enhanced star, CS 31078-018. This star has [Fe/H],
[Eu/Fe], and [Ba/Eu]. CS 31078-018 exhibits an ``actinide
boost'', i.e. much higher [Th/Eu] than expected and at a similar level to CS
31082-001. Our spectra allow us to further constrain the abundance scatter at
low metallicities, which we then use to fit to the zero-metallicity Type II
supernova yields of Heger & Woosley (2008). We find that supernovae with
progenitor masses between 10 and 20 M provide the best matches to our
abundances.Comment: 48 pages, 30 figures, 17 tables. Updated to ApJ version. Multiple
typos and errors fixe
The accuracy of stellar atmospheric parameter determinations: a case study with HD 32115 and HD 37594
We present detailed parameter determinations of two chemically normal late
A-type stars, HD 32115 and HD 37594, to uncover the reasons behind large
discrepancies between two previous analyses of these stars performed with a
semi-automatic procedure and a "classical" analysis. Our study is based on high
resolution, high signal-to-noise spectra obtained at the McDonald Observatory.
Our method is based on the simultaneous use of all available observables:
multicolor photometry, pressure-sensitive magnesium lines, metallic lines and
Balmer line profiles. Our final set of fundamental parameters fits, within the
error bars, all available observables. It differs from the published results
obtained with a semi-automatic procedure. A direct comparison between our new
observational material and the spectra previously used by other authors shows
that the quality of the data is not the origin of the discrepancies. As the two
stars require a substantial macroturbulence velocity to fit the line profiles,
we concluded that neglecting this additional broadening in the semi-automatic
analysis is one origin of discrepancy. The use of FeI excitation equilibrium
and of the Fe ionisation equilibrium, to derive effective temperature and
surface gravity, respectively, neglecting all other indicators leads to a
systematically erroneously high effective temperature. We deduce that the
results obtained using only one parameter indicator might be biased and that
those results need to be cautiously taken when performing further detailed
analyses, such as modelling of the asteroseismic frequencies or characterising
transiting exoplanets.Comment: Accepted for publication by MNRA
Spatial variation in the fine-structure constant -- new results from VLT/UVES
(abridged) We present a new analysis of a large sample of quasar
absorption-line spectra obtained using UVES (the Ultraviolet and Visual Echelle
Spectrograph) on the VLT (Very Large Telescope) in Chile. In the VLT sample
(154 absorbers), we find evidence that alpha increases with increasing
cosmological distance from Earth. However, as previously shown, the Keck sample
(141 absorbers) provided evidence for a smaller alpha in the distant absorption
clouds. Upon combining the samples an apparent variation of alpha across the
sky emerges which is well represented by an angular dipole model pointing in
the direction RA=(17.3 +/- 1.0) hr, dec. = (-61 +/- 10) deg, with amplitude
(0.97 +0.22/-0.20) x 10^(-5). The dipole model is required at the 4.1 sigma
statistical significance level over a simple monopole model where alpha is the
same across the sky (but possibly different to the current laboratory value).
The data sets reveal a number of remarkable consistencies: various data cuts
are consistent and there is consistency in the overlap region of the Keck and
VLT samples. Assuming a dipole-only (i.e. no-monopole) model whose amplitude
grows proportionally with `lookback-time distance' (r=ct, where t is the
lookback time), the amplitude is (1.1 +/- 0.2) x 10^(-6) GLyr^(-1) and the
model is significant at the 4.2 sigma confidence level over the null model
[Delta alpha]/alpha = 0). We apply robustness checks and demonstrate that the
dipole effect does not originate from a small subset of the absorbers or
spectra. We present an analysis of systematic effects, and are unable to
identify any single systematic effect which can emulate the observed variation
in alpha.Comment: 47 pages, 35 figures. Accepted for publication by Monthly Notices of
the Royal Astronomical Society. Please see
http://astronomy.swin.edu.au/~mmurphy/pub.html for an ASCII version of table
A1 and the full set of Voigt profile fits for appendix
Resource availability affects investment in carnivory in Drosera rotundifolia
Carnivory in plants is restricted to nutrient-poor and open habitats presumably because of high benefits and/or low costs of carnivory in these conditions. Carnivory is costly because the plants need specific adaptations to capture prey. Drosera rotundifolia produces sticky substances on its leaf surface to catch prey. These substances are primarily carbon-based, and their production can be expected to be lower in shade. The benefit of carnivory is in terms of the increased nutritional gain which will be low when inorganic nutrients are available in the growth medium. We expected that investment in carnivory would be lower in shade and nutrient-rich conditions. A factorial experiment involving shading and the addition of inorganic nutrients confirmed these predictions in the carnivorous, perennial herb D. rotundifolia . Plants growing in shade or in media with nutrients added had less sticky leaves and had reduced their investment in carnivory. Interestingly, the observed changes in the stickiness of the leaves were in accord with the carbon/nutrient balance theory, whereas a carbon-based secondary compound, 7-methyljuglone, in the leaves did not respond to shading or nutrient addition
Initial Results from the USNO Dispersed Fourier Transform Spectrograph
We have designed and constructed a “dispersed Fourier Transform Spectrometer” (dFTS), consisting of a conventional FTS followed by a grating spectrometer.