1,188 research outputs found
Stellar Oscillations Network Group
Stellar Oscillations Network Group (SONG) is an initiative aimed at designing
and building a network of 1m-class telescopes dedicated to asteroseismology and
planet hunting. SONG will have 8 identical telescope nodes each equipped with a
high-resolution spectrograph and an iodine cell for obtaining precision radial
velocities and a CCD camera for guiding and imaging purposes. The main
asteroseismology targets for the network are the brightest (V<6) stars. In
order to improve performance and reduce maintenance costs the instrumentation
will only have very few modes of operation. In this contribution we describe
the motivations for establishing a network, the basic outline of SONG and the
expected performance.Comment: Proc. Vienna Workshop on the Future of Asteroseismology, 20 - 22
September 2006. Comm. in Asteroseismology, Vol. 150, in the pres
Properties of oscillation modes in subgiant stars observed by Kepler
Mixed modes seen in evolved stars carry information on their deeper layers
that can place stringent constraints on their physics and on their global
properties (mass, age, etc...). In this study, we present a method to identify
and measure all oscillatory mode characteristics (frequency, height, width).
Analyzing four subgiants stars, we present the first measure of the effect of
the degree of mixture on the l=1 mixed modes characteristics. We also show that
some stars have measurable l=2 mixed modes and discuss the interest of their
measure to constrain the deeper layers of stars.Comment: Accepted to Ap
Butterfly diagram of a Sun-like star observed using asteroseismology
Stellar magnetic fields are poorly understood but are known to be important
for stellar evolution and exoplanet habitability. They drive stellar activity,
which is the main observational constraint on theoretical models for magnetic
field generation and evolution. Starspots are the main manifestation of the
magnetic fields at the stellar surface. In this study we measure the variation
of their latitude with time, called a butterfly diagram in the solar case, for
the solar analogue HD 173701 (KIC 8006161). To that effect, we use Kepler data,
to combine starspot rotation rates at different epochs and the
asteroseismically determined latitudinal variation of the stellar rotation
rates. We observe a clear variation of the latitude of the starspots. It is the
first time such a diagram is constructed using asteroseismic data.Comment: 8 pages, 4 figures, accepted in A&A Letter
Asteroseismic detection of latitudinal differential rotation in 13 Sun-like stars
The differentially rotating outer layers of stars are thought to play a role
in driving their magnetic activity, but the underlying mechanisms that generate
and sustain differential rotation are poorly understood. We report the
measurement of latitudinal differential rotation in the convection zones of 40
Sun-like stars using asteroseismology. For the most significant detections, the
stars' equators rotate approximately twice as fast as their mid-latitudes. The
latitudinal shear inferred from asteroseismology is much larger than
predictions from numerical simulations.Comment: 45 pages, 11 figures, 4 tables, published in Scienc
Combining pressing and alkaline extraction to increase protein yield from Ulva fenestrata biomass
Many seaweed species have a high production potential and attract interest as future protein sources. A high fiber and ash content, however, demand extraction of the protein to improve its digestibility and protein utilization in food or feed. This study explores three different approaches for protein extraction from Ulva fenestrata in order to maximize the protein extraction yield. Soluble protein was recovered either by mechanical pressing or by homogenization and osmotic shock of the biomass followed by alkaline extraction. The soluble protein was then concentrated by isoelectric precipitation. A combined procedure was carried out by pressing the biomass and following subjecting the residual pulp fraction to homogenization, osmotic shock and alkaline extraction. The three methods were ranked as follows with respect to protein extraction yield (as % of biomass protein); the combined method (23.9 \ub1 0.3%)> the alkaline extraction (6.8 \ub1 0.2%)> mechanical pressing (5.0 \ub1 0.2%). The significant increase when combining the methods was ascribed to a high precipitation yield after alkaline extraction of the pulp, hypothesized to be due to a reduced conductivity of the alkali-soluble protein fraction when derived from pulp rather than whole biomass
When things go wrong : intra-season dynamics of breeding failure in a seabird
We thank all fieldworkers who helped monitor nests and deploy/retrieve GPS loggers, notably Muriel Dietrich, Elisa Lobato, Julien Gasparini, Vincent Staszewski and Thierry Chambert. We are grateful to Victor GarciaâMattarranz from the Ministerio de Medio Ambiente y Medio Rural y Marino (MARM, Spain) and Jacob GonzalĂšsâSolĂs from University of Barcelona for their help on PTTs functioning and deployment. We thank Nina Dehnhard and two anonymous referees who provided useful comments and suggestions to improve this manuscript and Matthieu Authier for statistical advice. This study was funded by the French Polar Institute (IPEV, programme n°333 PARASITOâARCTIQUE), CNRS, ANR, OSU OREME, NINA, University of TromsĂž, SEAPOP (www.seapop.no) and CEDREN. All work was carried out in accordance with standard animal care protocols and approved by the Ethical Committee of the French Polar Institute and the Norwegian Animal Research Authority. The PhD thesis of A. P. is partly funded via a RĂ©gion LanguedocâRoussillon program âChercheur d'Avenir' support to T. B. and University of Montpellier 2.Peer reviewedPublisher PD
Accurate Determination of the Solar Photospheric Radius
The Solar Diameter Monitor measured the duration of solar meridian transits
during the 6 years 1981 to 1987, spanning the declining half of solar cycle 21.
We have combined these photoelectric measurements with models of the solar
limb-darkening function, deriving a mean value for the solar near-equatorial
radius of 695.508 +- .026 Mm. Annual averages of the radius are identical
within the measurement error of +- .037 Mm.Comment: 6 pages, 2 figures Submitted to Astrophys. J. Lett., March 9 1998
Uses AASTeX Macro package aas2pp
Signatures of Emerging Subsurface Structures in Acoustic Power Maps
We show that under certain conditions, subsurface structures in the solar
interior can alter the average acoustic power observed at the photosphere above
them. By using numerical simulations of wave propagation, we show that this
effect is large enough for it to be potentially used for detecting emerging
active regions before they appear on the surface. In our simulations,
simplified subsurface structures are modeled as regions with enhanced or
reduced acoustic wave speed. We investigate the dependence of the acoustic
power above a subsurface region on the sign, depth, and strength of the wave
speed perturbation. Observations from the Solar and Heliospheric
Observatory/Michelson Doppler Imager (SOHO/MDI) prior and during the emergence
of NOAA active region 10488 are used to test the use of acoustic power as a
potential precursor of magnetic flux emergence.Comment: 7 pages, 5 figures, accepted for publication in Solar Physics on 21
March 201
Oscillations in the Sun with SONG: Setting the scale for asteroseismic investigations
Context. We present the first high-cadence multi-wavelength radial-velocity
observations of the Sun-as-a-star, carried out during 57 consecutive days using
the stellar \'echelle spectrograph at the Hertzsprung SONG Telescope operating
at the Teide Observatory. Aims. The aim was to produce a high-quality data set
and reference values for the global helioseismic parameters {\nu_{max}}, and
{\Delta \nu} of the solar p-modes using the SONG instrument. The obtained data
set or the inferred values should then be used when the scaling relations are
applied to other stars showing solar-like oscillations which are observed with
SONG or similar instruments. Methods. We used different approaches to analyse
the power spectrum of the time series to determine {\nu_{max}}; simple Gaussian
fitting and heavy smoothing of the power spectrum. {\Delta\nu} was determined
using the method of autocorrelation of the power spectrum. The amplitude per
radial mode was determined using the method described in Kjeldsen et al.
(2008). Results. We found the following values for the solar oscillations using
the SONG spectrograph: {\nu_{max}} = 3141 {\pm} 12 {\mu}Hz, {\Delta\nu} =
134.98 {\pm} 0.04 {\mu}Hz and an average amplitude of the strongest radial
modes of 16.6 {\pm} 0.4 cm/s. These values are consistent with previous
measurements with other techniques.Comment: 5 pages, 5 figures, letter accepted for A&
Ulva fenestrata protein â Comparison of three extraction methods with respect to protein yield and protein quality
Seaweed is gaining attention as a possible alternative and sustainable source of proteins. This study investigates three protein extraction methods and their effect on protein yield and quality when applied to Ulva fenestrata. Two of the methods included alkaline extractions (pH-shifts); one version solubilizing the proteins at pH 8.5 and one solubilizing them at pH 8.5 followed by pH 12 (pH 8.5 + 12). The third method was a mechanical pressing, using a double screw press. All extraction methods were followed by isoelectric precipitation to concentrate the proteins. Extraction at pH 8.5 gave the significantly highest total protein yield after the isoelectric precipitation, followed by extraction at pH 8.5 + 12 and lastly mechanical extraction gave the lowest yield. Proteins extracted with both alkaline methods had a significantly higher solubility at pH 7 and pH 9, compared to proteins from the mechanical pressing. There were no significant differences between the three methods in total D/L-amino acid ratio. Amino acid cross-links measured as lysinoalanine (LAL) and lanthionine (LAN) where found in significantly higher amounts in alkali-extracted proteins compared to mechanically extracted, however not to a degree that expect to compromise functional or nutritional quality. Further, no significant difference in protein in vitro digestibility was found between extraction methods. In conclusion, results indicated that protein extraction at pH 8.5 can be recommended, especially regarding total protein yield and solubility of the final protein extract
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