2,374 research outputs found
Accurate fundamental parameters for Lower Main Sequence Stars
We derive an empirical effective temperature and bolometric luminosity
calibration for G and K dwarfs, by applying our own implementation of the
InfraRed Flux Method to multi-band photometry. Our study is based on 104 stars
for which we have excellent BVRIJHK photometry, excellent parallaxes and good
metallicities. Colours computed from the most recent synthetic libraries
(ATLAS9 and MARCS) are found to be in good agreement with the empirical colours
in the optical bands, but some discrepancies still remain in the infrared.
Synthetic and empirical bolometric corrections also show fair agreement. A
careful comparison to temperatures, luminosities and angular diameters obtained
with other methods in literature shows that systematic effects still exist in
the calibrations at the level of a few percent. Our InfraRed Flux Method
temperature scale is 100K hotter than recent analogous determinations in the
literature, but is in agreement with spectroscopically calibrated temperature
scales and fits well the colours of the Sun. Our angular diameters are
typically 3% smaller when compared to other (indirect) determinations of
angular diameter for such stars, but are consistent with the limb-darkening
corrected predictions of the latest 3D model atmospheres and also with the
results of asteroseismology. Very tight empirical relations are derived for
bolometric luminosity, effective temperature and angular diameter from
photometric indices. We find that much of the discrepancy with other
temperature scales and the uncertainties in the infrared synthetic colours
arise from the uncertainties in the use of Vega as the flux calibrator. Angular
diameter measurements for a well chosen set of G and K dwarfs would go a long
way to addressing this problem.Comment: 34 pages, 20 figures. Accepted by MNRAS. Landscape table available
online at http://users.utu.fi/luccas/IRFM
Testing Asteroseismic Radii of Dwarfs and Subgiants with Kepler and Gaia
We test asteroseismic radii of Kepler main-sequence and subgiant stars by
deriving their parallaxes which are compared with those of the first Gaia data
release. We compute radii based on the asteroseismic scaling relations as well
as by fitting observed oscillation frequencies to stellar models for a subset
of the sample, and test the impact of using effective temperatures from either
spectroscopy or the infrared flux method. An offset of 3%, showing no
dependency on any stellar parameters, is found between seismic parallaxes
derived from frequency modelling and those from Gaia. For parallaxes based on
radii from the scaling relations, a smaller offset is found on average;
however, the offset becomes temperature dependent which we interpret as
problems with the scaling relations at high stellar temperatures. Using the
hotter infrared flux method temperature scale, there is no indication that
radii from the scaling relations are inaccurate by more than about 5%. Taking
the radii and masses from the modelling of individual frequencies as reference
values, we seek to correct the scaling relations for the observed temperature
trend. This analysis indicates that the scaling relations systematically
overestimate radii and masses at high temperatures, and that they are accurate
to within 5% in radius and 13% in mass for main-sequence stars with
temperatures below 6400 K. However, further analysis is required to test the
validity of the corrections on a star-by-star basis and for more evolved stars.Comment: 12 pages, 9 figures. Accepted for publication in MNRA
Clusters and Groups of Galaxies in the Simulated Local Universe
We compare the properties of galaxy groups extracted from the Updated Zwicky
Catalogue (UZC) with those of groups extracted from N-body simulations of the
local Universe, in a LambdaCDM and a tauCDM cosmology. In the simulations, the
initial conditions of the dark matter density field are set to reproduce the
present time distribution of the galaxies within 80 Mpc/h from the Milky Way.
These initial conditions minimize the uncertainty originated by cosmic
variance, which has affected previous analyses of this small volume of the
Universe. The simulations also model the evolution of the photometric
properties of the galaxy population with semi-analytic prescriptions. The
models yield a galaxy luminosity function sensibly different from that of the
UZC and are unable to reproduce the distribution of groups and their luminosity
content. The discrepancy between the model and the UZC reduces substantially,
if we redistribute the luminosity among the galaxies in the simulation
according to the UZC luminosity function while preserving the galaxy luminosity
rank. The modified LambdaCDM model provides the best match to the UZC: the
abundances of groups by harmonic radius, velocity dispersion, mass and
luminosity are consistent with observations. We find that this model also
reproduces the halo occupation number of groups and clusters. However, the
large-scale distribution of groups is marginally consistent with the UZC and
the redshift-space correlation function of galaxies on scales larger than 6
Mpc/h is still more than 3-sigma smaller than observed. We conclude that
reproducing the properties of the observed groups certainly requires a more
sophisticated treatment of galaxy formation, and possibly an improvement of the
dark matter model.Comment: 20 pages, 18 figures, accepted by MNRAS. Minor revisions according to
referee's comments. Conclusions unchange
'Rapid fire' spectroscopy of Kepler solar-like oscillators
The NASA Kepler mission has been continuously monitoring the same field of
the sky since the successful launch in March 2009, providing high-quality
stellar lightcurves that are excellent data for asteroseismology, far superior
to any other observations available at the present. In order to make a
meaningful analysis and interpretation of the asteroseismic data, accurate
fundamental parameters for the observed stars are needed. The currently
available parameters are quite uncertain as illustrated by e.g. Thygesen et al.
(A&A 543, A160, 2012), who found deviations as extreme as 2.0 dex in [Fe/H] and
log g, compared to catalogue values. Thus, additional follow-up observations
for these targets are needed in order to put firm limits on the parameter space
investigated by the asteroseismic modellers. Here, we propose a metod for
deriving accurate metallicities of main sequence and subgiant solar-like
oscillators from medium resolution spectra with a moderate S/N. The method
takes advantage of the additional constraints on the fundamental parameters,
available from asteroseismology and multi-color photometry. The approach
enables us to reduce the analysis overhead significantly when doing spectral
synthesis, which in turn will increases the efficiency of follow-up
observations.Comment: 3 pages, 2 figures. Proceedings from Asteroseismology of Stellar
Populations in the Milky Way 2013 to appear in 'Astrophysics and Space
Science Proceedings
The Swiss Tropical and Public Health Institute: past, present and future
Compared internationally, the history of the Swiss Tropical and Public Health Institute (Swiss TPH) is unusual. Founded in 1944, at a time of utmost isolation, it was a response to specific needs of the government of Switzerland during the Second World War. In 1943, the Swiss Federal Council approached universities in Switzerland and asked them to submit project proposal that had the potential to mitigate possible post-war unemployment and threatening economic isolation. Members of the University of Basel proposed to establish a Swiss Tropical Institute (today: Swiss TPH). With its harbour at the River Rhine, Basel was an important international transport hub. The city was and still is the headquarters of important pharmaceutical companies, such as Novartis Pharma AG and F. Hoffmann-La Roche AG, which were looking for new markets overseas. Last but not least, scientific expeditions to Africa were rather common in the 19(th) and the beginning of the 20(th) century for members of Basel's bourgeoisie. Initially, Swiss TPH focused primarily on basic research into diseases of poverty, but over the years it has developed into an important player in public, international and global health. This article sees the development of the institute as a reflection of the visions of its directors from the founder Professor Rudolf Geigy to Professor Jurg Utzinger, who is the current Swiss TPH director. It includes interviews with the four latest of them, discussing their experiences and attempts to adapt the institute to an ever changing global environment. From these lessons learnt we hope to gain insights that could be relevant for today's leaders of scientific institutes; foster public-private partnerships and contribute to solve some of the most pressing global health challenges
The dissimilar chemical composition of the planet-hosting stars of the XO-2 binary system
Using high-quality spectra of the twin stars in the XO-2 binary system, we
have detected significant differences in the chemical composition of their
photospheres. The differences correlate strongly with the elements' dust
condensation temperature. In XO-2N, volatiles are enhanced by about 0.015 dex
and refractories are overabundant by up to 0.090 dex. On average, our error bar
in relative abundance is 0.012 dex. We present an early metal-depletion
scenario in which the formation of the gas giant planets known to exist around
these stars is responsible for a 0.015 dex offset in the abundances of all
elements while 20 M_Earth of non-detected rocky objects that formed around
XO-2S explain the additional refractory-element difference. An alternative
explanation involves the late accretion of at least 20 M_Earth of planet-like
material by XO-2N, allegedly as a result of the migration of the hot Jupiter
detected around that star. Dust cleansing by a nearby hot star as well as age
or Galactic birthplace effects can be ruled out as valid explanations for this
phenomenon.Comment: ApJ, in press. Complete linelist (Table 3) available in the "Other
formats -> Source" downloa
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