686 research outputs found
Microplastic exposure increases predictability of predator avoidance strategies in hermit crabs
The contamination of natural systems with plastic debris has become one of the most pressing global environmental issues. Microplastics (MPs) are of particular concern because their ubiquity and small size make them available for ingestion by a range of aquatic biota. MP exposure studies are hence proliferating rapidly but are typically limited to the analyses of population-level responses in toxicity endpoints across treatments. Potential contaminant-induced alterations in behavioural patterns, however, could manifest on numerous levels of variation: at the population-level, between individuals and within individuals. Here, we used repeated measures on startle response durations – a risk-avoidance mechanism – in European hermit crabs, Pagurus bernhardus, to measure behavioural responses to MP exposure across multiple levels of variation. We found that MP exposure led to a significant decrease of startle duration at the population-level as well as a reduction of intra-individual variation. In other words, crabs became less risk averse on average and their behaviour became more predictable with increasing MP concentrations. Collectively, our findings indicate that MP pollution might increase susceptibility to predation in hermit crabs
KIC 4768731: a bright long-period roAp star in theKeplerfield
We report the identification of 61.45 d−1 (711.2 μHz) oscillations, with amplitudes of 62.6 μmag, in KIC 4768731 (HD 225914) using Kepler photometry. This relatively bright (V = 9.17) chemically peculiar star with spectral type A5 Vp SrCr(Eu) has previously been found to exhibit rotational modulation with a period of 5.21 d. Fourier analysis reveals a simple dipole pulsator with an amplitude that has remained stable over a 4-yr time span, but with a frequency that is variable. Analysis of high-resolution spectra yields stellar parameters of Teff = 8100 ± 200 K, log g = 4.0 ± 0.2, [Fe/H] = +0.31 ± 0.24 and v sin i = 14.8 ± 1.6 km s−1.
Line profile variations caused by rotation are also evident. Lines of Sr, Cr, Eu, Mg and Si are strongest when the star is brightest, while Y and Ba vary in antiphase with the other elements. The abundances of rare earth elements are only modestly enhanced compared to other roAp stars of similar Teff and log g. Radial velocities in the literature suggest a significant change over the past 30 yr, but the radial velocities presented here show no significant change over a period of 4 yr
Spectral analysis of Kepler SPB and Beta Cep candidate stars
We determine the fundamental parameters of SPB and Beta Cep candidate stars
observed by the Kepler satellite mission and estimate the expected types of
non-radial pulsators by comparing newly obtained high-resolution spectra with
synthetic spectra computed on a grid of stellar parameters assuming LTE and
check for NLTE effects for the hottest stars. For comparison, we determine Teff
independently from fitting the spectral energy distribution of the stars
obtained from the available photometry. We determine Teff, log(g),
micro-turbulent velocity, vsin(i), metallicity, and elemental abundance for 14
of the 16 candidate stars, two of the stars are spectroscopic binaries. No
significant influence of NLTE effects on the results could be found. For hot
stars, we find systematic deviations of the determined effective temperatures
from those given in the Kepler Input Catalogue. The deviations are confirmed by
the results obtained from ground-based photometry. Five stars show reduced
metallicity, two stars are He-strong, one is He-weak, and one is Si-strong. Two
of the stars could be Beta Cep/SPB hybrid pulsators, four SPB pulsators, and
five more stars are located close to the borders of the SPB instability region.Comment: 10 pages, 10 figures, 10 table
MOST light-curve analysis of the gamma Dor pulsator HR 8799, showing resonances and amplitude variations
Context: The central star of the HR 8799 system is a gamma Doradus-type
pulsator. The system harbours four planetary-mass companions detected by direct
imaging, and is a good solar system analogue. The masses of the companions are
not known accurately, because the estimation depends strongly on the age of the
system, which is also not known with sufficient accuracy. Asteroseismic studies
of the star might help to better constrain the age of HR 8799. We organized an
extensive photometric and multi-site spectroscopic observing campaign for
studying the pulsations of the central star.
Aims: The aim of the present study is to investigate the pulsation properties
of HR 8799 in detail via the ultra-precise 47-d-long nearly continuous
photometry obtained with the MOST space telescope, and to find as many
independent pulsation modes as possible, which is the prerequisite of an
asteroseismic age determination.
Methods: We carried out Fourier analysis of the wide-band photometric time
series.
Results: We find that resonance and sudden amplitude changes characterize the
pulsation of HR 8799. The dominant frequency is always at f1 = 1.978 c/d. Many
multiples of one ninth of the dominant frequency appear in the Fourier spectrum
of the MOST data: n/9 f1, where n={1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14, 17,
18}. Our analysis also reveals that many of these peaks show strong amplitude
decrease and phase variations even on the 47-d time-scale. The dependencies
between the pulsation frequencies of HR 8799 make the planned subsequent
asteroseismic analysis rather difficult. We point out some resemblance between
the light curve of HR 8799 and the modulated pulsation light curves of Blazhko
RR Lyrae stars.Comment: Accepted for publication in Astronomy and Astrophysics. 8 pages, 4
figure
The orbits of subdwarf B + main-sequence binaries. I: The sdB+G0 system PG 1104+243
The predicted orbital period histogram of an sdB population is bimodal with a
peak at short ( 250 days) periods. Observationally, there
are many short-period sdB systems known, but only very few long-period sdB
binaries are identified. As these predictions are based on poorly understood
binary interaction processes, it is of prime importance to confront the
predictions to observational data. In this contribution we aim to determine the
absolute dimensions of the long-period sdB+MS binary system PG1104+243.
High-resolution spectroscopy time-series were obtained with HERMES at the
Mercator telescope at La Palma, and analyzed to obtain radial velocities of
both components. Photometry from the literature was used to construct the
spectral energy distribution (SED) of the binary. Atmosphere models were used
to fit this SED and determine the surface gravity and temperature of both
components. The gravitational redshift provided an independent confirmation of
the surface gravity of the sdB component. An orbital period of 753 +- 3 d and a
mass ratio of q = 0.637 +- 0.015 were found from the RV-curves. The sdB
component has an effective temperature of Teff = 33500 +- 1200 K and a surface
gravity of logg = 5.84 +- 0.08 dex, while the cool companion is found to be a
G-type star with Teff = 5930 +- 160 K and logg = 4.29 +- 0.05 dex. Assuming a
canonical mass of Msdb = 0.47 Msun, the MS component has a mass of 0.74 +- 0.07
Msun, and its Teff corresponds to what is expected for a terminal age
main-sequence star with sub-solar metalicity. PG1104+243 is the first
long-period sdB binary in which accurate physical parameters of both components
could be determined, and the first sdB binary in which the gravitational
redshift is measured. Furthermore, PG1104+243 is the first sdB+MS system that
shows consistent evidence for being formed through stable Roche-lobe overflow.Comment: Accepted by A&A on 05-10-201
Domesticating Fears and Fantasies of ‘the East’: integrating the Ottoman legacy within European heritage
'Europe' has no fixed geographical, historical, religious or cultural boundaries. Claims for the existence of European civilization as a discrete construct are continually made yet dissolve on close scrutiny. Here, we examine these claims at one of the grandest points of existential crisis and belonging for Europe, the relationship with the 'Other within': Turkey, the Balkans and Ottoman heritage in Europe. Through a hybrid semiotic and Foucauldian analysis of catalogues of eight high-profile exhibitions in the United Kingdom, Turkey, Belgium and Portugal we argue that an unsettled discursive struggle is at play, in which one 'Europe' articulates 'reconciliation' of profound civilizational difference while another, Ottoman, 'Europe' stakes a claim of right as an intrinsic component of what it means to be European in a contemporary context. We attempt to trace the role of museum marketing in the perennial accommodation/exclusion of the Ottoman Empire as an intrinsic component in the diversity of Europe’s cultural heritage
Spectrum Analysis of Bright Kepler Gamma Doradus Candidate Stars
Ground-based spectroscopic follow-up observations of the pulsating stars
observed by the Kepler satellite mission are needed for their asteroseismic
modelling. We aim to derive the fundamental parameters for a sample of 26 Gamma
Doradus candidate stars observed by the Kepler satellite mission to accomplish
one of the required preconditions for their asteroseismic modelling and to
compare our results with the types of pulsators expected from the existing
light curve analysis. We use the spectrum synthesis method to derive the
fundamental parameters like Teff, logg, [M/H], and vsini from newly obtained
spectra and compute the spectral energy distribution from literature photometry
to get an independent measure of Teff. We find that most of the derived Teff
values agree with the values given in the Kepler Input Catalogue. According to
their positions in the HR-diagram three stars are expected Gamma Dor stars, ten
stars are expected Delta Sct stars, and seven stars are possibly Delta Sct
stars at the hot border of the instability strip. Four stars in our sample are
found to be spectroscopic binary candidates and four stars have very low
metallicity where two show about solar C abundance. Six of the 10 stars located
in the Delta Sct instability region of the HR-diagram show both Delta Sct and
Gamma Dor-type oscillations in their light curves implying that Gamma Dor-like
oscillations are much more common among the Delta Sct stars than predicted by
theory. Moreover, seven stars showing periods in the Delta Sct and the Delta
Sct-Gamma Dor range in their light curves are located in the HR-diagram left of
the blue edge of the theoretical Delta Sct instability strip. The consistency
of these findings with recent investigations based on high-quality Kepler data
implies the need for a revision of the theoretical Gamma Dor and Delta Sct
instability strips.Comment: 10 pages, 3 figures, 7 tables; accepted for publication in MNRA
On the merit of a Central Limit Theorem-based approximation in statistical physics
The applicability conditions of a recently reported Central Limit
Theorem-based approximation method in statistical physics are investigated and
rigorously determined. The failure of this method at low and intermediate
temperature is proved as well as its inadequacy to disclose quantum
criticalities at fixed temperatures. Its high temperature predictions are in
addition shown to coincide with those stemming from straightforward appropriate
expansions up to (k_B T)^(-2). Our results are clearly illustrated by comparing
the exact and approximate temperature dependence of the free energy of some
exemplary physical systems.Comment: 12 pages, 1 figur
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