1,438 research outputs found
Solar-like oscillations in the G9.5 subgiant beta Aquilae
An interesting asteroseismic target is the G9.5 IV solar-like star beta Aql.
This is an ideal target for asteroseismic investigations, because precise
astrometric measurements are available from Hipparcos that greatly help in
constraining the theoretical interpretation of the results. The star was
observed during six nights in August 2009 by means of the high-resolution
\'echelle spectrograph SARG operating with the TNG 3.58 m Italian telescope on
the Canary Islands, exploiting the iodine cell technique. We present the result
and the detailed analysis of high-precision radial velocity measurements, where
the possibility of detecting time individual p-mode frequencies for the first
and deriving their corresponding asymptotic values will be discussed. The
time-series analysis carried out from \sim 800 collected spectra shows the
typical p-mode frequency pattern with a maximum centered at 416 \muHz. In the
frequency range 300 - 600 \muHz we identified for the first time six high S/N
(\gtrsim 3.5) modes with l = 0,2 and 11 < n < 16 and three possible candidates
for mixed modes (l = 1), although the p-mode identification for this type of
star appears to be quite difficult owing to a substantial presence of avoided
crossings. The large frequency separation and the surface term from the set of
identified modes by means of the asymptotic relation were derived for the first
time. Their values are \Delta \nu = 29.56 \pm 0.10 \muHz and \epsilon = 1.29
\pm 0.04, consistent with expectations. The most likely value for the small
separation is \delta\nu_{02} = 2.55 \pm 0.71 \muHz.Comment: 8 pages, 8 figures, 3 tables, accepted by A&
First Attempt at Spectroscopic Detection of Gravity Modes in a Long-Period Pulsating Subdwarf B Star -- PG 1627+017
In the first spectroscopic campaign for a PG 1716 variable (or long-period
pulsating subdwarf B star), we succeeded in detecting velocity variations due
to g-mode pulsations at a level of 1.0-1.5 km/s.The observations were obtained
during 40 nights on 2-m class telescopes in Arizona, South Africa,and
Australia. The target,PG1627+017, is one of the brightest and largest amplitude
stars in its class.It is also the visible component of a post-common envelope
binary.Our final radial velocity data set includes 84 hours of time-series
spectroscopy over a time baseline of 53 days. Our derived radial velocity
amplitude spectrum, after subtracting the orbital motion, shows three potential
pulsational modes 3-4 sigma above the mean noise level, at 7201.0s,7014.6s and
7037.3s.Only one of the features is statistically likely to be real,but all
three are tantalizingly close to, or a one day alias of, the three strongest
periodicities found in the concurrent photometric campaign. We further
attempted to detect pulsational variations in the Balmer line amplitudes. The
single detected periodicity of 7209 s, although weak, is consistent with
theoretical expectations as a function of wavelength.Furthermore, it allows us
to rule out a degree index of l= 3 or l= 5 for that mode. Given the extreme
weakness of g-mode pulsations in these stars,we conclude that anything beyond
simply detecting their presence will require larger telescopes,higher
efficiency spectral monitoring over longer time baselines,improved longitude
coverage, and increased radial velocity precision.Comment: 39 pages, 9 figures, 4 tables, ApJ accepted. See postscript for full
abtrac
A search for solar-like oscillations in K giants in the globular cluster M4
To expand the range in the colour-magnitude diagram where asteroseismology
can be applied, we organized a photometry campaign to find evidence for
solar-like oscillations in giant stars in the globular cluster M4. The aim was
to detect the comb-like p-mode structure characteristic for solar-like
oscillations in the amplitude spectra. The two dozen main target stars are in
the region of the bump stars and have luminosities in the range 50-140 Lsun. We
collected 6160 CCD frames and light curves for about 14000 stars were
extracted. We obtain high quality light curves for the K giants, but no clear
oscillation signal is detected. High precision differential photometry is
possible even in very crowded regions like the core of M4. Solar-like
oscillations are probably present in K giants, but the amplitudes are lower
than classical scaling laws predict.Comment: 14 pages, 16 figures, accepted for publication in A&
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
The MultiSite Spectroscopic Telescope campaign: 2m spectroscopy of the V361 Hya variable PG1605+072
We present results and analysis for the 2m spectroscopic part of the
MultiSite Spectroscopic Telescope (MSST) campaign undertaken in May/June 2002.
The goal of the project was to observe the pulsating subdwarf B star PG1605+072
simultaneously in velocity and photometry and to resolve as many of the >50
known modes as possible, which will allow a detailed asteroseismological
analysis. We have obtained over 150 hours of spectroscopy, leading to an
unprecedented noise level of only 207m/s. We report here the detection of 20
frequencies in velocity, with two more likely just below our detection
threshold. In particular, we detect 6 linear combinations, making PG1605+072
only the second star known to show such frequencies in velocity. We investigate
the phases of these combinations and their parent modes and find relationships
between them that cannot be easily understood based on current theory. These
observations, when combined with our simultaneous photometry, should allow
asteroseismology of this most complicated of sdB pulsators.Comment: 9 pages, 5 figures, accepted for publication in A&A; Figure 1 at
lower resolution than accepted versio
Three ways to solve the orbit of KIC11558725: a 10 day beaming sdB+WD binary with a pulsating subdwarf
The recently discovered subdwarf B (sdB) pulsator KIC11558725 features a rich
g-mode frequency spectrum, with a few low-amplitude p-modes at short periods,
and is a promising target for a seismic study aiming to constrain the internal
structure of this star, and of sdB stars in general.
We have obtained ground-based spectroscopic Balmer-line radial-velocity
measurements of KIC11558725, spanning the 2010 and 2011 observing seasons. From
these data we have discovered that KIC11558725 is a binary with period P=10.05
d, and that the radial-velocity amplitude of the sdB star is 58 km/s.
Consequently the companion of the sdB star has a minimum mass of 0.63 M\odot,
and is therefore most likely an unseen white dwarf.
We analyse the near-continuous 2010-2011 Kepler light curve to reveal orbital
Doppler-beaming light variations at the 238 ppm level, which is consistent with
the observed spectroscopic orbital radial-velocity amplitude of the subdwarf.
We use the strongest 70 pulsation frequencies in the Kepler light curve of the
subdwarf as clocks to derive a third consistent measurement of the orbital
radial-velocity amplitude, from the orbital light-travel delay.
We use our high signal-to-noise average spectra to study the atmospheric
parameters of the sdB star, deriving Teff = 27 910K and log g = 5.41 dex, and
find that carbon, nitrogen and oxygen are underabundant relative to the solar
mixture.
Furthermore, we extract more than 160 significant frequencies from the Kepler
light curve. We investigate the pulsation frequencies for expected period
spacings and rotational splittings. We find period-spacing sequences of
spherical-harmonic degrees \ell=1 and \ell=2, and we associate a large fraction
of the g-modes in KIC11558725 with these sequences. From frequency splittings
we conclude that the subdwarf is rotating subsynchronously with respect to the
orbit
Precise Modeling of the Exoplanet Host Star and CoRoT Main Target HD 52265
This paper presents a detailed and precise study of the characteristics of
the Exoplanet Host Star and CoRoT main target HD 52265, as derived from
asteroseismic studies. The results are compared with previous estimates, with a
comprehensive summary and discussion. The basic method is similar to that
previously used by the Toulouse group for solar-type stars. Models are computed
with various initial chemical compositions and the computed p-mode frequencies
are compared with the observed ones. All models include atomic diffusion and
the importance of radiative accelerations is discussed. Several tests are used,
including the usual frequency combinations and the fits of the \'echelle
diagrams. The possible surface effects are introduced and discussed. Automatic
codes are also used to find the best model for this star (SEEK, AMP) and their
results are compared with that obtained with the detailed method. We find
precise results for the mass, radius and age of this star, as well as its
effective temperature and luminosity. We also give an estimate of the initial
helium abundance. These results are important for the characterization of the
star-planet system.Comment: 9 pages, 6 figures, 7 tables, to be published in Astronomy and
Astrophysic
K-shell photoionization of ground-state Li-like carbon ions [C]: experiment, theory and comparison with time-reversed photorecombination
Absolute cross sections for the K-shell photoionization of ground-state
Li-like carbon [C(1s2s S)] ions were measured by employing the
ion-photon merged-beams technique at the Advanced Light Source. The energy
ranges 299.8--300.15 eV, 303.29--303.58 eV and 335.61--337.57 eV of the
[1s(2s2p)P]P, [1s(2s2p)P]P and [(1s2s)S 3p]P
resonances, respectively, were investigated using resolving powers of up to
6000. The autoionization linewidth of the [1s(2s2p)P]P resonance was
measured to be meV and compares favourably with a theoretical result
of 26 meV obtained from the intermediate coupling R-Matrix method. The present
photoionization cross section results are compared with the outcome from
photorecombination measurements by employing the principle of detailed balance.Comment: 3 figures and 2 table
Unaccounted uncertainty from qPCR efficiency estimates entails uncontrolled false positive rates
BACKGROUND: Accurate adjustment for the amplification efficiency (AE) is an important part of real-time quantitative polymerase chain reaction (qPCR) experiments. The most commonly used correction strategy is to estimate the AE by dilution experiments and use this as a plug-in when efficiency correcting the ΔΔC(q). Currently, it is recommended to determine the AE with high precision as this plug-in approach does not account for the AE uncertainty, implicitly assuming an infinitely precise AE estimate. Determining the AE with such precision, however, requires tedious laboratory work and vast amounts of biological material. Violation of the assumption leads to overly optimistic standard errors of the ΔΔC(q), confidence intervals, and p-values which ultimately increase the type I error rate beyond the expected significance level. As qPCR is often used for validation it should be a high priority to account for the uncertainty of the AE estimate and thereby properly bounding the type I error rate and achieve the desired significance level. RESULTS: We suggest and benchmark different methods to obtain the standard error of the efficiency adjusted ΔΔC(q) using the statistical delta method, Monte Carlo integration, or bootstrapping. Our suggested methods are founded in a linear mixed effects model (LMM) framework, but the problem and ideas apply in all qPCR experiments. The methods and impact of the AE uncertainty are illustrated in three qPCR applications and a simulation study. In addition, we validate findings suggesting that MGST1 is differentially expressed between high and low abundance culture initiating cells in multiple myeloma and that microRNA-127 is differentially expressed between testicular and nodal lymphomas. CONCLUSIONS: We conclude, that the commonly used efficiency corrected quantities disregard the uncertainty of the AE, which can drastically impact the standard error and lead to increased false positive rates. Our suggestions show that it is possible to easily perform statistical inference of ΔΔC(q), whilst properly accounting for the AE uncertainty and better controlling the false positive rate
The mass and age of the first SONG target: the red giant 46 LMi
Context. The Stellar Observation Network Group (SONG) is an initiative to build a worldwide network of 1m telescopes with high-precision radial-velocity spectrographs. Here we analyse the first radial-velocity time series of a red-giant star measured by the SONG
telescope at Tenerife. The asteroseismic results demonstrate a major increase in the achievable precision of the parameters for red-giant
stars obtainable from ground-based observations. Reliable tests of the validity of these results are needed, however, before the accuracy
of the parameters can be trusted.
Aims. We analyse the first SONG time series for the star 46 LMi, which has a precise parallax and an angular diameter measured from interferometry, and therefore a good determination of the stellar radius. We use asteroseismic scaling relations to obtain an accurate mass, and modelling to determine the age.
Methods. A 55-day time series of high-resolution, high S/N spectra were obtained with the first SONG telescope. We derive the asteroseismic parameters by analysing the power spectrum. To give a best guess on the large separation of modes in the power spectrum, we have applied a new method which uses the scaling of Kepler red-giant stars to 46 LMi.
Results. Several methods have been applied: classical estimates, seismic methods using the observed time series, and model calculations to derive the fundamental parameters of 46 LMi. Parameters determined using the different methods are consistent within the uncertainties. We find the following values for the mass M (scaling), radius R (classical), age (modelling), and surface gravity (combining mass and radius): M = 1.09 ± 0.04 M⊙, R = 7.95 ± 0.11 R⊙ age t = 8.2 ± 1.9 Gy, and log g = 2.674 ± 0.013.
Conclusions. The exciting possibilities for ground-based asteroseismology of solar-like oscillations with a fully robotic network have been illustrated with the results obtained from just a single site of the SONG network. The window function is still a severe problem which will be solved when there are more nodes in the network
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