566 research outputs found
The CoRoT B-type binary HD50230: a prototypical hybrid pulsator with g-mode period and p-mode frequency spacings
B-type stars are promising targets for asteroseismic modelling, since their
frequency spectrum is relatively simple.
We deduce and summarise observational constraints for the hybrid pulsator,
HD50230, earlier reported to have deviations from a uniform period spacing of
its gravity modes. The combination of spectra and a high-quality light curve
measured by the CoRoT satellite allow a combined approach to fix the position
of HD50230 in the HR diagram.
To describe the observed pulsations, classical Fourier analysis was combined
with short-time Fourier transformations and frequency spacing analysis
techniques. Visual spectra were used to constrain the projected rotation rate
of the star and the fundamental parameters of the target. In a first
approximation, the combined information was used to interpret multiplets and
spacings to infer the true surface rotation rate and a rough estimate of the
inclination angle.
We identify HD50230 as a spectroscopic binary and characterise the two
components. We detect the simultaneous presence of high-order g modes and
low-order p and g-modes in the CoRoT light curve, but were unable to link them
to line profile variations in the spectroscopic time series. We extract the
relevant information from the frequency spectrum, which can be used for seismic
modelling, and explore possible interpretations of the pressure mode spectrum.Comment: 26 pages, 12+6 figures, accepted for publication in Astronomy and
Astrophysic
The CoRoT target HD175726: an active star with weak solar-like oscillations
Context. The CoRoT short runs give us the opportunity to observe a large
variety of late-type stars through their solar-like oscillations. We report
observations of the star HD175726 that lasted for 27 days during the first
short run of the mission. The time series reveals a high-activity signal and
the power spectrum presents an excess due to solar-like oscillations with a low
signal-to-noise ratio. Aims. Our aim is to identify the most efficient tools to
extract as much information as possible from the power density spectrum.
Methods. The most productive method appears to be the autocorrelation of the
time series, calculated as the spectrum of the filtered spectrum. This method
is efficient, very rapid computationally, and will be useful for the analysis
of other targets, observed with CoRoT or with forthcoming missions such as
Kepler and Plato. Results. The mean large separation has been measured to be
97.2+-0.5 microHz, slightly below the expected value determined from solar
scaling laws.We also show strong evidence for variation of the large separation
with frequency. The bolometric mode amplitude is only 1.7+-0.25 ppm for radial
modes, which is 1.7 times less than expected. Due to the low signal-to-noise
ratio, mode identification is not possible for the available data set of
HD175726. Conclusions. This study shows the possibility of extracting a seismic
signal despite a signal-to-noise ratio of only 0.37. The observation of such a
target shows the efficiency of the CoRoT data, and the potential benefit of
longer observing runs.Comment: 8 pages. Accepted in A&
Seismic and spectroscopic characterization of the solar-like pulsating CoRoT target HD 49385
The star HD 49385 is the first G-type solar-like pulsator observed in the
seismology field of the space telescope CoRoT. The satellite collected 137 days
of high-precision photometric data on this star, confirming that it presents
solar-like oscillations. HD 49385 was also observed in spectroscopy with the
NARVAL spectrograph in January 2009. Our goal is to characterize HD 49385 using
both spectroscopic and seismic data. The fundamental stellar parameters of HD
49385 are derived with the semi-automatic software VWA, and the projected
rotational velocity is estimated by fitting synthetic profiles to isolated
lines in the observed spectrum. A maximum likelihood estimation is used to
determine the parameters of the observed p modes. We perform a global fit, in
which modes are fitted simultaneously over nine radial orders, with degrees
ranging from l=0 to l=3 (36 individual modes). Precise estimates of the
atmospheric parameters (Teff, [M/H], log g) and of the vsini of HD 49385 are
obtained. The seismic analysis of the star leads to a clear identification of
the modes for degrees l=0,1,2. Around the maximum of the signal (nu=1013
microHz), some peaks are found significant and compatible with the expected
characteristics of l=3 modes. Our fit yields robust estimates of the
frequencies, linewidths and amplitudes of the modes. We find amplitudes of
about 5.6 +/- 0.8 ppm for radial modes at the maximum of the signal. The
lifetimes of the modes range from one day (at high frequency) to a bit more
than two days (at low frequency). Significant peaks are found outside the
identified ridges and are fitted. They are attributed to mixed modes.Comment: 13 pages, 14 figures, accepted in A&
Pervasive protein thermal stability variation during the cell cycle
Quantitative mass spectrometry has established proteome-wide regulation of protein abundance and post-translational modifications in various biological processes. Here, we used quantitative mass spectrometry to systematically analyze the thermal stability and solubility of proteins on a proteome-wide scale during the eukaryotic cell cycle. We demonstrate pervasive variation of these biophysical parameters with most changes occurring in mitosis and G1. Various cellular pathways and components vary in thermal stability, such as cell-cycle factors, polymerases, and chromatin remodelers. We demonstrate that protein thermal stability serves as a proxy for enzyme activity, DNA binding, and complex formation in situ. Strikingly, a large cohort of intrinsically disordered and mitotically phosphorylated proteins is stabilized and solubilized in mitosis, suggesting a fundamental remodeling of the biophysical environment of the mitotic cell. Our data represent a rich resource for cell, structural, and systems biologists interested in proteome regulation during biological transitions
CoRoT's view of newly discovered B-star pulsators: results for 358 candidate B pulsators from the initial run's exoplanet field data
We search for new variable B-type pulsators in the CoRoT data assembled
primarily for planet detection, as part of CoRoT's Additional Programme. We aim
to explore the properties of newly discovered B-type pulsators from the
uninterrupted CoRoT space-based photometry and to compare them with known
members of the Beta Cep and slowly pulsating B star (SPB) classes. We developed
automated data analysis tools that include algorithms for jump correction,
light-curve detrending, frequency detection, frequency combination search, and
for frequency and period spacing searches. Besides numerous new, classical,
slowly pulsating B stars, we find evidence for a new class of low-amplitude
B-type pulsators between the SPB and Delta Sct instability strips, with a very
broad range of frequencies and low amplitudes, as well as several slowly
pulsating B stars with residual excess power at frequencies typically a factor
three above their expected g-mode frequencies. The frequency data we obtained
for numerous new B-type pulsators represent an appropriate starting point for
further theoretical analyses of these stars, once their effective temperature,
gravity, rotation velocity, and abundances will be derived spectroscopically in
the framework of an ongoing FLAMES survey at the VLT.Comment: 22 pages, 30 figures, accepted for publication in A&
Solar-like oscillations with low amplitude in the CoRoT target HD 181906
Context: The F8 star HD 181906 (effective temperature ~6300K) was observed
for 156 days by the CoRoT satellite during the first long run in the centre
direction. Analysis of the data reveals a spectrum of solar-like acoustic
oscillations. However, the faintness of the target (m_v=7.65) means the
signal-to-noise (S/N) in the acoustic modes is quite low, and this low S/N
leads to complications in the analysis. Aims: To extract global variables of
the star as well as key parameters of the p modes observed in the power
spectrum of the lightcurve. Methods: The power spectrum of the lightcurve, a
wavelet transform and spot fitting have been used to obtain the average
rotation rate of the star and its inclination angle. Then, the autocorrelation
of the power spectrum and the power spectrum of the power spectrum were used to
properly determine the large separation. Finally, estimations of the mode
parameters have been done by maximizing the likelihood of a global fit, where
several modes were fit simultaneously. Results: We have been able to infer the
mean surface rotation rate of the star (~4 microHz) with indications of the
presence of surface differential rotation, the large separation of the p modes
(~87 microHz), and therefore also the ridges corresponding to overtones of the
acoustic modes.Comment: Paper Accepted to be published in A&A. 10 Pages, 12 figure
CoRoT high-precision photometry of the B0.5 IV star HD 51756
OB stars are important constituents for the ecology of the Universe, and
there are only a few studies on their pulsational properties detailed enough to
provide important feedback on current evolutionary models. Our goal is to
analyse and interpret the behaviour present in the CoRoT light curve of the
B0.5 IV star HD 51756 observed during the second long run of the space mission,
and to determine the fundamental stellar parameters from ground-based
spectroscopy gathered with the CORALIE and HARPS instruments after checking for
signs of variability and binarity, thus making a step further in mapping the
top of the Beta Cep instability strip. We compare the newly obtained
high-resolution spectra with synthetic spectra of late O-type and early B-type
stars computed on a grid of stellar parameters. We match the results with
evolutionary tracks to estimate stellar parameters. We use various time series
analysis tools to explore the nature of the variations present in the light
curve. Additional calculations are carried out based on distance and historical
position measurements of the components to impose constraints on the binary
orbit. We find that HD 51756 is a wide binary with both a slow (v sin i \approx
28 km s^-1) and a fast (v sin i \approx 170 km s^-1) early-B rotator whose
atmospheric parameters are similar (T_eff \approx 30000 K and log g \approx
3.75). We are unable to detect pulsation in any of the components, and we
interpret the harmonic structure in the frequency spectrum as sign of
rotational modulation, which is compatible with the observed and deduced
stellar parameters of both components. The non-detection of pulsation modes
provides a feedback on the theoretical treatment, given that non-adiabatic
computations applied to appropriate stellar models predict the excitation of
both pressure and gravity modes for the fundamental parameters of this star.Comment: Accepted for publication in Astronomy and Astrophysics on 14/01/2011,
11 pages, 9 figures, 4 table
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