114 research outputs found
The Core-Wing Anomaly of Cool Ap Stars: Abnormal Balmer Profiles
Paper by Cowley et al. The Core-Wing Anomaly Etc. The profiles of H
in a number of cool Ap stars are anomalous. Broad wings, indicative of
temperatures in the range 7000-8000K end abruptly in narrow cores. The widths
of these cores are compatible with those of dwarfs with temperatures of 6000K
or lower. This profile has been known for Przybylski's star, but it is seen in
other cool Ap's. The H profile in several of these stars shows a similar
core-wing anomaly (CWA). In Przybylski's star, the CWA is probably present at
higher Balmer members. We are unable to account for these profiles within the
context of LTE and normal dwarf atmospheres. We conclude that the atmospheres
of these stars are not ``normal.'' This is contrary to a notion that has long
been held.Comment: 4 Pages 5 Figures. Submitted to Astronomy and Astrophysics 4 Dec.
200
Synthesis of Nanoscale TiO2 and Study of the Effect of Their Crystal Structure on Single Cell Response
To study the effect of nanoscale titanium dioxide (TiO2) on cell responses, we synthesized four modifications of the TiO2 (amorphous, anatase, brookite, and rutile) capable of keeping their physicochemical characteristics in a cell culture medium. The modifications of nanoscale TiO2 were obtained by hydrolysis of TiCl4 and Ti(i-OC3H7)4 (TIP) upon variation of the synthesis conditions; their textural, morphological, structural, and dispersion characteristics were examined by a set of physicochemical methods: XRD, BET, SAXS, DLS, AFM, SEM, and HR-TEM. The effect of synthesis conditions (nature of precursor, pH, temperature, and addition of a complexing agent) on the structural-dispersion properties of TiO2 nanoparticles was studied. The hydrolysis methods providing the preparation of amorphous, anatase, brookite, and rutile modifications of TiO2 nanoparticles 3–5 nm in size were selected. Examination of different forms of TiO2 nanoparticles interaction with MDCK cells by transmission electron microscopy of ultrathin sections revealed different cell responses after treatment with different crystalline modifications and amorphous form of TiO2. The obtained results allowed us to conclude that direct contact of the nanoparticles with cell plasma membrane is the primary and critical step of their interaction and defines a subsequent response of the cell
Regular frequency patterns in the young delta Scuti star HD 261711 observed by the CoRoT and MOST satellites
We concentrate on an asteroseismological study of HD 261711, a rather hot
delta Scuti type pulsating member of the young open cluster NGC 2264 located at
the blue border of the instability region. HD 261711 was discovered to be a
pre-main sequence delta Scuti star using the time series photometry obtained by
the MOST satellite in 2006. High-precision, time-series photometry of HD 261711
was obtained by the MOST and CoRoT satellites in 4 separate new observing runs
that are put into context with the star's fundamental atmospheric parameters
obtained from spectroscopy. With the new MOST data set from 2011/12 and the two
CoRoT light curves from 2008 and 2011/12, the delta Scuti variability was
confirmed and regular groups of frequencies were discovered. The two pulsation
frequencies identified in the data from the first MOST observing run in 2006
are confirmed and 23 new delta Scuti-type frequencies were discovered using the
CoRoT data. Weighted average frequencies for each group are related to l=0 and
l=1 p-modes. Evidence for amplitude modulation of the frequencies in two groups
is seen. The effective temperature was derived to be 8600200 K, log g is
4.10.2, and the projected rotational velocity is 531km/s. Using our
Teff value and the radius of 1.80.5 Rsun derived from SED fitting, we get
a log L/Lsun of 1.200.14 which agrees well to the seismologically
determined values of 1.65 Rsun and, hence, a log L/Lsun of 1.13. The radial
velocity of 142 km/s we derived for HD 261711, confirms the star's
membership to NGC 2264. Our asteroseismic models suggest that HD 261711 is a
delta Scuti-type star close to the zero-age main sequence (ZAMS) with a mass of
1.8 to 1.9Msun. HD 261711 is either a young ZAMS star or a late PMS star just
before the onset of hydrogen-core burning.Comment: 12 pages, 13 figures, A&A accepte
Comprehensive study of the magnetic stars HD 5797 and HD 40711 with large chromium and iron overabundances
We present the results of a comprehensive study of the chemically peculiar
stars HD 5797 and HD 40711. The stars have the same effective temperature, Teff
= 8900 K, and a similar chemical composition with large iron (+1.5 dex) and
chromium (+3 dex) overabundances compared to the Sun. The overabundance of
rare-earth elements typically reaches +3 dex. We have measured the magnetic
field of HD 5797. The longitudinal field component Be has been found to vary
sinusoidally between -100 and +1000 G with a period of 69 days. Our estimate of
the evolutionary status of the stars suggests that HD 5797 and HD 40711, old
objects with an age t \approx 5 \times 108 yr, are near the end of the core
hydrogen burning phase.Comment: 26 pages, 5 Encapsulated Postscript figure
He and Si surface inhomogeneities of four Bp variable stars
We present ground-based multi-colour Geneva photometry and high-resolution spectra of four variable B-type stars: HD 105382, HD 131120, HD 138769 and HD 55522. All sets of data reveal monoperiodic stars. A comparison of moment variations of two spectral lines, one silicon line and one helium line, allows us to exclude the pulsation model as being the cause of the observed variability of the four stars. We therefore delete the four stars from the list of candidate slowly pulsating B stars. We attribute the line-profile variations to non-homogeneous distributions of elements on the stellar surface and we derive abundance maps for both elements on the stellar surface by means of the Doppler Imaging technique. We confirm HD 131120 to be a He-weak star and we classify HD 105382, HD 138769 as new He-weak stars. HD 55522 has the solar helium abundance but the mean abundance value of He varies by 0.8 dex during the stellar rotation. For HD 131120 and HD 105382, helium is enhanced in regions of the stellar surface where silicon is depleted and depleted in regions where silicon is enhanced. Based on observations obtained with the Swiss photometric telescope and ESO's CAT/CES telescope, both situated at La Silla, Chile. Appendix A, Tables 1 and 2 and Figs. 9, 11, 13 are only available in electronic form at http://www.edpsciences.orgPeer reviewe
The radius and effective temperature of the binary Ap star beta CrB from CHARA/FLUOR and VLT/NACO observations
The prospects for using asteroseismology of rapidly oscillating Ap (roAp)
stars are hampered by the large uncertainty in fundamental stellar parameters.
Results in the literature for the effective temperature (Teff) often span a
range of 1000 K. Our goal is to reduce systematic errors and improve the Teff
calibration of Ap stars based on new interferometric measurements. We obtained
long-baseline interferometric observations of beta CrB using the CHARA/FLUOR
instrument. To disentangle the flux contributions of the two components of this
binary star, we obtained VLT/NACO adaptive optics images. We determined limb
darkened angular diameters of 0.699+-0.017 mas for beta CrB A (from
interferometry) and 0.415+-0.017 mas for beta CrB B (from surface brightness-
color relations), corresponding to radii of 2.63+-0.09 Rsun (3.4 percent
uncertainty) and 1.56+-0.07 Rsun (4.5 percent). The combined bolometric flux of
the A and B components was determined from satellite UV data, spectrophotometry
in the visible and broadband data in the infrared. The flux from the B
component constitutes 16+-4 percent of the total flux and was determined by
fitting an ATLAS9 model atmosphere to the broad-band NACO J and K magnitudes.
Combining the flux of the A component with its measured angular diameter, we
determine the effective temperature Teff(A) = 7980+-180 K (2.3 percent). Our
new interferometric and imaging data enable a nearly model-independent
determination of the effective temperature of beta CrB A. Including our recent
study of alpha Cir, we now have direct Teff measurements of two of the
brightest roAp stars, providing a strong benchmark for an improved calibration
of the Teff scale for Ap stars. This will support the use of potentially strong
constraints imposed by asteroseismic studies of roAp stars.Comment: 7 pages, accepted by A&
Echography of young stars reveals their evolution
We demonstrate that a seismic analysis of stars in their earliest
evolutionary phases is a powerful method to identify young stars and
distinguish their evolutionary states. The early star that is born from the
gravitational collapse of a molecular cloud reaches at some point sufficient
temperature, mass and luminosity to be detected. Accretion stops and the
pre-main sequence star that emerges is nearly fully convective and chemically
homogeneous. It will continue to contract gravitationally until the density and
temperature in the core are high enough to start nuclear burning of hydrogen.
We show that there is a relationship between detected pulsation properties for
a sample of young stars and their evolutionary status illustrating the
potential of asteroseismology for the early evolutionary phases.Comment: 23 pages, 9 figures, includes Supplementary Material. Science,
published in Science Express on July 3, 201
The first planet detected in the WTS: an inflated hot Jupiter in a 3.35 d orbit around a late F star
We report the discovery of WTS-1b, the first extrasolar planet found by the WFCAM Transit Survey, which began observations at the 3.8-m United Kingdom Infrared Telescope (UKIRT) in 2007 August. Light curves comprising almost 1200 epochs with a photometric precision of better than 1 per cent to J ˜ 16 were constructed for ˜60 000 stars and searched for periodic transit signals. For one of the most promising transiting candidates, high-resolution spectra taken at the Hobby-Eberly Telescope (HET) allowed us to estimate the spectroscopic parameters of the host star, a late-F main-sequence dwarf (V = 16.13) with possibly slightly subsolar metallicity, and to measure its radial velocity variations. The combined analysis of the light curves and spectroscopic data resulted in an orbital period of the substellar companion of 3.35 d, a planetary mass of 4.01 ± 0.35 MJ and a planetary radius of 1.49-0.18+0.16 RJ. WTS-1b has one of the largest radius anomalies among the known hot Jupiters in the mass range 3-5 MJ. The high irradiation from the host star ranks the planet in the pM class
The diameter of the CoRoT target HD 49933. Combining the 3D limb darkening, asteroseismology, and interferometry
Context. The interpretation of stellar pulsations in terms of internal
structure depends on the knowledge of the fundamental stellar parameters.
Long-base interferometers permit us to determine very accurate stellar radii,
which are independent constraints for stellar models that help us to locate the
star in the HR diagram. Aims: Using a direct interferometric determination of
the angular diameter and advanced three-dimensional (3D) modeling, we derive
the radius of the CoRoT target HD 49933 and reduce the global stellar parameter
space compatible with seismic data. Methods: The VEGA/CHARA
spectro-interferometer is used to measure the angular diameter of the star. A
3D radiative hydrodynamical simulation of the surface is performed to compute
the limb darkening and derive a reliable diameter from visibility curves. The
other fundamental stellar parameters (mass, age, and Teff) are found by fitting
the large and small p-mode frequency separations using a stellar evolution
model that includes microscopic diffusion. Results: We obtain a limb-darkened
angular diameter of {\theta}LD = 0.445 \pm 0.012 mas. With the Hipparcos
parallax, we obtain a radius of R = 1.42 \pm 0.04 Rsun. The corresponding
stellar evolution model that fits both large and small frequency separations
has a mass of 1.20 \pm 0.08 Msun and an age of 2.7 Gy. The atmospheric
parameters are Teff = 6640 \pm 100 K, log g = 4.21 \pm 0.14, and [Fe/H] =
-0.38.Comment: 4 pages, 4 figure
Asteroseismology and Interferometry
Asteroseismology provides us with a unique opportunity to improve our
understanding of stellar structure and evolution. Recent developments,
including the first systematic studies of solar-like pulsators, have boosted
the impact of this field of research within Astrophysics and have led to a
significant increase in the size of the research community. In the present
paper we start by reviewing the basic observational and theoretical properties
of classical and solar-like pulsators and present results from some of the most
recent and outstanding studies of these stars. We centre our review on those
classes of pulsators for which interferometric studies are expected to provide
a significant input. We discuss current limitations to asteroseismic studies,
including difficulties in mode identification and in the accurate determination
of global parameters of pulsating stars, and, after a brief review of those
aspects of interferometry that are most relevant in this context, anticipate
how interferometric observations may contribute to overcome these limitations.
Moreover, we present results of recent pilot studies of pulsating stars
involving both asteroseismic and interferometric constraints and look into the
future, summarizing ongoing efforts concerning the development of future
instruments and satellite missions which are expected to have an impact in this
field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume
14, Issue 3-4, pp. 217-36
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