19 research outputs found
Multiplicity among chemically peculiar stars II. Cool magnetic Ap stars
We present new orbits for sixteen Ap spectroscopic binaries, four of which
might in fact be Am stars, and give their orbital elements. Four of them are
SB2 systems: HD 5550, HD 22128, HD 56495 and HD 98088. The twelve other stars
are : HD 9996, HD 12288, HD 40711, HD 54908, HD 65339, HD 73709, HD 105680, HD
138426, HD 184471, HD 188854, HD 200405 and HD 216533. Rough estimates of the
individual masses of the components of HD 65339 (53 Cam) are given, combining
our radial velocities with the results of speckle interferometry and with
Hipparcos parallaxes. Considering the mass functions of 74 spectroscopic
binaries from this work and from the literature, we conclude that the
distribution of the mass ratio is the same for cool Ap stars as for normal G
dwarfs. Therefore, the only differences between binaries with normal stars and
those hosting an Ap star lie in the period distribution: except for the case of
HD 200405, all orbital periods are longer than (or equal to) 3 days. A
consequence of this peculiar distribution is a deficit of null eccentricities.
There is no indication that the secondary has a special nature, like e.g. a
white dwarf.Comment: 31 pages, 15 figures, A&A accepte
Towards a new image processing system at Wendelstein 7-X: From spatial calibration to characterization of thermal events
Wendelstein 7-X (W7-X) is the most advanced fusion experiment in the stellarator line and is aimed at proving that the stellarator concept is suitable for a fusion reactor. One of the most important issues for fusion reactors is the monitoring of plasma facing components when exposed to very high heat loads, through the use of visible and infrared (IR) cameras. In this paper, a new image processing system for the analysis of the strike lines on the inboard limiters from the first W7-X experimental campaign is presented. This system builds a model of the IR cameras through the use of spatial calibration techniques, helping to characterize the strike lines by using the information given by real spatial coordinates of each pixel. The characterization of the strike lines is made in terms of position, size, and shape, after projecting the camera image in a 2D grid which tries to preserve the curvilinear surface distances between points. The description of the strike-line shape is made by means of the Fourier Descriptors
Forward modeling of collective Thomson scattering for Wendelstein 7-X plasmas: Electrostatic approximation
In this paper, we present a method for numerical computation of collective Thomson scattering (CTS). We developed a forward model, eCTS, in the electrostatic approximation and benchmarked it against a full electromagnetic model. Differences between the electrostatic and the electromagnetic models are discussed. The sensitivity of the results to the ion temperature and the plasma composition is demonstrated. We integrated the model into the Bayesian data analysis framework Minerva and used it for the analysis of noisy synthetic data sets produced by a full electromagnetic model. It is shown that eCTS can be used for the inference of the bulk ion temperature. The model has been used to infer the bulk ion temperature from the first CTS measurements on Wendelstein 7-X
The roAp star α
We report on an analysis of high-precision, multi-colour photometric
observations of the rapidly-oscillating Ap (roAp) star Cir. These
observations were obtained with the BRITE-Constellation, which is a coordinated
mission of five nanosatellites that collects continuous
millimagnitude-precision photometry of dozens of bright stars for up to 180
days at a time in two colours (Johnson B and R). BRITE stands for BRight Target
Explorer. The object Cir is the brightest roAp star and an ideal
target for such investigations, facilitating the determination of oscillation
frequencies with high resolution. This star is bright enough for complementary
interferometry and time-resolved spectroscopy. Four BRITE satellites observed
Cir for 146 d or 33 rotational cycles. Phasing the photometry
according to the 4.4790 d rotational period reveals qualitatively different
light variations in the two photometric bands. The phased red-band photometry
is in good agreement with previously-published WIRE data, showing a light curve
symmetric about phase 0.5 with a strong contribution from the first harmonic.
The phased blue-band data, in contrast, show an essentially sinusoidal
variation. We model both light curves with Bayesian Photometric Imaging, which
suggests the presence of two large-scale, photometrically bright (relative to
the surrounding photosphere) spots. We also examine the high-frequency
pulsation spectrum as encoded in the BRITE photometry. Our analysis establishes
the stability of the main pulsation frequency over the last 20 years, confirms
the presence of frequency f7, which was not detected (or the mode not excited)
prior to 2006, and excludes quadrupolar modes for the main pulsation frequency.Comment: 10 pages, 11 figures, accepted by Astronomy & Astrophysic