93 research outputs found
Stellar variability in open clusters. I. A new class of variable stars in NGC 3766
Aims. We analyze the population of periodic variable stars in the open
cluster NGC 3766 based on a 7-year multi-band monitoring campaign conducted on
the 1.2 m Swiss Euler telescope at La Silla, Chili.
Methods. The data reduction, light curve cleaning and period search
procedures, combined with the long observation time line, allow us to detect
variability amplitudes down to the milli-magnitude level. The variability
properties are complemented with the positions in the color-magnitude and
color-color diagrams to classify periodic variable stars into distinct
variability types.
Results. We find a large population (36 stars) of new variable stars between
the red edge of slowly pulsating B (SPB) stars and the blue edge of delta Sct
stars, a region in the Hertzsprung-Russell (HR) diagram where no pulsation is
predicted to occur based on standard stellar models. The bulk of their periods
ranges from 0.1 to 0.7 d, with amplitudes between 1 and 4 mmag for the majority
of them. About 20% of stars in that region of the HR diagram are found to be
variable, but the number of members of this new group is expected to be higher,
with amplitudes below our milli-magnitude detection limit.
The properties of this new group of variable stars are summarized, and
arguments set forth in favor of a pulsation origin of the variability, with
g-modes sustained by stellar rotation. Potential members of this new class of
low-amplitude periodic (most probably pulsating) A and late-B variables in the
literature are discussed.
We additionally identify 16 eclipsing binary, 13 SPB, 14 delta Sct and 12
gamma Dor candidates, as well as 72 fainter periodic variables. All are new
discoveries.
Conclusions. We encourage to search for the existence of this new class of
variables in other young open clusters, especially in those hosting a rich
population of Be stars.Comment: Accepted for publication in A&A. Size of pdf file ~7Mo. Figures 12,
13, 14 and in the Appendix are of lower quality. Full quality images
published in A&
Praxisnahe Ausbildung in Technik und Betrieb an der Abteilung Chemie der Ingenieurschule beider Basel
Practice-oriented training in technical theory and operational procedures in the Chemisty Department of the Basle State Institute of Technology, Switzerland. The process technology center is presented
Kombi-Verdampferanlage zur Ausbildung von Chemiker/-innen und Ingenieur/-innen an der Ingenieurschule beider Basel
A pilot evaporation plant designed and built to train future chemists and process engineers at the Basle State Institute of Technology, Switzerland, is presented and first experiences from running it are discussed
Close binary evolution. III. Impact of tides, wind magnetic braking, and internal angular momentum transport
Massive stars with solar metallicity lose important amounts of rotational
angular momentum through their winds. When a magnetic field is present at the
surface of a star, efficient angular momentum losses can still be achieved even
when the mass-loss rate is very modest, at lower metallicities, or for
lower-initial-mass stars. In a close binary system, the effect of wind magnetic
braking also interacts with the influence of tides, resulting in a complex
evolution of rotation. We study the interactions between the process of wind
magnetic braking and tides in close binary systems. We discuss the evolution of
a 10 M star in a close binary system with a 7 M companion using
the Geneva stellar evolution code. The initial orbital period is 1.2 days. The
10 M star has a surface magnetic field of 1 kG. Various initial
rotations are considered. We use two different approaches for the internal
angular momentum transport. In one of them, angular momentum is transported by
shear and meridional currents. In the other, a strong internal magnetic field
imposes nearly perfect solid-body rotation. The evolution of the primary is
computed until the first mass-transfer episode occurs. The cases of different
values for the magnetic fields and for various orbital periods and mass ratios
are briefly discussed. We show that, independently of the initial rotation rate
of the primary and the efficiency of the internal angular momentum transport,
the surface rotation of the primary will converge, in a time that is short with
respect to the main-sequence lifetime, towards a slowly evolving velocity that
is different from the synchronization velocity. (abridged).Comment: 11 pages, 13 figures, accepted for publication in Astronomy and
Astrophysic
Gaia eclipsing binary and multiple systems. Two-Gaussian models applied to OGLE-III eclipsing binary light curves in the Large Magellanic Cloud
The advent of large scale multi-epoch surveys raises the need for automated
light curve (LC) processing. This is particularly true for eclipsing binaries
(EBs), which form one of the most populated types of variable objects. The Gaia
mission, launched at the end of 2013, is expected to detect of the order of few
million EBs over a 5-year mission.
We present an automated procedure to characterize EBs based on the geometric
morphology of their LCs with two aims: first to study an ensemble of EBs on a
statistical ground without the need to model the binary system, and second to
enable the automated identification of EBs that display atypical LCs. We model
the folded LC geometry of EBs using up to two Gaussian functions for the
eclipses and a cosine function for any ellipsoidal-like variability that may be
present between the eclipses. The procedure is applied to the OGLE-III data set
of EBs in the Large Magellanic Cloud (LMC) as a proof of concept. The bayesian
information criterion is used to select the best model among models containing
various combinations of those components, as well as to estimate the
significance of the components.
Based on the two-Gaussian models, EBs with atypical LC geometries are
successfully identified in two diagrams, using the Abbe values of the original
and residual folded LCs, and the reduced . Cleaning the data set from
the atypical cases and further filtering out LCs that contain non-significant
eclipse candidates, the ensemble of EBs can be studied on a statistical ground
using the two-Gaussian model parameters. For illustration purposes, we present
the distribution of projected eccentricities as a function of orbital period
for the OGLE-III set of EBs in the LMC, as well as the distribution of their
primary versus secondary eclipse widths.Comment: 20 pages, 29 figures. Submitted to A&
The impact of Gaia and LSST on binary stars and exo-planets
Two upcoming large scale surveys, the ESA Gaia and LSST projects, will bring
a new era in astronomy. The number of binary systems that will be observed and
detected by these projects is enormous, estimations range from millions for
Gaia to several tens of millions for LSST. We review some tools that should be
developed and also what can be gained from these missions on the subject of
binaries and exoplanets from the astrometry, photometry, radial velocity and
their alert systems.Comment: 8 pages, 2 figures, Proceedings of the IAU Symposium No. 282: From
Interacting Binaries to Exoplanets: Essential Modeling Tools. Tatranska
Lomnica, Slovaki
The Impact of Gaia and LSST on Binaries and Exoplanets
Two upcoming large scale surveys, the ESA Gaia and LSST projects, will bring a new era in astronomy. The number of binary systems that will be observed and detected by these projects is enormous, estimations range from millions for Gaia to several tens of millions for LSST. We review some tools that should be developed and also what can be gained from these missions on the subject of binaries and exoplanets from the astrometry, photometry, radial velocity and their alert system
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