17,906 research outputs found
Analytic discs in the boundary and compactness of Hankel operators with essentially bounded symbols
AbstractWe derive conditions for compactness of Hankel operators Hf:A2(Ω)→L2(Ω) (Hf(g):=(I−P)(f¯g)) with bounded, holomorphic symbols f for a large class of convex and bounded domains Ω with Ω⊆Dk
Insights from Asteroseismology of Massive Stars: The Need for Additional Angular Momentum Transport Mechanisms
In massive stars, rotation and oscillatory waves can have a tight interplay.
In order to assess the importance of additional angular momentum transport
mechanisms other than rotation, we compare the asteroseismic properties of a
uniformly rotating model and a differentially rotating one. Accordingly, we
employ the observed period spacing of 36 dipole g-modes in the Kepler
M target KIC 7760680 to discriminate between these two models. We favor
the uniformly rotating model, which fully satisfies all observational
constraints. Therefore, efficient angular momentum transport by additional
mechanisms such as internal gravity waves, heat-driven modes and magnetic field
is needed during early main sequence evolution of massive stars.Comment: Proceedings of "Seismology of the Sun and the Distant Stars 2016".
Editors: M\'ario J. P. F. G. Monteiro, Margarida S. Cunha, Jo\~ao Miguel T.
Ferreir
The BRITE-Constellation Nanosatellite Space Mission And Its First Scientific Results
The BRIght Target Explorer (BRITE) Constellation is the first nanosatellite
mission applied to astrophysical research. Five satellites in low-Earth orbits
perform precise optical two-colour photometry of the brightest stars in the
night sky. BRITE is naturally well suited for variability studies of hot stars.
This contribution describes the basic outline of the mission and some initial
problems that needed to be overcome. Some information on BRITE data products,
how to access them, and how to join their scientific exploration is provided.
Finally, a brief summary of the first scientific results obtained by BRITE is
given.Comment: 5 pages, 1 figure, to appear in the proceedings of "Seismology of the
Sun and the Distant Stars 2016. Using Today's Successes to Prepare the
Future. Joint TASC2/KASC9 Workshop - SPACEINN/HELAS8 Conference", ed. M. J.
P. F. G. Monteir
Stellar magnetic activity and exoplanets
It has been proposed that magnetic activity could be enhanced due to
interactions between close-in massive planets and their host stars. In this
article, I present a brief overview of the connection between stellar magnetic
activity and exoplanets. Stellar activity can be probed in chromospheric lines,
coronal emission, surface spot coverage, etc. Since these are manifestations of
stellar magnetism, these measurements are often used as proxies for the
magnetic field of stars. Here, instead of focusing on the magnetic proxies, I
overview some recent results of magnetic field measurements using
spectropolarimetric observations. Firstly, I discuss the general trends found
between large-scale magnetism, stellar rotation, and coronal emission and show
that magnetism seems to be correlated to the internal structure of the star.
Secondly, I overview some works that show evidence that exoplanets could (or
not) act as to enhance the activity of their host stars.Comment: Based on the review talk presented at "Seismology of the Sun and the
Distant Stars 2016", July 2016, Azores, Portugal. To appear in the
Proceedings "Seismology of the Sun and the Distant Stars 2016" Eds. Mario J.
P. F. G. Monteiro, Margarida S. Cunha, Joao Miguel T. Ferreir
Galactic Archaeology with TESS: Prospects for Testing the Star Formation History in the Solar Neighbourhood
A period of quenching between the formation of the thick and thin disks of
the Milky Way has been recently proposed to explain the observed
age-[{\alpha}/Fe] distribution of stars in the solar neighbourhood. However,
robust constraints on stellar ages are currently available for only a limited
number of stars. The all-sky survey TESS (Transiting Exoplanet Survey
Satellite) will observe the brightest stars in the sky and thus can be used to
investigate the age distributions of stars in these components of the Galaxy
via asteroseismology, where previously this has been difficult using other
techniques. The aim of this preliminary study was to determine whether TESS
will be able to provide evidence for quenching periods during the star
formation history of the Milky Way. Using a population synthesis code, we
produced populations based on various stellar formation history models and
limited the analysis to red-giant-branch stars. We investigated the
mass-Galactic-disk-height distributions, where stellar mass was used as an age
proxy, to test for whether periods of quenching can be observed by TESS. We
found that even with the addition of 15% noise to the inferred masses, it will
be possible for TESS to find evidence for/against quenching periods suggested
in the literature (e.g. between 7 and 9 Gyr ago), therefore providing stringent
constraints on the formation and evolution of the Milky Way.Comment: 4 pages, 3 figures, proceedings of "Seismology of the Sun and the
Distant Stars 2016", Mario J. P. F. G. Monteiro, Margarida S. Cunha, Joao
Miguel T. Ferreira editor
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