1,088 research outputs found
Tidal Flows in asynchronous binaries: The beta-factor
We discuss the potential role that tidal flows in asynchronous binary stars
may play in transporting chemically enriched material from deep layers towards
the surface and the corresponding observational consequences of these
processes. We suggest that the time-dependent velocity field induced by
asynchronous rotation may contribute significantly to the mixing, thus
providing a channel for the formation of chemically enriched slowly rotating
massive stars.Comment: in Setting New Standards in Binary Star Research, A. Tkachenko & K.
Pavlovski (eds), EAS Publication Series, in Pres
Long uninterrupted photometric observations of the Wolf-Rayet star EZ CMa by the Toronto {\em{BRITE}} satellite reveal a very fast apsidal motion
Context. The variability of the Wolf-Rayet star EZ CMa has been documented
for close to half a century, and a clear periodicity of 3.7 days is
established. However, all attempts to prove that it is a binary have failed
because the photometric, spectroscopic, and polarimetric variations are not
coherent over more than a few orbital cycles.
Aims. In this letter we show that the lack of coherence in the variability
can be explained with a very rapid apsidal motion in a binary orbit.}
Methods. We measured the times of minima in a recently published
exceptionally long photometric light curve obtained by the Toronto
{\emph{BRITE}} satellite. The apsidal motion and the system eccentricity are
determined from the length of the time intervals between these minima, which
alternate in their duration, following a pattern that is clearly associated
with apsidal motion. These minima are superposed on brightness enhancements of
the emission from a shock zone, which occur at about the times of periastron
phases.
Results. We determine the orbital periodicity, d, and the
period of the apsidal motion, d, which together yield an
average sidereal period of d. The eccentricity is found to be
close to 0.1. The rate of periapsis retreat changes significantly over the
period of observation and is determined to be at
the beginning of the observing period and at the
end.
Conclusions. We demonstrate that by introducing a fast apsidal motion, the
basic photometric variability is very well explained. The binary nature of EZ
CMa is now established. This might imply that other apparently single
Wolf-Rayet stars that emit hard X-rays, similar to EZ CMa, are also binaries.Comment: A&A Letter in press, 5 pages, 3 figure
FUSE observations of HD 5980: The wind structure of the eruptor
HD 5980 is a unique system containing one massive star (star A) that is
apparently entering the luminous blue variable phase, and an eclipsing
companion (star B) that may have already evolved beyond this phase to become a
Wolf-Rayet star. In this paper we present the results from FUSE observations
obtained in 1999, 2000, and 2002 and one far-UV observation obtained by
ORFEUS/BEFS in 1993 shortly before the first eruption of HD 5980. The eight
phase-resolved spectra obtained by FUSE in 2002 are analyzed in the context of
a wind-eclipse model. This analysis shows that the wind of the eruptor obeyed a
very fast velocity law in 2002, which is consistent with the line-driving
mechanism. Large amplitude line-profile variations on the orbital period are
shown to be due to the eclipse of star B by the wind of star A, although the
eclipse due to gas flowing in the direction of star B is absent. This can only
be explained if the wind of star A is not spherically symmetric, or if the
eclipsed line radiation is "filled-in" by emission originating from somewhere
else in the system, e.g., in the wind-wind collision region. Except for a
slightly lower wind speed, the ORFEUS/BEFS spectrum is very similar to the
spectrum obtained by FUSE at the same orbital phase: there is no indication of
the impending eruption. However, the trend for decreasing wind velocity
suggests the occurrence of the "bi-stability" mechanism, which in turn implies
that the restructuring of the circumbinary environment caused by the transition
from "fast, rarefied wind" to "slow, dense wind" was observed as the eruptive
event. The underlying mechanism responsible for the long-term decrease in wind
velocity that precipitated this change remains an open issue.Comment: 19 pages, 13 figure
Carl Gustav Jacob Jacobi : Rede zu der ... Feier der 100. Wiederkehr seines Geburtstages ... 1904 / neu hrsg. von Gabriele Dörflinger, Universitätsbibliothek Heidelberg
Gedenkrede auf den Mathematiker Carl Gustav Jacob Jacobi (1804-1851), der die Grundlagen der Theorie der elliptischen Funktionen schuf, im Rahmen des III. Internationalen Mathematiker-Kongresses in Heidelberg 1904. Der Neuausgabe wurde ein Bildnis Jacobis beigegeben
First detection of phase-dependent colliding wind X-ray emission outside the Milky Way
After having reported the detection of X-rays emitted by the peculiar system
HD5980, we assess here the origin of this high-energy emission from additional
X-ray observations obtained with XMM-Newton. This research provides the first
detection of apparently periodic X-ray emission from hot gas produced by the
collision of winds in an evolved massive binary outside the Milky Way. It also
provides the first X-ray monitoring of a Luminous Blue Variable only years
after its eruption and shows that the dominant source of the X-rays is not
associated with the ejecta.Comment: 13 pages, 3 figures and 1 table, accepted for publication in ApJ
(letters
Festreden in der Heidelberger Akademie der Wissenschaften / gehalten von Leo Koenigsberger. Neu hrsg. von Gabriele Dörflinger
Leo Koenigsberger (1837-1921), der an der Gründung der Heidelberger Akademie der Wissenschaften im Jahr 1909 aktiv beteiligt war, war 1909, 1911 und 1913 geschäftsführender Sekretär der Akademie.
Seine Rede in der Eröffnungssitzung befasst sich mit den Aufgaben der Akademie; die Rede 1911 erinnert an den Heidelberger Philosophieprofessor Jakob Fries (1773-1843); seine letzte Rede 1913 thematisiert die Einordnung der Mathematik in die Wissenschaften
Planet heating prevents inward migration of planetary cores
Planetary systems are born in the disks of gas, dust and rocky fragments that
surround newly formed stars. Solid content assembles into ever-larger rocky
fragments that eventually become planetary embryos. These then continue their
growth by accreting leftover material in the disc. Concurrently, tidal effects
in the disc cause a radial drift in the embryo orbits, a process known as
migration. Fast inward migration is predicted by theory for embryos smaller
than three to five Earth masses. With only inward migration, these embryos can
only rarely become giant planets located at Earth's distance from the Sun and
beyond, in contrast with observations. Here we report that asymmetries in the
temperature rise associated with accreting infalling material produce a force
(which gives rise to an effect that we call "heating torque") that counteracts
inward migration. This provides a channel for the formation of giant planets
and also explains the strong planet-metallicity correlation found between the
incidence of giant planets and the heavy-element abundance of the host stars.Comment: 19 pages, 4 figure
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