673 research outputs found
The MUCHFUSS photometric campaign
Hot subdwarfs (sdO/Bs) are the helium-burning cores of red giants, which lost
almost all of their hydrogen envelopes. This mass loss is often triggered by
common envelope interactions with close stellar or even substellar companions.
Cool companions like late-type stars or brown dwarfs are detectable via
characteristic light curve variations like reflection effects and often also
eclipses. To search for such objects we obtained multi-band light curves of 26
close sdO/B binary candidates from the MUCHFUSS project with the BUSCA
instrument. We discovered a new eclipsing reflection effect system
(~d) with a low-mass M dwarf companion ().
Three more reflection effect binaries found in the course of the campaign were
already published, two of them are eclipsing systems, in one system only
showing the reflection effect but no eclipses the sdB primary is found to be
pulsating. Amongst the targets without reflection effect a new long-period sdB
pulsator was discovered and irregular light variations were found in two sdO
stars. The found light variations allowed us to constrain the fraction of
reflection effect binaries and the substellar companion fraction around sdB
stars. The minimum fraction of reflection effect systems amongst the close sdB
binaries might be greater than 15\% and the fraction of close substellar
companions in sdB binaries might be as high as . This would result in a
close substellar companion fraction to sdB stars of about 3\%. This fraction is
much higher than the fraction of brown dwarfs around possible progenitor
systems, which are solar-type stars with substellar companions around 1 AU, as
well as close binary white dwarfs with brown dwarf companions. This might be a
hint that common envelope interactions with substellar objects are
preferentially followed by a hot subdwarf phase.Comment: accepted for A&
D'atri spaces of type k and related classes of geometries concerning jacobi operators
In this article we continue the study of the geometry of -D'Atri spaces,
( denotes the dimension of the manifold) began by
the second author. It is known that -D'Atri spaces, are related
to properties of Jacobi operators along geodesics, since she has shown
that , are invariant
under the geodesic flow for any unit tangent vector . Here, assuming that
the Riemannian manifold is a D'Atri space, we prove in our main result that
is also invariant under the geodesic flow if . In addition, other properties of Jacobi operators related to the
Ledger conditions are obtained and they are used to give applications to
Iwasawa type spaces. In the class of D'Atri spaces of Iwasawa type, we show two
different characterizations of the symmetric spaces of noncompact type: they
are exactly the -spaces and on the other hand they are -D'Atri
spaces for some In the last case, they are -D'Atri for all
as well. In particular, Damek-Ricci spaces that are -D'Atri
for some are symmetric.
Finally, we characterize -D'Atri spaces for all as the -spaces (geodesic symmetries preserve the principal curvatures of
small geodesic spheres). Moreover, applying this result in the case of 4%
-dimensional homogeneous spaces we prove that the properties of being a D'Atri
(1-D'Atri) space, or a 3-D'Atri space, are equivalent to the property of being
a -D'Atri space for all .Comment: 19 pages. This paper substitute the previous one where one Theorem
has been deleted and one section has been adde
Simultaneous time-series spectroscopy and multi-band photometry of the sdBV PG 1605+072
We present time-series spectroscopy and multi-band photometry of the sdBV PG
1605+072 carried out simultaneously at the Calar Alto 2.2m and 3.5m telescopes.
The periodogram analysis of the radial velocity curves reveals three
frequencies at 2.078, 2.756, and 1.985 mHz for Hbeta and at 2.076, 2.753, and
1.978 mHz for Hgamma. The corresponding radial velocity amplitudes are 12.7,
8.0, and 7.9 km/s for Hbeta and 14.3, 6.5, and 7.2 km/s for Hgamma.
Furthermore, we found five frequencies that are present in all wavelength bands
of the BUSCA photometer. The frequencies detected in the radial velocity curves
are recovered by the photometric measurements. Moreover, additional frequencies
were present in the periodograms which could not be identified in all four
bands simultaneously. The comparison of the amplitudes presented here with
previous results from radial velocity and photometric observations of PG
1605+072 shows a significant change or even switch in the power of the modes
within short time scales, i. e. about one year. No changes in frequency were
registered and the phases of the modes show no wavelength dependency within our
multi-band photometry.Comment: 8 pages, 12 figures, accepted by A&
Multi-wavelength photometric variation of PG1605+072
In a large coordinated attempt to further our understanding of the -mode
pulsating sdB star PG1605+072, the Multi-Site Spectroscopic Telescope (MSST)
collaboration has obtained simultaneous time-resolved spectroscopic and
photometric observations. The photometry was extended by additional WET data
which increased the time base. This contribution outlines the analysis of the
MSST photometric light curve, including the four-colour BUSCA data from which
chromatic amplitudes have been derived, as well as supplementary FUV spectra
and light curves from two different epochs. These results have the potential to
complement the interpretation of the published spectroscopic information.Comment: 6 pages, to be published in "Interpretation of asteroseismic data",
proceedings of the HELAS NA5 Workshop, eds. W. Dziembowski, M. Breger and M.
Thompson, Communications in Asteroseismology, 15
Energy-sensitive imaging detector applied to the dissociative recombination of D2H+
We report on an energy-sensitive imaging detector for studying the
fragmentation of polyatomic molecules in the dissociative recombination of fast
molecular ions with electrons. The system is based on a large area (10 cm x 10
cm) position-sensitive, double-sided Si-strip detector with 128 horizontal and
128 vertical strips, whose pulse height information is read out individually.
The setup allows to uniquely identify fragment masses and is thus capable of
measuring branching ratios between different fragmentation channels, kinetic
energy releases, as well as breakup geometries, as a function of the relative
ion-electron energy. The properties of the detection system, which has been
installed at the TSR storage ring facility of the Max-Planck Institute for
Nuclear Physics in Heidelberg, is illustrated by an investigation of the
dissociative recombination of the deuterated triatomic hydrogen cation D2H+. A
huge isotope effect is observed when comparing the relative branching ratio
between the D2+H and the HD+D channel; the ratio 2B(D2+H)/B(HD+D), which is
measured to be 1.27 +/- 0.05 at relative electron-ion energies around 0 eV, is
found to increase to 3.7 +/- 0.5 at ~5 eV.Comment: 11 pages, 12 figures, submitted to Physical Review
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