30,368 research outputs found
Accelerator Constraints on Neutralino Dark Matter
The constraints on neutralino dark matter \chi obtained from accelerator
searches at LEP, the Fermilab Tevatron and elsewhere are reviewed, with
particular emphasis on results from LEP 1.5. These imply within the context of
the minimal supersymmetric extension of the Standard Model that m_\chi \ge 21.4
GeV if universality is assumed, and yield for large tan\beta a significantly
stronger bound than is obtained indirectly from Tevatron limits on the gluino
mass. We update this analysis with preliminary results from the first LEP 2W
run, and also preview the prospects for future sparticle searches at the LHC.Comment: Presented by J. Ellis at the Workshop on the Identification of Dark
Matter, Sheffield, September, 1996. 14 pages; Latex; 12 Fig
Strong latitudinal shear in the shallow convection zone of a rapidly rotating A-star
We have derived the mean broadening profile of the star V102 in the region of
the open cluster IC4665 from high resolution spectroscopy. At a projected
equatorial rotation velocity of vsini = (105 +- 12)km/s we find strong
deviation from classical rotation. We discuss several scenarios, the most
plausible being strong differential rotation in latitudinal direction. For this
scenario we find a difference in angular velocity of DeltaOmega = 3.6 +- 0.8
rad/d (DeltaOmega/Omega = 0.42 +- 0.09). From the Halpha line we derive a
spectral type of A9 and support photometric measurements classifying IC4665
V102 as a non-member of IC4665. At such early spectral type this is the
strongest case of differential rotation observed so far. Together with three
similar stars, IC4665 V102 seems to form a new class of objects that exhibit
extreme latitudinal shear in a very shallow convective envelope.Comment: accepted for A&A Letter
TPCI: The PLUTO-CLOUDY Interface
We present an interface between the (magneto-) hydrodynamics code PLUTO and
the plasma simulation and spectral synthesis code CLOUDY. By combining these
codes, we constructed a new photoionization hydrodynamics solver: The
PLUTO-CLOUDY Interface (TPCI), which is well suited to simulate
photoevaporative flows under strong irradiation. The code includes the
electromagnetic spectrum from X-rays to the radio range and solves the
photoionization and chemical network of the 30 lightest elements. TPCI follows
an iterative numerical scheme: First, the equilibrium state of the medium is
solved for a given radiation field by CLOUDY, resulting in a net radiative
heating or cooling. In the second step, the latter influences the (magneto-)
hydrodynamic evolution calculated by PLUTO. Here, we validated the
one-dimensional version of the code on the basis of four test problems:
Photoevaporation of a cool hydrogen cloud, cooling of coronal plasma, formation
of a Stroemgren sphere, and the evaporating atmosphere of a hot Jupiter. This
combination of an equilibrium photoionization solver with a general MHD code
provides an advanced simulation tool applicable to a variety of astrophysical
problems.Comment: 13 pages, 10 figures, accepted for publication in A&
Apsidal motion in the massive binary HD152218
Massive binary systems are important laboratories in which to probe the
properties of massive stars and stellar physics in general. In this context, we
analysed optical spectroscopy and photometry of the eccentric short-period
early-type binary HD 152218 in the young open cluster NGC 6231. We
reconstructed the spectra of the individual stars using a separating code. The
individual spectra were then compared with synthetic spectra obtained with the
CMFGEN model atmosphere code. We furthermore analysed the light curve of the
binary and used it to constrain the orbital inclination and to derive absolute
masses of 19.8 +/- 1.5 and 15.0 +/- 1.1 solar masses. Combining radial velocity
measurements from over 60 years, we show that the system displays apsidal
motion at a rate of (2.04^{+.23}_{-.24}) degree/year. Solving the
Clairaut-Radau equation, we used stellar evolution models, obtained with the
CLES code, to compute the internal structure constants and to evaluate the
theoretically predicted rate of apsidal motion as a function of stellar age and
primary mass. In this way, we determine an age of 5.8 +/- 0.6 Myr for HD
152218, which is towards the higher end of, but compatible with, the range of
ages of the massive star population of NGC 6231 as determined from isochrone
fitting.Comment: Accepted for publication in Astronomy & Astrophysic
Fifteen years in the high-energy life of the solar-type star HD 81809. XMM-Newton observations of a stellar activity cycle
Aims. The data set of the long-term XMM-Newton monitoring program of HD 81809
is analyzed to study its X-ray cycle, to investigate if the latter is related
to the chromospheric one, to infer the structure of the corona of HD 81809, and
to explore if the coronal activity of HD 81809 can be ascribed to phenomena
similar to the solar ones and, therefore, considered an extension of the solar
case. Methods. We analyze the observations of HD 81809 performed with
XMM-Newton with a regular cadence of 6 months from 2001 to 2016 and
representing one of the longest available observational baseline (~yr)
for a solar-like star with a well-studied chromospheric cycle (with a period of
~yr). We investigate the modulation of coronal luminosity and
temperature and its relation with the chromospheric cycle. We interpret the
data in terms of a mixture of solar-like coronal regions, adopting a
methodology originally proposed to study the Sun as an X-ray star. Results. The
observations show a well-defined regular cyclic modulation of the X-ray
luminosity that reflects the activity level of HD 81809. The data covers
approximately two cycles of coronal activity; the modulation has an amplitude
of a factor of (excluding evident flares, as in the June 2002
observation) and a period of ~yr, consistent with that of the
chromospheric cycle. We demonstrate that the corona of HD 81809 can be
interpreted as an extension of the solar case and it can be modeled with a
mixture of solar-like coronal regions along the whole cycle. The activity level
is mainly determined by a varying coverage of very bright active regions,
similar to cores of active regions observed in the Sun. Evidence of unresolved
significant flaring activity is present especially in proximity of cycle
maxima.Comment: 11 pages, 5 Figures, A&A accepte
The Ca II infrared triplet's performance as an activity indicator compared to Ca II H and K
Aims. A large number of Calcium Infrared Triplet (IRT) spectra are expected
from the GAIA- and CARMENES missions. Conversion of these spectra into known
activity indicators will allow analysis of their temporal evolution to a better
degree. We set out to find such a conversion formula and to determine its
robustness.
Methods. We have compared 2274 Ca II IRT spectra of active main-sequence F to
K stars taken by the TIGRE telescope with those of inactive stars of the same
spectral type. After normalizing and applying rotational broadening, we
subtracted the comparison spectra to find the chromospheric excess flux caused
by activity. We obtained the total excess flux, and compared it to established
activity indices derived from the Ca II H & K lines, the spectra of which were
obtained simultaneously to the infrared spectra.
Results. The excess flux in the Ca II IRT is found to correlate well with
and , as well as , if the
-dependency is taken into account. We find an empirical conversion formula
to calculate the corresponding value of one activity indicator from the
measurement of another, by comparing groups of datapoints of stars with similar
B-V.Comment: 16 pages, 15 figures. Accepted for publication in Astronomy &
Astrophysic
Time series of high resolution spectra of SN 2014J observed with the TIGRE telescope
We present a time series of high resolution spectra of the Type Ia supernova
2014J, which exploded in the nearby galaxy M82. The spectra were obtained with
the HEROS echelle spectrograph installed at the 1.2 m TIGRE telescope. We
present a series of 33 spectra with a resolution of R = 20, 000, which covers
the important bright phases in the evolution of SN 2014J during the period from
January 24 to April 1 of 2014. The spectral evolution of SN 2014J is derived
empirically. The expansion velocities of the Si II P-Cygni features were
measured and show the expected decreasing behaviour, beginning with a high
velocity of 14,000 km/s on January 24. The Ca II infrared triplet feature shows
a high velocity component with expansion velocities of > 20, 000 km/s during
the early evolution apart from the normal component showing similar velocities
as Si II. Further broad P-Cygni profiles are exhibited by the principal lines
of Ca II, Mg II and Fe II. The TIGRE SN 2014J spectra also resolve several very
sharp Na I D doublet absorption components. Our analysis suggests interesting
substructures in the interstellar medium of the host galaxy M82, as well as in
our Milky Way, confirming other work on this SN. We were able to identify the
interstellar absorption of M82 in the lines of Ca II H & K at 3933 and 3968 A
as well as K I at 7664 and 7698 A. Furthermore, we confirm several Diffuse
Interstellar Bands, at wavelengths of 6196, 6283, 6376, 6379 and 6613 A and
give their measured equivalent widths.Comment: 11 pages, 10 figures, accepted for publication in MNRA
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