5,036 research outputs found
Bisectors of the HARPS Cross-Correlation-Function. The dependence on stellar atmospheric parameters
Bisectors of the HARPS cross-correlation function (CCF) can discern between
planetary radial-velocity (RV) signals and spurious RV signals from stellar
magnetic activity variations. However, little is known about the effects of the
stellar atmosphere on CCF bisectors or how these effects vary with spectral
type and luminosity class. Here we investigate the variations in the shapes of
HARPS CCF bisectors across the HR diagram in order to relate these to the basic
stellar parameters, surface gravity and temperature. We use archive spectra of
67 well studied stars observed with HARPS and extract mean CCF bisectors. We
derive previously defined bisector measures (BIS, v_bot, c_b) and we define and
derive a new measure called the CCF Bisector Span (CBS) from the minimum radius
of curvature on direct fits to the CCF bisector. We show that the bisector
measures correlate differently, and non-linearly with log g and T_eff. The
resulting correlations allow for the estimation of log g and T_eff from the
bisector measures. We compare our results with 3D stellar atmosphere models and
show that we can reproduce the shape of the CCF bisector for the Sun.Comment: 13 pages, 20 figures. Accepted by A&
Angle Bisectors of a Triangle in Lorentzian Plane
In Lorentzian geometry, limited definition of angles restricts the use of
angle bisectors in study of triangles. This paper redefines angle bisectors so
that they can be used to study attributes of triangles. Using the new
definition, this paper investigates the existence of the incenter and the
isogonal conjugate of a triangle in Lorentzian plane.Comment: 15 pages, 7 figure
On bisectors in quaternionic hyperbolic space
In this paper, we study a problem related to geometry of bisectors in
quaternionic hyperbolic geometry. We develop some of the basic theory of
bisectors in quaternionic hyperbolic space . In particular, we show that
quaternionic bisectors enjoy various decompositions by totally geodesic
submanifolds of . In contrast to complex hyperbolic geometry, where
bisectors admit only two types of decomposition (described by Mostow and
Goldman), we show that in the quaternionic case geometry of bisectors is more
rich. We describe an infinite family of different decompositions of bisectors
in by totally geodesic submanifolds of isometric to complex
hyperbolic space .Comment: 16 page
Granulation in K-type Dwarf Stars. II. Hydrodynamic simulations and 3D spectrum synthesis
We construct a 3D radiative-hydrodynamic model atmosphere of parameters Teff
= 4820 K, log g = 4.5, and solar chemical composition. The theoretical line
profiles computed with this model are asymmetric, with their bisectors having a
characteristic C-shape and their core wavelengths shifted with respect to their
laboratory values. The line bisectors span from about 10 to 250 m/s, depending
on line strength, with the stronger features showing larger span. The
corresponding core wavelength shifts range from about -200 m/s for the weak Fe
I lines to almost +100 m/s in the strong Fe I features. Based on observational
results for the Sun, we argue that there should be no core wavelength shift for
Fe I lines of EW > 100 mA. The cores of the strongest lines show contributions
from the uncertain top layers of the model, where non-LTE effects and the
presence of the chromosphere, which are important in real stars, are not
accounted for. The comparison of model predictions to observed Fe I line
bisectors and core wavelength shifts for a reference star, HIP86400, shows
excellent agreement, with the exception of the core wavelength shifts of the
strongest features, for which we suspect inaccurate theoretical values. Since
this limitation does not affect the predicted line equivalent widths
significantly, we consider our 3D model validated for photospheric abundance
work.Comment: A&A, in pres
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