450 research outputs found
Investigation of the Praesepe cluster. III. Radial velocity and binarity of the F5-K0 Klein-Wassink stars
Coravel observations of 103 F5-K0 stars in the Praesepe cluster yielded 24
spectroscopic binaries (3 are non-members), and 20 orbits were determined, with
periods from 4 to 7400 days. Based on a complete sample in the colour range
0.40 < B-V < 0.80 (80 stars, including KW 244 = TX Cnc), the companion star
fraction CSF = 0.45. The percentage of spectroscopic binaries with P < 1000d is
20% (16/80). The combined photometric and spectroscopic analysis showed that 12
among 18 single-lined spectroscopic binaries are located within the "single"
star sequence in the (V,B-V) diagram and cannot be detected by the photometric
analysis in the UBV system. In addition, seven photometrically analysed
binaries were not detected with the radial velocity observations, but are
confirmed members. The number of single:binary:triple stars is 47:30:3.Comment: 10 pages, 3 tables, 7 eps figures. Accepted for A&A. LaTe
Detection of Planetary Transits Across a Sun-like Star
We report high precision, high cadence photometric measurements of the star
HD 209458, which is known from radial velocity measurements to have a planetary
mass companion in a close orbit. We detect two separate transit events at times
that are consistent with the radial velocity measurements. In both cases, the
detailed shape of the transit curve due to both the limb darkening of the star
and the finite size of the planet is clearly evident. Assuming stellar
parameters of 1.1 R_Sun and 1.1 M_Sun, we find that the data are best
interpreted as a gas giant with a radius of 1.27 +/- 0.02 R_Jup in an orbit
with an inclination of 87.1 +/- 0.2 degrees. We present values for the
planetary surface gravity, escape velocity, and average density, and discuss
the numerous observations that are warranted now that a planet is known to
transit the disk of its parent star.Comment: 10 pages, 3 figures, accepted by ApJ Letter
Chirality in curved polyaromatic systems
Carbon allotropes constituted of sp(2)-hybridised carbon atoms display a variety of properties that arise from their delocalised Pi-conjugated electronic structure. Apart from carbon's planar allotropic form graphene, bent or curved structures, such as carbon nanotubes or fullerenes, respectively, have been discovered. In this Tutorial Review, we analyse and conceptually categorise chiral synthetic molecular fragments of non-planar sp(2)-carbon allotropes, including hypothetical forms of carbon that have been proposed to exist as stable entities. Two types of molecular systems composed of equally or differently sized rings are examined: bent with zero Gaussian curvature and curved with positive or negative Gaussian curvature. To affirm that a system is chiral, two conditions must be fulfilled: (1) both reflective symmetry elements, an inversion centre and a mirror plane, must be absent and (2) the system must be stereochemically rigid. It is therefore crucial to not only consider the symmetry of a given system as if it was a rigid object but also its structural dynamics. These principles serve as guidelines for the design of molecular fragments that encode and transcribe chirality into larger systems
The "missing link": a 4-day period transiting exoplanet around OGLE-TR-111
We report the discovery of a transiting hot Jupiter around OGLE-TR-111, from
our radial velocity follow-up of OGLE transiting candidates in Carina. The
planet has a mass of 0.53 +- 0.11 M_J and a radius of 1.0 +0.13-0.06 R_J. Three
transiting exoplanets have already been found among OGLE candidates, all with
periods near 1.5 days. The planet presented here, with P=4.0 days, is the first
exoplanet detected by transits with the characteristics of a "normal" hot
Jupiter, as found in abundance by radial velocity surveys The radius of
OGLE-TR-111b and the scarcity of hot Jupiters detected among OGLE transit
candidates tend to indicate that the case of HD209458b, with a radius of 1.4
R_J, is exceptional, with most hot Jupiters being smaller.Comment: 4 pages, 4 figures, to be published in A&A Letter
Determining Inversion Barriers in Atrop- isomers - A Tutorial for Organic Chemists
Dynamic behavior is a fascinating property of natural and artificial systems and its understanding has significantly impacted the transformation of molecular interchanges into controlled molecular motion. In this tutorial, the key descriptors of enantiomeric stability are examined in-depth. Enantiomerization and racemization are discussed and differentiated on a fundamental level proposing a unified and distinct nomenclature. Their mathematical meanings and relations are described and deduced cohesively in the context of atropisomerization. The calculation of inversion barriers from thermodynamic and kinetic data is demonstrated and the interdependences between the latter are explained mathematically. Using current examples from our group, the determination of rate constants and the thermodynamic parameters is shown in a step-by-step manner using the most common techniques. The tutorial is concluded with aspects and considerations concerning statistical data analysis and error determination of measurements including a practical guide to Monte-Carlo simulations
Oscillations on the star Procyon
Stars are sphere of hot gas whose interiors transmit acoustic waves very
efficiently. Geologists learn about the interior structure of Earth by
monitoring how seismic waves propagate through it and, in a similar way, the
interior of a star can be probed using the periodic motions on the surface that
arise from such waves. Matthews et al. claim that the star Procyon does not
have acoustic surface oscillations of the strength predicted. However, we show
here, using ground-based spectroscopy, that Procyon is oscillating, albeit with
an amplitude that is only slightly greater than the noise level observed by
Matthews et al. using spaced-based photometry
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