71 research outputs found
The impact of CoRoT on close binary research
The space experiment CoRoT will provide continuous monitoring and high
accuracy light curves of about sixty thousand stars. Selected binary systems
will be observed in the Additional Program frame as targets of long and
continuous pointed observations. Moreover, thousands of new binaries will
certainly be detected and hundreds of them will have extremely accurate light
curves. This will allow studies of fine effects on the light curves, monitoring
of stellar activity and, in combination with ground-based observations, will
provide exquisite determination of stellar parameters.
Among the new discoveries of interesting systems of special value will be
those of low mass binaries.Comment: 6 pages, 2 figures, contribution to "Colse binaries in the 21th
century", Syros (Greece), June 2005. To be published by Ap&S
Disentangling effective temperatures of individual eclipsing binary components by means of color-index constraining
Eclipsing binary stars are gratifying objects because of their unique
geometrical properties upon which all important physical parameters such as
masses, radii, temperatures, luminosities and distance may be obtained in
absolute scale. This poses strict demand on the model to be free of systematic
effects that would influence the results later used for calibrations, catalogs
and evolution theory. We present an objective scheme of obtaining individual
temperatures of both binary system components by means of color-index
constraining, with the only requirement that the observational data-set is
acquired in a standard photometric system. We show that for a modest case of
two similar main-sequence components the erroneous approach of assuming the
temperature of the primary star from the color index yields temperatures which
are systematically wrong by ~100K.Comment: 6 pages, 3 figures, 1 table; to appear in proceedings of the Close
Binaries in the 21st Century conference in Syros, Greec
Eclipsing Binaries in Open Clusters
Detached eclipsing binaries are very useful objects for calibrating
theoretical stellar models and checking their predictions. Detached eclipsing
binaries in open clusters are particularly important because of the additional
constraints on their age and chemical composition from their membership of the
cluster. I compile a list containing absolute parameters of well-studied
eclipsing binaries in open clusters, and present new observational data on the
B-type systems V1481 Cyg and V2263 Cyg which are members of the young open
cluster NGC 7128.Comment: 4 pages, 2 colour figures. Poster presentation for IAUS 240 (Binary
Stars as Critical Tools and Tests in Contemporary Astrophysics), Prague,
August 2006. The poster itself can be dowloaded in ppt and pdf versions from
http://www.astro.keele.ac.uk/~jkt/pubs.htm
Photometric Observation And Period Study of GO Cygni
Photometric observations of GO Cyg were performed during the July-October
2002, in B and V bands of Johnson system. Based on Wilson's model, the light
curve analysis were carried out to find the photometric elements of the system.
The O-C diagram which is based on new observed times of minima suggests a
negative rate of period variation (dP/dt<0) for the system.Comment: 12 pages, 6 figures, 4 tables, submitted to Ap&S
Freedom in Nature
The paper starts with the proposal that the cause of the apparent
insolubility of the free-will problem are several popular but strongly
metaphysical notions and hypotheses. To reduce the metaphysics, some ideas are
borrowed from physics. A concept of event causality is discussed. The
importance of Hume's Principle of Causality is stressed and his Principle of
Causation is weakened. The key concept of the paper, the so-called relative
freedom, is also suggested by physics. It is a kind of freedom that can be
observed everywhere in nature. Turning to biology, incomplete knowledge is
defined for all organisms. They cope with the problem by Popper's trial and
error processes. One source of their success is the relative freedom of choice
from the basic option ranges: mutations, motions and neural connections.
Finally, the conjecture is adopted that communicability can be used as a
criterion of consciousness and free will is defined as a conscious version of
relative freedom. The resulting notion is logically self-consistent and it
describes an observable phenomenon that agrees with our experience.Comment: Changes: Improved formulation, three references added; 22 pages, no
figure. Comments are welcom
Reanalysis of two eclipsing binaries: EE Aqr and Z Vul
We study the radial-velocity and light curves of the two eclipsing binaries
EE Aqr and Z Vul. Using the latest version of the Wilson & Van Hamme (2003)
model, absolute parameters for the systems are determined. We find that EE Aqr
and Z Vul are near-contact and semi-detached systems, respectively. The primary
component of EE Aqr fills about 96% of its 'Roche lobe', while its secondary
one appears close to completely filling this limiting volume. In a similar way,
we find fill-out proportions of about 72 and 100% of these volumes for the
primary and secondary components of Z Vul respectively. We compare our results
with those of previous authors.Comment: 13 pages, 8 figures, 10 table
Masses and Radii of Low-Mass Stars: Theory versus Observations
Eclipsing binaries with M-type components are still rare objects. Strong
observational biases have made that today only a few eclipsing binaries with
component masses below 0.6 Msun and well-determined fundamental properties are
known. However, even in these small numbers the detailed comparison of the
observed masses and radii with theoretical predictions has revealed large
disagreements. Current models seem to predict radii of stars in the 0.4-0.8
Msun range to be some 5-15% smaller than observed. Given the high accuracy of
the empirical measurements (a few percent in both mass and radius), these
differences are highly significant. I review all the observational evidence on
the properties of M-type stars and discuss a possible scenario based on stellar
activity to explain the observed discrepancies.Comment: 8 pages, 1 figure, proceedings of the meeting "Close Binaries in the
21st Century
Biology and Life Cycle of Siganus vermiculatus (Siganidae, Pisces)
The herbivorou s fish Siganus vermiculatus (Valenciennes)
(Siganidae; Pisces), a mangrove swamp dweller, was studied in the field and in
captivity in Fiji. The fish has a lunar spawning cycle, benthic sticky eggs, and
pelagic larvae. Metamorphosis occurs between 23 and 27 days after hatching.
The fry live in small schools in brackish or fresh water among mangrove roots.
The young and adults are found mainly in shallow, murky water of mangrove
swamps where they move in and out with the tides . The adults are sometimes seen
in clear water near coral reefs or over sandy bottoms. Feeding takes place during
the day and at night and consists mainly of grazing on algae and mangrove roots.
A tolerance of extreme fluctuations in physicochemical parameters (temperature
19 to 38°C; salinity 2 to 55 ppt; dissolved oxygen 1.2ppm; pH 6.2 to 8.4) permits
the species to live in mangrove swamps
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