Μελέτη των Μακροχρόνιων Παρατηρούμενων Μεταβολών της Τροχιακής Περιόδου στα Διπλά Εκλειπτικά Αστρικά Συστήματα

Doctoral Dissertation uoadl:1309127 473 Read counter

Unit:
Τομέας Αστροφυσικής, Αστρονομίας και Μηχανικής
Library of the School of Science
Deposit date:
2012-06-30
Year:
2012
Author:
Νανούρης Νικόλαος
Dissertation committee:
Επικ. Καθηγ. Ευγενία Αντωνοπούλου (Επιβλέπουσα), Καθηγ. Παναγιώτης Νιάρχος, Επικ. Καθηγ. Ελένη Λιβανίου-Ροβίθη, Επικ. Καθηγ. Μαίρη Κοντιζά (Αντικατέστησε την κα Ε. Λιβανίου-Ροβίθη την 08/02/2011 λόγω συνταξιοδότησης)
Original Title:
Μελέτη των Μακροχρόνιων Παρατηρούμενων Μεταβολών της Τροχιακής Περιόδου στα Διπλά Εκλειπτικά Αστρικά Συστήματα
Languages:
Greek
Summary:
The way that various physical processes act in binary systems can be
disentangled by interpreting their orbital period changes. Especially in the
case of eclipsing binary systems, this may happen by analyzing their O-C
diagrams, i.e. by monitoring their eclipse timing variations. The present
doctoral thesis aims towards the way that specific physical mechanisms -acting
individually or combined- modulate the O-C differences and, consequently, fix
the morphology of the O-C diagrams. The first goal this study aims to achieve
is the derivation of analytical expressions (to be referred as synthetic O-C
diagrams) describing the variations of the O-C differences under the action of
individual physical processes. Each of these synthetic O-C diagrams actually
represents a pure signal that finally becomes observable after its embedment in
a white noise background (mainly caused by errors in times of minimum light
detection and in solar-type activity). Since the time windows spanned the O-C
diagrams are limited, we specify in a second step, the minimum time interval
(i.e. number of orbital cycles) over which a pure O-C signal could be
observable. To realize this task, we have developed the appropriate methodology
via which the minimum required time span (with observations) becomes known in
order each examined mechanism to be measurable by means of O-C diagrams
analysis. The way that these intervals are modulated by crucial factors such as
the noise level, the orbital period and the intensity of the examined
mechanisms, is also investigated. Concerning the case of mass loss/exchange, it
is revealed that the inferred intervals do not depend on the (reference) period
while magnetic braking is proven to be very sensitive on the orbital period and
on the braking law adopted for inference. The second goal concerns the extent
at which very common presumptions, adopted so far in literature, are reliable
(e.g. the parabolic trend as a signature of long-term mechanisms). The proposed
approach has also led to useful and simple mathematical relations through which
important physical parameters, regarding the involved mechanisms, are rendered
known by means of O-C diagrams analysis. Finally, the modulation of O-C
diagrams under the combined action of properly parameterized physical
mechanisms is examined in the aforementioned way. The conditions, under which
the examined processes with opposite direction counterbalance each other, are
also presented. Especially in the case of detached binaries, we stress our
efforts to elucidate whether or not the impact of wind-driven magnetic braking
in period variations is measurable with certainty since it has been a subject
of debate for long time. It is revealed that magnetic braking is capable of
compensating the effects of mass loss, locking the orbital period invariable in
time. Several short-period RS CVn-type binaries (i.e. YY Gem, CV Boo, DU Leo,
HS Hya and WZ Oph), where this regime is expected to prevail, are also
examined.
Keywords:
Eclipsing Binary Systems, Stellar Wind, Mass and Angular Momentum Loss, Times of Minima, Synthetic O-C Diagrams
Index:
No
Number of index pages:
0
Contains images:
Yes
Number of references:
330
Number of pages:
xix, 366
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