Doctoral theses
Current Record: 1990 of 2443
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| Identifier |
uch.physics.phd//2008antoniou |
| Title |
The X-ray Source Population of the Small Magellanic Cloud |
| Alternative Title |
Ο πληθυσμός των πηγών ακτίνων Χ στο μικρό νέφος του Μαγγελάνου |
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Author
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Αντωνίου, Βαλσάμω
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Thesis advisor
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Χατζηδημητρίου, Δέσποινα
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| Abstract |
In this work we study the X-ray source population of the Small Magellanic Cloud (SMC).
The SMC is our second nearest star-forming galaxy, which allows us to identify the optical
counterparts of the X-ray binary population (XRB) and therefore directly study their link
with star-formation (SF). Using Chandra, XMM-Newton and optical photometric catalogs
we study the young XRB population of this galaxy, down to luminosity levels of quiescent
X-ray source populations. The Chandra observations in particular cover the central,
densest and most active region of the SMC, while the XMM-Newton survey is designed to
probe regions of different stellar populations (10− 500Myr). Based on the comparison of
these observations with comprehensive stellar catalogs of the SMC, we propose for the first
time 25 candidate High Mass X-ray Binaries, of which 16 are candidate Be X-ray binaries
(Be-XRBs; 9 new candidates in the Chandra survey and 7 in the XMM-Newton fields).
Moreover, we confirm previous classification of Be-XRBs for 19 sources (18 in Chandra,
and 1 in the XMM-Newton survey). We also examine the “overabudance” of Be-XRBs in
the SMC fields with respect to the Milky Way. In luminosities down to ∼ 1034 erg s-1 , we
find that Be-XRBs are ∼ 2 times more common in the SMC when compared to the Milky
Way even after taking into account the difference in the formation rates of OB stars. This
residual excess can be attributed to the lower metallicity of the SMC. Finally, we find that
the mixing of Be-XRBs with other than their natal stellar population is not an issue in our
comparisons of Be-XRBs and stellar populations in the SMC. Instead we find indication
for variation of the XRB populations of the SMC on kiloparsec scales, related to local
variations of the formation rate of OB stars and slight variation of their age, which results
in different relative numbers of Be stars and therefore XRBs. Comparison of the Be-XRB
populations with their local star-formation history shows that they are observed in regions
with SF rate bursts ∼ 30−70 Myr ago. The age range coincides with the age of maximum
Be-star formation, based on independent studies of Galactic and SMC Be stars. We also
find a strong correlation between the number of Be-XRBs and the strength of the SF at
the age of maximum Be-star formation (i.e. ∼ 40 Myr ago), while regions with strong but
more recent SF (e.g. the Wing) are deficient in Be-XRBs. Regions that host HMXBs,
which however have not been proved yet to be Be-XRBs, show a similar SF history (with
a significant burst at ∼ 40 Myr ago). We thus conclude that the majority of the optically
unidentified SMC HMXBs have a Be nature. The very strong correlation of the young
X-ray sources with the stellar population in scales of a few arcminutes (∼ 0.5kpc) provides
strong evidence for relatively small supernova kicks during the formation of the compact
object. Finally, we have used the 2dF (Two-degree Field) spectrograph on the 3.9m
Anglo-Australian Telescope (AAT) to confirm the classification of candidate Be-XRBs as
emission line stars and identify their spectral type and luminosity class when possible.
Our sample is selected from the Chandra survey and existing XMM-Newton observations
of the SMC. These observations show that the distribution of spectral types of Be-XRBs
in the SMC agrees with that of the LMC, while it is in contrast to the population of Be-
XRBs in the Milky Way. In addition we confirmed the different distributions of spectral
type of Be stars in XRB systems and individual Be stars. With these spectra we also
discover the second supergiant X-ray binary in the SMC. Overall this study demonstrates
the importance of the Be-XRBs as a dominant component of young XRB populations,
and shows evidence for strong evolution of the X-ray source populations of ages < 100Myr
and different metallicities.
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| Language |
English |
| Issue date |
2008-05-12 |
| Collection
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School/Department--School of Sciences and Engineering--Department of Physics--Doctoral theses
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Type of Work--Doctoral theses
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| Permanent Link |
https://elocus.lib.uoc.gr//dlib/a/e/f/metadata-dlib-user1214805032-31716.tkl
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| Views |
741 |
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