This Thesis is devoted to the study of the optical companions of Millisecond
Pulsars in Galactic Globular Clusters (GCs) as a part of a large project started at
the Department of Astronomy of the Bologna University, in collaboration with other
institutions (Astronomical Observatory of Cagliari and Bologna, University of Virginia),
specifically dedicated to the study of the environmental effects on passive stellar evolution
in galactic GCs.
Globular Clusters are very efficient “Kilns” for generating exotic object, such as
Millisecond Pulsars (MSP), low mass X-ray binaries(LMXB) or Blue Straggler Stars
(BSS). In particular MSPs are formed in binary systems containing a Neutron Star which
is spun up through mass accretion from the evolving companion (e.g. Bhattacharia & van
den Heuvel 1991). The final stage of this recycling process is either the core of a peeled
star (generally an Helium white dwarf) or a very light almos exhausted star, orbiting a very
fast rotating Neutron Star (a MSP). Despite the large difference in total mass between the
disk of the Galaxy and the Galactic GC system (up a factor 103), the percentage of fast
rotating pulsar in binary systems found in the latter is very higher. MSPs in GCs show spin
periods in the range 1.3 ÷ 30ms, slowdown rates ˙P 1019 s/s and a lower magnetic field,
respect to ”normal” radio pulsars, B 108 gauss . The high probability of disruption of a
binary systems after a supernova explosion, explain why we expect only a low percentage
of recycled millisecond pulsars respect to the whole pulsar population. In fact only the
10% of the known 1800 radio pulsars are radio MSPs.
Is not surprising, that MSP are overabundant in GCs respect to Galactic field, since
in the Galactic Disk, MSPs can only form through the evolution of primordial binaries,
and only if the binary survives to the supernova explosion which lead to the neutron star
formation. On the other hand, the extremely high stellar density in the core of GCs,
relative to most of the rest of the Galaxy, favors the formation of several different binary
systems, suitable for the recycling of NSs (Davies at al. 1998).
In this thesis we will present the properties two millisecond pulsars companions
discovered in two globular clusters, the Helium white dwarf orbiting the MSP PSR 1911-5958A in NGC 6752 and the second case of a tidally deformed star orbiting an eclipsing
millisecond pulsar, PSR J1701-3006B in NGC6266
| Identifer | oai:union.ndltd.org:unibo.it/oai:amsdottorato.cib.unibo.it:631 |
| Date | 28 March 2008 |
| Creators | Cocozza, Gabriele <1974> |
| Contributors | Ferraro, Francesco Rosario |
| Publisher | Alma Mater Studiorum - Università di Bologna |
| Source Sets | Università di Bologna |
| Language | English |
| Detected Language | English |
| Type | Doctoral Thesis, PeerReviewed |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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