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Identifier

000388331

Title

Investigation of the high-mass X-ray binary populations in the small Magellanic cloud

Alternative Title

Μελέτη των διπλών αστρικών συστημάτων εκπομπής ακτίνων -Χ μεγάλης μάζας στο μικρό νέφος του Μαγγελάνου

Author

Μαραβέλιας, Γρηγόρης

Thesis advisor

Ζέζας, Ανδρέας

Reviewer

Παπαδάκης, Ιωσήφ
Pablo, Reig
Χατζηδημητρίου, Δέσποινα
Κυλάφης, Νικόλαος
Παυλίδου, Βασιλική
Τάσσης, Κώστας

Abstract

We investigated the High-Mass X-ray Binary (HMXB) population in the Small Magellanic Cloud (SMC), using two methods to obtain their observational parameters (spectral types, Hα excess), and we developed two techniques for automated and quantitative spectral classification. A spectroscopic survey to obtain optical spectra for a large number of SMC HMXBs identified in previous Chandra and XMM-Newton surveys, resulted in the identification of the spectral types for 5 new HMXBs, and the confirmation of the spectral classification of 15 known HMXBs. We find marginal evidence for difference between the spectral type distributions between the HMXB populations in the SMC and our Galaxy, but no statistically significant differences for their orbital periods and the eccentricities. We provide evidence that the well known supergiant B[e] star LHA 115-S 18 is the optical counterpart of the weak X-ray source CXOU J005409.57-724143.5, and we discuss the scenario of an obscured supergiant X-ray binary. To overcome the subjectivity in the stellar spectral classification, based on the visual inspection of their spectra, we developed two diagnostic schemes by measuring the equivalent (EW) width of diagnostically important spectral lines for early-type stars: (a) the Continuous Fit approach gives the spectral type of a star as the solution of an equation involving the EWs of different spectral lines, and succesfully classifies the majority of the sources (~65%), (b) a Naive Bayesian Classifier gives the probability that a spectrum corresponds to a given spectral type, based on the distribution of EWs of diagnostic lines of different stellar spectral types, and correctly classifies the majority (~70%) of early-type stars in our samples (limited only by the training sample). We performed Hα imaging for 6 fields in the SMC with recent star formation, to search for new Hα emitting counterparts for X-ray sources detected by the XMM-Newton survey (Sturm et al., 2013). We identified 4747 Hα emission sources down to R=18.7 mag (equivalent to ~B8 type Main Sequence stars), providing support in favor of the HMXB nature for 8 candidate HMXBs. We find that OBe stars are 13% of the total OB stellar population in the SMC, and their Hα excess peaks at spectral range O9-B2. The fraction of confirmed and candidate HMXBs with respect to the OBe stars is found to be in the range ~ 0.0005-0.0014 HMXB/OBe, a direct measurement of the formation rate of HMXBs in the SMC.

Language

English

Subject

Emission-line/BE stars

Galaxy

HA imaging

Massive stars

Optical spectroscopy

X-ray binaries

Άστρα εκπομπής/άστρα BE

Άστρα μεγάλης μάζας

Απεικόνιση HA