Mathematics – Logic
Scientific paper
Mar 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009phdt.........2v&link_type=abstract
PhD thesis. 160 pages. Legal deposit: B.29632-2009. ISBN: 978-84-692-3663-5. Advisors: Carme Jordi & Ignasi Ribas
Mathematics
Logic
Stars: Binaries: Eclipsing, Stars: Fundamental Parameters, Stars: Distances, Galaxies: Individual: M31
Scientific paper
The Andromeda Galaxy (M31) is an excellent distance calibrator in the Cosmological Distance Ladder. We present the first direct distance determination to M31 using eclipsing binaries (EBs). EBs provides direct distance determinations because the fundamental properties of their components can be measured without any previous calibration. Distance determination with EBs requires, at least, two data sets: time series photometry and spectroscopy. We obtained high quality light curves (rms~0.01 mag) from a 34'x34' photometric survey in M31 (in Johnson B and V filters) carried out at the 2.5 m Isaac Newton Telescope (La Palma, Spain). This survey provided light curves for almost 4000 variable stars, with over 400 EBs and 400 Cepheids. The 24 brightest EBs (V<20.5 mag) with deeper eclipses (dV>0.2 mag) were selected as optimum candidates for distance determination. Five of these EBs (located in a 5'x5' region) were selected to be observed with the multi-object spectrograph (GMOS) at the Gemini-North telescope. We obtained accurate radial velocities for the four brightest EBs observed with GMOS, enabling the first direct determination of masses and radii of stars in M31. Two of these EBs were used to derive a direct distance determination to M31 of (m-M)o=24.36+/-0.08 mag. Another system is the most massive EB with apsidal motion ever reported, enabling the analysis of the distribution of matter in the interior of stars with masses larger than 40 Msun. In all cases, the direct determination of masses and radii allowed a direct comparison with stellar evolutionary models, providing the evolutionary stage for each system. In addition to the EB analysis, we also performed a comprehensive study of Cepheids in M31. The obtained results showed that blending is as important as metallicity correction when determining Cepheid distances to Local Group galaxies and provided an additional distance determination to M31 of (m-M)o=24.32+-0.12 mag, fully compatible with the EB distance. Finally, we also discovered a large flare during the acquisition of the photometric catalog. The performed study revealed that the underlying source was a dM star having one of the most energetic flares ever observed.
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