Introduction - Aims 1948 X-ray sources XMM-Newton EPIC observations of the largest Local Group spiral galaxy M 31, taken between June 2006 and February 2008, together with archival observations (Pietsch et al.2005) from June 2000 to July 2004 yielded a total of 1948 X-ray sources ( keV) covering (for the first time) the entire D25 ellipse of M 31, down to a limiting luminosity of ~10 35 erg/s in the keV band (Stiele et al. 2010). These sources include sources within M31, i.e. X-ray binaries, supernova remnants and supersoft sources foreground (galactic) stars (Hatzidimitriou et al. 2006, Bonfini et al. 2009) background objects, i.e. mostly active galactic nuclei, some normal galaxies and a few clusters of galaxies The XMM-Newton M31 Large Project Bonfini et al. 2009, A&A, 507, 705 Hatzidimitriou et al. 2006, A&A, 451, 835 Hatzidimitriou et al. 2011, in preparation Massey et al. 2006, AJ, 131, 2478 Meusinger et al. 2010, A&A, 512, 1 Pietsch et al.2005, A&A, 434, 483 Stiele et al. 2010, A&A, under revision References The XMM-Newton Large Project for M 31: The search for High-Mass X-ray Binaries Hatzidimitriou D. 1,2, Williams B.F. 3, Pietsch W.N. 4, Stiele H. 5, Green G.M. 3, Haberl F. 4, Bonfini, P. 6,2 1 University of Athens, Department of Physics – Section of Astrophysics, Astronomy & Mechanics, Greece, 2 Foundation of Research and Technology – Hellas, Heraklion, Greece, 3 Department of Astronomy, University of Washington, Seattle, USA, 4 Max-Planck-Institut für extraterrestrische Physik, Garching, Germany, 5 Osservatorio Astronomico di Brera, Italy, 6 Department of Physics, University of Crete, Heraklion, Crete, Greece XMM-Newton M31 – LP XMM-Newton M31 – LP : RGB image using bands , , keV Classification criteria of X-ray Sources Hardness ratios X-ray variability Correlations with catalogues in other wavelengths (optical, radio) – e.g. Local Group Survey (LGS: Massey et al. 2006) Locus of candidate counterparts on optical Colour Magnitude Diagrams and X-ray Hardness Ratio Diagrams High Mass X-ray binaries are expected to be classified as hard sources  A high percentage (65%) of the sources can only be classified as “hard” sources, i. e. they can be X-ray binaries (LMXB and HMXB) or Crab-like supernova remnants in M 31, or X-ray sources (mainly AGNs) in the background. Be-XRBs are expected to have early B spectral types (blue stars) and H-alpha emission Optical Spectroscopy Sample: Hard sources with blue counterparts, brighter than V~21 We have obtained optical spectra for a sample of 33 objects from the Apache Point Observatory in New Mexico using the 3.5 meter telescope, equipped with the medium dispersion Dual Imaging Spectrograph. For the blue branch, a 400 lines/mm grating was used, while the red branch was equipped with a 300 lines/mm grating. The spectra cover the wavelength ranges ~ Å, and ~ Å, with a nominal resolution of 1.83 Å/pixel and 2.31 Å/pixel, respectively. Figure 2 In Figure 2, the positions of the objects observed are overlayed on an optical image of M31 (Calar Alto, using HDAP) Figures 3-4 Examples of spectra obtained are shown in Figures 3-4 Results Four optical counterparts (of sources 407, 688, 696, 757) observed have early B spectral types, visual magnitudes, Figures 5-7 reddening free parameter “Q” values, and hardness ratios consistent with Be XRBs Figures 5-7 Τwo of these [407 (Fig. 3) and 688] show Hα emission (but there is also diffuse Hα emission in both cases) These are possible Be-XRBs in M31 candidate Supergiant-HMXB One Of supergiant which can be candidate Supergiant-HMXB. Two composite spectra candidate HMXB Wolf Rayet WN + O star  HII region + WR star of WN type: candidate HMXB Wolf Rayet WN + O star (Fig. 4)– colliding wind shock emission  supernova remnant + embedded early type (OB) star LMXB Two old globular cluster spectra, and therefore the X-ray emission may be coming from a LMXB (one of the sources also shows transient behaviour) Background sourcesNine Seyfert 1 galaxies Background sources: Nine Seyfert 1 galaxies with redshifts z~ peculiar flaring quasar (Meusinger et al. 2010). Foreground sourcesOne cataclysmic variableone U-Gem (dwarf nova) Foreground sources: One cataclysmic variable and one U-Gem (dwarf nova) variable in the Milky Way New Classification Criteria for identification of X-ray sources, e.g. using Figures 6-7 New Classification Criteria for identification of X-ray sources, e.g. using Figures 6-7 (Hatzidimitriou et al. 2011) Candidate HMXRB WN+OB (Embedded in HII region) [PFH 2005] 146 Brightest counterpart HII region Single counterpart Candidate Be XRB? (+ H α diffuse emission) Colour magnitude Diagram of all candidate counterparts O & B stars Hardness-Ratio Diagram Fig.1 Fig.2 Fig. 3 Fig. 4 Fig. 7 Fig.1 Introduction - Aims M31 is the nearest spiral galaxy to our own (780 kpc), and thanks to its moderate galactic foreground absorption and favorable inclination (78 o ), it is an ideal target for a detailed X-ray inventory of an archetypal low-star formation rate galaxy Identification and spectral classification of X-ray sources in nearby galaxies is necessary for correctly interpreting the properties of more distant ones, particularly since we can classify nearby systems with X-ray and optical data, while more distant ones via X-rays alone The HMXRB population in M31 remains elusive, and no HMXRB has been confirmed optically yet. The occurrence of HMXRBs, of the Be type in particular, are a sensitive star-formation indicator, and probably also sensitive to the metal abundance of the parent galaxy Our aim is to identify HMXRBs among the 1948 X-ray sources discovered by XMM-Newton in the direction of M31, by combining X ray and Our aim is to identify HMXRBs among the 1948 X-ray sources discovered by XMM-Newton in the direction of M31, by combining X ray and optical properties optical properties Be stars (MW) Fig. 6 Fig. 5 Q-parameter distribution for different classes of object [PFH 2005] 407 O + B stars in sample AGNs in sample All counterparts in LGS