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VLTI observations of the central parsec of our Galaxy AMBER workshop Grenoble March 2007 Jörg-Uwe Pott I. Physik. Institut University of Cologne, Germany Outline of the presentation: • Introduction to the Galactic Center (GC; central pc) • Observational results achieved with AMBER • Outlook for AMBER & PRIMA Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected] ) Intro ) Observations ) Outlook The center of the Milky Way is the nearest nucleus of a galaxy: – harbors closest supermassive BHs (SMBH, 3*106M⊙) at only 8 kpc distance (1as~40mpc) – next similar galactic nucleus (Andromeda) is 100x farther – unique to study SMBH-host interaction – we have to understand star formation in the immediate vicinity of a SMBH and investigate the typical radiative properties to understand spatially unresolved observations Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected] ) Intro ) Observations ) Outlook • Current knowledge of the central stellar cluster: – lots of hot and massive stars ionizing the local ISM – indications for favoured massive star formation, ‘top-heavy IMF‘ – solar metallicity, ongoing star formation, Avis25 J&K two color K-Naco < GCIRS 7, K=6.5 < Sgr A* Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected] ) Intro ) Observations ) Outlook • Current knowledge of the central stellar cluster (II): Schödel+‘07 – stellar cusp due to the gravitational potential of the SMBH appears in stellar number counts – single telescope confusion limit at K~16mag (seeing limited) and K~17-18mag (AO-limited at 8, class teles.) Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected] ) Intro ) Observations ) Outlook • Current knowledge of the central stellar cluster (III): Pott+’06,‘07 – indications for a central outflow of SgrA*, of unknown importance for the stellar surroundings – a lot of warm dust in the MIR, shock-heated material, ionized gas – VLTI/MIDI can be used to study dust formation: Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected] ) Intro ) Observations ) Outlook • Why to search for binaries at the GC with VLTI? – help to understand / distinguish stellar properties of the central cluster and local star formation – dust formation in windy binary systems – analyze recently found ‘comoving groups‘ like IRS13E and IRS16 cluster, which have been suggested to harbour intermediate mass black holes of 103-4M⊙ • AMBER advantages: Schödel+‘05 – the closure phase can be more sensitive to binaries than the visibility measurements (e.g. Weigelt+’07) – only UT interferometry is sensitive enough for GC – only OLBI has sufficient angular resolution (currently only one eclipsing binary is known: IRS 16SW, Ott+‘99) Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected] ) Intro ) Observations ) Outlook • Current phase of the project: NIR dust emission MIR-10m MIDI obs – facing the real life: start to observe and gain experience (e.g.: learn how to select frames...) – AMBER with UTs in LR-mode is the only option due to sensitivity – first target: GCIRS7: red M1 supergiant, Teff=3600K, expected diameter: 0.5mas, if there is NO hot dust! Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected] ) Intro ) Observations ) Outlook • First observational results: visibility could be measured and calibrated at short baseline (U3-U4), but still low SNR Special thanks to S. Kraus, MPIfR 0.8-- Raw visibilities: where is my banana? best 10% best 30% best 10% best 30% 7 • ThinkGCIRS positive: Data might indicate: HD 153368 – calibrated visibility slightly increase with wavelength – 0.9Vis0.95 -> target slightly resolved -> 2mas – extended structure / binary possible Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected] ) Intro ) Observations ) Outlook • Feasibility of GC-AMBER observations was demonstrated – aggravating circumstances (high airmass, baseline tracking problems, strong piston error due to LRmode, bright calibrator etc.) avoided the measurement of CP, longer baseline visibilities and higher accuracy in Mar06 • Phase referencing on GCIRS7 appears to be possible • Extended structure might exist – > telescope time was awarded to redo this pioneering study and measure the long baseline visibilities and the closure phase in LR-mode in May07 Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected] ) Intro ) Observations ) Outlook • Potential sources for (phase-referenced) AMBER observations: Sources around the Galactic Center Black Hole Radius (arcsec) 3.5 3 2.5 2 R(1995.4) 1.5 Rmin 1 0.5 0 8 10 12 14 16 18 [data: Ghez+’98,‘05] – current Klim~9-10mag (Petrov+‘07), UT-vibro limited K-band Magnitude – already potential Klim~11 would help – off-axis phase-referencing with PRIMA/STS and FSU or FINITO will dramatically increase No. of targets – even SgrA* NIR-flares (Genzel, Eckart+) are within reach Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected] ) Intro ) Observations ) Outlook • Future: PRIMA astrometry at the GC to increase precision of stellar orbit measurements and prove the existence non-Keplerian due to GeneralRelativity [Schödel+’04] – several orbiting S-Stars (K=14..15: #5; K=15..17: #12) within 0.5 arcsec to SgrA* – stellar multiplicity and background influence of theses stars have to be known to understand astrometric errors (impact on spatial filtering) – >AMBER measurements can help to investigate these errors Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected] Thank You for your attention! Any questions? Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]