1.  AMBER workshop Grenoble March 2007 Jörg-Uwe Pott I. Physik. Institut University of Cologne, Germany VLTI observations of the central parsec of our Galaxy

2. Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: pott@ph1.uni-koeln.de Introduction to the Galactic Center (GC; central pc) Observational results achieved with AMBER Outlook for AMBER & PRIMA Outline of the presentation:

3. Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: pott@ph1.uni-koeln.de The center of the Milky Way is the nearest nucleus of a galaxy: –harbors closest supermassive BHs (SMBH, 3*10 6 M ⊙ ) 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  ) Intro  ) Observations  ) Outlook

4. Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: pott@ph1.uni-koeln.de 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, A vis  25  ) Intro  ) Observations  ) Outlook < GCIRS 7, K=6.5 < Sgr A* J&K two color K-Naco

5. Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: pott@ph1.uni-koeln.de Current knowledge of the central stellar cluster (II): –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.)  ) Intro  ) Observations  ) Outlook Schödel+‘07

6. Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: pott@ph1.uni-koeln.de Current knowledge of the central stellar cluster (III): –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:  ) Intro  ) Observations  ) Outlook Pott+’06,‘07

7. Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: pott@ph1.uni-koeln.de 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 10  3-4 M ⊙ AMBER advantages: –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)  ) Intro  ) Observations  ) Outlook Schödel+‘05

8. Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: pott@ph1.uni-koeln.de Current phase of the project: –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, T eff =3600K, expected diameter: 0.5mas, if there is NO hot dust! NIR dust emission  MIR-10  m MIDI obs  ) Intro  ) Observations  ) Outlook

9. Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: pott@ph1.uni-koeln.de First observational results: visibility could be measured and calibrated at short baseline (U3-U4), but still low SNR Raw visibilities: where is my banana? GCIRS 7 HD 153368 best 30% best 10% Think positive: Data might indicate: –calibrated visibility slightly increase with wavelength –0.9  Vis  0.95 -> target slightly resolved -> 2mas –extended structure / binary possible  ) Intro  ) Observations  ) Outlook Special thanks to S. Kraus, MPIfR 0.8--

10. Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: pott@ph1.uni-koeln.de Feasibility of GC-AMBER observations was demonstrated –aggravating circumstances (high airmass, baseline tracking problems, strong piston error due to LR- mode, 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  ) Intro  ) Observations  ) Outlook

11. Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: pott@ph1.uni-koeln.de Potential sources for (phase-referenced) AMBER observations: –current K lim ~9-10mag (Petrov+‘07), UT-vibro limited –already potential K lim ~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 [data: Ghez+’98,‘05]  ) Intro  ) Observations  ) Outlook

12. Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: pott@ph1.uni-koeln.de [Schödel+’04] Future: PRIMA astrometry at the GC to increase precision of stellar orbit measurements and prove the existence non-Keplerian due to GeneralRelativity –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  ) Intro  ) Observations  ) Outlook

13. Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: pott@ph1.uni-koeln.de the end Thank You for your attention! Any questions?