1. Science with the Very Large Telescope Interferometer (VLT-I) Jean-Baptiste Le Bouquin (ESO, Chile) for VLTI Team, AMBER team, MIDI team, PRIMA team… The VLTI at Cerro Paranal (II region)

2. 2 Betelgeuse ~ largest star on the sky (model by Freytag et al.) The diffraction limit: Spatial resolution versus telescope size 1.5 mas = VLTI 40 mas = 8m telescope with perfect AO (best NACO performances) 0.5as = 8m telescope (FORS with seeing of 0.5”) 8 mas = 40m ELT with perfect AO

3. 3 The evolved star Mira imaged by HST in the UV. And not only Betelgeuse has interesting features Indirect reconstruction of AB Dor (magnetic spots) Long term goal: image other stars as we image the Sun ! Betelgeuse (model of convection) A normal star with its 5 branches

4. 4 Beyond the diffraction limit… The power of interferometric fringes Objects Single Telescope of 8m 2 Telescopes of 8m separated by 50m Small ! Big ! Any differences ?

5. 5 Practice: What is this object ? 8m Telescope Object: a close binary (here as seen with a single telescope of 50m) 2 Telescopes of 8m separated by 50m… … and with different baseline angles

6. 6 The Very Large Telescope Interferometer

7. 7 Emulate a 180m telescope at cerro Paranal, by optical Interferometry 4 UTs : 8m, fixed telescopes (~few night per month) 4 ATs : 1.8m movable telescopes (every night) Instruments:  AMBER  MIDI  PRIMA  Future instruments 4 movable ATs 4 fixed UTs

8. 8 The Very Large Telescope Interferometer Overview of Cerro Paranal Full power: ~200x120m telescope Current VLTI: ~120x80m telescope Limiting magnitude Spatial resolution E-ELT 40m telescope

9. 9 Current Instrumentation AMBER  3 telescopes  J, H and K bands (near-IR)  spectrograph  R=45, 1.200, 10.000  FOV: 150mas  Spatial resolution: 2mas  Limiting magnitude: K~8mag MIDI  2 telescopes  N band (mid-IR)  spectrograph  FOV: ~2arcsec  Spatial resolution: 15mas  Limiting magnitude: ~5Jy

10. 10 Science with VLTI VINCI commissioning instrument (~40 referee papers)  First radius measurements of very low mass stars with the VLTI  Direct diameter measurement of a star filling its Roche lobe  Gravitational-darkening of Altair from interferometry  Cepheid distances from infrared long-baseline interferometry  … MIDI instrument (~40 referee papers)  Monitoring of the dust formation event of the Nova V1280 Sco  Extended envelopes around Galactic Cepheids  Probing the dusty environment of the nucleus in NGC 3783  The post-AGB binary IRAS 08544-4431: circumbinary disc resolved  … AMBER instrument (~20 referee papers)  Spatially resolving the hot CO around the young Be star 51 Oph  A young high-mass star rotating at critical velocity  Diameter and photospheric structures of Canopus  …

11. 11 Science with VLTI : examples

12. 12 Stellar parameters and stellar activity Diameter of V3879 Sgr (M4III) This star is pulsating:  perfectly radial pulsations ?  follow the pulsation This star is convective:  why we don’t see any asymmetries ?  upper limits on the convective cell contrast : ~1% diam = 7.52mas +/- 0.2%, and perfectly circular BUT

13. 13 Density waves in circum-stellar disks Model of Be star: photosphere + rotating disk AMBER astrometry across a line formed in the disk Disk has a right/left asymmetry = density wave Is it counter-rotating ?

14. 14 Resolving the photosphere of fast rotators HST images AMBER astrometry Fomalhaut Disk and star are aligned, like in the solar system Does the star and the planet rotate the same way ?

15. 15 Evolved stars : shell around Mira stars H-band (water)H-bandK-band (CO) How these stars (T=3500K) can create molecules ? How is this material dispersed in the Interstellar Medium ?

16. 16 Incoming: precise astrometry with PRIMA Product and strategy:  precise astrometry between the 2 stars (10micro-as)  long term follow-up (several years) Goals:  real mass of known planets (unveiling V from Vsini)  new detections  stellar activity (spots, convection)  off-axis fringe-tracking for AMBER and MIDI  … Concept:  dual-beam (2 stars)  2 telescopes

17. 17 Toward full power…

18. 18 Future Instrumentation : GRAVITY Relativistic orbits of stars close to the horizon of Sgr A* Hot spots in the last stable orbit Current observations of stars around Sgr A* Put into test the strong field limit of General Relativity (untested so far)

19. 19 Future instrumentation : GRAVITY Combining 4 UTs  imaging capability AO with IR wavefront-sensor  no bright visible source around Sgr A* Off-axis fringe-tracking  K~10 for the bright on-axis one  K~15 for the faint, off-axis one Detecting the hot spots on the last stable orbit:  5 micro-as precision  at K~15  in few minutes

20. 20 Future instrumentation : general purpose imaging instruments (MATIS, VSI…) Goal: provide the community with images at few mas spatial resolution, in the J,H, K and N-band, in one night of observation, down to a magnitude K~11 20mas Science goals:  Formation of stars and planets  Imaging stellar surfaces  Evolved stars, stellar remnants & stellar winds  Active Galactic Nuclei & Super massive Black Holes An evolved star imaged by current VLTI

21. 21 VLT-I: a complementary facility in the ALMA and E-ELT area