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Science with the Very Large Telescope Interferometer (VLT-I)
Jean-Baptiste Le Bouquin (ESO, Chile)for
VLTI Team, AMBER team, MIDI team, PRIMA team…
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The VLTI at Cerro Paranal (II region)
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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 ELTwith perfect AO
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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
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Beyond the diffraction limit…The power of interferometric fringes
Objects Single Telescope of 8m2 Telescopes of 8m separated by 50m
Small !
Big !
Any differences ?
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Practice: What is this object ?
8m TelescopeObject: a close binary
(here as seen with a single telescope of 50m)
2 Telescopes of 8m separated by
50m…
… and with different
baseline angles
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The Very Large Telescope InterferometerQuickTime™ et undécompresseur
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The Very Large Telescope Interferometer
• 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
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4 movable ATs
4 fixed UTs
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The Very Large Telescope Interferometer
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Overview of Cerro Paranal
Full power:~200x120m telescope
Current VLTI:~120x80m telescope
Limiting magnitude
Spatial resolution
E-ELT40m telescope
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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
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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 …
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Science with VLTI : examplesQuickTime™ et undécompresseur
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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
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Density waves in circum-stellar disks
Model of Be star:photosphere + rotating disk
AMBER astrometryacross a line formed in the disk
• Disk has a right/left asymmetry = density wave• Is it counter-rotating ?
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Resolving the photosphere of fast rotators
HST imagesAMBER astrometry
Fomalhaut
• Disk and star are aligned, like in the solar system• Does the star and the planet rotate the same way ?
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Evolved stars : shell around Mira stars
H-band (water) H-band K-band (CO)
• How these stars (T=3500K) can create molecules ?
• How is this material dispersed in the Interstellar Medium ?
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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 …
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• Concept: dual-beam (2 stars) 2 telescopes
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Toward full power…
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Future Instrumentation : GRAVITY
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• 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)
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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
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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
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VLT-I: a complementary facility in the ALMA and E-ELT area