Transcript model of convection

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)
The diffraction limit:
Spatial resolution versus telescope size
0.5as = 8m telescope
(FORS with seeing of 0.5”)
Betelgeuse ~ largest star on the sky
(model by Freytag et al.)
40 mas = 8m telescope with perfect AO
(best NACO performances)
8 mas = 40m ELT
with perfect AO
1.5 mas = VLTI
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And not only Betelgeuse has
interesting features
Betelgeuse
(model of convection)
A normal star with its 5
branches
The evolved star
Mira imaged by
HST in the UV.
Indirect reconstruction
of AB Dor
(magnetic spots)
Long term goal: image
other stars as we
image the Sun !
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Beyond the diffraction limit…
The power of interferometric fringes
Small !
Any differences ?
Big !
Objects
Single Telescope of 8m
2 Telescopes of 8m
separated by 50m
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Practice: What is this object ?
Object: a close binary
8m Telescope
(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
Interferometer
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The Very Large Telescope Interferometer
• Emulate a 180m telescope at cerro
Paranal, by optical Interferometry
4 fixed UTs
• 4 UTs : 8m, fixed telescopes
(~few night per month)
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• 4 ATs : 1.8m movable telescopes
(every night)
• Instruments:
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AMBER
MIDI
PRIMA
Future instruments
4 movable ATs
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The Very Large Telescope Interferometer
Overview of Cerro Paranal
Limiting magnitude
Spatial resolution
Full power:
~200x120m telescope
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Current VLTI:
~120x80m telescope
E-ELT
40m telescope
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Current Instrumentation
• AMBER
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3 telescopes
J, H and K bands (near-IR)
spectrograph
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R=45, 1.200, 10.000
FOV: 150mas
Spatial resolution: 2mas
Limiting magnitude: K~8mag
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• MIDI
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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)
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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)
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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
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• AMBER instrument (~20 referee papers)
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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 : examples
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Stellar parameters and stellar activity
Diameter of V3879 Sgr (M4III)
diam = 7.52mas +/- 0.2%,
and perfectly circular
BUT
• This star is pulsating:
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perfectly radial pulsations ?
follow the pulsation
• This star is convective:
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why we don’t see any
asymmetries ?
upper limits on the convective
cell contrast : ~1%
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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 ?
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Resolving the photosphere of fast rotators
AMBER astrometry
HST images
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
• How these stars (T=3500K) can
create molecules ?
• How is this material dispersed in
the Interstellar Medium ?
H-band (water)
H-band
K-band (CO)
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Incoming: precise astrometry with PRIMA
• Concept:
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dual-beam (2 stars)
2 telescopes
• Product and strategy:
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precise astrometry between the 2
stars (10micro-as)
long term follow-up (several
years)
• Goals:
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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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Toward full power…
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Future Instrumentation : GRAVITY
Current observations of
stars around Sgr A*
• Relativistic orbits of stars close
to the horizon of Sgr A*
• Hot spots in the
last stable orbit
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• Put into test the strong field limit of General
Relativity (untested so far)
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Future instrumentation : GRAVITY
• Combining 4 UTs
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imaging capability
• AO with IR wavefront-sensor
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no bright visible source around Sgr A*
• Off-axis fringe-tracking
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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:
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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
• Science goals:
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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
20mas
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VLT-I: a complementary facility in the ALMA and
E-ELT area
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