Science with Optical/NIR Interferometers
Interferometry Week
ESO Santiago, 14-16 January 2002
A. Richichi (ESO Garching)
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Layout of the Tutorial - I
Interferometers
• Types of interferometers under consideration
• Types of interferometry not considered here
• Characteristics of interferometers vs. science drivers
• Illustration of a few representative facilities
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Layout of the Tutorial - II
Stars & PMS Stars
• Fundamental Stellar Parameters- diameters, limb darkening, flattening- temperatures- masses- ages
• Binaries
• Stellar Pulsation
• Circumstellar Matter
• Distances
Science with Interferometers
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Layout of the Tutorial - III
Exoplanets and BD
• Detection and discrimination
• Basic parameters
• Relationship to other EP/BD detection methods
Extragactic sources
• Detection
• Basic parameters
• Observation strategies
Miscellaneous
• Microlensing
• Solar system objects
Science with Interferometers ctd.
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VLTI Science - Main ReferencesESO Symposia: Science with the VLT - 1994 (Walsh/Danziger)
Science with the VLTI - 1996 (Paresce)
From Extrasolar Planets to Cosmology - 1999 (Renzini)
SPIE Interferometry in Optical Astronomy: 1998 Kona, 2001 JENAM,
2000 Munich (22 papers on science with ground-based interferometers)
Workshops: i.e., ESO April 2001, June 2001
Schools: i.e., 1999 Michelson Summer School, 2000 NOVA/ESO/ESA Summer School, 2002 EuroWinter School.
Scientific Objectives of the VLT Interferometer (Paresce, March 2001) (http://www.hq.eso.org/projects/vlti/, abridged in Messenger, 104)
AMBER Scientific Analysis Report, PDR 2000 - MIDI misc.
Science Demonstration Team, PRIMA White Book, ... PR 18/03/01
and 5/11/01
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Layout of the Tutorial - IV
Science with the VLT Interferometer• Facility instrumentation (¶ Schöller)
- wavelengths & limiting magnitudes- dates of availability- scientific applications
• Getting ready to observe with the VLTI - guidelines on object selection and proposal preparation- calibrators
• VLTI Data (see Messenger 106, P. Ballester et al.)- format- pipeline- data analysis
• Examples and simulations of VLTI results (given throughout)
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Characteristics of Interferometers
• optical to thermal IR ( 0.5m to 20m)- types of detectors- background- atmospheric turbulence (tip-tilt, fringe tracking, AO)- mechanical and optical constraints
• Michelson vs. Fizeau interferometers- homothetic mapping, field of view- types of baselines
• number of telescopes- number of baselines- beam combination (multi-axial, co-axial)- efficiency- closure phases
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Other Interferometric Methods
• single-telescope- speckle interferometry- aperture masking
• multi-telescope- intensity interferometer- heterodine detection- nulling interferometry
• space instruments- SIM, Darwin, GAIA
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Overview of current Interferometers
facility funding location n. of baseline year ofapertures primary secondary max (m) first fringes
CHARA USA Mt. Wilson 6 1.0 350 1999COAST UK Cambridge 5 0.4 48 1991GI2T F Calern 2 1.5 65IOTA USA, F Mt. Hopkins 2-3 0.45 38 1993ISI USA Mt. Wilson 2-3 1.65 75 1988KECK USA Mauna Kea 2(4) 10 1.8 85(140) 2001LBT USA, D, I Mt. Graham 2 8.4 23 in constr.MIRA-I.2 J Tokyo 2 0.30 6 2001MRO USA New Mexico 3 2.4 100 fundedNPOI USA Arizona 3-6 0.35 64 1994PTI USA Mt. Palomar 3 0.40 110 1995SUSI AUS New South Wales 2 0.14 640VLTI ESO Paranal 4(3) 8.2 1.8 130(205) 2000
apertures (m)
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Interferometers on the WEB
facility URL
CHARA http://www.chara.gsu.edu/CHARA/array.htmlCOAST http://www.mrao.cam.ac.uk/telescopes/coast/index.htmlGI2T http://wwwrc.obs-azur.fr/fresnel/gi2t/gi2t.htmIOTA http://cfa-www.harvard.edu/cfa/oir/IOTA/ISI http://isi.ssl.berkeley.edu/KECK http://huey.jpl.nasa.gov/keck/LBT http://medusa.as.arizona.edu/lbtwww/lbt.htmlMIRA-I.2 http://tamago.mtk.nao.ac.jp/mira/MIRA-I_2/mira_1_2.htmlMRO http://www.physics.nmt.edu/research/MRO.htmlNPOI http://ftp.nofs.navy.mil/projects/npoi/PTI http://huey.jpl.nasa.gov/palomar/SUSI http://www.physics.usyd.edu.au/astron/susi/VLTI http://www.hq.eso.org/projects/vlti/
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Design vs. Science Drivers
Baseline Length
• Resolution improves with Baseline- “correlated” magnitude decreases- relative errors increase
• Calibrators - accuracy vs baseline- magnitude vs baseline- density- boot-strapping
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Wavelength vs. Science Drivers
Wavelength
• Angular Resolution- resolution -1
• Atmospheric Turbulence- phase errors -1 - isoplanatic patch 6/5 - seeing -1/5 - coherence time 6/5
• Source Spectrum - many (but not all!) sources are red- spectral features
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Geometry vs. Science Drivers
Telescopes
• Number of telescopes- number of baselines N(N-1)- number of phase closures (N-1)(N-2)/2
• Beam Combiner- complexity drives cost (and size)- efficiency decreases with number of telescopes- new approaches
• Array Geometry- non-redundancy- configuration- NS vs. EW orientation- relocation of telescopes
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Closure Phases
from J.D. Monnier, 1999
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Examples of Array Geometries - CHARA
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Examples of Array Geometries - NPOI
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Examples of Array Geometries - VLTI
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Stellar effective temperatures
and Fbol are the keys to direct Teff estimates
Teff ()½ (Fbol) ¼ ( /) < 5% typically required
102 stars measured by LO, LBI
Fbol = a 2Teff4
Direct check for theoretical models of stellar atmospheres
• determination of physical characteristics
• understanding of energy production/dissipation mechanisms, stellar evolution, chemical abundances, etc.
• population synthesis models
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Teff Direct Measurements - a)
Early and intermediate spectral types, Barnes et al. (1976)
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Teff Direct Measurements - b)
Late spectral types, Barnes & Evans (1976)
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Teff Direct Measurements - c)
Late spectral types, Barnes & Evans (1976)
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Teff Calibration for Cool Giants
Ridgway et al. 1980 Dyck et al. 1996 Perrin et al. 1998 Richichi et al. 1999
Currently 646 measurements of 253 class III stars in CHARM catalogue (Richichi & Percheron 2001)
Teff is still uncertain for types cooler than M7 (several parameters at play). Need monitoring of spectra and photometry.
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Teff of Mira stars
From Van Belle et al. 1996
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Teff of carbon stars
From Richichi et al. 1995
Y Tau
Teff needs Fbol:
photometric monitoring is strictly required!
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Teff calibration for carbon stars
From Van Belle et al. 2000
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Multiwavelength monitoring
Teff = 3500 K = 2.0mas
Teff = 2500 K = 3.9mas
Fbol ~ 6%
V K
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Teff of cool MS stars
Rationale:
• Direct Teff measurements are very scarce: 7 K and 1M dwarfs (~50 times less than giants)
• Important implications for many fields of astronomy: most common field stars
• Transition to L-BD regime / Outliers
• Mass loss / envelopes / circumstellar environment
• surface features
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Name V Sp K phi(mas)16 40 200
HD 128621 1.33 K1V -0.67 7.20 0.851 0.336 0.000V450 Aql ? 6.48 M8V -0.27 4.49 0.940 0.671 0.00541 Ara 5.46 M0V 1.86 2.66 0.978 0.872 0.001BD+20 4139B 8.18 M9 0.88 2.43 0.982 0.892 0.014V1365 Ori 6.84 M6V 1.26 2.37 0.983 0.897 0.019eps Ind 4.69 K4.5V 2.19 2.18 0.986 0.912 0.048HD 45724 6.2 M1 2.25 2.13 0.986 0.916 0.059HD 45588 6.07 M0 2.47 2.01 0.988 0.925 0.089HD 210090 6.35 M1 2.4 1.99 0.988 0.927 0.095BD+29 4582B 8.3 M8 1.55 1.94 0.989 0.930 0.110NSV 1874 6.34 M0V 2.74 1.78 0.990 0.941 0.170GJ 702A 4.2 K0V 2.37 1.76 0.990 0.942 0.175DY Eri 4.41 K1V 2.41 1.74 0.991 0.943 0.184HD 40397 6.8 M2.5 2.53 1.73 0.991 0.944 0.190HD 209709 6.43 M0 2.83 1.70 0.991 0.946 0.201BD+04 4223 8.6 M8 1.85 1.69 0.991 0.946 0.207HD 112278 6.97 M3 2.4 1.68 0.991 0.947 0.211HD 85461 6.52 M0 2.92 1.63 0.992 0.950 0.233CD-48 3065 8.1 M7 1.92 1.63 0.992 0.950 0.237DO 4490 8.7 M8 1.95 1.61 0.992 0.951 0.243
baseline(m)
visibility
Some cool MS stars visible from Paranal
Cen B
not complete nor accurate!^2
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• Select K-M main sequence stars
• Apply Paranal limits
• V<10, K<5
• Use B-V (measured or estimated) to infer angular diameter
• Total ~610 stars
• Best targets 90% < Vis < 20%
0
100
200
300
400
500
600
700
1 0.98 0.95 0.9 0.5 0.15 0
Visibility
# S
tars
16 m
100 m
200 m
Statistics of MS cool stars
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7
8
9
10
11
12
13
275030003250350037504000
T eff [K]
M B
ol
• With 1% absolute error on visibility, errors on the angular diameters are between 1% and 5%
• Assume 5% error on bolometric flux
• Errors in Teff would be 1.8% to 3.8%
7
8
9
10
11
12
13
275030003250350037504000
T eff [K]
M B
ol
• Assume 0.5 mag random error on absolute magnitude
• Simulate random distribution of 200 stars
Simulated Teff calibration
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Teff of PMS stars
Rationale:
• Direct Teff measurements do not exist yet
• Permit model-independent location of the stars in the HR diagram
• Check of theoretical tracks
• Implications for age estimates, star and disk formation mechanisms, ...
Practical difficulties:
• they have very small angular diameters!
• a solar precursor ( 5 R ) has 0.30 mas at the distance of Tau-Aur SFR, 0.8 mas at TW Hya
• effect of circumstellar environment
• effect of spots
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Surface features in T Tau stars
Doppler imaging of the surface of a T Tau star, V410 Tauri.
Adapted from Surdin & Lamzin (2001).
Desirable to model the effects on visibility.
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The age and masses of PMS starsFrom Gomez et al. 1992
Mazzitelli (1989) tracks
3x105 yrs
1x106 yrs
3x106 yrs
1x107 yrs
Relatively high accuracy is required on Teff
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Resolving PMS stars with the VLTI
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Same diameter, 3 different LD
0.0000
0.2000
0.4000
0.6000
0.8000
1.0000
1.2000
0.00
8.00
16.00
24.00
32.00
40.00
48.00
56.00
64.00
72.00
80.00
88.00
96.00
Baseline [m]
Vis
ibil
ity
Limb-darkening
Important to measure around the first zero of the visibility
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Limb-darkening measurements
From Wittkowski et al. (2001)
NPOI, 0.65 to 0.85 m
3 baselines 19 to 38 m
UD =6.82 mas
LD =7.44 mas
FD =7.85 mas
~ 0.1mas
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Potential LD measurements with VINCI
Psi Phe, preliminary result: =8.3 ±0.3mas
analysis by M. Wittkowski
ESO/NEVEC IDL DRS
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Asymmetries
Fast rotators.
Recent detection of 14% equator/pole flattening in Altair (P=10.4hours, V_eq=210 km/s)
For a solar analogue, flattening is 0.001%
Flattening ratios up to 20% are expected for many B & A fast rotating stars. Details of visibility curves will depend strongly on orientation of the polar axis, and on surface temperature (brightness) differences.
Narrow-band and emission line observations.
Good models are required!
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• orbital motions --> masses
• different informations from different types of binary systems
• frequency among YSOs--> key to star formation
• dynamics and evolution of binary/disk systems
• “Special binary stars”: BD companions, hot Jupiters
Two approaches are available to measure orbital motions:
• accurate visibilities (Self-contained, lower precision)
• narrow-angle astrometry (wrt to nearby stars)
Binary stars
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Main parameters of binary systems
taken from J. Davis, 1996
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Visibilities of binary stars
Simulations of some representative cases of binary systems
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Spica: the full picture
taken from J. Davis, 1996
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Binaries among YSO
VIMA
VIMA
VISA
Apparent excess of binary stars in Taurus/Auriga, wrt to the solar stars in the solar neighbourhood.
Possible excess in Oph/Sco.
No excess in Orion.
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What can the VLTI do?
Short term
Survey nearby SFRs
• Resolution range
• Include all stars
Benefits
• Calibration
• Fast science results
Spectroscopy
• IR spec. binaries
Survey distant SFRs
• Include fainter stars
Long Term
Nearby SFRs
• Orbits close binaries
• Disks
Distant SFRs
• Potential x103
• Diversity
• SF mechanisms
Extended SEDs
• IR companions
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0.0
0.2
0.4
0.6
0.8
1.0
0 20 40 60 80 100 120 140 160 180 200
Baseline [m]
Vis
ibil
ity 1.00 mas
1.10 mas
Accurate visibilities vs. diffraction limit
21.3%
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0.90
0.95
1.00
0 20 40 60 80 100 120 140 160 180 200
Baseline [m]
Vis
ibil
ity 1.00 mas
1.01 mas
Orbital motions from accurate visibilities
0.2%
Binary with two point sources, 1:50 Br. Ratio, J band
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Orbital motions by phase referencing
Narrow-angle astrometry can measure the separation from a
distant reference star with 10as accuracy
•
•
Orbital motions in a 10AU system (P30 yrs) at 50pc(0.2” separation) could be detected
in one day.
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Circumstellar Structure
Close circumstellar shells
Mass loss
Close companions, tidal interactions
Jets
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IRC +10216
Note: no long-baseline interferometric observations yet!
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Atmospheres of AGB stars
(Karovska et al. 1997)
HST observation of Mira
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Circumstellar emission
From Mennesson et al. (2000).
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Asymmetric envelope with the VLTI
Diameter vs. Hour Angle
0.820.840.860.880.900.920.940.960.981.001.02
0:00 1:12 2:24 3:36 4:48 6:00 7:12 8:24
UT Time
No
rmal
ized
Dia
met
er
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26.00
27.00
28.00
29.00
30.00
31.00
32.00
33.00
-3.00 -2.00 -1.00 0.00 1.00 2.00 3.00
Hour Angle
An
g.
Dia
m (
mas
) 23-Oct
24-Oct
10-Nov
16-Nov
18-Nov
VLTI commissioning observations of Mira
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Detection of the envelope around Mira
20.0
22.0
24.0
26.0
28.0
30.0
32.0
34.0
36.0
38.0
40.0
-20.0 -15.0 -10.0 -5.0 0.0
23-Oct
24-Oct
10-Nov
16-Nov
18-Nov
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The environment around YSO
500 AU Model for IRAS 16293:1629, adapted from Surdin & Lamzin (2001)
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Herbig AeBe stars
HAEBEs are young intermediate mass PMS stars
Ages in the 105 and 107 yrs range, distances 100-300pc
Masses in the 2-8 M range
Analogue to T Tauris
Likely progenitors of Vega-like debris disk stars
Very large IR excess due to CS material in a disk, possible site of planetary formation
some have mm interferometry sizes of several 100AU (~sec”)
~1AU in K, 10-20AU in N slides from R. van Boekel, F. Paresce
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Disks around Herbig AeBe starsSED can be reproduced by
a passive irradiated flaring disk model (Dullemond et al., 2001) determined mainly by:
m, L, Te and d of star (known)
total mass and opacity of dust
Rin, Rout inner and outer disk radius
Hrim, height of inner wall
inclination of disk to LOS
VLTI Objective is to test the spatial predictions of the model and to strongly constrain free parameter space
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Model visibilities and parameters
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Other parameters
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Consistency with SED
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Observations of T Tau
Akeson et al. 2001
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Refining dust models by interferometry
Akeson et al. 2001
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Measuring distances by interferometry
Parallax
Astrometry is possible with some interferometers. Precisions of 10-100 arcsec are possible.
Cepheids
Traditionally the standard candles in the distance scale. The angular diameter of the nearest ones is now potentially within reach of interferometers.
Eclipsing Spectroscopic Binaries
An alternative standard candle.
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Rationale:
• Period-Luminosity Law
• Standard Candle
• Non-Radial modes?
• Details of pulsation lightcurves not yet completely understood
What modern interferometry can achieve:
• Measurement of angular diameters, with spectacular improvement over current data
• A priori information available, high efficiency
• Repeated measurements necessary
Cepheid Stars
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^2
Some Cepheids visibile from Paranal
Data provided by P. Kervella
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Simulated Observations of Zeta Geminorum withVINCI/VLTI Siderostats
1.500
1.550
1.600
1.650
1.700
1.750
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Phase
Angular size (milliarcsec)
Single measurement: +/- 4 asAbsolute calibration: +/- 9 as
IOTA/Fluor
Kervella et al. (2000)
Zeta Gem
Simulation by P. Kervella
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Rationale:
• Eclipses give orbital elements in absolute units
• By-product: stellar radii (calibration, still uncertain, could yield distance)
• Astrometric orbit: yield distance with higher accuracy
• Use as a standard candle
Furthermore:
• Case of binaries with partially resolved discs
• Characteristics (br. ratio, period, epoch) can be estimated in advance, high efficiency
• Repeated measurements desirable
Eclisping spectroscopic binaries
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Orbits of well-detached eclipsing binaries
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Orbits of contact eclipsing binaries
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Eclipsing binaries as M-m indicators
Distance to the LMC from the eclipsing binary HV 2274 (Guinan et al. 1998, Udalski et al. 1998).
Uncertainty due to reddening introduces a significant difference in the [M-m]
(18.47 vs. 18.22)
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d V K Spectrum a[mas]estim.
Zet Phe 1.0823082 -55.144474 3.97 4.3 B6V+... 0.598
Del Lib 15.0058349 -8.310820 4.95 5.0 B9.5V 0.684
TZ For 3.1440093 -35.332759 6.89 5.3 G2V 3.254
TY Pyx 8.5942722 -27.485869 6.90 5.3 G5V 1.021
SZ Psc 23.1323786 2.403158 7.44 5.6 K1IV-V+... 0.792
V624 Her 17.4417247 14.243624 6.20 5.8 A3m 0.540
HU Tau 4.3815830 20.410500 5.86 5.9 B8V 0.506
Z Her 17.5806980 15.082190 7.27 5.9 F4IV-V 0.716
CD Tau 5.1731153 20.075463 6.77 5.9 F7V 0.848
ZZ Boo 13.5609518 25.550736 6.78 5.9 F2V 0.765
GG Lup 15.1856375 -40.471760 5.59 5.9 B7V 0.351
U Oph 17.1631716 1.123796 5.90 5.9 B5Vnn+... 0.315
Quick referecence dataCoordinatesCross–Identifications
Some eclipsing binaries from Paranal
Data provided by B. Paczynski
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The hunt for extrasolar planets
Mass function of extrasolar planets in units of Jupiter mass detected so far out of ~1000stars from Queloz (ESA SP-451, 2000)
Need direct detection, to derive separation and resolve the orbital parameters.
Interferometry is the most promising technique from the ground.
73
Extrasolar planets as special binary stars
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Astrometry with PRIMA
Phased implementation plan
Accuracy: 50 arcsec initially, later 10 arcsec
Reference star within 30”
Limiting magnitudes eventually K>18 UTs, 15 ATs.
equip ATs first, later UTs
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Detection without PRIMA
From Lopez & Petrov (1999)
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Extragalactic Science
• Quasars, AGNs, Seyferts
• SNe in distant galaxies
Requirements
Can we find a reference star nearby? PRIMA!• Limit set by AT/UT, wavelength, visibility, field separation
• Statistical approach
What can we expect to measure?• Issue of field of view, imaging vs. parametric models
• Does [magnitude x visibility] kill us?
• Quasars, AGNs, Seyferts
• SNe in distant galaxies
Requirements
Can we find a reference star nearby? PRIMA!• Limit set by AT/UT, wavelength, visibility, field separation
• Statistical approach
What can we expect to measure?• Issue of field of view, imaging vs. parametric models
• Does [magnitude x visibility] kill us?
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Kmag=9.3 witin 0.2”. [J-H]=7.0 [H-K]=3.8
NGC 1068 observed with AO (K, H) [Rouan et al. 1998]
NGC 1068
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NGC 1068 by speckle Wittkowski et al. (1998)
K band, 6m (0.076mas)
Note: when the visibility goes down, the SNR goes down.
The visibility of NGC 1068
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The issue of image complexity4 telescopes, 6 hoursModel 8 telescopes, 6 hours
Simulation made by
C. Haniff (COAST)
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t1
t2
Position of photocenter wrt nearby bright star
New position of photocenter
Phase Shift
SN and transient phenomena
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Microlensing
Delplancke, Gorski, Richichi (2001)
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Photocenter wobble
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Min_d=300 mas
MF606W=26.5
Using D=61pc
M=1.4M
Predicted shift=0.6mas
Duration ~1 year
Aim: direct mass determination of an isolated neutron star, with high accuracy and
independently of model assumptions.
The neutron star RX J185635-3754
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Aim: direct determination of the diameter of TNO. The largest one, recently observed with AVO, has a size of 1200km @ 1.5DN, or ~40mas.
VLTI case: one can measure ~10x smaller TNOs with the VLTI. The luminosity will decrease correspondingly. KX76 has K~18, so we need to go fainter than that.
At the same time, UT measurements of objects as large as KX76 will sample the visibility beyond the first minimum, permitting studies on 2nd order geometrical properties.
The size of Trans-Neptunian Objects
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MIDI overviewInstrument Overview - MIDI
MIDI
[D/F/NL; PI: Heidelberg]
Paranal: November 2002
First Fringes with UTs: December 2002
Mid IR instrument (10–20 m) , 2-beam, Spectral Resolution: 30-260
Limiting Magnitude N ~ 4 (1.0Jy, UT with tip/tilt, no fringe-tracker) (0.8
AT)
N ~ 9 (10mJ, with fringe-tracker) (5.8 AT)
Visibility Accuracy 1%-5%
Airy Disk 0.26” (UT), 1.14” (AT)
Diffraction Limit [200m] 0.01”
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AMBER
[F/D/I; PI: Nice]
Paranal: January 2003
First Fringes with UTs (AO): July 2003
Near IR Instrument (1–2.5 m) , 3-beam combination (closure phase)
Spectral dispersion: ~35, ~1000, ~10000
Limiting Magnitude K =11 (specification, 5, 100ms self-tracking)
J=19.5, H=20.2, K=20 (goal, FT, AO, PRIMA, 4
hours)
Visibility Accuracy 1% (specification), 0.01% (goal)
Airy Disk 0.03”/0.06” (UT), 0.14”/0.25” (AT) [J/K band respectively]
Diffraction Limit [200m] 0.001” J, 0.002” K
AMBER overview
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MIDI Goals for GTO, first runs
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AMBER Scientific Drivers
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Idiosyncrasies of interferometry
☼ two telescopes do not point as one
☼ night shadows on Paranal
☼ left is right, up is down, 30 = 435 = 254 = 10!
☼ get your dark hours right
☼ magnitudes are not your usual magnitudes
☼ integration time and Earth rotation
☼ living in Fourier space
☼ always shoot in the right spot
☼ calibrate, calibrate, calibrate!
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Calibrators!
VLTI October 24-25, 2001
59.0%
61.0%
63.0%
65.0%
67.0%
69.0%
71.0%
73.0%
UT TIME
Tra
nsf
er F
un
ctio
n
Cal 1
Cal 2
Cal 3
Cal 4
Aver. 67.3% 2.3%
Cal 1 w.m 67.7% 0.2%Cal 2 w.m. 68.6% 0.2%Cal 3 65.2% 0.4%Cal 4 w.m. 62.8% 1.0%
Vm,1= Vo,1
Vm,2= Vo,2
=transfer f.
Fringes on the WEB
ESO VLTI:
http://www.hq.eso.org/projects/vlti/
AMBER and MIDI:
http://buz.obs-nice.fr/amber/
http://www.mpia-hd.mpg.de/MIDI/
This presentation:
http://www.eso.org/~arichich/download/iwtutorial/