Infrared Interferometry for Astronomy

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1 Infrared Interferometry for Astronomy Martin Vannier Universidad de Chile, European Southern Observatory (ESO, Chile)

2 Infrared Interferometry for Astronomy Basic introduction to stellar interferometry Technical concepts and developments on current interferometers Science case. Achievements and perspectives on the VLTI Observing on a long-baseline interferometer

3 Introduction to Stellar Interferometry What is interferometry? A high-angular resolution technique Uses physically dispersed apertures to provide information on the spatial distribution of a source See: Introduction to Stellar Interferometry, Glindemann (ESO VLTI site, And more ressources an OLBIN site

4 Young's experiment: Interference through pinholes The wavefront interfers coherently with itself to form fringes Depending on the Optical Path Difference (OPD), light sums up constructively (bright) or destructively (dark) Interfringe spacing = interferometric resolution = λ/b

5 Michelson Interferometer Light from separate apertures (e.g. two telescopes) is recombined coherently on the focal plane In order to get fringes, one must control that Optical Path Difference OPD 0 between the beams, down to a precision ± λ ~λ/b ~λ/d IR The telescope diffraction Airy pattern (of size λ/d) gives the enveloppe around the fringes (of separation λ/b).

6 Visibility and Phase The fringe is a complex function, defined by its visibility modulus V: contrast of the amplitude V = (Imax Imax )/ (Imax + Imin ) ~λ/b ~λ/d phase f: position of the fringe packet. It is measured relatively between two fringe patterns (i.e. different objects or spectral channels) Both depend on: Spatial distribution of source [ Atmospheric and instrumental factors ]

7 Phase θ If the wavefront is inclined (light source at angle θ), the fringes are shifted by an angle: φ = 2π (OPDint + OPDsky)/λ where: OPDsky= difference between optical paths, from the target to the telescope. In this case: OPDsky = B.u = B sin θ Astrometry (PRIMA) OPDint = is controlled and monitored by a Delay Line

8 Visibility V = (Imax Imax )/ (Imax + Imin ) If the source is punctual (and no instrumental bias), V=1 If the size of the source is not negligeable with respect to the interferometric resolution λ/b, V is lower V is a measurable of small angular sizes (~ a few mas to a few 10s mas)

9 What do V and φ say about my source? Let I(ξ,η)be the brightness distribution of the source at angular coordinates (ξ,η) The complex visibility Γ is the Fourier transform of I. For spatial frequency (u,v), it is: For each baseline and wavelength, the interferometer measures Γ(u,v), where (u,v)=b/λ

10 α0 Visibility function

11 Visibility : Measuring angular diameter using a uniform-disk model Fit of a visibility curve Vdisk(f) through 3 points

12 Visibility function Other examples

13 Image reconstruction vs model fitting? 1 baseline x 1 wavelength = 1 interferometry point = FT of the source brightness distribution at 1 spatial frequency With enough Γ(ui,vi) points to cover the frequency plane (u,v), the brightness distribution I(ξ,η)(i.e. the image of the source) might be reconstructed by inverse FT But at a high observational cost, so currently only a few points are available for model fitting

14 Technical concepts Developments on current interferometers

15 Long-baseline optical interferometers Keck Interferometer, Mauna Kea (U. Berkeley, USA): D=2 x 10m, B=85m Very Large Telescope Interferometer (VLTI), ESO, Paranal (Chile)

16 More interferometers Many smaller interferometers: Name Chara & ISI COAST GI2T IOTA NPOI SUSI Location Mount Wilson USA Cambridge, UK Calern, F Whipple, USA Lowell, USA Australia Ntel x Dtel 6 x 1m 5 x 0.4 m 2 x 1.5 m 3 x 0.45 m 6x 0.5 m 2 x 0.14 m Baseline 56 m 22 m 12 to 65 m 38 m 2 to 437 m 5 to 640 m Ground-Based Interferometry Projects Under Development: Magdalena Ridge Observatory (USA), : 3x 2.5, B= 250m O'HANA, Mauna Kea, Mauna Kea, (USA)

17 O'HANA Link up the big telescopes (from 3.6m to 10m!!) on Mauna Kea in a giant interferometric infrared array

18 VLTI On Cerro Paranal (Chile) D=2, 3 (4?) x 8.2m Unit Telescopes (UT) 3 x 1.8 m Auxiliary Telescopes (AT, 2005) [ 2 x 0.4 m Siderostats (for tests) ] B=35200 m

19 VLTI

20 From the telescopes to the Interferometric lab Pupil image on M8: MACAO adaptive optics (or FAST tip/tilt correction Gain in coherent flux ~ 100 Delay Lines equalize internal OPD 120m long Resolution < 5nm Stability < 14nm RMS, controled by laser metrology

21 The interferometric lab : Instrumentation VLTI FINITO VINCI: Commissioning instrument to get first fringes. 16,000 observations of hundreds of objects collected and available publicly over the ESO archive on the WEB Provides internal source at

22 Instrumentation at VLTI FINITO AMBER: Near-infrared, 2 or 3 beams dispersive recombiner

23 AMBER 2 or 3 beams dispersive recombiner Near-infrared range: J-H-K bands (1-2.4 mm) spectral resolutions: ~35, ~100, ~12000 Diffraction limit: 2 marcsec Limit magnitude: K=11 (AMBER alone) K=20 (+ FINITO + PRIMA, 4 hours) First fringes: February '04 Open Time: April/October '05 (AMBER alone)

24 Instrumentation at VLTI FINITO MIDI: Mid-IR 2-beams dispersive recombiner

25 MIDI 2 beams dispersive recombiner Near-infrared range: J-H-K bands (1-2.4 mm) spectral resolutions: ~ Diffraction limit: 10 marcsec Limit magnitude: N=4 (alone), i.e 1 Jy N=9 (+ FINITO + PRIMA) First fringes: February '02 Open Time: October/April '04

26 Science case Achievements and perspectives on the VLTI

27 Science achievements : Measuring angular diameter using a uniform-disk model Fit of a visibility curve Vdisk(f) through 3 points

28 Science achievements With VINCI + Siderostats: Shape of LBV Eta Carinae: core resolved (0.005 as) mass loss, rotation and stellar wind(van Boekel 2004) Radii of rapidly rotating Be star Achernar: distorted ellipsoide (a/b=1.6) (de Souza et al, 2003)

29 Science achievements With VINCI: Diameter of several Cepheids Relation luminosity/periodicity, distance scale(kervella 2003, 2004) Radius as a function of phase of Mira star prototype o Cet, Dimensions of symbiotic Mira R Aquarii, Radius (& age) of Vega-like stars (Di Folco 2004)

30 Science achievements With MIDI + UTs: Central Region in Active Galaxy NGC 1068 (Jaffe et al., Nature, 2004) Resolved the dusty torus of galactic nucleus of size ~ 0.03 arcsec (i.e. 10 lightyears), and its innermost core, of temperature 500 deg and size ~ 3 light-years. Infrared spectra of the central region constrains the chemical composition of the heated dust (alumino-silicate)

31 Science achievements & perspectives With MIDI + UTs: Mid-infrared sizes of circumstellar disks around Herbig Ae/Be stars (e.g. HD ) Eta Carinae Future perspectives of MIDI Size and inner structures of dust shells and disks, composition of dust Young and evolved stars...see MIDI Guaranted Time proposals

32 AMBER : GTO Astrophysical objectives 45% Proposals 40% UTs 35% ATs 30% 25% 20% 15% 10% 5% 0% s em t s sy ion a rs t t n s u l o of lo vo a ti y cn i s r o e t m e a r c r i t sm fo lla ne ert ala e r a p g t Co l a s p d St pro of an nd l s a a s t e en xie cts tag a e s m l j a ob Ga ate nd s u L s F a -m w Lo gy lei uc (p)o: (partially) Observed, NYO: Not Yet Observed,

33 Hot Be Star Alfa Ara: Disk rotation and winds Alfa Ara : Close Be (hot and active) Star, with rotating outer layer Observed accross Brγ line (AMBER SDT, 2005) Visibilities and phase compatible with thin disk + polar winds model Stellar rotation close to critical Keplerian rotation disk (Meilland, et al, accepted 2006) Visibility(λ) Phase(λ)

34 Hot Be Star Alfa Ara: Disk rotation and winds Alfa Ara : Close Be (hot and active) Star, with rotating outer layer Observed accross Brγ line Brightness distribution map fitting AMBER data (AMBER SDT, 2005) across K band, with central star and continuum Visibilities and phase substracted (SNECMA code). compatible with thin disk + polar winds model Stellar rotation close to critical Keplerian rotation disk (Meilland, et al, accepted 2006) Brightness distribution map fitting AMBER data in K band, from SNECMA code.

35 Binary systems : γ2 Velorum (Millour et al, accepted 2006) γ Vel : WR + O stars, δ=4 mas Flux from each component and binary separation derived from V and Φ ( δ of system) Additional continuum component discovered: Expanding shell (shockwave)?

36 Afterburst of recurrent Nova RS Oph (Chesneau et al, accepted 2006) Medium Resolution K-band observation of nova 5 days after outburst (3UTs, ToO) Fits with highly flattened elliptical models for continuum, Br γ, He I Model: continuum (4.9mas ellipse) + skewed ring for different RV shifts around Br γ line. Superimposition of model (continuum + Br g + He I) with radio structure observed at 13.8 d. Visibilities and phase Data (cros with fits from skewed ring mode around Br γ.

37 Inner structure of a complex nebula : Eta Carinae (HST image) Measured with AMBER in K band (GTO, 2005) Structures of Eta Car still quite complex and puzzling Safe interpretation requires compaison with traditional imaging (NACO) to constrain the largest structures and/or more points for HR image reconstruction

38 Star Formation / Pre main-sequence PMS parameters : stellar diameters, Teff vs Sp.T., tests of evolutionary models (NYO, ATs) : Inner disks morphology around TTS, FU Orionis (NYO, ATs), HAeBe/Be stars (O, UTs) Disks (HH): Imaging of TTauri jets (O, UTs), survey within 10AUs around various YSO (NYO, ATs) Outflows Binaries and Young Clusters: determination of dynamical mass, calibration of PMS models (NYO, ATs) Young

39 Low-mass objects & Planetary Systems Brown Dwarfs : mass-radius and massluminosity -metallicity relations (NYO, many sources, ATs) Extrasolar planets : Direct detection, mass & spectroscopy of known Pegasi planets(po, UTs/ATs) Solar-system bodies: asteroid angular diameter, binarity (po, Uts/ATs, )

40 Evolved stars (post)agbs : spectrometry and (circum)stellar sizes ( mass ouflows and stellar disks/ dust shell interactions) (NYO, many sources, ATs) Miras: stellar surface, molecular envelope (NYO, one source, ATs) Massive stars: morphology around Eta Car, Antares, Betelgeuse, WR (po, UTs/ATs) Symbiotic stars: morphology of envelope/disk/jets (po, Uts/ATs) RS Oph Final Stages: Jet of galactic micro-quasars, jet of X-ray binaries (po, UTs/ATs)

41 More Stellar physics... Fundamental parameters: rotation, diameter age, calibration across HR diagram(nyo, ATs) Stellar activity and magnetism: pulsating B stars, atmospheric dynamics in Cepheids (NYO, UTs/ATs) hot Be/B[e] stars: non-radial pulsations, dynamics of winds & disks,... (po, UTs/ATs)

42 Cosmology & Extra Galactic Distance scale : determination of angular diameter and amplitude variation of Cepheids (NYO, many sources K<4 with ATs) Geometry and MR spectro of AGNs (NYO, faint sources K 10, most of them to be observed in GTO) dust in QSOs BLRs: geometry and kinematics of BLRs in QSOs and Seyfert Galaxies (NYO, faint sources)

43 Science perspectives AMBER Very broad: all high-angular-resolution in near-ir Spectral resolution allows the look of color-differential visibility and phase Ranges from structures of accretion disks to envelopes of evolved star, asteroseismology, binaries and extrasolar planets...see AMBER Guaranted Time proposals FINITO, PRIMA Going to fainter magnitudes (Dm=7 or 8) Extra-galactic range (AGNs),... High-precision astrometry with PRIMA

44 Observing at VLTI Use the existing data? ESO archive on the WEB. Phase I: Science case: Interest of getting High Angular Resolution on your source? In which spectral range and resolution? VLTI is not very sensitive (yet). Check the (near-)ir flux of your target? ATs or UTs Relevant angular size(s) of your target : a few mas (AMBER), a few tens mas (MIDI) baseline(s)

45 Observing at VLTI Phase II: Calibrator stars Timing, direction of baseline with respect to source Specific instrumental configuration and observational procedure VISITOR vs. SERVICE observation mode After the observation Data reduced by ESO pipeline Use the offered software(s) and/or your own model for analysis and interpretation

46 Summary Infrared Interferometry gives high-resolution angular information (λ/b ~ 4 mas) Large ground based projects: VLTI, Keck,... With a few measurement points in the frequency plane, it constrains a model of brightness distribution and/cinematics With more points and phase reference, reconstruction of images will be possible Some interest for your field of research? Use archive data or apply for some time on the VLTI...