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Science with Optical/NIR Interferometers

Science with Optical/NIR Interferometers. A. Richichi (ESO Garching). Interferometry Week ESO Santiago, 14-16 January 2002. Layout of the Tutorial - I. Interferometers Types of interferometers under consideration Types of interferometry not considered here

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Science with Optical/NIR Interferometers

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  1. Science with Optical/NIR Interferometers A. Richichi (ESO Garching) Interferometry Week ESO Santiago, 14-16 January 2002

  2. 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 Interferometry Week, ESO Santiago 16-01-02

  3. Layout of the Tutorial - II Science with Interferometers • Stars & PMS Stars • Fundamental Stellar Parameters • diameters, limb darkening, flattening • temperatures • masses • ages • Binaries • Stellar Pulsation • Circumstellar Matter • Distances Interferometry Week, ESO Santiago 16-01-02

  4. Layout of the Tutorial - III Science with Interferometers ctd. • 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 Interferometry Week, ESO Santiago 16-01-02

  5. VLTI Science - Main References ESO 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

  6. 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) Interferometry Week, ESO Santiago 16-01-02

  7. Characteristics of Interferometers • optical to thermal IR ( 0.5m to 20m) • 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 Interferometry Week, ESO Santiago 16-01-02

  8. Other Interferometric Methods • single-telescope • speckle interferometry • aperture masking • multi-telescope • intensity interferometer • heterodine detection • nulling interferometry • space instruments • SIM, Darwin, GAIA Interferometry Week, ESO Santiago 16-01-02

  9. Overview of current Interferometers Interferometry Week, ESO Santiago 16-01-02

  10. Interferometers on the WEB Interferometry Week, ESO Santiago 16-01-02

  11. 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 Interferometry Week, ESO Santiago 16-01-02

  12. 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 Interferometry Week, ESO Santiago 16-01-02

  13. 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 Interferometry Week, ESO Santiago 16-01-02

  14. Closure Phases from J.D. Monnier, 1999 Interferometry Week, ESO Santiago 16-01-02

  15. Examples of Array Geometries - CHARA Interferometry Week, ESO Santiago 16-01-02

  16. Examples of Array Geometries - NPOI Interferometry Week, ESO Santiago 16-01-02

  17. Examples of Array Geometries - VLTI Interferometry Week, ESO Santiago 16-01-02

  18. Stellar effective temperatures • 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 Fbol = a 2Teff4 •  and Fbol are the keys to direct Teff estimates • Teff ()½ (Fbol) ¼  ( /) < 5% typically required • 102 stars measured by LO, LBI Interferometry Week, ESO Santiago 16-01-02

  19. Teff Direct Measurements - a) Early and intermediate spectral types, Barnes et al. (1976) Interferometry Week, ESO Santiago 16-01-02

  20. Teff Direct Measurements - b) Late spectral types, Barnes & Evans (1976) Interferometry Week, ESO Santiago 16-01-02

  21. Teff Direct Measurements - c) Late spectral types, Barnes & Evans (1976) Interferometry Week, ESO Santiago 16-01-02

  22. 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. Interferometry Week, ESO Santiago 16-01-02

  23. Teff of Mira stars From Van Belle et al. 1996 Interferometry Week, ESO Santiago 16-01-02

  24. Teff of carbon stars Teff needs Fbol: photometric monitoring is strictly required! Y Tau From Richichi et al. 1995 Interferometry Week, ESO Santiago 16-01-02

  25. Teff calibration for carbon stars From Van Belle et al. 2000 Interferometry Week, ESO Santiago 16-01-02

  26. Multiwavelength monitoring Teff = 3500 K  = 2.0mas Teff = 2500 K  = 3.9mas Fbol ~ 6% V  K Interferometry Week, ESO Santiago 16-01-02

  27. 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 Interferometry Week, ESO Santiago 16-01-02

  28. Some cool MS stars visible from Paranal not complete nor accurate! ^2  Cen B Interferometry Week, ESO Santiago 16-01-02

  29. Statistics of MS cool stars • 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% Interferometry Week, ESO Santiago 16-01-02

  30. Simulated Teff calibration • 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% • Assume 0.5 mag random error on absolute magnitude • Simulate random distribution of 200 stars Interferometry Week, ESO Santiago 16-01-02

  31. 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 Interferometry Week, ESO Santiago 16-01-02

  32. 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. Interferometry Week, ESO Santiago 16-01-02

  33. The age and masses of PMS stars From Gomez et al. 1992 Relatively high accuracy is required on Teff 3x105 yrs 1x106 yrs 3x106 yrs 1x107 yrs Mazzitelli (1989) tracks Interferometry Week, ESO Santiago 16-01-02

  34. Resolving PMS stars with the VLTI Interferometry Week, ESO Santiago 16-01-02

  35. Limb-darkening Important to measure around the first zero of the visibility Interferometry Week, ESO Santiago 16-01-02

  36. Limb-darkening measurements 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 From Wittkowski et al. (2001) Interferometry Week, ESO Santiago 16-01-02

  37. Potential LD measurements with VINCI Psi Phe, preliminary result: =8.3 ±0.3mas analysis by M. Wittkowski ESO/NEVEC IDL DRS Interferometry Week, ESO Santiago 16-01-02

  38. 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! Interferometry Week, ESO Santiago 16-01-02

  39. Binary stars • 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) Interferometry Week, ESO Santiago 16-01-02

  40. Main parameters of binary systems taken from J. Davis, 1996 Interferometry Week, ESO Santiago 16-01-02

  41. Visibilities of binary stars Simulations of some representative cases of binary systems Interferometry Week, ESO Santiago 16-01-02

  42. Spica: the full picture taken from J. Davis, 1996 Interferometry Week, ESO Santiago 16-01-02

  43. Binaries among YSO 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. VIMA VIMA VISA Interferometry Week, ESO Santiago 16-01-02

  44. 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 Interferometry Week, ESO Santiago 16-01-02

  45. Accurate visibilities vs. diffraction limit 21.3% Interferometry Week, ESO Santiago 16-01-02

  46. Orbital motions from accurate visibilities Binary with two point sources, 1:50 Br. Ratio, J band 0.2% Interferometry Week, ESO Santiago 16-01-02

  47. Orbital motions by phase referencing Narrow-angle astrometry can measure the separation from a distant reference star with 10as accuracy • Orbital motions in a 10AU system (P30 yrs) at 50pc(0.2” separation) could be detected in one day. • Interferometry Week, ESO Santiago 16-01-02

  48. Circumstellar Structure Close circumstellar shells Mass loss Close companions, tidal interactions Jets Interferometry Week, ESO Santiago 16-01-02

  49. IRC +10216 Note: no long-baseline interferometric observations yet! Interferometry Week, ESO Santiago 16-01-02

  50. Atmospheres of AGB stars HST observation of Mira (Karovska et al. 1997) Interferometry Week, ESO Santiago 16-01-02

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