1. Astrometry from Long- Baseline OIR Interferometers A. Boden, R. Akeson, A. Sargent, J. Carpenter – Caltech G. Torres & D. Latham – CFA/Harvard A. Quirrenbach – Heidelberg M. Colavita & M. Shao – JPL D. Hutter & J. Benson – USNO Flagstaff D. Boboltz & K. Johnston – USNO M. Massi & K. Menten – MPIfR Bonn L. Loinard & R. Torres – UNAM

2. 21July2009VLBA Astrometry -- AFB 2 Outline Intro – Long-Baseline Optical/Near-IR Interferometry OIR Interferometric Astrometry (Crash Course) Differential Astrometry Results Survey Absolute Astrometry Results Survey Summary

3. 21July2009VLBA Astrometry -- AFB 3 Sampling of the incident radiation field Transport to a common location (Internal) compensation for geometric (external) delay Combination of the beams Detection of the resulting output A cartoon astronomical interferometer

4. 21July2009VLBA Astrometry -- AFB 4 Kinds of Science with OIR Interferometry Visibility Modeling/Parametric Imaging – modeling of sparse u-v coverage and/or visibility amplitude data: stellar diameters, rotational oblateness, circumstellar material Differential astrometry over narrow field (mas – 10s arcsec). Narrow-field binaries. Fractional accuracies ~ 10 -5 – 10 -6 Wide-angle astrometry over wide-ish fields (10s of degrees). Fractional accuracies ~ 10 -6 – 10 -7 For what follows I want to (mostly) focus on astrometric results…

5. 21July2009VLBA Astrometry -- AFB 5 Interferometric Astrometry How a (dilute aperture) interferometer does astrometry… Single telescope beam & coherence length – imaging (or “parametric” imaging) Multiple beam and/or coherence length – differential delay Single-beam – measure differential delay in delay “sweeping”, or measuring delays serially Dual-beam – measure multiple fringe packets simultaneously & relate the two delays through metrology Showing examples of all these techniques

6. 21July2009VLBA Astrometry -- AFB 6 For a field (10s of mas) covered by single beam & coherence length… Imaging (“parametric” imaging) astrometry proceeds by interpreting fringe observable (e.g. fringe “visibility”) for multiple sources Usually “parametric” because spatial frequency content is low and “systems” are simple (e.g. binary stars), so images are never synthesized Most published results (e.g. binary orbits) are done through this parametric imaging Interferometric “imaging” astrometry Armstrong et al 2006 Hyades Binary  2 Tau

7. 21July2009VLBA Astrometry -- AFB 7 Binary “Parametric Imaging” When the scene is simple… State of the art is integrated visibility & RV modeling to estimate binary orbits ( Herbison-Evans et al 1971, Armstrong et al 1993, Hummel et al 1998, Boden et al 1999 ) This is what (essentially) everyone in the business does Boden et al 1999

8. 21July2009VLBA Astrometry -- AFB 8 Differential delay astrometry For multiple beams and/or coherence lengths, the delay (OPD) offset between fringes on multiple sources becomes the observable proxy for sky separation 12 Per/CHARA Bagnolo et al 2006

9. 21July2009VLBA Astrometry -- AFB 9 Binary Star Contributing Facilities Intensity Interferometer Herbison-Evans et al Mark III (Mt Wilson) Armstrong, Pan, Hummel HST FGS e.g. Benedict, Nelan, Henry PTI (Palomar Observatory) Boden, Konacki, Koresko, Muterspaugh, Pan NPOI (Anderson Mesa) Armstrong, Hummel, North, Zavalla SUSI (Narrabri) Davis, Tango, North KI (Mauna Kea) Boden et al, Schafer et al IOTA (Mt. Hopkins) Krauss et al, Zhao et al CHARA (Mt Wilson) Bagnuolo, Raghavan, Zhao HST: Image Credit NASA PTI: Image Credit National Geographic

10. 21July2009VLBA Astrometry -- AFB 10 12 Boo  Boden et al 2000 & 2005 : 12 Boo components are (nearly) equal- mass (dynamical masses at 0.3% precision), but a factor of two different in luminosity.  Due to primary evolution off main sequence; primary at the MS Turnoff – entering the subgiant phase, establishing a thick H- burning shell.  “Apparent” (evolutionary model) ages are discrepant at the 10% level (much larger than experimental errors); no single isochrone matches both components.  Miglio et al 2007 proposed convective overshooting differences to explain discrepancy, and astroseismic photometry to test proposal – results pending Boden, Torres, & Hummel 2005

11. 21July2009VLBA Astrometry -- AFB 11 Binary dynamical masses Quite a number (34) of systems have been interferometrically analyzed and published over the past 20 years… Cunha et al 2007

12. 21July2009VLBA Astrometry -- AFB 12 Measuring both astrometric and physical (3-D) orbits, one can determine system distances free of any model (beyond Keplerian motion) d = a physical /a” These distances are typically as good as (or better than) the best available stellar distances (Hipparcos) Binary-Derived Distances V773 Tau A Boden et al 2007

13. 21July2009VLBA Astrometry -- AFB 13 Atlas/Pleiades/ Pan et al 2004  Continuing controversy between “conventional” and Hipparcos estimates of Pleiades distance  Atlas visual orbit + system mass estimate yields Atlas distance  Result strongly favors “conventional” distance  (Additional eclipsing system reinforces Atlas result – Munari et al 2004; FGS parallaxes Soderblom et al 2005)  Hipparcos sticking with their guns: van Leeuwen 2009 puts Pleiades at 122 +/- 2 pc Pan, Shao, & Kulkarni 2004, Nature 427, 396 Zwahlen et al 2004, A&A 425, L45

14. 21July2009VLBA Astrometry -- AFB 14 Object Distance Comparisons Van Leeuwen 2007 lamented lack of direct comparisons with Hipparcos parallaxes Interferometric binaries provide excellent opportunity to assess precision & accuracy of original & revised Hipparcos parallaxes (Tomkin 2005) No sign of systematic bias, but room for small-scale correlations Boden & Quirrenbach in prep

15. 21July2009VLBA Astrometry -- AFB 15 VLBI Astrometry Integration: V773 Tau A Including VLBI possible for radio- emitting systems: V773 Tau A Lestrade et al 1999 estimated distance 148.4 +/- 5.5 pc w/VLBA Boden et al 2007 (to be) updated by Torres et al 2009 (see Thursday) analysis by joint VLBI, Keck Interferometry, & RV Derived orbital dist (134.5 +/- 3.2 pc) in excellent agreement with new trigonometric distance (134.7 +/- 3.8 pc); accuracy and precision D (pc)M Aa (Msun) M Ab (Msun) B2007136.2 (3.7) 1.54 (0.14) 1.33 (0.10) T2009134.5 (3.2) 1.48 (0.12) 1.28 (0.07) Boden et al 2007 Torres et al 2009

16. 21July2009VLBA Astrometry -- AFB 16 Radiometric Modeling It’s important to invest similar care in radiometric modeling as in astrometry & kinematics Luminosities, temperatures, absolute magnitudes, colors, extinction In the end we want to test/refine astrophysical models Boden et al 2007

17. 21July2009VLBA Astrometry -- AFB 17 Differential delay astrometry Muterspaugh et al 2006a Differential delay results Technique is to measure (and calibrate!) delay offset between separated fringe packets Implementations in a single telescope beam & in separate beams

18. 21July2009VLBA Astrometry -- AFB 18 Single-beam results Over a very narrow field (sub-arcsec), technique yields 10-20 uas precision  Peg (triple) Muterspaugh et al 2006b Sample of narrow-field results  Equueli (Muterspaugh et al 2005)  Peg (Mutterspaugh et al 2006b) V819 Tau (Muterspaugh et al 2006c) 12 Per (Bagnolo et al 2006)

19. 21July2009VLBA Astrometry -- AFB 19 Narrow-Field Astrometry: Fractional Precision (With phase referencing), very high precisions are possible PTI PHASES typically delivers 15 uas precision over 500 mas field – 3 parts in 10 5 !

20. 21July2009VLBA Astrometry -- AFB 20 Dual Beam Astrometry Primary star Used to phase individual apertures Used to co-phase the interferometer Secondary star Used as positional reference for primary star Delay line difference Observable proxy for angular separation between stars Angular separation reflects periodic reflex motion of stars due to planetary companions For exo-planet reflex detection 10s of uas (O(10 -11 rad)) Delay Line Differential “ Primary ” Star “ Secondary ” Star Beam Combiners Delay Lines Delay Lines Objective: ground-based astrometric detection of exo-planets ~ 50 -- 200 uas @ PTI (10 uas @ VLTI)

21. 21July2009VLBA Astrometry -- AFB 21 PTI Astrometry on 61 Cygni

22. 21July2009VLBA Astrometry -- AFB 22 PTI Astrometry on 61 Cyg (2) 2000x PTI demonstration fractional precision: 100 uas/30 arcsec = 3 parts in 10 6 !

23. 21July2009VLBA Astrometry -- AFB 23 Absolute Astrometry with Interferometers Long-baseline O/IR interferometers are making absolute (global) astrometry measurements as well… Where positions are referenced to some external standard (e.g. a priori positions from Hipparcos) Allow for refining global parameters such as proper motion and parallax

24. 21July2009VLBA Astrometry -- AFB 24 Mark III results Mozurkewich et al 1998 Shao et al 1990 Hummel et al 1994 Shao et al 1990 Hummel et al 1994 Precisions ~ 6-10 mas (Shao et al 1990) Accuracies ~ 15-20 mas (Hummel et al 1994)

25. 21July2009VLBA Astrometry -- AFB 25 Wide Angle (Absolute) Astrometry with an Interferometer Measure d, calculate s Voila…stellar position But it’s not that simple… Measured delays corrupted by atmospheric turbulence Internal optical paths vary rapidly from thermal effects Baselines vary rapidly due to mechanical and thermal effects on siderostats/mounts Impact of these effects increases with field!

26. 21July2009VLBA Astrometry -- AFB 26 Atmospheric Correction Delay residuals from predicted delay are dominated by atmospheric fluctuations (Kolmogorov turbulence) Error of mean reduces only as 6 th root of Nobs Air delay calculated by fitting dispersed fringes - atmosphere dispersive in visible - vacuum delay lines allow wide bandpass Corrected delays (Fig. 1 minus Fig. 2)  = 3.09 mm White noise   mean = 3.09 mm/√(N) For 100s observation (500, 200ms frames)  mean = 0.13 mm astrometric precision = 1.3 mas (20 m baseline) Fig. 1 Fig. 2 Fig. 3

27. 21July2009VLBA Astrometry -- AFB 27 Internal Path Length (C-term) Metrology Internal feed beam metrology injection Feed beam metrology cube corner reflector Benson et al 2004 Johnston et al 2006

28. 21July2009VLBA Astrometry -- AFB 28 External metrology Apply baseline metrology data: Laser metrology beams monitor hemispherical “cat’s-eye” reflector on each siderostat mirror Laser source and distribution optics on temperature-stabilized reference table Reference table referenced to bedrock by “optical anchors” Benson et al 2004 Johnston et al 2006

29. 21July2009VLBA Astrometry -- AFB 29 Preliminary Astrometric Solutions 14 Stars, delta Ra, delta Dec: 28 parameters 4 Baseline parameters, 3 low-order polynomials 28 or 35 parameters (non-trivial problem) Applied robust Bayesian modeling techniques Delay residuals after stellar positions fit Dispersion & C-term corrected delays

30. 21July2009VLBA Astrometry -- AFB 30 Preliminary Astrometric Solutions Single night, single baseline (East-West) Precisions of ~ 10 mas in RA Fractional precision 10 mas/30 deg ~ 1 part in 10 7 !!!  ra  dec

31. 21July2009VLBA Astrometry -- AFB 31 Summary Ground-based LB OIR Interferometers making important astrometric contributions: Resolving and analyzing binary systems inaccessible any other way (stellar astrophysics in many HR-diagram sectors – e.g. PMS systems) Demonstrating potential relevance to astrometric exo- planet studies (e.g. PTI PHASES, VLTI PRIMA – just coming on line!) Potential future contributions in global astrometry (in advance of GAIA and SIM) (NPOI)

32. 21July2009VLBA Astrometry -- AFB 32 Backup

33. 21July2009VLBA Astrometry -- AFB 33 Differential Delay Astrometry Multiple sources => multiple fringe patterns Metrology measuring the relative delay This relative delay is the astrometric observable

34. 21July2009VLBA Astrometry -- AFB 34 Intro Talking about long-baseline (LB) optical/near-IR (OIR) interferometry in general, and interferometric astrometry in particular I will not be talking about filled-aperture (speckle) interferometry

35. 21July2009VLBA Astrometry -- AFB 35 Interference fringes are variations in detected power vs relative delay (OPD) Polychromatic interference fringe packet centered at “zero OPD” (packet size  coh  0 2 /  ) This zero OPD (and the internal delay at which is occurs) is the obs. proxy for astrometric measurements Fringes & polychromatic response

36. 21July2009VLBA Astrometry -- AFB 36 Differential Astrometry Survey Survey of Differential Astrometry results from LB OIR interferometers Interferometric “imaging” results Differential delay results

37. 21July2009VLBA Astrometry -- AFB 37 Classical imaging/relative astrometric techniques Speckle Long-baseline interferometry Capella with Mt Wilson Interferometer Spica  Vir) with intensity interferometer Mark III HST FGS NPOI PTI SUSI KI IOTA CHARA Binary Studies By Interferometers

38. 21July2009VLBA Astrometry -- AFB 38 HD 98800: PMS quad system, B an SB2 with 315d period & mid-IR excess Physical orbit from KI V 2, HST FGS, & RV data; dynamical masses of two low- mass PMS components Suggestion that HD 98800 (& TW Hya stars) have sub-solar metallicity? Verified (?) in Laskar et al 2009 KI/PMS Binary HD 98800 B Boden et al 2005 14 Apr 2006 18 May 2006 2 May 2007

39. 21July2009VLBA Astrometry -- AFB 39 Interferometric Astrometry Technology Technologies relevant to LB OIR interferometric astrometry “Dual-star” feed mechanisms Beam combination/fringe measurement Metrology (internal, external) Phase referencing of multiple beam combiners

40. 21July2009VLBA Astrometry -- AFB 40 Dual-star feed schematic (PTI, KI, VLTI) SSSM Collimator & FSM Collimator & FSM Field separator

41. 21July2009VLBA Astrometry -- AFB 41 PTI Central Optics Primary Secondary

42. 21July2009VLBA Astrometry -- AFB 42

43. 21July2009VLBA Astrometry -- AFB 43 Dual-Beam Phase Referencing HD 177724 4 Aug 1999 Lane & Colavita 2003 Objectives: long synthetic coherence time for faint-object detection & x-combination delay comparison > Phase referenced interferometry: the analog of single-aperture AO Fringe tracking piston correction signal on one object is used to correct the piston on a second, nearby (isoplanatic separation) object. Required for KI (and VLTI) faint-object interferometry Phase error with and without loop closed between the two PTI fringe trackers. Two data segments taken within 200 s of each other. Lane & Colavita 2003