Palomar Testbed Interferometer (PTI) & Keck Interferometer (KI) Mark Colavita 7/29/2005 Michelson Summer School Pasadena, CA

Transcription

1 Palomar Testbed Interferometer (PTI) & Keck Interferometer (KI) Mark Colavita 7/29/2005 Michelson Summer School Pasadena, CA

2 PTI as seen from the catwalk of the 200 telescope

3 Michelson Interferometer stellar wavefront collector beamsplitter detector collector detector optical delay line

4 PTI Description NASA funded, tech dev. for Keck and other interferometers; first fringes way system, 110 m max baseline 40 cm collecting apertures Active broadband fringe tracking at K (2-2.4 mm) or H ( mm) Angle tracking at R + I ( mm) Single-beam capability for visibility and very-narrow-angle astrometry (<1 ) Dual-beam capability for very-narrow-angle astrometry (1-1 ) Refs: ApJ 510, 505 (1999) N-W baseline 85 m N-S baseline 110 m

5 PTI block diagram Primary Beam Combiner Fringe Sensor Incoming starlight Short delay line Angle Sensor Acquisition camera Fast-steering mirrors Primary star Secondary star Beam compressors Inputs from other arm Siderostat Telescope Dual-star feed Long delay line Angle Sensor Fringe Sensor Secondary Beam Combiner

6 Siderostat & compressor

7 Delay Lines (background), switchyard (foreground), primary (right) and secondary (left) combiners

8 Primary beam combiner table

9 A "Typical" Night of PTI V 2 Data... Observe > 100 scans/night ~ 50 calibrated V 2 measured

10 Cepheid Studies PTI made the first direct detection of Cepheid pulsations Lane et al Cepheid modeling combined PTI and NPOI data Lane et al. 2000, Nature 407, 485 Lane et al. 2002, ApJ 573, 330

11 Astrometry with an Interferometer collector wavefront, star #2 wavefront, star #1 s r B r The delay d is the dot product d = B. s + C of the vector connecting the two collectors and the unit vector to the star; C is a fixed offset optical delay line collector The (measured) extra delay required to get fringes on star #2 compared to star #1 is a measure of the angle between them Delay line position, star 1 Delay line position, star 2

12 Single-Beam Astrometry Fringe Scanning Examples Images Courtesy Of M. Muterspaugh

13 12 Boo Analysis A.F. Boden, M.J. Creech-Eakman, and D. Queloz, 2000, ApJ, 536, 880.

14 Dual-Star Concept star 1 star 2 common metrology fiducials, common baseline Beam Combiner 1 field separator star selector mirror Beam Combiner 2

15 Phase referencing with PTI Analogous to adaptive optics on a large telescope Approach Fringe track on a bright star within the isoplanatic patch of the target star Use as a probe of the atmospheric effects on the target star Correct using optical delay lines by» Feedback same signal to both stars delay lines» or... Feedforward signal to secondary star s delay line Advantage Allows longer integration times that would ordinarily be possible

16 Lane & Colavita, AJ, 125, Phase referencing with PTI

17 Astrometry Observation Primary Combiner Track Primary Star Secondary Combiner (chops between primary and secondary) Track Primary Star Track Secondary Star Track Primary Star repeat...

18 Raw data hrs microns Secondary fringe tracker tracking primary star Differential separation Secondary fringe tracker tracking secondary star Outliers removed

19 61 Cyg Astrometry

20 Constant-term metrology Corner cube in dual-star feed Metrology launch Subaperture polarizers Metrology detect

21

22 Keck Interferometer Keck Interferometer links the two 10 m Keck telescopes NASA-funded joint development: JPL, Keck, Caltech (MSC) 3-22 Refs: SPIE 5491, 454 (2004); SPIE 4838, 79 (2003)

23 Keck Interferometer modes High sensitivity fringe visibility (V 2 ) measurements Combines the AO-corrected beams V 2 measurements in the near-ir Infrared nulling at 10 um Nulling beam combiner to suppress central star Measure zodiacal dust around nearby stars Differential-phase interferometry Multi-color fringe measurements Detect the fringe shift caused by hot companions to nearby stars

24 Michelson Interferometer stellar wavefront collector beamsplitter detector collector detector optical delay line

25 Configuration at the Summit

26 Telescope & AO Extract beam in collimated space on AO bench after deformable mirror 9 m inscribed circle on Keck primary mirror maps to 112 mm collimated beam 80.4 : 1 demagnification

27 Dual star module Slides in adjacent to AO system like other Nasmyth instruments Sends collimated beam into coude beam train Secondary M4 Fold Mirror Extraction Beamsplitter Primary M4 DSM Fold Mirror Keck AOB

28 Beam Combining Lab Optical path Beam Injection and Switching Keck 2 Keck 1 Fast delay lines Switchyard Long delay lines Imaging and nulling combiners Fringe trackers Angle trackers Auto-aligner

29 Long delay lines Installed in coude tunnel Provides coarse delay positioning (static during observation) Double-height mirror accommodates two beams for phase referencing

30 Fast delay lines 4-stage cat s-eye design Fiber-fed laser metrology Delay range +/- 15m High speed position and rate commanding Metrology launchers

31 FATCAT (Fringe tracker) Free-space Michelson beam combination at H and K bands HAWAII array camera fed by single-mode fluoride fibers White-light and spectrometer channels; frame rates of Hz Fringe tracking with coherent fringe demodulation, closed-loop to delay line

32 Angle tracker Electronics IR Camera Primary Mirror Secondary Mirror Keck 1 FM H and J band angle tracking DCR corrector for good sky coverage Images from two Kecks multiplexed onto one quadrant of HAWAII array 100 Hz readout High-speed updates to local tip/tilt mirror Low-speed off-loads to AO system Keck 2 FM

33 Visibility-Mode observations at KI

34 National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology KI first results: NGC4151 Swain et al., 2003, ApJL, 596, L163 First detection of any source outside our galaxy with infrared interferometry NGC 4151 is a Seyfert galaxy at a distance of ~13 Mpc The interferometer clearly resolved the emission Examined several possible sources of emission Star cluster: too big Dust torus: too big Jet: did not fit SED Accretion disk: consistent with observations Data implies the emission comes from a region < 0.1 parsec across Towards Earth BLR θ = 40 Dust torus R ~ 1 pc Radio jet

35 Technologies Enabling technologies for very narrow angle interferometric astrometry Laser metrology» Nuller uses 16 systems to measure and control Fringe tracking» Nuller uses 2 K-band trackers along with 3 trackers at N band (not simultaneous) Phase referencing» Used to stabilize N band fringes; similar function to stabilizing primary star while scanning secondary one

36 Internal pathlength (CT) metrology Secondary M4 Inconel Extraction Fold Mirror Beamsplitter Corner cube Annular mirror Primary M4 Fold Mirror DSM Visible Beamsplitter Keck AOB Adds laser metrology of (almost) entire optical path, not just FDL Measured position error combined with local FDL metrology to control FDL position Keck 2 Keck 1 Beam Injection and Long delay lines Switching Fast delay lines Switchyard Imaging and nulling combiners Rugate filters CT launchers Fringe trackers Angle trackers Auto-aligner

37 Phase reference test -Plotted is fringe phase vs. time on the primary nuller -Green bars indicate times when K-band to nuller phase referencing was enabled -Nuller was operated with zero gain, so all stabilization is attributable to phase referencing

38 Approach: Dual-baseline Nulling K1 Implement dual-baseline nulling to remove both star and thermal background Use subapertures on Keck telescopes Cross-Combiner Two step beam combination Null star on pair of K1-K2 baselines Nuller MIR cam Nuller Measure exozodi fringe with rapid scan between two nulled outputs Cross-Combiner Operates at µm (+) Resembles some TPF approaches K2

39 Keck nulling beam-combiner: 2 nullers & 2 X-combiners in Nuller 1 Nuller 2 out Cross-combiners

40 Nuller Summit Installation KALI Camera Stimulus Nuller Fast Delay Line Lab Fringe Tracker Dewar Fringe Tracker Foreoptics

41 Nuller Summit Installation Fast Delay Line Lab Fast Delay Line Lab Beam Switchyard

42 Nuller Summit Installation Video Link to Summit I/F Control Room Video Links to K1 & K2 Operators Waimea Remote Control Room Post-Processed White Light (10-um) Interferogram

43