1 / 30

Tuesday June 4, 2002 Frédéric Derie, Françoise Delplancke, Andreas Glindemann, Samuel Lévêque,

P hase R eferenced I maging and M icro-arsec A strometry (PRIMA) an introduction to technical description and development. Tuesday June 4, 2002 Frédéric Derie, Françoise Delplancke, Andreas Glindemann, Samuel Lévêque, Serge Ménardi, Francesco Paresce, Rainer Wilhelm, K. Wirenstrand

rasul
Download Presentation

Tuesday June 4, 2002 Frédéric Derie, Françoise Delplancke, Andreas Glindemann, Samuel Lévêque,

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Phase Referenced Imaging and Micro-arsec Astrometry(PRIMA)an introduction to technical description and development Tuesday June 4, 2002 Frédéric Derie, Françoise Delplancke, Andreas Glindemann, Samuel Lévêque, Serge Ménardi, Francesco Paresce, Rainer Wilhelm, K. Wirenstrand European Southern Observatory (ESO) Karl Schwarzschild Strasse 10, D-85748 Garching München (Germany) Email:fderie@eso.org

  2. Contents • Introduction • Main Scientific Objectives of PRIMA • Overall Description and Principles • Four Sub-Systems of PRIMA • GENIE and PRIMA • Development in three Phases • Planning • Conclusion GENIE Workshop Leiden 04.06.02

  3. Introduction • PRIMA is designed to make use of the Dual feed capability of the VLTI for both UT and AT and is compatible with VINCI, AMBER, MIDI • Gain of about six magnitudes in H, K and N. • PRIMA is designed to perform: • faint Object Observation in J, H, K and N Bands • high accuracy (10 µas) narrow angle astrometry in band H or K, • aperture synthesis (phase reference imaging) and model constrained imaging in J, H, K and N • In the astrometric mode, the prime observable is the optical differential delay between the object and a reference. • In Imaging mode, the observable are phase and amplitude of the object visibility. • Observation on a number of baselines :minimum two for Astrometry, more for Imaging. • PRIMA is composed of four major sub-systems: Star separator, Differential Delay Lines, Metrology, Fringe Sensor Units and one overall control system and software GENIE Workshop Leiden 04.06.02

  4. Main Scientific Objectives Detection and Characterization of extra-solar planets and their birth environment. • astrometric and the imaging capability of PRIMA. The astrometric capability will determine the main physical parameters of planets orbiting around nearby stars already found by radial velocity (RV) techniques including their precise mass, orbital inclination and a low resolution spectrum (with Amber). Another key objective for VLTI with PRIMA will be the exploration of the nuclear regions of galaxies including our own High precision astrometry with PRIMA might even go so far as to probe the central BH to a few times its Schwarzschild radius (2.5*10-7 pc). H High resolution imaging with the VLTI of the nearest AGN (Cen-A is at ~ 3.5Mpc) has a crucial role to play in this area especially with MIDI at 10 and 20. GENIE Workshop Leiden 04.06.02

  5. Main Scientific Objectives Astrometry allows the search for planets to stars that cannot be properly covered by the RV technique, (e.g. particular pre-main sequence (PMS) stars). The crucial exploration of the initial conditions for planetary formation in the stellar accretion disk as a function of age and composition will be finally possible. The reach of the VLTI in the local star forming regions where the expected magnitude of the reflex motion of the object specified is plotted as a function of distance. GENIE Workshop Leiden 04.06.02

  6. Main Scientific Objectives The simultaneous image at mas resolution or better of the accretion disk from which any particular planet is born will add a new and exciting dimension to our understanding of both planetary and stellar formation mechanisms since the complex accretion disk is expected to be the cradle of these objects. The expected disk structure open to VLTI with PRIMA might look something like: GENIE Workshop Leiden 04.06.02

  7. PRIMA Diagram FSU A/B Delaylines ? AT

  8. Overall Description and Principles The recorded distance between white fringes of the reference and the object is given by the sum of four terms: (ΔS . B) the Angular separation (< 1 arcmin) times Baseline; + (Ф ) the Phase of Visibility of Object observed for many baselines; + (ΔA) the Optical Path Difference caused by Turbulence (supposed averaged at zero in case of long time integration); + (ΔC) the Optical Path Difference measured by Laser Metrology inside the VLTI. n.b. For astrometry both Objects are supposed to have the Phase of their complex visibility = zero (point source object) GENIE Workshop Leiden 04.06.02

  9. Main System Performance Faint Objects Observation Gain of about 6 Magnitudes Model Independent Imaging (Aperture Synthesis) Phase referenced imaging on faint objects with AMBER, MIDI, VINCI Visibility accuracy < 1% 10µas astrometry Phase and Group Delay measurement with FSU A and Metrology, Angular resolution < 10 µarcsec Baselines from 8 to 200m Limiting Magnitude with tracking with FSU B(in band K)

  10. Main System Performance(con’t) Sky Coverage Probability to find a star of MK within field of x arcsec A. Robin Model Obs Besançon, stellar formation in the galaxy

  11. Main System Performance(con’t) Anisoplanatic OPD and visibility loss • Fringe visibility is attenuation is related to off-axis observation. This visibility loss has two effects on the observation of the faint object: • it reduces the limiting magnitude on the faint object • it reduces the accuracy with which the visibility of the object is measured. • The visibility loss can be calibrated on reference stars. N K R0=0.5m R0=1m R0=1m R0=0.5m

  12. Main System Performance(con’t) Optical Path Difference Tracking Residual OPD noise dominated by Fringe tracking noises (sensor and loop noises)linked to band pass and atmospheric turbulance Current DL have 44.6 Hz Band Pass, OPD residual about 100 nm. For small angular separation the DDL with high sampling rate can optimise the OPD residual but only for < 3” in K and bright stars.

  13. Main System Performance(con’t) Total Observation Time Short exposure visibility and phase measurements averages incoherently, for Paranal typical atmospheric condition 18µas/hr, baseline 200m, 10” separation: 10µas astrometry accuracy : about 3 hr per baseline 1% accuracy in imaging : about 40 min per baseline and in K band Single Exposure Time

  14. STS Function/Performance • The Star Separator is located at Coudé Focus of UT and AT, it is in charge of: • picking up 2 stars in the Coudé field of view up to 120 arcsec Ø, • collimating them in two beams of 80mm diameter separated by 240mm, • compensate for field rotation, • adjusting and stabilizing the beam tip-tilt and the output pupil transversal position, • allowing PRIMA calibration by injecting the same star in both feeds, • transmitting the metrology and not interrupting it, especially at the calibration step. • A possibility of (counter-)chopping is also foreseen for the operation @ 10µm. • Tracking accuracy 10 mas and resolution 2mas, • Output beam and pupil stability and OPD stability as for other VLTI sub-system GENIE Workshop Leiden 04.06.02

  15. DDL Function/Performance • Differential Delay Line (one per beam and per arm), is used to compensate the relative OPD introduced between the the primary and of the secondary objects. • Range differential OPD 70 mm • OPD accuracy 5 nm • Stability (OPD noise) 14 nm RMS over 8 ms • Sampling Rate 8 kHz • Pupil relay GENIE Workshop Leiden 04.06.02

  16. FSU Function/Performance • The Fringe Sensor Unit (FSU) is where the stellar beam combination is taking place. The FSU comprises two identical channels (A and B) handling respectively the secondary and the primary objects. • The role of each FSU channel is to: • Detect the fringes (DL and DDL for the secondary object are scanning the OPD. • Deliver at a high rate the fringe pattern position (phase delay and group delay) to the OPD controller, in charge of closing the various OPD control loops. • Store the measured data over the whole observation time. GENIE Workshop Leiden 04.06.02

  17. FSU Function/Performance (con’t) • In imaging mode, FSU B performs the Fringe Trackingfor both objects,by feeding-back its measurements to the main DL. The secondary object can be observed by MIDI or AMBER with long integration times and its phase measured, for several interferometric baselines, with respect to the “constant point” provided by FSU B, thanks to the PRIMA Metrology System. • In astrometric mode, both FSU channels are operated and one OPD control loop is closed for each object, at a frequency which depends on the object magnitude. The FSU records the residual group delay for each object, which is processed off-line to derive the astrometric data. GENIE Workshop Leiden 04.06.02

  18. Ck B A C D Φ Φ Φk FSU FSU Function/Performance (con’t) The selected instrument concept uses co-axial beam combination, which consists of adding the incident beams amplitudes at a semi-reflective surface, close to a pupil plane. The beam combiner provides simultaneously four interferometric outputs (optical beams resulting from the superimposed incident beams), with /2,  and 3/2 relative phase shifts. This enables using the so-called ABCD algorithm to derive the phase delay, without introducing any temporal OPD modulation. PRIMA metrology beams are inserted in (and extracted from) the stellar path after the FSU beam combiner. Therefore the OPD is monitored by the metrology system over the whole FSU internal path

  19. MET PRIMA Metrology A highly accurate metrology system is required to monitor the PRIMA instrumental optical path errors to ultimately reach a final instrumental phase accuracy limited by atmospheric piston anisoplanatism. The metrology system must measure the internal differential delay, DL, between both stars in both interferometer arms with a 5 nm accuracy requirement over typically 30 min. This accuracy requirement is driven by the PRIMA astrometric mode. DOPD =B.(S2 -S1)+ f/k +DL GENIE Workshop Leiden 04.06.02

  20. MET PRIMA Metrology Requirements

  21. MET Concept Super Heterodyne Laser interferometry: • Two heterodyne interferometers with different heterodyne frequencies f1 and f2 • Frequency offset Dn between the two interferometers for suppressing cross talks in calibration mode • Direct measurement of DL after frequency mixing • DL coded in phase of (f1-f2) carrier signal • No need for 2 independent high bandwidth and highly synchronised measurements of L1 and L2 • Digital Phase meter using principle of time interval measurement • with on-board averaging capability GENIE Workshop Leiden 04.06.02

  22. n n+38Mhz n-39.55Mhz n+38.65Mhz n-40Mhz I1(t) = cos(2πf1t + f1) f2= 450kHz f1= 650 kHz f1= 650 kHz f2= 450 kHz I2(t) = cos(2πf2t + f2) Crosstalk noise 80MHz Intensity noise 200 kHz 0 Df1=50 kHz Df2=50kHz Imeas(t) = I12cos[2π(f1-f2).t+ f1- f2) MET Super-Heterodyne Laser interferometer 1.1 µm (Si)<l<1.45 µm (H band) Lc >> 500 m Dl/l < 10-8

  23. A.O.M’s +38.65 MHz +38.MHz -39.55 MHz -40 MHz Nd-Yag, 1319nm MET Prototyping and testing ESO/IMT collaboration Beam Launcher/combiner (1 channel) 25mm

  24. 40 Arm length= 520m (return way) 20 0 -20 OPD [microns] -40 -60 -80 Time [min] 0 5 10 15 20 25 30 35 MET Testing at Paranal • Objectives: • Check the performance of the concept & prototype hardware under representative operating conditions • Characterise Internal OPD fluctuations • Check interfaces with VLTI Optical configuration in the VLTI optical lab

  25. MET Main Results • Fibre pigtailed photodetector: • NEP=0.2pW/Hz (Johnson noise) • 10MHz bandwidth • Phase measurement: • Resolution: 2p/1024 rad or 0.64 nm in double-pass (using 200MHz clock ) • Max. Sampling Frequency: Fsmax=200kHz • Electronic noise < 0.64nm rms for Popt>100nW per arm and V=70% • Accuracy (contribution of photodetection & phase measurement chain): • 2p/800 rad or 0.8 nm in double-pass • for Popt>20nW per arm, V=70% and 50kHz Bandwidth • OPD Measurements • Reliable L and DL Meas. along 520m arm length(return way) during 30min (PRIMA integration time) • Polarisation measurements (return way, l=1319nm ) • TVLTI(s)=17.1% ; TVLTI(p)=19.4% ; fp- fs =10.5 deg • References • S. Lévêque,Y. Salvadé,R. Dändliker,O.Scherler, “High accuracy laser metrology enhances the VLTI”, Laser Focus World, April 2002. • Y. Salvadé, R. Dändliker, S. Lévêque, “Superheterodyne Laser Metrology for the Very Large Telescope Interferometer", ODIMAP III, 3rd topical meeting on Optoelect. Distance / Displacement Meas..and Appl., University of Pavia,20–22/09/01

  26. GENIE and PRIMA • GENIE can benefit from PRIMA technology • GENIE requirements for OPD control accuracy (closed loop): • 20 nm RMS for nulling in N band • 5–7 nm RMS for nulling in L band (preferable because of background in N) •  Need for a very fast OPD control system • Strongest benefit: Fringe Tracking on Reference Star GENIE Workshop Leiden 04.06.02

  27. GENIE and PRIMA (2) • Two-stage fringe tracking concept: • “Classical” VLTI fringe tracking loop, plus a • Fast “GENIE fringe tracking loop” • Sensor: • PRIMA FSU for both loops, plus • PRIMA Laser Metrology for GENIE loop to monitor OPD, e.g., due to telescope vibrations • Actuator: • Main DL for classical VLTI loop • Fast GENIE DL for GENIE loop; 2 possibilities: • GENIE-internal delay line (Piezo actuator) • PRIMA DDL with up-graded performance GENIE Workshop Leiden 04.06.02

  28. Based on Recommendations of the Ad-Hoc Committee for VLTI (Tiger Team, Nov 2001) Phase 1: 2002-2004 Astrometry (10 µas, Band K) and Phase Referencing Imagery (Bands H, K, N) with 2 ATs (ML15/12 in K, 8 in N), . [2 STS AT, MET, FSU A/B, CTL S/W] Phase 2: 2005-2008 Phase Referencing Imagery (ML20/15 in K, 11 in N), and Astrometry with 2 UTs (50 µas, K Band) [2 STS UT, upgrade MET & CTL] Phase 3: 2008-2010 Phase Referencing Imagery and 10 µas Astrometry with any pair of UTs in Band K and H [2 more STS UT, 4 DDL, Upgrade MET & FSU A/B & CTL] PRIMA Three Phases GENIE Workshop Leiden 04.06.02

  29. Phase 1(only) Kick Off June 2002 (low level kick Off STS, FSU June 2002) PDR January 2003 (low level PDR STS, FSU, MET Dec 2002) PDR CTL S/W May 2003 FDR July 2003 (low level FDR STS, FSU, MET June 2003) FDR S/W December 2003 PAE STS, FSU, MET November 2004 Assembly and Commissioning on site Q1 and Q2 2005 PRIMA Operation May 2005 PRIMA Planning GENIE Workshop Leiden 04.06.02

  30. PRIMA will enable VLTI to perform high precision narrow-angle astrometry down to the atmospheric limit of 10 μas, real imaging of objects fainter than K~14 and nulling at contrast levels of ~10-4. The first goal is to implement 10 µas astrometry in 2004, in order to search for exoplanets. In parallel, ESO should make sure that the first images of extragalactic objects can be obtained and that the necessary actions be taken to get to faint objects in 2006. PRIMA is driven by the scientific objectives and competitive situation, but it also provides for the most logical sequence of technical developments. GENIE can benefit on PRIMA development : FSU, DDL, MET, STS UT. Conclusions GENIE Workshop Leiden 04.06.02

More Related