SONG Stellar Observations Network Group. The prototype

Transcription

1 SONG Stellar Observations Network Group The prototype F. Grundahl1, J. Christensen Dalsgaard1, U. G. Jørgensen2, H. Kjeldsen1,S. Frandsen1 and P. Kjærgaard2 1) Danish AsteroSeismology Centre, University of Aarhus 2) Niels Bohr Institute, Copenhagen University Third SONG workshop, Beijing, 2010

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4 Overall design driver: Optimize the design for the primary science purposes: Ultra precise radial velocities (bright stars) asteroseismology and exoplanets Photometry in crowded fields exoplanets High duty cycle and long timebase time series Robust operations and a long lifetime operation costs

5 Where are we now? All major components in house or ordered: Telescope, dome, echelle grating, iodine cells, spectrograph mirrors, CCD camera, container... Design of nearly all units in place or going through finishing touches Mechanical production of spectrograph components, nasmyth instrument Electronics design, motor control ongoing/completed Database system for observatory control has been developed, servers are in house and setup tests, script development is ongoing (Frandsen talk). How will the system look:

6 Telescope and dome Contract to Astelco Systems, GmBH, Aug Critical design review, Dec. 15, 2009 Acceptance, Tenerife, Feb Mar Location: Izaña, Tenerife (IAC)

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15 1m telescope, alt az mount 5 pointing precision and ZD < 80 Thin (5cm), controllable primary mirror with Shack Hartmann WFS M2 on high precision hexapod Rapid re pointing (20deg/s) 2 Nasmyth foci (< 60s switching) ADC (lucky imaging) Optical de rotator 4.5m diameter dome w. sideports Wind screen for dome Window to allow solar obs. M2 and M3 dimensioned for ø15' field in the 2nd Nasmyth port

16 Nasmyth Instrumentation

17 Nasmyth Instrumentation Functions: Dual color lucky imaging Telescope focus monitor Filter wheel(s), 6 positions. Entrance to Coude path Aux. port

18 RED From Telescope AUX. VIS

19 Nasmyth characteristics Camera model Andor, IxonEM+ DU897 Pixel size 16µm, 0."09 on sky Detector size and Field of view pixels (46" x 46" on sky). 550nm ~95% 800nm ~75% Max. Readout speed 10 MHz Max. Full frame rate 34Hz Read noise (e, max. frame 49e (rms.) in conventional mode rate) Read noise with L3 operation < 1, but effective QE reduced by ~2 Wl. split between VIS/RED channel 650nm.

20 Due to its modest aperture and high image quality, the SONG telescope is well suited to do lucky imaging. In the I band r0 ~ 20cm when the V band seeing is ~1" Lucky imaging works well already for D/r0 < 10 The diffraction limit is ~0".2 for a 1m telescope Initial experiments with microlensing observations at the Danish 1.54m telescope on La Silla started in 2009 and continues in 2010.

21 Good! BAD! Martin Glitrup, Experiment with Danish 1.54m on La Silla, Summer, 2009, same pixel size (0".09) as SONG. DFOSC 0".4 per pix. DFOSC 100% 5%

22 Coudé path

23 Use mirrors and lenses with optimized coatings over the spectrograph working wavelength range (off the shelf products!): R > 99% T > 99% Coudé path in vacuum 0.01 x atmospheric pressure, this reduces maintenance and prolong coating lifetime. Eliminates effect of thermal gradients in optical path.

24 Spectrograph and pre slit unit

25 Iodine Cell Flat field and wavelength calibration source (ThAr). Telescope pupil monitoring/control (M7). Focus monitoring. Guiding and slit viewing. Tip/Tilt correction. LIGHT FROM TELESCOPE

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29 Slit pos Resolution (λ/δλ) Width ( ) Width (µm) Length (µm) Sampling (pixels) Wide slit Pinhole ø=20 9 Alignment ø=20,100

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31 Velocity precision of the SONG spectrograph 55s. exposure

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33 Summary of capabilities Telescope and dome 1m telescope, alt az mount with <5 pointing precision and ZD < 80 Thin (5cm), controllable primary mirror with Shack Hartman WFS M2 on high precision hexapod Rapid re pointing (20deg/s) 2 Nasmyth foci (< 60s switching) ADC and Optical de rotator 4.5m diameter dome w. sideports Wind screen for dome and window to allow daytime solar obs. M2 and M3 dimensioned for ø15' field in the 2nd Nasmyth port

34 Summary of capabilities Coudè focus Ultimate RV. precision of 1m/s expected with iodine cell. Wavelength range Å. R = (higher possible with undersampling). Uniform PSF over detector area. High throughput (~7% TOTAL expected). Tip tilt correction. Pupil correction/control/monitoring. Focus control and monitoring. Photon weighted midtime of exposure calculation. Ordinary operation is possible (no I2 cell, ThAr calib.)

35 Summary of capabilities Nasmyth focus Dual color lucky imaging wavelength split at 650nm. FOV 46" 46" with 0.09 pixels to sample diffraction limited imaging. Up to 6 filters possible for each channel (minus dark+grey filter). Continuous monitoring of the focus. Full frame rate up to 34Hz. Near diffraction limited performance during best weather conditions. Conventional CCD mode possible with low RON and ~1s readout. Extra port available to cover up to 75 field in third position.

36 The next steps: Assemble, test and integrate the spectrograph in Aarhus. Assemble, test and integrate the nasmyth instrument in Copenhagen. Move to container, install weather station. Develop the control software, integrate with Astelco. Ship to Tenerife, early Install telescope (January 2011). Install instruments... and test, test, test, test, test.

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38 IF V FWHM is 0."7 then D/r0 ~ 7.5 for these observations

39 Billede: Anton Norup Sørensen, Niels Bohr Institutet, København.

40 Billede: Anton Norup Sørensen, Niels Bohr Institutet, København.