Parasitic science with SONG or How to push the limits of a 1m telescope

1
Parasitic sciencewith SONGorHow to push the
limits of a 1m telescope

• Michael I. Andersen
• Astrophysikalisches Institut Potsdam

2
Why bother with a network?

• Ideal for Target-of-Opportunity
• What you want for phase coverage
• The telescopes must be autonomous!
• Is the way to keep small telescopes
• in service for the community!

3
An emerging technologyElectron Multiplication
(L3) CCDs

• Based on a high-gain register, converting a
  photo-electron to many electrons
• in principle similar to a photo-multiplyer
• Operation is similar to a normal CCD
• Allows photon counting operation
• 512 x 512 pixel format avaialble
• (1k x 1k device may become avaialble)

4
Condition for photon counting operation

• Gain 100 x gt readnoise
• (efficient thresholding)
• Less than 0.1 photo-electron/pix/exposure to
  avoid coincidence loss
• ? fast readout (up to 100 FPS) and/or
• faint targets and/or small telescope
• More than 0.01 photo-electron/pix/exposure
• to overcome spurious charge (adjust frame rate)

5
A photon counting spectrograph for SONG

• R 20.000 cross dispersed echelle with a 30mm
  beam and 1.5 slit.
• 4000Å-8000Å fixed format spectral coverage
• System efficiency of 25 feasible

6
Gamma-ray burst redshifts
7
Being on the spot and not
8
Gamma-ray Burst spectroscopy I
9
Gamma-ray Burst spectroscopy II

• z 0.4 Detect host galaxy emission lines (OII
  3727, OIII 5007, H-alpha).
• Host galaxy limiting magnitude 22 in 1h
• 0.4 z 2.5 Detect metal absorption lines in
  the afterglow spectrum
• Limiting magnitude 22 in 1h.
• 2.5 z Detect Lyman-alpha/Lyman forest
• Limiting magnitude 23 in 1h.

10
Stellar radial velocities

• 1 min integration on a 18mag solar type star
  gives a signal-to-noise of 0.5
• (1 photon for every 4 spectral elements).
• With 1000 strong spectral lines reconded this
  yields an accuracy of 300m/s.
• Bright limit (multiple photon events) around 11th
  magnitude.

11
High resolution imaging I

• The Fried parameter, r?, is the area across
  which the wavefront is diffraction limited.
• If D/r? lt 4, the wavefront is diffraction
  limited, if tip/tilt (image motion) is removed.
  Can be achieved in software from fast readout
  (30Hz) imaging with a reference star in the field
• For a 1m, this condition is fullfilled if
  seeing is better than 0.4, 0.5 and 0.7 in V,R
  and I respectively.

12
High resolution imaging II

• Lucky imaging from the NOT

13
Why a 1m telescope

• One hour limiting magnitudes for a 1m is
  about 24.5-25.5.
• One min limting magnitude is about 22-23 with
  time resolution Ideal for Gamma-ray Burst
  afterglow detection
• In the tip/tilt corrected domain, required
  exposure time scales as D-4
• For crowded (planet microlensing) fields,
  0.01mag error is reached in 1min at I18.
  Resolution crusial for this application!

14
Having parasites onboard I

• Increased weight of science cases may allow for
  more telescopes and/or larger aperture.
• More shoulders to carry the project throught
  times with problems.
• SONG should not be too sensitive to seeing
  offer observing time with good/excellent seeing
  but with a high price tag.

15
Having parasites onboard II

• Makes everything more complicated.
• Scheduling becomes an issue which requires
  significant attention.
• There must be strict rules for how to cover the
  operational costs.
• ALL THESE ISSUES MUST BE
• AGREED ON UP FRONT!

16
Network operation

• Experience suggest that it is very challenging to
  achieve robotic operation.
• Better approach may be autonomous telescopes
  with one on-duty network astronomer.

17
Conclusions

• Photon counting instrumentation has a great
  potiential of enhancing the capabilities of 1m
  telescopes.
• Having a photon counting spectrograph and camera
  on SONG telescopes could allow others to find
  additional funding.
• ? more sites
• Added science capabilities
• ? added complexity