Exoplanets with ELTs

1
Exoplanets with ELTs

• ELT Issues we must think carefully about
• Disunity is death. Next Decadal Review process
  forthcoming.
• Technology opens funding coffers, and leverages
  IP.
• Diffraction-limited AO vs Natural Seeing Light
  Bucket
• What is Wide Field?
• MCAO on 30m J-band, 2 f.o.v., ?/D?7mas? 17140
  x 17140 resolution elements
• Seeing on 30m J-band, 20 f.o.v., seeing ?
  300mas? 4000 x 4000 resolution elements
• cf 8K mosaics on 4m give 33 f.o.v., seeing ?
  750mas ? 2700x2700
• MCAO on a 30m is more wide field than natural
  seeing!
• Natural seeing drives instruments 4 times larger
  than currently on an 8m.

2
Exoplanets

• Wow factor science (in order)
• 1) Evidence for biological activity on planets
  around other stars
• Detection of bio-markers from spectroscopy
  (terrestrial, gas giants or satellites)
• 2) Potentially life-supporting terrestrial
  planet(s) around other stars
• Detection of terrestrial planets in habitable
  zones (NIR imaging orbits)
• 3) Detailed understanding of a multiplicity of
  terrestrial and gas giant planetary systems.
• Detection and orbits for many gas giant and
  terrestrial planets - not necessarily habitable
  (NIR imaging orbits, NIR spectroscopy, MIR
  imaging of young forming systems)
• 4) Detailed understanding of a multiplicity of
  gas giant planetary systems.
• Detection and orbits for many gas giants (as
  above).

3
Exoplanets

• 5) Detection and characterisation of young
  planetary systems and disks. (this is easier
  as they are brighter)
• (NIR imaging orbits, NIR spectroscopy, MIR
  imaging of young forming systems)
• 6) Detection and characterisation of free
  floating planets in star forming regions
• (NIR imaging orbits, NIR spectroscopy)

4
Exoplanets

• Indirect detection
• Radial velocities (figure in CELT,Magellan and
  VLOT cases!)
• 3m/s or better ?R ?50-100K. Time sampling.
  S/N/pix?300. Vgt8 (targets gtgt sky)? Light
  Bucket

5
Single Mirror 30m Light Buckets.

• Bright targets ? Sky brightness irrelevant ?
  small slits only needed to control spectrograph
  size deliver high resolution.
• All the money spent on making a 30m telescope
  deliver 0.3 images is a waste. All you need is a
  3 image and an image slicer.
• eg. an array of 225 x 1m telescopes fibre feeding
  spectrograph can deliver photons at high res at
  fraction of cost (A15m) of a 0.3 image quality
  15m telescope (A200m).
• but this is a separate discussion for a separate
  facility .

6
Exoplanets

• Indirect detection
• Radial velocities (figure in CELT,Magellan and
  VLOT cases!)
• 3m/s or better ?R ?50-100K. Time sampling.
  S/N/pix?300. Vgt8 (targets gtgt sky)? Light
  Bucket? not science for the envisaged 30m
  telescopes.
• Transit Detection
• Discovery needs wide fields of view ( 106 stars)
  GCs with AO?
• Follow-up needs objects bright enough for
  spectroscopy. ? better done with space based
  satellites.
• Reflected / Scattered light from known exo-planet
  systems
• ? Light Bucket
• Astrometry 7mas resolution should do lt700µas
  astrometry making some astrometric wobble work
  feasible.

7
Direct Resolution / Detection

• In exoplanet science, all the 30m action is in
  resolving systems, getting rid of as much parent
  starlight as possible, and studying the planets.
• Key issues
• Resolution
• Magnitude difference parent starlight
  suppression
• Sticking light from a coronagraph down a
  spectrograph

8
Resolution
100 known exoplanetsApril 2003

• 1-5 of FGK have exoplanets _at_ lt 3au
• More to come?
• Have to go out to 50pc (not 10pc)
• Jupiter _at_ 100mas
• Earth _at_ 20mas

9
Resolution

• AO Coronagraphsgt 4?/D for Sgt0.8(Sivaramakrishna
  n et al. ApJ, 552, 397, 2001)
• 30m ? gt30mas
• 30 known gas giants resolvable
• Resolve Jupiters to 166pc.
• Resolve Earths to 33 pc

Log10 Periastron Apastron (mas)
100 known exoplanetsApril 2003
10
Magnitude difference

• Signal ? Dtel2 (S A d2 ?) / (D2 r2)Dtel is
  telescope diameter, S is Strehl, A is albedo, d
  is planet diameter, ? is phase function,
  rorbital radius, D is distance of system
• Noise ? aimage Dtel2 (1-S) ( s/(?2s/2)2
  C)0.5aimage is solid angle of image (?/Dtel)2 ?
  N independent of Dtel, s is seeing FWHM, ?r/D,
  s/(?2s/2)2 is AO halo profile
• Sensitivity scales as Dtel2. 30m is 15x more
  sensitive than 8m and 225x faster

11
Seeing exoplanets - with OWL ...

• Gas giants accessible to 30m out to 50pc
• Detect. Orbits. Albedos. Spectroscopy?

12
The Killer Applications

• Detect Gas Giants.Measure Orbits Understand
  migration.Albedos for more than 4 gas giants.
• NIR Spectroscopy from the coronograph
• Young planets make problem 103 easier.
• Terrestrial planets probably not feasible.
• CELT Green Book project to find terrestrial
  planets via rv around M-dwarfs really not
  brilliant.
• MIR Imager to probe young disks at 70mas at 10um
  at 125pc ? 9au
• or debris disks about nearer objects?