1. The SOLARC Off-axis Coronagraph Why a ground-based solar coronagraph SOLARC design and performance Future prospects J.R. Kuhn, R. Coulter, H. Lin, D. Mickey NASA/SRT, UH/IfA, NSF/ATST

2. SOHO/LASCO Available Daily

3. Only the magnetic field will tell... (from Chen et al., Low, Gibson)

4. Our “dark energy problem”

5. Empirical encouragement 3.9 m Eclipse Off-bandOn-band SiIX? Judge et al. claim spectroscopic detection (ApJ, in press)

6. Why an IR (reflecting) off-axis coronagraph? Zeeman magnetic sensitivity Lower scattered sky background Lower scattered instrument optics background Lowered scattered dust background

7. Scattering sources Atmosphere –“seeing” –aerosols –atomic molecular scattering Telescope –diffraction –mirror roughness –mirror dust

8. Atmospheric backgrounds

9. Optical backgrounds 0.5 m 4.0 m

10. SOLARC Reflecting - broadband, IR Off-axis - unobscured, low scattering All major National solar telescope facilities are off-axis or unobscured (Dunn, Evans, McMath)

11. Off-axis telescope “myths” “Aberrations are worse than conventional telescopes” “They can’t be aligned” “Large off-axis mirrors aren’t manufacturable”

12. Aberrations This is not an asymmetric optical system, it is a “decentered” system The full aperture is not illuminated dy Q f e For small angles, Q, blur is astigmatic and only weakly dependent on off-axis distance. SOLARC is diffraction limited over 15 arcmin field

13. SOLAR-C Optics

14. Linear Alignment Algorithms Linear algorithm minizes cos(2theta) and sin(2theta) spot distributions (and rms spot size) while varying M2 tilt and decenter…. Coma and astigmatism easily separated: Starting optical performance...After 2 iterations

15. SOLAR-C M1: 0.5m F/3.7 M2 Gregorian focus 8m f.l. F/20, efl 8m, prim-sec 1.7m 0.5m, 1.5m fl primary 55mm, secondary l/10 p-v figure diff. Limited @ 1micron over 15’fov 10.4 deg tilt angle

16. before baffling

18. First light images

19. PSPT “blue” disk photometry

20. Measured secondary PSF Over 5 orders of magnitude no mirror or other spurious scatter terms detected Short exposure images nearly diffraction limited l = 656 nm

21. Green-line coronal photometry Measured Evans photometer sky Integrated Kolmogorov + solar disk Integrated Kolmogorov+dust SOLARC measured sky l = 530 nm

22. Summary The SOLARC off-axis coronagraph on Haleakala is operational Optical fabrication and alignment issues are no more difficult than for a conventional telescope Post-focus instrumentation includes –Mid-IR imager –Near and mid-IR spectrograph