1. New Solar Telescope in Big Bear Solar Observatory
Philip R. Goode
Big Bear Solar Observatory
Center for Solar-Terrestrial Research
New Jersey Institute of Technology
This is a progress report on the 1.6 m off-axis solar telescope for BBSO being built in collaboration with KASSI and UHawaii.

2. Motivations for NST Fundamental Scale of Solar Magnetism Space Weather
Solar magnetic field (bundled) fibers
Flares and CMEs origins
Satellite data a complement
Space Weather
Solar storms can damage space assets and terrestrial telecommunications/power grid
Telescope Technology Challenges
Off-axis Telescope
Heat Control
Adaptive Optics
Big Bear Solar Observatory
3 April 2019

3. New Solar Telescope (NST)
Collaborators
UHawaii
UArizona
KASI/SNU
Federal Funding
NSF
AFOSR
NASA
KoSF
Big Bear Solar Observatory
3 April 2019

4. BBSO/NSTers Roy Coulter Nicolas Gorceix Jeff Nenow John Varsik
Sergey Shumko
Mark Vincent
Vlad Abramenko
Randy Fear
Big Bear Solar Observatory
3 April 2019

5. Big Bear Solar Observatory
BBSO was built by Caltech in The dome sits at the end of a 1000 ft. causeway on Big Bear Lake’s north shore at 6,750 foot elevation.
Observatory was transferred from Caltech to NJIT in July 1997.
The surrounding waters of Big Bear Lake reduce ground level convection, and predominate winds bring smooth air flows across the flat surface of the lake providing superb conditions for solar observing.
The old hemispherical dome has been replaced by a 5/8 sphere to house the larger NST

6. Telescope
Big Bear Solar Observatory
3 April 2019

7. The New Solar Telescope Polarimeters and SNU-FISS Spectrograph
Big Bear Solar Observatory
New Solar Telescope
The New Solar Telescope Polarimeters and SNU-FISS Spectrograph
Instrumentation
Two instrument stations will be used with the NST:
The coude’ lab provides stable optical benches in a temperature controlled environment. A spectrograph and 2 magnetographs are planned for the initial observing campaigns.
The coude’ will be fed by the adaptive optics module allowing diffraction-limited imaging at all wavelengths.
Air is forced by fans along the fiberglass plenum and vented across the mirror where it is gathered and a returned to the heat exchanger. The vents can control the portion that flows above and below the mirror.

8. NST –BBSO/UH/KASSI/UA
1.6 m clear aperture (1.7m blank) – being figured by Steward Mirror Lab
Active optics (36 actuators in PM mirror cell) to control thermally induced variations & airknifes, backside cooling
Primary: f/# 2.4, 4.4 m telescope length, <20 nm surface quality, <10 Å μ–roughness, and blank of Zerodur with CTE of (0.0±1.0)  10-7 per °C
Observable wavelengths: 0.39–1.6 μm with AO and >0.39 μm without AO
FOV: 180” in optical labs or 1/2° in prime focus
Real–time telescope alignment
Polarization, wavefront sensing and calibration optics immediately before M3
Diffraction limit: 0.5 μm and 1.56 μm
Some NST details.
Big Bear Solar Observatory
3 April 2019

9. Primary Mirror Big Bear Solar Observatory 3 April 2019
1) The PM came from Schott as a 1.7 m/ 10 cm thick meniscus. It was generated at Kodak (now ITT) before shipping to Steward Observatory, where it was figured on the stress lap secondary tool.
Big Bear Solar Observatory
3 April 2019

10. Optical testing : measuring aspheric surfaces
Interferometers use light to measure to ~1 nm surface errors, for spherical or flat surfaces
We need to measure aspheric (non-spherical) surfaces
CGH can change spherical wavefronts to aspheric, allowing the use of interferometers for measuring aspheric surfaces
Aspheric surface to be measured
aspherical wavefront
Spherical wavefront
Interferometer
CGH
Big Bear Solar Observatory

11. Optical test for NST mirror
50 cm mirror
10 cm CGH
15 cm lens
4D interferometer
10 µm alignment tolerances
1.7-m primary mirror
Off-axis piece of f/0.7 parent
NST primary mirror status 8/4/05

12. Mirror Testing
Big Bear Solar Observatory
3 April 2019

13. PM Final Figuring
Big Bear Solar Observatory
3 April 2019

14. Residual Figure Errors
Big Bear Solar Observatory
3 April 2019

15. Primary Mirror (M1) Thermal Control
Function: Mitigate mirror seeing
seeing
-0.69x10-6 K-1
0.28x10-6 mbar-1
Outline here:
What are we talking about?
Thermal Performance I
Gemini tests
MuSES modeling
Validation using Gemini data
Hybrid
Retractable
Is this good enough?
Seeing Performance
Formulation: thermally disturbed layers
Chart, in terms of average temperature of upstream skin
BBSO tests to verify/sanity check
Thermal Performance II
Hardware modifications, hybrid
Hardware modifications, retractable
MuSES results w/mods
Summarize
Big Bear Solar Observatory
3 April 2019

16. Big Bear Solar Observatory
New Solar Telescope
Telescope Design
The NST is an off-axis section of 5.3 meter, f#0.73 Gregorian telescope. The result is an f#2.4, 1.6 meter system.
The design offers an unobstructed pupil allowing superior adaptive optics performance and low scattered light. The prime focus, where most of the solar radiation must be reflected/absorbed, is accessible without obstructing the light path.
A small (3.5 mm) field stop (UH) at prime focus limits the radiation loads transmitted to the downstream optics.
Polarization optics before M3

17. Adaptive Optics
Big Bear Solar Observatory
3 April 2019

18. Adaptive Optics Big Bear Solar Observatory 3 April 2019
We emphasize that for AO-308, according to our error budget analysis, we realistically expect to achieve a Strehl ratio of 0.3 in the detector plane in
the visible (0.5$\mu$m) for median BBSO seeing conditions, which turns out to imply steady, diffraction limited data. The Strehl,
generally used to quantify the performance of an AO system, is the ratio of the maximum intensity in the AO corrected image in the
detector plane to that from a theoretical, perfect imaging system operating at the diffraction limit.
Forward modeling using MHD simulations combined with radiative transfer and modeled AO Point-Spread-Functions provide simulated observations that can be used to determine the ``ground truth'' of the MHD simulations. Such comparisons also indicate that, in particular, because of the
extended nature of the observed object, high Strehl ratios (S$\ge$0.3) are required to obtain reliable quantitative
measurements of the solar structure. In particular, polarimetric observations with low Strehl are from difficult to impossible to
interpret. The problem here is that the requisite opposite polarity measurements are often closely (tenths of arcsecs) spaced.
To obtain meaningful predictions of the Strehl ratio, we performed extensive performance modeling in order to estimate the expected
performance, quantified by the Strehl ratio in the detector plane of the post-focus instruments. This comprehensive analysis includes adaptive optics residuals (e.g., fitting/aliasing, bandwidth, and wavefront sensor noise) as well as realistic estimates of uncorrectable wavefront error contributions from the telescope (e.g., mirror seeing and dome seeing) and the instrument(s) (e.g., non-common path errors). The analysis uses the ATST site survey data and is partially based on the extensive error budget modeling that was done for the ATST. The results are shown in the form of histograms of the predicted Strehl that we expect to obtain with AO-308 at visible and NIR wavelengths. For comparison we show the expected AO-76 performance in left figure, which is to be compared with that for AO-308 shown in right figure. While for AO-308, the Strehl for the visible (0.5~$\mu$m) peaks around 0.3, for AO-76 that Strehl shows no peak. This implies AO-76 will not enable observations in visible except under the most extraordinary seeing conditions. Thus, the figures clearly demonstrate the need for a high order AO for the highest resolution observations.
Big Bear Solar Observatory
3 April 2019

19. Optical Support Structure
Moves in DEC. Right Ascension
Big Bear Solar Observatory
3 April 2019

20. Dome Removal
Big Bear Solar Observatory
3 April 2019

21. New Dome
Big Bear Solar Observatory
3 April 2019

22. Old Telescope Removal
Big Bear Solar Observatory
3 April 2019

23. Fly Away
Big Bear Solar Observatory
3 April 2019

24. Fork and Spectrograph, etc.
Big Bear Solar Observatory
3 April 2019

25. “Empty” Dome
Ala Saadeghvaziri
Big Bear Solar Observatory
3 April 2019

26. New Pier
Big Bear Solar Observatory
3 April 2019

27. New Pier
Big Bear Solar Observatory
3 April 2019

28. Secondary Mirror(s) SM is Zerodur from Schott (plano-plano)
Space Optics Research Lab has figured 0.5 m mirror on axis
Cut into two concave elliptical SMs (140 and 145 mm)
<20 nm surface quality and foci downstream at f1= mm (if measured from on-axis mirror optical center) and f2= mm
Mirrors silver coated
Mirrors in BBSO and were tested in UA Mirror Lab in Summer 2007
Big Bear Solar Observatory
3 April 2019

29. Prime Focus
Big Bear Solar Observatory
3 April 2019

30. Nasmyth Focus
Big Bear Solar Observatory
3 April 2019

31. Telescope Control System
Big Bear Solar Observatory
3 April 2019

32. Timeline Dome complete – Mar. 2008 OSS Delivery – May 2008
Big Bear Solar Observatory
New Solar Telescope
Timeline
Dome complete – Mar. 2008
OSS Delivery – May 2008
PM Delivery – Apr 2008
Telescope Installation – May 2008
First Light - May 2008
Full operation – Spring 2009