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.

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

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

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

Big Bear Solar Observatory BBSO was built by Caltech in 1969. 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 The old hemispherical dome has been replaced by a 5/8 sphere to house the larger NST

Telescope Big Bear Solar Observatory 3 April 2019

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.

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: 0.06” @ 0.5 μm and 0.2” @ 1.56 μm Some NST details. Big Bear Solar Observatory 3 April 2019

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

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

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

Mirror Testing Big Bear Solar Observatory 3 April 2019

PM Final Figuring Big Bear Solar Observatory 3 April 2019

Residual Figure Errors Big Bear Solar Observatory 3 April 2019

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

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

Adaptive Optics Big Bear Solar Observatory 3 April 2019

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

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

Dome Removal Big Bear Solar Observatory 3 April 2019

New Dome Big Bear Solar Observatory 3 April 2019

Old Telescope Removal Big Bear Solar Observatory 3 April 2019

Fly Away Big Bear Solar Observatory 3 April 2019

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

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

New Pier Big Bear Solar Observatory 3 April 2019

New Pier Big Bear Solar Observatory 3 April 2019

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=300 0.5 mm (if measured from on-axis mirror optical center) and f2=6482 10 mm Mirrors silver coated Mirrors in BBSO and were tested in UA Mirror Lab in Summer 2007 Big Bear Solar Observatory 3 April 2019

Prime Focus Big Bear Solar Observatory 3 April 2019

Nasmyth Focus Big Bear Solar Observatory 3 April 2019

Telescope Control System Big Bear Solar Observatory 3 April 2019

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