BBSO Instrumentation

BBSO exploits the excellent climatic conditions of Big Bear Lake to study the Sun, source of life on Earth. The observatory is located in the middle of Big Bear Lake to reduce the image distortion which usually occurs when the Sun heats the ground and produces convection in the air just above the ground. Turbulent motions in the air near the observatory are also reduced by the smooth flow of the wind across the lake instead of the turbulent flow that occurs over mountain peaks and forests. These conditions, combined with the usually cloudless skies over Big Bear Lake and the clarity of the air at 2,000 meters (6,750 feet) elevation, make the observatory a premier site for solar observations.

BBSO is the site of the high-order adaptive-optics (AO) corrected GST and its post-focus instrumentation, which consists of i) a broadband filter imager — BFI; ii) visible imaging spectrometer — VIS; iii) near-infrared imaging spectropolarimeter — NIRIS; iv) fast-imaging solar spectrograph — FISS; and v) a cryogenic infrared spectrograph — Cyra).

BBSO instrumentation is described in a number of publications, available here.

Also on the site is an H-alpha full-disk imager, a Global Oscillations Network Group (GONG ) station, and NSO SOLIS  facility.

BFI

Broadband Filter Imager

The broad-band filter imager provides continuum context data over an AO-corrected field using a highspeed 2048x2048 CCD camera. Three bands currently used are G-band (430.5 nm, 0.5 nm bandpass) with a field of view of 55" and 0.027"/pixel image scale, red continuum (668.4 nm, 0.4 nm bandpass) and TiO (705.7 nm, 1 nm bandpass) with a field of view of 70" at 0.034"/pixel image scale. Filtergrams are typically taken in short bursts of 100 frames every 15 s, and processed via speckle reconstruction to achieve diffraction-limited images (resolutions of 0.06" in G-band, 0.09" in TiO and red continuum).

Visible Image Spectrometer

VIS currently uses a single Fabry-Pérot etalon to produce a narrow 0.07-Å bandpass over a 70" circular field of view, tunable from 550-700 nm. Plans are underway to upgrade VIS to a dual-etalon system. Available spectral lines include H-alpha, Fe I 630 nm, and Na I D2 (589 nm). Plans are underway to add the He I D3 line. The image scale is 0.029"/pixel, and typically 11 line positions are sampled in 15 s, although the number of line positions (and corresponding time resolution) is a settable parameter. Bursts of typically 25 frames are used for speckle reconstruction at each line position. The purpose of VIS is to provide spectral diagnostics of solar features at the diffraction limit of the telescope.

VIS
NIRIS

Near Infra-Red Imaging Spectropolarimeter - NIRIS

NIRIS uses dual Fabry-Pérot etalons that provide an 85" round field of view. It uses a Teledyne camera with 2024x2048 HgCdTe, closed-cycle He cooled IR array. The system utilizes half the chip to capture two simultaneous polarization states side-by-side, each 1024x1024 pixels in size, providing an image scale of 0.083"/pixel. The other half of the chip will be used in the future for two out-off-focus images to be used for phase-diversity correction. The primary lines used by NIRIS are the Fe I 1565 nm doublet, and the He I 1083 nm multiplet. The Fe I bandpass is 0.01 nm, while the He I bandpass is 0.005 nm. The polarimetry is done via a rotating waveplate that samples 16 phase angles at each line position, and more than 100 line positions at a cadence of 10 s per full spectroscopic measurement (full-Stokes I, Q, U and V). The inversion of these data to provide magnetograms and other spectral diagnostics is currently under development. The system can also be operated in a fixed-phase-angle, dual-polarization mode that would allow speckle reconstruction of I and V images for diffractionlimited line-of-sight magnetic field diagnostics.

Fast-Imaging Solar Spectrograph - FISS

FISS is a scanning Echelle-type spectrograph provided as an GST post-focus instrument through a collaboration between two Korean groups, Seoul National University (SNU) and Korean Astronomy and Space Institute (KASI). Lines typically observed by FISS are the Ca II H and K lines near 854 nm and the H-alpha line. Both spectral regions can be observed simultaneously using a dual-camera system. The spectrograph slit is 40" long, and a field of view of 40"x60" is typically scanned in 10 s. The H-alpha camera is a 512 x 512 CCD, while the Ca II camera is a 1004x1000 CCD. The slit width is 32 µm, which corresponds to a spatial sampling of 0.16". The spectral sampling at H-alpha is typically 0.0019 nm and at Ca II it is 0.0025 nm, and the resolving power (λ/∆λ = 1.4x105) gives a spectral resolution of 0.005 nm and 0.006 nm, respectively. The purpose of FISS is to study fast dynamics of solar features at moderate spatialresolution. See full description of the instrument in a Solar Physics publication.

FISS
CYRA

Cryogenic Infra-Red Spectrograph - Cyra

Cyra is still under development, and when completed will constitute a fully cryogenic, folded Czerny-Turner spectrograph based on a 2048 x 2048 HgCdTe array sensitive through the 1-5 µm region. A correlation tracker is available for tip-tilt correction, and an image-rotator has been completed and is undergoing tests now. When complete, the system will include a rotating waveplate and polarizing beam splitter for dual-beam, full-Stokes polarimetry. Test observations of the CO lines near 4667 nm (resolving power 250,000) have succeeded in showing off-limb emission. Photospheric lines of interest are Fe I 1565 nm, Ti I 2231 nm, Fe I 4064 nm, and Si I 4143 nm, while chromospheric lines are Ca I 3697 nm, Mg I 3682 nm, and the aforementioned CO lines. The instrument scan cadence will be a function of total integration time, number of Stokes parameters, and scanned field of view, but is expected to be less than 1 min.

High-Order and Multi-Conjugate Adaptive Optics - MCAO

MCAO is a technology allowing to enlarge the field of view that is corrected for atmospheric turbulence as compared to classical adaptive optics (CAO). CAO systems deliver their best correction across only a small field. A wider corrected field of view would allow one to capture much more solar surface in great detail all at the very same instant. The MCAO system at BBSO also enables us to study fundamental design questions in solar MCAO experimentally. The system utilizes three deformable mirrors (DMs). One of which is conjugated to the telescope pupil, and the other two to distinct higher altitudes. The high-altitude DMs can be separately and quickly conjugated to various altitudes between 2 and 8 km. Three Shack-Hartmann WFS units are available, one for low-order, multi-directional sensing and two high-order on-axis sensing.

MCAO
FISS

Off-limb AO System

We developed a classical AO system tuned for off-disk use. It utilizes chromospheric emission in diverse structures, such as prominences, for wavefront sensing and achieve diffraction-limited performance. Our high-order system uses a conventional correlating Shack-Hartmann sensor tuned on chromospheric emission in the H$\alpha$ line at 656.3 nm. Obtained data can processed with speckle image reconstruction, which further improves the signal-to-noise and field-dependent correction of the high-resolution image. The off-disk AO system can achieve closed-loop operation on a wide array of off-limb features.

Full Disk H-alpha Telescope

The 10 cm Full Disk H-alpha telescope (FDHA) located in the Ash Dome and is mounted on an astrophyscs 1500 mount together with an earthshine telescope. It uses a Zeiss Lyot Filter with a 0.025 nm bandpass and a JAI PULNIX TM4200GE Camera with a Kodak KAI 4021 2048x2048 pixel detector with a dynamic range of 12 bit.

Before starting the daily high-cadence observations with a frequency of usually 1 frame per minute, a dark frame and several flat field frames are obtained. From these frames a flat field image, a quiet Sun image, and a contrast enhanced H-alpha image are computed. The typical exposure time for the H-alpha full-disk images obtained at BBSO is 50 ms. The exposure time of the calibration frames and full-disk images is usually the same during the daily observing run.

FDHA
ES

Earthshine Telescope

A global and absolutely calibrated albedo can be determined by measuring the amount of sunlight reflected from the Earth and, in turn, back to the Earth from the dark portion of the face of the Moon (the "earthshine" or "ashen light"), as well as measuring the brightside ("moonshine") moonlight. For over two decades, we have been measuring the Earth's large-scale reflectance from BBSO right up to the present moment. The observations are done remotely utilizing our earthshine coronagraph located in the Ash Dome next to the GST dome.

Wide-band High-resolution Imaging Spectro-Polarimetric Explorer

WHISPER will employ an image reconstruction scheme developed for slit spectrographs to undo the effect of the residual seeing, optical aberrations and modulation transfer, allowing us to achieve the special resolution of 50 km on the Sun, as well as to restore the original image contrast and signal amplitudes. WHISPER will capture a carefully chosen very wide spectral range that comprises a plethora of spectral lines for diagnosing the photosphere and chromosphere, thus drastically increasing the signal-to-noise ratio when inferring parameters of solar atmosphere. This will substantially increase the ability to study solar processes including the formation of sunspots and superstrong solar magnetic fields.

WHISPER
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BBSO operation is supported by US NSF AGS-2309939 grant and New Jersey Institute of Technology. GST operation is partly supported by the Korea Astronomy and Space Science Institute and the Seoul National University.
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© BBSO/NJIT - Last modified: January 27, 2025 by Vasyl Yurchyshyn