Advanced Technology Solar Telescope Research Articles

Monitoring the Sun: A Global Space Weather Enterprise

Monitoring the Sun: A Global Space Weather Enterprise

The Local Seeing Environment at Big Bear Solar Observatory

ABSTRACTThe site survey for the Advanced Technology Solar Telescope (ATST) of the National Solar Observatory was initiated in 2002 to find the best location for a 4 m aperture solar telescope. At the end of a 4 year survey, three sites (Big Bear Solar Observatory [BBSO] in California, Mees Solar Observatory [MSO] on Haleakala, Maui, Hawaii, and Observatorio Roque de los Muchachos, on La Palma, Spain) were identified as excellent sites for high‐resolution solar observations. MSO was ultimately chosen as the future ATST site. We present a subset of the ATST site survey data, focusing on the local seeing environment at BBSO. In particular, we are interested in the seeing characteristics at a mountain lake‐site observatory, its relation to the local environment and climate, and its implications for the 1.6 m New Solar Telescope (NST) currently being built at BBSO. We find a close correlation of very good seeing conditions with the prevailing wind direction and speed. The observatory building, located at the end of a 300 m causeway, is surrounded by the cool waters of Big Bear Lake, which effectively suppress the ground‐layer seeing. Very good seeing conditions from sunrise to sunset are a unique feature of BBSO, which makes it ideally suited for synoptic observations and sustained high‐resolution studies of solar activity and space weather.

Optical control of the Advanced Technology Solar Telescope

The Advanced Technology Solar Telescope (ATST) is an off-axis Gregorian astronomical telescope design. The ATST is expected to be subject to thermal and gravitational effects that result in misalignments of its mirrors and warping of its primary mirror. These effects require active, closed-loop correction to maintain its as-designed diffraction-limited optical performance. The simulation and modeling of the ATST with a closed-loop correction strategy are presented. The correction strategy is derived from the linear mathematical properties of two Jacobian, or influence, matrices that map the ATST rigid-body (RB) misalignments and primary mirror figure errors to wavefront sensor (WFS) measurements. The two Jacobian matrices also quantify the sensitivities of the ATST to RB and primary mirror figure perturbations. The modeled active correction strategy results in a decrease of the rms wavefront error averaged over the field of view (FOV) from 500 to 19 nm, subject to 10 nm rms WFS noise. This result is obtained utilizing nine WFSs distributed in the FOV with a 300 nm rms astigmatism figure error on the primary mirror. Correction of the ATST RB perturbations is demonstrated for an optimum subset of three WFSs with corrections improving the ATST rms wavefront error from 340 to 17.8 nm. In addition to the active correction of the ATST, an analytically robust sensitivity analysis that can be generally extended to a wider class of optical systems is presented.

Development of solar scintillometer

The index of scintillation measurement is a good parameter to compare different sites for image quality or ‘seeing’. We have developed a scintillometer, which is deployed on the high resolution SPAR telescope in the island site of Udaipur Solar Observatory, for the site characterization to specify the proposed MAST (Multi Application Solar Telescope). The scintillometer consists of a miniature telescope, termed as micro telescope (4 mm aperture, 15 mm focal length) mounted on a drive which tracks the Sun continuously, associated amplifiers and a data acquisition system. A photodiode is used as the detector. The telescope along with detector was obtained from National Solar Observatory (NSO), and is similar to the one used for Advanced Technology Solar Telescope (ATST) site survey. At USO we developed the amplifier and data acquisition system for the scintillometer. A 24-bit analog to digital converter based system was designed, assembled, tested and used as the data acquisition system (DAS). In this paper, we discuss the instrumentation and present the initial results.

Advanced technology solar telescope multiple Fabry-Pérot interferometer telecentric optical design

We present four preliminary designs for a telecentric optical train supporting the Advanced Technology Solar Telescope (ATST) multiple Fabry-Perot interferometer (MFPI), which is to be used as an imaging spectrometer and imaging spectropolarimeter. The point of departure for all three designs is the F/40 telecentric image at the Coude focus of the ATST. The first design, representing the high-spectral-resolution mode of operation, produces an intermediate F/300 telecentric image within the triple etalon system and a 34-arcsec field of view (FOV). The second design, intermediate between high- and low-spectral-resolution modes of operation, produces an intermediate F/150 telecentric image at the etalons and a 1.1-arcmin FOV. The third and fourth designs each represent a low-resolution mode of operation, producing an F/82 telecentric image at the etalons and a 2-arcmin FOV. Each design results in good telecentricity and image quality. Departures from telecentricity at the intermediate image plane cause field-dependent shifts of the bandpass peak, which are negligible compared to the bandpass FWHM. The root mean square (rms) geometric spot sizes at the final image plane fit well within the area of a camera pixel, which is itself in accordance with the Nyquist criterion, half the width of the 28-µm-wide resolution element (as determined from the diffraction limit of the ATST). For each configuration, we also examine the impact that the Beckers effect (the pupil apodization caused by the angle-dependent amplitude transmittance of the MFPI) has on the image quality of the MFPI instrument.

Selecting the site for the advanced technology solar telescope

Selecting the site for the advanced technology solar telescope

Solar Site Survey for the Advanced Technology Solar Telescope. I. Analysis of the Seeing Data

ABSTRACTThe site survey for the Advanced Technology Solar Telescope concluded recently after more than 2 years of data gathering and analysis. Six locations, including lake, island, and continental sites, were thoroughly probed for image quality and sky brightness. The present paper describes the analysis methodology employed to determine the height stratification of the atmospheric turbulence. This information is crucial, because daytime seeing is often very different between the actual telescope aperture (∼30 m) and the ground. Two independent inversion codes have been developed to simultaneously analyze data from a scintillometer array and a solar differential image monitor. We show here the results of applying them to a sample subset of data from 2003 May that was used for testing. Both codes retrieve a similar seeing stratification through the height range of interest. A quantitative comparison between our analysis procedure and actual in situ measurements confirms the validity of the inversions. The sample data presented in this paper reveal a qualitatively different behavior for the lake sites (dominated by high‐altitude seeing) and the rest (dominated by near‐ground turbulence).

Evaluation of seeing-induced cross talk in tip-tilt-corrected solar polarimetry.

We reanalyze the effects of atmosphere-induced image motions on the measurement of solar polarized light using a formalism developed by Lites. Our reanalysis is prompted by the advent of adaptive optics (AO) systems that reduce image motion and higher-order aberrations, by the availability of liquid crystals as modulation devices, and by the need to understand how best to design polarimeters for future telescopes such as the Advanced Technology Solar Telescope. In this first attempt to understand the major issues, we analyze the influence of residual image motion (tip-tilt) corrections of operational AO systems on the cross talk between Stokes parameters and present results for several polarization analysis schemes. Higher-order wave-front corrections are left for future research. We also restrict our discussion to the solar photosphere, which limits several important parameters of interest, using some recent magnetoconvection simulations.

Background-Induced Measurement Errors of the Coronal Intensity, Density, Velocity, and Magnetic Field

The effect of a background signal on the signal-to-noise ratio is discussed, with particular application to ground-based observations of emission lines in the solar corona with the proposed Advanced Technology Solar Telescope. The concepts of effective coronal aperture and effective coronal integration time are introduced. Specific expressions are developed for the 1σ measurement errors for coronal intensity, coronal electron density, coronal velocity, and coronal magnetic field measurements using emission lines and including a background.

The Advanced Technology Solar Telescope Site Survey Sky Brightness Monitor

ABSTRACTThe Advanced Technology Solar Telescope (ATST) will be a 4 m aperture off‐axis telescope with advanced high‐resolution and low scattered light capabilities for the observation of the solar photosphere and corona. The site characteristics that are critical to the success of the ATST coronal observations are the sky brightness, the precipitable water vapor content, and the number and size distributions of the dust particles. Therefore, part of the ATST site survey effort is to obtain measurements of these atmospheric properties at all the potential ATST sites. The ATST site survey Sky Brightness Monitor (SBM) is a new instrument specifically developed for this task. The SBM is a modified externally occulted coronagraph capable of imaging the solar disk and sky simultaneously. The ability to image the Sun and the sky simultaneously greatly simplifies the calibration of the sky‐brightness measurements. The SBM has a very simple optical configuration that makes it a compact and low‐maintenance instrument. The SBM is sensitive to sky brightness below 1 × 10-6 disk center intensity, with a field of view extending from 4 to 8 R⊙. It measures the solar disk and sky brightness at three continuum bandpasses located at 450, 530, and 890 nm. A fourth bandpass is centered at the 940 nm water vapor absorption band. With measurements of disk and sky brightness at these four wavelengths, site characteristics such as extinctions, aerosol content, and precipitable water vapor content can be derived. This paper documents the design, specifications, calibration procedures, and performance of the SBM.

Science Goals and Development of the Advanced Technology Solar Telescope

The Advanced Technology Solar Telescope (ATST) will perform high-resolution studies of the Sun's magnetic fields needed to understand their role in the fundamental processes responsible for solar variability. The generation of magnetic fields through dynamo processes, the amplification of fields through the interaction with plasma flows, and the destruction of fields remain poorly understood. There is incomplete insight as to what physical mechanisms are responsible for heating the corona, what causes variations in the radiative output of the Sun, and what mechanisms trigger flares and coronal mass ejections. Progress in answering these critical questions requires study of the interaction of the magnetic field and convection with a resolution sufficient to observe scales fundamental to these processes. The 4-m aperture ATST is designed as a unique scientific tool, with excellent angular resolution, a large wavelength range, and low scattered light. With its integrated adaptive optics, the ATST will achieve a spatial resolution nearly 10 times better than any existing solar telescope. To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Multiconjugation Optical Relay for an Off‐Axis Solar Telescope

ABSTRACTThe Sun is an ideal object for the development and application of multiconjugate adaptive optics (MCAO). An effort to develop solar MCAO is pursued by the National Solar Observatory (NSO) Adaptive Optics Project. In developing solar MCAO, we bear in mind its possible implementation into the proposed 4 m Advanced Technology Solar Telescope (ATST). Two possible relay optical designs feeding an MCAO section and the coudé section of a 4 m off‐axis solar telescope, such as the proposed ATST, are presented and discussed here.

Extinction and Sky Brightness at Two Solar Observatories

The Advanced Technology Solar Telescope site survey Sky Brightness Monitor simultaneously images the solar disk and the sky to about 8 solar radii in four wavelengths at 450, 530, 890 and 940 nm. One day of data from Mees Solar Observatory on Haleakala and from the National Solar Observatory at Sacramento Peak (Sunspot, New Mexico) are analyzed. Both sites show strong Rayleigh extinction, but while Haleakala shows a larger aerosol component, Sunspot shows a large variation in the aerosol component. Overall the Haleakala extinction varies as λ−2 whereas the Sunspot extinction changes from about λ−3.5 to about λ−2, suggesting an increasing aerosol component during the day. Water vapor absorption measurements from both sites are similar, though Sunspot shows larger time variations than Haleakala. The instrument-corrected sky brightness from both sites show comparable values, and again the Sunspot data show more variations. The sky brightness values show a radial dependence of sky brightness of r−0.1 at Haleakala, but a dependence of r−1.0 at Sunspot. The wavelength variation of the sky brightness at Haleakala is relatively constant at λ−1.5 but varies at Sunspot from λ−1.5 to λ−0.1 again suggesting an increasing aerosol contribution during the day at Sunspot. Finally, dust measurements near the ground are compared with the extinction wavelength exponent for data taken at Haleakala on 24 Feb. 2003. The measurements suggest more large dust particles are present near the ground than averaged over the whole air column.

1.6 M SOLAR TELESCOPE IN BIG BEAR - THE NST

New Jersey Institute of Technology (NJIT), in collaboration with the University of Hawaii (UH), is upgrading Big Bear Solar Observatory (BBSO) by replacing its principal, 65 cm aperture telescope with a modern, off-axis 1.6 m clear aperture instrument from a 1.7 m blank. The new telescope offers a significant incremental improvement in ground-based infrared and high angular resolution capabilities, and enhances our continuing program to understand photospheric magneto-convection and chromospheric dynamics. These are the drivers for what is broadly called space weather - an important problem, which impacts human technologies and life on earth. This New Solar Telescope (NST) will use the existing BBSO pedestal, pier and observatory building, which will be modified to accept the larger open telescope structure. It will be operated together with our 10 inch (for larger field-of-view vector magnetograms, Ca II K and Ha observations) and Singer-Link (full disk H, Ca II K and white light) synoptic telescopes. The NST optical and software control design will be similar to the existing SOLARC (UH) and the planned Advanced Technology Solar Telescope (ATST) facility led by the National Solar Observatory (NSO) - all three are off-axis designs. The NST will be available to guest observers and will continue BBSO`s open data policy. The polishing of the primary will be done in partnership with the University of Arizona Mirror Lab, where their proof-of-concept for figuring 8 m pieces of 20 m nighttime telescopes will be the NST`s primary mirror. We plan for the NST`s first light in late 2005. This new telescope will be the largest aperture solar telescope, and the largest aperture off-axis telescope, located in one of the best observing sites. It will enable new, cutting edge science. The scientific results will be extremely important to space weather and global climate change research.

Design and development of the Advanced Technology Solar Telescope

AbstractLed by the National Solar Observatory, plans have been made to design and to develop the Advanced Technology Solar Telescope (ATST). The ATST will be a 4‐m general‐purpose solar telescope equipped with adaptive optics and versatile post‐focus instrumentation. Its main aim will be to achieve an angular resolution of 0.03 arcsec (20 km on the solar surface). The project and the telescope design are briefly described.

The Advanced Technology Solar Telescope

The Advanced Technology Solar Telescope is the largest solar optical facility currently under development. The National Solar Observatory and its partners have just started the design and development phase with first light being planned for late this decade. The 4-m telescope will provide an angular resolution down to 0.025 arcsec, a large photon flux for precise magnetic and velocity field measurements, and access to a broad set of diagnostics from 0.3 to 28 μm. We summarize the currently envisioned scientific capabilities of the telescope and its suite of instruments along with a glimpse at some of the early concepts.