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The Cryogenic Near-Infrared Spectro-Polarimeter (Cryo-NIRSP) is a combination slit-based spectrograph and context-imaging instrument designed and built for the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST). It is optimized for polarimetric observations of spectral band-passes between 1 and 5 microns, which makes it uniquely suited for polarimetric observations of the solar corona, while also enabling access to other important infrared diagnostics such as the CO fundamental band at 4.6 microns. Integration, testing, and commissioning occurred between 2019 and 2020, and it is now conducting science experiments as part of DKIST early operations. In this article, we discuss its science mission, the requirements driving the design, its fabrication and installation, current capabilities, and the first science data.

We present an overview of the National Science Foundation’sDaniel K. Inouye Solar Telescope(DKIST), its instruments, and support facilities. The 4 m aperture DKIST provides the highest-resolution observations of the Sun ever achieved. The large aperture of DKIST combined with state-of-the-art instrumentation provide the sensitivity to measure the vector magnetic field in the chromosphere and in the faint corona, i.e. for the first time with DKIST we will be able to measure and study the most important free-energy source in the outer solar atmosphere – the coronal magnetic field. Over its operational lifetime DKIST will advance our knowledge of fundamental astronomical processes, including highly dynamic solar eruptions that are at the source of space-weather events that impact our technological society. Design and construction of DKIST took over two decades. DKIST implements a fast (f/2), off-axis Gregorian optical design. The maximum available field-of-view is 5 arcmin. A complex thermal-control system was implemented in order to remove at prime focus the majority of the 13 kW collected by the primary mirror and to keep optical surfaces and structures at ambient temperature, thus avoiding self-induced local seeing. A high-order adaptive-optics system with 1600 actuators corrects atmospheric seeing enabling diffraction limited imaging and spectroscopy. Five instruments, four of which are polarimeters, provide powerful diagnostic capability over a broad wavelength range covering the visible, near-infrared, and mid-infrared spectrum. New polarization-calibration strategies were developed to achieve the stringent polarization accuracy requirement of 5×10−4. Instruments can be combined and operated simultaneously in order to obtain a maximum of observational information. Observing time on DKIST is allocated through an open, merit-based proposal process. DKIST will be operated primarily in “service mode” and is expected to on average produce 3 PB of raw data per year. A newly developed data center located at the NSO Headquarters in Boulder will initially serve fully calibrated data to the international users community. Higher-level data products, such as physical parameters obtained from inversions of spectro-polarimetric data will be added as resources allow.

The Cryogenic Near Infrared Spectropolarimeter for the Daniel K Inouye Solar Telescope is designed to measure polarized light from 0.5 to 5 μm. It uses an almost all reflective design for high throughput and an R2 echelle grating to achieve the required resolution of up to R = 100,000. The optics cooled to cryogenic temperatures reduce the thermal background allowing for IR observations of the faint solar corona. Both the spectrograph and its context imager use H2RG detector arrays with a newly designed controller to allow synchronized exposures at frame rates up to 10 Hz. All hardware has been built and tested and the key components met their design goals. 1) The cryogenic system uses mechanical closed cycle coolers which introduce vibrations. Our design uses a two stage approach with a floating mounting disk and flexible cold links to reduce these. The vibration amplitudes on all critical stages were measured and are smaller than 1μm. 2) The grating stage of the spectrograph uses a double stack of harmonic drives and an optical encoder to provide sub-arcsecond resolution and a measured repeatability of better than 0.5 arcsec.

The Imaging Vector Magnetograph (IVM) at the Mees Solar Observatory, Haleakalā, Maui, Hawai’i, obtained many years of vector magnetic-field data in the photospheric Fe i 630.25 nm line. In the latter period of its operation, the IVM was modified to allow routine observations in the chromospheric Na i D1 line, as well as the Fe i line. We describe the sodium observational data in detail, including the data-reduction steps that differ from those employed for the Fe i 630.25 nm line, to obtain calibrated Stokes polarization spectra. We have performed a systematic comparison between the observational data and synthetic NLTE Na i D1 Stokes spectra derived for a variety of solar-appropriate atmospheric and magnetic configurations. While the Na i D1 Stokes polarization signals from the solar atmosphere are expected to be weak, they should generally be within the IVM capability. A comparison between synthetic spectra and observational data indicates that this is indeed the case.

We calculate the total and the free magnetic energy for solar NOAA active region 10486 on 2003 October 29 using chromospheric vector magnetograms observed with the Imaging Vector Magnetograph at Mees Solar Observatory in the Na I λ5896 spectral line. The magnetic energy is derived from the magnetic virial theorem using observations spanning the X10 flare that occurred at 20:39 UT. Although poor atmospheric seeing prevented us from discerning changes in the free energy associated with the flare, there was an unusually large amount of free magnetic energy in NOAA AR 10486: (5.7 ± 1.9) × 1033 ergs, which is consistent with the very high level of activity observed in this active region. It is thus plausible that the extreme activity was powered by the magnetic free energy.

An X3-class flare occurred on 2002 July 15 with white-light emission and a complex filament eruption. Observations were made in the optical continuum, Hα, UV continuum, microwave, and soft X-rays, as well as with high-cadence longitudinal magnetograms. Within the preflare phase, intense heating is observed accompanying upward motion of the filament. At the onset of the impulsive phase, filament Doppler acceleration is increased from -1.5 to -7.0 km s-2. Flare impulsive emission is double-peaked, possibly corresponding to two magnetic reconnection events: the first occurs above the active region in the corona, while the second takes place in a thin current sheet underneath the eruptive filament. It is probable that a twisted helical flux rope, seen in C IV TRACE images, is formed during the second reconnection. The energy released by the white-light flare is ~1033 ergs and dominates the flare emission spectra. Within the flare impulsive phase, the emission profiles show both abrupt and gradual components in white light, UV, and Hα. These variations are independently reflected in the transverse motions of flare kernels: the abrupt emission phase corresponds to a rapid kernel motion, while the gradual phase corresponds to a more modest kernel motion.

I describe a method for quickly and accurately determining the plate parallelism in a tunable Fabry-Perot interferometer. The method takes advantage of the fact that our Fabry-Perot is installed in a spectropolarimeter: we measure profiles of solar or telluric absorption lines in three differently polarized telescope subapertures and use the residual polarization profiles to determine the plate parallelism error. An example of the error as a function of time during the observing day is also shown; it changes in a consistent way with telescope hour angle but the drift is enough to require frequent adjustment.

It is widely believed that solar magnetic fields are force-free in the solar corona but not in the solar photosphere at all. In order to examine the force-freeness of active region magnetic fields at the photospheric level, we have calculated the integrated magnetic forces for 12 vector magnetograms of three flare-productive active regions. The magnetic field vectors are derived from simultaneous Stokes profiles of the Fe I doublet λλ6301.5 and 6302.5 obtained by the Haleakala Stokes Polarimeter of Mees Solar Observatory, with a nonlinear least-squares method adopted for field calibration. The resulting vertical Lorentz force normalized to the total magnetic pressure force |Fz/Fp| ranges from 0.06 to 0.32 with a median value of 0.13, which is smaller than the values (~0.4) obtained by Metcalf et al., who applied a weak field derivative method to the Stokes profiles of Na I λ5896. Our results indicate that the photospheric magnetic fields are not so far from force-free as conventionally regarded. As a good example of a linear force-free field, NOAA Active Region 5747 is examined. By applying three different methods (a most probable value method, a least-squares fitting method, and comparison with linear force-free solutions), we have derived relatively consistent linear force-free coefficients for NOAA AR 5747. It is found that the scaled downward Lorentz force (|Fz/Fp|) in the solar photosphere decreases with increasing |α|. Our results also show that the force-freeness of photospheric magnetic fields depends not only on the character of the active region but also on its evolutionary status.

Active or adaptive optics often require the ability to characterize wavefront aberrations using natural extended sources. The task becomes especially challenging when dealing with widely extended sources such as the solar granulation. We propose a new approach based on the processing of oppositely defocused images. This method, which is a generalization of a technique known as curvature sensing, derives the wavefront curvature from the difference between two oppositely defocused images and determines the second momenta of the point spread function. The proposed method measures the wavefront aberration from the images themselves, requires little computational resources, is fast enough to be used in a real-time adaptive optics system and is particularly adapted to random patterns such as solar granulation or spot penumbras whose morphology evolves during the observation. We envision the application of the method to real-time seeing compensation in solar astronomical telescopes, and to the correction of optical system aberrations in remote sensing instrumentation. This effort is directed towards building a curvature sensor for the real-time applications.

Time series of 2-dimensional spectro-polarmetric data were obtained with the intent of studying the temporal behavior of velocity, magnetic flux, and characteristics of the Stokes V profile in a small region of a larger sunspot. Full Stokes profiles in I, Q, U, and V were obtained. Velocity oscillations were found at frequencies of 3.3 mHz in each of the profiles. Acoustic power maps indicate that locations of highest power correspond to areas in which the polarization signal was greatest, therefore no conclusion about the type of wave mode participating in the oscillations can be made. Velocity amplitudes were I: 71 m s−1, Q: 47 m s−1, U: 65 m s−1 and V: 86 m s−1. Oscillatory behavior was also detected in longitudinal field strength, with an r.m.s. amplitude of 22 G, at 2.6 and 3.3 mHz. The power was localized at the umbral/penumbral boundary. A phase analysis indicates a −130° phase difference with Stokes V velocity oscillations at 3.3 mHz and a 75° difference at 2.6 mHz. Results are consistent with magnetic field lines swaying in response to a p-mode driver. No oscillatory behavior was seen in Stokes V asymmetry or amplitude splitting.

The Imaging Vector Magnetograph (`IVM') at Mees Solar Observatory, Haleakalā, Maui, Hawai`i, is designed to measure the magnetic field vector over an entire solar active region on the Sun. The first step in that process is to correct the raw data for all known systematic effects introduced by the instrument and Earth's atmosphere. We define a functional model of the atmosphere/instrument system and measure the corrections for the degradation introduced by each component of the model. We demonstrate the feasibility of this method and assess the accuracy of the IVM spectra with a direct comparison of the resulting Stokes spectra to a well-described spectropolarimeter.

Measurements of the vector magnetic field in the solar atmosphere with high spatial and temporal resolution over a large field of view are critical to understanding the nature and evolution of currents in active regions. Such measurements, when combined with the thermal and nonthermal X-ray images from the upcoming Solar-A mission, will reveal the large-scale relationship between these currents and sites of heating and particle acceleration in flaring coronal magnetic flux tubes. The conceptual design of an imaging vector magnetograph that combines a modest solar telescope with a rotating quarter-wave plate, an acousto-optical tunable prefilter as a blocker for a servo-controlled Fabry-Perot etalon, CCD cameras, and a rapid digital tape recorder are described. Its high spatial resolution (1/2 arcsec pixel size) over a large field of view (4 x 5 arcmin) will be sufficient to significantly measure, for the first time, the magnetic energy dissipated in major solar flares. Its millisecond tunability and wide spectra range (5000 to 8000 A) enable nearly simultaneous vector magnetic field measurements in the gas-pressure-dominated photosphere and magnetically dominated chromosphere, as well as effective co-alignment with Solar-A's X-ray images.

We describe an instrument we have built and installed at Mees Solar Observatory on Haleakala, Maui, to measure polarization in narrow-band solar images. Observations in Zeemansensitive photospheric lines have been made for nearly all solar active regions since the instrument began operations in 1992. The magnetograph includes a 28-cm aperture telescope, a polarization modulator, a tunable Fabry-Perot filter, CCD cameras and control electronics. Stokes spectra of a photospheric line are obtained with 7 pm spectral resolution, 1 arc sec spatial resolution over a field 4.7 arc min square, and polarimetric precision of 0.1%. A complete vector magnetogram observation can be made every eight minutes. The flexibility of the instrument encourages diverse observations: besides active region magnetograms we have made, for example, composite vector magnetograms of the full solar disk, and Hα polarization movies of flaring regions.

The active region NOAA 7260 rotated onto the north solar hemisphere as a mature bipole: a dominant negative-polarity sunspot with trailing plage and scattered small spots in attendance. The dominant p spot itself had strong magnetic fields and covered almost 400 x 10(exp -6) of a solar hemisphere. For a period of seven days beginning 14 August, 1992 this active region displayed rapid and drastic evolution: no fewer than 50 magnetic bipoles emerged in the area trailing the large sunspot, increasing the region's magnetic flux by more than 10(exp 22) Mx. This new group of sunspots formed a complex Beta gamma delta configuration with two delta spots and a high degree of magnetic shear. This region was very well observed by Yohkoh and various ground-based instruments. It presented opportunities to study new emerging flux, flares, and also the decay of a large sunspot. For the benefit of later studies we present a description of the global characteristics of this active region, a detailed 'roadmap' of its evolution during disk passage including the development of the two delta regions. We compare proper motion trends and flaring activity to observations of other delta-spots reported in the literature. We also comment on the observed outflow of magnetic elements from the decaying p spot.

The paper compares completely independent vector magnetic field measurements from two very different polarimetric instruments. The Marshall Space Flight Center's (MSFC's) imaging vector magnetograph is based on a birefringent filter, routinely measuring all four Stokes parameters integrated over the filter bandpass (1/8 A) which is tunable across the Fe I 5250 line in 10 mA steps. The Haleakala Stokes Polarimeter of the Mees Solar Observatory (MSO) is based on a spectrometer, routinely measuring all four Stokes parameters of the Fe I 6302.5 line simultaneously and then spatially scanning to build up a vector magnetogram. Active region magnetic field data were obtained with both the MSFC and MSO systems on five days during June 1985. After interpolating the MSFC vector fields onto the more coarse spatial grid of MSO, a point-by-point comparison of the two vector fields is made for data obtained on two of these days (June 8 and 9). From this comparison it is concluded that the spatially-averaged line-of-sight components agree quite well, and that although the MSO spatial grid is coarser, the quality of the MSO image is better than that of the MSFC data because of better seeing conditions.

The Mees CCD (MCCD) instrument is an imaging spectroscopy device which uses the 25 cm coronagraph telescope and the 3.0 m Coude spectrograph at Mees Solar Observatory (MSO) on Haleakala, Maui. The instrument works with resolving power up to R ≈ 200 000 with significant throughput from λ3934 A (Caii K) to λ ≈ 10 000 A. A fast guiding active mirror stabilizes the image during observations. A rapidly writing magnetic tape storage system allows observations to be recorded at 256 kbytes s−1. Currently, the MCCD is used for imaging spectroscopy of solar flares at λ6563 A (Hα), and velocity measurements of umbral oscillations; future plans include emission line studies of active region coronae, and photospheric studies of solar oscillations.

This paper addresses the issue of calibrating the Advanced Technology Solar Telescope for high-precision polarimetry, in particular of the optical train above the Gregorian station (where suitable calibration optics will be placed). Conventional techniques would not be adequate for this telescope given its large aperture. Here we explore two different methods that are currently being considered by the design team. The first one is the "sub-aperture" method, which uses small calibration optics above the primary mirror to calibrate a small sub-aperture of the system. This calibration is then extended to the full aperture by means of actual observations. The second method is based on analyzing the polarization observed in a spectral line with a peculiar Zeeman pattern, such as the FeII 614.9 nm line, which does not produce any intrinsic linear polarization. Numerical simulations are presented that show the robustness of both techniques and their respective advantages and disadvantages are discussed.

A 0.5m aperture off-axis coronagraphic telescope is described. Its fabrication, imaging, and scattered light performance is discussed in the context of simple model expectations.

We calculate the magnetic free energy as a function of time for NOAA active region 8299 on 1998 August 11 using vector magnetic field measurements in the Na I 5896 spectral line observed with the Imaging Vector Magnetograph at Mees Solar Observatory. The free energy dipped to a value consistent with zero for one hour during the observation. Yohkoh /SXT images reveal that around the time of this dip in the free energy the coronal structure of AR 8299 and the nearby AR 8297 changed significantly. SXT observed the brightening of a cusp connecting AR 8299 and AR 8297 and observed coronal dimming in both active regions, suggesting that a gradual CME was launched as the magnetic energy dipped. Further, the magnetic connection between AR 8299 and AR 8297 was temporarily severed during the energy dip and the magnetic field took on a more open configuration afterwards. Unfortunately, LASCO data were not available to confirm the existence of a halo CME. However, the circumstantial evidence points to the magnetic free energy as the energy source for the postulated event.

All existing night-time astronomical telescopes, regardless of aperture, are blind to an important part of the universe - the region around bright objects. Technology now exist to build an unobscured 6.5 m aperture telescope which will attain coronagraphic sensitivity heretofore unachieved. A working group hosted by the University of Hawaii Institute for Astronomy has developed plans for a New Planetary Telescope which will permit astronomical observations which have never before ben possible. In its narrow-field mode the off-axis optical design, combined with adaptive optics, provides superb coronagraphic capabilities, and a very low thermal IR background. These make it ideal for studies of extra-solar planets and circumstellar discs, as well as for general IR astronomy. In its wide-field mode the NPT provides a 2 degree diameter field for surveys of Kuiper Belt Objects and Near-Earth Objects, surveys central to current intellectual interests in solar system astronomy.

We describe and evaluate the performance of a wavefront sensor based on curvature sensing which can be used to detect static aberrations given an extended reference source. The description includes a full mathematical treatment of the sensor signal, as well as how this signal is relate to the Laplacian of the wavefront. Evaluation of the technique is performed with computer simulations. A Monte-Carlo simulation is utilized to evaluate the performance of the technique in the presence of noise. The sensor was found to provide accurate measurement of the wavefront coefficients on high-contrast extended objects. It behaves well in the presence of a field stop, and in the presence of additive Gaussian noise.

We are developing a high-resolution cross-dispersed echelle spectrograph for installation at one of the coude foci of the new AEOS 3.67 meter telescope, operated by the Air Force Space Command on Haleakala, Maui, Hawaii. The spectrograph will consist of two major subsystems, an optical arm for the wavelength range 0.5-1.0 microns and a SWIR arm for the range 1.0-2.5 microns. The optical arm will include a mosaic 4096 by 4096 thinned CCD array, providing coverage of the wavelength range in two settings at a resolving power of 50,000. The CCD camera will be operated in frame-transfer mode. The IR arm will consist of a compact, folded cross- dispersed cryogenic echelle spectrography. The SWIR detector will be a 2048 by 2048 HgCdTe array, based on the existing HAWAII 1024 by 1024 devices. The large-format detector will permit coverage of the entire J or H band in a single grating setting with a resolving power of 60,000, and the K band in two settings. The high resolution, coupled with careful attention to scattering and stray light in the optical system, will permit exploitation of the low sky background between the strong OH airflow lines. Adequate order separation will be maintained to permit work on moderately extended objects while still retaining sky subtraction capability. The spectrography is expected to be available for use in early 2000.

We present results of simulations involving a curvature-based wavefront sensor which uses an extended pattern as a reference source. The proposed sensor provides measurements of both symmetric and asymmetric aberration terms by comparing the Fourier transforms of two oppositely defocused images. Symmetric terms such as defocus and astigmatism can be measured without regard to the object distribution. The asymmetric terms, such as tip and tilt, rely on averaging the signal over many atmospheric realizations in order to determine the object phase, or on defining an arbitrary reference phase. Only after removal of the object Fourier transform phase can the asymmetric terms be identified. Although this paper reports on preliminary results, we believe the proposed sensor will be useful for both real-time compensation of atmospheric distortions while imaging the Sun, and post-facto compensation of optical misalignments in Earth-pointing satellites.

Observations made during the 1991 total solar eclipse and recent observations from NSO/Sac Peak are discussed. The ground-based density measurements will be complimentary to SOHO observations, particularly SOHO electron density measurements.

We reexamine the possibility of detecting p-mode oscillations in Sun-like stars with ground-based telescopes. Previous attempts to make such observations with photometric techniques have been limited to subgiant stars in M67 and have illustrated the great difficulties involved in performing ground-based asteroseismology. Substantial gains in observing efficiency can be realized from new diagnostic techniques and improvements in instrumentation, especially with newer CCD camera systems. We show that for appropriately selected field stars observed with a network of telescopes or at a high duty cycle site, it will be possible to detect p-mode oscillations from the ground. An alternative to a network of telescopes for asteroseismology would be to develop a dedicated observatory for this purpose at a high duty cycle site, i.e., the South Pole. We estimate the scintillation, the main noise source in asteroseismology, at the pole by modeling the index of refraction structure parameter from meterological data. The model results show that at the Pole the variance of the relative intensity fluctuations--i.e., the scintillation--should be a factor of 5 smaller than at at Mauna Kea. Taking into account the improvements possible with target selection and instrumentation, the South Pole would be an excellent site for asteroseismological work on Sun-like stars.

We examine the spatial and temporal relationship between coronal structures observed with the soft X-ray telescope (SXT) on board the Yohkoh spacecraft and the vertical electric current density derived from photospheric vector magnetograms obtained using the Stokes Polarimeter at the Mees Solar Observatory. We focus on a single active region: AR 6952 which we observed on 7 days during 1991 December. For 11 independent maps of the vertical electric current density co-aligned with non-flaring X-ray images, we search for a morphological relationship between sites of high vertical current density in the photosphere and enhanced X-ray emission in the overlying corona. We find no compelling spatial or temporal correlation between the sites of vertical current and the bright X-ray structures in this active region.

Electric current systems in solar active regions and their spatial relationship to sites of electron precipitation and high-pressure in flares were studied with the purpose of providing observational evidence for or against the flare models commonly discussed in the literature. The paper describes the instrumentation, the data used, and the data analysis methods, as well as improvements made upon earlier studies. Several flare models are overviewed, and the predictions yielded by each model for the relationships of flares to the vertical current systems are discussed.

Polarimetric observations at 12 microns of two sunpots are reported. The horizontal distribution of parameters such as magnetic field strength, inclination, azimuth, and magnetic field filling factors are presented along with information about the height dependence of the magnetic field strength. Comparisons with contemporary magnetostatic sunspot models are made. The magnetic data are used to estimate the height of 12 micron line formation. From the data, it is concluded that within a stable sunspot there are no regions that are magnetically filamentary, in the sense of containing both strong-field and field-free regions.

The range of applicability of the weak-field approximation for the inference of magnetic field vectors is studied from the profiles of the Stokes parameters. It is shown that, for typical solar lines in the visible, this approximation may be applied to an accuracy of ∼ 20% for field strengths as great as 3500/g L G, where g L is the Lande factor, provided that the work is realised in the line wings. A systematic underestimate of the field strength seems to occur for strong fields, observations in several related spectral lines may allow a calibration of this effect, and so for an increase in accuracy of the inferences

Observations of solar IR intensity variations at 50, 100, and 200 microns were made simultaneously and cospatially with Doppler measurements in the sodium D1 line at 5896 A. Brightness temperature variations of several K in amplitude are highly correlated with five minute Doppler oscillations. The brightness variations are attributed to work done on the chromospheric medium by compression, driven by the five minute oscillations. The Doppler oscillations lead the brightness variations by about 47 deg in phase at 50 and 100 microns and by about 72 deg in phase at 200 microns.

The results of two methods for deriving photospheric vector magnetic fields from the Zeeman effect, as observed in the Fe I line at 6302.5 A at high spectral resolution (45 mA), are compared. The first method does not take magnetooptical effects into account, but determines the vector magnetic field from the integral properties of the Stokes profiles. The second method is an iterative least-squares fitting technique which fits the observed Stokes profiles to the profiles predicted by the Unno-Rachkovsky solution to the radiative transfer equation. For sunspot fields above about 1500 gauss, the two methods are found to agree in derived azimuthal and inclination angles to within about + or - 20 deg.

A versatile Stokes polarimeter for solar observations has been developed. Recent improvements to the instrument include a high-resolution echelle spectrometer coupled to the telescope by optical fibers, and 128-element diode array detectors. The on-axis design on the telescope and polarimeter limit instrumental polarization to .0001, and the spectrometer detector combination provides spectral resolving power of 160,000 for any wavelength between 4000 and 11,000 A. This paper describes the Haleakala polarimeter and in particular the spectrometer with its fiber-optic coupling. Examples of Stokes line profiles observed in a sunspot are presented, together with derived vector magnetic field maps.

Observations of a number of helium triplet (10830, 4713, 4471, 3889, 4026 A) and hydrogen (H-gamma, delta, eta, and theta) emission-line intensities in six quiescent prominences are presented. The regions of prominence and neighboring corona were raster-scanned by the telescope, and all lines were measured concurrently at each point. The results are compared with previous observations and theory. In particular, the intensity of the 10830-A emission relative to the other triplets is found to differ strongly from the predictions of the recent detailed calculations of Heasley et al. (1974) for model quiescent prominences.

Full disk, He I 10 830 A solar spectroheliograms have been generated using the Haleakala Stokes polarimeter-spectrometer. The spectroheliograms, with spatial resolution of 10 × 16 arc sec and wavelength bandpass of 0.53 A, were developed for the detection of coronal holes, and have been compared with nearly simultaneous Hα and Ca K flltergrams.

A sensitive polarimeter-photometer has been constructed for solar studies by the Institute for Astronomy on Mt. Haleakala. It can be used to study either the corona or the Sun's disk, and operates over a wide range in photon arrival rates. Since significant polarization as small as 10-5 is observed on the Sun's disk, noise and other sources of spurious modulation become of great importance. In this paper we present our measure-ments of the magnitude of these effects.© (1972) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Observations made during the interval March 1-31, 1988, are presented which were designed to provide a synoptic context in which data from the March 18, 1988, total solar eclipse can be interpreted. Daily observations made with the Mark III K-coronameter and the H-alpha prominence monitor at the Mauna Loa Solar Observatory, along with photographic records of the Sun in H-alpha from the flare patrol at Mees Solar Observatory on Haleakala, Maui, are included. Observations of the longitudinal component of the photospheric magnetic field made at Mees Solar Observatory were also gathered around the period of the eclipse. Together with the white-light image of the corona at the eclipse, these coronal and magnetic field observations assembled into synoptic maps for this epoch, are presented. On the basis of these observations, an interpretation of the global density distribution of the corona at the time of the eclipse is constructed.

During a 60-day period in the summer of 1982, a joint observing project between the High Altitude Observatory and the University of Hawaii was undertaken to collect a set of solar photospheric, chromospheric, and coronal data. From these data, the relationships between quantities recognized to be related to solar activity are specified. The amplitude of rotational modulation of the diagnostic parameters derived for the full disk was approximately equal to the modulation observed over an entire solar cycle. Those integrated solar data have been used as diagnostics of generalized stellar activity. A relationship between the Ca II line K flux and total inferred coronal mass of the sun existed during this observation period, and this fact leads to the hypothesis that ca II flux modulation in other stars may be used to infer stellar coronal conditions.

Observations are presented of the corona during the June 11, 1983 total solar eclipse, together with preliminary results of a coordinated observing program conducted to investigate the relationship between the corona and the lower parts of the solar atmosphere. Synoptic observations of the white light corona and disk in H-alpha are compared with the eclipse image, together with the inferred longitudinal component of the photospheric magnetic field measured using the magnetically sensitive Fe line at 6303 A. Using these data, an interpretation of the global three-dimensional coronal structure is attempted; showing that the eclipse image contains bright features which are far from the plane of the sky, and that it is dominated by streamers over polar filament neutral lines.

Linear polarization up to 15 percent in the Fe XIV 5303-A line has been measured photoelectrically in the solar corona. The polarization deviates only slightly from the radial direction and increases with increasing height.