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FINAL REPORT

OSO-VI

NAS5-9274

TO INSTRUMENT A SOLAR-POINTED

SPECTROMETER-SPECTROHELIOMETER FOR OSO-G

Principal Investigator: Leo Goldberg

May 1972

b.

INTRODUCTION

Contract NAS5-9274 between the National Aero-nautics and Space Administration and Harvard CollegeObservatory continued from June 7, 1966 through Febru-ary 8, 1972. It provided for the preparation of asolar pointed spectrometer-spectroheliometer instrumentfor the orbiting solar observatory G, OSO-G, (also knownas OSO-VI) and two and one half years of post launch dataanalysis.

This report completes the documentation require-ments of NAS5-9274 with summaries of the hardware effortand post launch data analysis efforts. The following twosections, INSTRUMENTATION and SCIENTIFIC DATA ANALYSIS,are addressed to these two aspects of the final reportrequirement.

Virtually all of the scientific and technicalaspects of work performed under this contract have alreadybeen reported elsewhere. The BIBLIOGRAPHY section of thisreport contains subcontractor documentation, in-house mem-oranda, scientific publications and presentations. Be-cause so much published material is already available, thisfinal report will be brief.

INSTRUMENTATION

The hardware effort involved two separate instru-ment designs. The first instrument design was subcontractedto American Science and Engineering, Incorporated (ASE) andthe program proceeded through complete fabrication of aprototype instrument. Several problem areas surfaced whichsignificantly affected schedule and cost, the most notablewas the inability due to manufacturing problems to procurereliable integrated circuits. This impact upon the launchschedule and the additional constraint of limited available

- NASA funds compelled pursuance of a less desirable alterna-tive, namely to refurbish the spare OSO-D instrument. The

-- 2 ---2-

ASE subcontract was terminated and the in-house effortentitled the OSO-G1 was begun. The historical recordof the ASE subcontract was given in the monthly prog-ress reports number 1 through 32 and in the specificASE documents listed in the BIBLIOGRAPHY.

The OSO-D instrument was modified to improveits performance characteristics, increase its reliability,and meet spacecraft interface requirements. The moresignificant modifications included:

-a new high voltage power supplydesign with special emphasis placedupon construction of reliable trans-former coils.

-reduced entrance slit size improvingthe spatial resultion from 60 to 35arc seconds.

-replacing the spherical telescopemirror with an off axis paraboloiddrastically reducing optical aberra-tions.

-interface bracket and connector box.

-improved UV detector and associatedelectronics.

The OSO-G1 instrument was calibrated, environmen-tally tested, integrated into the spacecraft and launched.The historical record of the instrumentation phase is givenin progress reports number 26 through 32. Additional pub-lished material and in-house memoranda are given in theBIBLIOGRAPHY.

_-'3 _-3

The OSO-VI instrument collected scientificdata which were transmitted via the HCO quick-lookdata link for approximately nine months, from August C13, 1969 through May 12, 1970. During this period oftime the instrument returned approximately 120,000 smallrasters, 5500 large rasters, and 1500 spectral scansof a variety of solar features such as quiet areas,active regions, flares and filaments.

The instrument was operated continuously ina pre-programmed schedule from May 29, 1970 untilJuly 10, 1971 for engineering evaluation of the vari-ous subsystems. Details are reported in progress re-ports numbers 33 through 38, however, no electronicor mechanical failures were observed.

SCIENTIFIC DATA ANALYSIS

The OSO-VI experiment has resulted in substan-tial advances in the available solar observations andgreatly enlarged our understanding of the physics ofthe outer solar atmosphere. The spatial resolution of35 arc seconds was the highest spatial resolutionachieved to date in the wavelength range in questionwith photoelectric techniques. The versatility of theOSO spacecraft pointing system allowed us to obtainphotometric spectra from any 35 arc second area of thesolar disk or of features above the limb and the corona.As outlined below, we now have, for the first time, EUVspectra of numerous solar features (active regions,filaments, prominences, coronal holes), spectra of dis-tinct regions of the quiet sun (equatorial regions,polar regions), as well as spectra of transient eventssuch as solar flares. The small raster capability ofthe spacecraft has allowed us to obtain spectroheliograms

. . .~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~4

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of a restricted region (7 arc minute square) withthe excellent time resolution of approximately 30 seconds, thus allowing observations of the rapidlydeveloping phenomena such as solar flares. Duringthe instrument's lifetime of about nine months ornine solar rotations, it collected much unique datashowing the temporal and spatial development of ac-tive regions and the solar corona.

Much of the data have been analyzed andreported in publications or presented at scientificmeetings. The BIBLIOGRAPHY gives the updated listof reported findings however, analysis of these datacontinues. The photometric and aspect data, includingcalibration information and other aids, were forwardedto the National Space Science Data Center.

The next few paragraphs give a summary of thetype of solar observations made and a brief synopsisof the resulting analyses.

QUIET SUN: The EUV quiet sun spectrum was obtained inabsolute photometric intensities with the highest spatialresolution (35 arc seconds) to date. Fourier transformanalysis is being applied to the spectrum to suppressnoise and to allow resolution of closely spaced lines.This technique promises a greatly improved spectrum reso-lution. In addition, the equatorial center-to-limb vari-ation in line intensity is being prepared from the spectrafor most intense lines and continua. Such variations pro-vide a powerful tool for the derivation of solar models.Spectra of polar regions have been analyzed to determinemodels of the transition layer. Studies of the Lyman con-tinuum indicate that the density at the poles is approximately

/30% less than at the equator. Lower polar densities have not

- 5 -

been detected below the temperature of formation of theLyman continuum imputing these regions are features inthe coronal spectrum.

A series of EUV spectra made at the center ofthe solar disk exhibited the chromospheric network andits extension into the corona. The network can be ob-served with almost identical structure, in lines formedin the chromosphere and chromospheric-coronal transitionlayer. At coronal heights, the network changes but someresidual structure is observed in the lines of Mg X andSi XII, but little or no evidence is found in Fe XVI.

The OSO-VI data have allowed the constructionof an extended model of the solar atmosphere from theupper photosphere to the chromospheric-coronal transitionlayer. A non-LTE analysis was applied to the H I, C I,and S I spectra in order to interpret observations of theirrespective EUV continua. Most of the EUV observations canbe reproduced with this model, and additional informationfrom absolute continuous intensities at longer wavelengthsin the visible and infrared.

Regions of abnormally low coronal EUV emission(so-called coronal holes) have been recognized for thefirst time. Detailed study of two such regions revealsthat the coronal temperature is approximately 106 °K incontrast with the "normal" coronal temperature of 1.6 - 1.8x 106 °K. The coronal electron pressure is lower than normal,by a factor of 2 to 3. Moreover, the temperature gradientin the chromospheric-coronal transition layer is lower bya factor of 4 to 10.

- 6 -

Diagnostic techniques for determining theelectron density in regions of line formation have beendeveloped for lines in the beryllium isoelectronic se-quence. In particular, lines from C III and 0 V haveproved valuable. Such techniques allow us to map thevariation of electron density from quiet to active re-gions of the sun and provide a powerful diagnostic toolfor other features as well. Investigation continues onthe effects of structures smaller than 35 arc second ofintensity gradients, of solar rotation and of spacecraftpointing jitter upon the accuracy of densities derivedfrom line ratios.

ACTIVE REGIONS: This experiment obtained the first pho-tometric EUV spectra at different positions in activeregions, thus providing an unparalleled opportunity tostudy the structure and development of active regions.'With the many plasma diagnostic techniques availablethese spectra allow us to determine the variation of tem-perature and density at different heights.

The enhancement of line intensities in activeregions over the intensities observed in the quiet solaratmosphere provides a powerful diagnostic parameter forline identification as well as insight into line excita-tion processes. Two new members of the Li isoelectronicsequence (Na IX, Al XI) have been identified in this way.More line identifications will undoubtedly be found asstudy continues.

EUV spectroheliograms including both active andquiet solar regions can be used for mapping the spatialvariation of the coronal electron density and the temperaturegradient in the solar transition layer. The relationshipbetween the coronal electron temperature, the transition-

- 7 -

layer temperature gradient, the EUV chromospheric emis-sion, and the photospheric magnetic field strength wasderived. In general, all of these parameters are in-creased in active regions when compared to their quietsun values.

PROMINENCES AND FILAMENTS: The OSO experiment providedthe first quantitative EUV spectra of prominences andfilaments and enables investigation of the physical con-ditions within and the structure surrounding these fea-tures, at all temperature levels. Study continues onthe analysis of EUV observations of prominences and fila-ments and the development of models for the transitionregion between cool prominence (or filament) materialthat is visible from the ground in Ha and the hot sur-rounding gas.

FLARES: Good time and spatial resolution of the instru-ment made possible extensive investigation of solar flares.Preliminary results indicate that all EUV lines brightennearly simultaneously, thus indicating some type of rapidcollective excitation during the flare. The close correla-tion between the EUV brightening, and impulsive X-ray andmicrowave bursts suggest a causal relation between emis-sions in these widely different wavelength regions. Amodel is being developed with non-thermal electrons as theprimary source of plasma heating.

OTHER OBSERVATIONS: The spectroheliograms in EUV lines onthe solar disk provide unique data to measure the solar ro-tation rate in the chromosphere, transition region, andcorona. Differential rotation (variation of the rotationrate with solar latitude) was observed but no apparentvariation with height was found.

- 8 -

The total solar eclipse of March 7, 1970provided an opportunity to investigate the solar at-mosphere in the EUV and obtain information complemen-tary to ground based observations. For a two-weekperiod prior to the eclipse, EUV measurements weremade on an intensive schedule, so that the developmentand state of the corona at the time of the eclipsewas well recorded. Electron density maps from Mg Xline intensities were constructed. Detailed study ofcoronal structure and its relation to the magneticfield configuration continues.

Properties of the terrestrial atmosphere canalso be studied with the OSO experiment. The intensityvariation of the Mg X 625 A line while sighting throughpart of the atmosphere can be expected to supply valuesof the atomic oxygen density over the altitude range350 - 450 km. Using dawn and dusk profiles, variationsin exospheric temperature for August-December 1969 werecorrelated to solar and geomagnetic activity. Further-more the molecular oxygen densities at lower altitudescan be obtained from the O VI 1032 A line data gatheredduring the same period. Analysis of these data continues.

SUMMARY

As evidenced in the preceding summaries, theinstrument returned a large quantity of well definedultra-violet observations for a variety of solar fea-tures. Analysis of these photometric data contribute toa better definition of the solar atmospheric structure andto an increased understanding of the relationship among thevarious solar features. Analysis of the data, althoughextensive at this date, will continue for the next few years.

- 9 -

BIBLIOGRAPHY

CONTRACTUAL REPORTING AND DOCUMENTATION

Periodic Reporting

Harvard College Observatory, Progress Reports .

NAS5-9274, Issues 1 through 38

American Science and Engineering, Inc., Progress

Reports, purchase order A24660, Issues 1 through

30

Subcontracts Documentation

American Science and Engineering, Inc.,

ASE-1286; Construction, Test, and Field Support

of the HCO OSO-G Spectrometer-Spectroheliometer

(A Proposal), June 1966

ASE-1464A; Program Plan for Fabrication, Test

and Field Support of the HCO OSO-G Spectrometer-

Spectroheliometer, January 1967

ASE-1477; Studies of Integrated Circuit Appli-

cability for the HCO OSO-G Spectrometer-Spectro-

heliometer, December 1966

ASE-1490; Study of the Feasibility of Adding a

Second Detector System to the HCO OSO-G Spectrom-

eter-Spectroheliometer, December 1966

ASE-1491; Study of the Feasibility of Enlarging

the Telescope Mirror System of the HCO OSO-G

Spectrometer-Spectroheliometer, December 1966

ASE-1492; Study of the Feasibility of Adding a

Sequential Selector to the HCO OSO-G Spectrometer-

Spectroheliometer, December 1966

- 10 -

ASE-1503; Experiment Package Environment

Specifications, February 1967

ASE-1505; Preliminary Design Specification

for the OSO-G Grating Drive System, January

1967

ASE-1508B; Reliability/Quality Control Program

Plan for the Fabrication, Test and Field Sup-

port of the HCO OSO-G Spectrometer-Spectro-

heliometer, August 1967

ASE-1525; Supplementary Information on the.

Feasibility of Adding a Second Detector System

and a Sequential Wavelength Selector to the

OSO-G Experiment, January 1967

ASE-1531; Report of the OSO-G Interface Meeting,

AS&E and BBRC, 5 and 6 January

ASE-1555A; Design and Performance Specifications

for the HCO OSO-G Spectrometer-Spectroheliometer,

January 1969

ASE-1556; Preliminary Electrical Interface

Specifications for the HCO OSO-G Spectrometer-

Spectroheliometer, January 1967

ASE-1561; Reliability Analysis of the HCO OSO-G

Spectrometer-Spectroheliometer, March 1967

ASE-1574; Qualification and Acceptance Test Plan


May 1967,

ASE-1595; Ground Support Equipment Specifications

for the HCO OSO-G Specteometer-Spectroheliometer,

August 1967

- 11 -

ASE-1628; American Science and Engineering

-Quality Control Manual, Volume 2: Quality

Control Inspection Instructions, May 1967

ASE-1920; Letter Report on Vibration Tests

of the Engineering Model of the OSO-G Instru-

ment, April 1968

ASE-1970; American Science and Engineering

Life Test Report for the HCO OSO-G Slit Change

Mechanism Assembly, June 1968

ASE-2210; Alignment Procedures for the HCO

OSO-G Spectrometer-Spectroheliometer, March

1969

ASE-2263; American Science and Engineerin'

Module Test Procedures for the HCO OSO-G

Spectrometer-Spectroheliometer, June 1969

ASE-2229; Design and Development of the HCO

OSO-G Spectrometer-Spectroheliometer, Final

Report, April 1969

ASE-S122-036; Preliminary Test Specifications


December 1967

ASE-S122-037; HCO OSO-G Mechanical/Electrical

Interface Summary, October 1967

ASE-S122-038; Procurement Specification for

Environmental Test Services for HCO OSO-G

Spectrometer-Spectroheliometer, November 1967

ASE-TP122-042; Calibration and Checkout Procedure

for the HCO OSO-G Electronic Support Equipment,

December 1968

- 12 -

S122-501; Specification for OSO-G High

Voltage Power Supply, Revision E, January

1968

ASE-Revision D; Procurement Specifications

for the OSO-G Low Voltage Power Supply

No. 1, June 1968

ASE-S122-503;Procurement Specification for

the OSO-G Low Voltage Single Output Power

Supply No. 2

ASE-S122-507; Corona Check Procedure for

.HCO OSO-G Spectrometer-Spectroheliometer,

June 1968

Dynatich Corporation

"Transient Thermal Analysis of a Pointed

Experiment for OSO-D" by Bonneville, J.M.

and Sze, Dai Kai, December 1966

- 13 -

REFERENCES

Hazen, Nathan, Proposed Program.Definition OSO-G1

Instrument, August 1968 (An In-House

Memo)

Huber, Martin, Experimenter's Manual for the OSO-G

Experiment, October 1968

Huber, Martin Efficiency Measurements on OSO-G1

Flight Gratings, File Memorandum,

May 1968

Huber, Martin, Proposed Scientific Parameters of the

OSO-Gl Instrument & Operating Descrip-

tion, September 1968 (An In-House Memo)

Huber, Martin, List of Required Tests & Checks for

the HCO OSO-G Instrument, August 1969

(An In-House Memo)

Goldberg, Leo, Final Contract Report - To Instrument

An Orbiting Solar Observatory, NASW-184

- 14 -

PUBLICATIONS

- 15 -

Avrett, E. H.

"Radiative Interaction between the Solar Chromosphereand Corona in the Far Ultraviolet"

Smithsonian Astrophysical Observatory. 1972.

Presented at 132nd meeting of AAS, Boulder, Colorado,June 9-12, 1970.

Bull. Amer. Astron. Soc., 2, #4 (1970) 292.

NASA Contract #NAS 5-9274.

AbstractThe source function for resonance scattering normallyis smaller than its equilibrium value throughout anextended atmospheric region measured from the boundary.This behavior not only can be cancelled but can be re-versed by the effect of a high-temperature boundarylayer of small optical thickness. The solar Lyman-continuum source function at unit Lyman-continuumoptical depth is shown to be affected in this mannerby temperatures in the transition region between thechromosphere and corona, when the Lyman lines areassumed to be in detailed balance. When this assumptionis not made, the Lyman lines tend tQ reduce the Lyman-continuum intensity. The line and continuum intensitiesare correlated in the sense that a stronger Lyman-alphaline inhibits to a lesser extent the production ofphotons in the Lyman continuum.

- 16 -

Avrett*, E.H.; Linsky**, J.L.

"A Model of the Solar Temperature-Minimum Region"

*Smithsonian Astrophysical Observatory. **Joint Institutefor Laboratory Astrophysics, Cambridge, Mass.

Abstract presented at 131st meeting of AAS, New York,December 8-11, 1969.

Bull. Amer. Astron. Soc., 2, #2 (1970) 181.

AbstractWe solve the hydrostatic equilibrium and ionizationequilibrium equations for atomic hydrogen to obtain asolar model from an assumed temperature variation withheight. From the model we compute a theoretical spec-trum in the region 10 p-1 cm, and compare the resultswith recent microwave observations. We exhibit atemperature-height distribution that leads to goodagreement with these observations.

The atmospheric model also is used in the solution ofstatistical equilibrium and radiative transfer equa-tions for a five-level Ca II ion. Profiles of the Hand K lines, and infrared triplet lines are computedand are compared with observed profiles.. The inter-mediate wings of H and K and the cores of the infraredlines are found to be sensitive to properties of thetemperature-minimum region and the initial chromosphericrise in temperature. The temperature distribution thatwe adopt leads to reasonable agreement between computedand observed Ca II line profiles at the center of thesolar disk. -

The proposed temperature distribution has a minimum4value of about 4300 K at a value of T 000O near 3xlO ,and a steeper initial chromospheric fi crease than thatof the Bilderberg reference model.

- 17 -

Blumenthal, G.R.; Tucker, W.H.; Wood, A.T.

"The Physical Conditions in Solar Flare Plasmas"

Harvar.d College Observatory. Solar Satellite Project.

.-. .. .

Presented at 136th Meeting of AAS, San Juan, PuertoRico, December 5-8, 1971.

Bull. Amer. Astron. Soc., 3, #4, Pt. 1 (1971) 461.

NASA Contract #NAS-5-9274.NASA Grant #NGR-22-007-211.

AbstractThe rate of cooling for solar flare plasmas-due tothe effects of radiation cooling, expansion, thermalconduction, and the generation of hydromagnetic wavesis estimated., The need for energy input subsequentto the flash phase of a solar fl.are is investigated.For flares not requiring-subsequent heating, parametersare deduced to account for the ultraviolet and non-

. thermal X-ray burst and the more slowly varying softX-ray flare. Also considered is the possibility thatohmic heating with anomalous resistivitycan accountfor the heating-necessary to produce the optical andsoft X-ray emission in cases where heating is necessary.

. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ .

- 18 -

Chipman, E.G.

"Analysis of Solar UV Lines"

Harvard College Observatory.T.R. #26. January, 1972.

Published as SAO Special Report Number 338.

NASA Contract #NAS5-9274.NASA Grant #NGR-22-007-211.

Abstract iWe have made a detailed study of the formation Iof the strongest ultraviolet emission lines ofMg II, 0 I, C II, and C III in the solar atmosphere.We solve, the equations of statistical equilibrium -

and radiative transfer for each ion, using a general computer program that is capable of solvingnoH-LTE line-formation problems for arbitrary atmospheric and atomic models. Interpreting theresults in terms of the structure of the solar tatmosphere, we conclude that the HSRA atmospherehas a temperature too low by abDut 500 K near h = 1100 km and that a temperature plateau with T 18,000 K and width close to 60 km exists inthe upper chromosphere. We also investigate the structure of the solar atmosphere in the range20,000 to 100,000 K and the effects of microturbu-lence on the formation of lines.

We solve some approximate analytic line-formationproblems relevant to the more exact solutionsderived later. In the Appendix we attempt to makethe best possible fit to the Ca II K line center-to-limb profiles with a one-component atmosphere,with an assumed source function and micro-turbulentvelocity.

- 19 -

Chiuderi, C.; Chiuderi-Drago, F.; Noci, G.

"Coronal Abundances and a Model of the QuietSun from Radio Observations"

..Harvard College Observatory. Solar Satellite Project.Z'-.

Abstract submitted for 137th AAS Solar Physics Divisionmeeting on Flares and Particle Acceleration--SpaceObservations of EM Radiation, College Park, Maryland,April 4-6, 1972.

Bull. Amer. Astron. Soc., to be published.

NASA Contract #NAS-5-9274.

NASA Grant #NGR-22-007-211.

Abstract In this paper the best known measurements of thebrightness temperature of the quiet sun are usedas the basis for building up a model of the transi-tion region. From the radio spectrum a simple equationrelating electron density, electron temperature, andtemperature gradient is obtained in a straightforwardway. By means of this equation and known values ofthe total intensity of ultraviolet-lines, absoluteabundances are calculated that'are in agreementwith previous determinations. Finally, with thermalequilibrium assumed, the equation relating electrondensity, electron temperature, and temperaturegradient is solved, yielding a model of the transitionregion and low corona. The conductive flux turns outto be constant in the upper5 ansition region, itsvalue being dependent on T (TC = coronal temperature).If the value of Tcderived from the radio observationsis adopted, the value of the conductive flux turnsout to be about four times smaller than the valuebased on the analysis of the ultraviolet lines. Itis suggested that agreement between radio and UV modelscan be obtained if a nonuniformly emitting sun isassumed.

~~~~~~~~~~~~~~~~~~~~·. .·

:~~~~~~~~~~~~~~~~

· · - . .. .'. .··

- 20 -

Dower, R.; Diamond, Stanley; Hazen, N.

"Harvard College Observatory OSO-G1 ExperimentHandbook"

Harvard College Observatory. Solar Satellite Project.T.R. #10. May, 1969.

NASA Contract NAS 5-9274.

)

Abstract This report gives a comprehensive introduction -to the Harvard College Observatory (HCO) OrbitingSolar Observatory (OSO-G1) instrument. Thisinstrument is scheduled to orbit with the OSO-Gspacecraft in the summer of 1969. The instrumentis a spectrometer and spectroheliometer designedto examine the extreme ultraviolet (EUV) portionof the sun's electromagnetic radiation.

- -This report presents a summary of the scientificobjectives of the instrument, a detailed descrip- -tion of the instrument's components, a .list of instrument-spacecraft interface parameters, and a description of appropriate handling, storage, inspection, and testing procedures. The reportattempts to give sufficient technical background material to make it useful to persons of variedtechnical knowledge. The report is also intended -to be used as a major source of information for

.- persons actually handling the instrument. -

- · . ., . . . - . ...

: - ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~. ---.]-,: : .;

-~~~~~~~~~~~~ ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .: .

% -.~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ . - ': ,- .: '7

'21 -

_ Dupree, A.K.

"EUV Solar Satellite Spectra: Abundance Deter-minations in Quiet and Active Regions"

Harvard College Observatory. Solar Satellite. Project..

: . ..,

Presented at :134th Meeting of the American AstronomicalSociety, Baton Rouge, Louisiana, March-April 1971.

Bull. Amer. Astron. Soc., 3 2, Pt.I (1971) 246 (A).


AbstractThe .Harvard College Observatory spectroheliometersaboard OSO-IV and OSO-VI obtained extreme ultraviolet(3001400 R) spectra of restricted regions on thesolar disk. The spatial resolution of 1 arc minute(OSO-IV) and 35 arc second (OSO-VI) and the offsetpointing capability of the spacecraft allowed spec-tral scans to be made of both the quiet sun andactive regions. The' averaged quiet sun'spectrum..from OSO-IV (Dupree, A.K. and Reeves, E.M., Ap.J.,' May 1971) and selected spectral scans from OSO-VIhave been analyzed to determine relative coronalabundances of carbon, nitrogen, oxygen, neon, sodium,magnesium, aluminum, silicon, and sulfur. This

: analysis also leads to a determination of thetemperature gradient in the transition region from

*' which the temperature profile can be constructed.

. . '., .·

I

' Iii

- 22 -

Dupree, A.K.

"Solar Abundances Determined from the EUV

-Spectrum of the Quiet Sun"

Harvard College Observatory. Solar Satellite Project.

Solar Physics, to be submitted.

NASA Contracts #NASw-184, NAS-5-9274.

- 23 -

Dupree_ AAK.; Goldberg, L.; Huber, M.C.E.; No es, R.W.;Parkinson, W.H.; Reeves, E.M.; Withbroe, G.L.

"OSO-VI: The EUV Spectrum of Solar Active Regions"


Presented at 131st Meeting of American AstronomicalSociety, New York, December 1969.

Bull. of Amer. Astron. Soc., 2, #2 (1970) 191 (Abstr.).

NASA Contract SNAS-5-9274.

AbstractSpectral scans of active regions have been obtainedwith the Harvard photoelectric spectrometer-spec-troheliometer by using the offset-point capabilityof the OSO-VI spacecraft. The wavelength intervalof the instrument includes the resonance lines ofa variety of elements and ionization stages: H Ito Fe XVI. Spectra of a number of evolving activeregions have been obtained. The paper will presentwavelength identifications, a discussion of lineintensities in active regions, and a comparison withthe spectrum of the quiet sun.

* v

- 24 -'

-Dupree, A.K.; Munro, R.H., Noyes, R.W.; Withbroe, G.L.

"EUV Emission Lines: Density Sensitive MultipletRatios"


Paper presented at the American Astronomical Societymeeting, Solar Physics Division, Huntsville,Alabama, Nov. 17-19, 1971.

Bull. Amer. Astron. Soc., 3, #2, II (1971) 260 (A).

NASA Contract #NAS-5-9274.NASA Grant NGR 22-007-211.

Abstract . ..A standard two-level approximation is found to beinadequate to analyze the intensities of multipletsfrom ions of the Beryllium sequence (i.e., C III,N IV, 0 V, Ne VII, Mg IX etc.). Statisticalequilibrium calculations show that each multiplet inan ion has a different dependence on electron den-sity. Consequently, ratios of multiplet intensitymay be used as a direct measure of the electrondensity in the region of line formation. Theoreticalintensity ratios are used in conjunction with farultraviolet spectra from'the Harvard experiment onOSO-VI to violet spectra' from the Harvard experimenton OSO-VI to derive electron densities in bothactive and quiet regions of the solar atmosphere.The implications of these results upon abundancedeterminations will also be discussed.

-;. .. ~ ~~~~~~~~ ~ . ' ' .:

- ~ ~~~~~~~~~~~~~~~~ ' ..' .

Goldberg,' L.

"The Interpretation of XUV Solar Radiation"

Harvard College Observ-atory. Solar Satellite Project.

Presented at XIV General Assembly of IAU, JointDiscussion on Atomic Data, Brighton, England, August

1970.In: DeJager, C. Highlights of Astronomy, Vol. 2-Dordrecht, Holland: D. Reidel Publishing Co., 1971,pp. 476-485.


AbstractSolar ultraviolet and X-radiation arriving at the Earthis emitted mainly by highly-charged ions in theouter layers of the Sun, where departures from thermo-dynamic equilibrium are extreme. Hence the diagnosisof physical conditions from spectral intensitiesentails the use of accurate cross sections for avariety of physical processes governing the excita-tion and ionization of emitting ions. Now that thefull potential of satellites for solar data acquisi-tion has begun to be realized, the need for atomicdata of all kinds is more acute than ever before. Inthis review, I shall illustrate the importance oflaboratory an-d theoretical investigations for theanalysis of solar ultraviolet and X-ray data by refer-ring to five problems to which space experimentersare currently devoting a great deal of attention:(1) the temperature minimum at the interface betweenthe photosphere and the chromosphere,(2) the temperature and density profiles of the lowchromosphere,(3) the transition zone at the chromosphere-coronainterface,(4) the corona,(5) solar flares.

- 26 -

Goldberg, L.; Avrett, E.; Dupree A.K.; Huber, M.C.E.; Noyes,R.W.; Parkinson, W.H.; Reeves, E.M.; Withbroe, G.L.

"Results from the Harvard 0SO-VI Experiment"


Presented at Second OSO Workshop, Goddard Space FlightCenter, Greenbelt, Maryland, December 1970.

Results summarized by Thomas, R.J.; Maran, S.P., "WhatTwo Sun-Observing Satellites Tell Us", Sky and Telescope,hl41, #5 (CMay 1971) 268-272.


- 27 -

Iazen N.L., Huber_ M.C.E., Reeves, E.M.

"If"High Voltage Breakdown in an OSO-IV PointedExperiment"

Harvard College Observatory. Solar satellite Project.* T.R. #11. March, 1969.

Presented at Second Workshop on Voltage Breakdown ii

,,Electronic Equipment, Low Pressures Workshop, JetPropulsion Laboratory, Pasadena, California,March 5-7, 1969.In: Bunker, E.R. Jr. Proceedings of the SecondWorkshoo on Voltage Breakdown in Electronic Eqauioment.NASA-Ti4-33-147, Pasadena, California, Jet Propulsion

Laboratory, June 30, 1970, pp. 155-168 . .

NASA Contract /NASw-184.

AbstractA high voltage failure occurred in the HarvardSolar Spectrometer-Spectroheliometer experimentaboard the OSO-IV spacecraft five weeks afterlaunch. This failure is analyzed'and traced.to a sequential process comprising two modeswhich took place within the high voltage powersupply. The primary failure was within thetransformer. The test history o'f this and pre-vious instruments is discussed, including per-ti.nent work on sub-assemblies and modules. Thistesting included extensive thermal-vacuum workand corona and plasma exposure. Preventivemeasures that are being taken on a later experi-ment to fly in August 1969 are discussed, in-eluding pertinent recommendations in manufac-turing technique, qualification and acceptancetests, and an overload switch that automaticallyturns off the high voltage power supply.

- 28 -

Huber, M.C.E.; Dupree, A.K.; Goldberg, L.; Noyes, R.W.;ParkinsonL =.H.; Reeves, E.M.; Withbroe, G.L.

"OSO-VI: The Harvard Experiment"

Harvard College Observatory. Solar SatelliteProject..

Presented at 131st Meeting of American AstronomicalSociety, New York, December 1969.

Bull. of Amer. Astron. Soc., 2, #2 (1970) 200.

NASA Contract #NA:S_5-,9274.

AbstractThe photoelectric spectrometer-spectroheliometerdesigned by Harvard College Observatory was success-fully flown aboard Orbiting Solar Observatory VI (OSO-VI). The experiment and its operational capabilitieshave been described. The instrument consists of atelescope mirror (off-axis parabola) illuminating theentrance slit plate of a normal-incidence spectrometerthat is equipped with a solar-blind magnetic electronmultiplier. Entrance and exit slits of the spectro-meter give a spatial resolution of 35 arc sec and aspectral resolution of better than 2 i, over the wave-length range 280-1370 i. By combining the experimentoperating modes with the spacecraft pointing and rastermodes, spectra at -ny selected positions on or nearthe solar disk, as well as large and small spectro-heliograms of many solar features, can be obtained.Observations made from 13 August 1969 to date comprise1400 wavelength scans, 1800 large and 95 000 smallraster pictures. We studies spectra at several positionsin approximately 15 different active regions. Spectraof both active and quiet regions have been obtained ata number of positions on the disk, near and beyond thelimb. Spectra and small spectroheliograms of promi-nences, of filaments, and of areas where the coronalemission is very low have also been secured. Fouractive regions (McMath Nos. 283, 351, 385, and 432)that produced numerous subflares as well as some class 1and class 2 flares were monitored almost continuouslyas they crossed the solar disk.

- 29 -

Kirshner, R.P.; Noyes, R.W.

"Extreme Ultraviolet Observations of a Surge"

Harvard College Observatory. Solar Satellite Project.T;R. #19. June, 1971.

Solar Physics, 20, #2. (Noy. 1971) 428-437.

NASA Contract #NAS5-9274.

AbstractA flare surge at the limb was observed in C III977 1 by the Harvard oSo-6 spectroheliometer.The kinematic behavior of the surge is the samein C III and in Ha. The amount of C III emissionis consistent with a model in which the C IIIions occupy sheaths with thickness l100 km sur-rounding the cooler Ha-emitting threads. The massof the material containing C III ions is about10- 2 of the mass emitting Ha.

- 30 -

' Kirshner., R.P.

"Ultraviolet Observations of Solar Prominences"


Senior Honors Thesis, Harvard College, 1970.


AbstractThe first part of the thesis is a history of obser-vations of solar prominences. The importance ofnew types of instruments for the study of prominencesis stressed. The similarity is noted between Secchi'sdiscovery in 1860 that some prominences were recordedon photographs in the near ultraviolet even thoughthey 'did not appear to the eye in the visible part ofthe spectrum and the fact that the Harvard 00S-6instrument observed a prominence in the extreme ultra-violet which was not observed in the visible.

The second part of the thesis contains analyses ofthree groups of extreme ultraviolet observations.First, the surge of September 15, 1969, observed inC III 977w with oso-6, is examined; the kinematicbehavior was the same in C III and in Ha.

Second, OSO-4 spectroheliograms have been examinedto yield models of prominences. Third, spectral scansfrom oSO-6 have been used to derive temperatures andpressures at the centers of prominences. It is con-cluded that both surge and quiescent prominences emitmost of their ultraviolet from thin layers surroundingcool threads. The temperature is about l10000 K.

- 31 -

Macar, P.J; Rechavi, J.; Huber, M.C.E.; Reeves, E.M.

"Solar-Blind Photoelectric Detection Systems forSatellite Applications"

Harvard College Observatory. Solar Satellite Project.T.R. #9. July, 1969.

Applied Optics. 9 #3 (Mar,1970) 581-593.

NASA Contract #NASw-184 and NAS-5-9274.

AbstractThe characteristics of open Magnetic ElectronMultipliers (MEM) with continuous dynode andfield strips are discussed in view of their

use in satellite borne detection systems.

Special emphasis is placed on selection, thermalstabilization, calibration, and long-time per-formance of the detectors. Practical aspectsof the design of satellite borne detectionsystems, such as monitoring capabilities,immunity to charged particles, and electricalbreakdown are also described.

Laboratory studies with fast electronics showedthat the useful linear range of an MEM is re-stricted, because of afterpulses. Most char-acteristics of MEM's reported in the literatureappear to be due to the use of relatively slowelectronics that did not resolve the after-pulses. Statistical studies of afterpulsesare reported and a tentative explanation forthe generation of afterpulses is outlined.

- 32 -

Munro, R.H.; Dupree, A.K.; Withbroe, G.L.

"Electron Densities Derived from Line IntensityRatios: Beryllium Isoelectronic Sequence"

Harvard College Observatory, Solar Satellite Project.T.R. #23. February, 1971.

Solar Physics, 19, #2 (Sept. 1971) 3117-355.

NASA Contract #NAS5-9274.

AbstractA direct method for determining electron densitiesfrom emission line intensities of ions in theberyllium iso-electronic sequence is describedand then applied to the analysis of extreme ultra-violet C III and 0 V spectra from both quiet andactive areas in the solar transition region. Therejlts are consistent with a value of N T = 6 x

3 ~~~~~e e10 c -3K for the quiet sun at. temperatures of5 x 10 to 3 x 10 5K. Electron densities areapproximately five times greater in active regionsthan in the quiet sun.

-33 -

Munro, R.H.; Withbroe, G.L.

"-Properties of a Coronal "Hole" from EUVObservations" -

Harvard College Observatory. Solar Satellite Project.T.R. #31.

Submitted to the American Astronomical Society meeting,University ofr/axyland, College Park, Md., April 4-6, 1972.

NASA Grant #NGR-22-007-211. -

AbstractA coronal "hole" is characterized by significantdeficiency in the intensity of coronal emissionlines, yet there is little change in lines andcontinua formed below 800,000 K except for theHe I and II emission features. Comparison of thehole with the normal quiet sun indicates that theelectron pressure is reduced by'a factor of three,the coronal temperature is lower by 600,000 K,and the temperature gradient in the chromospheric-coronal transition layer is less steep by an orderof magnitude. The apparent insensitivity of thelines formed in the transition layer to the physicalconditions of the hole imply that the conductiveflux from the corona is proportional to the squareof the electron pressure.

- 34 -

Noyes R.W.; Withbroe, G.L.

"The. Solar EUV-Emitting Plasma"


Presented at the Third Symposium on Ultraviolet andX-Ray Spectroscopy of Astrophysical and LaboratoryPlasmas, Utrecht, The Netherlands, August 24-26, 1971.

Space Science Review (to be submitted).


-35 -

Noyes, R.W.- Withbroe, G.L.; Kirshner., R.P.

"Extreme Ultraviolet Observations of ActiveRegions in the Chromosphere and Corona"

- - . . . .'

Harvard College Observatory. Solar Satellite Project.T.R. #14. October, 1969.

.Presented at conference at High Altitude Observatory,National Center for Atmospheric Research, BoulderColorado, August 25-27, 1969.In: Proceedings Chromosphere-Corona TransitionRegion. Boulder, Colorado: NCAR., December 1969,pp. 125-149.

Solar..-Physics, 11 (1969) 388-98.

NASA Contract #NASw-184.

AbstractNew observations of solar active regions havebeen obtained by the Harvard College ObservatoryEUV spectroheliometer aboard the OSO-IV space-craft. From the observations we have determinedthe enhancement in active regions of the emissionfrom ions formed at various temperatures in thechromosphere and corona. The results are.inaccord Vith a simple model of active regions,for which the active region pressure is aboutfive times the quiet sun.pressure; the temperaturegradient in the transition zone is about fivetimes the quiet sun value; and the coronal tem-perature above active regions is slightly increased.

. X~~

- 36 -

Noyes, R. W.

"Ultraviolet Studies of the Solar Atmosphere


Ann. Rev. Astron. Astronhys., 9 (1971) 209-236 (ed. byLeo Goldberg, David Layzer-and John G. Phillips,Palo Alto, Calif: Annual Reviews Inc. 1971).


Abstract Extreme ultraviolet (EUV) solar observations fromspace have made great progress in recent years,largely from the development of new instrumentationwith improved spatial or spectral resolution.. Theseobservations advances have allowed EUV solar astronomyto progress 'from a young and largely qualitative dis-cipline to a mature and quantitative one. Differentinvestigations now appear to be converging on a commondescription of the average physical conditions in thesolar atmosphere. At the same time, high resolutionobservations have begun to reveal the scarcely sur-prising existence of inhomogeneous structure, bothin the active and in the quiet atmosphere. Solar EUVresearch in the next few years will undoubtedly focuson the physical nature of the inhomogeneous solar atmosphere, in order to determine for individualfeatures the run of temperature, density,magnetic field, thermal conduction, mechanical flux, and otherdynamic behavior. This in turn may be basic forunderstanding the physical nature of the atmosphereas a whole.

Although we will discuss below the evidence for in-homogeneous structure and some of its implications,the main emphasis of this review will be on the meanstructure of the solar atmosphere, in both quiet andactive regions. Of course, the mean solar atmosphere,like all idealizations, is in some sense fictitious.Nevertheless, it serves as a very useful zero-orderframework for investigation of the problem of overallenergy balance in the solar atmosphere, and, we hope,will be a valid starting point for the more sophisticatedstudies that surely will follow.

- 37 -

Noyes, R.W.

"Models of the Quiet and Active Solar Atmospherefrom Harvard OSO Data"

Harvard-College Observatory. Solar Satellite Project.

Presented at the NATO Advanced Study Institute on the

Physics of the Solar Corona, Cavouri-V.ouliagmei,Greece, September, 1970.In: Macris, C.J. Physics of the Solar Corona.Dordrecht, Holland: D. Reidel Publishing Co., 1971,pp. 192-218.


- 38 -

Reeves, E.M.; Parkinson, W.H.

"The Contribution of Active Regions to theTotal EUV Solar Flux"

Harvard College Observatory. Solar Satellite Project.T.R. #32. March, 1972.

NASA Contracts #NASw-184, NAS 5-9274.NASA Grant #NGR-22-007-211.

AbstractThe paper discusses the contribution of activeregions to the flux from the entire solar disk asmeasured in the extreme ultraviolet region from300-1400R. The contribution is measured as the ratioof the signal from the active regions on the disk andon the limb, reduced by the average background in thedisk or limb, to the signal from the whole sun. Thecontribution from active regions as observed from thedata from the OSO 4 satellite is found to be approximatelyconstant at 10 per cent for lines formed between 10,000

0and 500,000 , that is for lines of the chromosphere andtransition region. As the temperature increases intothe corona, the contribution from active regions risesquickly to approximately 50 per cent in the high coronaat 3.5 x 10 OK.- The data from the OSO 6 satellite inwhich the spatial resolution was increased from 1 arcminutes to 35 arc seconds are also discussed and in-idicate a slightly larger contribution from activeregions.

. .~~~~~~~~~~~~~~~~~~.

- 39 -

Reeves, E.M.; Parkinson, W.H.

"EUV Obscrvations of the Chromospheric Network"

Harvard College Observatory. Solar Satellite.Project.

T.R. #28. December, 1971.

Solar Physics,

NASA Contract #NAS 5-9274.NASA Grant #NGR 22-007-211.

AbstractExtreme ultraviolet observations of a quietregion of the sun on August 18, 1969 withthe Harvard spectroheliometer on OSO-VI in-dicate that the chromospheric network canbe observed in lines of the chromosphereand transition region (T = 8.4 x 10 K) withalmost identical structure. At coronal heights,the network changes but some residual structurecan still be discerned in Mg X and perhapsSi XII (T = 2.3 x 10 K), although there islittle or no gvidence remaining in Fe XVI(T = 3.5 x 10 K).

'7

'' .\..~~ ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .=.

: ... - .-

- 40 -

Reeves, E.M.; Dupree, A.K.; Goldberg, L.; Huber, M.C.E.; Noyes, R.W.; Parkinson, W.H.; lTithbroe, G.L.

"S0O-VI: Surges, Flares, and the Development ofActive Regions"


Presented at 131st Meeting of American AstronomicalSociety, New York, December 8-11, 1969.

Bull. Amer. Astron. Soc., 2 (1970) 215 (Abstr.).

NASA Contract INAS-5-9274.

AbstractThe small raster mode of the OSO-VI spacecraftprovides spectroheliograms over a 7 min of arcfield at 30-sec intervals in single-selectedwavelength in the instrument wavelength range.Observations of a small flare in an active regionon the disk will be presented together with asequence showing a surge on the limb observedin C III. Full sun spectroheliograms over arange of ionization energies will be used toillustrate some other aspects of the observa-tions.

: ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ :

-..

- 41 -

Reeves, E.M.; Huber, M.C.E.; Withbroe, G.L.; Noyes, R.W.

"Real Time Control of the Observing Program of anOrbiting Solar Observatory"

Harvard College Observatory. Solar Satellite Project.. ]

Presented at IAU Symposium No. 41, Munich, Germany,August 10-14, 1970.In: LaBuhn, F. & LUst, R. Proceedings of IAUSymposium No. 41, New Techniques in Soace Astronomy.New York: Springer-Verlag, 1971, pp. 336-347.


AbstractThis paper departs somewhat from the usual interpre-tation of the subject of this symposium, in whichinstrumental techniques normally deal with diverseaspects of experiment design or construction. Rather,we will concern ourselves here with some innovationsin the ground control optimization of the modes ofdata acquisition once an instrument is in orbit. Al-though the fullest possible utilization of the datagathering capability of a device is of vital interestto the success of the experiment and the mission, thesubject has not been discussed at length in the openforum of scientific meetings. The planning of thedata gathering and processing aspects of a mission mustreceive as careful attention as instrument design andtest if the characteristics of the instrument are tobe fully exploited.

In this paper we discuss a specific example, namely,the Harvard experiment on OSO 6, although the elementsof our problem apply to many types of experiments inspace, particularly those in which the experimenter isrequired to choose from among many possible experimentmodes in direct response to the telemetered data andthe specific conditions at the source: (in this casethe Sun). Extensive preflight planning of diverse seriesof data gathering patterns is assumed to have been ful-filled, and the purpose of the real-time or near-realtime mission control is to complete as many of theobjectives as possible, in the fashion best suited toconditions on the Sun at the time, and to assess thequality of the data gathered in order to determinewhether the observations are of the necessary qualityand quantity to satisfy the observing objective.

- 42 -

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..·Reid, R.H.G.; Withbroe, G.L.

"The Density and Vibrational Distribution ofMolecular Oxygen in the Lower Atmosphere"

Harvard College Observatory. Solar Satellite Project.T.R. #16. April, 1970.

Planet. Space Sci., 18, (1970) 1255-1265.

NASA Contracts #NASw-184; #NAS-5-9274.NASA Grant NGL22-007136

AbstractObservations of solar ultraviolet radiation fromthe satellite OSO-IV are analysed. The atmosphericabsorption of 1032 R (0 VI) can be reproducedtheoretically by a static diffusion model of the0 density abovel 20 _m with a density of(3.6 + 0.4) x 10 cm at 120 km. The atmosphericabsorption of 1335 R (C II) appears to requirean effective absorption cross section of 0 that2decreases with increasing altitude. The decreasecould result from an increasing vibrational devel-opment of 02-such that the fraction of molecules

2in the ground vibrational state is less than about0.9 at 130 km, 0.7 at 150 km and 0.5 above 160 km.

- 43 -

Simon, G.W.; Noyes, R.W.

"Observations of the Coronal Network".- -~~~.. .. ..


Presented at IAU Symposium No. 43, Paris, France,September, 1970.In: Howard,'R. ed. Solar Magnetic Fields. Dordrecht,Holland: D. Reidel, 1971, pp. 663-..

NASA Contracts#NASw-184, NAS 5-9274. i

I

I

- 44 -

Simon, G.W.; Noyes, R.W.

"Observed Heights of EUV Lines Formed in theTransition Zone and Corona"

Harvard College Observatory. Solar Satellite Project.T.R. #27. October, 1971.

Solar Physics, -

.NASA Contracts NASw-184, NAS5-9274.NASA Contracts //NASw-184, NAS5-9274.

AbstractThe heights of formation of a number of extremeultraviolet lines in active regions have beenmeasured from OSO-IV spectroheliograms. Usingthe Lyman continuum at 2000 km above the whitelight limb as a reference, we find heights forHe I, He II, C III, N III, 0 IV, 0 VI, Ne VIII,Mg X, Si XII, Fe XV and Fe XVI that are inapproximate agreement with models based on analysisof EUV emission intensities. The height of C IIis anomalously high. The accuracy of measurementis typically about 2000 km. The data suggestthat the transition zone is less steep than cal-culated from EUV emission intensities; however,

~* higher resolution observations are necessary toresolve the discrepancy.

N

I. . .

.

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.

. - .

.

. . .

- 45 -

. - -Simon, G.W. Noyes, R.W.

"Observed Heights of EUV Lines Formed in the·Transition Zone and Corona"

Harvard College Observatory. Solar Satellite Project.'

Paper presented at American Astronomical Society meeting,Solar Physics Division, Huntsville, Alabama, Nov. 17-19,1971.

Bull. Amer. Astron. Soc., 3, #2, Pt.II (1971) 264 (Abstr.).

NASA Contract #NAS-5-9274.NASA Grant NGR 22-007-211.

AbstractThe'heights of formation of a number of EUV linesin active regions have been measured from OSO-IVspectroheliograms. From a least square fit ofthese data we find Ly B 1026, Ly C 938, Ly y 972,and the Ly continuum at 2000 km above the white lightlimb, He I 584, He II 304, C II 1335, and C III 977at 3000 km, N III 991 and 0 IV 791' at 4000 km;O VI 1032 at 5000 km, Ne VIII 770 at 8000o km;MgX 625 at 11000 km, Si XII 499 at 13000 km, Fe XV417 at 14000 km, and Fe XVI 361 at 15000 km. Measure-ment errors are typically 2000 km, and all the'quoted figures are rounded to the nearest 1000 km.

- 46 -

Simon, G.W.; Noves. R.W.

"Solar Rotation as Measured in EUV Chromosphericand Coronal Lines"


Presented at the American Astronomical Society meeting,Solar Physics Division, Huntsville, Alabama,Nov. 17-19, 1971.

Bull. Amer. Astron. Soc., 3, #2, II (1971) 263 (Abst-r.).


NASA Grant #NGR 22-007-211.

AbstractActive regions were followed across the disk onOSO-IV spectroheliograms. Using the Ly Continuum,MgX, and Si XII, all the observations showeddifferential rotation, and an increase in the equa-torial rotation with height. The sidereal rate is14.3 degrees/day in the Ly Continuum and 15.0 degrees

- in MgX, with measurement errors of 0.6 to 1.1 degrees/day.

- '47 -

Vernazza, J.E.; Noyes, R.W.

"Inhomogeneous Structure of the Solar Chromospherefrom Lyman-Continuum Data"

Harvard College Observatory. Solar Satellite Project.T.R. #25. September, 1971.

Solar Physics, 20, #2 (Nov. 1971) 514 (Abstr.).

NASA Contracts #NASw-18h, NAS5-9274.

AbstractWe describe a new model of the chromosphere basedon Lyman continuum observations by-Harvard spec-trometers aboard the satellites OSO 4 and OSO 6.The model assumes (a)that a random distributionof optically thick inhomogeneities overlies a plane-parallel homogeneous atmosphere, and (b)that theLyman continuum in the chromosphere is opticallythick and the only significant opacity sourcebetween 600 and 912 i.

The temperature, gas pressure, electron pressure,particle densities, and b I (the hydrogen ground-state departure coefficient) are calculated as afunction of height in the chromosphere.

The model reproduces the observed quiet-region in-tensities in the Lyman continuum from 912 to 750 ,the millimeter brightness temperatures and the center-to-limb variation in the Lyman continuum. The in-homogeneous structures, which we believe to be spicules,are inferred to be optically thick in the Lyman con-tinuum and to have a source function below that of themean chromosphere. If they are also optically thickin the free-free (millimeter) continuum and coolerthan about 5090 K, they could produce the observedlimb darkening at 1 and 3 mm. Such low temperaturesare at odds with current spicule models, but couldexist in the cores of spicules.

The Lyman-continuum emission shortward of 750 ~ showsan excess emission over the predicted by the abovemodel. This is found to be consistent with theexistence of a temperature plateau with T % 22000 Kin the very high chromosphere.

- 48 -

Vernazza, J.E.; Noyes, R.W.

"On the Difference between the Poles and Equatorin the Region of Formation of the Lyman Continuum"

Harvard College Observatory. Solar Satellite ProJect.

Submitted to the 137th AAS Solar Physics Division meetingon Flares and Particle Acceleration--Space Observa-tions of EM Radiation, College Park, Maryland,April 4-6, 1972.

Bull. Amer.. Astron. Soc., to be published.


Abstract

From the analysis of Harvard OSO IV Lyman continuumspectroheliograms, differences in brightness andcolor temperature between poles and equator are found.These differences are interpreted as a result of alower chromospheric density and a smaller temperaturegradient at the poles, as compared with the equator.Two models, one for the poles and one for the equator,giving temperature and density .as a function ofheight explain the Lyman continuum observations.At 2 To 2 = 0.1, the polar pressure is 0.10 dyne/cm . e2 differences begin in the middle chromospherearound 1300 km above T5000 = 1, and increase towardthe transition zone.

- 49 -

Wang, Y.M.

"Temperature Density Structure in Two Regions ofthe Solar Atmosphere from OSO Observations"

Harvard' College Observatory. Solar Satellite Project.

Senior Honors Thesis, Harvard College, 1971.

NASA Contracts#NAS-5-9274, NASw-184.

AbstractThis thesis is in two entirely distinct parts. Thefirst part is an attempt to determine the temperature-density structure of the chromospheric-coronal transi-tion region and low corona from OSO-IV spectroheliogramsof four ions formed in this region; the second partis an attempt to determine part of the temperaturestructure of the low chromosphere from OSO-VI observa-tions of the Carbon I continua. These two regions ofthe solar atmosphere have little in common. For instance, the radiation emitted by the chromospheric-coronal transition region and low corona is opticallyvery thin because of the steep temperature gradientand/or low densities in this region; this allows cer-tain approximations for the source function and makesthe radiative transfer problem very simple. On theother hand, the radiation emitted by the low chromosphereis optically thick, but not enough so to allow an LTEapproximation; thus a complex non-LTE situation mustbe handled. In the first part, then, it was much easierto deal directly with the structure of the region.

\ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ -' .

- 50 -

Wattsi R.N.,Jr.

"Far-Ultraviolet Solar Observatory"

Smithsonian Astrophysical Observatory.

Sky and Telescope, 38, #6 (December 1969) 290-291.

NASA Contracts#NASw-184, NASq-5-9274.

A

- 51 _

Withbroe, G.L.

"The Chemical Composition of the Photosphereand the Corona"


Presented at symposium held at Harvard Coiiege Observatory,Cambridge, Massachusetts, April 8-9, 1971.In: Gebbie, Katherine B. The Menzel Symposium onSolar Physics, Atomic Spectra and Gaseous Nebulae,NBS, SP-353, August 1971, pp. 127-135.

NASA Contract #NAS-5-9274.NASA Grant #NGL-22-007-006.

- 52-

- Withbroe, G.L.

"The Derivation of Temperature Gradient andElectron Density Maps from EUV Spectroheliograms"

Ifarvard College Observatory. Solar Satellite Project.-: T.R. #29. January,1972.

Solar Physics, in press.

NASA Contract #NAS-5-9274.NASA Grant #NGR 22-007-211.

AbstractWe discuss spatial variations in electron density'at the base of the corona and in the temperaturegradient in the chromospheric-coronal transitionlayer as determined from analysis of maps constructedfrom Mg X and 0 VI spectroheliograms. Both themapping techniques and results of analyzing EUVspectra from OSO-VI observations are presented.Comparisons of these maps with photospheric magneto-grams and spectroheliograms made in chromosphericEUV lines and continua indicate that the electrondensity and temperature gradient 'in the transitionlayer tend to be enhanced-in areas-where the photo-spheric magnetic field and chromospheric EUV'emission are enhanced. The coronal electron density,transition layer temperature gradient, chromosphericemission, and photospheric magnetic field strengthrelationships-are derived.

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-53-

Withbroe, G.L.

"Observatory, Astronomical"


In: The McGraw-Hill Yearbook of Science and Technology.. New York: McGraw-Hill, 1971, p. 300..

NASA Contracts #NASwv-184, NAS 5-9274.

I

I

- 54 -

Withbroe, G.L.

"Sola.r XUV Limb Brightening Observations andInterpretation. II: Lines Formed in theChromospheric-Coronal Transition Region"

Harvard College Observatory. Solar Satellite Project.T.R. #13. November, 1969.

Presented at the High Altitude Observatory, NationalCenter for Atmospheric Research Conference onthe Solar Chromosphere-Corona Transition Region,as "Limb-brightening Observations and Determina-tion of Density-Temperature Models", Boulder,Colorado, August 25-27, 1969, pp. 93-124.

Solar Physics, 11, (1970) 208-221.

NASA Contract #NASw-184.

AbstractLimb brightening of XUV lines of the ions C III,N III, N IV, 0 III, 0 IV, 0 V and Si IV is comparedwith that predicted by a modified version'of acoronal model developed by Dupree and Goldberg'(1967).Systematic differences between the predicted andobserved limb brightening are found. These differencescan be eliminated by introducing into the model theeffects of spicules that extend up into the chromo-spheric-coronal transition region. The spiculesare assumed to be opaque to radiation between 500 and900A because of absorption in the hydrogen Lymancontinuum.

.:!

4''

- 55 -

Withbroe, G.L.

"t Comparison of Solar EUV and K-CoronameterIntensity Measurements"

Harvard College Observatory. Solar Satellite Project.T:.R._22. April, 1971.

Sola Physics, 18, /3 (July, 1971) 458-.473.

ASA AContracts I/NASw-184, NAS5-9274.

4~~ "

AbstractEUV data from the Hlarvard experiment on OSO-IV arecompared with K-coronameter measurements in orderto yield to hydrogen. Within the uncertainties ofthe analysis, these coronal abundances are in agree-ment with corresponding photospheric values.

Characteristics of the emission observed above thesolar limb in four EUV lines, Si XII X4997 Mg X X625,Ne VIII k770, and 0 VI X1032, are discussed. Themean temperature of the. corona, derived from theratios of the intensities of Si XII X499 and Mg XX625, is 1.8 million K. There do not appear to besignificant temperature differences between regionswith low and those with high EUV intensities, suggestingthat the EUV emission from the lithiumm-ike ionsdepends primarily on the integral of n e along the lineof sight.

i

- 56 -

Withbroe, G.L.; Noyes, R.W..

"Solar EUV Observations: Lines of Lithium-like Ions"


Presented at AAS Meeting, Division of Solar Physics,Huntsville, Alabama, November 17-19, 1970.

Bull. Amer. Astron. Soc., 3, #2, Pt.II (1971) 265-266(Abstr.).


AbstractA preliminary analysis of OSO-VI observationsof extreme ultraviolet (EUV) li.nes from thelithium isoelectronic sequence has shown that:(1) Differences in the intensities of the Mg XA625 and Si XII X499 lines from point to pointon the solar disk appear to be caused primarily bydifferences in the density in the lower corona.(2) The coronal temperatures measured by theratios of these lines are usually between 1.6-and 2.0 million K, with a mean value of 1.8

0million K for both quiet and active areas.(3) The geometrical thickness of the chromospheric-coronal transition layer decreases with increasingpressure in the transition region until it reachesa minimum value and then it remains at the minimumthickness for further increases in pressure. Thethickness in active areas is 3 to 5 times smallerthan in quiet areas. (4) The chromospheric EUVemission does not appear to be directly correlatedwith the amount of heat conducted from the corona,to the chromosphere.

- : . -~~~~~~~

# . . . . .~~~~~~~~~~~~~~~~~~~~~~~~~~

- 57 -

Withbroe, G.L.; Dupree, A.K.; Goldberg, L.; Huber, M.C.E.;Noyes, R.W.; Parkinson, W.H.; Reeves, E.M.

"Coronal Electron Density Maps from March 7, 1970,Derived from Mg X %625 Spectroheliograms"


Presented at IAU Sympcsium on the Total Solar Eclipse of7 March 1970, Seattle, Washington, June, 1971.

Solar Physics, in press.

NASA Contract #NAS 5-9274.

- 58 -

Wood, A.T.Jr.; Donnelly, R.Ft

"EUV Emissions of Solar Flares: A Comparisonof OSO 6 Observations and SFD's"

Harvard& College Observatory. Solar Satellite Project.*American Science & Engineering Co., Cambridge, Mass.

Submitted to the 137th AAS Solar Physics Division meetingon Flares and Particle Acceleration--Space Observa-tions of EM Radiation, College Park, Maryland,April 4-6, 1972.


NASA Contract #NAS-5-9274.NASA Grant #NGR 22-007-211.

AbstractThe time structure and energy flux of EUVemissions of solar flares observed with theHarvard College Observatory spectroheliographaboard OSO 6 were compared with the 10-103Renergy flux enhancement deduced from SFD ob-servations. The average ratio of the emissionline flux enhancement to the 10-103R fluxenhancement during the impulsive rise of theseemissions is 0.04 for C II 1335a (2 flares),0.02 for 0 IV 554h 1 flare), 0.07 for 0 VI 1032R(11 flares) and 0.003 for Mg X 625R (4 flares).The C II emission rose rapidly like the 10-1030Oburst. The time structure of the 0 IV, 0 VI and MgX flares generally showed good agreement withthe 10-1030O enhancements to within the timeresolution of the OSO 6 data (X%1/2 min). The MgX 625k bursts studied were dominated by the impul-sive component of the flares whereas OSO 3 EUVobservations (L.A. Hall, Solar Phys., 21, 173.)indicated that coronal lines including Mg X weredominated by the slow component of the flares..An observational upper limit was determined for'any contribution to the 10-1030 flux enhancementfrom synchrontron emission. An empirical two-component model for the EUV flare emissions willbe discussed.

I.. ...

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- 59 -:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Wood, A.T. Jr.; Noyes, R.W.; Reeves, E.M.

"EUV Observations of Solar Flares"


Paper presented at American Astronomical Society Meeting,Division of Solar Physics, Huntsville,. AlabamaNovember 17-19, 1970. ,

Bull. Amer. Astron. Soc., 3, #2, Pt.II (1971) 266 (Abstr.).

To be published.


.j.~~~~~j

AbstractThe Harvard College Observatory experiments flownon the satellites OSO-IV and OSO-VI have, for thefirst time, provided spatially resolved observationsof solar flares in the extreme ultraviolet. Severalhundred flares have been observed from both OSO-IVand OSO-VI, with time resolutions as short as 30seconds. Analysis of these observations showsl)the flare intensity usually reaches maximum in theEUV 2-3 minutes before Ha, and also 2-3 minutesbefore the soft x-rays; 2)the flare enhancementpeaks for spectral lines normally formed, in thesolar transition zone; 3)the energy released in EUVlines in a flare is typically 3-4 orders of magnitudeless than the energy released in Ha. We will proposea new model for the flare phenomenon which accountsfor most of the observations.

- 60 -

Wood, A.-. T., Jr.

"Solar Flares in the Extreme Ultraviolet"


Presented at 135th Meeting of American AstronomicalSociety, Amherst, Massachusetts, August 24-27, 1971.

Bull. Amer. Astron. Soc., 3,' #3, Pt.! (1971) 382 (Abstr.).


- - '- .

IV~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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Abstract Further observations of solar flares in the extremeultraviolet (XX 300A - 1300A) from OSO-4 and oso-6are reported. Correlations of EUV data ..vith avail-able Ha, X-ray, radio and SFD observations havebeen performed. 'The principal results of these studiesare: l)when a non-thermal X-ray burst is observed,the EUV, Ha, X-ray and radio burst all reach maximumintensity simultaneously, in agreement with the ob-.servations of Kane and Donnelly (1971 Astrophys. J.,164, 151.) and Parks and Winckler (1971 Solar Phys.

.1-X, 186.); 2)the EUV peak intensity is correlatedwith burst rise rate and also with the reported Haclass; 3)detailed agreement of time structure inthe EUV and other spectral ranges with time scales

.longer than 30 seconds has been observed. We concludethat the EUV is excited quasi-thermally in a high

* : density (N > 101 0 cm -3) plasma which is heated bythe collision of the flare-accellerated electrons

- responsible for the X-ray and radio burst. .

- 61 -

Wood, A.T. Jr.

"EUV Emissions of Solar Flares: OSO 4 and OSO 6Observations"

Harvard. College Observatory. Solar Satellite Project.

Submitted to the 137th AAS Solar Physics Division meeting

on Flares and Particle Acceleration--Space Observa-t'ions of EM Radiation, College Park, Maryland,April 4-6, 1972.



AbstractThe observations of solar flares- made by the HCOexperiments on board OSO 4 and OSO 6 show that:1) EUV flares have two components, analogous-tothe nonthermal (impulsive) and thermal (slow) X-raybursts, respectively; 2) EUV peak intensity is afunction of burst rise time and is correlated withthe X-ray burst characteristics; 3) the detailedtime structure of many bursts is identical in theX-ray, EUV and radio ranges. These results can beinterpreted in terms of an empirical model in whichnonthermal electrons, accelerated in the flare insta-bility, lose their energy throyuh coulomb collisionswith the high density (N 10 12cm 3 ) ambientplasma. In this model, the impulsive X-ray and radiobursts are produced by nonthermal bremsstrahlung andsynchrotron emission, while the EUV is produced quasi-thermally as a result of the excitation and ioniza-tion by the ambient electrons heated by the losses ofthe nonthermal flare electrons. The development ofthe post-impulsive phase can be explained by theredistribution of temperature in the ambient plasmathrough thermal conduction. The temperature struc-ture that results is in substantial agreement withobservations, not only in the EUV, but also in thesoft X-ray and radio regions.

. . ..~~~~~~~~~~~~

- 62 -

Wood, A.T. Jr.; Noyes, R.W.; Dupree, A.K.; Huber,;..E;Parkinson, W.H.; Reeves, E.M.; Withbroe. G.L.

"Solar Flares in the Extreme Ultraviolet.I: The Observations"

,Harvard College Observatory. Solar Satellite Project.T.R. #30. January, 1972.

Solar Physics,

NASA Contracts #NAS 5-9274, NASw-184.NASA Grant #NGR 22-007-211.

Abstract-Solar-flare observations in the extreme ultra-violet (300-1350 i) are reported. Some 269 flaresobserved by the Harvard College Observatory (HCO)experiment on OSO 4 and 211 flares observed by theHCO experiment on OSO 6 have been analyzed. Theflares were observed in spectral lines and continuaemitted by majy ionic species over a temperaturerange from 10 to 3.5 x 10 K. The EUV data havebeen correlated with X-ray, Ha, and radio obser-vations, and a significant number of EUV burstsnot associated with reported Ha, X-ray, or radiobursts have been identified and investigated.The results indicate that these latter EUV eventsare less energetic by about a factor of 2 thanEUV bursts associated with -F subflares.

- 63 -

Wood, A.T.Jr.; Noyes, R.W.

"Solar Flares in the Extreme Ultraviolet.II: Comparisons with Other Observations"

Harvard College Observatory. Solar Satellite Project.T.R. #30. January, 1972.

Solar Physics,

NASA Contracts #NAS 5-9274, NASw-184.NASA Grant #NGR 22-007-211.

AbstractExtreme-ultraviolet (300-1350 ~) observations ofnearly 500 solar flares from the satellites OSO 4and oS0 6 have been compared with data in X-rayand radio wavelengths. It is found that EUV flaresare closely associated with nonthermal X-ray andmicrowave bursts. The EUV maximum intensity generallyprecedes the maximum intensity in Ha or soft X-raysby up to several minutes. The EUV e-folding risetime and peak intensity both depend on the X-rayburst characteristics. Nonthermal X-ray eventsare usually associated with weaker, more slowlyrising EUV flares. These relations are consistentwith a picture of the flare in which theYEUV radiationis produced thermally inma region of high (chromo-spheric) density, which is being heated by collisionallosses of the nonthermal electrons responsible forthe impulsive X-ray and microwave burst.

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- 64 -

UNPUBLISHED PAPERS PRESENTED AT MEETINGS

- 65 -

Avrett, E.H.

"Studies of the Upper Chromosphere and LowerTransition Region"

Harvard College Observatory. Solar Satellite Projectand Smithsonian Astrophysical Observatory.

Presented at the Second OSO Workshop, Goddard SpaceFlight Center, Greenbelt, Maryland, December 2-4,1970.


II

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i. .I!

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- 66 -

Dupree, A.K. .

"Rece-nt Advances in Solar Physics".. '. .-. . .


~~~. o-

Presented at meeting of American Physical Society,Cambridge, Massachusetts', December, 1-971.

NASA Grant #NGR 22-007-211. .

~~.. .- -.

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I

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: . -: - - .. . -.. . - . , f . . . s

- 67 -

* Dupree, A.K.; Goldberg, L.

"New Information on the Structure of the Quiet Chromo-sphere and Corona from OSO IV and 030 VI Data"


Presented at IAU Commission 12, Brighton, England,August 1970.Mentioned in: Proceedings of the XIV General Assembly,Transactions of the IAU, XIVB (1971) 112.

NASA Contracts.;fNASw-184, NAS-5-9274.

AbstractA report was given based on the two OSO satellites(observations between 300 and 1400 ~ with about3 R resolution) and on a 1969 rocket experimentwith a photoelectric scanning spectrometer for theregion 1350 to 1825 R. A model of the chromosphere,the transition region and the corona has been builtto fit these observations.

. . . . . .\

.. .

- 68 -

Huber, M.C.E.

"The Use of Refractivity in Quantitative Spectroscopy"


Presented at IAU Colloquium No. 8, Experimental Tech-niques for the Determination of Fundamental Spec-troscopic Data, Imperial College London, England,September 1-4, 1970.


. . I

- 69 -

Noyes, PR.W.

"EUV Studies of Active Reaions by the Harvard Observatory"

Harvard College Observatory. Solar Satellite Project. 1970.

Presented at IAU Commission 12, Brighton, Enaland,

August, 1970.

Mentioned in: Proceedinas of the XIV General Assembly,

Transactions of the IAU. Vol. XIV B (1971) 107.


- 70 -

Reeves, E.M.

"The Harvard Instrument. I. Instrument Description"


Presented at OSO Workshop, Goddard Space Flight Center,Greenbelt, Maryland, December 2-4, 1970.

NASA Contracts iNASw-184, NAS-5-9274.

N

* . |~~~~~~

I

I

- 71 -

Reeves, E.M.; Dupie ,_A.K_;GoldbergL.; Huber, M.C.E.;Noyes, R.W.; Parkinson, W.H.; Withbroe, G.L.

"Observations of Active Regions and Solar Flares inExtreme Ultraviolet"


Presented at Solar-Terrestrial Physics Symposium,Leningrad, USSR, May, 1970.

NASA Contracts #NASw-i84, NAS-5-9274.I.

t

- 72-

Llceves c F,.4. ; Parkinson, W.H.

"Obscrvutions of thc Sun in the Extreme Ultraviolet"

Harvard Collecge Observato-ry. Solar Satellite Project.

Presented at Internationa. Astronomical C6olloquiumConference on Advanced Transitions and Laboratory-Astrophysics, Toronto, Canada, November, 1969.

NASA ContractsJ,'NASw-184.NAS-5-9274

. .~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~·

IJ

- 73 -

Reeves, E.M.; Dupree, A.K.: Goldberg, L. tIuber, M.C.-;Noyes, R.W.; Parkinson. W.H.: Withbroe. G.L.

"The Solar Spectrum From Quiet Regions X300- 1394"1

Harvar.d College Observatory. Solar Satellite Project.

Presented at Solar-Terrestrial Physics Symposium,Leningrad, USSR, May, 1970.

NASA Contract .#NAS-5-9274.

o.

., , . ':

- 74 -

Reeves, E.M.

"Solar Ultraviolet Observations with OSO-IVand OSO-VI"


Presented at meeting of American Association for theAdvancement of Science, Boston, Massachusetts,December, 1969.

NASA Contracts #NASw-184, NAS-5-927.4..

- 75 -

PUBLICATIONS IN PROGRESS

- 76 -

Avrett*,_E.H.;_;_ L__oqeseer R VernazzaJE

'"Structure of the Solar Chromosphere. I.Computations"

Harvard College Observatory. Solar Satellite*Smithsonian Astrophysical Observatory.

The Basic

Project.


, i,

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. . .

: :. . . .

: .

- 77 -

Avrett, E.H.; Vernazza, J.E.; Wang, Y.-M.

"Strubture of the Solar Chromosphere. II. The C Iand Si I Continua"

Harvard College Observatory. Solar Satellite Project.*Smithsonian Astrophysical Observatory.


-i

.

I

- 78 -

Bechis, D.; Dupree, A. K.

"..:"Time Development of Active Regions"

Harvard College Observatory.. Solar Satellite Project.1972.

NASA Contract #NAS 5-9274NASA Grant #NGR 22-007-211.

I . .

i . .

\

79

Dupree, A.K.

"Studies of the Lower Transition Region fromBeryllium Sequence Ions"

Harvard College Observatory. Solar Satellite Project.1972.


I.

- 80 -

Dupree, A.K.; Goldberg, L.; Huber, M.C.E.; Noyes,R.W-.;Parkinson, W.IH.; Reeves, E.M.; Withbroe, G.L.

"0oso-6 EUV Limb Spectra".;. (-·. ·


NASA Contract INAS-5-9274.NASA Grant #NGR-22-007-211.

.4:

I

i

J,

- 81 -

Dupree, A.K.; Goldberg, L.; Huber, M.C.E.; Noyes, R.W.;Parkinson, W.H.; Reeves, E.M.; Withbroe, G.L.

"EUV Spectrum of an Active Region"

Harvard College Observatory.1972.


Solar Satellite Project.

- 82 -

Dupree, A. K.; Henze, W.; Withbroe, G. L.

"Rotation of the Mg X Corona as Determined from EUVEmission Lines"



- 83 -

-, ~~, o. , . '

Dupree, A. K.; Jones, C.

"Correlations of EUV Emission and Magnetic FieldStrengths"



I. - . .. I

- 84 -

Gurman, J. B.; Withbroe, G. L.; Noyes, R. W.; Harvey, J. W.

"A Comparison of EUV Spectroheliograms and PhotosphericMagnetograms"

Senior Thesis, Harvard College, 1972.


.. .~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- 85 -

Gurman, J.B.; Withbroe, G.L.

"Models for the Chromospheric-Coronal TransitionLayer"v



--, '.~~~~~~~~~~~~~~~~~~~~~~~' ' I ' ' I. - .

- 86.-

Huber, M.C.E.;_Dupree, A.K.; Goldberg.,_L. A Noyes R.WParkinson _.H.* Reeves_, E.M.; Withbroe, G.L.

".The Harvard Experiment on OSO-6. I. Calibrationand Operation of the Instrument and AbbreviatedObservations Catalog"



- 87 -

Munro, R.H.

"An'Analysis of Density Sensitive EUV Line Ratios"

Ph.D. Thesis, Harvard Uniyersity, 1972.

NASA-Contract #NAS-5-9274.NASA Grant #NGR-22-007-211.

. . ,

.i

.

. .

- 88 -

Noyes,-R.W.; Dupree, A.K.; Goldberg, L.; Huber, M.C.E.;Parkinson, W.H.; Reeves, E.M.; Withbroe, G.L.

"Center-to-Limb Variations of EUV Lines from0S0-6 Spectra"


.NASA Contract #NAS-5-9274.NASA Grant #NGR-22-007-211.

-- 89 -

Noyes, R.W.; Dupree, A.K.; Goldberg, L.; Huber, M.C.E.;Kirshner, R.P. ; Parkinson, W.H.; Reeves, E.M. ; Withbroe,G.L.

"EUV Observations of Solar Prominences"


NASA Contract I/NAS 5-9274.


~~~~~~~~~~~~~~~~~~~~~~~~~.-

I

C-

- 90 -

Noyes, R.W.

"Models of Solar Prominences from EUV Data"

Harvard College 0bservatory. Solar Satellite Project.


- 91 -

Raghavan, N.; Withbroe, G.L.

"Analysis of EUV Observations of an Active Regionon the Limb"



, -,I

-92 -

Reeves, E.M.; Ifenze, W.; Vernazza, J.E.; Dupree, A.K.;Goldberg, L.; Huber, M.C.E.; Noyes, R.W,; Parkinson,W.H.; Withbroe, G.L.;

"The Extreme Ultraviolet Spectrum of the QuietSun as Observed by OSO-6"



-93-

Vernazza, J.E.

"A Model of the Chromosphere Derived fromUltraviolet Observations by Satellite"

Ph.D. thesis, Harvard University,

NASA Contract #NAS-5-9274.NASA Grant I#NGR-22-007-211.

- 94

Wang, Y.-M.; Withbroe, G.L.

"An Analysis of EUV Observations of the Solar PolarRegion"



- 95 -

Withbroe, G. L.

"The Analysis of EUV Spectra--Utilizing a New AnalysisTechnique"



, ~ ~~~ ~ ~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~~~~~~~~~

- 96 -

Withbroe, G.L; Dupree, A.K.; Huber, M.C.E.; Goldberg, L.;Noyes, R.W.; Parkinson, W.H.; Reeves, E.M.

"An Atlas of Mg X Spectroheliograms August 14, 1969to May 12, 1970"

:.;. ::

:Harvard College Observatory. Solar Satellite Project.


- 97 -

Woods A.T., Jr.

"An Analysis of EUV Observations of Solar Flares"

Ph.D. Thesis, Harvard University.

NASA Contract #NASw-184, NAS 5-9274.NASA Grant #NGR 22-007-211.

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nasa :ga-~a · much of the data have been analyzed and reported in publications or presented at...

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