The Yohkoh (Solar-A) Mission

115 Pages·1991·3.468 MB·English

by  Y. Ogawara, T. Takano, T. Kato, T. Kosugi, S. Tsuneta (auth.), Zdeněk à vestka, Yutaka Uchida (eds.)

THEYOHKOH(SOLAR-A)MISSION
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ISBN 978-94-010-5161-3 ISBN 978-94-011-2626-7 (eBook)
DOI 10.1007/978-94-011-2626-7
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© 1991 Springer Science+Business Media Dordrechl
Originally published by K1uwer Academic Publishers in 1991
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THE YOHKOH (SOLAR-A) MISSION
ASeries o/Invited Contributions
Edited by
ZDENEKSVESTKA
Laboratory for Space Research Utrecht, SRON, The Netherlands
and
Center for Astrophysics and Space Sciences, UCSD, La Jolla, CA 92093, U.S.A.
and
YUTAKA UCHIDA
Department ofA stronomy, University ofTokyo, Bunkyo-ku, Tokyo 113, Japan
Reprinted from Solar Physics, Volume 136, No. 1, 1991
SPRINGER SCIENCE+BUSINESS MEDIA, B.V.
KATSUO TANAKA
(1943-1990)
On January 2, 1990,our colleague, the prominent solar physicist Katsuo Tanakadied
in Tokyo after a long battle with leukemia. He was only 46.
BorninTokyoin 1943,Tanakagraduatedfrom the UniversityofTokyoin 1965. He
was awarded a Ph.D. in 1971 for his study ofthe solar chromosphere based on the
eclipse data.
In 1970 he began working with the Tokyo Astronomical Observatory, where his
interests shifted to the observation of solar activity, particularly solar flares, in high
resolution.In 1971,hebeganacooperativeresearchprojectwithH. ZirinattheBigBear
Solar Observatory. Their work on the largeflares ofAugust 1972remains a landmark
achievement in the field.
After returning to Tokyo, he played a key role in the ASTRO-A project. The
ASTRO-A satellite, which Tanaka named 'HINOTORI' (Japanese for Phoenix), ob
served more than 700 flares during its mission (February 1981 to October 1982).
Combiningthe datafrom his X-ray spectrometerwith the hard X-rayimages taken by
the X-ray telescopeon HINOTORI, heclassified X-rayflares into three types: (1)hot
thermalflares, (2)impulsiveflares, and (3)gradual hardflares. Thesedifferencescould
originate,hebelieved,from theenvironmentalvarietyofflare sites. Hesummarizedhis
viewinaninvitedreviewpaperinthePublicationsoftheAstronomicalSocietyofJapan
in 1987. In 1985, Tanaka was3warded the Inoue Science Foundation Prize for his
achievements in flare research.
Followingthe success ofthe HINOTORI project,Tanakabecamea drivingforce in
establishing the SOLAR-A (Yohkoh) project In 1983, however, he was diagnosed as
suffering from fatal leukemia.
In 1988heobtainedagrantandstartedconstructiononauniquetelescopetoobserve
the magnetic field, velocity field, HO(, and white-light images of solar active regions
simultaneously.Hebelievedthattheenergysourceofflaresistheemergenceofmagnetic
flux tubes, which are twisted (stressed) underneath the solar surface. His contribution
to this issue ofSolar Physics is the culmination ofthis research.
In Japanese, the name Katsuo means 'victory' and 'quickness', perhaps best
symbolizinghisgreatachievementsin such ashortlife. Wedeeplyregretthelossofthis
talented scientist.
E. HIEI and T. SAKURAI
SolarPhysics 136:v, 1991.
Contents
THE YOHKOH (SOLAR-A) MISSION
(A Series ofInvited Contributions)
OBITUARY v
OGAWARA,Y., TAKANO,T, KATO, T, KOSUGI, T., TSUNETA, S., WATA
NABE,T.,KONDO, I.,andUCHIDA, Y./TheSOLAR-AMission: anOverview
KOSUGI, T, MAKISHIMA, K., MURAKAMI,T, SAKAO,T, DOTANI,T,
INDA, M., KAI, K., MASUDA, S., NAKAJIMA, H., OGAWARA,Y., SAWA, M.,
and SHIBASAKI, K. / The Hard X-Ray Telescope (HXT) for the SOLAR-A
Mission 17
TSUNETA, S., ACTON, L., BRUNER, M., LEMEN,J., BROWN, W., CARAVAL
HO, R, CATURA, R, FREELAND, S., JURCEVICH, B., MORRISON, M.,
OGAWARA, Y., HIRAYAMA,T, and OWENS,J. / The Soft X-Ray Tele-
scope for the SOLAR-A Mission 37
YOSHIMORI, M., OKUDAIRA, K., HIRASIMA, Y., IGARASHI,T., AKASAKA, M.,
TAKAI, Y., MORIMOTO, K., WATANABE,T., OHKI, K., NISHIMURA,J.,
YAMAGAMI,T, OGAWARA,Y., and KONDO, I. / The Wide Band Spec-
trometer on the SOLAR-A 69
CULHANE, J. L., HIEI, E., DOSCHEK, G. A., CRUISE,A. M., OGAWARA,Y.,
UCHIDA, Y., BENTLEY, R D., BROWN,C. M., LANG,J., WATANABE,T.,
BOWLES,J. A., DESLATTES, R D., FELDMAN, U., FLUDRA,A., GUTT
RIDGE, P., HENINS, A., LAPINGTON,J., MAGRAW,J., MARISKA,J. T.,
PAYNE,J., PHILLIPS, K. J. H., SHEATHER, P., SLATER, K., TANAKA, K.,
TOWNDROW, E., TROW, M. W., and YAMAGUCHI, A. / The Bragg Crystal
Spectrometer for SOLAR-A 89
MORRISON, M. D.,LEMEN,J. R,ACTON, L. W.,BENTLEY, R. D.,KOSUGI, T.,
TSUNETA, S., OGAWARA, Y., and WATANABE, T. / SOLAR-A Reformatted
Data Files and Observing Log 105
THE SOLAR-A MISSION: AN OVERVIEW*
Y.OGAWARA,T.TAKANO,T. KATO
Institute ofSpace andAstronauticalScience, Sagamihara, Kanagawa 229,Japan
T. KOSUGI, S.TSUNETA
Institute ofAstronomy. University ofTokyo. Mitaka, Tokyo 181,Japan
T. WATANABE
NationalAstronomical Observatory, Mitaka, Tokyo 181,Japan
I. KONDO
Faculty ofSystems Engineering. Shibaura Institute ofTechnology, Tameihara, Fukasaku. Omiya,
Saitama 330, Japan
and
Y. UCHIDA
Department ofAstronomy, Faculty ofScience, University ofTokyo, Bunkyo-ku, Tokyo 113,Japan
(Received 10 April, 1991; in revised form 17 June, 1991)
Abstract.TheSOLAR-AspacecraftistobelaunchedbytheInstituteofSpaceandAstronauticalScience,
Japan(ISAS)inAugust, 1991.As asuccessorofHINOTORI,thismissionisdedicatedprincipallytothe
studyofsolarflares,especiallyofhigh-energyphenomenaobservedintheX-andgamma-rayranges.The
SOLAR-A will be the unique space solar observatory during the current activity maximum period
(1989-1992).WithacoordinatedsetofinstrumentsincludinghardX-rayandsoftX-rayimagingtelescopes
aswellasspectrometerswithadvancedcapabilities,itwillrevealmanynewaspectsofflaresandhelpbetter
understandtheirphysics,supportinginternationalcollaborationswithground-basedobservatoriesaswell
astheoreticalinvestigations.Anoverviewofthismission,includingthesatellite,itsscientificinstruments,
and its operation,isgiven in this paper. Also the scientificobjectives are brieflydiscussed.
1. Introduction
The SOLAR-A spacecraft is scheduled to be launched by the Institute of Space and
Astronautical Science, Japan (ISAS) in August 1991 from the Kagoshima Space
Center. The main goal ofthis spacecraft is to observe energetic phenomenarelated to
solar flares in X- and gamma-rays with a coordinated set ofinstruments.
Thefirst Japanese spacecraftdedicated toflare studies, HINOTORI, was launched
closeto the previous solar activity maximum in February 1981. At that time the Solar
MaximumMission(SMM)had beeninoperationfor aboutayear, pursuingalmostthe
same objectives as HINOTORI. The two missions successfully revealed new aspects
ofsolarflares inX-andgamma-rays(e.g.,Kundu andWoodgate, 1986;Tanaka, 1987).
Thehard X-rayimagerson boardthetwo spacecraft,for thefirst time, madeimages
offlares in the hard X-ray range above a few keY. These novel observations showed
* After the launch the name ofSOLAR-Ahas been changedto YOHKOH.
SolarPhysics 136: 1-16, 1991.
© 1991 KluwerAcademicPublishers.
2 Y. OGAWARA ET AL.
thatinimpulsiveflares (typeBofTanaka, 1987)twoormore separatesources brighten
almost simultaneously in hard X-rays, and that extended hard X-ray sources (typeC)
arelocatedhighinthecoronaataltitudesofafew times 104 km abovethephotosphere
in gradual X-ray flares.
The production and evolution ofhigh-temperature plasmas in flares has been sys
tematically studied via soft X-ray emission lines observed with high-resolution Bragg
crystal spectrometers on board the P78-1, TanseiIV, SMM, and HINOTORI space
craft. The precise diagnostics obtainablefrom various high-temperatureemission lines
revealed the dynamics of plasmas trapped in flaring loops; these include the violent
heatingofthe transition region and the chromosphere due to precipitation ofenergetic
electrons, turbulentmotions, andevaporation(ablation)ofthe chromosphericmaterial
seen as blue-shiftedcomponents ofemissionlines in theinitialphaseofflares. Agroup
of flares (type A) showed prominent hydrogen-like iron emissions from 'superhot'
(T> 3 x 107 K) thermal plasmas.
Anumberofgamma-ray-producingflares were also detected. Itwas found that ions
can be accelerated to few-MeV energieswithin a few seconds and simultaneouslywith
electrons at theflare onset. This has put strongconstraints on theories ofacceleration
mechanisms.Gamma-rayeventswerepreferentiallyobservednearthesolarlimb,which
suggests anisotropy ofgamma-ray radiation and particle motions.
These discoveries from the last activity maximum, and their tantalizing physical
interpretations,demandedfurtherinvestigations.TheimagestakenwiththehardX-ray
imagers had relatively low spatial resolution and their energy ran'!e was below about
30 keV sothat the'hard' X-rayimages could becontaminated byX-rays from thermal
sources. Another deficiency was the lack of reflecting telescopes for the soft X-ray
wavelengths,whereonecanalmostdirectlyseethecoronalmagneticstructuresinwhich
flares occur. Such reflecting telescopes were flown previously only on SKYLAB in
1973-1974. The Bragg crystal spectrometers showed vividly the existence ofchromo
spheric evaporation owing to high spectral resolution, but due to low sensitivities no
clean data could be obtained at the very onset ofa flare. Most gamma-rayflares were
observed without simultaneous imaging at hard X-ray energies.
Based upon this scientific motivation, SOLAR-A was planned and constructed as
aninternationalcollaborativeprojectincludingmanyinstitutionsinJapan,intheUnited
States,andinthe United Kingdom. Theparticipatinginstitutionsandtheirresponsibili
ties are summarized in TableI. In the present paper, we will give an overview ofthe
SOLAR-A mission from the viewpoints ofthe scientific instruments in Section 2, the
spacecraft design in Section 3, and the flight operations in Section4. The scientific
objectives will be briefly discussed in Section 5. In thispaper, as wellas in thefollowing
seriesofpapersinthisSolarPhysicsissue, we willcallthismissionbyitsdevelopmentname
SOLAR-A, but it is to be noted that the mission willbeformally given a new name after
launch according to the ISAS tradition.
THE SOLAR-A MISSION: AN OVERVIEW 3
TABLE I
The SOLAR-A mission
Mission objectives Investigationofhigh-energy phenomenaon the Sun
Launch August 1991
Mission life ~2years (orbital life ~3-4years)
Organization
Projectmanager Yoshiaki Ogawara(ISAS)
Project scientist Yutaka Uchida(Univ. ofTokyo)
Principal investigators
Hard X-rayTelescope(HXT) Keizo Kaia (NAOJ) and Kazuo Makishima (Univ. of
Tokyo)
SoftX-rayTelescope(SXT) TadashiHirayama(NAOJ)andLorenW.Acton (LPARL;
U.S. PI to NASA)
Wide Band Spectrometer(WBS) Jun Nishimura (ISAS)
BraggCrystal Spectrometer(BCS) EijiroHiei(NAOJ)and J.Leonard Culhane(MSSL; U.K.
PI to SERC)
Major participating institutions
Japan: 1SAS,NationalAstronomicalObservatory(NAOJ),Univ.ofTokyo,RikkyoUniv.,KyotoUniv.,
Nagoya Univ., etc.
U.S. SXTteam: Lockheed PaloAlto Research Laboratory(LPARL), StanfordUniv., U. Californiaat
Berkeley,and Univ. Hawaii
U.K.andU.S.BCSteam:MullardSpaceScienceLab.(MSSL),RutherfordAppletonLab.,E.O.Hulburt
Centerfor Space Research, and the NationalInstituteofStandards and Technology
Deceased 1991 March II.
a
2. Scientific Instruments
SOLAR-A carries the following scientific instruments: the Hard X-ray Telescope
(HXT),the SoftX-rayTelescope(SXT),theWide Band Spectrometer(WBS), and the
Bragg Crystal Spectrometer (BCS). As the technical detillis ofthese instruments are
described in separate papers, only a briefsummary is given below and in TableII.
2.1. HARD X-RAY TELESCOPE (HXT)
The HXT(KosugietaI., 1991)is a Fourier synthesis telescope. Itconsists of64 bigrid
modulation collimators, each with 2.3 x 2.3 cm cross-section and a 0.5 cm thick
NaI(TI) crystal attached to a I-inch square phototube. The individual subcollimators
measure spatially-modulatedphoton counts,thus providing32complex 'Fourier' com
ponents at appropriate position angles and wave numbers in the (u, v)-plane. Thefield
ofviewcoversthewhole Sun,whilethesynthesisaperture,determined bythegrid pitch
corresponding to the fundamental wave number, is about 2x 2arc min. The angular
resolution isabout5arc sec. Imagesinfourenergybands(15-24-35-57-100 keY)will
be obtained simultaneously with a temporal resolution up to 0.5 s.
2.2. SOFT X-RAY TELESCOPE (SXT)
The SXT (Tsuneta etal., 1991) is a grazing-incidence reflecting telescope in the soft
X-rayband(3-60 A)withaCCDdetectorof1024 x 1024pixels. Itsfield ofviewcovers
4 Y. OGAWARA ET AL.
TABLE II
SOLAR-A scientificinstruments
Hard X-rayTelescope(HXT)
Instrument Fourier-synthesis type collimator(64elements)
Energy bands 15-24-35-57-100keY (4 bands)
Angularresolution -5arcsec
Fieldofview Full solardisk
Effectivearea -70cm2
Time resolution 0.5s
SoftX-rayTelescope(SXT)
Instrument Modified Wolter type I grazing incident mirror+CCD with
coalignedopticaltelescope
Wavelength range (X-ray) 3-60A(selectablewithfilters)
(optical) 4600-4800Aor4293-4323A
Angular resolution -2.5arcsec
Fieldofview Full solardisk
Time resolution upto 0.5 s
Wide Band Spectrometer(WBS)
Detectors Gas proportionalcounter(soft X-rays; 2-30keY)
Nal scintillationcounter(hard X-rays; 20-400keY)
BGO scintillationcounter(gamma-rays; 0.2-100MeY)
Time resolution (count-ratedata)0.125,0.25,or0.5 s
(pulse-heightspectrumdata) I, 2,or4s
BraggCrystal Spectrometer(BCS)
Instruments Bentcrystal spectrometers
Spectral lines and resolutions
Sxv (5.0385 A) 5.0160-5.1143Awith 3.232rnA resolution
Caxlx(3.1769 A) 3.1631-3.1912Awith0.918 rnA resolution
Fexxv (1.8509 A) 1.8298-1.8942Awith0.710 rnA resolution
FeXXVI(1.7780A) 1.7636-1.8044Awith0.565 rnA resolution
Time resolution upto 0.125 s
the whole Sun. The angular resolution ofthe optical system ofSXT is on the order of
2arc sec across the solar disk, slightly better than that determined by the CCD pixel
size(2.4arc sec).Twofilterwheels andashutterdeviceareplacedinfront oftheCCD
detectortochooseenergybandandexposuretimeproperly.Filterandexposureselection
as well as data acquisition arecontrolledby a dedicated microprocessor, following the
commands dispatched bythe main data processoron board the spacecraft. When the
Sunis quiet, whole-Sunimages aretaken togetherwith up tofour bright active regions
which are monitored at a moderate rate. When a flare occurs, the observation will be
concentrated on the brightest region by taking 'partial-frame' images with up to 0.5 s
time resolution.
2.3. WIDE BAND SPECTROMETER (WBS)
The WBS (Yoshimori etal., 1991)consists offour types ofdetectors: the Soft X-ray
Spectrometer (SXS), the Hard X-ray Spectrometer (HXS), the Gamma-Ray Spec-