Observations, analysis and interpretation with non-LTE of chromospheric structures on the Sun [Elektronische Ressource] / vorgelegt von Bruno Sánchez-Andrade Nuño

Sujets

• Astronomie

Informations

• Publié par: georg-august-universitat_gottingen
• Publié le: 01 janvier 2008
• Nombre de lectures: 18
• Langue: English
• Poids de l'ouvrage: 8 Mo

Extrait

Observations,analysisand
interpretationwithnon LTEof
chromosphericstructuresoftheSun
Dissertation
zurErlangungdesDoktorgrades
derMathematisch NaturwissenschaftlichenFakultäten
derGeorg August UniversitätzuGöttingen
vorgelegtvon
BrunoSánchez AndradeNuño
ausOviedo,Asturias,Spanien
Göttingen 2008BibliografischeInformationDerDeutschenBibliothek
Die Deutsche Bibliothek verzeichnet diese Publikation in der Deutschen
Nationalbibliografie;detailliertebibliografischeDatensindimInternetüber
http://dnb.ddb.deabrufbar.
CoverFigure: Fig. 4.17-LowerLeft.
D7
Referent: Prof. Dr. F.Kneer
Korreferent: Prof. Dr. W.Kollatschny
TagdermündlichenPrüfung: 15Februar,2008
ISBN 978 3 936586 81 7
CopernicusPublications2008
http://publications.copernicus.org
c BrunoSánchez AndradeNuño
PrintedinGermanyFormyparentsConchitaandJulio,
mysisterDeva...
...andallthosewhoshalllearn
somethingfromthiswork.Contents
Summary 7
1 Introduction 9
1.1 TheSun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.2 Thechromosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.3 Aimandoutlineofthiswork . . . . . . . . . . . . . . . . . . . . . . . . 15
2 Spectrallines 17
2.1 Radiativetransferandspectrallineformation . . . . . . . . . . . . . . . 17
2.2 HydrogenBalmer-αline(Hα) . . . . . . . . . . . . . . . . . . . . . . . 19
2.3 He 10830Å multiplet . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3 Observations 21
3.1 AngularresolutionandSeeing . . . . . . . . . . . . . . . . . . . . . . . 21
3.2 Telescope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.2.1 KiepenheuerAdaptiveOpticsSystem . . . . . . . . . . . . . . . 23
3.3 Highspatialresolution . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.3.1 Instrument . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.3.2 Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.3.3 Datareduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.3.3.a Speckleinterferometryofthebroadbandimages . . . . 33
3.3.3.breconstructionofthenarrow band . . . 35
3.3.3.c Multiobjectmultiframeblinddeconvolution . . . . . . 36
3.4 Infraredspectrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.4.1 Instrument . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.4.2 Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.4.3 Datareduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4 Highresolutionimagingofthechromosphere 45
4.1 Darkclouds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.2 Fasteventsandwaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.2.1 Observationsanddatareduction . . . . . . . . . . . . . . . . . . 49
4.2.2 Physicalparameters . . . . . . . . . . . . . . . . . . . . . . . . 51
4.2.3 FasteventsinHα . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.2.4 Magnetoacousticwaves . . . . . . . . . . . . . . . . . . . . . . 59
4.2.5 Summaryonsomepropertiesoftheactivechromosphere . . . . . 73
5Contents
4.3 Comparisonbetweenspeckleinterferometryandblinddeconvolution . . 74
5 Spiculesatthelimb 81
5.1 SpiculeemissionprofilesobservedinHe 10830Å . . . . . . . . . . . . 81
5.1.1 Observationalintensityprofilesandintensityratio . . . . . . . . 82
5.1.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5.1.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
5.2 Highresolutionimagingofspicules . . . . . . . . . . . . . . . . . . . . 87
6 Conclusionsandoutlook 91
Bibliography 95
Publications 103
Acknowledgements 105
Lebenslauf 107
6Summary
This thesis is based on observations performed at the Vacuum Tower Telescope at the
Observatorio del Teide, Tenerife, Canary Islands. We have used an infrared spectropo
larimeter (Tenerife Infrared Polarimeter – TIP) and a Fabry Perot spectrometer (“Göt
tingen” Fabry Perot Interferometer – G FPI). Observations were obtained during several
campaigns from 2004 to 2006. We have applied methods to reduce the atmospheric dis
tortions both during the observations and afterwards in the case of the G FPI data using
imageprocessingtechniques.
We have studied chromospheric dynamics inside the solar disc. The G FPI provides
meanstoobtainveryhighspatial,spectralandtemporalresolution. Weobserveatseveral
wavelengths across the Hα line. With different post processing techniques, we achieve
00spatial resolutions better than 0.5. We present results from the comparison of the dif
ferent image reconstruction methods. A time series of 55 min duration was taken from
◦AR10875atϑ≈ 36 . Fromthewealthofstructuresweselectedareasofinteresttofurther
study in detail some ongoing processes. We apply non LTE inversion techniques to infer
physical properties of a recurrent surge. We have studied the occurrence of simultaneous
sympatheticmini flares. Usingtemporalfrequencyfilteringonthetimeseriesweobserve
waves along fibrils. We study the implications of their interpretations as wave solutions
fromalinearapproximationofmagneto hydrodynamics. Weconludethatalineartheory
ofwavepropagationinstraightmagneticfluxtubesisnotsufficient.
Furthermore, emission above the solar limb is investigated. Using infrared spectro
scopic measurements in the He  10830Å multiplet we have studied the spicules outside
solar disc. The analysis shows the variation of the off limb emission profiles as a func
tion of the distance to the visible solar limb. The ratio between the intensities of the blue
and the red components of this triplet (R = I /I ) is an observational signature ofblue red
the optical thickness along the light path, which is related to the intensity of the coronal
irradiation. The observable R as a function of the distance to the visible limb is given.
We have compared the observational R with the intensity ratio obtained from Centeno
(2006), using detailed radiative transfer calculations in semi empirical models of the so
lar atmosphere assuming spherical geometry . The agreement is purely qualitative. We
argue that this is a consequence of the limited extension of current models. With the ob
servationalresultsasconstraints,futuremodelsshouldbeextendedoutwardstoreproduce
ourobservations. Tocompleteouranalysisofspiculeswereportobservationalproperties
fromhigh resolutionfiltergramsintheH αspectrallinetakenwiththeG FPI.Wefindthat
spicules can reach heights of 8 Mm above the limb. We show that spicules outside the
limbcontinueasdarkfibrilsinsidethedisc.
One and a half centuries after the hand drawings by Secchi, the chromosphere is still
asourceofunforeseenandexcitingnewdiscoveries.
71 Introduction
This thesis deals with the chromosphere of the Sun. To give some insight to the readers
which are not familiar with the topics of this work we introduce in Section 1.1 the main
characteristicsoftheSunwithashortgeneraldescription. Thiswillelucidatetheposition
of the chromosphere in the solar structure and its role for the outer solar atmosphere. In
the subsequent Section 1.2, those aspects of the chromosphere which are treated in the
presentworkarespecified. FinallySection1.3indicatesthestructureofthisthesiswork.
1.1 TheSun
Itisjustaballofburninggas
...right?
The Sun is the central object of the Solar System, which also contains planets and
many other bodies such as planetoids (small planets), comets, meteoroids and dust parti
cles. However, the Sun on its own harbors 99.8% of the total mass of the system, so all
otherobjectsorbitaroundit.
TheSunitselforbitsthecenterofourGalaxy,theMilkyWay,withaspeedof217km/s.
The period of revolution is∼ 230 million years (the last time the Sun was on this part of
theGalaxywasthetimetheDinosaursappeared). Comparedtothepopulationofstarsin
ourgalaxy,theSunisamiddle aged,middle sized,commontypestar. Inastrophysicist’s
languageitisofspectraltypeG2andofluminosityclassV,locatedonthemainsequence
of stars in the Hertzsprung Russell diagram. According to our understandings derived
from models, it has been on the main sequence for 5000 million years and it will remain
thereforanother5000millionyearsbeforestartingthegiantphase.
TheSunisthecloseststartous,thenextonebeing250000timesfurtheraway,butstill
light from the Sun’s surface takes around 8 minutes to reach the Earth. It is the only star
fromwherewegetenoughenergytostudyitsspectrumingreatdetailandwithshorttem
poral cadence. With indirect methods, we can produce images of the surface structuring
onothernearbystarts. ButontheSun,withcurrenttelescopesandtechniques,weresolve
structuresdownto100kmsizeonitssurface,whichrepresentsapproximatelytheresolu
tion limit in this thesis work. We can also investigate the structure of its atmosphere and
theeffectsofitsmagnetism. Actually,weareembeddedinthesolarwindthathasitsori
ginintheoutersolaratmosphere,thecoronaoftheSun. Thus,wecanmakein situ mea
surements. With special techniques and models, we can reconstruct the properties of its
interior.
91 Introduction
The Sun is the most brilliant object in
the sky, 12 orders of magnitude brighter
than the second brightest object, the full
Moon, which actually only reflects the
sunlight. Itslightwarmsthesurfaceofthe
Earthandisusedbypla