Slitless spectra of the chromosphere, observed cinematographically at the total solar eclipse of 10 July 1972, were reduced. The surface brightness distribution of the helium D3 line in the undisturbed chromosphere was obtained in agreement with results by other observers. The available eclipse data on the D3 absolute brightness was analysed by means of theoretical curves of growth. Intensity data by some observers were found to be certainly too high. A trend was found that the D3 absolute brightness in the quiet chromosphere decreases with the increasing solar activity (sunspot number). This perhaps indicates a variation of the spicule number over the solar surface during a sunspot cycle.

The Brightness of the Helium D 3 Line in the Undisturbed Chromosphere from Eclipse Observations

It is shown that in practice the method by Julius (1906) is incapable to determine the limb intensity drop. The brief intensity reversal near the extreme limb as derived from cinematography of flash spectra can be explained by diffraction.

On the Sun's limb brightening in the visible

We study novel spectra from 310 nm to 5.5 μm obtained during the 2017 August 21 eclipse. Four spectrometers were deployed at Camp Wyoba (altitude 2402 m) on Casper Mountain, WY. Three low-resolution (  1000) Avantes spectrometers obtained useful spectra from 310 nm to 2.3 μm, at cadences from 8 to 500 ms. To maximize photometric precision, these instruments were fed with optical fibers placed in the pupil planes of two small (D= 5 cm) telescopes, thereby integrating all light from the field of view. We also acquired higher-resolution ( ≈ 30000) spectra with a new infrared Fourier Transform Spectrometer, fed by a Sun-tracking heliostat, at a 2.5 s cadence. We calibrate the fluxes using counts obtained during partial eclipse, with known limb-darkened photospheric intensities. Fluxes of chromospheric lines, including Ca II H, K, and Hα, obtained near third contact, were measured every 20 ms, a sampling in height above the limb of 5.6 km. The behavior found corresponds to that found in traditional (image-plane) flash spectra. Two unknown chromospheric emission lines are noted. Based upon our measurements and earlier calculations, we propose new eclipse experiments to uncover clues to the origin and structure of spicules.

https://opensky.ucar.edu:/islandora/object/articles%3A22539/datastream/PDF/view

High-cadence visible and infrared spectra of the Sun during eclipse

Les regions d'interface du Soleil de la photosphere a la chromosphere et au dela de la basse couronne ont ete etudiees depuis longtemps a partir des spectres eclairs obtenus durant les eclipses totales de Soleil. Les eclipses sont les plus adaptees a ce type d'observation, car l'occultation a lieu en dehors de l'atmosphere terrestre et sont exemptes de lumiere parasite provenant du " disque occulteur " (c'est-a-dire la Lune), une propriete de grande importance lorsqu'on observe tres pres du limbe. La resolution temporelle des premiers spectres eclairs ne permettait pas de resoudre les basses couches de la region de transition et etaient degrades par des effets non-lineaires qui affectaient les films photographiques. Les images Extreme-UV des regions du limbe obtenues recemment dans l'espace sont analysees avec des modeles hydrostatiques a une dimension, comme les modeles VAL, mais cette methode ne tient pas compte du phenomene d'emergence du champ magnetique, associe au reseau chromospherique qui est responsable de: i) les spicules et le milieu interspiculaire, ii) les jets coronaux et macrospicules, et iii) l'ovalisation de la chromosphere. Les composants de la region d'interface sont dynamiques et differents types d'ondes et de reconnexions magnetiques sont supposees agir. Un saut de temperature de 0.01 a 1 MK est observe autour de 2 Mm d'altitude plus loin, et produit plus loin le flot du vent solaire permanent. Le processus de chauffage responsable du saut de temperature et la source du vent solaire ne sont pas encore compris. Dans cette these, nous traitons ces problemes a partir de spectres eclairs recents realises avec les technologies actuelles de detecteurs CCD rapides, images d'eclipse en lumiere blanche et des images EUV obtenues avec des instruments de missions spatiales. Nous illustrons les mecanismes des emissions des raies a faible potentiel de premiere ionisation (FIP) presents dans les basses couches de l'atmosphere solaire. Nous identifions plus precisement les raies associees aux elements low FIP a la fois a l'interieur et en dehors des protuberances. Nous caracterisons en detail les enveloppes d'helium dans les interfaces. Methodes: 1) technique des spectres eclairs sans fente avec imagerie CCD rapide (eclipses 2006, 2008, 2009, 2010 et 2012). 2) Analyses des spectres du continu entre la myriade de raies d'emission au dela du limbe solaire et construction de courbes de lumiere de quelques raies d'emission low FIP et high FIP. 3) Evaluations d'inversions d'integrales d'Abel pour deduire des echelles de hauteurs et discussion de variations de temperature et de densite. 4) Analyse d'images EUV obtenues aux memes instants depuis AIA/SDO, SWAP, SOT/Hinode des missions spatiales, images en lumiere blanche pour discuter des constituants de la couronne. Principaux resultats: i) Le bord du Soleil et la bifurcation de temperature : le vrai continu a partir du spectre observe aux altitudes de 400 a 600 km au dessus du limbe dans le contexte de de mesures de diametre solaire et processus d'emission. ii) raies d'emission visibles dans les regions d'interface comprenant les raies He I et surtout la raie He II Pα visible a partir de 800 km au dessus du limbe, produite par photo-ionisation, montrant des enveloppes autour du Soleil et permettant le sondage de l'interface protuberance-couronne. iii) La contribution de structures de petite taille comme les spicules et macrospicules commencant a 1 Mm au dessus du limbe et montrant que les modeles hydrostatiques stratifies 1D ne sont pas adaptes pour les couches superieures. Nous montrons que les raies low FIP sont sur-abondantes dans l'interface photosphere-chromosphere, que la couronne solaire est alimentee en permanence par ces elements. Le titane est un element abondant dans le milieu interspiculaire, et une analogie sur les gradients de temperature entre les interfaces photosphere-chromosphere et protuberance-couronne peut etre etablie.

L'interface photosphère solaire/chromosphère et couronne : apport des éclipses et des images EUV

Total eclipse observations were performed in 2008 and 2009 to study the He I and He II shells near the 1 Mm heights above the solar limb. They suggest that the corona penetrates deep into the chromosphere following magnetic chanels. Thanks to the use of a fast CCD camera, the observation of a second ionized helium shell is evidenced for the first time. The transition region is then seen at very low altitude where spicules are emerging. Spicule feet are also discussed, using the best resolution SOT/Hinode HCaII images processed with the non linear operator Madmax to look at details of this ubiquitous part of the solar atmosphere.

The He I and He II chromospheric shells and the Transition Region

The flash spectra of the partial Sun and the chromosphere were obtained at the total solar eclipse on 7 March, 1970. We studied the distributions of the surface brightness of the continuum at six wavelengths in the visual region to compare them with the previous observations and the existing model atmospheres. All of the distributions show a shallow dip and a small hump similar to those of Heintze's observation at the 1954 eclipse. But the hump in our results is of quite a different type from that given by Heintze's revised model. It was found that none of the existing model atmospheres can reproduce this hump. The intensity distribution in the low chromosphere was also examined.

K. Nakayama

Papers

The continuum of the extreme limb and the chromosphere at the 1970 eclipse