On a difference in the dimensions of photospherical granules in the vicinity and far from the sunspot penumbra

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MSA TT F-8322

ON A DIFFERENCE IN TBE DIMENSIONS OF PHOTOSPHERIGAl

GRANULES IN THE YICINITI AND FAR FROM 'EHE

SMSPOT PENUMBRA

by
C. J. Maoris
T* J, Prokakis

(FEANGE)

W 71- 71283

S (ACCESSION NUMBER)

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(PAGES)

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^ (NASA tROR TMX OR AD NUMBER)

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NATIONAL JffiRONATJTICS 11© SPACE ADMINISTRATION
WASHINGTON 107EMEER 1962

DRAFT TEAN3LATI0U NASA TT F-8322

NOV 2 61962

ON A DIFFEEENCE IN THE DIMENSIONS OF PHQTQSPHEBICAL

GRANTEiES IN THE VICINITY AND FAB FROM TEE

SUNSPOT PENUMBRA *

(FRANCE)

Comptes Rendus A«Sc« by C, J. Maoris

T.255, No, 16, pp.1862-^ T* J* Prokakis

15 October 1962, Paris.

(Presented by M* Andre Danjon)

Abstract / /^^ ^

A difference is noted between the dimensions of photo-
spherical granules measured in the vicinity and far from the
penumbra of sunspots. This phenomenofL is attributed to the effect
of the magnetic field of the spots* - ^^

*

One of us Cl3 found some years ago that the dimensions
of photospherical granules are smaller in the vicinity of the
penumbra of sunspots than those measured far from the spots.
The cause of this difference in dimensions was attributed to the
peculiar conditions existing in the 'vicinity of the spots, due to
thermal gradients and more particularly to the intensity of the
magnetic field. Dollfus [2] attributed that difference to intense
radial magnetic fields, just as A. E* Danielson did C3l when uti-
lizing photographs taken by the stratoscope and finding smaller
dimensions for the granules in certain regions in the vicinity of
a sunspot .

Working on solar granulation with the aid of a Gautier
refractor of kO cm aperture at the National Observatory of Athens,

* Sur une difference des dimensions des granules photospheriques
au voisinage at loin de* la penombre des taches solaires.

\

z.

we found on good quality photos very pronounced differences of
character above in granule dimensions* In order to study this pheno-
menon relative .to sunj^pot structure and to the intensity of their

I
magnetic fields ,-^e have selected four negatives sonong the best

taken with the aid of the above-mentioned device by M« G» Banos,
whose data are compiled briefly in Table 1 hereafter :

TABLE I

Fo.

Date i960

ITrT.

Filter
(i)

Heliographic
coordinates

Emulsion

1

31 May

O6li44»30"

6000

IQS -32 W

Duplopan-

2

22 Sept

06 14 24

5250

20S-13W

Gevaert

3

22 Sept

06 00 56

5250

19S-25E

II

4

22 Nov,

08 05 45

6000

7N-17W

ri

The magnetic field intensity of the above simspot groups
was communicated to us by the Potsdam andoMountvpilson Observato-
ries. The dimensions of granules were measured in the selected
regions on the first negatives with the aid of observatory.^s
Eidell measuring device.

IToted in the Figures 1 and 2 the regions where the dimensions
of photospherical granules were measured: a and b refer to measure-
ments made in the vicinity of spot penumbra and c — to those made
far from it# On the photos 5 and h^ a and c point to regions in
which measurements were respectively effected in the vicinity and
far from the penumbra. The spots' magnetic field intensities and
the results of measurements of granule dimensions are given in
Table II (next page). These data allow the following conclusions :

The dimensions of photospherical granules in the vicinity
of sunspots of complex structure and with intense magnetic fields
are smaller than those measured far from the spots.

3.

TABLE

II

Groupe - Date

Magnetic field

Difference

Mean

Comments

intensity

in grsmule
dimensions

error

1. (31 May)

Mt. Wilson

G — a = 0"51

+0"10

Complex struct.

S 2200 G

^ c - b = 0"43

+0"l6

group

for 30, 7 May -^

2. (22 Sep)

Potsdam

c - a = 0"84

0"22

Remarkable compl

S2300-N2700 G
(for 22, h Sep)

c - b =0"69

0"19

structure group
two nuclei of
opposed magnet,
polarity in the
same penumbra.

3. (22 Sep)

Potsdam

S 2500 G

(for 22, 4 Sep)

c - a = 0"21

0"12

Unipolar spot
of small surf.

4. (22 ITov)

Mt .Wilson

N 1500 G,

(for 20, 3 Nov)

Potsdam

N 2500 G

(for 24, 5 Nov)

c — a = 0"06

0"l8

Unipolar spot
of small surf •

The dimensions of photospherical granules in the vicinity
of unipolar sunspot penumbra show to the contrary very small differen-
ces relative to the dimensions measured far from spots, even if they
present intense magnetic fields ♦

It is quite probable that this difference in the dimension
of granules in the vicinity and far from the pentimbra of . apots of
complex structure (bipolar and multipolar groups) is due to the shape
of magnetic fields and their intensity repartitite* The nonexistence
of appreciable differences between the dimensions of granules measured
near and far from the penumbra of unipolar spots may be explained by

h.

Fig.l

Fig. 2

the fact that, acceirding to tlie law of variation of magnetic field
intensity in simple and isolated spots, the latter becomes zero
at about the limit of the penumbra and of the photosphere*

***j| THE EKD **«*
KBFEEENCES

1* C. MAORIS , Ann.Astrophys, l6, No. 1, p. 10, 1953.

2. A« DOLLFUS . Astronomie, p, if22, Oct-November 1959.

3. H. E. DANIELSOIT , Ap. J. 25^, No. 2, p. 28?, September I961.

Translated by ANDHE L* BEICHANT
for the

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

25 November I962.