Spectrographic Sun chromosphere observations
at Pic Du Midi "Lunette Jean Rösch" with the eShel spectrograph

July 2009

Jean-Pierre Rozelot, Valérie Desnoux, Christian Buil

The Jean Rösch refractor atop Pic du Midi Observatory
(2870 m - French Pyrénées). Photo V. Desnoux.

The very peculiar dome interior of LJR instrument.
At first plane, the eShel spectrograph (
see details here).

Valérie Desnoux adjust the position of eShel fiber interface. A Baader Herschel helioscope reduce the sun flux.

Video image (Watek 120 N camera) of Sun taken with eShel interface. Note the size of the sun image (only a very small part can be see here), and the size of optical fiber hole (diameter: 50 microns, 1.6 arcsec on the sky).

The acquisition computer. Note the echelle spectrum on the screen.

The important image! The aspect of H
a line is function of fiber position on sun surface. The hydrogen emission contrast
increase near the disk limb. The line profile is inverted at chromosphere level (from absorption to emission). The Pos #1 sounding point
correspond to geometric sun center. The Pos #4 sounding is outside the sun disk (the presence of photospheric
absorption lines is the consequence of atmopsheric diffusion - thin cirrus cloud are presents in the sky).

The ratio of spectra taken at Pos #4 (outside the sun limb) and Pos #1 (disk center). The operation erase the photospheric
lines and now, a pure chromospheric emission spectrum car be observed. Here the H
a region.

Same operation (Pos #4 / Pos #1) for the sodium doublet region (D1 & D2). Note also the presence of 587A He I line (D3 line).

Chromosphere spectrum in the vicinity of green magnesium triplet. Note also the presence of many faint emission lines.

The H
b emission.

The violet region is rich of many chromspheric emission lines.

The global echelle spectrum of sun chromosphere (Pos #4).


The 50 cm diameter lens of LJR refractor (6.5 meters focal length). Photo V. Desnoux.

Comparison of chromosphere spectra for sounding points #2, #3, #4 (relative to #1). H
a region.

Same for D1, D2 and D3 region. The disk intensity of He I line is very weak (red profile).

The large intensity of helium D3 line inversion at the limb interface is confirmed in these
spectroheliogram, comparative to H
a or Mg lines (Lhires II spectrograph acquisition, click here for details).

Comparison of Mg b1, b2 and b3 lines intensity as function of radial position of the optical fiber.

b comparative intensity (very similar to Ha).

The violet part of chromosphere spectrum.

Download here the P#2/P#1, P#3/P#1 and P#4/P#1 spectra.

Lines identification example. The spectrum is equivalent to a flash spectrum observerd during total solar eclipses.
A very good reference for lines indentification is S. A. Mitchell, ApJ, 71, 1-61, 1930 (available from

Goto observations index page