Fe XIV, 530.3 nm
Our expedition observed emission from the following ions in the visible
and near IR wavelength range: Fe IX (435.9 nm), Fe X (637.4 nm),
Fe XI (789.2 nm), Fe XIII (1074.7 nm), Fe XIV (530.3 nm)
and Ni XV (670.2 nm). These emission lines provide an excellent
diagnostic tool
for probing the physics of the solar corona. One of the tools is clear from the following graph.
Fe XIV line at 530.3 nm is the most prominent emission line in the visible part of the
coronal spectrum.
Even though Fe XIV is the strongest emission line in the visible part of the coronal spectrum it
is not easy to obtain an image of Fe XIV only. It is not as simple as deep sky photography of emission
nebulae where only sufficiently narrow band filter is needed to isolate the emission line. The light of
solar corona is dominated by continuum - photospheric light scattered on free electrons. The light emitted
by different atoms and ions is very weak relative to the continuum. See the following two unprocessed images.
The
left one was taken through a narrow band filter (bandwidth 0.5 nm) with the transmission band centered on the
Fe XIV 530.3 nm emission line. The right image was taken through a filter with the transmission band outside
the Fe XIV line in the continuum. It is clearly visible that except for the active region (9 o'clock position)
the
left image is dominated by continuum which is stronger than
Fe XIV emission nearly everywhere in the image. It is not advisable to use a filter with a narrower band
of transmission because
the emission line is thermally broadened. Hence, a narrower band filter would make the situation even worse.
Therefore it is necessary to make a precise photometric calibration of all images and than subtract the
continuum - the right image from the left one. You may see these two images as an
animation.
It is obvious that imaging in Fe XIV at 530.3 nm through any narrow band filter without
continuum subtraction is misleading because the image is strongly dominated by continuum. If the
bandwidth of the filter is wider than about 5 nm the image is nearly identical to the broadband
white-light image taken without any filter. From the point of contamination by continuum Fe XIV
503.3 nm it is the worst emission line in solar corona because its wavelength is very near the maximum
of the solar photospheric irradiance. On the other hand Fe XIV ions are strongly excited by photospheric
light and therefore the Fe XIV emission is observable very far from the Sun. It is
clearly visible if you compare the Fe XIV image presented on this page with the
Fe XIII image at 1074.7 nm where the
intensity of continuum relative to 530.3 nm is approximately 3× weaker.
More images of Fe ion emission obtained during the 2017 eclipse can be found in the following pages:
Click on the image or on the following reference to display the
higher resolution image version (997 KB, PNG format).
|
| Image | Fe_XIV_Mitchell_ACHF.jpg |
| Date | 21. 08. 2017 |
| Time | 2nd contact 17:21:11 UT, 3rd contact 17:23:14 UT |
| Place | near Mitchell, Oregon, USA |
| Coordinate | N 44° 31.539', W 119° 54.459', Alt. 1100 m |
| Conditions | Clear sky but some smoke from forest fires, solar altitude 43° above horizon |
| Optics | 2× Achromat 4/300 mm equipped with following narrow band filters:
On-band filter: Andover, center wavelength: 530.3 nm, bandwidth 0.5 nm
Off-band filter: Andover, center wavelength: 527.3 nm, bandwidth 0.5 nm |
| Camera | 2×Atik 314L |
| Exposure | 0.05 - 6.4 s |
| Processing | Composition of 64 eclipse images (32 On-band and 32 Off-band) taken with two cameras. Images were calibrated by means of dark frames and flat-fields, aligned by means of phase correlation, composed by means of LDIC 6.0 software, continuum was removed from Fe XIV emission by subtracting the Off-band images. The resulting image was processed using Corona 5.0 software in order to visualize coronal structures. The final processing was done using ACC 6.1 software.
Image processing by Miloslav Druckmüller |
| Software | Astro D3F 2.0, PhaseCorr 7.0, LDIC 6.0, Corona 5.0, Sofo ACC 6.1 |
| Copyright | © 2017 Miloslav Druckmüller, Shadia Habbal, Pavel Štarha, Judd Johnson,
Jana Hoderová |
|
Miloslav Druckmüller
Institute of Mathematics, Faculty of Mechanical Engineering
Brno University of Technology, Czech Republic
druckmuller@fme.vutbr.cz
|
Page last update: 26.11.2019
|
|
