Solar spectroscopy

Solar spectroscopy

Solar spectroscopy

Dr Nicolas Labrosse

School of Physics and Astronomy

University of Glasgow

Solar spectroscopy

26/01/2012 Dr Nicolas Labrosse - Talk to Renfrewshire Astronomical Society 2

Solar spectroscopy

Important dates

• Newton (1704) observed the dispersion of light by a prism


Solar spectroscopy

Important dates

• Herschel (1800) detects infrared radiation using thermometers


Solar spectroscopy

Important dates

• Wollaston (1802) notices dark lines in the spectrum of the Sun


Solar spectroscopy

Important dates

• Fraunhofer (1817) describes the dark lines in Sun’s spectrum:

spectroscopy is born!


Solar spectroscopy

Important dates

• Solar chemical composition in the 1860s


map of the solar spectrum published

in 1863 by Kirchhoff, showing the

identification of a large number of

spectral lines with various chemical

elements

Solar spectroscopy

Important dates

• Lockyer (1868) revealed the presence of an unknown element: helium


Solar spectroscopy

Important dates

• The 1879 eclipse revealed a coronal green line at 530.3 nm

– Origin unknown for 50 years: was this “coronium”?


Solar spectroscopy

Important dates

• 1939: Edlén showed this line is emitted by highly ionised iron (Fe XIV,

which has lost 13 electrons)

– Corresponding to

temperature over

1 million K!


Solar spectroscopy

High resolution solar spectrum (type G2)


400 nm

700 nm

Solar spectroscopy

High resolution spectrum of Procyon (type F5)


400 nm

700 nm

Solar spectroscopy

High resolution spectrum of Arcturus (type K1)


400 nm

700 nm

Solar spectroscopy

Spectral lines

• Lines characterised by intensity, position, and width

• In solar spectroscopy, width affected by (among others)

– Instrumental profile

– Temperature

– Collisions

– Unresolved motions


Solar spectroscopy

Spectroscopic instruments

• Needed to obtain physical parameters, such as

– Temperature

– Magnetic field

– Flow speed

• Measurements are multi-dimensional:

– Two spatial dimensions

– Wavelength

– Time

• At present, detectors only record 2 dimensions at a time.

– Filter instruments record 2D images at a fixed wavelength

– Slit spectrographs record 1 spatial dimension and a certain wavelength

range.


Solar spectroscopy

What do we know?

The Sun is a huge ball of plasma – a gas which is not

neutral but contains free electric charges

– Although one speaks of the solar surface, the Sun has neither

solid or liquid matter anywhere inside it.

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Solar spectroscopy

What do we know? • Constitution

– Sun’s energy output comes from nuclear reactions at centre

– Energy transported outwards through radiative zone then convective zone

– 70% hydrogen, 28% helium (by mass)

• Photosphere

– Temperature ~ 5800 K

– Sunspots

• Chromosphere

– Temperature ~ 20 000 K

• Corona

– Temperature ~ 1 million K (!!!)

– Visible only during solar eclipses with the unaided eye

– Holes

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Solar spectroscopy

Dr Nicolas Labrosse - Talk to Renfrewshire Astronomical Society 18

Courtesy G. Doschek

Solar spectroscopy


Courtesy G. Doschek

Solar spectroscopy

26/01/2012 Dr Nicolas Labrosse - Talk to Renfrewshire Astronomical Society 21 Courtesy H. Peter

Solar spectroscopy


Solar spectroscopy

Multi-wavelength view of the solar atmosphere

(SDO/AIA)

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Solar spectroscopy

X-ray and EUV spectroscopy

• Visible to ~1900 Å: Dominated by the continuum, mostly absorption lines

• 1700 – 1100 Å: The photosphere, chromosphere, lower transition region. A

few coronal lines for above the limb (no coronal disk observations)

– Temperatures from 10 000 K to about 250 000 K

• 1100 Å – 500 Å: the lower and upper transition region but limited coronal

access for disk observations, some forbidden lines for flares, e.g., Fe XVII,

Fe XVIII, Fe XIX, Fe XXII

– Temperatures from 250 000 K up to about 1 million K

• 500 Å – 170 A: the corona and flares (some transition region lines)

– Temperatures from about 800 000 K up to about 20 million K

• Below 170 Å : flare allowed lines of Fe XVIII through Fe XXIII between about

90 Å and 140 Å.


Solar spectroscopy


Solar spectroscopy

Line intensity and width (Hinode/EIS obervations)


Solar spectroscopy

Hinode/EIS observations of solar flares


Data from a major solar flare that occurred near Sun center on 18 February 2011.

The strong signal at 192.0 Å shows that the temperature in the flare has reached

15 million degrees!

Solar spectroscopy

Summary

• Solar spectroscopy tells us how the solar atmosphere is

structured...

• ... and points to what we need to work on in the future

– Solve the puzzle of the hot corona

– Identify mechanisms behind energy transport, bulk flows, particle

acceleration, ...

• A rich discipline relying on complex quantum mechanics

calculations to predict the spectra emitted by atoms, ions,

and molecules


Solar spectroscopy

Additional information and resources

• K. M. Harrison, "Astronomical Spectroscopy for

Amateurs". Patrick Moore's Practical Astronomy Series.

Springer, 2011. ISBN 9781441972385


Solar spectroscopy

Documents

Transcript of Solar spectroscopy