Spectroscopy in Different Wavelength Regimes of … › lectures › ADSEM › WS0809_Kupka.…SPECTROSCOPY IN DIFFERENT WAVELENGTH REGIMES Advisor Seminar ‟Nuclei in the Cosmos”

SPECTROSCOPY IN DIFFERENT WAVELENGTH REGIMES

Advisor Seminar ‟Nuclei in the Cosmos”January 14th, 2009

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Spectroscopy in Different Wavelength Regimes of Astronomy

Friedrich KupkaMax-Planck-Institute for Astrophysics

Hydrodynamics [email protected]

based on seminar material kindly provided by Roland Diehlpresented in the ‟Advisor Seminar” held during WS 2006/2007

and on material for the lecture course ‟Introduction to Astrophysics” held during WS 2004/2005 by Friedrich Kupka

mailto:[email protected]

mailto:[email protected]



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Astronomical Spectroscopy I



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Astronomical Spectroscopy IITopics covered in the following• Introduction focussing on stellar spectroscopy in the optical region

– spectral classification: the role of temperature, pressure, chemical composition

– diffusion processes, time dependent spectroscopy, Doppler imaging

• Spectroscopy in different wavelength bands (for various objects)– the ultraviolet (UV) regime: interstellar medium (ISM) spectroscopy– X-ray studies of galaxy-cluster gas and of accretion (examples for

optical and X-ray regions)– γ-ray studies: nuclear processes and the ISM of our galaxy– infrared (IR) studies of interstellar dust– studies at radio wavelengths: CO emission and the 21 cm line of H in

our galaxy



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Spectral Classification I• Early history of spectral classification– Pioneering studies were first carried out by Fraunhofer in 1815 in

Munich. He discovered the ‛Fraunhofer’ absorption lines of the Sun. – Kirchoff and Bunsen in Heidelberg identified the D-lines as sodium-

absorption in the Sun and other stars (1859). They also discovered the previously unknown elements caesium and rubidium.

– Doppler predicts the ‛Doppler’-effect in 1842 in Vienna. Scheiner in Potsdam and Keeler at Lick Observatory verified his prediction around 1890.

– The spectral classification was started by Secchi and Vogel and improved by Draper around 1880. Under surveillance of Annie Jump Cannon the extended Henry-Draper catalogue with 200000 stars is compiled from 1918–1924 using objective prism plates.



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Spectral Classification II

examples from the original Harvard sequence



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Spectral Classification IIIPage 22

Variation of absorption lines along the Harvard sequence, i.e. as a function of Teff

Roman number indicate the ionization stage of the atoms: e.g., H I means neutral hydro-gen, He II corresponds to He+, Si III to SI++ etc.

Astrophysics Introductory Course Fall 2002



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Stellar RadiationRadiation depends on conditions at its origin• temperature

– of molecules and dust– of neutral an ionised atoms

• pressure (respectively density)• chemical composition

– abundance of species (atom, molecule, ...) emitting / absorbing the radiation

– abundance of other species involved in creating the radiation• velocity fields at the origin (Doppler effect)• magnetic fields (Zeeman effect)



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Spectral Classification IV

Harvard sequence: pressure dependence at a given temperature ― the influence of gravity at the stellar surface



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Chemical Composition I

Przybylski’s star, Teff ≈6500 K

Procyon, Teff =6540 K



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Chemical Composition IIChemical peculiarities changing observed spectraAnalysis of HD 101065 and comparison with the Sun (cf. C, O, Fe, Nd)(Cowley et al. 2000, Mon. Not. Roy. Astr. Soc. 317, 299)



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Chemical Composition IIIStratification of species in the photosphere of CP2 starsas a function of optical depth at 500 nm: model calculations. Similar profiles are required to reproduce observed spectra (F. LeBlanc et al., T. Ryabchikova, IAU Symp. 224)



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Chemical Composition IVStratification of Ca in the photosphere of γ Equ

(Ryabchikova et al. 2002, Astron. & Astrophys. 384, 545). Black: observed, blue / red: without / with stratification & diffusion. Normalised flux (continuum = 1) as a function of wavelength (1 Å = 0.1 nm).



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Time Resolved Spectroscopy I• Doppler imaging ― an example for time resolved spectroscopy• Aim: invert a time series of high resolution line profiles, for

instance, to a 2D map of a stellar surfaceVisibility and Doppler shifts of profile distortions contain direct information on the latitude and longitude of structures at the stellar surface !

The measurement of wavelength positions of distortions within the line profile broadened due to the Doppler effect permits extraction on information about the longitude.



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• Doppler imaging ― integration of the line profile Il ... intensity with spectral line, IC ... intensity with continuum only ϕ ... azimuthal angle, θ ... polar angle, λ ... wavelength, Δ λD ... Doppler shift, dM ... area

– numerical integration: grid of n steps in latitude and m steps in longitude

• literature– first idea: A. Deutsch, IAU Symp. 6, 209 (1958) (Camb. Univ. Press)– present name of method: S. Vogt et al., Astrophys. Jour. 321, 496 (1987)– good description: N. Piskunov et al., Astron. & Astroph. 230, 363 (1990)

Time Resolved Spectroscopy II

Rcalc(!,") =

∫∫Il[M, #,! + !!D(M,")] cos # dM∫∫

Ic(M, #,!)] cos # dM



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Time Resolved Spectroscopy III

• Construction of the 2D map

– inversion ➔ map surface structure as function of location M(i,j)

– ill posed problem: there is no unique solution !– thus: definition of an error function:

➔ regularized mean quadratic error



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Time Resolved Spectroscopy IV

• Regularization by

– MEM (maximum entropy method) ― considers neighbouring surface elements as independent of each other➔ biased towards structures with high contrast

– or Tikhonov regularization ― smoothes contrast between neighbouring surface elements



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Time Resolved Spectroscopy V

➔ Doppler imaging has the highest spatial resolution among all observational methods used in astrophysics (~10-8 to 10-11 arc seconds !)

The temporal variation of the line profile distortions depends on the latitude of the corresponding surface structures.

The resolution depends on the(thermal, e.g.) Doppler broadening of the (local) line profile (~ΔλDop), as well as on the (projected)rotational velocity vr sin i, (with i = inclination towards the observer), but only indirectly on the distance.



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Kochukhov et al. 2004

Magnetic Doppler Imaging Ireconstruction of the magnetic field and variation of the chemical composition at the surface by time resolved spectropolarimetry over the entire rotational period of 53 Carmelopardalis

meaning of the fourStokes parameters:

I intensityV circular polarizationQ linear polarization (0°)U linear polarization (45°)



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Magnetic Doppler Imaging II

direct comparison of Stokes spectra and solution of the inverse problem

high resolution observations for allfour Stokes parameters

synthetic (calculated) stellar spectra

surface maps (magnetic field, temperature, chemical composition, ...)literature: N. Piskunov, O. Kochukhov, Astron. &

Astrophys. 381, 736 (2002), e.g.



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Koc

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2004



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Koc

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2004



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UV Spectroscopy of the ISM I



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UV Spectroscopy of the ISM II



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X-ray Studies of Galaxy-Cluster Gas I



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X-ray Studies of Galaxy-Cluster Gas IIPredicted X-ray emission ofoptically thin plasma at different temperatures and1/3 of solar element abundance

at increasing temperature more and more elements become completely ionised➔ lines vanish



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X-ray Studies: Accretion I

An example for the optical (visual) spectral region



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X-ray Studies: Accretion II

An example for the X-ray spectral region



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Gamma-rays: Nuclear Processes I



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Gamma-rays: Nuclear Processes II



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Gamma-ray Studies of our Galaxy I



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Gamma-ray Studies of our Galaxy II



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Interstellar Dust and the Infrared I



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Interstellar Dust and the Infrared II



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Radio Emission I



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Radio Emission II



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ConclusionsWhat can we learn from astronomical spectroscopy ?• What are the physical conditions in the region the radiation originates from ?

– temperature, pressure, chemical composition, magnetic fields, flow fields

• What are the physical conditions in region the radiation is passing through ?• Physical processes: radioactive decay, ... ➔ indirect probes of evolution

of the physical system studied• measurement of velocities: Doppler effect ➔ cosmological applications, ...

(not covered in this talk)• ‟tomography”: mapping of astrophysical objects

➔ the full potential of observations of astronomical objects is only unleashed once all possible information carried by photons is analysed: energy, intensity, time dependence, spatial dependence, polarization



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...THANK YOU FOR YOUR TIME !

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Spectroscopy in Different Wavelength Regimes of … › lectures › ADSEM › WS0809_Kupka.…SPECTROSCOPY IN DIFFERENT WAVELENGTH REGIMES Advisor Seminar ‟Nuclei in the Cosmos”