A hands-on lesson on classical spectroscopic methods

A hands-on lesson on classical spectroscopicmethods

Maria Tsantaki

Osservatorio Astrofisico di Arcetri-INAF

22 September 2021

Stellar spectroscopy and Astrophysical parametrisation from Gaia to LargeSpectroscopic surveys, 21-23 September 2021

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Outline

- How to create a synthetic spectrum

- How to derive atmospheric parameters with spectral synthesis(Teff , log g , [M/H], vmic, vmac, vsini)

- How to derive chemical abundances with spectral synthesis

- How to derive atmospheric parameters from the EW of iron(Teff , log g , [Fe/H], vmic)

- Examples

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What’s on the market?

Synthesis (with EW analysis) Equivalent Width Machine Learning

iSpec (Blanco-Cuaresma+ 2014) FAMA (Magrini+ 2013) The Cannon (Ness+ 2015)

fasma (Tsantaki+ 2018) ARES+MOOG (Sousa+ 2008) The Payne (Ting+ 2019)

SME (Piskunov+ 2017) GALA (Mucciarelli+ 2013) NN for RAVE (Guiglion+ 2020)

BACCHUS (Masseron+ 2016) StePar (Tabernero+ 2019) ML for APOGEE (Garcia-Dias+ 2018)

... ... ...

There are also hybrid methods: e.g. SP Ace (Boeche+ 2016),MATISSE (Recio-Blanco+ 2006)Differences on:

- analysis methods- model atmosphere physics- time consumption- atomic line data- a few publicly available (and fewer user friendly)- many, many more ...

Choose your package depending on the specific problem(e.g. spectral type, rotation, resolution)

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1. How to create a synthetic spectrum

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1. How to get the flux at the top of the photosphere

Ingredients:

• Stellar atmospheric parameters (Teff , log g , [M/H], vmic)• Model atmosphere

- MARCS (LTE, plane parallel/spherical geometry): cool stars- Kurucz (LTE, plane parallel): extended grid- TLUSTY (non-LTE, plane parallel): hot stars

• Line data: wavelengths, excitation potentials, oscillatorstrengths, broadening parameters

- Vienna Atomic Line Database (VALD)- National Institute of Standards & Technology (NIST) Database

• Radiative solver

- MOOG- Turbospectrum

• Convolution with rotation kernels (vmac, vsini) &instrumental resolution

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1. How to get the flux at the top of the photosphere

Ingredients:

• Stellar atmospheric parameters (Teff , log g , [M/H], vmic)• Model atmosphere







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Let’s create a Sun!

Ingredients:

• Stellar atmospheric parameters (5777, 4.44, 0.0, 1.0)• Model atmosphere







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Ingredients:








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Let’s create a Sun!Caution: Spectral synthesis is model dependent!• Stellar atmospheric parameters (5777, 4.44, 0.0, 1.0)• Model atmosphere

- MARCS (LTE, plane parallel/spherical geometry): cool stars

Interpolation within the grids in needed.

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+ optical depth at standard wavelengths+ temperature in K+ number density of free electrons+ number density of all other particles= Calculate the radiative transfer equation → Flux

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Interpolation within the grids in needed(e.g. scipy.interpolate.griddata)

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Interpolation within the grids in needed(e.g. scipy.interpolate.griddata)

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Ingredients:








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Let’s create a Sun!Ingredients:• Stellar atmospheric parameters (5777, 4.44, 0.0, 1.0)• Model atmosphere


• Line data: wavelengths, excitation potentials (EP), oscillatorstrengths (loggf), broadening parameters (vdwaals)

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Tsantaki+ 2018

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0.75

0.8

0.85

0.9

0.95

1

6091 6092 6093 6094 6095

Nor

mal

ized

flux

Wavelength (Å)

υsini = 10 km/sυsini = 15 km/sυsini = 20 km/s

υsini = solar

Caution on rotation16 / 52




0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

6497.5 6498 6498.5 6499 6499.5 6500 6500.5 6501

Flu

x

Wavelength

Fe

I −−

Fe

I −−

R=110k (HARPS)R=48k (FEROS)

R=17k (GIRAFFE)R=2500 (VIMOS)

Caution on resolution17 / 52


Ingredients:








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Let’s create a Sun!Ingredients:





• Radiative solver- MOOG- Turbospectrum


astropy: pyasl.rotBroad, pyasl.instrBroadGaussFast19 / 52

Let’s create a Sun!Putting everything together

python-based spectral synthesis package:github.com/MariaTsantaki/FASMA-synthesis

yalm configuration file

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github.com/MariaTsantaki/FASMA-synthesis

Questions?

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2. How to derive stellar parameters

[

lT[

�4

Modelspectrum

Observedspectrum

Comparison

Basicmodelatmospheretheory(usuallytailoredtoagivenclassofstars):non-LTE(NLTE),3Dhydrodynamics,magneticfields,winds,

sphericity,molecularopacities,binarity,chromospheres,etc

Stellarparameters:Teff,

surfacegravity(P)velocities,

chem.abundancesupto100dimensions!

SpectrumsynthesisModelatmosphere

Credit to M. Bergemann

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Pre-process the observed spectrum

• input format (fits, dat)

• cosmetic improvements

• wavelength re-sampling

• (local) normalization

Minimization process

• χ2 minimization (mpfit,Levenberg-Marquardt)

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• initial conditions

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• refine minimization options

- clean for bad/missing lines

- vmic: Teff ,log g , [Fe/H](Tsantaki+ 2013, Mortier+ 2013)

- vmac: Teff (Valenti+ 2005)

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• refine minimization options

• fixed parameters

- log g : seismic, trigonometric

- vmic: Teff , log g , [Fe/H](Tsantaki+ 2013, Mortier+ 2013)

- vmac: Teff (Valenti+ 2005)

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Error analysis

High resolution

−100

−50

0

50

100

∆ T

eff

(K)

Sun Procyon Arcturus HD201891 del Eri

−0.2

−0.1

0

0.1

0.2

∆ l

og

g (

dex

)

−0.1

0

0.1

0 50 100 150 200 250 300

∆ [

M/H

] (d

ex)

S/N

(Tsantaki+ 2014) 34 / 52


Error analysis

−200

−100

0

100

200

∆ T

eff

(K)

Procyon Sun Arcturus del Eri HD201891

−0.3

−0.2

−0.1

0

0.1

0.2

0.3

∆ l

og

g (

dex

)

−0.2

−0.1

0

0.1

0.2

0 5 10 15 20 25 30 35 40 45 50

∆ [

M/H

] (d

ex)

vsini (km/s)

(Tsantaki+ 2014) 35 / 52


Error analysis

−300

−200

−100

0

100

200

300

1 1.5 2 2.5 3 3.5 4 4.5 5

∆ T

eff

(K)

logg (dex)

−300

−200

−100

0

100

200

300

−3 −2.5 −2 −1.5 −1 −0.5 0 0.5∆

Tef

f (K

)

[Fe/H] (dex)

−1.5

−1

−0.5

0

0.5

1

1.5

4000 5000 6000

∆ l

ogg (

dex

)

Teff (K)

−1.5

−1

−0.5

0

0.5

1

1.5

−3 −2.5 −2 −1.5 −1 −0.5 0 0.5

∆ l

ogg (

dex

)

[Fe/H] (dex)

−0.4

−0.2

0

0.2

0.4

4000 5000 6000

∆ [

Fe/

H]

(dex

)

Teff (K)

−0.4

−0.2

0

0.2

0.4

1 1.5 2 2.5 3 3.5 4 4.5 5

∆ [

Fe/

H]

(dex

)

logg (dex)

Correlations in parameters with the benchmark values (Tsantaki+2014)

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Putting everything together!

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Questions?

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3. How to derive chemical abundances

- Overall metallicity ([M/H]) is derived from all the elements ina region

- Individual chemical abundances ([El/H]) are derived for aspecific element

• Create a synthetic spectrum of aknown star (Teff , log g , [M/H],vmic, vmac, vsini) of the specificspecies

• [El/H] is the only free parameter

• χ2 minimization → best-fit value

• Select from: Li, Na, Mg, Al, Si,Ca, Sc, Ti, V, Cr, Mn, and Ni

e.g. Lithium

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3. How to derive chemical abundances

Putting all together!

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Questions?

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5. The Equivalent Width method

Ingredients:

• Line list of neutral (FeI) and ionized species (FeII)

• EW measurements (IRAF, daospec, ARES)

• Calculate [Fe/H] from the curve of growth

• Model atmospheres (MARCS, Kurucz)

• excitation balance of FeI lines → Teff

ionization balance of FeI and FeII lines → log g

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5. The Equivalent Width methodIngredients:• Line list of Fe isolated lines

-400

-200

0

200

4500 5000 5500 6000 6500

Thi

s W

ork

- SO

08

Teff (K) This Work

4500

5000

5500

6000

6500

Tef

f (K

) SO

08

<∆Teff

>=-31 K

σ=53 K

• EW measurements (IRAF, daospec, ARES)• Calculate [Fe/H] from the curve of growth• Model atmospheres (MARCS, Kurucz)• excitation balance of FeI lines → Teff

ionization balance of FeI and FeII lines → log g43 / 52

5. The Equivalent Width methodIngredients:

• Line list of Fe isolated lines

• EW measurements with ARES

• Calculate [Fe/H] from the curve of growth

• Model atmospheres (MARCS, Kurucz)



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Ingredients:



• Calculate [Fe/H] from the curve of growth: MOOG+MARCS



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7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8

0 1 2 3 4 5

A(F

e I)

E.P. (eV)

7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8

-5.8 -5.6 -5.4 -5.2 -5 -4.8 -4.6

A(F

e I)

Reduced EW

Fe I = Fe II

- Microturbulence:A(FeI) vs reduced EW (=log EW /λ)

- Teff : Excitation BalanceAll abundances from Fe should agreefor all excitation potentials

- log g : Ionization BalanceAverage logA obtained fromdiffering ionization stages mustagree

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5. The Equivalent Width methodIngredients:• EW measurements with ARES• Calculate [Fe/H] from the curve of growth: MOOG+MARCS• excitation balance of FeI lines → Teff


(Andreasen+ 2017)47 / 52






(Andreasen+ 2017)

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www.iastro.pt/fasma

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www.iastro.pt/fasma

References

• Books- The Observation and Analysis of

Stellar Photospheres, Gray D.,Cambridge University Press, 2015

• Free packages for parameters- SME (Valenti+ 1996)- GALA (Mucciarelli+ 2013)- FAMA (Magrini+ 2013)- q2 (Ramirez+ 2014)- iSpec (Blanco-Cuaresma+ 2014)- fasma (Tsantaki+ 2018)- StePar (Tabernero+ 2019)

• Radiative transfer codes- MOOG (Sneden+ 1973)- SYNTHE (Kurucz+ 1981)- SPECTRUM (Gray+ 1992)- Turbospectrum (Plez+ 2012)

• Model atmospheres- Kurucz (Kurucz+ 1999)- PHOENIX (Hauschildt+ 1997)- MARCS (Gustafsson+ 2008)

• Atomic data / Line lists- NIST (Kramida+ 2020)- VALD (Ryabchikova+ 2015)- Kurucz (Kurucz 1995)- Surveys: Gaia-ESO, APOGEE- Specific for K-type (Tsantaki+

2013)- Specific for M-type (Marfil+ 2021)

• Free packages for EWs- ARES (Sousa+ 2007)- DAOSPEC (Stenson+ 2008)- VoigtFit (Krogager+ 2018)

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Finally remarksThings conviniently neglected:

• Non-LTE

• 3D hydrodynamics

• magnetic fields

• winds

• sphericity

• molecules

Don’t use the codes as black boxes. Be patient... astronomers arenot programers.

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8. Exercise

Your turn!

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Documents

A hands-on lesson on classical spectroscopic methods