Tips for measuring Equivalent Widths

TipsformeasuringEquivalentWidths

@DrJorgeMelendezDep.Astronomia,Univ.SãoPaulo

LineprofileisconvoluFonofGaussian&Lorentzian:Voigtprofile

•  Instrumentalprofileis~Gaussian

EquivalentWidth(EW)measurements:nottrivial

GaussianVoigtLorentzian

EquivalentWidth(EW)measurements:nottrivial

H.-G. Ludwig, 2012

“Caffau et al. like”

“Asplund et al. like”

73mÅ

82mÅ

61mÅ48mÅ

69mÅ54mÅ

Oxygen triplet in the Sun EW using Voigt profiles for both Asplund & Caffau

CN blends for O I triplet (Meléndez,IAUSymp)

CNblendsmustbetakenintoaccount,otherwisetheEWmaybeoverorunderesDmated

Other blend

CN CN CN CN CN CN

VoigtprofilerequiresbothLorentzian&Gaussianbroadening

V (Δν,ΔνD,γ ) =γ 4π 2

(Δν −Δν1)2 + (γ 4π )2

*0

∞

∫ 1π 1 2ΔνD

e−

ΔνΔνD

%

&'

(

)*2

dν1

D.Gray

OxygentripletintheSunandsolartwin18Sco

Sun18Sco

JorgeMelendez,fromUVESspectra

Gaussianprofilesarepreferred:moreprecisedifferenFalmeasurements

R=110000

Themostimportant(anddemanding)partinthedifferenFalworkaretheEWmeasurements

•  Evenifyou’reusingsophisFcatedmodelatmospheresorlineformaFon,yourresultswillbewrongifthemeasurementsarewrong

•  DifferenFalmeasurements:makethesame(sensible)choicesforyourstar&standard

•  AllstartswithacarefullineselecFon

Case study: carbon l Higherabsoluteabundances!

C I

CN

l CIlinesat7111,4&7113,2Å

CN

CN

CN CN CN

CN CN CN CN

C I

EquivalentWidthsforPrecisionSpectroscopy

Hand(manualmeasurements).

ForautomaFcEW:DAOSPEC,iSpec,ARES….

DifferenFalabundancesAX(elementX)log (W/λ) = cte + AX + log (g f ) + log λ - θ χexc - log kcont,λ

Bedell, Meléndez, Bean et al. 2014

1.  PrecisedifferenFalEWmeasurementsarekeyforPreciseAbundances

2.Line-by-linedifferenFalmethodworksbekerfortwinstars

SomeFps•  TrytodoconsistentobservaFonsusingthesameinstrument/configuraFon.

•  VerifyyourrelaFveconFnuumnormalizaFon

Measuringlines•  Wheneverpossiblechoosethecleanestlines•  Ifthelinesarenotperfectlyclean,trytochoosealineclosetoaconFnuumregion

Bedelletal.2014,ApJ,795,23

Measuringlines

Bedelletal.2014,ApJ,795,23

NHintheultraviolet,toobtainnitrogenabundances

NH

UVAtlaso

fthe

Arcturus(andSolar)Spe

ctrum1150-3800A,H

inkleetal.2005

conFnuum

Solartwinspectra

•  HIP79672.fits(18Sco,3Gyr)•  Juno.fits(Sun,4.6Gyr)•  HIP102152.fits(oldsolartwin,7Gyr)

Linelist(sun2015_05_18.moog)Lambdaionexc.potlog_gfC60.0EWcomment4788.75726.03.237-1.7630.175E-310.067.7FeII

-PlotstarandstandardtochoosebestconFnuumregion

-Useawindowof~5-6Å,meaning±3Åfromlinecenter(insomecasesalargerwindowmaybeneeded)

Ex.:FeI4950.1Å(usingUVESspectra):splotHIP102152xmin=4947.1xmax=4953.1

ConFnuumregiontoosmall(±1Å)

VerifyingconFnuumwithsolaratlas

Wallaceetal.2011

Beker,±2,5Åor±3Å

FiHngaVoigtprofile:uncertainwings

Deblendingusinggaussians:carefulaboutuncertainFesin(exaggerated)

contribuFonofcomponents!

Usingasinglegaussian:carefulaboutusingthewholewings(blendscontribute)

Usingasinglegaussian:carefulaboutusingthewholewings(blendscontribute)

RecommendedforprecisiondifferenFalabundances

Overploqng(“o”“g”…)Sun’sspectrum

GoodconFnuumpoints

HIP102152

Limitstofitthelineprofile(“k”“k”withsplot)

MeasuringFeIlineinHIP102152“k”insplot(atthechosenconFnuumand

letlimitforprofilefiqng)

MeasuringFeIlineinHIP102152“k”insplot(atthechosenconFnuumand

rightlimitforprofilefiqng)

EW=79,0mÅ

MeasuringFeIlineintheSun“k”atchosenconFnuumandlet/rightlimits

EW=78,5mÅ

kk

FeI4994,1ÅHIP102152 Sun

GoodconFnuumpoints

Limitstofitthelineprofile(“k”“k”withsplot)

EW=108,9mÅinHIP102152

EW=107,4mÅinSun

EW=107,8mÅinHIP79672(18Sco)

HIP102152 Sun

GoodconFnuum

point

Deblending3linesinHIP102152

Deblending3linesinHIP102152

Deblending3linesinHIP102152

Deblending3linesinHIP102152

FeIlineat5577Å

FeIlineat5577Å

GoodconFnuumpoint

HIP102152:12,3mÅ,Sun(Juno):11,8mÅ18Sco(HIP79672):12,9mA

NaIat6160.8Å:inclinedconFnuum

Bedelletal.2014,ApJ,795,23

ConFnuumhasslopedueto(Lorentzian)wingofstrongnearbyline

NaI

gaussiangaussian

Voigt

PerhapstryasinglegaussianwithlocalconFnuum.Borderlinecase:eitherflator

someslopeshouldbeOK

FinalFp:trytohaveagood

sampleoflines

(differentexc.potandlinestrengths)