Effects of Non-Solar Abundance Ratios on Star Spectra: PowerPoint Presentation, PPT - DocSlides

Effects of Non-Solar Abundance Ratios on Star Spectra: PowerPoint Presentation, PPT - DocSlides

2015-11-20 33K 33 0 0

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. Comparison of Observations and Models.. Overview. :-. Importance of element abundances. New measurements. Comparisons with models. . Spectra and line strengths. Interpretation, . SNIa. timescales and improvements.. ID: 199411

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Presentations text content in Effects of Non-Solar Abundance Ratios on Star Spectra:

Slide1

Effects of Non-Solar Abundance Ratios on Star Spectra: Comparison of Observations and Models.

Overview:-Importance of element abundancesNew measurementsComparisons with models Spectra and line strengthsInterpretation, SNIa timescales and improvements.

Anne

Sansom Andre Milone (INPE), Alex Vazdekis (IAC) + extended MILES team.

Slide2

Importance of element abundances

Affects stellar atmosphere models, structure, spectra.

Stars summed to give simple stellar populations (SSPs).

SSPs used to interpret star cluster & galaxy spectra:

age, chemistry, IMF, duration of SF (SNII/SNIa), SFH etc.Response functions R = changes of Lick line strengths to element abundance changes from theoretical star spectra of Korn et al. (2005).Example applications:-

Thomas, Johansson, Maraston (2010, 2011)Used R of Korn et al. (2005).Derived Ages, and 6 elements [X/Fe] for X=C,N,O,Mg,Ca,Ti (if [Fe/H]>-1 dex. Investigated chemical patterns in globular clusters.

Annibali

et al. (2011)Used R of R Korn et al. (2005).Derived Ages, & [/Fe] for dwarf and giant galaxies. Find strong morphology – [/Fe] relation (=ETG dwarf, = bright ETG).

Slide3

Comparison between spheroidsGreen=E,S0 Red=S bulges Blue=LLE,E(Sansom & Northeast 2008)

Trends of abundance patterns with

galaxy  and age.

Slide4

Importance of element abundances

[

/Fe] ratios used as a

clock

for SF timescales and extents:-SNII provide rapid enrichment (,Fe rare elements) (108>t>3106 yrs)SNIa provide extended enrichment over time (Fe) (prompt+delayed, t>108 yrs?)IMS provide C,N,O enrichment (t>108 yrs)Uncertainties:-

E.g. Tout 2005; Hashisu et al. 2008; Claeys et al. 2011Enrichment from SNIa - Uncertain progenitors (SD,DD,H,He,MCh,SubMCh...?) and timescale (delay time distributions).

Importance

:-

We

need to be able to

accurately measure

[

α

/Fe] ratios

in stellar populations to be able to

interpret them accurately

.

Slide5

New spectral measurements

Magnesium sensitive features

at 5183 Å and 5528 Å - Measured [Mg/Fe] for 752 stars in MILES stellar library. (HR & MR results).[Mg/Fe] as a proxy for [/Fe].(Milone, Sansom & Sanchez-Blazquez 2011 Fig 3).See also the Poster by Milone et al. on abundance ratio measurements.

Example star:

Slide6

[Mg/Fe] proxy for [/Fe](Milone et al. 2011: [Mg/Fe] catalogue)

HR

Mg5183

Mg5548

Both

Slide7

Model and Observed spectral changes: Varying [/Fe]

MILES spectral rangeRecent models by Coelho et al. 2007Observations :-MILES stellar library (Sanchez-Blazquez et al. 2006 – Teff, Log(g), [Fe/H]) Extended to include [Mg/Fe] (Milone et al. 2011) & [O/H] via Bensby et al. 2004, 2010.

Cassisi

et al. 2004 models.

Slide8

Ratios of enhanced /solar spectra Comparison of observations and theory

Dwarf stars

Theoretical (

Coelho et al. 2007

)

Empirical (MILES library 2006)

Ratio = Dwarf stars: (Teff=5500K, Log(g)=4.0, [Z/H]=0.0) Giant stars: (Teff=4500K, Log(g)=2.0, [Z/H]=0.0) Find: Excess flux in blue region of enhanced spectra. Differences between obs. & theory. E.g. CaHK, Mg3835, CNO3862 (Serven et al. 2005).

CNO3862

CN 

Mgb 

00

Theoretical (Coelho et al. 2007)

Empirical (MILES library 2006)

Giant stars

Slide9

Element response functions

Base model SSPs (empirical or theoretical spectra)Spectral line strengths (optical) versus Age & [Fe/H]Lick standard – Worthey et al 2004, 2007Abundance pattern (theoretical spectra of stars)Differential corrections. Approximate (weak lines) R=Response fn (Xi2Xi) Xi=element iCorrect from base star (I0) to new star [Fe/H], then [/Fe].Response functions by Korn et al. 2005 (K05) widely used.Plot ratios of new/base indices for stars with the same Teff, Log(g).

Slide10

Testing K05 Response functions: Fe-sensitive indicesObservations versus models

Key: = 1:1 line (agreement) = Cool dwarf stars (CD) = Turnoff stars (TO) = Cool giant stars (CG)Open symbols = low [Fe/H] <-0.4Error bars are plotted on base stars.

Similarly good agreement for other Fe sensitive features

(Fe4383, Ca4455, Fe4531, C

2

4668, Fe5015, Fe5270, Fe5335, Fe5406)

plus weaker features (Fe5709, Fe5782).

Model ratio

Slide11

Testing K05 Response functions: Fe-sensitive indices

Obs. versus modelsKey: = 1:1 line (agreement) = Cool dwarf stars (CD) = Turnoff stars (TO) = Cool giant stars (CG)Open symbols = low [Fe/H] <-0.4Error bars are plotted on base stars.

Slide12

Testing K05 Response functions: H-Balmer indicesObservations versus models

Key:

= 1:1 line (agreement)

= Cool dwarf stars (CD) = Turnoff stars (TO) = Cool giant stars (CG)Open symbols = low [Fe/H] <-0.4Error bars are plotted on base stars.

Slide13

Testing K05 Response functions: -element indicesObservations versus models

Key: = 1:1 line (agreement) = Cool dwarf stars (CD) = Turnoff stars (TO) = Cool giant stars (CG)Open symbols = low [Fe/H] <-0.4Error bars are plotted on base stars.

Slide14

Results:

Fe sensitive features well modelled by K05 response functions (R[X/H]). H Balmer features – models differ from observations:– H insensitive to [/Fe] in CG & TO .– H, K05 underestimates R for TO , over for CD & CG . Mg, Ca, CN sensitive features – larger scatter (>errors). Caution for extrapolation (e.g. Mg1 TO ). Differences between empirical and theoretical [/Fe] effects on spectra. Particularly important in the blue (<4500 Å). Empirical library will help to calibrate spectral responses to abundances. New observations underway to improve coverage for [/Fe] range.

U

B

V

R

Blue excess for [

/Fe]=0.4

Slide15

Summary and Interpretation

Element response functions R:-

Fe indices – work well

H-

Balmer

systematics

– need revisiting

Mg, Ca, CN indices – large scatter but expected trends

Empirical stellar libraries:-

Vital for testing spectral dependence on

abundance patterns

MILES library now has [Mg/Fe] measurements

Will improve

-element measurements in populations

UV/Blue part most sensitive to abundance pattern.

Future:-

H-

Balmer

indices – side bands influence on [/Fe] dependence.

New features in the blue can now be explored.

SNIa

contributions need better understanding (level, progenitors, timing) for [/Fe] interpretation of extended SFHs.


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