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Effects of Non-Solar Abundance Ratios on Star Spectra: Comparison of Observations and Models. Anne Sansom Andre Milone (INPE), Alex Vazdekis (IAC) + extended MILES team. Overview :- Importance of element abundances New measurements Comparisons with models

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effects of non solar abundance ratios on star spectra comparison of observations and models

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

Anne Sansom

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

Overview:-

Importance of element abundances

New measurements

Comparisons with models

Spectra and line strengths

Interpretation, SNIa timescales and improvements.

importance of element abundances
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 spectraof Korn et al. (2005).

Example applications:-

Annibali et al. (2011)

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

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.
comparison between spheroids green e s0 red s bulges blue lle e sansom northeast 2008
Comparison between spheroidsGreen=E,S0Red=S bulgesBlue=LLE,E(Sansom & Northeast 2008)

Trends of abundance patterns with galaxy  and age.

importance of element abundances1
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. 2011

  • Enrichment 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.
new spectral measurements
New spectral measurements

Example star:

  • Magnesium sensitive featuresat 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 2011Fig 3).

See also the Poster by Milone et al. on abundance ratio measurements.

model and observed spectral changes varying fe

Cassisi et al. 2004 models.

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

MILES spectral range

Recent modelsby Coelho et al. 2007

Observations :-

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.

ratios of enhanced solar spectra comparison of observations and theory
Ratios of enhanced /solar spectra Comparison of observations and theory

CNO3862

Giant stars

Dwarf stars

CN

Mgb

Theoretical (Coelho et al. 2007)

Theoretical (Coelho et al. 2007)

Empirical (MILES library 2006)

Empirical (MILES library 2006)

00

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).

element response functions
Element response functions
  • Base model SSPs (empirical or theoretical spectra)
    • Spectral line strengths (optical) versus Age & [Fe/H]
    • Lick standard – Worthey et al 2004, 2007
  • Abundance pattern (theoretical spectra of stars)
    • Differential corrections. Approximate (weak lines)
    • R=Response fn (Xi2Xi)

Xi=element i

    • Correct 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).
testing k05 response functions fe sensitive indices observations versus models

Key:

= 1:1 line (agreement)

= Cool dwarf stars (CD)

= Turnoff stars (TO)

= Cool giant stars (CG)

Open symbols = low [Fe/H] <-0.4

Error bars are plotted on base stars.

Testing K05 Response functions: Fe-sensitive indicesObservations versus models

Model ratio

Similarly good agreement for other Fe sensitive features

(Fe4383, Ca4455, Fe4531, C24668, Fe5015, Fe5270, Fe5335, Fe5406)

plus weaker features (Fe5709, Fe5782).

testing k05 response functions fe sensitive indices

Obs. versus models

Key:

= 1:1 line (agreement)

= Cool dwarf stars (CD)

= Turnoff stars (TO)

= Cool giant stars (CG)

Open symbols = low [Fe/H] <-0.4

Error bars are plotted on base stars.

Testing K05 Response functions: Fe-sensitive indices

testing k05 response functions h balmer indices observations versus models

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] <-0.4

Error bars are plotted on base stars.

testing k05 response functions element indices observations versus models

Key:

= 1:1 line (agreement)

= Cool dwarf stars (CD)

= Turnoff stars (TO)

= Cool giant stars (CG)

Open symbols = low [Fe/H] <-0.4

Error bars are plotted on base stars.

Testing K05 Response functions: -element indicesObservations versus models

results

Fe sensitive features well modelled by K05 response functions (R[X/H]).

  • H Balmerfeatures – models differ from observations:
    • – H insensitive to [/Fe] in CG & TO .
    • – H, K05 underestimates R for TO , over for CD & CG .
  • Mg, Ca, CNsensitive 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.

Results:

Blue excess for [/Fe]=0.4

B

V

R

U

summary and interpretation

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.