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Effects of Non-Solar Abundance Ratios on Star Spectra: Comparison of Observations and Models. Overview:-  Importance of element abundances  New measurements.

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Presentation on theme: "Effects of Non-Solar Abundance Ratios on Star Spectra: Comparison of Observations and Models. Overview:-  Importance of element abundances  New measurements."— Presentation transcript:

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

2 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).

3 Comparison between spheroids Green=E,S0 Red=S bulges Blue=LLE,E (Sansom & Northeast 2008) Trends of abundance patterns with galaxy  and age.

4 Importance of element abundances [  /Fe] ratios used as a clock for SF timescales and extents:- – SNII provide rapid enrichment ( ,Fe rare elements) (10 8 >t>3  10 6 yrs) – SNIa provide extended enrichment over time (Fe) (prompt+delayed, t>10 8 yrs?) – IMS provide C,N,O enrichment (t>10 8 yrs) Uncertainties:- E.g. Tout 2005; Hashisu et al. 2008; Claeys et al Enrichment from SNIa - Uncertain progenitors (SD,DD,H,He,M Ch,SubM Ch...?) 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.

5 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:

6 [Mg/Fe] proxy for [  /Fe] (Milone et al. 2011: [Mg/Fe] catalogue) HR Mg5183 Mg5548 Both

7 Model and Observed spectral changes: Varying [  /Fe] MILES spectral range Recent models by Coelho et al Observations :- MILES stellar library (Sanchez-Blazquez et al – Teff, Log(g), [Fe/H]) Extended to include [Mg/Fe] (Milone et al. 2011) & [O/H] via Bensby et al. 2004, Cassisi et al models.

8 Ratios of enhanced /solar spectra Comparison of observations and theory Dwarf stars Theoretical (Coelho et al. 2007) Empirical (MILES library 2006) Ratio = Dwarf stars: (T eff =5500K, Log(g)=4.0, [Z/H]=0.0) Giant stars: (T eff =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

9 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 (X i  2X i ) X i =element i – Correct from base star (I 0 ) to new star [Fe/H], then [  /Fe]. – Response functions by Korn et al (K05) widely used. Plot ratios of new/base indices for stars with the same T eff, Log(g).

10 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. Similarly good agreement for other Fe sensitive features (Fe4383, Ca4455, Fe4531, C , Fe5015, Fe5270, Fe5335, Fe5406) plus weaker features (Fe5709, Fe5782). Model ratio

11 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.

12 Testing K05 Response functions: H-Balmer 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.

13 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.

14 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

15 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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