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

1. 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.

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 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.

3. Comparison between spheroidsGreen=E,S0Red=S bulgesBlue=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) (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.

5. 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.

6. [Mg/Fe] proxy for [/Fe](Milone et al. 2011: [Mg/Fe] catalogue) HR Mg5183Mg5548Both

7. 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.

8. 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).

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 (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).

10. 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).

11. 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

12. 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.

13. 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

14. 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

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.