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:
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.
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).
Comparison between spheroids Green=E,S0 Red=S bulges Blue=LLE,E (Sansom & Northeast 2008) Trends of abundance patterns with galaxy and age.
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. 2011 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.
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:
[Mg/Fe] proxy for [ /Fe] (Milone et al. 2011: [Mg/Fe] catalogue) HR Mg5183 Mg5548 Both
Model and Observed spectral changes: Varying [ /Fe] MILES spectral range Recent models by 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. Cassisi et al. 2004 models.
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
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. 2005 (K05) widely used. Plot ratios of new/base indices for stars with the same T eff, 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. 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
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: 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.
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.
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
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.