Effects of Non-Solar Abundance Ratios on Star Spectra: PowerPoint Presentation, PPT - DocSlides
. 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: 199411Embed code:
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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.
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.
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.
Importance of element abundances
/Fe] ratios used as a
for SF timescales and extents:-SNII provide rapid enrichment (,Fe rare elements) (108>t>3106 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).
need to be able to
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.
[Mg/Fe] proxy for [/Fe](Milone et al. 2011: [Mg/Fe] catalogue)
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.
et al. 2004 models.Slide8
Ratios of enhanced /solar spectra Comparison of observations and theory
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).
Theoretical (Coelho et al. 2007)
Empirical (MILES library 2006)
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 (Xi2Xi) 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
4668, Fe5015, Fe5270, Fe5335, Fe5406)
plus weaker features (Fe5709, Fe5782).
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
= 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
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.
Blue excess for [
Summary and Interpretation
Element response functions R:-
Fe indices – work well
– need revisiting
Mg, Ca, CN indices – large scatter but expected trends
Empirical stellar libraries:-
Vital for testing spectral dependence on
MILES library now has [Mg/Fe] measurements
-element measurements in populations
UV/Blue part most sensitive to abundance pattern.
indices – side bands influence on [/Fe] dependence.
New features in the blue can now be explored.
contributions need better understanding (level, progenitors, timing) for [/Fe] interpretation of extended SFHs.