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From Bolometric to Monochromatic

From Bolometric to Monochromatic. One isochrone of given (AGE,Z) is {m, L, Te}. {R g Te}. Divide isochrone in small cells with (m,L,Te) Each cell corresponds to (g,Te)  F λ (m) either observed stellar spectra or model atmospheres

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From Bolometric to Monochromatic

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  1. From Bolometric to Monochromatic One isochrone of given (AGE,Z) is {m, L, Te} {R g Te} Divide isochrone in small cells with (m,L,Te) Each cell corresponds to (g,Te)  Fλ(m) either observed stellar spectra or model atmospheres R  Lλ(m) Then sum up along the isochrone Get the Spectral Energy Distribution of the SSP Compute Colors by convolving with photometric system Lectures on Stellar Populations

  2. An Alternativebest suited for FCT applications The monochromatic contributions of the PMS phases are weighted with the Fuel Burned in each phase Lectures on Stellar Populations

  3. Exercise: the Bolometric Correction of an SSP The Bolometric Correction of each portion of the isochrone is weighted by its contribution to the bolometric light: cells with a small contribution to total L are not important to the bolometric correction of the SSP Lectures on Stellar Populations

  4. Contributions of individual phases At short wavelenghts we see the MS (turn off, mostly) In the K band the MS is never important Notice the AGB phase transition and the RGB dominating past approx 3 Gyr Lectures on Stellar Populations

  5. Contributions of individual phases: Z dependence BOL: MS,AGB,RGB V: MS, RGB At Low Z HB is important K: AGB and RGB Lectures on Stellar Populations

  6. Calibration of AGB Total Fuel will depend on Z More important: The C - M share depends on Z Based on: dependence of envelope mass at the first pulse on age; scaling of Renzini & Voli models behaviour with metallicity Lectures on Stellar Populations

  7. SSPs at AGB phase transition In the optical there’s no difference In the IR the flux is 3 times higher than without TP AGB Notice the strong absorption features due to C (C2, CN) and M (TiO,H2O) stars The V-K color jumps by more than 1 mag Lectures on Stellar Populations

  8. SSPs across AGB phase transition At higher Zs the O-rich stars are favoured At older ages the TP AGB becomes less important Lectures on Stellar Populations

  9. SSP: Integrated Colors Older SSPs are redder Metal rich SSPs are redder Past 2-3 Gyr the colors dependence on age is mild Frascati vs Padova tracks: B-V bluer with Padova Larger TO mass at given age V-K redder with Padova Redder RGB at solar Z The discrepancy between The various authors is > than the systematics due to the use of different tracks Lectures on Stellar Populations

  10. Integrated Colors: Comparison with ObservationsOLD SSPs Models: Maraston 2004 13 Gyr old SSPs blue and intermediate HB at [Z/H]<-1 solid Kroupa dashed; Salpeter dotted Bruzual & Charlot 2003 Data: MW Globulars from Harris et al. [Z/H] on Zinn & West scale Colors are not affected by IMF Most lum comes from stars within a small mass range Agreement is good but for B-V Likely Color-Temperature transformation Lectures on Stellar Populations

  11. Integrated Colors: Comparison with ObservationsINTERMEDIATE AGE Filled circles: MC Globulars with SWB type in 3 – 6 (several authors) Models: younger than 2 Gyr and with Z=0.5 Zo solid Maraston 2004 dashed PEGASE dotted Bruzual & Charlot 2003 Optical – IR colors span a wide range among these clusters: a sizeable effect from the development of the AGB must be present Open Triangles: Clusters in NGC7252, a merger remnant Lectures on Stellar Populations

  12. SEDs: Comparison with ObservationsACROSS the AGB PHASE TRANSITION Lectures on Stellar Populations

  13. Mass to Light Ratios IMF effect M/L increases with age in every band But notice the AGB phase transition in K M/L increases with Z But notice the small span in the K band Reasonable agreement among authors Notice the Y scale BC2003 have different tracks Worthey : possibly too much light on RGB Vazdekis ? Lectures on Stellar Populations

  14. What have we learnt • Each isochrone portion contributes to the total BC factor weighted by its contribution to the total bolometric light of the SSP • Short wavelenghts (U,B,V) best sample the MS Turn off • Long wavelenghts (IR) best sample RGB and AGB • The contribution of the various phases in the various bands depend on Z at low Z the HB becomes important in optical light at high Z the MS always dominates the optical • The treatment of the TP AGB is very critical for SSPs between 0.2 – 2 Gyr still a lot of work to do, but a sizeable contribution from this phase IS needed • Considerable discrepancies still in the integrated colors from different authors because of (a) different tracks (b) different atmospheres (c) different codes • M/L ranges from about unity to about tens from young to old SSPs • In the K band the M/L ratio is almost independent of metallicity Lectures on Stellar Populations

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