Bolometric Corrections and Colors

1. Bolometric Correctionsand Colors depends on .... stellar radius system throughput We do not observe Bolometric, we observe through filters: depends on Teff, gravity and Z Lectures on Stellar Populations

2. Average of Observed Stellar Spectra:Dwarfs TSp T(K) F c.g.s. Lectures on Stellar Populations

3. B V I U Dwarfs SED & Filters BC strongly depends on TSp Cool stars detected in Red Hot stars detected in Blue COLORS: are Temperature Indicators Cool stars are Red Hot stars are Blue Lectures on Stellar Populations

4. B0 M5 B5 M2 K5 A0 Effect of gravity Gravity effects are very Important for very cool stars Lectures on Stellar Populations

5. Johnson 1966 ARAA 4 193 COLORS: Empirical B-V colors are good Teff indicators for late A, F, G and early K stars For Hot stars TSp is preferred Lectures on Stellar Populations

6. Bolometric Corrections: Empirical Hottest and Coolest stars are 3-4 mags fainter in V than in Bolometric Gravity dependence can amount to 0.5mags Lectures on Stellar Populations

7. Models Empirical Model Atmospheres:Kurucz Grid revised by Castelli Lectures on Stellar Populations

8. Model Atmospheres:dependence on gravity Models Empirical Lectures on Stellar Populations

9. Molecules Blanketing Model Atmospheres:dependence on Metallicity Lectures on Stellar Populations

10. Model Atmospheres:Calibration • The Models do a good job for the SED of Dwarfs, especially for intermediate Spectral Types • Not too bad for Giants and Supergiants also • Major problems are met al low Temperatures (Opacity, Molecules) • Anyway, the use of Model Atmospheres becomes a MUST because: they allow us to compute Colors and BCs for various Metallicities AND for whatever filters combinations To do that we: Take a grid of Models Perform calibration Produce Tables of BC, Col function of (Teff ,Log g, [M/H]) Lectures on Stellar Populations

11. Balmer Jump Go Back Lectures on Stellar Populations

12. Colors from Model Atmospheres Origlia and Leitherer 1998: Bessel, Castelli and Pletz models through Ground Based Filters Lectures on Stellar Populations

13. Bolometric Correction from Model Atmospheres Nice and smooth BUT Probably off for Late K and M stars Have you noticed that lines of different colors Span different Temperature Range? THIS IS NOT A SUPERMONGO FALIURE: Lectures on Stellar Populations

14. Tracks on the Log Teff – Log g Plane WE LACK LOW GRAVITY MODELS FOR MASSIVE STARS WE LACK LOW TEMPERATURE AND LOW GRAVITY MODELS FOR LOW MASS STARS (AT HIGH METALLICITIES) Lectures on Stellar Populations

15. M&M: attach empirical calibrations Go back Montegriffo et al. (1998) traslated Lectures on Stellar Populations

16. Bessel, Castelli & Pletz (1998, A&A 333, 231) Compare Kurucz’s revised models (ATLAS9)+ Gustafsson et al revised (NMARCS) models for red dwarfs and giants to empirical colors and BCs for stars in the Solar Neighbourhood (i.e. about solar metallicity). They show color-temperature, color-color, and BC-color relations. Conclude that : • There is a general good agreement for most of the parameter space • B-V predicted too blue for late type stars, likely due to missing atomic and molecular opacity • NMARCS to be preferred to ATLAS9 below 4000 K Lectures on Stellar Populations

17. A-K Dwarfs Hot Dwarfs GKM Giants The models are shown as curves The data are shown as points The ptype encodes the literature source Lectures on Stellar Populations

18. NM K Dwarfs Giants Lectures on Stellar Populations

19. Dwarfs Giants Dwarfs Lectures on Stellar Populations

20. BaSeL Grid(Lejeune, Cuisinier and Buser 1997 +) • Collect Model Atmospheres from Kurucz • +Bessel + Fluks (for RGs) + Allard (for M dwarfs) • Correct the model spectra so as to match empirical • calibration • Put the corrected models on the net Lectures on Stellar Populations

21. Lejeune Models: Z dependenceCheck with Globulars’ Ridge Lines BaSeL 2.2 : Corrected Models at solar Z & Z theoretical dependence BaSeL 3.1: Corrected models at various Z based on GCs Ridge Lines 5 GGs with [Fe/H]=-2.2 to -0.7 in UBVRIJHKL For each get Te from V-K (using BaSel 2.2)  BCs vs (Te,g) BaSeL 3.1 Padova 2000: Correction at various Z made to match GCs Ridge Lines with Padova 2000 isochrones ”It is virtually impossible to establish a unique calibration In terms of Z which is consistent with both color –temperature Relations AND GCs ridge lines (with existing isochrones)” Westera et al. 2002 Lectures on Stellar Populations

22. Libraries with high Spectral resolution Recently developed for Population Synthesis Studies, Stellar spectroscopy, Automatic Classification of Stellar and Galaxy Spectra … not so important for Broad Band Colors Observational Libraries take a sample of well observed stars with known parameters Log Te, Log g, [Fe/H] and derive their spectra INDO-US – Valdes et al. 2004 885 spectra between 3460 and 9464 A + 400 with smaller wavelength range sp. res. ~ 1 A STELIB – Le Borgne et al. 2003 249 spectra between 3200 and 9500 A, sp.res. ~ 3 A Lectures on Stellar Populations

23. ADSD: DATA BASE OF DATA BASES Sordo and Munari 2006: WEB interface to access to a Large (294) number of spectroscopic Databases Total number of stars is 16046 Interrogation tool to search in the Database is included Lectures on Stellar Populations

24. Libraries with high Spectral resolution THEORETICAL MODELS Usually constructed on top of a model atmosphere (Kurucz) + Code for synthetic spectrum which solves monochromatic radiative transport with a large list of lines not very important for broad band colors, but could suggest diagnostic tools Martins et al. 2005: 1654 spectra between 3000 and 7000 A with sp. res. ~0.3 A Special care to describe non-LTE and sphericity effects Lectures on Stellar Populations

25. Check versus STELIB stars Check versus INDO-US stars Martins et al. 2005 30000 4.5 0.02 3500 1.0 0.01 3700 1.3 0.01 30262 4.18 0.02 14000 4.5 0.02 4000 1.0 0.02 3910 1.6 0.01 13622 3.80 0.05 7000 4.0 0.02 3500 0.0 0.02 3540 0 0.02 7031 4.04 0.01 4540 0.88 0.02 4500 0.0 0.01 Lectures on Stellar Populations

26. Other Models: Munari et al. : 67800 spectra between 2500 and 10500 A with res of ~1 A cover Te from 3500 to 47500 K, Log g from 0 to 5 [M/H] from -2.5 to +0.5 and [A/Fe]=0,+0.4 Bertone et al. : 2500 spectra with resolution of ~ 0.3 A UV grid Optical grid between 850 and 4750 A 3500 and 7000 A Te from 3000 to 50000 K 4000 to 50000 K Log g from 1 to 5 0 to 5 [M/H] from -2.5 to +0.5 -3 to +0.3 Coelho et al. : spectra between 3000 and 1800 A with res of ~0.02 A cover Te from 3500 to 7000 K, Log g from 0 to 5 [M/H] from -2.5 to +0.5 and [A/Fe]=0,+0.4 Lectures on Stellar Populations

27. Converted Tracks: B and V Lectures on Stellar Populations

28. Converted Tracks: V and I Lectures on Stellar Populations

29. What have we learnt When passing from the theoretical HRD to the theoretical CMD we should remember that: • At Zo the model atmospheres are adequate for most TSp • There are substantial problems for cool stars, especially at low gravities • The theoretical trend with Z is not well tested • The tracks on the CMD reflect these uncertainties The transformed tracks make it difficult to sample well the upper MS (large BC); the intermediate MS merges with the blue part of the loops; the colors (and the luminosities) of the Red giants and Supergiants are particularly uncertain. Lectures on Stellar Populations

30. Uncertainty of Stellar Models Gallart, Zoccali and Aparicio 2005compare various sets of models (isochrones) to gauge the theoretical uncertainty when computing simulations with one set. Lectures on Stellar Populations

31. Age-dating from Turn-off Magnitude In general the turn-off magnitude at given age agrees Teramo models fit the turn off Magnitude with older ages (at intermediate ages) Notice some difference in isochrone shapes , and SGB for old isochrones Lectures on Stellar Populations

32. Deriving metallicity from RGB The RGBs can be very different especially at high Z The difference is already substantial at MI=1.5 where the BCs can still be trusted (Te ~ 4500) The comparison to Saviane’s lines Seem to favour Teramo at high Z, but the models do not bend enough at the bright end. Lectures on Stellar Populations

33. Deriving distance from RGB Tip The RGB Tip is an effective distance indicator in the I band and at low Zs The theoretical location depends on the bolometric magnitude and on The BC in the I band. There is a trend of Padova models to yield relatively faint TRGB at all metallicities. Observations are not decisive, But undersampling at TRGB should lead to systematically faint observed TRGB. Lectures on Stellar Populations

34. Magnitude location of the HB The HB luminosity can be used as distance indicator as well as to derive Ages of GCs, from the difference between the HB and the TO luminosity (dependence on Z is crucial for this). • The models show substantial discrepancies, • again with Padova models fainter than • Teramo. • Observations are very discrepant as well; • major difficulties stem from • the correction for luminosity evolution on the • Horizontal Branch; • the necessity to trace the ZAHB to the same • Teff point in both observations and models. Lectures on Stellar Populations

35. Summary • The TO magnitude at given age of the stellar population seems • independent of the set of tracks , except for obvious systematics with • input physics (but Teramo models need further investigation) • this feature can be safely used for age-dating; • The TO temperatures, and in general the shape of the isochrones, seems • more uncertain, asthey differ in different sets; • The colors of RGB stars and their dependence on metallicity are very • uncertain; the derivation of Z and Z distribution from RGB stars needs • a careful evaluation on systematic error; • The magnitude level of the ZAHB and its trend with Z show a substantial • discrepancy in the various sets of models AND in the various observational • data sets. This is a major caveat for the distance and age determinations • based on the level of HB stars.A theoretical error of about 0.2 is also to • be associated to the distance determination from the TRGB. Lectures on Stellar Populations