June 2006Lectures on Stellar Populations Bolometric Corrections and Colors We do not observe Bolometric, we observe through filters: system throughput depends on Teff, gravity and Z depends on.... stellar radius

June 2006Lectures on Stellar Populations Average of Observed Stellar Spectra: Dwarfs O e+14 A e+11 G e+10 M e+09 TSp T(K) F c.g.s.

June 2006Lectures on Stellar Populations Dwarfs SED & Filters IVB U Cool stars detected in Red Hot stars detected in Blue BC strongly depends on TSp COLORS: are Temperature Indicators Cool stars are Red Hot stars are Blue

June 2006Lectures on Stellar Populations Effect of gravity Gravity effects are very Important for very cool stars A0 B0 B5 K5 M2 M5

June 2006Lectures on Stellar Populations COLORS: Empirical Johnson 1966 ARAA B-V colors are good Teff indicators for late A, F, G and early K stars For Hot stars TSp is preferred

June 2006Lectures on Stellar Populations Bolometric Corrections: Empirical Hottest and Coolest stars are 3-4 mags fainter in V than in Bolometric Gravity dependence can amount to 0.5mags

June 2006Lectures on Stellar Populations Model Atmospheres: Kurucz Grid revised by Castelli ModelsEmpirical

June 2006Lectures on Stellar Populations Model Atmospheres: dependence on gravity ModelsEmpirical

June 2006Lectures on Stellar Populations Model Atmospheres: dependence on Metallicity Blanketing Molecules

June 2006Lectures on Stellar Populations 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 calibrationcalibration Produce Tables of BC, Col function of (Teff,Log g, [M/H])

June 2006Lectures on Stellar Populations Balmer Jump Go Back

June 2006Lectures on Stellar Populations Colors from Model Atmospheres Origlia and Leitherer 1998: Bessel, Castelli and Pletz models through Ground Based Filters

June 2006Lectures on Stellar Populations 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:

June 2006Lectures on Stellar Populations 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 )

June 2006Lectures on Stellar Populations M&M: attach empirical calibrations Montegriffo et al. (1998) traslated Go back

June 2006Lectures on Stellar Populations 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.color-temperaturecolor-colorBC-color relations Conclude that : 1.There is a general good agreement for most of the parameter space 2.B-V predicted too blue for late type stars, likely due to missing atomic and molecular opacity 3.NMARCS to be preferred to ATLAS9 below 4000 K

June 2006Lectures on Stellar Populations Hot Dwarfs A-K Dwarfs GKM Giants The models are shown as curves The data are shown as points The ptype encodes the literature source

June 2006Lectures on Stellar Populations Dwarfs Giants K NM

June 2006Lectures on Stellar Populations Giants Dwarfs

June 2006Lectures on Stellar Populations BaSeL Grid (Lejeune, Cuisinier and Buser ) 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

June 2006Lectures on Stellar Populations Lejeune Models: Z dependence Check 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

June 2006Lectures on Stellar Populations 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 STELIB – Le Borgne et al spectra between 3200 and 9500 A, sp.res. ~ 3 A INDO-US – Valdes et al spectra between 3460 and 9464 A with smaller wavelength range sp. res. ~ 1 A

June 2006Lectures on Stellar Populations 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 Interrogation tool to search in the Database is included

June 2006Lectures on Stellar Populations 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

June 2006Lectures on Stellar Populations Martins et al Check versus STELIB stars Check versus INDO-US stars

June 2006Lectures on Stellar Populations Other Models: 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 K 4000 to K Log g from 1 to 5 0 to 5 [M/H] from -2.5 to to +0.3 Munari et al. : spectra between 2500 and A with res of ~1 A cover Te from 3500 to K, Log g from 0 to 5 [M/H] from -2.5 to +0.5 and [A/Fe]=0,+0.4 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

June 2006Lectures on Stellar Populations Converted Tracks: B and V

June 2006Lectures on Stellar Populations Converted Tracks: V and I

June 2006Lectures on Stellar Populations 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.

June 2006Lectures on Stellar Populations Uncertainty of Stellar Models Gallart, Zoccali and Aparicio 2005 compare various sets of models (isochrones) to gauge the theoretical uncertainty when computing simulations with one set.

June 2006Lectures on Stellar Populations 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

June 2006Lectures on Stellar Populations Deriving metallicity from RGB The RGBs can be very different especially at high Z The difference is already substantial at M I =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.

June 2006Lectures on Stellar Populations 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.

June 2006Lectures on Stellar Populations 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.

June 2006Lectures on Stellar Populations 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, as they 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.