last modification: 6 Dec 2005
This database contains the grid of evolutionary tracks described in Pietrinferni, Cassisi, Salaris & Castelli (2006, ApJ, 642, 797) - in Pietrinferni, Cassisi, Salaris & Castelli (2004, ApJ, 612, 168) - Cassisi, Salaris, Castelli & Pietrinferni (2004, ApJ, 616, 498) - - Cassisi, Pietrinferni, Salaris, Castelli, Cordier & Castellani (2005, MmSAI, 77, 71). Both stellar evolution models and isochrones, stored in this archive, have been extended along the Asymptotic Giant Branch (AGB) stage to cover the full thermal pulse phase, using the synthetic AGB technique (Iben & Truran 1978, ApJ, 220, 980) (see below).
The models do not include gravitational settling, radiative acceleration, convective overshooting, rotational mixing, but otherwise they are based on up-to-date physics, as detailed in the quoted paper.
We strongly encourage people interested in a specific set of evolutionary tracks (not yet available in this database) to contact us, either by e_mail or by compiling the request form (present in this web site). We'll try to perform these computations within a week upon receiving the request.
We have presently stored evolutionary models with the following chemical compositions:
| |||
The values Z=0.0198 (zsun) and Y=0.2734 (ysun) correspond to the abundances obtained from the calibration of the solar model (for more details we refer to Pietrinferni et al. 2004).
All models have been computed by using the following alpha enhanced heavy elements distribution:
|
All models include mass loss according to the Reimers (1975) law (eta=0.2 and eta=0.4) and the mass range goes from 0.5Mo to 10.0Mo. Please note that the mass spacing is suitably small: we adopt a mass step equal to, respectively, 0.1Mo in the range (0.5 - 2.6) Mo, 0.2Mo between 2.6Mo and 3.0Mo, and 0.5Mo for more massive models.
Each file contains:
in the fifth line - 1) the number of evolutionary points, 2) the global metallicity [M/H], 3) the abundance by mass of metals (Z), 4) the initial He abundance (Y), 5) the inital mass (in solar unit); starting from the ninth line the following quantities are listed:
1 column) the logarithmic of the age in years; 2 column) the logarithmic of the surface luminosity in solar unit; 3 column) the logarithmic of the effective temperature (K); 4 column) the present mass in solar unit; 5 column) the visual absolute magnitude; 6 column) the (B-V) color; 7 column) the (U-B) color; 8 column) the (V-I) color; 9 column) the (V-R) color; 10 column) the (V-J) color; 11 column) the (V-K) color; 12 column) the (V-L) color; 13 column) the (H-K) color;from the Zero Age main Sequence until the first few thermal pulses (for masses larger than about 0.7Mo).
We have employed a simplified treatment of the AGB synthetic evolution that - as demonstrated by the few tests shown below - allows one to reproduce satisfactorily several integrated properties of stellar populations in the near-IR bands, which are greatly affected by the presence of AGB thermal pulsing stars. Given that the purpose of this library of stellar models and isochrones is to provide a reliable tool to be employed in stellar population synthesis studies, we feel confident that our simplified AGB treatment is adequate for our purposes.
For each stellar model of a given initial chemical composition and mass, we started the synthetic AGB
evolution at the beginning of the Thermal Pulse (TP) phase, where the full evolutionary models were stopped.
The first model of the synthetic TP-AGB evolution is characterized by the total mass M,
Carbon-Oxygen (CO) core mass Mco, luminosity L, effective temperature Teff
and surface chemical composition (X,Y,Z) of the last fully evolutionary model.
The TP-AGB phase is then followed by increasing (after a given timestep dt) Mco and
L according to Eqs. 5-7 in Wagenhuber & Groenewegen (1998, A&A, 340, 183 - WG98), which contain a
term mimicking the effect of the Hot Bottom Burning, when appropriate.
The hydrogen mass fraction in the envelope (an input of Eq. 6 of WG98)
is approximated as 1-(Y+0.01)-Z all along the TP evolution.
Mass loss from the envelope is included using Eqs. 17-18 in Girardi & Bertelli (1998, MNRAS, 300, 533).
For any given value of M and Mco, the effective temperatures are
computed using the relationships plotted in Fig.8 of WG98 (see Wagenhuber 1996, PhD thesis, TU Muenchen).
To ensure continuity, the zero points of the equations describing the evolution of L,
Mco and Teff have been adjusted to reproduce the corresponding values of the last
fully evolutionary model, at the beginning of the TP phase.
The synthetic evolution is stopped when the mass of the envelope has been reduced below 10-4 Mo.
At this stage the models have already started to evolve at constant luminosity towards their White Dwarf
cooling sequence.
From the full evolution extended until the end of the TP phase we have computed theoretical isochrones in exactly the same way as for the non extended models. The only difference is that we added two additional key-point (key-point number 17 and 18 - see below ), corresponding respectively to the start of the first TP and to the end of the TP phase, when the models start to turn towards higher Teff. A total of 10 points is distributed between key-points 16 and 17, and 240 points are distributed between key-points 17 and 18. The total number of points along each isochrone is 2250.
Broadband colours and magnitudes of both models and isochrones have been computed by supplementing the
transformations used in
Cassisi et al.(2004, ApJ, 616, 498) with the Westera et al.(2000, A&A, 381, 524) ones
for RGB and AGB stars with Teff < 3750K. To ensure continuity, the bolometric corrections and
colours of Westera et al.(2000) have been shifted to match the other sets of transformations when
Teff = 3750K.
Along the TP-AGB phase, when the (J-K) colours reach (J-K)=1.2 mag,
we used the (J-K)-Teff and (H-K)-Teff relationships by Bergeat, Knapik & Rutily (2001, A&A, 178, 209)
that are appropriate in the Carbon star regime.
The coding of the file names is as follows:
abcdZedfYghiaes_agb.nor_c05ext | | evolutionary track for a model with --> initial mass = ab.cd Mo --> metallicity Z= e.d x 10^(-f) --> initial He abundance Y = 0.ghi --> misture = aplha enhanced (ae)
The suffix "s" denotes models computed by adopting a Standard evolutionary scenario (no atomic diffusion, no overshooting). The suffix "nor" indicates that the evolutionary sequence has been "reduced" to a suitable number of points. This has been accomplished by fixing some key stage along the evolutionary path, and distributing for each track the same number of points between two consecutive stages. This allows a straightforward interpolation for producing isochrones of a given age, and for determining tracks and isochrones for other metallicities within the range spanned by the computed grid of models.
Example: 0130z402y303aes_agb.nor_c05ext ---> 1.30 Mo AGB-extended canonical model with Z=4.0E-2 and Y=0.303 |
The whole set of evolutionary tracks can be downloaded as a single compressed tar archive.
As for the choice of the key stages, we provide some information in the following.
In the present version of BASTI, we have accounted for 17 key stages along the evolutionary track, more in detail:
Low-mass stars denotes in this case all objects which do not develop a convective core during the whole central H-burning phase; the high-mass structures are all the others.
For those structures which do not present the Bump along the RGB, we have - arbitrarily - chosen as representative of the key points 6 and 7, two points whose brightness was intermediate between the luminosities corresponding to the key points 5 and 8.
For those structures which do not experience the TP-AGB phase (i.e. those models which ignite C-burning) we have - arbitrarily - chosen as representative of the key points 17 and 18 the evolutionary stages immediately subsequent that chosen as key point 16.
The correspondence between key stages and rows is the following:
For more details about the adopted key stages, please contact one of the authors.
In the following we show some comparisons between various empirical evidence and theoretical predictions based on scaled-solar set of AGB-extended stellar models:
Our best regards!!!
Request Form |