From Bolometric to Monochromatic

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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?(m)
either observed stellar spectra or model
atmospheres
R
? L?(m)
Then sum up along the isochrone Get the Spectral
Energy Distribution of the SSP Compute Colors by
convolving with photometric system
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An Alternativebest suited for FCT applications
The monochromatic contributions of the PMS phases
are weighted with the Fuel Burned in each phase
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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
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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
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Contributions of individual phases Z dependence
BOL MS,AGB,RGB
V MS, RGB At Low Z HB is important
K AGB and RGB
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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
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SSPs at AGB phase transition
In the optical theres 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
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SSPs across AGB phase transition
At higher Zs the O-rich stars are favoured
At older ages the TP AGB becomes less important
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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
gt than the systematics due to the use of
different tracks
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Integrated Colors Comparison with
ObservationsOLD SSPs
Models Maraston 2004 13 Gyr old SSPs blue and
intermediate HB at Z/Hlt-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
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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 Z0.5 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
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SEDs Comparison with ObservationsACROSS the
AGB PHASE TRANSITION
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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 ?
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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