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Bolometric Corrections and Colors. depends on .... stellar radius. system throughput. We do not observe Bolometric, we observe through filters:. depends on Teff, gravity and Z. Average of Observed Stellar Spectra: Dwarfs. TSp T(K) F c.g.s. B. V. I. U. Dwarfs SED & Filters. - PowerPoint PPT Presentation
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June 2006 Lectures on Stellar Populations
Bolometric Correctionsand Colors
We do not observe Bolometric, we observe through filters:
oioi
ii M
L
LLogM ,
,
5.2
0
dSLL ii
system throughput
kL
LLogMMBC
iiboli
5.2 k
F
FLog
i
5.2
depends on Teff, gravity and Z
depends on .... stellar radius
ijjiBCBCCol
June 2006 Lectures on Stellar Populations
Average of Observed Stellar Spectra:Dwarfs
O 50000 3.5e+14
A 10000 5.7e+11
G 6000 7.3e+10
M 3500 8.5e+09
TSp T(K) F c.g.s.
June 2006 Lectures on Stellar Populations
Dwarfs SED & Filters
IVB
U
Cool stars detected in Red
Hot stars detected in Blue
BC strongly depends on TSp
COLORS:
kL
LLogMM
2
121 5.2
are Temperature Indicators
Cool stars are Red
Hot stars are Blue
June 2006 Lectures on Stellar Populations
Effect of gravity
Gravity effects are very
Important for very cool stars
A0
B0
B5
K5
M2
M5
June 2006 Lectures on Stellar Populations
COLORS: Empirical
Johnson 1966 ARAA 4 193
B-V colors are good Teff indicators
for late A, F, G and early K stars
For Hot stars TSp is preferred
June 2006 Lectures 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 2006 Lectures on Stellar Populations
Model Atmospheres:Kurucz Grid revised by Castelli
Models Empirical
June 2006 Lectures on Stellar Populations
Model Atmospheres:dependence on gravity
Models Empirical
June 2006 Lectures on Stellar Populations
Model Atmospheres:dependence on
Metallicity
Blanketing
Molecules
June 2006 Lectures 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 calibration
Produce Tables of BC, Col function of (Teff ,Log g, [M/H])
June 2006 Lectures on Stellar Populations
oV
obol
V
bolV
oVobolVo
V
bolV
F
FLog
F
FLogBC
MMBC
kF
FLogBC
,
,
,,
5.25.207.0
07.0
5.2
Vega
Vega
Vega
F
FLog
F
FLogCol
Col
kF
FLogCol
,2
,1
2
1
2
1
5.25.2
0
5.2
Balmer Jump
Go Back
June 2006 Lectures on Stellar Populations
Colors from Model Atmospheres
Origlia and Leitherer 1998: Bessel, Castelli and Pletz models through Ground Based Filters
June 2006 Lectures 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 2006 Lectures 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 2006 Lectures on Stellar Populations
M&M: attach empirical calibrations
Montegriffo et al. (1998) traslated
Go back
June 2006 Lectures 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.
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 2006 Lectures 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 2006 Lectures on Stellar Populations
Dwarfs
Giants
K
NM
June 2006 Lectures on Stellar Populations
GiantsDwarfs
Dwarfs
June 2006 Lectures on Stellar Populations
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
June 2006 Lectures on Stellar Populations
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 calibrationIn terms of Z which is consistent with both color –temperatureRelations AND GCs ridge lines (with existing isochrones)”
Westera et al. 2002
June 2006 Lectures 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 Librariestake a sample of well observed stars with known parameters Log Te, Log g, [Fe/H]
and derive their spectra
STELIB – Le Borgne et al. 2003249 spectra between 3200 and 9500 A, sp.res. ~ 3 A
INDO-US – Valdes et al. 2004 885 spectra between 3460 and 9464 A+ 400 with smaller wavelength rangesp. res. ~ 1 A
June 2006 Lectures on Stellar Populations
ADSD: DATA BASE OF DATA BASES
Sordo and Munari 2006:
WEB interface to access to aLarge (294) number of spectroscopic Databases
Total number of stars is 16046
Interrogation tool to search in theDatabase is included
June 2006 Lectures on Stellar Populations
Libraries with high Spectral resolution
THEORETICAL MODELSUsually 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 ASpecial care to describe non-LTE and sphericity effects
June 2006 Lectures on Stellar Populations
Martins et al. 2005
30262 4.18 0.02
13622 3.80 0.05
7031 4.04 0.01
4540 0.88 0.02
3700 1.3 0.01
3540 0 0.02
Check versus STELIB stars
Check versus INDO-US stars
3910 1.6 0.01
300004.50.02
140004.50.02
35001.00.01
45000.00.01
70004.00.02
40001.00.02
35000.00.02
June 2006 Lectures on Stellar Populations
Other Models:
Bertone et al. : 2500 spectra with resolution of ~ 0.3 A UV grid Optical gridbetween 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
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
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 2006 Lectures on Stellar Populations
Converted Tracks: B and V
June 2006 Lectures on Stellar Populations
Converted Tracks: V and I
June 2006 Lectures 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 2006 Lectures 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 2006 Lectures on Stellar Populations
Age-dating from Turn-off Magnitude
In general the turn-off magnitudeat given age agrees
Teramo models fit the turn offMagnitude with older ages(at intermediate ages)
Notice some difference in isochrone shapes , and SGBfor old isochrones
June 2006 Lectures on Stellar Populations
Deriving metallicity from RGB
The RGBs can be very differentespecially at high Z
The difference is already substantialat MI=1.5 where the BCs can stillbe trusted (Te ~ 4500)
The comparison to Saviane’s linesSeem to favour Teramo at high Z,but the models do not bendenough at the bright end.
June 2006 Lectures on Stellar Populations
Deriving distance from RGB Tip
The RGB Tip is an effective distance indicator in the I band and at low ZsThe theoretical location depends on the bolometric magnitude and onThe BC in the I band.
There is a trend of Padova models to yield relatively faint TRGB atall metallicities.
Observations are not decisive,But undersampling at TRGB shouldlead to systematically faint observed TRGB.
June 2006 Lectures on Stellar Populations
Magnitude location of the HB
The HB luminosity can be used as distance indicator as well as to deriveAges 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 thanTeramo.
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 sameTeff point in both observations and models.
June 2006 Lectures 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 withinput 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.