Stelle ed evoluzione chimica

The Chemical Evolution of the Milky Way 23-27 Jan. 2012, Sesto 

Stellar parameters, ages and distances in F,G,K stars 

from spectra analysis via Lick/SDSS indices 

M. Franchini, C. Morossi, P. Di Marcantonio 

INAF-Osservatorio Astronomico Trieste, Italy 

M.L. Malagnini 

Dip. Astronomia, Univ. Trieste, Italy 

INAF-Osservatorio Astronomico Trieste, Italy 

M. Chavez 

INAOE, Mexico 

A. Spagna, M.Lattanzi 

INAF-Osservatorio Astronomico Torino, Italy 

+ F. Venturi & M. Pinamonti 

undergraduate students 

INAF – Osservatorio Astronomico di Trieste M. Franchini

Main Goals 

To study the chemo-dynamical properties of the 

different groups of stars of our Galaxy as traced by 

intermediate and late type stars (F,G,K) 

To contribute in understanding the role of different 

sources of chemical enrichment in various epochs of 

the Galaxy lifetime 


Observational databases 

Atmospheric parameters T eff, logg, [Fe/H] 

Chemical composition , [Mg/Fe], [Ca/Fe] 

Radial velocities 

Distances 

Proper motions 

Orbits 

Age 

Ingredients 


•High Resolution 

Pointed observations 

Observational databases 

Huge amount of information 

but 

Time consuming and limited number of objects 

•Medium/Low Resolution (e.g., SDSS, SEGUE, SEGUE-2, LAMOST) 

Extended spatial coverage 

Large and homogeneous number of objects 

but 

low/medium S/N and loss of information due to spectral broadening 



• High Resolution 

Accurate estimates 

but 

Not homogenous estimates and limited number of objects 

• Medium/Low Resolution surveys 

Homogeneous estimates for large number of objects 

but 

Less accurate estimates 



• SPSS (Segue Stellar Parameter Pipeline): 

Provides (table sppParams) individual estimates of T eff, logg, [Fe/H] 

T eff 11 estimates 

Log g 10 estimates 

[Fe/H] 12 estimates 

but (Franchini et al. ApJ 2010, 719, 240) 

Systematic differences are present among the 11 T eff estimates 

Not always T eff, log g, [Fe/H] are simultaneously derived 

Mean values lack of internal consistency 

Systematic overestimates of T eff values for giants 

therefore ….. 

Derived with different techniques 



•From Lick/SDSS library (Franchini et al. ApJ 2011, 730, 117) 

We derive atmospheric parameters on the basis of the Lick/SDSS synthetic 

library (Franchini et al. ApJ 2010, 719, 240) by comparing synthetic and 

observed spectral indices 

Indices are negligibly affected by errors in flux calibration and by 

reddening 

Narrow-band indices allow the measurement of the intensity of features 

of different chemical species separately 

Indices are characterized by higher S/N than the original spectra 

Homogeneous and self-consistent atmospheric parameter estimates 


Lick/SDSS library 

Computed starting from synthetic spectra degraded at R=1800 (like SDSS) 

Two grid of HiRes synthetic spectra: 

Solar Scaled [ /Fe] = +0.0 (SSA) and -enhanced [ /Fe] = +0.4 (NSSA) 

starting from Kurucz atmosphere models (ATLAS9) computed with solar and enhanced 

ODF’s by Castelli (2003) 

using SPECTRUM V.2.75 (Gray and Corbally 1994) 

There is full consistency between synthetic spectra and the ODF 

of the atmosphere models 

Teff : 3500-7000 K (250 K step) 

log g: 0.5- 5.0 dex (0.5 dex step) 

[Fe/H]=-2.5,-2.0,-1.5,-1.0,-0.5,0.0,+0.2,+0.5 (SSA) 

[Fe/H]=-2.5,-2.0,-1.5,-1.0,-0.5,0.0,+0.2,+0.5 (NSSA) 


Lick/SDSS Spectral Indices 

Name Feature Bandpass Pseudocontinua Units IDS Error Measures 

------------------------------------------------------------------------------------ 

01 Cahk 3900.000-4000.000 * 3837.000-3877.000 Ang 0.64 CaII 

4040.000-4080.000 

02 CN 1 4143.375-4178.375 4081.375-4118.875 mag 0.021 CN, FeI 

4245.375-4285.375 

03 CN 2 4143.375-4178.375 4085.125-4097.625 mag 0.023 CN, FeI 

4245.375-4285.375 

04 Ca4227 4223.500-4236.000 4212.250-4221.000 Ang 0.27 CaI, FeI, FeII 

4242.250-4252.250 

05 G4300 4282.625-4317.625 4267.625-4283.875 Ang 0.39 CH, FeI 

4320.125-4336.375 

06 Fe4383 4370.375-4421.625 4360.375-4371.625 Ang 0.53 FeI, TiII 

4444.125-4456.625 

07 Ca4455 4453.375-4475.875 4447.125-4455.875 Ang 0.25 CaI, FeI, NiI, 

4478.375-4493.375 TiII, MnI, VI 

08 Fe4531 4515.500-4560.500 4505.500-4515.500 Ang 0.42 FeI, TiI, FeII, 

4561.750-4580.500 TiII 

9 H beta 4847.875-4876.625 4827.875-4847.875 Ang 0.22 H, FeI 

4876.625-4891.625 

10 Fe5015 4977.750-5054.000 4946.500-4977.750 Ang 0.46 FeI, NiI, TiI 

5054.000-5065.250 

11 Mg1 5069.125-5134.125 4895.125-4957.625 mag 0.007 MgH, FeI, NiI 

5301.125-5366.125 

12 Mg2 5154.125-5196.625 4895.125-4957.625 mag 0.008 MgH, MgI, FeI 

5301.125-5366.125 

13 Mgb 5160.125-5192.625 5142.625-5161.375 Ang 0.23 MgI 

5191.375-5206.375 

14 Fe5270 5245.650-5285.650 5233.150-5248.150 Ang 0.28 FeI, CaI 

5285.650-5318.150 

15 Fe5335 5312.125-5352.125 5304.625-5315.875 Ang 0.26 FeI 

5353.375-5363.375 

16 Fe5406 5387.500-5415.000 5376.250-5387.500 Ang 0.20 FeI, CrI 

5415.000-5425.000 

17 Fe5709 5698.375-5722.125 5674.625-5698.375 Ang 0.18 FeI, NiI, MgI, 

5724.625-5738.375 CrI, VI 

18 Fe5782 5778.375-5798.375 5767.125-5777.125 Ang 0.20 FeI, CrI, CuI, 

5799.625-5813.375 MgI 

19 Na D 5878.625-5911.125 5862.375-5877.375 Ang 0.24 NaI 

5923.875-5949.875 

* 3931.5-3935.5, 3965.5-3970.5 excluded 

[α/Fe] 

sensitive group (red) 

intermediate group 

(green) 

quasi-indipendent 

group (blue). 

Lick-like 

Indices 

(Worthey et al. 1994) 

but 

R=1800 



The reliabilty of the synthetic Lick/SDSS indices in reproducing the 

behaviours of observational ones with T eff, logg, [Fe/H], has been 

tested by using stars and stellar parameters from: 

ELODIES, INDO-US, MILES (EIM) empirical libraries 

541 dwarfs (log g=4.5±0.5) and 391 giants. (log g=2.5±0.5) 


Hß 

dwarfs 

θ 


Hß 

giants 

INAF – Osservatorio Astronomico di Trieste M. Franchini 

θ


Well reproduced 


T Fit, logg Fit, [Fe/H] Fit, Fit 

Best-Fit parameters values (T Fit, logg Fit, [Fe/H Fit, Fit) for each 

star are derived using a χ 2 method to minimize the differences 

between observational and synthetic Lick/SDSS indices 

1. Based on MINUIT minimization package 

2. Internal uncertainties in the derived parameter estimates were evaluated via a 

MonteCarlo technique 

3. Reliability of the results was checked by applying the fitting procedure to a test 

set of the 333 “bona fide” F,G,K (EIM) stars previously selected with very 

reliable atmospheric parameters. 

4. Systematic difference (-0.1 dex) between Fit and [Mg/Fe] (Borkova and 

Marsakov, 2005) values which can be explained recalling that Fit 

estimates the average enhancement of α-elements 


Results for the EIM test sample 





Results for the 

SDSS-DR7 sample 

4381 stars 

Filled histogram 

1880 stars with 

S/N≥30 


CaHK 

Mgb 

Chemical composition [Ca/Fe], [Mg/Fe] 

•The derived Fit values cannot be directly associated with the 

enhancement of any individual α-elements 

•We take advantage of the strong sensitivity of some Lick/SDSS indices 

mainly to [Ca/Fe] or [Mg/Fe] 

___ SSA 

___ NSSA 

Θ=5040/T eff 



For more than 4000 F,G,K stars (sub-set of SDSS-DR7 spectra) the 

abundance ratios [Mg/Fe], [Ca/Fe] were derived by comparing synthetic 

and observational CaHK and Mg2 Lick/SDSS indices: 

1. The two strongest Ca and Mg features in the SDSS wavelength range 

2. Two pairs ( 0.0 CaHK, + 0.4 CaHK) & ( 0.0 Mg2, + 0.4 Mg2) at T Fit, logg Fit, [Fe/H] Fit 

3. We assume a linear dependence of each index on element abundance and we derive 

for each star estimates of [Ca/Fe] and [Mg/Fe] by linear interpolating the 

synthetic pairs at the corresponding CaHK and Mg2 observational values 




To investigate the [Mg/Fe] and [Ca/Fe] scatter 

We need to separate stars belonging to different Galactic component 

Different possibilities --- stars with similar: 

• Kinematics 

• Age 

• birth place / environment 

• Orbital parameters 

We need: 

• distances 

• Radial velocities 

• Proper motions 


Awaiting for GAIA 

Simultaneous Bayesian estimates of spectroscopic 

distances and ages from isochrones: 

We compare stellar position in (logT eff , log g) plane with isochrones 

(Girardi 2004) by using derived Fit to convert measured [Fe/H] Fit 

into [M/H] Fit (Degl’ Innocenti et al. 2005) 

Bayesian technique: 

prob ( Yo| 

X ) 

prob ( X | Yo) 

prob ( Yo ) 

 

prob ( Yo | X ) exp 

prob (X ) 

prob ( X 

([ M / H] 

) 

2 

2 

fit [ 

M / H]) 

(log gfit 

log g) 

(log Tfit 

log T 

2 

2 

Fe 

X physical parameters to be determined (i.e. age, M V) 

Yo the observational quantities (i.e. T eff, log g, [M/H]). 

By integrating over mass and metallicity in fixed intervals of age and M v we 

obtain a bi-dimensional posterior probability P(τ,M v) 

2 

2 

g 

2 

2 

T 


exp 

Prior probability (e.g. IMF, age, Z, …) 

exp 

) 

2

Examples of bi-dimensional posterior probability P(τ,M v) 


Examples of bi-dimensional posterior probability P(τ,M v) 

WARNING. sometimes the τ and M V corresponding to the peak of P(τ,M V) are different from 

those of the maximum of the 1-D P(τ) and of the maximum of the 1-D P(M V), respectively 


Other examples and reliability tests 

• from 

(T eff,M v,[M/H]) 

Blue box is ±2 

• from 

(T eff,logg,[M/H]) 

Contour levels: 

0.8, 0.6, 0.4, 0.2 


Some examples and reliability tests 

EIM stars 

with parallactic 

distances 


Some examples and reliability tests 

Check: Relative distribution of derived ages for 

Hyades MS stars (peak 0.7 Gyr; = 0.6± 0.12 Gyr) 


Orbits 

Back-integrating the equation of motion using: 

A Galactic Potential 

A model must be assumed: 

e.g. Johnston 1996, ApJ 465, 278 

Radial velocity 

Via cross-correlation with synthetic spectra templates 

proper motions 

From literature (SDSS GSC-II Catalogue) 

distances 

Bayesian determination 


Some examples 

For a sample of SN stars 

taken from Venn et al. 

2004, AJ 128,1177 

X current position of the Sun 

∆ current position of the star 


Some examples 

For a sample of SN stars 

taken from Venn et al. 

2004, AJ 128,1177 

X current position of the Sun 

∆ current position of the star 


An example of selection of groups of 

stars with similar orbits 

[El/H] from literature 

Group1 Box 

Group2 Box 

Rocket 

Group3 Box 

Rocket 

Caotic 

Tube 

Selection 

Orbit Z max 

Results 

 


kpc 

kpc 

Group1 0.08 0.08 

 

219 

Group2 1.12 0.42 180 

Group3 6.88 0.83 -4 

R min 

kpc 

< 0.15 >5.5 

0.7-1.5 

> 3 

2-5 

km/s

An example of selection of groups of 

stars with similar orbits 

Group1 Box 

Group2 Box 

Rocket 

Group3 Box 

Rocket 

Caotic 

Tube 

Selection 

Orbit Z max 

Results 

 


kpc 

kpc 

Group1 0.08 0.08 

 

219 

Group2 1.12 0.42 180 

Group3 6.88 0.83 -4 

R min 

kpc 

< 0.15 >5.5 

0.7-1.5 

> 3 

2-5 

km/s

Work in progress 

• We are computing a new set of synthetic Lick/SDSS indices starting 

from atmosphere models and synthetic spectra which do not assume 

that all the α-elements vary in lock-step: 

Atlas12 must be used instead of Atlas9 

use of newly determined empirical (solar) log gf values in the wavelength 

bands of the Lick/SDSS indices 

• Atmospheric parameters, [Ca/Fe] and [Mg/Fe] for F, G, K spectra in 

SDSS-DR8 

• Refinement of Bayesage determinations of ages and distances 

• Orbit calculations with a time dependent Galactic Potential 


Thank you

Stelle ed evoluzione chimica

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