SHELLS OF DUST AROUND AGB STARS: EFFECTS ON THE

INTEGRATED SPECTRUM OF SSPs

Granada - VIII Torino Workshop on Nucleosynthesis in AGB Stars 7 Feb 2006

Lorenzo PiovanDepartment of Astronomy (Padova)

Piovan, L., Tantalo, R., Chiosi, C., (2003), A&A, v.408, p.559-579

Classical SEDs of SSPs do not take into account the presence of the DUST in two stellar evolutionary phases:

• Stars formation occurs into the cores of giant molecular clouds, the so called “clumps” first evolutionary phases of young stars are hidden to the observer and only after first SNe have exploded, newly born stars become optically visible.

• AGB evolution is characterized by a mass loss rate that increases with the period until the so called superwind phase AGB stars evolve embedded in a circumstellar dusty envelope.

Papers: Bressan et al. (1998) , Mouhcine & Lançon (2002), Mouhcine (2002), Lançon & Mouhcine (2002).

Classical SEDs of SSPs : what the problems are?

Modelling AGB stars circumstellar dusty envelopes

dSk r r dr Key parameter is the optical depth of the shell:

Using the equation of mass conservation, the dust-to-gas ratio and doing some hypothesis about mass loss, radial velocity of the matter and the absorption coefficient for unit mass, we can obtain:

1

4 in

M k

v r

and do not depend from the position in the shell

v M

k the internal radius of the shell is much smaller than the outer radius

in outr r

Linking optical depth parameters to typical parameters of stars

1

4 in

M k

v r

log 11.4 0.0125 100 2.5M

M PM

Vassiliadis & Wood (1993)Ivezic & Elitzur (1994)

log 2.07 1.94log 0.9R M

PR M

Vassiliadis & Wood (1993)

Habing et al. (1994), Bressan et al.(1998), Blanco et al.(1998)

0.50.5

44ind

L Lr

T L

1 13.5 0.056outv Km s P

1 LM

cv L

0.3 0.5

415 /

10 0.0025 // 0.01out

Lv Km s

L

, , , , inM k v r

, , , ,effL T R M P

Modelling AGB dusty shells in SSPs: Dust properties

In our dust model the opacities change: (i) passing from O-rich to C-rich stars (ii) for each spectral type with the optical depth.

Carbonstars

Oxygen rich stars

We allowed for:- Different compositions between Oxygen rich stars and Carbon stars.

- Different mixtures for different optical depths.But… the mixture of dust is the same for different metallicities!

Modelling AGB stars circumstellar dusty envelopes

Parameters of the shell requested by the radiative transfer code DUSTY (Ivezic & Elitzur 1997):

• Distribution of the dimensions of the grains:

• Dust condensation temperature over the inner boundary of the circumstellar shell:

• Density distribution: ; in some work or are considered more suitable for the fit with OH/IR stars.

0n a a a

dT2r 1r 3r

Modelling AGB dusty shells in SSPs: AGB stars O to C transitions

The magnitude range spanned by AGB stars at varying initial mass and metallicity. The transition O to C star is shown. We compare the AGB models by Tantalo et al. (1998) with the Vassiliadis & Wood (1993) mass loss rate (thick red lines) with the TP-AGB models by Marigo et al. (1999).

C-rich stars region

O-rich stars region

IRAS two color diagram: [12-25] vs.[25-60]

Identification of OHIR stars has been obtained from Lewis et al. (1990); Le Squeren et al. (1992); David et al. (1993); Blommaert et al. (1993); Chengalur et al. (1993); Loup et al. (1993); Xiong et al. (1994); Lepine et al. (1995); Lewis (1997); van Loon et al. (1998). The template of C stars has been taken from Epchtein et al. (1990); Egan & Leung (1991); Volk et al. (1992); Chan (1993); Guglielmo et al. (1993); Volk et al. (1992); Groenewegen (1995); Guglielmo et al. (1997,1998).

• Theoretical colors of two isochrones by Tantalo et al (1998) for selected ages are superposed to the observational data for C and OH-IR stars (red circle in the left corner).

IRAS two color diagram [12-25] vs. [25-60]

• Two isochrones with shells of dust around AGB stars are superposed to the observational data of C and OH/IR stars. Each isochrone has been plotted up to the AGB tip.

Identification of OHIR stars has been obtained from Lewis et al. (1990); Le Squeren et al. (1992); David et al. (1993); Blommaert et al. (1993); Chengalur et al. (1993); Loup et al. (1993); Xiong et al. (1994); Lepine et al. (1995); Lewis (1997); van Loon et al. (1998). The template of C stars has been taken from Epchtein et al. (1990); Egan & Leung (1991); Volk et al. (1992); Chan (1993); Guglielmo et al. (1993); Volk et al. (1992); Groenewegen (1995); Guglielmo et al. (1997,1998).

• Two isochrones with shells of dust around AGB stars are superposed to the observational data of C and OH/IR stars. Each isochrone has been plotted up to the AGB tip.

IRAS two color diagram: [12-25] vs. [25-60]

In particular we have used

60

33

cirr

F

as an upper limit for uncontaminated fluxes, following Ivezic & Elitzur (1995).

[J-H] vs. [H-K] two color diagram

• Two color diagram [J-H], [H-K] in the near infrared.

• OH/IR stars data are taken from Lepine et al. (1995); Xiong et al. (1994); Olivier et al. (2001); Whitelock & Feast (1994).

• C stars data are derived from Epchtein et al. (1990); Guglielmo et al. (1993,1997,1998); Olivier et al. (2001).

• Superposed to the data are three isochrones of selected ages.

Old SSPs SEDs

• Old SEDs of SSPs with Z=0.008.

• Tantalo et al. (1998) set of isochrones.

• Range of ages between 0.25 Gyr and 10 Gyr from the top to the bottom.

New SSPs SEDs

• New SEDs of SSPs with Z=0.02.

• The isochrones set is that one of Tantalo et al. (1998).

• Range of ages between 0.25 Gyr to 10 Gyr, from the top to the bottom.

• Old spectra of SSPs (red lines) and new spectra of SSPs (purple lines) for four selected ages.

Differences: The features at the 1 - 2

microns. Flux shifted to longer

wavelengths. The features at 10 and 11.3

microns.

SSPs SEDs old and new

Evolution of the 11.3μm SiC and 9.7μm Si-O

• Evolution of the 11.3μm SiC and 9.7μm features for a SSP of metallicity Z=0.008 starting from 0.3Gyr until to 5Gyr.

• Dashed vertical lines indicate 11.3μm SiC feature.

• Dotted vertical lines indicate 9.7μm Si-O stretching mode feature.

Two color diagram [J-H] vs. [H-K]

Infrared data of young clusters are the same of Mouhcine and Lançon (2002) that have selected a young sample from Persson et al. (1983). Also some recent data of LMC clusters are shown (Pretto, private communication).

• Data for LMC (open black circles and purple squares) and SMC clusters (filled black circles) are taken from Persson et al. (1983) and Pretto (private communication)

Piovan et al. (2003)

Mouhcine & Lançon(2003)

Tantalo et al. (1998)

The thin and thick lines are for Z=0.02 and Z=0.008

Two color diagram [H-K], [V-K]

• Data for LMC (open black circles) and SMC clusters (filled black circles) are taken from Persson et al. (1983).

Infrared data of young clusters are the same of Mouhcine and Lançon (2002) that have selected a young sample from Persson et al. (1983).

Piovan et al. (2003)

Mouhcine & Lançon(2002)

Tantalo et al. (1998)

The thin and thick lines are for Z=0.02 and Z=0.008

Near-infrared color evolution of SSPs

The SSPs colors [J-H], [J-K]And [V-K] as function of the age in theRange 0.1 to 20 Gyr for SSPs withZ=0.02 (on the left) and Z=0.008(on the right).

Piovan et al. (2003)Girardi et al. (2002)Mouhcine & Lançon (2002)

Tantalo et al. (1998)

Near-infrared color evolution of SSPs

Near-infrared color evolution of LMC clusters in [J-K] and [H-K]. Observational data are taken from Kyeong et al. (2003).

SOME QUESTIONS….

1) Why Girardi et al. (2002) IR colors are redder than all the others for the youngest ages where the contribution of AGB stars is important?

2) Why Tantalo et al. (1998) colors are bluer and corrected for the effect of dusty shells around AGB stars they become bluer with some

exceptions?

Causes of disagreement:

Spectral libraries

The Path in the HR-diagram is different because of the slightly

different physics adopted: mixing length parameter, opacities, mass-loss rate, L-Teff-Core mass relationship.

(0.3 Gyr, Z=0.02)

Number of AGB stars: we plot the cumulative contribution to the total flux by stars in different evolutionary stages.

Four steps are represented:

• up to turn-off (TO)• from TO to the T-RGB (T-RGB)

• from T-RGB to the end of HeB (HeB)• from the end of HeB to T-AGB (AGB)

Lumping togheter all stages up to HeB we note that the cumulative flux

predicted by Girardi et al. (2002) is lower than that predicted by Tantalo

(1998): the situation is reversed when the contribution from AGB is added.

Using dusty SEDs to study mid-infrared emission of elliptical galaxies – part 1

Observed fluxes at 3.6, 4.5, 5.8, 8 and 24 micron for NGC 584 (open circles), NGC

1316 (filled circles), NGC 3923 (open squares), NGC 4472 (filled squares), NGC 4552 (open triangles), NGC 4649 (filled

triangles), NGC 5813 (crosses), NGC 5846 (stars) and NGC 6703 (open hexagons). SEDs for single stellar

populations from Piovan et al. (2003) are shown at 3 Gyrs (dashed line) and 12 Gyrs

(solid line).

The ratio F_{15 micron}/F_{I-band} within R_e/8 plotted against optically determined ages for each galaxy. The lines show the predicted ratio by our

single stellar population models. These overlapping lines for populations with abundances of Z = 0.008,

0.004, and 0.02 show that this flux ratio is essentially independent of the stellar abundance.

Temi et al. (2005), Astrophys.J., 622, 235-243

Temi et al., (2005) Astrophys.J., 635 , pp. L25-L28

Using dusty SEDs to study mid-infrared emission of elliptical galaxies – part 2

IRS spectra of passively evolving early-type galaxies in the Virgo cluster. Superimposed are SSP

models from Bressan et al. (1998) normalized at 5.5 micron. The dotted

line is a 10 Gyr, Z=0.02 SSP computed without accounting for

dusty circumstellar envelopes. Dashed lines from bottom to top are

10 Gyr SSPs with metallicity Z=0.008, Z=0.02 and Z=0.05

respectively, computed with dusty circumstellar envelopes. The dot-

dashed line is a young (5 Gyr) metal poor (Z=0.008) SSP intended to show that also the MIR spectral region suffers from degeneracy.

Bressan et al. (2006), Astrophys. J. L., accepted

Problems and future improvements• Stellar spectral library: we used the theoretical library of spectra of Lejeune (1998): Kurucz (1995), for the lowest temperature Allard & Hauschildt (1995) (for dwarf stars), Fluks et al. (1994) and Bessell et al. (1989,1991) (for giant stars). We need better theoretical models for early AGB and also as input for circumstellar dusty shells.

• More realistic mass-loss models, maybe with a connection of the profile of the matter to the thermal pulses;

• Transition between early AGB stars and dust enshrounded AGB;

• New isochrones of Girardi (2004) with the variable molecular opacities of Marigo (2002) including the evolution of AGB stars at varying surface C/O ratio.

• Models with different dust composition for the various metallicities, maybe using calculation of the changes in the surface abundances because of the dredge up connected with a nucleation theory able to describe dust formation.

Variable molecular opacities: effect on AGB stars

Predicted H-R tracks of TP-AGB models with initial metallicity

Z=0.02. Calculations are carried out with both fixed (bottom

panel) molecular opacities for solar composition, and variable opacities (top panel) related to

the current photospheric abundances of C and O (hence

C/O ratio) during the evolution.

Effective temperatures as a function of the C/O ratio in

Galactic giants. Observed data (circles) are compared to

predictions of synthetic TP-AGB models with dredge-up (lines), adopting either ``chemically-

fixed'‘ opacities (bottom panel), or ``chemically-variable''

opacities (top panel).

Near-infrared colour-colour diagram for oxygen-rich (M-

type) and carbon-rich (C-type) stars in the Solar

neighbourhood. The predicted colour evolution on the TP-

AGB is shown (solid lines, the direction is indicated by

arrows) for different initial stellar masses and

fixed/variable molecular opacities.Marigo (2002), A&A, 387, pp. 507-519

Variable molecular opacities: effect on AGB stars

Distribution of candidate LMC AGB stars in the colour-magnitude diagram (J-K, K). Stars selected

from the 2MASS data are shown in black (M-type) and red (C-type) whilestars selected from the DCMC data are shown in blue (M-type) and cyan (C-type). Note that 2MASS selected sources most probably include

genuine RGB stars at the faintest magnitudes of M-type candidates aswell as more stars than selected from

DCMC data distributed overall.

Simulated CMDs for models that assume constant SFR, and two different values of metallicity for stars of all

ages: Z=0.004 (left panel), Z=0.008 (right).

Simulated CMDs for models with a constant metallicity, Z=0.008, and two different cases of varying SFR:

decreasing (left panel), and increasing (right panel) with stellar age.

Cioni, Girardi, Marigo & Habing (2006), A&A, accepted for publication