Claudia Paladini
Josef Hron
Walter Nowotny
(Brussels)
Gioia Rau
(Vienna)
Bernhard Aringer
Paola Marigo
(Vienna)
(Padova)
The dynamic atmospheres of
carbon rich giants:
constraining models via interferometry
K. Eriksson
S. Höfner
(Uppsala)
Supported by:
1
Dynamic atmospheres*: properties
• (much) larger extension than hydrostatic atmospheres
• local density/velocity variations (shocks, dust)
• additional parameters (pulsation, dust)
• C-rich: dust driven mass loss for strong pulsation
• "warm layers" develop naturally
phase
(Nowotny et al. 2005, 2009)
Rau et al., CS19
= 2.3 AU
* DMA, Höfner/Uppsala-type models
2
Dynamic atmospheres: interferometry
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•
•
•
•
interferometry provides independent constraints from SED or spectrum
intensity profiles & visibilities largely different from uniform disk (UD)
strong wavelength dependence
small effects due to local structures (mostly at high spatial frequ.)
dependence on pulsational phase 0.1 in visibilities

FT
Rau et al., CS19
Paladini et al. (2009)
3
The sample of C-rich stars
Rau et al.
(A&A, 2015)
• RU Vir
• R Lep
• R Vol
Mira
• R For
• Y Pav
• U Hya
• AQ Sgr
SRb & Lb
Rau et al.
(in prep. &
PhD thesis)
• X TrA
Rau et al., CS19
4
Observational data
• Photometry:
SAAO, ESO, ASAS
CO+C3
SiC dust
• Spectroscopy:
ISO SWS/IRAS/IRTF
spectra
C 2H 2
+HCN
• Interferometry:
C2 H2
+HCN
VLTI/MIDI
C 2H 2
+HCN
RU Vir
Rau et al. (2015)
C2H2+HCN
SiC dust
Rau et al., CS19
NOTE:
data not taken at same phase or cycle!
5
Fitting the SED and MIDI data to DMA
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•
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DMA grid (Eriksson et al., 2014):
540 models with 140 000 timesteps (different phases and
pulsation cycles)
main DMA parameters:
L, Teff, M, log(g), P, C/O, Δu, fL
fitting procedure:
1) find model & time-step
best fitting the SED
2) add SiC opacity a posteriori to
all time steps of that model
3) compute synthetic visibilities
4) find time-step of that model
best fitting the MIDI data
Rau et al., CS19
Eriksson et al. (2014)
6
SED fits
R Lep (Mira)
Y Pav (SRb)
U Hya (SRb)
• good fits for >1m
• less agreement for BV(RI)
Rau et al., CS19
7
Visibility fits: V vs. spatial frequency
Y Pav
R Lep
Miras:
SRVs:
• evidence for extended atmospheres
• not enough data for reconstructing
• more compact
• less pronounced
the intensity profiles
Rau et al., CS19
shells in models
8
Visibility fits: V vs. wavelength
R Lep (Mira)
U Hya (SRb)
• models have steeper slope for Miras
• SiC feature sharper in models
• somewhat peculiar case of X TrA
X TrA (Lb)
Rau et al., CS19
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Fundamental stellar parameters
•
T(DMA)  T(V-K)
•
L(DMA)  L(obs)
(except AQ Sgr, Y Pav)
•
C/O(DMA)  C/O(tracks)
(except Y Pav)
•
M(DMA)1M M(track)
(except X TrA)
Tracks from Marigo et al. (2013)
Tross = T(DMA) @ Rross(DMA)
Lross = L(Rross, Teff)
Rau et al., CS19
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Conclusions and prospects
• MIDI: best agreement for all stars for 8-10m region
• (probably) data related SED differences at <1m
• evidence for larger extension of Miras
• stellar parameters from DMA-fits (mostly) consistent with observations
• SiC:
 observations consistent with Tcond(SiC)  Tcond(amC)
 feature shape in DMA too peaked (grain sizes/shapes?)
 Miras may need >10% of SiC dust
• somewhat peculiar cases of RU Vir and X TrA
• major progress expected with MATISSE
(2019 @ VLTI, 3-10m interferometric imaging)
Rau et al., CS19
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Rau et al., CS19
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Rau et al., CS19
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DIFFERENT OPACITIES
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Discrepancies between models and obs in V vs. wavel
around the SiC shape —> we tried different opacities to
see if any change in the amC dust can affect the V
shape, considering no SiC!
From Andersen et al. (1999) we selected amC opacities
with the best extinction efficiency—> (1) Roleau & Martin
(1991); (2) Zubko et al. (1996); (3) Jager et al. (1998)
We obtained that the V shape remains the same, and
the only small change detected among the different
opacities resides in the wavel shortward of 10mu—
>amC opacities do not influence the V shape longward
Rau et al., CS19
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Standard: Roleau&Martin WITH SiC
Jager+ (1998) (NO SIC)
Roleau&Martin (1991) (NO SIC)
Zubko+ (1996) (NO SIC)
Rau et al., CS19
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•
•
To detect any change in the dust emitting beyond 10mu—>
we tried different values of the condensed dust material for
amC and SiC (R Lep)
Results: changing the value of the amount of Si condensed
in SiC dust, the shape of the SiC feature can be better
reproduced—>best result with the fraction of SiC increased
by 30%, and the one of amC 100%
Normal 90% C, 10% SiC
Rau et al., CS19
100% C, 30% SiC
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Rau et al., CS19
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Synthetic Visibilities: UD radii
• R(UD) increases for , mass loss , Teff 
• R(UD) always (much) larger than continuum or Rosseland radius
• variations with phase not strictly following pulsation (Rmin ~ min. light)
• much larger R(UD)/Rinit. model than for M-stars (dust!)
• L-band most sensitive to model parameters (MATISSE!)
Rau et al., CS19
Paladini et al. (2009)
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