Transcript The uniqueness of Antarctica for the study of AGB stars

The uniqueness of Antarctica for the
study of AGB stars undergoing
thermal pulses.
Optical and Infrared Wide-Field
Astronomy in Antarctica
Paris - 16/06/2006
Roald Guandalini – University of Perugia
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Optical and Infrared Wide-Field
Astronomy in Antarctica
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ABSTRACT
Main Topics:
•Introduction on ground-based observations
from Antarctica of AGB stars
p. 3-7
•Importance of mid-IR observations and variability
for AGB stars
p. 8-19
•Mid-IR observations from Antarctica:
p. 20-21
•Some preliminary results and possible
improvements through
ground-based observations
p. 22-31
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Introduction:
Why AGB stars…..
There are still many unclear points in the study of the AGB evolution…
Uncertain Parameters…
Stellar
LUMINOSITY (whose uncertainty
influences estimates of other parameters…);
Stellar
MASS;
MASS
LOSS rates as a function of the
evolutionary stage and of total mass;
Production
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of CHEMICAL ELEMENTS.
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Introduction:
Mid-Infrared Bands
Mid-IR Bands……
Very important in the study of AGB
stars (see later):


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3-5 um.
>10 um up to 30 um.
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Introduction:
Why Ground-Based Observations…..
ISO
MSX
AGB stars have been observed by several space-borne telescopes in the mid-IR:
IRAS, ISO, MSX, IRTS.
BUT
IR space-borne observations present some disadvantages:
The duration of the operational period is expected to be quite limited.
Observations with long time of integration are difficult.
Single-epoch observations in most cases.
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Introduction:
Why Dome C…..
Dome C:
Best place on the Earth to perform astronomical observations in the mid-IR.
See previous talks:
1) Site testing Dome C
2) Comparison of Dome C with other ground-based locations
(i.e. Mauna Kea)
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Introduction:
Why Surveys from Dome C…..
Important analysis needed for AGB stars:
A. Light curves and therefore variability.
B. Accurate study of the variations of luminosity (variability) over the
wide region of the electromagnetic spectrum including optical
and IR.
Which kind of observations can be done from the ground ?
 Surveys through wide field (future) or small area (IRAIT) imaging of
interesting stellar systems.
 Multiple observations of chosen AGB sources at different epochs &
wavelengths.
N.B. Extended wavelength coverage is fundamental. Indeed…..
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Mid-IR and Variability:
Mid-IR Observations with ISO(SWS)
Lb
Mira
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Sr
PostAGB
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Astronomy in Antarctica
Mira
PostAGB
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Mid-IR and Variability:
Period-Luminosity
The contribute from mid-IR is fundamental
to estimate luminosity of AGB stars.
Period-luminosity relations are important to
estimate important parameters of AGB stars.
Wood et al. 1999
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Kwok et al. 1999
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Mid-IR and Variability:
Variability and Evolution
Luminosity varies with time during the
evolution of the star on the AGB phase.
Commonly believed so far:
Semiregulars in the the post-flash dips,
Miras at the top of interpulse luminosity.
Hence, one expects more Miras than SRs.
Instead, the 2 populations are more or less
equal (Guandalini et al 2006).
 The variability is also dependent on the
evolutionary status.
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Mid-IR and Variability:
Bolometric Variability (ISO)
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Mid-IR and Variability:
Bolometric Variability (ISO)
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Mid-IR and Variability:
Bolometric Variability (ISO)
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Mid-IR and Variability:
Bolometric Variability (ISO)
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Mid-IR and Variability:
Bolometric Variability (ISO)
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Mid-IR and Variability:
Bolometric Variability (ISO)
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Mid-IR and Variability:
Bolometric Variability (ISO)
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Mid-IR and Variability:
Bolometric Variability (ISO)
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Mid-IR and Variability:
Bolometric Variability (ISO)
Bolometric variability………
 How is this generated ?
1. Shock waves caused by dynamic events in the photosphere?
2. Magneto-hydrodynamical modes (and magnetic storms)?
 In which way we can examine it?
We need to observe AGB stars at different epochs ALSO in mid-IR!!
 Simultaneous observations in near & mid IR could be fundamental to
understand these phenomena.
 Moreover, correlation with optical variability could be necessary.
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Mid-IR Observations from Antarctica:
Magellanic Clouds
As mentioned before by Dolci (see talk)
IRAIT : valid observations for fluxes > 0.5 Jy
IRAIT will observe stars of the Magellanic Clouds down to the base AGB in mid-IR.
A 4m IR telescope placed in Antarctica could study stars of the Magellanic Clouds
down to the RGB. This telescope could also observe the AGB stars beyond the M31
group (see previous talk).
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Mid-IR Observations from Antarctica:
dSph Satellites of the Milky Way
An IR 4m telescope placed in
Antarctica will allow us also to
study stars in the final phases of
their evolution from all the Dwarf
Spheroidal Satellites of the Milky
Way, at very different metallicities.
(For the dSphs we could observe at
least the giants at the tip of the
RGB phase).
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Results with space-borne mid-IR observations :
Observations Used…..
 Surveys from the ground in near-IR: 2MASS/DENIS.
 Observations in mid-IR (mainly through space-borne telescopes):
ISO (SWS) :
3-45 um
MSX :
8-21 um
BUT
A low number of sources is observed and usually only with a single
observation.
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Results with space-borne mid-IR observations:
Post-AGB Stars
Different variability types are well
distinguished by IR colors.
Kwok et al. 1999
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Guandalini et al. 2006
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Results with ground-based mid-IR observations:
Post-AGB Stars and TIRCAM2
Busso et al. 2006
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Results with space-borne mid-IR observations:
Luminosity Of AGB Stars: C Stars
Milky Way
Magellanic Clouds
Costa & Frogel 1996;
Van Loon et al. 1999
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Results with space-borne mid-IR observations:
Luminosity Of AGB Stars: S Stars
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Results with space-borne mid-IR observations:
HR Diagrams for C stars
Marigo et al.
Molec. Opac. ?
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Results with ground-based mid-IR observations:
HR Diagram for C stars
Busso et al. 2006
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Results with space-borne mid-IR observations:
HR Diagram for S stars
S branch
SC branch
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Results with space-borne mid-IR observations:
Mass Loss – IR Colors
Guandalini et al. 2006
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Results with ground-based mid-IR observations:
Mass Loss – IR Colors
Guandalini et al. 2006
Busso et al. 2006
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Conclusions
There is the need of understanding the final evolutionary phases of AGB
sources (luminosity, mass loss…..):
 the amount of the matter returned to the InterStellar Medium
 chemical evolution
 mass of the White Dwarfs
Update of the photometrical analysis of these stars up to 40 um
(beyond 20 um this might require new detectors).
The future class of IR telescopes at Dome C can do studies like those
shown here for the Local Group.
Dome C might become THE place where stellar evolution gets clarified.
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