Interferometric Studies of Binary Stars

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VEGA a Visible spEctroGraph and polArimeter for
CHARA Science Cases description and examples
Philippe Stee CNRS - Département GEMINI UMR
6203 Observatoire de la Côte dAzur
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Outline

• Visible vs IR
• VEGA performances
• Cepheids
• Asteroseismology
• Fundamental parameters
• A nice exemple ? Arae (and the Be CPD 57-2874)
• Disk dissipation

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Outline

• Visible vs IR
• VEGA performances
• Cepheids
• Stellar Activity
• Asteroseismology
• Fundamental parameters
• A nice exemple ? Arae (and the Be CPD 57-2874)
• Disk dissipation

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Visible vs IR Physics
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Outline

• Visible vs IR
• VEGA performances
• Cepheids
• Stellar Activity
• Asteroseismology
• Fundamental parameters
• A nice exemple ? Arae (and the Be CPD 57-2874)
• Disk dissipation

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Summary of performances(preliminary estimations)

• Dispersed fringe mode (4 telescopes)
• Highest spectral resolution 35000
• 180 spectral channels of 0.02nm
• SNR10 in 1800s, Mlimbetween 5.5 and 6.5
  depending on seeing conditions.
• Lowest spectral resolution 1500
• 180 spectral channels of 0.4 nm
• SNR10 in 1800s, Mlimbetween 8.5 and 9.5
  depending on seeing conditions.
• Simultaneous polarizations measurement

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Outline

• Visible vs IR
• VEGA performances
• Cepheids
• Stellar Activity
• Asteroseismology
• Fundamental parameters
• A nice exemple ? Arae (and the Be CPD 57-2874)
• Disk dissipation

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Cepheids
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Projection factor and spectro-interferometry
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Projection factor and spectro-interferometry
Radius
 Probing the dynamical structure of ? Cep
atmosphere  N. Nardetto, F.
Fokin, D. Mourard, Ph. Mathias, 2005, submitted
to AA
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Distances determination and VEGA (case of ? Cep)
The angular diameter variation of distant
Galactic Cepheids is measurable by differential
interferometry (precision of 0.5?mas expected
with VEGA).
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Outline

• Visible vs IR
• VEGA performances
• Cepheids
• Asteroseismology
• Fundamental parameters
• A nice exemple ? Arae (and the Be CPD 57-2874)
• Disk dissipation

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Asteroseismology
Goals from the sun to other stars
probing the internal structure evolution
with time Jankov (2001) has demonstrated the
power of combining spectroscopy and differential
interferometry
Spherical projection of the brightness
perturbation for NRP m4, l5 mode
Requirements Need for high spectral resolution
and resolution less than 1 mas Interesting
spectral features below 0.6 µm Potential access
to solar type stars, ? Scuti, B stars and also
red giants.
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Ap stars with CHARA
Magnetic field observation

• Resolved target
• Large visibility effects
• Observations in the visibility lobes

Abundance spots of a fraction of stellar diameter
can be detected in the 2nd and 3rd visibility
lobes BUT Imaging will be difficult due to the
small number of telescopes
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Outline

• Visible vs IR
• VEGA performances
• Cepheids
• Asteroseismology
• Fundamental parameters
• A nice exemple ? Arae (and the Be CPD 57-2874)
• Disk dissipation

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Fundamental parameters

• Very low mass stars (Segransan et al.)
• Continue if ?(?)/? lt 1
• ? increase the angular resolution
• But very good accuracy required
• Binaries for a ,?i interactions

BlueVLTI, redPTI, blackEclips. binary
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Measuring dwarf size limb darkening (multi-?
2d lobe)
(from David)
Second lobe
1000
1100
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Outline

• Visible vs IR
• VEGA performances
• Cepheids
• Asteroseismology
• Fundamental parameters
• A nice exemple ? Arae (and the Be CPD 57-2874)
• Disk dissipation

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? Arae a nice exemple
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? Arae line profiles
VS
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??Araex-? studies with AMBER
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??Araex-? studies with AMBER
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Visibility phase
Amplitude 20 0.42 mas
Theoretical phase using the SIMECA code from
Stee 1996, AA, 311
AMBER phase
Keplerian rotation
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? Arae clearly a rotating Keplerian disk !
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Really Keplerian ?
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And for a Be star ?
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VLTI-AMBER Be CPD 57-2874
UT2-UT3
Differential phase
? (microns)
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Be star CPD 57-2874 clearly an outflow !
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• Possible studiesComparison of the disk/wind
  kinematics
• for- Be star
• LBV - Be star
• - HAe/Be

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HAe/Be star MWC 297
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Outline

• Visible vs IR
• VEGA performances
• Cepheids
• Asteroseismology
• Fundamental parameters
• A nice exemple ? Arae (and the Be CPD 57-2874)
• Disk dissipation

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Disk dissipation
Pole-on
from the outside-in
from the inside-out
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Disk dissipation
Equator-on
from the outside-in
from the inside-out
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Visibilities signature
GG Tau _at_ IRAM
from the outside-in
from the inside-out
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Conclusion

• Clearly a lot of potential and astrophysical
  subjects for VEGA on CHARA !
• It will make CHARA the interferometer with the
  largest spatial and spectral resolution
  worldwide