CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA VEGA: a Visible spEctroGraph and polArimeter for CHARA: Science Cases description and examples Philippe Stee CNRS - Département GEMINI UMR 6203 Observatoire de la Côte d’Azur
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VEGA: a Visible spEctroGraph and polArimeter for CHARA: Science Cases description and examples
VEGA: a Visible spEctroGraph and polArimeter for CHARA: Science Cases description and examples. Philippe Stee CNRS - Département GEMINI UMR 6203 Observatoire de la C ôte d’Azur. Outline. Visible vs IR VEGA performances Cepheids Asteroseismology Fundamental parameters - PowerPoint PPT Presentation
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CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
VEGA: a Visible spEctroGraph and polArimeterfor CHARA: Science Cases description and examples
Philippe SteeCNRS - Département GEMINI
UMR 6203Observatoire de la Côte d’Azur
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
Outline• Visible vs IR• VEGA performances• Cepheids• Asteroseismology• Fundamental parameters• A nice exemple: Arae (and the B[e] CPD 57-2874)• Disk dissipation
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
Outline• Visible vs IR
• VEGA performances
• Cepheids
• Stellar Activity
• Asteroseismology
• Fundamental parameters
• A nice exemple: Arae (and the B[e] CPD 57-2874)
• Disk dissipation
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
Visible vs IR Physics
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
Outline• Visible vs IR
• VEGA performances
• Cepheids
• Stellar Activity
• Asteroseismology
• Fundamental parameters
• A nice exemple: Arae (and the B[e] CPD 57-2874)
• Disk dissipation
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
spectral channelsof0.02nm SNR=10 in 1800sMlimbetween 5.5 and 6.5 depending on seeing
conditions.
– Lowest spectral resolution: 1500 180 spectral channels of 0.4 nm SNR=10 in 1800s, Mlimbetween 8.5 and 9.5 depending on seeing
conditions.
– Simultaneous polarizations measurement
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
Outline• Visible vs IR
• VEGA performances
• Cepheids
• Stellar Activity
• Asteroseismology
• Fundamental parameters
• A nice exemple: Arae (and the B[e] CPD 57-2874)
• Disk dissipation
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
Cepheids
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
Projection factor and spectro-interferometry
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
Projection factor and spectro-interferometry
« Probing the dynamical structure of Cep atmosphere »
N. Nardetto, F. Fokin, D. Mourard, Ph. Mathias, 2005, submitted to A&A
6%6%
35.1=p
27.1=p
PHA
SE
V
Radiu
s
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
Distances determination and VEGA (case of Cep)
The angular diameter variation of distant Galactic Cepheids is measurable by differential
interferometry (precision of 0.5mas expected with VEGA).
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
Outline• Visible vs IR
• VEGA performances
• Cepheids
• Asteroseismology
• Fundamental parameters
• A nice exemple: Arae (and the B[e] CPD 57-2874)
• Disk dissipation
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
Asteroseismology
Requirements:
Need for high spectral resolution and resolution less than 1 masInteresting spectral features below 0.6 µmPotential access to solar type stars, Scuti, B stars and also red giants.
Spherical projection of the brightness perturbation for NRP m=4, l=5 mode
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
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
Ap stars with CHARA
• Resolved target
• Large visibility effects
• Observations in the visibility lobes
Magnetic field observation
Polarized structures of a fraction of stellar diameter can be detected in the 2nd and 3rd visibility lobes
CHARA + REGAIN + CrB models
(Bagnulo et al., A&A, 358, 929)
CHARA
Line for polar +
Line for polar -
Abundance study
CHARA + REGAIN + 2CVn models
CHARA
Line for various
stellar phases
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
CHARA
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
Outline• Visible vs IR
• VEGA performances
• Cepheids
• Asteroseismology
• Fundamental parameters
• A nice exemple: Arae (and the B[e] CPD 57-2874)
• Disk dissipation
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA
Fundamental parameters
• Very low mass stars (Segransan et al.)
• Continue if 1%
increase the angular resolution
• But very good accuracy required
• Binaries for a ,i + interactions
€
0.6μm
300m≈
2.2μm
1100m
Blue=VLTI, red=PTI, black=Eclips. binary
CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA