VEGA: a Visible spEctroGraph and polArimeter for CHARA: Science Cases description and examples

1. 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

2. Outline • Visible vs IR • VEGA performances • Cepheids • Asteroseismology • Fundamental parameters • A nice exemple:  Arae (and the B[e] CPD 57-2874) • Disk dissipation

3. 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

4. Visible vs IR Physics

5. 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

6. Summary of performances(preliminary estimations) Dispersed fringe mode (4 telescopes) • Highest spectral resolution: 35000 • 180 spectral channelsof0.02nm • SNR=10 in 1800s, Mlimbetween 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

7. 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

8. Cepheids

9. Projection factor and spectro-interferometry

10. 6% 6% PHASE V Projection factor and spectro-interferometry Radius « Probing the dynamical structure of  Cep atmosphere » N. Nardetto, F. Fokin, D. Mourard, Ph. Mathias, 2005, submitted to A&A

11. 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).

12. Outline • Visible vs IR • VEGA performances • Cepheids • Asteroseismology • Fundamental parameters • A nice exemple:  Arae (and the B[e] CPD 57-2874) • Disk dissipation

13. 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 m=4, l=5 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.

14. Abundance study Line for various stellar phases Line for polar - Line for polar + CHARA CHARA CHARA 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 + REGAIN + 2CVn models 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

15. Outline • Visible vs IR • VEGA performances • Cepheids • Asteroseismology • Fundamental parameters • A nice exemple:  Arae (and the B[e] CPD 57-2874) • Disk dissipation

16. Very low mass stars (Segransan et al.) Continue if ()/ < 1%  increase the angular resolution But very good accuracy required Binaries for a ,i + interactions Fundamental parameters Blue=VLTI, red=PTI, black=Eclips. binary

17. Measuring dwarf size + limb darkening (multi- + 2d lobe) (from David) Second lobe 1000 1100

18. Outline • Visible vs IR • VEGA performances • Cepheids • Asteroseismology • Fundamental parameters • A nice exemple:  Arae (and the B[e] CPD 57-2874) • Disk dissipation

19.  Arae: a nice exemple

20.  Arae: line profiles VS

21. Arae:x- studies with AMBER

22. Arae:x- studies with AMBER

23. Amplitude ≈ 20° ≈ 0.42 mas Visibility phase Theoretical phase using the SIMECA code from Stee 1996, A&A, 311 AMBER phase Keplerian rotation

24.  Arae: clearly arotating Kepleriandisk !

25. Really Keplerian ?

26. And for a B[e] star ?

27. VLTI-AMBER : B[e] CPD 57-2874 UT2-UT3 Differential phase  (microns)

28. B[e] star: CPD 57-2874: clearly anoutflow !

29. Possible studies:Comparison of the disk/wind kinematics • for:- Be star • LBV - B[e] star • - HAe/Be

30. HAe/Be star: MWC 297

31. Outline • Visible vs IR • VEGA performances • Cepheids • Asteroseismology • Fundamental parameters • A nice exemple:  Arae (and the B[e] CPD 57-2874) • Disk dissipation

32. Disk dissipation Pole-on from the outside-in from the inside-out

33. Disk dissipation Equator-on from the outside-in from the inside-out

34. Visibilities signature GG Tau @ IRAM from the outside-in from the inside-out

36. 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…