vega: a visible spectrograph and polarimeter for chara: science cases description and examples

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

Summary of performances(preliminary estimations)

Dispersed fringe mode (4 telescopes)– Highest spectral resolution: 35000

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

Measuring dwarf size + limb darkening (multi- + 2d lobe)

1000 1100

Second lobe(from David)

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

Arae: a nice exemple

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

Arae: line profiles

VS

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

Arae:x- studies with AMBER

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

Arae:x- studies with AMBER

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

Visibility phase

AMBER phase Theoretical phase using the SIMECA codefrom Stee 1996, A&A, 311Keplerian rotation

Amplitude ≈ 20° ≈ 0.42 mas

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

Arae: clearly a rotating Keplerian disk !

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

Really Keplerian ?

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

And for a B[e] star ?

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

VLTI-AMBER : B[e] CPD 57-2874

(microns)

Diff

ere

ntia

l pha

se

UT2-UT3

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

B[e] star: CPD 57-2874: clearly an outflow !

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

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

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

HAe/Be star: MWC 297

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

Disk dissipation

from the outside-in from the inside-out

Pole-on

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

Disk dissipation

from the outside-in from the inside-out

Equator-on

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

Visibilities signature

from the outside-in from the inside-out

GG Tau @ IRAM

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

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sont requis pour visionner cette image.

CHARA Collaboration Year-Two Science Review Philippe Stee - Science with VEGA on CHARA

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…