Transcript Recent science results from VLTI commissioning

Recent science results from VLTI
commissioning
Francesco Paresce
European Southern Observatory
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P70 VINCI Shared Risk Proposals
• Time allocated: 150 hrs (~15 nights) on SIDS
• Proposals received: 40 for a total of > 600 hrs
• Ad-hoc scientific review committee: F.Paresce,
C.Leinert, J.Surdej, P.Lena
• Technical feasibility review: M.Schoeller,
P.Kervella, M.Wittkowski
• 16 Proposals accepted for 150 hrs
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Cepheid Angular Diameters, PI: Kervella, ESO
Hot rapid rotators, PI: Domiciano, Nice
Dusty environment of RAqr, PI: Driebe, Bonn
Circumstellar matter around SS Lep, PI: Lachaume,
Grenoble
VLTI Calibrators, PI: Percheron, Leiden
Central Source in Eta Car, PI: Schoeller, ESO
Radius of K&M dwarfs, PI: Segransan, Geneve
Simultaneous VLTI/VLBA measurements of Mira
stars, PI: Wittkowski, ESO
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• Observations of HR 4049, PI: Dominik, Amsterdam
• Rotation axis of V Hydra, PI: Haniff, Cambridge
• Asteroseismology of roApstars, PI: Cunha, CAUP,
Portugal
• Radii of Asteroseismic target stars, Texeira, CAUP &
IFA
• Resolve Orbit of Theta 1c Ori, PI: Preibisch, Bonn
• Observations of Rotationally Distorted Stars, PI: Van
Belle, JPL
• Short Period Binaries in Hierarchical triples, PI:
Queloz, Geneve
• Mass of the nearest WR star, PI: Buscher, Cambridge
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P71 VINCI Shared Risk Proposals
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Time allocated: 150 hrs (~15 nights) on SIDS
26 proposals received for ~ 500 hours
Proposals reviewed by OPC
16 proposals accepted in Category B for 270
hours
• Technical feasibility review indicates that 13
proposals are feasible for a total of 230 hours
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• Inner disk structure in HAeBe systems, PI:Testi
• Direct limb-darkening measurements of cool giant stars
as tests of stellar model atmospheres, PI: Wittkowski
• Direct interferometric measurement of the angular
diameters of southern Cepheids, PI: Kervella
• VINCI measurement of binaries using coherent
techniques in preparation for extra-solar planet
detection, PI: Meisner
• Unveiling Eta Car’s dust environment, PI: Weis
• Construction of a semi-empirical M-R relationship for
MS stars from B to K, PI: Kervella
• Probing and monitoring the core of Eta Car with mas
resolution, PI: Schoeller
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First Papers
• First radius measurements of very low mass stars with
the VLTI, Segransan et al., 2003, A&A, 397, L5
ESO Press Release 22/02,29 November 2002. How Small are Small Stars
Really? VLT Interferometer Measures the Size of Proxima Centauri and
Other Nearby Stars
• The diameters of Alpha Centauri A and B: a
comparison of the asteroseismic and VLTI views,
Kervella et al., 2003, A&A, 404, 1087
ESO Press Release 05/03,15 March 2003. A Family Portrait of the Alpha
Centauri System: VLT Interferometer Studies the Nearest Stars
• The spinning-top Be star Achernar from VLTI-VINCI,
Domiciano de Souza et al., 2003, A&A, in press
ESO Press Release 14/03. Flattest Star Ever Seen, VLT Interferometer
Measurements of Achernar Challenge Stellar Theory
• Calibration observations of Fomalhaut with the VLTI,
Davis et al., 2003, A&A, submitted
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First Papers (cont.)
• The interferometric diameter and internal structure of
Sirius A, Kervella et al., 2003, A&A submitted
• Direct measurement of the size of the star Eta
Carinae, Van Boekel et al., 2003, ApJ, submitted
• Tests of stellar model atmospheres by optical
interferometry: VLTI/VINCI limb-darkening
measurements of the M4 giant ψ Phe, Wittkowski et
al., 2003, A&A, submitted
• Introduction to VINCI/VLTI interferometric data
analysis, Kervella et al., 2003, A&A, submitted
• The diameter and evolutionary state of ProcyonA:
multi-technique modeling using asteroseismic and
interferometric constraints, Kervella et al., 2003,
A&A, submitted
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Eta Carinae: some basic facts
• In Tr 16 in Carina nebula (NGC 3372,) located at 2.5
+/- 0.3 kpc {MHII ~ 104 M ~ 103 x Orion}
• Super massive LBV: ~ 100 M
• Super luminous: 3-5x106 L (most lum. in MW) now
but ~30 x 106 L at outburst (2nd brightest object in sky)
• Super hot: 15-40 x 103 K
• Super active: survivor of 1843 eruption that created the
homunculus and expelled ~ 2-3M at up to 800 km/s
• Current rate of mass loss 0.3-3 x 10-3 M/yr
• Central object is not viewed directly but is obscured by
several mag of extinction in near IR
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Eta Carinae: Questions & Mysteries
• What was it? Yellow SG? Red SG?, WR?
• What is it? Single? Binary? Cluster? What is its current mass
loss rate exactly? What is its or their mass?
• What will it become? Normal star after more eruptions?
Collapse into SN or hypernova?
• Is it rotating? What is the origin of the 5.5yr periodicity in
some lines and x-rays? Is there a massive equatorial torus?
• What is the physical mechanism responsible for the violent
instability (outburst(s)), the homunculus bipolar geometry, the
double ring structure seen in the mid IR in the inner
homunculus and the x-ray emission?
• What is going to happen this summer at x-ray peak?
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Eta Carinae: why is it important?
• Formation and evolution of extremely massive stars
(most likely the first stars were this big): accretion
onto a single object or mergers?
• Dynamical and chemical interactions with their
environment
• The role of stellar instabilities in the outer envelopes
of single stars and/or of periodic tidal forcing by a
companion and the formation of asymmetric
nebulosity
• The relation of extremely massive stars to peculiar
supernovae and hypernovae.
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The key to understanding Eta Car is
to penetrate into the core and “see”
the central “object”. This is the
main objective of the VLT/VLTI
observations.
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Very High Resolution VLT Imaging
(70mas)
• NACO on Yepun at
2.39μ
• A unresolved at 70 mas
• 57% of total flux seen in
image (1.7” squared)
concentrated in A
corresponding to ~180Jy
• Blobs D,C already
detected by speckle
interferometry
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Very, very high resolution interferometry
with VLTI (1mas)
• Size of source = 5mas
• Responsible for 180 Jy
emission from an area of
~10 AU2 at 2.4 kpc
• For 2 mags of extinction,
Tmin ~ 4800 K
• Dust evaporates at
T>1500K so flux not due
to thermal emission from
dust
• Conclusion: star and
ionized wind spatially
resolved (for first time)!
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Analysis & Results
Wind model assumptions:
• Spherical star with dense, ionized and
isothermal stellar wind
• Gas accelerates from initial v0 to terminal
velocity v∞ as v(r) = v0+(1-R*/r)(v∞-v0)
• Wind is clumpy: f = <ρ>/ ρ
• Main sources of opacity: f-f and f-b
absorption and Thomson scattering
Using HST/STIS long slit spectra that give:
Mdot/√f = 3.16 10-3 M/yr (dashed line)
Results:
• Mdot = 1.5+/- 0.3 M/yr,
f = 0.2
• No other component is
contributing on spatial scales
between 5 and 70 mas at K (a
companion, material in orbital
plane, dust in line of sight etc)
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But, it’s not round!
• Clear variation of visibility with
projected baseline orientation
• Assuming gaussian shape of
wind: major axis = 8mas, minor
axis = 6mas with PA=31+/-10 º
• This PA is remarquably close to
45 º PA of major axis of
homunculus!
• Rapid rotation will cause
enhanced mass flux from poles
• Our observations mean that the
homunculus is roughly aligned
with the rotation axis of the star.
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• Observed de-projected aspect ratio = 1.6
• For rotation to flatten the star to this level, radiation driven
wind models require rotation at 0.8-0.9 of break-up
velocity!
• At such speeds, Mdot will be ~ 8x the non rotating case
• Wind asymmetries assumed to explain long slit HST results
(see figure above) are consistent with this scenario.
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Another very distorted star: Achernar
• Aerial view of VLTI ground
baselines for the two pairs of
siderostats used for Achernar
observations. Color magenta
represents the 66m counted
from North to East) and green
the 140m.
• Corresponding baseline
projections onto the sky (Bproj)
as seen from the star. Note the
very efficient supersynthesis
(different projections due to
Earth rotation) resulting in a
nearly complete coverage in
azimuth angles.
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Observations
• Fit of an ellipse over the
observed V2 points translated
to equivalent uniform disc
angular diameters. Magenta
points are for the 66m baseline
and green points are for the
140m baseline. The fitted
ellipse results in major axis
2a=2.53±0.06 mas, minor axis
2b=1.62±0.01 mas, and minoraxis orientation PA=39±1°
(from North to East). The
points distribution reveals an
extremely oblate shape with an
aspect ratio 2a/2b = 1.56±0.05.
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Analysis and Results
B3Vpe star models used include:
• Radiation transfer
• Gravity darkening (von Zeipel)
• Geometrical distortion due to solid
body rotation and mass concentrated
at the star center
• Stellar parameters from lit (225km/s
projected velocity etc)
An extreme uniform Roche model with
veq=vcrit and i=90° was also used
Results:
• Be star models don’t work
• Extreme (equator-on, rotation at
break-up speed) Roche model does
but…it is not consistent with known
properties of Be stars (not uniform or
rotating at critical speed)
But…maybe we don’t understand Be
stars!
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Science Demonstration Time in P71
3 nights with MIDI and the UTs without AO carried out in the
June 11-16, 2003 period with UT1+3. Program approved by IC
Program summary:
1. MIDI Observations of the heart of AGN: probing the dusty torus
Rottgering, Leiden (PI), NGC 1068
2. Probing the disk of Be and B[e] stars with MIDI.
Herbst, Heidelberg (PI), HD 316285
3. A study of disk structure around Herbig AeBe stars
Waters, Amsterdam (PI), HD 179218
4. Young stars
Malbet, Grenoble (PI), 51 Oph
5. Resolving the dust shells surrounding red giants
Preibisch, Bonn (PI), RR Sco, IRAS 17004-4119,
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Science Demonstration time in P72
• SD2 will be carried out in P72 with MIDI only.
Programs are approved by IC and represent about 6-7
nights of observing time.
• They include: Debris disks, Alf Ori, Asymmetries and
dust in AGB stars, Dusty disks in post-AGB binaries,
NGC 1068, massive disks in YSO, R Mon, 2 HAeBe
stars, and FU Ori.
• Because of the source coordinates, SD2 will be split
in two runs (November 6-9, 2003 and February 7-9,
2004) without and with FINITO/MACAO
respectively.
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