astrometry at vlti application to disk/exoplanet science...

Astrometry at VLTI application to disk/exoplanet

science case. JP Berger

European Southern Observatory

2010 May 27 1 Astrometry at VLTI disk/exoplanet

Outline

•  Astrometry with an (optical) interferometer •  PRIMA/VLTI •  GRAVITY/VLTI •  Brainstorming:

–  Exoplanet –  Multiplicity –  PMSequence environment

2010 May 27 2 Astrometry at VLTI disk/exoplanet LAOG and Gravity consortium

ASTROMETRY WITH AN INTERFEROMETER

2010 May 27 Astrometry at VLTI disk/exoplanet 3

What is astrometry ? •  Astrometry: science of measuring

positions in the universe •  Oldest astronomical discipline:

– Civilisations: Mesopotamia, Egypt, Grece, Tiwanaku, Aztek, Chinese …

– Astronomers: Hipparcos Ptolemy, Tycho, Kepler …

•  There are huge number of techniques to measure positions

•  Astrometry/exoplanet: review by Malbet http://www.pathways2009.net/programme.html


Interfero-astrometry

•  Why using interferometry ? –  Can give photocenter

position with (sub)-wavelength accuracy

–  Long-baseline interferometers: give access to increased angular resolution

•  Different observables provide astrometric information: –  Wide angle astrometry –  Narrow-angle

astrometry (relative) –  Differential phase –  Closure phase

•  Restriction of this talk: Ground and Europe


Wide/narrow angle astrometry


From Shao 2010

Narrow/very narrow angle astrometry •  From the ground the

atmosphere is a killer (not the only one though …)

•  Very narrow angle regime: relative astrometric error δ x improves with baseline B and reference star position θ


Shao & Colavita 1992

Narrow/Very narrow angle baseline dual star interferometry


Narrow angle interferometry requires to monitor the angular distance between the target and a few reference stars.

Practical implementation


Colavita 2008, VLTI school

Dual-star interferometry: precursors

•  Mark III stellar interferometer

•  NPOI (US Navy) •  Palomar Testbed

Interferometer: –  PHASES program –  ~100 µas residual

precision demonstrated (individual measuremens few 10 µas )


Lane et al 2000 Muterspaugh et al. 2005, 2006 Lane & Muterspaugh 2004

Difficulties •  Finding the relation between the measured delay and the “sky”

delay (sometimes called connecting the wide and narrow angle baseline). –  Requires a proper metrology monitoring as much of the

light path as possible; –  A precise calibration of any unmonitored delay

•  Example: reaching an accuracy of 10 µas on a 100m baseline requires –  To reach an internal delay accuracy of 5 nm; –  To know the baseline with an accuracy of 50 µm; –  To measure interferogram phase with 0.01 rad acc.

•  NUMEROUS adverse effects have to be taken into account


PRIMA


MOTIVATION


Perform astrometric planet search program with PRIMA @ VLTI

PRIMA and ESPRI consortium

•  ESPRI is leaded by Observatoire de Genève and MPIA Heidelberg

•  ESPRI contribution: DDL, astrometric operations, software

•  PRIMA development and implementation is supervised by ESO (PM F. Delplancke, Instrument Scientist: G. V Belle)


PRIMA description (I) •  Operated in K band •  Astrometry with the

ATs (2 at a time) •  Astrometry on UTs

affected by vibrations (but improving)

•  Phase Referenced imaging

•  Offering off-axis mode for AMBER and MIDI still considered but after astrometry

2010 May 27 Astrometry at VLTI disk/exoplanet 15 G. V Belle et al. Messenger 2009

PRIMA description (II)


All hardware on the mountain (more STS to come)

DDL

FSU

PRIMET

•  4 “new” hardware pieces added to VLTI

•  Star Separator Systems (STS)

•  Differential Delay Lines •  PRIMA metrology

(PRIMET) •  Fringe sensor units

STATUS •  FSU A tracks •  First commissioning

tracked to mk=9 •  PRIMET functionality

demonstrated •  Star Separator Systems

on the critical path for astrometry (situation currently assessed)

•  First dual star operation (end 2010-2011): to be confirmed


Sahlmann et al 2009

PRIMA expected performances •  Delicate matter: the instrument is being

commissioned lots of unknown; •  Measuring the narrow angle baseline propertly is the

key challenge. •  Two quantitative facts

– FSU has been demonstrated to track on K~9 stars;

–  System assessment of astrometric performances shows that the 10 µas might be hard to reach but still hope to reach 30 µas

•  MIDI and AMBER can make use of PRIMA subsystems to carry on limited imaging programs (phase referencing) and faint-object science with suitable off-axis reference


GRAVITY


Consortium •  PI: Eisenhauer, PS:T. Paumard, PM: S.

Gillessen •  Led by MPE Garching •  PHASE (LESIA-ONERA): France- G. Perrin •  MPIA Heidelberg-W. Brandner •  University of Cologne – A. Eckart •  LAO Grenoble – K. Perraut •  SIM (Portugal) – A. Amorim


1 0 0 1 0 2 1 0 4 1 0 6

m a x i m u m d i s t a n c e f r o m E a r t h ( p c )

single season campaign

three year program

ten year large

program

astrometric signal exo - Jupiter/Uranus

orbit of exo - Jupiter/Uranus

proper motions massive star cluster

detection of intermediate mass BH in GCs/Arches

detection of SR/GR effects in cusp star orbits

SgrA * flare dynamics

detection of ‘ dark halo ’ around SgrA *

stellar motions in nuclei of nearby galaxies

binary dynamics

gas flows in AGN

lensing

3 d dynamics of nuclear star cluster

imaging jets/disks in YSOs & CBs

evolution outflows in YSOs & micro - QSOs

GRAVITY SCIENCE GOALS


The Galactic Center with GRAVITY Solving the Paradox of Youth

Testing General Relativity

Exploring Physics at the Event Horizon


Exploring Physics at the Event Horizon


Testing General Relativity

S-star orbits

central cusp

flares

Galactic center


Gravity combines: - Imaging capability (10 milli arcsecond) with spectral resolution (~30,500, 5000) - Astrometric capability (10 micro arcsecond in 5 seconds) if suitable reference within 2 arcsec


Performances


Two modes: Narrow angle astrometry

2”

GC


Two modes: Interferometric Imaging

2”

GC

Contrast (B) <-> FourierTransform (Image)


STATUS •  PDR passed (Delta PDR adaptive optics) •  FDR: end 2011 (TBC) •  Still lot of R&D work •  First light: 2013-2014 (TBC)


Conclusion on Gravity •  Gravity’s main scientific goal is definitively

exciting but very challenging; •  There is a technical risk and Gravity should be

considered as an experiment; •  GC science is pushing the technical limits and

benefits to less demanding programs; •  Science cases are still opened …


BRAINSTORMING


PRIMA/GRAVITY


Characteristics PRIMA GRAVITY Field of view 30” 2” Imaging No Yes Sensitivity K ~9 measured K ~10 fringe tracking Astrometric max accuracy

30 mas 10 mas on K~15 with suitable reference (5mn)

Phase reference imaging

One baseline 6 baselines

Spectral resolution Small Low,medium,high (5000) First scientific light: 2010-2011 2014

PREDICTION

Exoplanet astrometric detection


Exoplanet astrometric detection

•  PRIMA has advantage: –  earlier on sky –  Larger reference field

of view

•  Gravity might have a niche in binary systems planetary detection: very efficient


Planet detection in binary systems •  Some binary systems provide suitable phase

reference for Gravity and authorize an astrometric search for planetary companions


24 Extrasolar Planets in Multi-Body Systems

Fig. 1. Left: minimum mass vs. orbital period for all the extrasolar planetary candidates

known in 2004. Planets orbiting a single star are represented as open circles, while

planets residing in binary or multiple systems are represented as dots. The dashed lineapproximately delimits the zone where only extrasolar planets belonging to binaries are

found. Right: eccentricity vs. orbital period for the same planetary candidates as before.

The dashed line approximately delimits the region where no planet-in-binary is found.

2004 we performed a statistical study considering both the period-mass and theperiod–eccentricity diagrams (Eggenberger et al. 2004b). As shown in Figure 1(left), our analysis confirmed that the few most massive (M2 sin i ! 2 MJup) short-period (P <! 40 days) planets all orbit a component of a binary or multiple star.However, the inclusion of several new planets in binaries with periods >100 daysand minimum masses in the range 3–5 MJup decreased the significance of thenegative period–mass correlation found by Zucker & Mazeh (2002). More recentstudies confirmed that only the observation that the few most massive short-periodplanets are all found in binary or multiple systems is a robust feature (Desidera& Barbieri 2007; Mugrauer et al. 2007).

Regarding the period–eccentricity diagram, our analysis emphasized that theplanets with a period P <! 40 days and residing in binaries tend to have low ec-centricities (e<! 0.05) compared to their counterparts orbiting single stars (Fig. 1,right). The confirmation – or refutation – of this trend looks more tricky (Desidera& Barbieri 2007; Mugrauer et al. 2007), probably because several di!erent mecha-nisms play a role in shaping the eccentricity distribution of extrasolar planets. Weplan to revisit this question once we have the final results from our two imagingprograms (Sect. 4).

Another intriguing feature is the observation that the four planets with thehighest eccentricities (e > 0.8) all have a stellar or brown dwarf companion (Tamuzet al. 2008). This association likely points towards eccentricity excitation by theKozai mechanism (Wu & Murray 2003; Takeda & Rasio 2005; Moutou et al. 2009).

Eggenberger EAS 2010

Planet detection in young systems •  Evidence for orbital evolution: signal probably

washed out, numerous caveats due to photometric variability but worth mentioning


Other exoplanet science


SPIN orbit alignment of Fomalhaut (Lebouquin et al 2008)

Exoplanet with closure phases

•  Phase information in an interferometer is lost due to the atmospheric fluctuations;

•  Closure phase cancels out atmosphere random fluctuations

•  State of the art error 0.1 degree R ~few 10

•  -> contrast 10^-3/510-4


From Monnier, 2007

Exoplanet with closure phases •  4 UTs simultaneously 3 nights •  Spectral resolution 100 •  Limited to bright host stars


Renard et al 2008.

K band low resolution (100) spectra of a selection of hot Jupiters that are NOT transiting their planets.

Young multiple systems studies

•  Astrometric detection of planetary induced Wobble using Gravity

•  Astrometric detection of close pairs (hard to do with RV)

•  Monitoring accretion in multiple systems

•  Disk truncation studies through imaging


Disk science •  Gravity will have a good

combination of imaging capability (4 telescopes) with spectral resolution but restricted to the K band

•  Disk science (with extrapolation) •  Disk radial temperature

distribution; •  Disk clumpiness •  Time variability •  Vertical structure (in favorable

cases) •  Dust and hot gas distribution

(CO, Br γ tracers)


!"#

$%&'()*%&!"#$*)+*&,)-

Inner rim of an Herbig Ae star with and without inner gas component

Young and debris disks

•  Gravity is also an imager

•  Precision interferometry: probable maximal dynamical range: 1000

•  Hot dust component monitoring

•  Potential phase reference imaging


Absil et al. 2006, 2008

Conclusions •  Two instruments at VLTI will provide

astrometric capability in the 2 to 5 years; •  Both could in principle have sufficent accuracy

to detect a stellar wobble induced by massive planetary companion

•  But Planet/Disk science case can take benefit of extended potential provided by PRIMA and GRAVITY

•  Off-axis faint mode (PRIMA) •  Imaging/Phase reference imaging (Gravity)

•  There is probably a lot more to do … 2010 May 27 Astrometry at VLTI disk/exoplanet 43

astrometry at vlti application to disk/exoplanet science...

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