Interferometry in the visibleInterferometry in the visible

Young Stellar Objects

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M. Benisty, S. Kraus, K. Perraut (leader), G. Schaefer, M. Simon

Science cases for visible interferometry – Nice, January, 15th

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Nuage moléculaire

10 pc ― 4°

Effondrement Fragmentation

1 pc ― 20’ 0.1 pc ― 2’(Taurus)

1000 AU ― 7’’ 300 AU ― 2’’ 30 AU ― 0.2’’

Accretion disk and bipolar ejection

Molecular clouds Collapse Fragmentation

Debris disk and protoplanets Planetary system

105 / 106 yrs old

[Bouvie

r &

Malb

et

20

01

]

Scientific rationaleScientific rationale

OutlineOutline

Fundamental parameters of YSO

Complex environment

Summary of High-Level Requirements

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OutlineOutline

Fundamental parameters of YSO

Complex environment

Summary of High-Level Requirements

4

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Fundamental parameters of YSOFundamental parameters of YSO

For low-mass (M < 1 Mʘ) young (< 10 Myr) PMS stars the mass and age estimates vary according to the evolutionary tracks used.

The mass spectrum of low mass stars (the majority!) is imprecisely known. The chronology of planet formation is also imprecisely known.

Situation and opportunitiesSituation and opportunitiesM < 1 Mʘ : Dynamical measurements of masses will

“calibrate” the theoretical calculations of evolution. Masses < 0.5 Mʘ are particularly required.

Studies of Taurus and Ophiuchus star forming regions (1 to few Myr; 120-160 pc)

M > 1 Mʘ : Theoretical calculations are consistent.Hence diameter measurements of a star determine its

age! Studies of stars in the older (10 Myr +), but closer

(few pc +) “Nearby Young Moving Groups”

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Interferometric measurementInterferometric measurement

1 AU orbit at 140 pc (eg Tau and Oph) subtends 7 mas. at 10 pc: 1.0 mas (Sun); 0.5 mas (M0V)

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Angular diameters in Tau or Oph unresolvable Interferometric measurement of dynamical masses in these

regions possible for visual binaries and some SB Diameters of F and G stars in Nearby Young Moving Groups

resolvable if close enough

Baseline (m) = 0.6 µm = 1.0 µm = 1.5 µm

100 0.62 1.03 1.5

200 0.31 0.51 0.77

300 0.21 0.34 0.5

Angular Resolution (mas) at

Census of dynamical massesCensus of dynamical masses

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EclipsingBinaries

ResolvedSpectroscopic

BinariesN=4

N=8 N=8

Masses with precisions measured to better than 10%

Few precise masses below 0.5 Mʘ

MIRC observations of Ori Aa-Ab [Schaefer et al., in prep]

MAa = 16.8 ± 0.4 M⊙

MAb = 12.8 ± 0.3 M⊙

d = 385 ± 3 pc

Resolving PMS Spectro binariesResolving PMS Spectro binariesTaurus-Auriga

OphiuchusSco-Cen

ChamaeleonOrion

NGC 2264

Spectral Types: F-M

V (mag)

a si

n i (

mas

)

R-band K-band

39 21

PMS binaries resolved with a baseline of 300 m

Going down to R-band doubles the sample

Resolved SB2

EclipsingSB2

3D structure of Taurus SFR3D structure of Taurus SFRStars with measured proper motions [Ducourant et al. 2005]

Stars with measured distances [Torres et al. 2009; Simon et al. 2013]

CO clouds[Dame et al. 2011]

The clumps where starsformed range from 131 to 161 pc.

Need distances to L1495N, L1551 (hosting GG Tau)

Nearby Young Moving GroupsNearby Young Moving Groups

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NYMGs are stars known to exist in the vicinity of the Sun as members of “moving groups” each consisting of stars moving in the same approximate direction with the solar neighborhood.

They are young: 8-12 Myr ( Pic moving group)~ 40 Myr (AB Dor moving group)

They are nearby: from a few to 100 pc.

Most members of the NYMGs are in Southern hemisphere but somemembers of Pic and AB Dor are inthe North.

Known members of Pic NYMG [Schlieder et al. 2012]. Spectral type is coded by color.

HIP 21547 (0.518 ± 0.009 mas)HIP 25486 (in progress)HIP 560 (0.492 ± 0.013 mas)

Measure diameter of stars in NYMGsMeasure diameter of stars in NYMGs

[Schlieder 2012, PhD Thesis]

AB Dor MG

Pic MG

NOTE: angular diameter (mas) scaled to a common distance of 10 pc

[Simon & Schaefer 2011]

Measure diameter of NYMG membersMeasure diameter of NYMG membersV mag Star number Spectral Type

3-4 1 A

4-5 1 A

5-6 3 2A, 1F

6-7 5 5F

7-8 6 4F, 1G, 1K

8-9 3

9-10 4 Mostly G and K

10-11 13

11-12 11

12-13 6 Mostly M

13-14 2

14-15 1Known members of Pic NYMG in 2008[Torres et al. 2008].

All the F stars can be resolved at 1 μm with baselines ≥ 100 m

F stars are in the “sweet spot” for angular diameter and hence age measurement: they are bright, near to us, their evolutionary tracks are reliable, and they are still above ZAMS.

OutlineOutlineFundamental parameters of YSO

Complex environment

Summary of High-Level Requirements

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Structure of a protoplanetary diskStructure of a protoplanetary disk

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[Dullemond & Monnier 2010]

Near-infrared (spectro-)interferometry directly probes the emission within the innermost astronomical unit (AU), where key quantities for the star-disk-protoplanet(s) interactions are set. The regions probed by this technique are much more complex than expected.

3D MHD simulations of accretion (driven by magneto-rotational instability) on to a rotating magnetized star with a tilted dipole magnetic field produce complex maps.

All these complicated inner disk structures are strongly time variable on a timescale of weeks to years …

The complex innermost regionsThe complex innermost regions

[Romanova et al. 2012]

Accretion via the accretion columns (T Tau) or the inner disk Connections star/inner disk, inner disk/dust disk ? Morphology of the inner rim of the dust disk ? Processus of dissipation and evolution of the disk ? Law of temperature, velocity, density in the disk ?

Ejection via a wind (star, disk, …) and jets Launching point and morphology of jets ? Mechanisms that favor jet collimation ? Mass-loss rate wrt mass-accretion rate ?

Formation of the Hydrogen emission lines Connection between accretion and ejection

Line forming regions ? Mechanisms that could explain the temporal variability ?

Accretion-ejection phenomenaAccretion-ejection phenomena

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H (and also Ca II triplet at 850/854/866 nm)

Accretion tracer [Hartmann et al. 1994], likely tracing structures on the stellar surface and in the magnetospheric accretion columns (3-5 R*)

Forbidden lines (e.g. [OI], [NII], [FeII], [SII])

Trace low-density gas, sometimes associated with jets and outflow. However, this emission is typically distributed over many arcseconds [Podio et al. 2011; Bacciotti et al. 2002]

possibly overresolved with interferometry

Visible spectral linesVisible spectral linesDG Tau vs. FU Ori spectra

1 R* = 0.07 mas @ 140 pc Requires very high angular resolution

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Visible spectral linesVisible spectral lines

Lines (nm) EW (Å)

H 656.2 20 - 150

Ca II triplet 849.8 854.2 866.2

0.5 - 50

He I lines 667.8 706.5

0.5 – 2

O I lines 777.2 844.6

-1.6 - 8

[0I] line 630 < 15

[SII] line 673.1 < 5

[FeII] line 715.5 < 2

Requires very high spectral resolution

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The He IThe He I1.083 line1.083 line

• A unique diagnostic of kinematic motion in the regions close to the star.

• High opacity: a very sensitive probe to the geometry of the mechanisms at play.

• He I line is composite:• Blue-shifted absorption (wind)• Red absorption (accretion)

[Edwards et al. 2003]

[Kurosawa et al. 2011]

Very compact wind (few R*) that requires very high angular resolution

• Stars orbit in a gap opened by tidal interactions inside a circumbinary disk.

• Young short period binaries (P < a few 10 days, sep ~ a few 0.1 AU) cannot support large circumstellar disks.

Circumbinary disk

• Evidence of enhanced emission line activity close to periastron passages (DQ Tau [Basri et al.1997], UZ Tau E [Martyn et al. 2005])non-axisymmetric accretion

Accretion in close binariesAccretion in close binaries

21[de Val-Borro et al. 2011]

V4046 Sgr

Simulated accretion streamersSimulated accretion streamers

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[de Val-Borro et al. 2011]

0.2 mas

R mag = 9.5

Interferometry will provide a critical test of simulations such as these.

Planets and brown dwarfsforming in the disk shouldexhibit accretion

signatures (H- emission)

Detecting low-mass companionsDetecting low-mass companions[Close et al. 2014]

w/o extinction

Brown Dwarf < 10-3

Jup. < 10-4

Expected contrast (companion/star)

Requires high contrast imaging at moderate spectral resolution

Contrast could be dramatically reduced due to extinction

Imaging in scattered light could reveal asymmetric structures that might be linked to planet formation, similar as seen in the outer disk [Mouillet et al. 2001]

Combining scattered light imaging in

VIS/NIR constraints dust size distribution

and vertical dust stratification(Mulders et al. 2013)

Total integrated scattered light contributions are about 100-times fainter than stellar flux

HD141569, HST

HD100546

Scattered light disk featuresScattered light disk features

Requires high-fidelity, high-contrast imaging Interest of polarimetric mode (SPHERE) or nulling

OutlineOutline

Fundamental parameters of YSO

Complex environment

Summary of High-Level Requirements

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Summary of High-Level SpecsSummary of High-Level Specs

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Science cases Baseline Spectral resolution

Imaging

Diameter of stars in SFR Unreachable

Diameter of stars in NYMGs

> 100 m

Dynamical masses 300 m

Accretion-ejection Hectometric A few 1000 (H)

1 few 10000

Yes

Companion Hectometric High-contrast

Scattered light Hectometric High-contrastHigh-fidelity

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From Kenyon et al. 2008

Limiting magnitudesLimiting magnitudes

In Ophiuchus, K-mags are similar but R are fainter because of greater extinction.

ConclusionsConclusionsYSO is a strong science case for interferometry in the

visible. Interferometric Imaging and Spectroscopy will provide

unique and complementary data for understanding star and planet formation. The techniques will probe the innermost regions protoplanetary disks and will enable diameter measurements of stars still contracting to the main sequence.

The science case is very challenging mainly because of the brightness of targets.

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Differences among modelsDifferences among models 1.0 Mʘ 0.1 Mʘ

Increasingly ideal gas in interior Increasingly non-ideal

Radiative transport increasingly Radiative transport less important important in core

Convection increasingly important

Peak of spectral energy distribution increasingly affected by broad molecular absorption

Therefore:1) Equation of state 2) Radiative and molecular opacities are very important.3) Treatment of convection4) Model atmospheres