Spatially Resolved RoSpatially Resolved Ro--Vibrational Vibrational HH22 Emission from the Disks of Emission from the Disks of Young Stars?Young Stars?

Tracy L. Beck (Tracy L. Beck (STScI)STScI)

Jeff Jeff BaryBary (Colgate University), with(Colgate University), with

Anne Anne DutreyDutrey,, StephaneStephane GuilloteauGuilloteau , Emmanuel , Emmanuel DiFolcoDiFolco (U. of Bordeaux)(U. of Bordeaux)

Vincent Vincent PietuPietu (IRAM), Steve (IRAM), Steve LubowLubow (STScI) and Mike Simon (U. Stony Brook)(STScI) and Mike Simon (U. Stony Brook)

Circumstellar Disks Around Young Stars

Williams & Cieza ARA&A 2011

8/2/2012 TBeck, AAS

Young, Classical T Tauri star phase “Classical” T Tauri star phase

Stellar Mass Accretion StopsPlanetesimals and 2nd

Generation Dust

Understanding Disk GAS and its

evolution/accretion/dissipation

is particularly important for

models of terrestrial planet

formation

Gas In

Classical T

Tauri Star Disks

Dis

k H

eig

ht

Disk

Is H2 emission from young star

disks centrally compact, arising

from the immediate vicinity of

the star (<20AU?)

8/2/2012 TBeck, AAS

Near IR ro-vibrational H2

Emission – Important Disk

cooling mechanism for

moderate density material

(103-107/cm3), within est.

<5AU distances from the

central star from these models

1-10 AU = Terrestrial planet

formation region Dis

k H

eig

ht

From Woitke et al.

2009

A Search for Spatially Resolved HA Search for Spatially Resolved H22 Emission from Emission from Young Star DisksYoung Star Disks

.

Gemini + NIFS AO-fed IFU Survey for H2 from the environments of

Young stars – the search for compact H2 gas from the inner disks9 Targets with past evidence for “disk-like” H2 gas (zero velocity shift, spatially unresolved):

• AA Tau

• AB Aur (Bitner et al. 2008; mid-IR detection of H2 rotational

8/2/2012 TBeck, AAS

• AB Aur (Bitner et al. 2008; mid-IR detection of H2 rotational

emission)

• DoAr 21

• GG Tau A

• GM Aur

• LkCa 15

• LkHαααα 264

• UY Aur

• V773 Tau

All but AB Aur are prior near-IR ro-vibrational

H2 detections (Bary et al. (2003), Itoh et al.

(2003), Carmona et al. (2008))

HH22 Emission from the Inner Disks of Emission from the Inner Disks of Young Stars?Young Stars?

.

NIFS Near-IR IFU Survey of 9

stars – Data from 2009

Queue program

K-band continuum images of

the young stars in the new

survey � but… every spatial

position in the field has an

*

8/2/2012 TBeck, AAS

position in the field has an

associated R~5000 spectrum!

FWHM typically -.”09 – 0.”12

(12-16 AU)

Binaries to 0.”2 are easily

spatially resolved. Young star

multiples = GG Tau, UY Aur,

V773 Tau

* - 0.”2 Occulting SpotYoung stars in the Taurus Star forming region, 0.”1 = 14AU

Spatially Resolved HSpatially Resolved H22 Emission?Emission?

.

Greyscale image of H2

Emission, with continuum

contours in BLUE.

Moderate the v=1-0

S(1) 2.12 µm H2 emission is

detected in 7 of the 9 sources

in this survey!

& in all 7 cases, Emission

*

8/2/2012 TBeck, AAS

& in all 7 cases, Emission

is Spatially Resolved!

Only AB Aur and LkCa 15 did

not have appreciable H2

emission detected

(& Our NIFS data had lower

line sensitivity than the past

high spectral resolution data)

* - 0.”2 Occulting Spot

GG Tau A GG Tau A –– “The Ring World”“The Ring World”

.

• GG Tau A – ~0.”25 binary

surrounded by a (massive)

circumbinary dust ring

(~120-180AU) with a dust-

cleared “hole”

encompassing the binary,

• Circumbinary Ring Circumbinary

8/2/2012 TBeck, AAS

• Circumbinary Ring

discovery by Dutrey et al.

(1994) – Imaged in

scattered light by

• Roddier et al. (1996) –

Contrasts of >103 at 1”

distances - An Early

Triumph of Ground-Based

Adaptive Optics!

Circumbinary

Ring

Because of it’s optimal orientation and massive circumbinary Ring, GG Tau A is ideally suited to

study the physics of mass accretion onto a central stellar binary (i.e., young star binaries,

evolved binarys, X-ray binaries, etc…)

Binary Star

Roddier et al. (1996)

Dynamical Models of Mass Accretion in Stellar Dynamical Models of Mass Accretion in Stellar BinariesBinaries

De

nsi

ty

Circumbinary Ring

Dynamically

8/2/2012 TBeck, AAS

Dynamical Binary+Disk Models of Gunther & Kley (2002)

De

nsi

tyDynamically

Cleared

CavityStars

Mass Accretion

“Streamers”

GG Tau A GG Tau A –– A Veritable Laboratory for Studying A Veritable Laboratory for Studying Binary Disk Binary Disk EvolutionEvolution

.H2 Emission from GG Tau A

8/2/2012 TBeck, AAS

GG Tau A – H2 emission Image - H2

arises from inside the dust ring, &

encompasses the inner binary – in

regions that should be dynamically

cleared on ~100’s of year timescales!

(Beck et al. 2012)

GG Tau A – The Controversy continues!

Ring Accretion “Streamers”? Or no Accretion Streamers?

(HST + ACS scattered light imaging – Krist et al. 2005)

GG Tau A – The Gemini +

Hokupa’a Polarimetric AO

Data (Potter et al.)

GG Tau AGG Tau AGas Accretion Streamers!Gas Accretion Streamers!

.

8/2/2012 TBeck, AASH2 Line Emission – detection of “Streamers” at good S/N

HH22 Emission from The GG Tau A Emission from The GG Tau A Inner RegionInner Region

.

H2 from GG Tau A

Weak detection of v=2-1 S(1)

emission, flux level of ~5% of

the flux of the v=1-0 S(1).

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Gives Tex~1700K for gas in LTE

This is rather high for gas at

~25-40AU distances – more

typical of shock excited

emission

(VERY HIGH CONTRAST - that’s

a ∆∆∆∆mag difference of ~9.0 mag

@0.”25 separations for

sensitivity to weak H2!!!)

GG Tau AGG Tau ADust Accretion Streamers?Dust Accretion Streamers?

.

8/2/2012 TBeck, AAS

1.1mm map of

the dust ring…

Detection of

dust accretion

streamer…?

Pietu et al.

2011

GG Tau A GG Tau A -- MassMassAccretion Streamers?Accretion Streamers?

. Peak H2 Emission Corresponds

exactly in location to the putative

dust “streamer”….

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H2 Tex~1700K

More typical of Shock Excited

Emission – Might we be seeing

Shocks from MASS ACCRETION

INFALL???

Gemini NIFS H2 Image with overplotted 1.1mm

continuum dust contours

GG Tau A GG Tau A -- MassMassAccretion Streamers?Accretion Streamers?

.

More Data is Needed to

Investigate the hypothesis of

Mass Accretion INFALL Shocks!

Pending Data…

• ALMA “Cycle 0” project for

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• ALMA “Cycle 0” project for

mm dust and CO gas maps

(Dutrey)

• VLT PIONIER interferometry

and VISIR Mid-IR

spectroscopy of Inner Disks

(PI=DiFolco)

• Hubble Space Telescope

“Cycle 20” UV Imaging of

low density Electronic H2

(Beck)

A Search for Spatially Resolved RoA Search for Spatially Resolved Ro--Vibrational H2 Vibrational H2 Emission from Young Star Disks?Emission from Young Star Disks?

.

• H2 Gas Emission is spatially resolved all of the targets we’ve detected it in! (w/ only 2 non-detections in the 9 star survey)

• The Proto-typical Circumbinary Ring System, GG Tau A, exhibits appreciable H2 emission from the regions within the ring, from areas that should be dynamically cleared on very short timescales.

8/2/2012 TBeck, AAS

appreciable H2 emission from the regions within the ring, from areas that should be dynamically cleared on very short timescales.

• H2 from GG Tau shows “streamer”-like extensions at high S/N, revealing evidence for gas emission likely flowing toward inner distributions of material (disks)

• Pending Observations of GG Tau A will provide the first comprehensive, multi-wavelength UV to sub-mm spatially resolved data set on gas and dust accretion in a binary star system!

The Goal: HThe Goal: H22 Emission from YSO Disks?…Emission from YSO Disks?…

.

Of the 9 new systems observed, two have H2 Emission that mostly

arises from within <0.”7 (<100AU) and is concentrated around the

central star(s) – consistent with disk models.

GM Aur, LkHα 264

8/2/2012 TBeck, AAS

H2 emission from LkHα 264 (Itoh et al. 2003; Carmona et al. 2008)

and GM Aur (Bary et al. 2003) is centrally compact – but it *is*

spatially resolved in our data. Integrated ~1-2 Lunar masses worth of

H2 emitting Gas at <~50 AU distances from the central star.

Evidence for Outflow Emission in the Evidence for Outflow Emission in the New SurveyNew Survey

.

V773 Tau – sub-arcsecond quadruple system, strong X-ray flares, with “IR companion”.

H2 strong at IR companion position, shows moderate velocity structure in two knots.

8/2/2012 TBeck, AAS

H2 Emission is likely excited by multiple processes?

V 773 Tau has the strongest integrated H2 line emission detected in this survey of nine stars.

H2 velocity structure

HH22 Emission from Disks?Emission from Disks?The Joy of IFU SpectroscopyThe Joy of IFU Spectroscopy

.

H2 gas from GG Tau A

8/2/2012 TBeck, AASH2 is 0.6% of the continuum flux.

Image Stretched for Dynamic Range,

Resolved H2 detection is very high S/N

A Search for HA Search for H22 Emission from YSO Emission from YSO Disks!Disks!

• We now have spatially resolved K-band spectroscopy of nearly 20 young stars – including Class I protostars, Classical T Tauris and “transition” disk systems with more “disk – like” H2.

• Very young protostars and Classical T Tauri stars that have active outflows all have H2 emission excited by shocks in the flows.

• Several sources with “disk-like” H2 emission also show evidence for shock-heating of the H , some have evidence for multiple emission components.

.

8/2/2012 TBeck, AAS

heating of the H2, some have evidence for multiple emission components.

• The two sources in our study that are known to have strong X-ray flare activity (DoAr 21 and V773 Tau) also exhibit significant spatially extended low-velocity H2, implying that X-rays likely can heat the molecular gas into emission even at large distances from the star (>100 AU!).

• Three systems in our study, GG Tau A, GM Aur, and LkHα 264 have H2emission that is consistent in morphology, kinematics and excitation (where available), with inner (disk) gas stimulated into emission by the central star.

• In no case do we find H2 v=2-1 (S1) / v=1-0 S(1) line ratios that are consistent with UV fluorescent excitation (this may not be surprising, moderate density non-thermal excitation environments will quickly reach LTE conditions).

H2 in the Inner 200 AU Environs ofYoung Stars

• UV Observations suggest moderate amounts of H2 emission excited by Lyα pumping,UV Fluorescence and/or Xray heating in the inner ~20-30 AU from a TT star (Ardilla et al. ‘02; Herczeg et al. ‘04; ‘06; 12; Walter et al. ’03)

• Detections of Near IR ro-vibrational emission, mid - IR rotational H2 from YSO disks (Bary et al. 2003; 2008, Bitner et al. ‘08)

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H2 from YSO disks (Bary et al. 2003; 2008, Bitner et al. ‘08)

• Seeing-limited spectra of near IR H2 also suggest emission from T~2000K - gas in LTE from Outflow Shocks (Davis et al. ‘00; ‘01; Takami et al. ‘04; ’06, Beck et al. 2008)

• Relationship between UV H2 electronic features, ro-vibrational IR H2 emission, and pure rotational emission detected in the mid-IR?

Existing H2 data consists of different wavelength regimes (probing different Avs), different sensitivities, & different spatial and

spectral resolutions. & H2 could be intrinsically time variable!

DoArDoAr 2121

.

YSO in Ophiuchus - Classified in the past as a

“transition disk” system – but is it?H2 Emission from DoAr 21

8/2/2012 TBeck, AAS

Little to no dust mid-IR excess emission

within 100 AU of the star. Significant

X-ray flare activity.

Jensen et al. (2009)

H2 Emission does follow extended mid-IR

excess flux… (particularly consistent with

18 micron dust map) Implying that X-ray

active flare stars can likely excite the gas

into emission at large distances from the

central star!

AB AB AurAur

.

Herbig AeBe star in Auriga - pure rotational H2

emission detected from 3 transitions, with a Temp

~670K.

H2 Emission from AB Aur

8/2/2012 TBeck, AASBitner et al. (2007)

H2 Emission is detected at only weak

level of significance (~3σ) immediately

around the star – but two extended

knots of H2 are detected with higher

confidence.

Evidence for Outflow Emission in the Evidence for Outflow Emission in the New SurveyNew Survey

.

AA Tau – A single star with a disk viewed

nearly edge-on. With periodic variations

in HI emission structure attributed to a

20degree tilted magnetosphere

compared to the star’s spin axis. This

results in a disk warp and periodicity

from the rotational structure as the inner

8/2/2012 TBeck, AAS

from the rotational structure as the inner

mass accretion columns occult the star

(Bouvier et al. 2007). Source has an inner

‘micro-jet’ (Cox et al.), with a wide

opening angle – poor collimation. IR

observations show water emission lines,

and strong [Ne II].

H2 Emission is detected south of the position of the star, most is extended in a “pie slice”

shaped region (is this the wide angle outflow?) – No velocity structure (v~45km/s) a bright

extended knot of H2 is detected at ~70AU. Tex ~ 2000K in the knot.

Evidence for Outflow Emission in the Evidence for Outflow Emission in the New SurveyNew Survey

. UY Aur – Significant H2 is seen all

around this 0.”9 young star binary.

H2 is stronger around the brighter

star, rather than the “infrared

companion”. Morphology shows an

8/2/2012 TBeck, AAS

companion”. Morphology shows an

arc around the brighter star, sort of

reminiscent of the arc of emission

seen in Haro 6-10, perhaps

encompassing the known HH jet (HH

386… ?).

AB AB AurAur

.

AB Aur H2 AB Aur – continuum subtraction uncertainty

0.”2 Occulting Spot

8/2/2012 TBeck, AAS

AB Aur – Movie in ~29km/s velocity steps

across the H2 emission wavelength…

For Comparison, movie across

continuum subtracted continuum

emission – e.g., as a measure of the

noise in the subtraction process.

AB AB AurAur

.

H2 Emission is detected at only

0.”2 Occulting Spot

8/2/2012 TBeck, AAS

AB Aur – Movie in ~29km/s velocity steps

across the H2 emission wavelength…

H2 Emission is detected at only

weak level of significance (~2σ)

immediately around the star.

But two extended knots of H2 are

detected with higher confidence

– one slightly blueshifted (south)

and one slightly redshifted

(north) compared to central

emission

H2 Lines Detected in the IR K-band (2.0-2.45 µm)

• Ro-vibrational diagram of the first

electronic level in the H2 molecule

• Features detectable in the IR K-band (2.-

=2.4µµµµm) include v=1-0, 2-1 and 3-2

transitions

TA Brief reminder on H2 level populations,

transitions in the IR

8/2/2012 TBeck, AAS

transitions

• V=1-0 S(1) at 2.12 microns is the brightest

IR transition

• Significant level population in the high v

and high J states in IR spectra is

characteristic of non-thermal excitation in

YSO environments - i.e., UV pumping and

resulting cascade through ro-vibrational

transitions. Non-thermal UV excitation in

astronomical environments has v=2-1 S(1)

/ v=1-0 S(1) ratios of ~0.5.V=1-0 Q(3) & S(1)

V=2-1 S(1)

The Disks of Young Stars

• Dust in the disks of Young stars:• Class I protostars (extended disks + remnant envelope material – very strong IR flux

excess

• Classical T Tauri Stars - optically thick dust disks

• “Transition” stars, with SED structure implying gaps or holes in the disks (initial stages of planet formation?).

• What about the gas? (For more on gas, See Ilaria’s “Hot Sci” talk – 8/11/10)

• Models for planet formation are very sensitive to the gas evolution and

8/2/2012 TBeck, AAS

• Models for planet formation are very sensitive to the gas evolution and gas-to-dust ratio in a young star’s disk.

• To date, measurements have variously found consistent and discrepant values to the ISM level of gas/dust ~100. (Thi et al. ‘10, Glauser et al. ’08)…• The preferential removal of gas in the disks is believed to help dust

instabilities develop (Throop & Bally ‘05)

• Photoevaporation can reduce the gas-to-dust ratio below the canonical value of 100, leading to an overestimate of disk mass in current studies.

• Accurate measurement of disk gas mass is difficult, and likely requires measurement and study of multiple emission species!

Molecular Hydrogen Gas in YSO Environs -Why do we care?

• H2 is the dominant constituent of ANY cool gas!

• Circumstellar YSO Disks = Cool Gas, Studies that seek to characterize future planet formation in YSO disks need to understand how the gas contributes to the evolution.

• So far, many studies done in UV, reveals inner excitation structure, but can penetrate to low Av only (Ardilla et al. 02, Herczeg et al. 04’; 06).

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penetrate to low Av only (Ardilla et al. 02, Herczeg et al. 04’; 06).

• “Trendy” topic - many papers on IR H2 in the last few years, some sources with known outflows - most conclude that the H2 arises from “quiescent” emission in disks (Ishii et al. 06; Bary et al. 03;08, Bitner et al. 08; Carmona et al. 08, Bitner et al. ‘08).

• Quiescent H2 gas in the solar-system regions of YSO disks could be spatially resolvable in the near-IR using present technologies (20-50AU = ~.”15-0.”35 @ 140pc; Nomura et al. 2008).

• Surprisingly little is known about the relation between quiescent H2 in planet-forming disks versus shocked emission in YSO outflows (Spatially resolving the emission location might help).