ALMA Cycle 0 Observation of Orion Radio Source I

Tomoya Hirota (Mizusawa VLBI observatory, NAOJ)

Mikyoung Kim (KVN,KASI)Yasutaka Kurono (ALMA,NAOJ)Mareki Honma (VERA, NAOJ)

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• Astrometry of Orion KL– VLBI Exploration of Radio Astrometry (VERA)– 2.29+/-0.10 mas = 437+/-19 pc (Hirota et al. 2007)

Distance to ONC

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• VERA– 437+/-19 pc (H2O maser in Orion KL: Hirota et al. 2007)– 418+/-6 pc (SiO maser in Orion KL: Kim et al. 2008)

• VLBA– 389 +24/-21 pc (GMR-A@15GHz continuum: Sandstrom et al. 2007)– 414+/-7 pc (4 WTTSs@8GHz continuum: Menten et al. 2007)

Distance to ONC

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Source I(masers)

1’ = 0.12pc

(NIR image of ONC; Menten et al. 2007)

• Key object to study formation of massive YSOs– Dominant source in KL nebula (Menten & Reid 1995)– One of the nearest massive protostar candidates– But, still enigmatic object (Tan, yesterday’s talk)

Orion KL Source I

Hirota et al. (2007)Kaifu et al. (2000)

Kim et al. (2008)

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• High-velocity explosive NW-SE outflow– NIR (Bally et al. 2011), CO (Zapata et al. 2009)

• Low-velocity bipolar NE-SW outflow– SiO, H2O masers (Greenhill et al. 2013)

Unresolved issues; outflow

Greehill et al. (1998/2004)Subaru NIR imageKaifu et al. (2000)

ALMA SV SiO thermal line (Niederhofer et al. 2012) 5

• 20M binary formed by dynamical decay – Proper motion (Bally et al. 2011, Goddi et al. 2011)

• 7M protostar with accretion disk– Velocity of SiO masers (Kim et al. 2008, Matthews et al. 2010)

Unresolved issues; mass

Goddi et al. (2011) Kim et al. (2008) 6

• 20M binary formed by dynamical decay – Chatterjee & Tan (2012) proposed alternative scenario

• 7M protostar with accretion disk– Velocity of SiO masers (Kim et al. 2008, Matthews et al. 2010)

Unresolved issues; formation

Kim et al. (2008)Chatterjee & Tan (2012) 7

• Geometry of outflow (and disk)– NW-SE? NE-SW? Both?

• Emission mechanism of radio continuum– Radio jet? Ionized disk? Neutral disk?

• Mass of Source I– 20M binary? 7M single?

• Formation mechanisms– Merging/dynamical decay? Accretion?

• Need more observations at high angular resolution

Unresolved issues

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• Spectral line observations at band 7– Three epochs on Jul. 16, Aug. 25, and Oct 21, 2012– Extended configuration with 21, 28, and 22 antennas– Spatial resolution ~0.4”

• Observed lines– H2O (v=0) 321 GHz (Eu=1862 K)– H2O (v=1) 336 GHz (Eu=2956 K)

ALMA cycle 0 observations

Array configuration 9

Distribution of 321 GHz line

• Distribution of 321 GHz H2O line– Detected only around the radio source I– Marginally resolved along the major axis– Velocity gradient along the minor axis

H2O (321GHz) Contour; intensity Color; peak velocity

Contour; Band 6 continuum Color; H2O (and HCOOCH3) 10

Velocity structure of 321 GHz line

• Velocity gradient of the H2O lines– Perpendicular to NE-SW outflow – Analogous to the SiO masers (Kim et al. 2008)

SiO (43 GHz, VERA)H2O (321GHz) Contour; intensity Color; peak velocity

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More detailed structure

• Detailed analysis of the 321 GHz line– Gaussian fitting of peak position at each velocity channel– “Inverted Z-shaped” structure

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More detailed structure

• Comparison with 321 GHz and SiO masers– Very similar to each other, suggesting common origin– Root of bipolar outflow arising from the disk surface– Magnetically driven disk wind (Greenhill et al. 2013)

PdBI map of SiO 86 GHz(Baudry et al. 1998)

VLA map of 43 GHz SiO(Menten et al. 1995) 13

Comparison with 321/336 GHz lines

• Distribution of 336 GHz H2O line– Vibrationally excited state at El~3000 K– More compact structure – Velocity gradient comparable to the 321 GHz line

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Velocity structure of 336 GHz line

• Comparison with 336 GHz and SiO masers– Anti-correlation with each other– Position-Velocity (PV) diagram indicates an edge-on rotating ring-like structure with an enclosed mass of ~7M

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Velocity structure of 336 GHz line

• Comparison with 336 GHz and SiO masers– 336 GH line is thermally excited (Alcolea & Menten 1992)– Spectral profile can be fitted with Tex ~ 3000 K– Hot/neutral gas with radius ~50AU

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Origin of sub-mm H2O lines

• Tracing hot/dense neutral gas– Strong evidence of rotating circumstellar disk around massive protostar Orion Source I

SiO thermal lines22 GHz H2O masers

SiO masers321GHz H2O line

336 GHz H2O lines

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• High excitation H2O line is detected by ALMA. • The vibrationally excited H2O line map shows a

velocity gradient consistent with a rotating ring-like structure with the enclose mass of 7Mo.

• Detection of high excitation (~3000K) molecular gas shows definite evidence of hot and neutral gas disk around Source I.

• But, … there are still unknown parameters!• To be continued to higher resolution ALMA cycle 1

(and 2) observations with multi-transitions

Summary

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