Early O-Type Stars in the W51-IRS2 ClusterA template to study the most massive (proto)stars

Luis ZapataMax Planck Institut für Radioastronomie, GERMANY

May 2009THE EVLA VISION: STARS ON AND OFF THE MAIN SEQUENCE

Outline

• Comments on the formation of massive stars

• The young and massive cluster W51 IRS2

• VLA and SMA observations of the W51 IRS2

• Tracing the evolutionary phases of the early O-type (proto)stars Hot massive disks, molecular rings, and HC and UC HII regions

• The ELVA vision of massive young stars

The formation of the massive stars

Some fundamental theoretical problems to form massive stars (M* > 10 Msun):

o The Kelvin-Helmholtz time is much shorter than the free-fall time -- radiation pressure (spherical geometry)

o The strong UV fields will ionize the surrounding molecular gas by so fast

o The short main-sequence lifetime of high-mass stars

Some observational problems to study massive (proto)stars:

o They are located far away, more than 1 kpc (with exception of Orion)

o There are a short number of massive (proto)stars

o They are very embedded in the molecular cloud -- only observable in radio and IR bands

Some possible solutions

o Circumstellar Large Disks A Natural outcome !!

o Very high accretion rates that quenched or trapped the formation HII regions

o Mergers of low mass stars

o Competitive accretion

W51 ComplexSagittarius Arm

HJK-InfraredCFHT

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W51VLA 3.6 cm.Lacy et al. (2007)

Infrared: grey scale (VLT) 3.6 cm: contours

W51 IRS2

W51 IRS1

W51 East

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W51 IRS2Infrared (JHK)Barbosa et al. (2008)

IRS2W (O3-type)

IRS2E (O4-type)

Lbol= = 3 x 106 Lsun

D ~ 6, 000 pc~ 30 O-type protostars

7000 AU

One of most luminous regions in the Galaxy

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Ammonia (J,K)=(3,3)W51 North & W51 D1VLA

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Ho et al. (1983) Gaume et al. (1993)

1.3 cm emission: dashed contoursNH3: continuous contours

NH3: dashed contours3.6 cm: continuous contours

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Imai et al. (2002)

Einser et al. (2003)

H2O and SiO Maser SpotsVLBI

Powerful Bipolar very compact NW-SE Outflow !

NH3: dashed contours

1.3 cm: continuous contours

W51 North

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Classical profile inverse P-cygni

Accretion rate ~ 10-3 Msun/yr

Low mass stars ~ 10-6 Msun/yr

Cyanogen (CN) molecular emissionSubmillimter Array3” resolution

Zapata et al. (2008)

Moment zero

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Very Large Array7 mmC-configuration~ 0.4 arcsec

Submillimeter Array1 mmVery extended configuration ~ 0.4 arcsec

SiO, SO2, CH3CH, H3CN…

Sensitive and high angular resolution study of W51 North

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W51d2HC HII region+ outflowFlat SED

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W51dHII regionCometary

SO2

SiO(5-4) 7 mm

Disk + outflowsteeper SED

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W51 IRS2Infrared ( 2 m)Lacy et al. (2006)

W51d2

W51d

W51 North

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W51 d2W51 d2

Molecular Ring

HC HII region

outflow

W51 d

Cometary HII Region

O-type stars

Evolutive Phases !

Infrared stars

ELVA Vision of Massive (proto)stars

Very sensitive continuum and line observations towards far away bright clusters, e.g. Srg B, W49, G10.47, and G29.9

- Search for massive and large circumstellar disks at such distances Are they common?

- Confirming the evolutionary phases (more cases are needed)

Best angular resolution at millimeter wavelengths until ALMA

Many lines between 40 to 50 GHz to be exploited

Wonderful correlator…

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SED

TB=80±10 K

From the 7mm and 1.3 mm

measurements

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H92 and He92 recombination lines

Mehringer et al. (1994)

SO2 PV

MoleculesMolecules

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W51 North

W51 d2

H2CO

More Molecules in the RingMore Molecules in the Ring

CH3OH

More Molecules in the RingMore Molecules in the Ring

Summary

Our interferometric observations toward the extremely young (proto)star W51 North, revealing the presence of:

• A possible massive dusty disk with a size of about 3000 AU

• A molecular rotating and infalling ring with a inner cavity of about 3000 AU

• A powerful and massive outflow with the orientation nearly perpendicular to that of disk and ring

• The water maser spots are tracing the innermost parts of the outflow

• The mass of (proto)star is larger than 90 Msun

• The mass of the dusty disk is 40 Msun

We think that possibly in the center of the molecular ring there are more than one diskdue to the high multiplicity of the massive stars.

The formation of the massive stars seems to The formation of the massive stars seems to be similar to that of low mass stars in the be similar to that of low mass stars in the very early phases of their evolution !very early phases of their evolution !