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Early O-Type Stars in the W51-IRS2 Cluster A template to study the most massive (proto)stars. Luis Zapata Max Planck Institut für Radioastronomie, GERMANY. May 2009. THE EVLA VISION: STARS ON AND OFF THE MAIN SEQUENCE. Outline. Comments on the formation of massive stars

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slide1

Early O-Type Stars in the W51-IRS2 Cluster

A template to study the most massive (proto)stars

Luis Zapata

Max Planck Institut für Radioastronomie, GERMANY

May 2009

THE EVLA VISION: STARS ON AND OFF THE MAIN SEQUENCE

slide2

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
slide3

The formation of the massive stars

  • Some fundamental theoretical problems to form massive stars (M* > 10 Msun):
  • The Kelvin-Helmholtz time is much shorter than the free-fall time
  • -- radiation pressure (spherical geometry)
  • The strong UV fields will ionize the surrounding molecular gas by so fast
  • The short main-sequence lifetime of high-mass stars
  • Some observational problems to study massive (proto)stars:
  • They are located far away, more than 1 kpc (with exception of Orion)
  • There are a short number of massive (proto)stars
  • They are very embedded in the molecular cloud
  • -- only observable in radio and IR bands
slide4

Some possible solutions

  • Circumstellar Large Disks
  • A Natural outcome !!
  • Very high accretion rates that
  • quenched or trapped the
  • formation HII regions
  • Mergers of low mass stars
  • Competitive accretion
slide5

W51 Complex

Sagittarius Arm

HJK-Infrared

CFHT

slide6

W51

VLA 3.6 cm.

Lacy et al. (2007)

W51 IRS2

W51 IRS1

Infrared: grey scale (VLT)

3.6 cm: contours

W51 East

slide7

One of most luminous regions in the Galaxy

W51 IRS2

Infrared (JHK)

Barbosa et al. (2008)

IRS2W (O3-type)

IRS2E (O4-type)

7000 AU

Lbol= = 3 x 106 Lsun

D ~ 6, 000 pc

~ 30 O-type protostars

slide8

Ammonia (J,K)=(3,3)

W51 North & W51 D1

VLA

NH3: dashed contours

3.6 cm: continuous contours

1.3 cm emission: dashed contours

NH3: continuous contours

Ho et al. (1983)

Gaume et al. (1993)

slide9

H2O and SiO Maser Spots

VLBI

NH3: dashed contours

1.3 cm: continuous contours

W51 North

Imai et al. (2002)

Powerful Bipolar very compact NW-SE Outflow !

Einser et al. (2003)

slide10

Cyanogen (CN) molecular emission

Submillimter Array

3” resolution

Moment zero

Classical profile inverse P-cygni

Accretion rate ~ 10-3 Msun/yr

Low mass stars ~ 10-6 Msun/yr

Zapata et al. (2008)

slide11

Sensitive and high angular resolution study of W51 North

Submillimeter Array

1 mm

Very extended configuration

~ 0.4 arcsec

SiO, SO2, CH3CH, H3CN…

Very Large Array

7 mm

C-configuration

~ 0.4 arcsec

slide13

W51d2

HC HII region

+ outflow

Flat SED

Disk + outflow

steeper SED

W51d

HII region

Cometary

  • SO2
  • SiO(5-4)
  • 7 mm
slide14

W51d

W51d2

W51 North

W51 IRS2

Infrared ( 2 m)

Lacy et al. (2006)

slide15

Evolutive Phases !

W51 d2

W51 d2

outflow

Infrared stars

W51 d

HC HII region

Molecular Ring

O-type stars

Cometary HII Region

slide16

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…

slide17

H92 and He92 recombination lines

SED

TB=80±10 K

From the 7mm and 1.3 mm

measurements

Mehringer et al. (1994)

slide18

Molecules

SO2

PV

W51 North

W51 d2

slide21

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 disk

due to the high multiplicity of the massive stars.

The formation of the massive stars seems to

be similar to that of low mass stars in the

very early phases of their evolution !

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