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ARC Meeting Multiplicity of O-type stars in the young open cluster NGC 2244 Laurent Mahy (GAPHE). Why study the multiplicity of O-stars in clusters? They have same age, same distance, and same chemical composition The knowledge of formation mechanisms of high masses stars

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ARC Meeting

Multiplicity of O-type stars in the young open cluster NGC 2244

Laurent Mahy (GAPHE)


Why study the multiplicity of O-stars in clusters?

  • They have same age, same distance, and same chemical

    composition

  • The knowledge of formation mechanisms of high masses stars

    are still fragmented (stellar collisions and mergers, accretion

    disk, accretion by radiative pressure,...)

  • A further complication to any model of massive star formation

    is that most massive stars are in binary systems

  • Study the multiplicity is interesting for understanding the

    physical properties of these objects


Multiplicity in NGC 2244 and Mon OB2

A first study was made by Garcia & Mermilliod (2001) concerning rich

O-star clusters from HETEROGENOUS DATA

IC 1805

NGC 6231

NGC 2244

IC 2944

NGC 6611

...

80%

79%

50%

44%

42%

...

What are our conclusions in NGC 2244 and the other clusters from homogenous data?


Multiplicity in NGC 2244 and Mon OB2

In NGC 2244 and Mon OB2 (Mahy et al. 2009):

Our dataset: 207 spectra over 9 years coming from:

  • The 1.52m telescope @ OHP (France) with Aurelie

  • The 1.93m telescope @ OHP (France) with Elodie

  • The 2.1m telescope @ SPM (Mexico) with Espresso

  • The 2.2m telescope @ La Silla (Chile) with FEROS

  • The 1.98m telescope @ Asiago (Italie)

Covers long and short timescales !!!


Multiplicity in NGC 2244

HD 46149:

  • From RVs:

    M1/M2 ~ 1.6

  • From Equivalent widths:

    L1/L2 ~ 2.3

Early B-type for the secondary

while

the primary is estimated to be O8V


Multiplicity in NGC 2244

HD 46150:

V sin i ~ 100 km/s

Classified as O5.5 V ((f))

TVS (Temporal Variance

Spectrum, Fullerton 1996) revealed variations but no secondary component

was found Binary candidate


Multiplicity in NGC 2244

HD 46202 & HD 46223:

km/s

km/s

  • HD 46202 O9V

    V sin i ~ 50 km/s

  • HD 46223 O4V ((f+))

    V sin i ~ 100 km/s

TVS

Probably single stars


Multiplicity in NGC 2244

HD 46056 & HD 46485:

Classified as O8V

V sin i ~ 350 km/s

Classified as O8V

V sin i ~ 300 km/s

Probably single stars


What about the binary fraction in young clusters?

Remind you the results of Garcia & Mermilliod (2001)

80%

79%

50%

44%

42%

...

IC 1805

NGC 6231

NGC 2244

IC 2944

NGC 6611

...

What about our results :

  • IC 1805 20-60% (4 stars not studied,1 short,1 long period binary)

    • Rauw & De Becker 2004; De Becker et al. 2006

  • NGC 6231 63-81% (Sana et al. 2008)

  • NGC 2244 17-33% (Mahy et al. 2009)

  • IC 2944 ???

  • NGC 6611 44-67% (Sana et al. 2009)


  • Link between different clusters?

    • Anticorrelation between the number of binaries and the density of

      clusters was proposed by Garcia & Mermillod (2001)

    • But, after our study, the correlation has appeared to be more

      probable

    • However, the recent investigation made by Sana et al (2009) on

      the multiplicity of NGC 6611 does not confirm the last assumption


    Future works

    • Investigation of binary fraction of O-type stars in OB

      associations which are less dense that open clusters.

    • Determination of the stellar and wind parameters of all these

      stars by using the atmosphere code CMFGEN

      (Hillier & Miller 1998).

    • Investigation of the CoRoT light curves of 4 stars of this

      sample to find periodic variations.


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