A Massive Star Census of the Starburst Cluster R136

We have carried out a comprehensive census of the most massive stars in the central parsec (4 arcsec) of the starburst cluster, R136, which powers the Tarantula Nebula in the LMC using HST/STIS. R136 is both sufficiently massive that the upper mass function is richly populated and young enough that its most massive stars have yet to explode as supernovae. The identification of very massive stars in R136, up to 300 solar masses, raises general questions of star formation, binarity and feedback in young massive clusters.

30 Doradus (HST/WFC3)

This 39 orbit Cycle 19 (GO 12465) + Cycle 20 (GO 13052) programme (PI Crowther) with HST/STIS complements the ongoing ESO/VLT Large Programme VLT-FLAMES Tarantula Survey (Chris Evans, PI) and 30 orbit Cycle 19+21 proper motion study of 30 Doradus with WFC3 and ACS (GO 12499, Danny Lennon, PI).



GO 12465/13052 (STIS)
This census enables the mass function of very massive stars to be measured for the first time, as a result of incomplete and inadequate spectroscopy to date. It also complements our Tarantula Survey, a ground-based VLT Large Programme, by including the most massive stars that are inaccessible to ground-based visual spectroscopy due to severe crowding. These surveys, together with existing integrated UV and optical studies will enable 30 Doradus to serve as a bona-fide template for unresolved extragalactic starburst regions.

The ultraviolet STIS spectral survey of all stars more massive than ~25 solar masses has revealed:

  • a) the bulk of the visual brightest members of R136 are O2-3 stars
  • b) comparison of wind velocities of early O stars with those elsewhere in the LMC and the Milky Way indicate somewhat lower velocities for R136 stars
  • c) physical parameter estimates reveal several dozen stars more massive than 50 solar masses, with 9 stars exceeding 100 solar masses (including R136c)
  • d) we obtain a cluster mass of approximately 1.5 Myr
  • e) we have considered the integrated UV spectrum of R136a - close to 100 per cent of the HeII 1640 flux and 32 per cent of the far-UV continuum arises from very massive stars. Prominent HeII emission in the integrated spectrum of young star clusters would favour a mass function that extends well above 100 solar masses
Identification of very massive stars in core of R136

Observing Description: Complete UV/optical scan across LMC star cluster R136 with 17 slits (width 0.2 arcsec) as shown in the figure, superimposed upon a F555W WFC3/UVIS Early Release Observation (green labels are illustrative magnitudes for the circled stars). Due to severe crowding in cluster core, initial acquisition (+peakup) is of an isolated bright star Melnick 34. Offset positions and position angle 64 degrees (E of N) are selected to ensure that both R136a1 and a2 are included in NW1 slit.

Analysis of the optical datasets are underway, and will investigate the binary properties of the massive stars, their rotational velocities and more robust physical and wind properties.

Details of observations are as follows:

Cycle 19 (GO 12465)
  • Visit 01 (4 orbits): STIS/CCD (G430M/3936) SE9 to NW1 (6 Apr 2012 @ 03:33)
  • Visit 07 (3 orbits): STIS/CCD (G430M/3936) NW2 to NW8 (20 Oct 2012 @ 12:08)
  • Visit 02 (4 orbits): STIS/CCD (G430M/4451) SE9 to NW1 (4 Apr 2012 @ 15:22)
  • Visit 08 (3 orbits): STIS/CCD (G430M/4451) NW2 to NW8 (20 Oct 2012 @ 20:29)
  • Visit 03 (4 orbits): STIS/CCD (G430M/4706) SE9 to NW1 (6 Apr 2012 @ 13:48)
  • Visit 09 (3 orbits): STIS/CCD (G430M/4706) NW2 to NW8 (23 Oct 2012 @ 10:00)
  • Visit 04 (4 orbits): STIS/MAMA (G140L) SE9 to NW3 (7 Apr 2012 @ 06:39)
  • Visit 05 (2 orbits): STIS/MAMA (G140L) NW4 to NW8 (8 Apr 2012 @ 06:34)
  • Visit 06 (5 orbits): STIS/CCD (G750M/6581) SE9 to NW8 (23 Oct 2012 @ 01:54)
Cycle 20 (GO 13052)
  • Visit 01 (4 orbits): STIS/CCD (G430M/4194) SE9 to NW1 (21 Oct 2012 @ 12:16)
  • Visit 02 (3 orbits): STIS/CCD (G430M/4194) NW2 to NW8 (3 Apr 2013 @ 16:12)