Rosette Nebula & the effect of more stars

The Rosette Nebula - an HII Region

The Rosette Nebula is a stunning HII region, shown at right.  Here, the colors denote three ionized elements - hydrogen (H-alpha) is shown in red, oxygen (OIII) in green, and sulfur (SII) in blue.  (For further information about observing HII regions in these elements, see Stephen Portillo’s nebula predictor).  We can see a hydrogen rich gaseous nebula, with luminous ionizing stars at the center.  Overlaid fine dark, filamentary structures are visible, due to dust.  Another interesting feature of the Rosette is the central cavity that has been cleared out around the central cluster of stars.

NGC 2244 - ionizing and blowing out material

At the heart of the Rosette Nebula lies NGC 2244 - an open cluster containing at least 17 O and B stars (CFHT reference).  Of these, the hottest are believed to be HD 46223, an O4V star, and HD 46150, an O5V star.  These stars have large ionizing luminosities, responsible for the HII region itself.

NGC 2244 is also responsible for stellar winds that blow gas outward from the cluster center, at roughly 20 km/s.  These winds are so strong that the central gas can be cleared out, leaving a noticeably visible cavity.  Stellar winds play a significant role in many HII regions, causing the regions to deviate from ideal uniform Strömgren spheres.

Rosette Nebula: Properties

The Rosette Nebula is observed to be 1.3 degrees on the sky, located 1600pc away (1parsec (pc) = 3.086e18 cm), giving it a diameter of 36 pc

Bruhweiler et al, 2008 find from modeling  UV data that the HII region has

*Radius: = 16.9 pc

*Expansion Velocity: = 13 km/s

*Electron Density: ne = 15 cm–3

(Their radius is consistent with the value that we roughly calculated from on-sky measurements.)

T. A. Rector et al, WIYN & NOAO/AURA/NSF

Observational connection

Stellar winds can blow out material, and should be remembered when looking at images and modelling realistic HII regions.

Try it out

The radius and ionized number density are given at right.  Using the fact that O4V stars have effective temperatures 48700K and O5V stars 46100K, try using the interactive module to see different parameter values and ages that could work for the Rosette Nebula.