The mass spectrum in the young cluster NGC1333

The mass spectrum in the young cluster NGC1333 in the star forming complex in Perseus

With an age of around 1Myr and a distance of only 300pc, NGC1333 is an excellent laboratory to study the outcome of star formation. In our long-term project SONYC (Substellar Objects in Nearby Young Clusters) we have identified more than 50 new very low mass members in this cluster, down to masses of 6 Jupiter masses (see link). The plot shows the number of objects in this cluster per mass bin derived from our survey in combination with the results from other groups.

In the most recent paper, we put strong limits on the number of planemos - free-floating objects with planetary masses - in this cluster. We give an upper limit of 8 planemos for NGC1333. Based on a very recent study with new information on the mid-infrared colours of young ultracool objects (Faherty et al. 2012, submitted to AJ), our estimate is probably too conservative, an upper limit of 4 might be more realistic. In other words, planemos are very rare, at least down to about 5 Jupiter masses (the limit of our survey).

Our upper limit for planemos is shown with a red arrow in the figure. The plot demonstrates that the mass spectrum continues smoothly down to masses of 0.02 Msol, corresponding to ~20 Jupiter masses, with a possible decline in the planemo domain. This is in contrast to recent findings based on microlensing surveys (Sumi et al., 2011, Nature, 473, 349), which indicate that 'unbound or distant Jupiter-mass objects' could be 'almost twice as common as main-sequence stars'. If the microlensing result is confirmed, those isolated Jupiter-mass objects must have a different origin from brown dwarfs and planemos observed in young clusters.

 

More information: Scholz, Jayawardhana, Muzic, Geers, Tamura, Tanaka, 2012: "Substellar Objects in Nearby Young Clusters (SONYC) VI: The planetary-mass domain of NGC1333", Astrophysical Journal, in press, appears on arxiv on 09/07/2012