Discovery of an Extraordinarily Massive Young Stellar Cluster

Donald F. FigerRochester Institute of Technology/STScI

J. MacKenty, M. Robberto, K. Smith (STScI), F. Najarro (CSIC), R. Kudritzki (UH),

A. Herrero (IAC)

Main Points

Our team is announcing that we have found the richest cluster of red supergiants in the Galaxy.

We made this finding using 2MASS, IRMOS, and the Spitzer Space Telescope.

We identified 14 red supergiants using spectra. The cluster is one of the most massive in Galaxy. The cluster is near rare high energy objects. The cluster is a hotbed of supernovae activity. The research was sponsored by NASA LTSA.

Logic Flow of Discovery

1. Selected target from list of possible clusters.2. Used 2MASS image to target stars for

spectroscopic observations.3. Obtained infrared spectra with IRMOS.4. Obtained mid-infrared fluxes from Spitzer.5. Compared data to well known red supergiants.6. Discovered 14 red supergiants in cluster.7. Associated high energy objects with cluster.8. Inferred age, mass, and status of cluster.

Location in Galaxy

Need for Infrared Observations

Optically visible stars in blue.

Suspected Red Supergiants

Infr

ared

Brig

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Infrared Color

Spectra Obtained with IRMOSIn

ten

sity

Conclusion:Stars are Red Supergiants

Red supergiants are one thousand times larger than the Sun and one hundred

times larger than a red giant.

(a quarter mile across on this scale!)

Cluster Age

Conclusion:Age~10 Myr

Theory

Observation

Brig

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ss

Cluster Mass

Supernovae Rate

5.8m+3.6m+20cm

HESS TeV Source Near Cluster

All High Energy TeV Sources in Sky

High Energy Objects

Most Massive Stars Project

Goal is to find the most massive stars in the Galaxy.

The sample includes hundreds of candidate stellar clusters.

The red supergiant cluster is the first target in the sample.

We will use IRMOS, Hubble, Spitzer, Chandra, VLA, and GTC to observe more candidates.

Conclusions

We found a new Galactic stellar cluster. It contains three times as many red

supergiants as any other Galactic cluster. It is associated with rare high energy

objects. It likely had an initial mass of >20,000 M.

There are likely more similar clusters.