Massive Stars in the Quintuplet Cluster

Abstract

We present near-infrared photometry and K-band spectra of newlyidentified massive stars in the Quintuplet cluster, one of the threemassive clusters projected within 50 pc of the Galactic center. We findthat the cluster contains a variety of massive stars, including moreunambiguously identified Wolf-Rayet stars than any cluster in theGalaxy, and over a dozen stars in earlier stages of evolution, i.e.,luminous blue variables (LBVs), Ofpe/WN9, and OB supergiants. One newlyidentified star is the second luminous blue variable in the cluster,after the ``Pistol star.'' Although we are unable to provide certainspectral classifications for the five enigmatic Quintuplet-propermembers, we tentatively propose that they are extremely dusty versionsof the WC stars found elsewhere in the cluster and similar to the dozenor so known examples in the Galaxy. Although the cluster parameters areuncertain because of photometric errors and uncertainties in stellarmodels, i.e., extrapolating initial masses and estimating ionizingfluxes, we have the following conclusions. Given the evolutionary stagesof the identified stars, the cluster appears to be about 4+/-1 Myr old,assuming coeval formation. The total mass in observed stars is ~10^3M_solar, and the implied mass is ~10^4 M_solar, assuming a lower masscutoff of 1 M_solar and a Salpeter initial mass function. The impliedmass density in stars is greater than or similar to a few thousandM_solar pc^-3. The newly identified stars increase the estimatedionizing flux from this cluster by about an order of magnitude withrespect to earlier estimates, to 10^50.9 photons s^-1, or roughly whatis required to ionize the nearby ``Sickle'' H II region (G0.18-0.04).The total luminosity from the massive cluster stars is ~10^7.5 L_solar,enough to account for the heating of the nearby molecular cloud,M0.20-0.033. We propose a picture that integrates most of the majorfeatures in this part of the sky, excepting the nonthermal filaments. Wecompare the cluster to other young massive clusters and globularclusters, finding that it is unique in stellar content and age, except,perhaps, for the young cluster in the central parsec of the Galaxy. Inaddition, we find that the cluster is comparable to small ``super starclusters.''