Candidate star clusters towards the inner Milky Way discovered on deep-stacked K$_s$-band images from the VVV survey

V.D. IVANOV, A.E. PIATTI, J.-C. BEAMÍN, D. MINNITI, J. BORISSOVA, R. KURTEV, M. HEMPEL, R. SAITO

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2017 vol. 600 p. 1 - 8

0004-6361

Context. The census of star clusters in the inner Milky Way is incomplete because of the extinction and crowding.Aims. We embarked on a program to expand the star cluster list in the direction of the inner Milky Way using deep stacks of K S bandimages from the VVV Survey.Methods. We applied an automated two-step procedure to the point-source catalog derived from the deep K S images: first, weidentified over-densities of stars, and then we selected only candidate clusters with probable member stars that match on the color-magnitude diagram an isochrone with a certain age, distance and extinction.Results. This pilot project only investigates the cluster population in part of one VVV tile ? b201. We identified nine cluster candidatesand estimated their parameters. The new candidates are compact with a typical radius on the sky of ∼0.2?0.4 arcmin (∼0.4?1.6 pcat their estimated distances). They are located at distances of ∼5?14 kpc from the Sun, and are subject to moderate extinction ofE(B−V)=0.4?1.0 mag. They are sparse, probably evolved, with typical ages log(t/1 yr)∼9. Based on the locations of the objectsinside the Milky way we conclude that one of them is probably associated with the disk or the halo, and the rest ? with thebulge or the halo.Conclusions. The cluster candidates reported here push the VVV Survey cluster detection to the limit. These new objects demonstratethat the VVV survey has the potential to identify thousands of additional cluster candidates. The sub-arcsec angular resolution andthe near-infrared wavelength regimen give it a critical advantage over other surveys.