A Catalog of Newly Identified Star Clusters in Gaia DR2

We present the Star cluster Hunting Pipeline (SHiP) that can identify star clusters in Gaia second data release (DR2) data and establish a star cluster catalog for the Galactic disk. A friend-of-friend-based cluster finder method is used to identify star clusters using five-dimensional stellar parameters, l, b, omega, mu(alpha) cos delta, and mu(delta). Our new catalog contains 2443 star cluster candidates identified from disk stars located within vertical bar b vertical bar = 25. and with G < 18 mag. An automatic isochrone fitting scheme is applied to all cluster candidates. With a combination of parameters obtained from isochrone fitting, we classify cluster candidates into three classes (Class 1, 2, and 3). Class 1 clusters are the most probable star cluster candidates with the most stringent criteria. Most of these clusters are nearby (within 4 kpc). Our catalog is crossmatched with three Galactic star cluster catalogs, Kharchenko et al., Gaudin et al., and Bica et al. The proper motion and parallax of matched star clusters are in good agreement with these earlier catalogs. We discover 76 new star cluster candidates that are not listed in these three catalogs. The majority of these are clusters older than log(age/yr) = 8.0 and are located in the inner disk with vertical bar b vertical bar < 5 degrees. The recent discovery of new star clusters suggests that current Galactic star cluster catalogs are still incomplete. Among the Class 1 cluster candidates, we find 56 candidates for star cluster groups. The pipeline, the catalog, and the member list containing all candidates star clusters and star cluster groups have been made publicly available.