STELLA Open Cluster Survey (SOCS): An improved understanding of stellar rotation and open clusters

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In recent years, the understanding of the rotation of cool stars has been making rapid progress. A key application has been the development of a way to derive the age of a main sequence star from its rotation period, a technique of wide-ranging importance in understanding the evolution of, for example, planets and star clusters, or more generally, chronologies in our Galaxy. Recent space-based observations have pushed prior studies out to older ages including near solar, and they have also confirmed and extended prior ground-based work on some of the nearest and well-known open clusters. However, there are no prospects for more studies of other essential clusters, to enable studies of various aspects of rotational evolution, and to sample in more detail the age and parameter space that is needed. In particular, we are interested in delineating a key main seqeunce rotational transition from fast to slow rotation in youngish open clusters. We are therefore proposing a ground-based study of these key clusters.Using our STELLA robotic observatory in Tenerife, we are able to provide time-series photometry with excellent nightly cadence over a months-long baseline, and millimag-level precision over wide areas of each cluster. We demonstrate this capability with a detailed description of our work on the open cluster M48. The imminent GAIA data release will enable us to construct clean membership lists for our clusters, and we will integrate this with relevant information from the literature and our own newly-acquired data.Our survey will provide deep, new, multi-color color-magnitude diagrams for the clusters down to low masses, together with consistent isochrone fits for all clusters, also using our recent YaPSI isochrones. We will also provide clean color-period diagrams for each target cluster, without contaminating non-members, and minimising period aliasing from short-baseline observations. These will enable the determination of precise rotational ages for each cluster. They will also enable a detailed understanding of the key transition from fast to slow rotation in open clusters, and a basis for evaluating and improving theoretical models, particularly with respect to core-envelope coupling, and magnetic transitions in young stars. Data products from this survey will be communicated broadly to the community in collaboration with e-science experts.