North-PHASE: Studying Periodicity, Hot Spots, Accretion Stability and Early Evolution in young stars in the northern hemisphere

TL;DR

North-PHASE is a five-year survey of young star clusters using the JAST80 telescope, revealing new young stellar objects, characterizing accretion, and studying disk evolution through variability analysis across multiple filters.

Contribution

The survey introduces new techniques for variability analysis and uncovers previously hidden aspects of star formation and cluster membership in young stellar populations.

Findings

Discovered 50 new YSOs in Tr37, including proper motion outliers.

Confirmed youth of astrometric members and distinguished accreting from non-accreting stars.

Revealed complex star formation history and variability patterns not captured by Gaia alone.

Abstract

We present the overview and first results from the North-PHASE Legacy Survey, which follows six young clusters for five years, using the 2 deg$^2$ FoV of the JAST80 telescope from the Javalambre Observatory (Spain). North-PHASE investigates stellar variability on timescales from days to years for thousands of young stars distributed over entire clusters. This allows us to find new YSO, characterise accretion and study inner disk evolution within the cluster context. Each region (Tr37, CepOB3, IC5070, IC348, NGC2264, and NGC1333) is observed in six filters (SDSS griz, u band, and J0660, which covers H$\alpha$), detecting cluster members as well as field variable stars. Tr37 is used to prove feasibility and optimise the variability analysis techniques. In Tr37, variability reveals 50 new YSO, most of them proper motion outliers. North-PHASE independently confirms the youth of astrometric members, efficiently distinguishes accreting and non-accreting stars, reveals the extent of the cluster populations along Tr37/IC1396 bright rims, and detects variability resulting from rotation, dips, and irregular bursts. The proper motion outliers unveil a more complex star formation history than inferred from Gaia alone, and variability highlights previously hidden proper motion deviations in the surrounding clouds. We also find that non-YSO variables identified by North-PHASE cover a different variability parameter space and include long-period variables, eclipsing binaries, RR Lyr, and $\delta$ Scuti stars. These early results also emphasize the power of variability to complete the picture of star formation where it is missed by astrometry.