Confirming the Tidal Tails of the Young Open Cluster Blanco 1 with TESS Rotation Periods

TL;DR

This study confirms the existence of tidal tails around the young open cluster Blanco 1 by analyzing TESS light curves to determine stellar rotation periods, supporting the cluster's extended structure and membership.

Contribution

It demonstrates the effectiveness of using TESS photometric rotation periods to verify tidal tail structures and cluster membership, expanding the methods for studying cluster dissolution.

Findings

Tidal tails of Blanco 1 are confirmed through rotation period analysis.

72-74% of tail and core members follow the gyrochronological sequence.

Field stars show only 8.5% conformity to the gyrochronological sequence.

Abstract

Blanco 1 is an $\approx 130\,\mathrm{Myr}$ open cluster located 240 pc from the Sun below the Galactic plane. Recent studies have reported the existence of diffuse tidal tails extending 50-60 pc from the cluster center based on the positions and velocities measured by Gaia. To independently assess the reality and extent of this structure, we used light curves generated from TESS full-frame images to search for photometric rotation periods of stars in and around Blanco 1. We detected rotation periods down to a stellar effective temperature of $\approx 3100\,\mathrm{K}$ in 347 of the 603 cluster member candidates for which we have light curves. For cluster members in the core and candidate members in the tidal tails, both within a temperature range of 4400 to 6200 K, 74% and 72% of the rotation periods are consistent with the single-star gyrochronological sequence, respectively. In contrast, a comparison sample of field stars yielded gyrochrone-consistent rotation periods for only 8.5% of stars. The tidal tail candidates' overall conformance to the core members' gyrochrone sequence implies that their contamination ratio is consistent with zero and < 0.33 at the $2\sigma$ level. This result confirms the existence of Blanco 1 tidal tails and doubles the number of Blanco 1 members for which there are both spatio-kinematic and rotation-based cluster membership verification. Extending the strategy of using TESS light curves for gyrochronology to other nearby young open clusters and stellar associations may provide a viable strategy for mapping out their dissolution and broadening the search for young exoplanets.