Open cluster survival within the solar circle : Teutsch 145 and Teutsch 146

Abstract

Teutsch 145 and Teutsch 146 are shown to be open clusters (OCs) orbiting well inside the solar circle, a region where several dynamical processes combine to disrupt most OCs on a timescale of a few 10 8 yr. BVI photometry from the GALILEO telescope is used to investigate the nature and derive the fundamental and structural parameters of the optically faint and poorly known OCs Teutsch 145 and 146. These parameters are computed by means of fieldstar- decontaminated colour–magnitude diagrams and stellar radial density profiles (RDPs). Cluster mass estimates are made based on the intrinsic mass functions (MFs). We derive the ages 200+100 −50 and 400 ± 100 Myr, and the distances from the Sun dʘ = 2.7 ± 0.3 and 3.8 ± 0.2 kpc, respectively, for Teutsch 145 and 146. Their integrated apparent and absolute magnitudes are mV ≈ 12.4 and 13.3 and MV ≈ −5.6 and −5.3. The MFs (detected for stars with m > ~1Mʘ) have slopes similar to Salpeter’s initial mass function. Extrapolated to the Hburning limit, the MFs would produce total stellar masses of ~1400Mʘ , typical of relatively massive OCs. Both OCs are located deep into the inner Galaxy and close to the Crux–Scutum arm. Since cluster-disruption processes are important, their primordial masses must have been higher than the present-day values. The conspicuous stellar density excess observed in the innermost bin of both RDPs might reflect the dynamical effects induced by a few 10 8 yr of external tidal stress.