Close Binary Open Cluster Systems: A Gaia DR3 Perspective on Alessi 36 and Collinder 135

Abstract

In this study, we examined the nearby open clusters (OCs) Alessi 36 and Collinder 135. Their spatial proximity was assessed using photometric and astrometric data from Gaia DR3. Likely member stars were identified based on a membership probability threshold (P ≥ 0.5), yielding 230 members for Alessi 36 and 342 members for Collinder 135. The mean proper-motion components (𝜇𝛼cos𝛿, 𝜇𝛿) were determined as (-9.681±0.072, 7.021±0.081) mas yr⁻¹ for Alessi 36 and (-10.061±0.083, 6.256±0.095) mas yr⁻¹ for Collinder 135, the parallax-based distances (d) were found to be 278±7 and 299±11 pc, while their estimated ages (t) were 39±5 and 36±5 Myr for Alessi 36 and Collinder 135, respectively. The Galactic orbital analysis of Alessi 36 and Collinder 135 reveals nearly circular orbits with low eccentricities and minor fluctuations in their apogalactic and perigalactic distances. The maximum heights they attain above the Galactic plane are 0.035±0.001 for Alessi 36 and 0.074±0.003 kpc for Collinder 135, respectively, supporting their classification as part of the young stellar disc population.