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 \textit{Gaia} DR3. Likely member stars were identified based on a membership probability threshold ($P \geq 0.5$), yielding 230 members for Alessi 36 and 342 members for Collinder 135. The mean proper-motion components ($\mu_\alpha \cos\delta, \mu_\delta$) were determined as $(-9.681 \pm 0.072, 7.021 \pm 0.081)$ mas yr$^{-1}$ for Alessi 36 and $(-10.061 \pm 0.083, 6.256 \pm 0.095)$ mas yr$^{-1}$ for Collinder 135. The parallax-based distances ($d$) were found to be $278 \pm 7$ and $299 \pm 11$ pc, while their estimated ages ($t$) were $39 \pm 5$ and $36 \pm 5$ 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 $0.035 \pm 0.001$ kpc for Alessi 36 and $0.074 \pm 0.003$ kpc for Collinder 135, supporting their classification as part of the young stellar disc population.