The VISCACHA survey

XIII. The extended main-sequence turnoff in intermediate-age low-mass clusters

¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
² Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, São Paulo 05508-900, Brazil
³ Instituto de Astronomía, Universidad Nacional Autónoma de México, A. P. 106, C.P. 22800, Ensenada, B.C., Mexico
⁴ Instituto de Astrofísica, Departamento de Física y Astronomía, Facultad de Ciencias Exactas, Universidad Andres Bello, Fernandez Concha, 700, Las Condes, Santiago, Chile
⁵ Universidade Estadual de Santa Cruz, DCEX, Rod. Jorge Amado km 16, Ilhíeus 45662-900, Bahia, Brazil
⁶ Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
⁷ Departamento de Física, ICEx – UFMG, Av. Antônio Carlos 6627, Belo Horizonte 31270-901, Brazil
⁸ Universidade Federal do Rio de Janeiro, Av. Athos da Silveira, 149, Cidade Universitária, Rio de Janeiro 21941-909, Brazil
⁹ Universidade Federal do Rio Grande do Sul, Departamento de Astronomia, CP15051, Porto Alegr, 91501-970, Brazil
¹⁰ Instituto de Astrofísica de La Plata (CONICET-UNLP), Paseo del bosque S/N, La Plata (B1900FWA), Argentina
¹¹ Facultad de Ciencias Astroníomicas y Geofísicas – Universidad Nacional de La Plata, Paseo del Bosque S/N, La Plata (B1900FWA), Argentina
¹² Vatican Observatory, V00120 Vatican City State, Italy
¹³ ESO – European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
¹⁴ Universidad Católica del Norte, Núcleo UCN en Arqueología Galáctica - Inst. de Astronomía, Av. Angamos 0610, Antofagasta, Chile
¹⁵ Laboratório Nacional de Astrofísica LNA/MCTI, 37504-364, Itajubá, MG, Brazil
¹⁶ NSF NOIRLab/NSF–DOE Vera C. Rubin Observatory HQ, 950 N. Cherry Ave., Tucson, AZ 85719, USA (AURA Staff)

^★ Corresponding author: s-souza@mpia.de

Received: 18 April 2025
Accepted: 21 July 2025

Abstract

The extended main-sequence turnoff (eMSTO), a significant broadening of the MSTO region, is a well-known feature observed in young and intermediate-age star clusters. Although prolonged star formation and stellar rotation have been proposed as possible explanations for this extension, no consensus has yet been reached. Most previous studies have focused on high-mass clusters. In this work, we extend the analysis to the less explored low-mass regime by investigating star clusters in the Magellanic Clouds using data from the VISCACHA survey. We employed a widely used method to quantify the MSTO width in terms of age spread. Additionally, to validate our approach, we used a cluster also observed with the HST. Our analysis confirms that the eMSTO phenomenon is also present in low-mass clusters and follows the known age– and mass–MSTO width relations. In particular, the least massive cluster in our sample does not show an eMSTO; this is further evidence in support of the proposed link between the eMSTO and the escape velocity of the cluster and provides a new lower limit to the age spread of 88 ± 40 Myr for the presence of an eMSTO. The consistent MSTO width measurements of the VISCACHA and HST photometries confirm the robustness of our method and demonstrate that the age spread determination is independent of the photometric system, showing also the power of ground-based observations for investigations of the eMSTO phenomenon.