Pre-main sequence stars in LH 91

¹ INAF-Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monte Porzio Catone (RM), Italy
e-mail: roberta.carini@inaf.it
² European Space Reasearch and Technoly Centre, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands
³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁴ European Southern Observatory, Karl-Schwarschild-STr.2, 85748 Garching, Germany
⁵ INAF-Osservatorio Astronomico d’Abruzzo, Via Mentore Maggini, s.n.c., 64100 Teramo, Italy

Received: 14 January 2022
Accepted: 21 March 2022

Abstract

Aims. We study the accretion properties of pre-main sequence (PMS) low-mass stars in the LH 91 association within the Large Magellanic Clouds.

Methods. Using optical multiband photometry obtained with the Hubble Space Telescope, we identify 75 candidates showing Hα excess emission above the 3σ level with equivalent width EWH_α ⩾ 10 Å. We estimate the physical parameters (effective temperature, luminosity, age, mass, accretion luminosity, and mass accretion rate) of the PMS stellar candidates.

Results. The age distribution suggests a period of active star formation ranging from a few million years up to ∼60 Myr with a gap between ∼5 Myr and 10 Myr. The masses of the PMS candidates span from 0.2 M_⊙ for the cooler objects to 1.0 M_⊙ with a median of ∼0.80 M_⊙. The median value of the accretion luminosity of our 75 PMS stars is about 0.12 L_⊙, the median value of the mass accretion rate is about 4.8 × 10⁻⁹ M_⊙ yr⁻¹ with higher values for the younger population (∼1.2 × 10⁻⁸ M_⊙ yr⁻¹), and lower values for the older candidates (∼4.7 × 10⁻⁹ M_⊙ yr⁻¹). We compare our results with findings for LH 95, the closest region to LH 91 for which accretion properties of PMS candidates were previously derived. An interesting qualitative outcome is that LH 91 seems to be in a more evolved stage. Moreover, we find that the PMS candidates are distributed homogeneously, without any evidence of clumps around more massive stars.