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Intermediate-mass stars (IMSs) represent the link between low-mass and high-mass stars, and cover a key mass range for giant planet formation. In this paper, we present a spectroscopic survey of 241 young IMS candidates with IR-excess, the most complete unbiased sample to date within 300 pc. We combined VLT/X-Shooter spectra with BVR photometric observations and Gaia DR3 distances to estimate fundamental stellar parameters such as T eff, mass, radius, age, and luminosity. We further selected those stars within the intermediate-mass range 1.5 ≤ M ⋆/M⊙ ≤ 3.5, and discarded old contaminants. We used 2MASS and WISE photometry to study the IR-excesses of the sample, finding 92 previously unidentified stars with IR-excess. We classified this sample into 'protoplanetary', 'hybrid candidates', and 'debris' discs based on their observed fractional excess at 12  |$\mu$| m, finding a new population of 17 hybrid disc candidates. We studied inner disc dispersal time-scales for |$\lambda < 10 \,\mu$| m and found very different trends for IMSs and low-mass stars (LMSs). IMSs show excesses dropping fast during the first 6 Myr independently of the wavelength, while LMSs show consistently lower fractions of excess at the shortest wavelengths, and increasingly higher fractions for longer wavelengths with slower dispersal rates. In conclusion, this study demonstrates empirically that IMSs dissipate their inner discs very differently than LMSs, providing a possible explanation for the lack of short period planets around IMSs. [ABSTRACT FROM AUTHOR]

Studies of young stellar objects (YSOs) in the Galaxy have found that a significant fraction exhibits photometric variability. However, no systematic investigation has been conducted on the variability of extragalactic YSOs. Here we present the first variability study of massive YSOs in an |$\sim 1.5\, \mathrm{deg^2}$| region of the Large Magellanic Cloud (LMC). The aim is to investigate whether the different environmental conditions in the metal-poor LMC (⁠|$\sim 0.4\!-\!0.5\, \mathrm{Z_{\odot }}$|⁠) have an impact on the variability characteristics. Multi-epoch near-infrared (NIR) photometry was obtained from the VISTA Survey of the Magellanic Clouds (VMC) and our own monitoring campaign using the VISTA telescope. By applying a reduced χ2-analysis, stellar variability was identified. We found 3062 candidate variable stars from a population of 362 425 stars detected. Based on several Spitzer studies, we compiled a sample of high-reliability massive YSOs: a total of 173 massive YSOs have NIR counterparts (down to |$K_s\sim 18.5\,$| mag) in the VMC catalogue, of which 39 display significant (>3σ) variability. They have been classified as eruptive, fader, dipper, short-term variable, and long-period variable YSOs based mostly on the appearance of their Ks -band light curves. The majority of YSOs are aperiodic; only five YSOs exhibit periodic light curves. The observed amplitudes are comparable or smaller than those for Galactic YSOs (only two Magellanic YSOs exhibit |$\Delta K_s\gt 1\,$| mag), not what would have been expected from the typically larger mass accretion rates observed in the Magellanic Clouds. [ABSTRACT FROM AUTHOR]

The stellar initial mass function (IMF) is an essential input for many astrophysical studies but only in a few cases has it been determined over the whole cluster mass range, limiting the conclusions about its nature. The 25 Orionis group (25 Ori) is an excellent laboratory for investigating the IMF across the entire mass range of the population, from planetary-mass objects to intermediate/high-mass stars. We combine new deep optical photometry with optical and near-infrared data from the literature to select 1687 member candidates covering a 1.1° radius area in 25 Ori. With this sample we derived the 25 Ori system IMF from 0.012 to 13.1 M⊙. This system IMF is well described by a two-segment power law with Γ = −0.74 ± 0.04 for m < 0.4 M⊙ and Γ = 1.50 ± 0.11 for m ≥ 0.4 M⊙. It is also well described over the whole mass range by a tapered power-law function with Γ = 1.10 ± 0.09, mp  = 0.31 ± 0.03 and β = 2.11 ± 0.09. The best lognormal representation of the system IMF has mc  = 0.31 ± 0.04 and σ = 0.46 ± 0.05 for m < 1 M⊙. This system IMF does not present significant variations with the radii. We compared the resultant system IMF as well as the brown dwarf/star ratio of 0.16 ± 0.03 that we estimated for 25 Ori with that of other stellar regions with diverse conditions and found no significant discrepancies. These results support the idea that general star-formation mechanisms are probably not strongly dependent on environmental conditions. We found that the substellar and stellar objects in 25 Ori do not have any preferential spatial distributions and confirmed that 25 Ori is a gravitationally unbound stellar association. [ABSTRACT FROM AUTHOR]