X-Shooter Survey of Young Intermediate Mass Stars -- I. Stellar Characterization and Disc Evolution

TL;DR

This study presents a comprehensive spectroscopic survey of young intermediate mass stars, characterizing their properties and disc evolution, revealing distinct dispersal patterns compared to low-mass stars and implications for planet formation.

Contribution

It provides the most complete unbiased sample of young IMSs within 300 pc, identifying new IR-excess stars and classifying disc types, highlighting different inner disc dispersal timescales from low-mass stars.

Findings

92 new IR-excess stars identified

Dispersal of inner discs occurs faster in IMSs than in LMSs

Different disc evolution trends suggest varied planet formation environments

Abstract

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 Teff, mass, radius, age, and luminosity. We further selected those stars within the intermediate mass range 1.5 <= Mstar/Msun <= 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 12microns, finding a new population of 17 hybrid disc candidates. We studied inner disc dispersal timescales 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 Myrs 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.