Abstract
Context. Debris discs orbiting young stars are key to understanding dust evolution and the planetary formation process. We take advantage of a recent membership analysis of the 30 Myr nearby open cluster IC 4665 based on the Gaia and DANCe surveys to revisit the disc population of this cluster. Aims. We aim to study the disc population of IC 4665 using Spitzer (MIPS and IRAC) and WISE photometry. Methods. We use several colour–colour diagrams with empirical photospheric sequences to detect the sources with an infrared excess. Independently, we also fit the spectral energy distribution (SED) of our debris-disc candidates with the Virtual Observatory SED analyser (VOSA) which is capable of automatically detecting infrared excesses and provides effective temperature estimates. Results. We find six candidate debris-disc host stars (five with MIPS and one with WISE), two of which are new candidates. We estimate a disc fraction of 24 ± 10% for the B–A stars, where our sample is expected to be complete. This is similar to what has been reported in other clusters of similar ages (Upper Centaurus Lupus, Lower Centaurus Crux, the β Pictoris moving group, and the Pleiades). For solar-type stars we find a disc fraction of 9 ± 9%, which is lower than that observed in regions with comparable ages. Conclusions. Our candidate debris-disc host stars are excellent targets to be studied with ALMA or the future James Webb Space Telescope (JWST).
Highlights
Debris discs are the result of collisions between planetesimals and their detection implies that the planet formation process was successful in forming bodies of a few hundred or a few thousand kilometres
We estimated that our MIPS photometry is complete down to [24] 11.8 in our sample
In this spectral range and in the central 1◦ × 1◦ area covered by MIPS (37 pc2), the disc fraction of IC 4665 is 5/32 or 16 ± 7%
Summary
Debris discs are the result of collisions between planetesimals and their detection implies that the planet formation process was successful in forming bodies of a few hundred or a few thousand kilometres (see e.g. Hughes et al 2018, for a recent review on debris discs). We start from a list of 819 candidate members of IC 4665 (Miret-Roig et al 2019) covering a magnitude range of 12.4 mag (7 < J < 19.4 mag) This sample was selected by combining photometry and astrometry from the Gaia Data Release 2 (DR2, Gaia Collaboration 2016, 2018) and the ground-based survey DANCe (Dynamical Analysis of Nearby Clusters, Bouy et al 2013) in a Bayesian membership algorithm. The resulting sample is expected to be significantly more complete and reliable than the one previously used by Smith et al (2011) to study debris discs in this cluster Their sample contained 40 spectroscopic low-mass members from Jeffries et al (2009), 33 brighter stars selected with proper motions and B, V photometry from the Tycho-2 catalogue (Høg et al 2000), and two additional members from Prosser & Giampapa (1994). The recent Gaia DR2 astrometry allows us to discard 24 of their 75 targets (32%) as non-members at a high level of confidence, motivating a re-analysis of the cluster disc frequency
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