Spitzer Mid-infrared Study of Sh 2-208: Evolution of Protoplanetary Disks in Low-metallicity Environments

Abstract

This study presents sensitive MIR photometry obtained with the Spitzer/IRAC for a young cluster in Sh 2-208 (S208) located in one of the lowest-metallicity H II regions in the Galaxy, [O/H] = −0.8 dex. Previous studies suggested that the cluster is ∼0.5-Myr old and has a distance of D = 4 kpc, which is consistent with the astrometric distance from Gaia EDR3. In ∼3.5 × 4-arcmin field, 96 sources were detected in at least one MIR band at ≥10σ, covering intermediate-mass stars with ∼1.0-M ⊙ mass detection limit. Total 41 probable cluster members were identified based on the spatial distributions of spectral-energy-distribution slopes derived from the NIR K S and IRAC bands and extinctions of the sources. The cumulative distribution of the SED slopes for the S208 cluster was not significantly different from those of other clusters in solar-metallicity environments with approximately the same age for intermediate-mass stars, if one also considers non-detected MIR sources identified as S208 cluster members from NIR observations. This suggests that the degree of dust growth/settling does not significantly change with metallicities as different as ∼1 dex. The fraction of stars with MIR disk emissions for the cluster members with ≥1-M ⊙ mass was 64%-93%, which is comparable to the results in solar-metallicity environments. Although this may suggest that dominant disk-dispersal mechanisms for intermediate-mass stars have either no, or very weak, dependence on metallicity, it can be argued alternatively that this may suggest that the disk dispersal process does not work effectively at this young stage.

Subaru Hyper Suprime-Cam Survey of Cygnus OB2 Complex -- I: Introduction, Photometry and Source Catalog

“…& Cieza 2011; Helled et al 2014;Ribas et al 2014). Although in a young cluster, disk fraction depends upon various factors such as the metallicity, stellar density, environmental factors like external and internal photoevaporation (Yasui et al 2016;Yasui 2021;Thies et al 2010;Guarcello et al 2016;Reiter & Parker 2019), a general trend of disk fraction declining with age is observed. It ranges between 60% -80% for clusters like NGC 1333 (Ribas et al 2014), NGC 2023, RCW36 (Richert et al 2018) with an age < 1 Myr (e.g ) to 5% -10% for clusters like LowCent-Crux (Hernández et al 2007), 25 Orionis (Pecaut & Mamajek 2016) with age ∼ 10 Myrs.…”