The Monitor project: rotation of low-mass stars in NGC 2362 – testing the disc regulation paradigm at 5 Myr

Jonathan Irwin,Estelle Moraux,Jerome Bouvier,Leslie Hebb,Simon Hodgkin,Mike Irwin,Suzanne Aigrain

doi:10.1111/j.1365-2966.2007.12725.x

Abstract

Abstract We report on the results of a time-series photometric survey of NGC 2362, carried out using the CTIO 4-m Blanco telescope and Mosaic-II detector as part of the Monitor project. Rotation periods were derived for 271 candidate cluster members over the mass range 0.1 ≲M/M⊙≲ 1.2. The rotation period distributions show a clear mass-dependent morphology, qualitatively similar to that in NGC 2264, as would be expected from the age of this cluster. Using models of angular momentum evolution, we show that angular momentum losses over the ∼1–5 Myr age range appear to be needed in order to reproduce the evolution of the slowest rotators in the sample from the ONC to NGC 2362, as found by many previous studies. By incorporating Spitzer IRAC mid-infrared (mid-IR) measurements, we found that three to four objects showing mid-IR excesses indicative of the presence of circumstellar discs were all slow rotators, as would be expected in the disc regulation paradigm for early pre-main-sequence angular momentum evolution, but this result is not statistically significant at present, given the extremely limited sample size.

Highlights

NGC 2362 is a very young open cluster, at a moderate distance
Dahm (2005) carried out an extensive spectroscopic survey, concentrating on the Hα 6563 Å and Li I 6707.8 Å features, finding that a large fraction (∼91 per cent) of the T Tauri star (TTS) population in NGC 2362 is composed of weak-line emitters (WTTS), as
∼0.7 M, these diagrams reveal a correlation between stellar mass and the longest rotation period seen at that mass, with a clear lack of slow rotators at very low masses

Summary

Introduction

NGC 2362 is a very young open cluster, at a moderate distance. We adopt the parameters of Moitinho et al (2001) for the remainder of this work: an age of 5+−12 Myr, distance 1480 pc and reddening E(B − V) = 0.10 mag. Note that there is some controversy in the literature regarding the age of this cluster, with estimates ranging from 3–9 Myr. Mayne et al (2007) have examined the relative ages of young open clusters, finding that NGC 2362 does seem to be older than the ONC, but that it may be younger than IC 348, and they suggest an age of ∼3 Myr. the extremely young age, and lack of substantial nebulosity or differential reddening in this cluster make it an ideal testing ground for theories of pre-main-sequence (PMS) stellar evolution. The extremely young age, and lack of substantial nebulosity or differential reddening in this cluster make it an ideal testing ground for theories of pre-main-sequence (PMS) stellar evolution. Dahm (2005) carried out an extensive spectroscopic survey, concentrating on the Hα 6563 Å and Li I 6707.8 Å features, finding that a large fraction (∼91 per cent) of the T Tauri star (TTS) population in NGC 2362 is composed of weak-line emitters (WTTS), as

Objectives

Methods

Results

Conclusion