Rotation-disk connection for very low mass and substellar objects in the Orion Nebula Cluster

Abstract

Aims. Angular momentum (J) loss requires magnetic interaction between the forming star and both the circumstellar disk and the magnetically driven outflows. In order to test these predictions many authors have investigated a rotation-disk connection in pre-main sequence objects with masses larger than about 0.4 M . For brown dwarfs (BDs) this connection was not investigated as yet because there are very few samples available. We aim to extend this investigation well down into the substellar regime for our large sample of ≈80 BDs in the Orion Nebula Cluster, for which we have recently measured rotational periods. Methods. In order to investigate a rotation-disk correlation, we derived near-infrared (NIR) excesses for a sample of 732 periodic variables in the Orion Nebula Cluster with masses ranging between ≈1.5-0.02 M and whose IJHK colors are available. Circumstellar NIR excesses were derived from the Δ[I − K] index. We performed our analysis in three mass bins (>0.4 M , 0.4-0.075 M , and <0.075 M ). Results. We found a rotation-disk correlation in the high and intermediate mass regime, in which objects with NIR excess tend to rotate slower than objects without NIR excess. Interestingly, we found no correlation in the substellar regime. A tight correlation between the peak-to-peak (ptp) amplitude of the rotational modulation and the NIR excess was found however for all objects with available ptp values (<0.4 M ). We discuss possible scenarios which may explain the lack of rotation-disk connection in the substellar mass regime. One possible reason could be the strong dependence of the mass accretion rateṀ on stellar mass in the investigated mass range (Ṁ ∝ M 2 − 2.8 star ), which is expected to result in a corresponding mass dependence ofJ/J.

Rotation of Low-mass Stars in Upper Scorpius and ρ Ophiuchus with K2

“…Several previous studies have claimed to find evidence that the correlation between disk presence and rotation was strongest for "high-mass" stars and was weaker or not present for very low-mass stars or brown dwarfs (Lamm et al 2005;Rodríguez-Ledesma et al 2010;Davies et al 2014;Scholz et al 2015). Our data do not support that conclusion.…”

“…There have been many papers devoted to that goal, primarily using data from the Orion Nebula Cluster or NGC2264 (e.g., Rebull et al 2006;Cieza & Baliber 2007;Biazzo et al 2009;Rodríguez-Ledesma et al 2010;Dahm et al 2012;Davies et al 2014;Venuti et al 2017). Those studies generally find evidence claimed to be supportive of disk locking.…”

Optical photometric variable stars towards the Galactic H ii region NGC 2282

“…Potentially, variability explores the young stars in the field population. Recent studies on PMS variable census allowed to probe rotation rates in the few Myrs young to several Myrs old clusters those include the Orion Nebula Cluster (Stassun et al 1999;Herbst et al 2002;Rodríguez-Ledesma et al 2010), Chamaeleon I (Joergens et al 2003), IC 348 (Cohen et al 2004), σ Orionis (Scholz & Eislöffel 2004;Cody & Hillenbrand 2010), NGC 2264 (Makidon et al 2004;Lamm et al 2005), NGC 2362 (Irwin et al 2008) and Taurus (Nguyen et al 2009). However, variability alone is not sufficient evidence to identify the young members, and sometimes might be false positive.…”

Variable stars in the Sh 2-170 H ii region

“…Since ∆(Ic − Ks) is sensitive to the inner part of the disc, we also used the available MIR data of these variables to compute an MIR index [[3.6] − [4.5]], which is a better indicator of the presence of disc and its evolution (Lada et al 2000;Rodríguez-Ledesma et al 2010). Since the presence of disc also induces the accretion activity, we have also used the information such as the disc accretion rate and the disc mass obtained from the SED fitting tool (cf.…”

“…The disc-locking mechanism can also be verified by checking the correlation of rotation periods with disc indicators such as: ∆(Ic − Ks), ∆(H − Ks), [[3.6] − [4.5]], Hα emission etc. (Herbst et al 2002;Rodríguez-Ledesma et al 2010). Correlation of rotation period of PMS stars with different stellar properties (age, mass, accretion rate etc.)…”