Rotational studies in the Orion Nebula Cluster: from solar mass stars to brown dwarfs

Abstract

Aims. Rotational studies at a variety of ages and masses are important for constraining the angular momentum evolution of young stellar objects (YSO). Of particular interest are the very low mass (VLM) stars and brown dwarfs (BDs), because of the significant lack of known rotational periods in that mass range. We aim to extend previous studies well down into the substellar regime, providing for the first time information on rotational periods for a large sample of young VLM stars and BDs. Methods. This extensive rotational period study of YSOs in the 1 Myr old Orion Nebula Cluster (ONC) is based on a deep photometric monitoring campaign using the Wide Field Imager (WFI) camera on the ESO/MPG 2.2 m telescope on La Silla, Chile. Time series data was obtained with about 95 data points spread over 19 nights. Accurate I-band photometry of 2908 stars was obtained within a magnitude range of 13 to 21 mag, i.e. extending three magnitudes deeper than previous studies in the ONC. Two different power spectral analysis techniques were used to search for periodic variability. In addition, the χ 2 variability test was used for the detection of irregular variables. Results. We found 487 periodic variables with estimated masses between 0.5 M and 0.015 M , 124 of which are BD candidates. This is by far the most extensive and complete rotational period data set for young VLM stars and BDs. In addition to the periodic variables, 808 objects show non-periodic brightness variations. We study the dependence of the period distribution on mass and variability level and compare this with known objects in the ONC with masses up to 1.5 M and with the ∼2 Myr old cluster NGC 2264. We find that substellar objects rotate on average faster than the VLM stars. In addition, our rotational data suggest a dependence of the rotational periods on position within the field, which can be explained by a possible age spread in the ONC with a somewhat younger central region. The results of a comparison between the period distributions of the ONC and NGC 2264 favours this hypothesis. In addition, periodic variables with larger peak-to-peak amplitudes rotate on average slower than those with small peak-to-peak amplitude variations, which can possibly be explained by different magnetic field topologies.

Evidence of early disk-locking among low-mass members of the Orion Nebula Cluster

“…More recently, Rebull et al (2006) and Cieza & Baliber (2007) find that in Orion and NGC 2264 stars with long periods are more likely than those with short periods to have IR excesses suggestive of disks. Very recently, Nguyen et al (2009) find in Taurus-Auriga and Chamaeleon I (∼2 Myr) that both accretors and non-accretors have similar distributions of v sin i, while Rodriguez-Ledesma et al (2009) confirm the result found by Herbst et al (2000Herbst et al ( , 2001Herbst et al ( , 2002 in ONC.…”

“…In particular, as shown in Fig. 1, about 62% of our sample is almost inside the circle with radius equal to the so-called cluster radius (R cluster ;Hillenbrand 1997) where Rodriguez-Ledesma et al (2009) find an indication of higher P rot compared to the stars outside R cluster . This could indicate objects closer to the Trapezium center tend to rotate on average slower than the outer ones.…”

A Vla Survey for Faint Compact Radio Sources in the Orion Nebula Cluster

“…These flares may be the result of magnetic reconnections on the protostellar surface, which would produce radio flares on the timescales of minutes (e.g., Dulk 1985;Bower et al 2003;Forbrich et al 2008). Interactions between the magnetic fields of the protostar and its disk could also produce flares on the timescales similar to the rotation periods of young stars, which are typically days to weeks in the ONC (e.g., Shu et al 1997;Forbrich et al 2006;Rodríguez-Ledesma et al 2009). …”

Herschelsurvey of brown dwarf disks inρOphiuchi

“…Whelan et al 2009), and are magnetically active showing evidence of rotational modulation of spots on their surface (e.g. Rodríguez-Ledesma et al 2009). It is therefore pertinent to ask whether brown dwarfs may also form and harbour planetary systems.…”