A deep staring campaign in the Sigma Orionis cluster. Variability in substellar members

Abstract

Deep optical imaging is used to study time-domain properties of young brown dwarfs in sigma Orionis over typical rotational time-scales and to search for new substellar and planetary-mass cluster members. We used VIMOS at the VLT to monitor a 24 arcmin x 16 arcmin field in the I-band. Using the individual images from this run we investigated the photometric time series of nine substellar cluster members with masses from 10 to 60 Mj. The deep stacked image shows cluster members down to $\approx$ 5 Mj. We search for new planetary mass objects by combining our deep I-band photometry with public J-band magnitudes and by examining the nearby environment of known very low mass members for possible companions. We find two brown dwarfs, with significantly variable, aperiodic light curves, both with masses around 50 Mj, one of which was previously unknown to be variable. The physical mechanism responsible for the observed variability is likely different for the two objects. The variability of the first object, a single-lined spectroscopic binary, is most likely linked to its accretion disc, the second may be caused by variable extinction by large grains. We find five new candidate members from the colour-magnitude diagram and three from a search for companions within 2000 au. We rule all eight sources out as potential members based on non-stellar shape and/or infrared colours. The I-band photometry is made available as a public dataset. We present two variable brown dwarfs. One is consistent with ongoing accretion, the other, exhibiting apparent transient variability without presence of an accretion disc. Our analysis confirms the existing census of substellar cluster members down to $\approx$ 7 Mj. The zero result from our companion search agrees with the low occurrence rate of wide companions to brown dwarfs found in other works.

9 pages, 7 figures

References in corpus (13)

• The Gaia mission
• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• The WFCAM Science Archive
• The UKIRT Wide Field Camera ZYJHK Photometric System: Calibration from 2MASS
• Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition
• Rotation and accretion of very low mass objects in the SigmaOri cluster
• Brown dwarf disks with ALMA: evidence for truncated dust disks in Ophiuchus
• Main-Seqence Fitting Distance to the sigma Ori Cluster
• A survey for low mass spectroscopic binary stars in the young clusters around sigma Orionis and lambda Orionis
• Stars and brown dwarfs in the sigma Orionis cluster: the Mayrit catalogue
• The low-mass content of the massive young star cluster RCW 38
• Long-term variability of T Tauri stars using WASP

Cited by in corpus (1)

• Clumpy dust rings around non-accreting young stars