STEADY AND TRANSIENT RADIO EMISSION FROM ULTRACOOL DWARFS

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dc.contributor.authorOsten, Rachel A.
dc.contributor.authorPhan-Bao, N.
dc.contributor.authorHawley, Suzanne L.
dc.contributor.authorReid, I. Neill
dc.contributor.authorOjha, Roopesh
dc.date.accessioned2020-04-29T13:54:39Z
dc.date.available2020-04-29T13:54:39Z
dc.date.issued2009-07-16
dc.description.abstractWe present the results of multi-frequency radio observing campaigns designed to elucidate the nature of radio emission from very low mass stars. We detect radio emission in an additional two epochs of the ultracool dwarf binary LP 349–25, finding that the observed emission is broad band and steady on timescales between 10 s and 10.7 hr, as well as on timescales of 0.6 and 1.6 years. This system is unusual for ultracool dwarfs with detectable radio emission, in exhibiting a lack of any large-scale variability, particularly the bursting (periodic or aperiodic) behavior exhibited by the other objects with detectable levels of radio emission. We explore the constraints that the lack of variability on long- and short-timescales, and flat spectral index, imply about the radio-emitting structures and mechanism. The temporal constraints argue for a high latitude emitting region with a large inclination so that it is always in view, and survives for at least 0.6 years. Temporal constraints also limit the plasma conditions, implying that the electron density be nₑ < 4 × 10⁵ cm⁻³ and B< 130 G in order not to see time variations due to collisional or radiative losses from high-energy particles. The observations and constraints provided by them are most compatible with a nonthermal radio emission mechanism, likely gyrosynchrotron emission from a spatially homogeneous or inhomogeneous source. This indicates that, similar to behaviors noted for chromospheric, transition region, and coronal plasmas in ultracool dwarfs, the magnetic activity patterns observed in active higher mass stars can survive to the substellar boundary. We also present new epochs of multi-frequency radio observations for the ultracool dwarfs 2MASS 05233822–140322 and 2MASS14563831–2809473(=LHS 3003); each has been detected in at least one previous epoch but are not detected in the epochs reported here. The results here suggest that magnetic configurations in ultracool dwarfs can be long-lasting, and support the need for further radio monitoring using a simultaneous, multi-frequency observing approach.en_US
dc.description.sponsorshipSupport for this work was provided by NASA through Hubble Fellowship grant HF-01189.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. for NASA, under contract NAS5-26555.en_US
dc.description.urihttps://iopscience.iop.org/article/10.1088/0004-637X/700/2/1750en_US
dc.format.extent9 pagesen_US
dc.genrejournal articlesen_US
dc.identifierdoi:10.13016/m2xx46-v7xe
dc.identifier.citationRachel A. Osten and N. Phan-Bao and Suzanne L. Hawley and I. Neill Reid and Roopesh Ojha, STEADY AND TRANSIENT RADIO EMISSION FROM ULTRACOOL DWARFS, The Astrophysical Journal, Volume 700, Number 2, 2009, doi; https://doi.org/10.1088%2F0004-637x%2F700%2F2%2F1750en_US
dc.identifier.urihttps://doi.org/10.1088%2F0004-637x%2F700%2F2%2F1750
dc.identifier.urihttp://hdl.handle.net/11603/18364
dc.identifier.urihttp://simbad.u-strasbg.fr/simbad/sim-ref?querymethod=bib&simbo=on&submit=submit+bibcode&bibcode=2009ApJ...700.1750O
dc.language.isoen_USen_US
dc.publisherIOPen_US
dc.relation.isAvailableAtThe University of Maryland, Baltimore County (UMBC)
dc.relation.ispartofUMBC Physics Department Collection
dc.relation.ispartofUMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)
dc.rightsThis item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author.
dc.rights© 2009. The American Astronomical Society. All rights reserved.
dc.titleSTEADY AND TRANSIENT RADIO EMISSION FROM ULTRACOOL DWARFSen_US
dc.typeTexten_US

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