VARIABLE AND POLARIZED RADIO EMISSION FROM THE T6 BROWN DWARF WISEP J112254.73+255021.5

Route & Wolszczan (2016) recently detected five radio bursts from the T6 dwarf WISEP J112254.73+255021.5 and used the timing of these events to propose that this object rotates with an ultra-short period of ~17.3 minutes. We conducted follow-up observations with the Very Large Array and Gemini-North but found no evidence for this periodicity. We do, however, observe variable, highly circularly polarized radio emission possibly with a period of 116 minutes, although our observation lasted only 162 minutes and so more data are needed to confirm it. Our proposed periodicity is typical of other radio-active ultracool dwarfs. The handedness of the circular polarization alternates with time and there is no evidence for any unpolarized emission component, the first time such a phenomenology has been observed in radio studies of very low-mass stars and brown dwarfs. We suggest that the object's magnetic dipole axis may be highly misaligned relative to its rotation axis.

[1]  G. Dulk,et al.  Radio Emission from the Sun and Stars , 1985 .

[2]  R. Stellingwerf.  Period determination using phase dispersion minimization , 1978 .

[3]  A. M. Zangari,et al.  A meta-analysis of coordinate systems and bibliography of their use on Pluto from Charon’s discovery to the present day , 2015 .

[4]  S. Hawley,et al.  The Palomar/MSU Nearby Star Spectroscopic Survey. III. Chromospheric Activity, M Dwarf Ages, and the Local Star Formation History , 2002, astro-ph/0203499.

[5]  Quiescent Radio Emission from Southern Late-Type M Dwarfs and a Spectacular Radio Flare from the M8 Dwarf DENIS 1048–3956 , 2005, astro-ph/0502365.

[6]  E. Berger,et al.  PERIODIC RADIO EMISSION FROM THE M7 DWARF 2MASS J13142039+1320011: IMPLICATIONS FOR THE MAGNETIC FIELD TOPOLOGY , 2011, 1107.1516.

[7]  Michael Biehl,et al.  Post‐correlation radio frequency interference classification methods , 2010, 1002.1957.

[8]  Michael C. Liu,et al.  HIGH-PRECISION RADIO AND INFRARED ASTROMETRY OF LSPM J1314+1320AB. II. TESTING PRE-MAIN-SEQUENCE MODELS AT THE LITHIUM DEPLETION BOUNDARY WITH DYNAMICAL MASSES , 2016, 1605.07182.

[9]  E. Berger,et al.  TRENDS IN ULTRACOOL DWARF MAGNETISM. I. X-RAY SUPPRESSION AND RADIO ENHANCEMENT , 2013, 1310.6757.

[10]  G. Hallinan,et al.  AURORAL RADIO EMISSION FROM LATE L AND T DWARFS: A NEW CONSTRAINT ON DYNAMO THEORY IN THE SUBSTELLAR REGIME , 2015, 1511.03661.

[11]  P. Uttley,et al.  False periodicities in quasar time-domain surveys , 2016, 1606.02620.

[12]  N. Lomb.  Least-squares frequency analysis of unequally spaced data , 1976 .

[13]  New Neighbors from 2MASS: Activity and Kinematics at the Bottom of the Main Sequence , 2000, astro-ph/0004361.

[14]  G. Micela,et al.  X-ray emission of brown dwarfs: towards constraining the dependence on age, luminosity, and temperature , 2005, astro-ph/0511168.

[15]  J. Brinkmann,et al.  Spectroscopic Properties of Cool Stars in the Sloan Digital Sky Survey: An Analysis of Magnetic Activity and a Search for Subdwarfs , 2004, astro-ph/0403486.

[16]  Peter Plavchan,et al.  WEATHER ON OTHER WORLDS. II. SURVEY RESULTS: SPOTS ARE UBIQUITOUS ON L AND T DWARFS , 2014, 1411.3051.

[17]  A. Wolszczan,et al.  RADIO FLARING FROM THE T6 DWARF WISEPC J112254.73+255021.5 WITH A POSSIBLE ULTRA-SHORT PERIODICITY , 2016, 1604.04543.

[18]  A. C. Riddle,et al.  Direct measurements by Voyagers 1 and 2 of the polarization of terrestrial kilometric radiation , 1978 .

[19]  David G. Monet,et al.  Dwarfs Cooler than “M”: The Definition of Spectral Type “L” Using Discoveries from the 2-Micron All-Sky Survey (2MASS) , 1999 .

[20]  R. Jayawardhana,et al.  STRONG BRIGHTNESS VARIATIONS SIGNAL CLOUDY-TO-CLEAR TRANSITION OF BROWN DWARFS , 2014, 1404.3247.

[21]  A. Wolszczan,et al.  THE 5 GHz ARECIBO SEARCH FOR RADIO FLARES FROM ULTRACOOL DWARFS , 2013, 1306.1152.

[22]  S. Hawley,et al.  The Radio Spectrum of TVLM 513-46546: Constraints on the Coronal Properties of a Late M Dwarf , 2005, astro-ph/0509762.

[23]  C. J. Schrijver,et al.  ON A TRANSITION FROM SOLAR-LIKE CORONAE TO ROTATION-DOMINATED JOVIAN-LIKE MAGNETOSPHERES IN ULTRACOOL MAIN-SEQUENCE STARS , 2009, 0905.1354.

[24]  Thierry Forveille,et al.  Spectroscopic Classification of Late-M and L Field Dwarfs , 1999 .

[25]  I. Hook,et al.  The Gemini–North Multi‐Object Spectrograph: Performance in Imaging, Long‐Slit, and Multi‐Object Spectroscopic Modes , 2004 .

[26]  E. Berger,et al.  THE ROTATION PERIOD AND MAGNETIC FIELD OF THE T DWARF 2MASSI J1047539+212423 MEASURED FROM PERIODIC RADIO BURSTS , 2015, 1502.06610.

[27]  I. Roxburgh,et al.  On the generation of the large-scale and turbulent magnetic fields in solar-type stars , 1993 .

[28]  G. Hallinan,et al.  Confirmation of the Electron Cyclotron Maser Instability as the Dominant Source of Radio Emission from Very Low Mass Stars and Brown Dwarfs , 2008, 0805.4010.

[29]  A. Wolszczan,et al.  THE ARECIBO DETECTION OF THE COOLEST RADIO-FLARING BROWN DWARF , 2012, 1202.1287.

[30]  M. Ossendrijver,et al.  The solar dynamo , 2003 .

[31]  J. Roerdink,et al.  A morphological algorithm for improving radio-frequency interference detection , 2012, 1201.3364.

[32]  E. Berger,et al.  TRENDS IN ULTRACOOL DWARF MAGNETISM. II. THE INVERSE CORRELATION BETWEEN X-RAY ACTIVITY AND ROTATION AS EVIDENCE FOR A BIMODAL DYNAMO , 2013, 1310.6758.

[33]  A. Benz,et al.  X-ray/microwave relation of different types of active stars , 1993 .

[34]  E. Schatzman.  Stellar and solar flares , 1967 .

[35]  Kenneth I. Kellermann,et al.  The Spectra of Opaque Radio Sources , 1969 .

[36]  D. A. Golimowski,et al.  Preliminary Parallaxes of 40 L and T Dwarfs from the US Naval Observatory Infrared Astrometry Program , 2004 .

[37]  J. Scargle.  Studies in astronomical time series analysis. II - Statistical aspects of spectral analysis of unevenly spaced data , 1982 .

[38]  A. Heinze,et al.  WEATHER ON OTHER WORLDS. III. A SURVEY FOR T DWARFS WITH HIGH-AMPLITUDE OPTICAL VARIABILITY , 2014, 1412.6733.

[39]  J. Linsky,et al.  The photospheric magnetic field of the dM3.5e flare star AD Leonis , 1985 .

[40]  E. Berger,et al.  QUASI-QUIESCENT RADIO EMISSION FROM THE FIRST RADIO-EMITTING T DWARF , 2013, 1301.2321.

[41]  E. Berger,et al.  SIMULTANEOUS MULTI-WAVELENGTH OBSERVATIONS OF MAGNETIC ACTIVITY IN ULTRACOOL DWARFS. III. X-RAY, RADIO, AND Hα ACTIVITY TRENDS IN M AND L DWARFS , 2009, 0909.4783.

[42]  E. Berger,et al.  SIMULTANEOUS MULTIWAVELENGTH OBSERVATIONS OF MAGNETIC ACTIVITY IN ULTRACOOL DWARFS. IV. THE ACTIVE, YOUNG BINARY NLTT 33370 AB (= 2MASS J13142039+1320011) , 2014, 1409.4411.

[43]  Harvard,et al.  CHARACTERIZATION OF THE BENCHMARK BINARY NLTT 33370, , 2014, 1401.0947.

[44]  Rotational Modulation of the Radio Emission from the M9 Dwarf TVLM 513–46546: Broadband Coherent Emission at the Substellar Boundary? , 2006, astro-ph/0608556.

[45]  Dominic J. Benford,et al.  THE FIRST HUNDRED BROWN DWARFS DISCOVERED BY THE WIDE-FIELD INFRARED SURVEY EXPLORER (WISE) , 2011, 1108.4677.

[46]  E. Berger,et al.  PERIODIC RADIO AND Hα EMISSION FROM THE L DWARF BINARY 2MASSW J0746425+200032: EXPLORING THE MAGNETIC FIELD TOPOLOGY AND RADIUS OF AN L DWARF , 2008, 0809.0001.

[47]  E. Momjian,et al.  Discovery of radio emission from the brown dwarf LP944-20 , 2001, Nature.

[48]  E. Berger,et al.  Flaring up All Over—Radio Activity in Rapidly Rotating Late M and L Dwarfs , 2001, astro-ph/0111317.

[49]  K. Covey,et al.  Spectroscopic Properties of Cool Stars in the SDSS , 2004 .

[50]  A. Brandeker,et al.  The Magnetic Properties of an L Dwarf Derived from Simultaneous Radio, X-Ray, and Hα Observations , 2005 .

[51]  C. Trigilio,et al.  3D modelling of stellar auroral radio emission , 2016, 1603.02423.

[52]  Lou‐Chuang Lee,et al.  A theory of the terrestrial kilometric radiation , 1979 .

[53]  D. Astronomia,et al.  AURORAL RADIO EMISSION FROM STARS: THE CASE OF CU VIRGINIS , 2011, 1104.3268.

[54]  Richard L. White,et al.  The FIRST Survey: Faint Images of the Radio Sky at twenty centimeters , 1995 .

[55]  M. Skrutskie,et al.  FURTHER DEFINING SPECTRAL TYPE “Y” AND EXPLORING THE LOW-MASS END OF THE FIELD BROWN DWARF MASS FUNCTION , 2012, 1205.2122.

[56]  Michael C. Liu,et al.  HIGH-PRECISION RADIO AND INFRARED ASTROMETRY OF LSPM J1314+1320AB. I. PARALLAX, PROPER MOTIONS, AND LIMITS ON PLANETS , 2016, 1605.07177.

[57]  E. Berger,et al.  Simultaneous Multiwavelength Observations of Magnetic Activity in Ultracool Dwarfs. II. Mixed Trends in VB 10 and LSR 1835+32 and the Possible Role of Rotation , 2007, 0710.3383.

[58]  C. Lynch,et al.  WIDEBAND DYNAMIC RADIO SPECTRA OF TWO ULTRA-COOL DWARFS , 2014, 1405.3516.

[59]  K. Cruz,et al.  FUNDAMENTAL PARAMETERS AND SPECTRAL ENERGY DISTRIBUTIONS OF YOUNG AND FIELD AGE OBJECTS WITH MASSES SPANNING THE STELLAR TO PLANETARY REGIME , 2015, 1508.01767.

[60]  A. V. Maanen.  The Photographic Determination of Stellar Parallaxes with the 60- and 100-INCH Reflectors. Seventeenth Series. , 1940 .

[61]  R. Treumann.  The electron–cyclotron maser for astrophysical application , 2006 .

[62]  J. Bochanski,et al.  CONSTRAINING THE AGE–ACTIVITY RELATION FOR COOL STARS: THE SLOAN DIGITAL SKY SURVEY DATA RELEASE 5 LOW-MASS STAR SPECTROSCOPIC SAMPLE , 2007, 0712.1590.