Searching for very low-mass stars and brown dwarfs 
with DENIS

Delfosse, X.; Tinney, C. G.; Forveille, T.; Epchtein, N.; Borsenberger, J.; Fouqué, P.; Kimeswenger, S.; Tiphéne, D.

doi:10.1051/aas:1999158

Cited by 98 publications

(94 citation statements)

References 29 publications

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“…General references for source properties: Wilking et al 1999;Cruz & Reid 2002;Cruz et al 2003;Lodieu et al 2002Lodieu et al , 2005Dahn et al 2002;Mohanty & Basri 2003;Reid 2003;Gizis 2002;Fuhrmeister & Schmitt 2004;Deacon & Hambly 2001;Gizis et al 2000;Leggett et al 2002;Golimowski et al 2004;Geballe et al 2002;Reid et al 2000Reid et al , 2002Reid et al , 2003aReid et al , 2003bCosta et al 2005;Salim & Gould 2003;Liebert et al 2003;Zapatero Osorio et al 2000;Martín & Ardila 2001;Neuhäuser et al 1999;Graham et al 1992;Knapp et al 2004;Hawley et al 2002;Martín et al 1999;Gizis & Reid 2006;Bouy et al 2003Bouy et al , 2004Kirkpatrick 2005;Bailer-Jones 2004;Ruiz et al 1997;Tinney 1998;Kendall et al 2003Kendall et al , 2004Schweitzer et al 2001;Kirkpatrick et al 1993Kirkpatrick et al , 2000Kirkpatrick et al , 2001Delfosse et al 1999;…”

Section: Physical Properties: Magnetic Field Strength Source Size Aunclassified

Radio Observations of a Large Sample of Late M, L, and T Dwarfs: The Distribution of Magnetic Field Strengths

Berger

2006

ApJ

203

237

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I present radio observations of 90 dwarf stars and brown dwarfs of spectral type M5YT8. Three sources exhibit radio activity, in addition to the six objects previously detected in quiescence and outburst, leading to an overall detection rate of $10% for objects later than M7. The inferred magnetic field strengths are $10 2 G in quiescence and nearly 1 kG during flares, while the majority of the nondetected objects have B P 50 G. Depending on the configuration and size of the magnetic loops, the surface fields may approach 1 kG even in quiescence, at most a factor of a few smaller than in early M dwarfs. With the larger sample of sources I find continued evidence for (1) a sharp transition around spectral type of M7 from a ratio of radio to X-ray luminosity of log (L R /L X ) $ À15:5 to kÀ12, (2) increased radio activity (L R /L bol ) with later spectral type, in contrast to H and X-ray observations, and (3) an overall drop in the fraction of active sources from $30% for M dwarfs to $5% for L dwarfs, consistent with H and X-ray observations. Taken together, these trends suggest that some late M and L dwarfs are capable of generating 0.1Y1 kG magnetic fields, but the overall drop in the fraction of such objects likely reflects changes in the structure of the chromospheres and coronae, possibly due to increasingly neutral atmospheres and /or a transition to a turbulent dynamo. These possibilities can best be tested through simultaneous observations, which can trace the effect of magnetic dissipation in a direct, rather than a statistical, manner. Still, a more extended radio survey currently holds the best promise for measuring the magnetic field properties of a large number of dwarf stars.

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Section: Physical Properties: Magnetic Field Strength Source Size Aunclassified

Radio Observations of a Large Sample of Late M, L, and T Dwarfs: The Distribution of Magnetic Field Strengths

Berger

2006

ApJ

203

237

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“…With typical 3-σ limits of I ∼ 19.0, J ∼ 16.0 and K s ∼ 13.5, the DENIS survey is very sensitive to very late M and L dwarfs (Delfosse et al 1999b;Martín et al 1999). We are extracting large statistical sample of such very low mass stars and brown dwarfs, by selecting sources with I −J ≥ 3.00 (later than M8) and |l II | ≥ 20…”

Section: Observational Datamentioning

confidence: 99%

New neighbours: II. An M9 dwarf at ${\vec d}\sim$ 4 pc, DENIS-P J104814.7-395606.1

Delfosse¹,

Forveille²,

Martín³

et al. 2001

A&A

Self Cite

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Abstract. We present the discovery of a previously unknown member of the immediate solar neighbourhood, DENIS-P J104814.7−395606.1 (hereafter DENIS 1048−39), identified while mining the DENIS database for new nearby stars. A HIRES echelle spectrum obtained with the 10-m Keck telescope shows that it is an M9 dwarf. DENIS 1048−39 has a very bright apparent magnitude (I = 12.67) for its spectral type and colour (I − J = 3.07), and is therefore very nearby. If it is single its distance is only 4.1 ± 0.6 pc, ranking it as between our 12th and 40th closest neighbour. It is also the closest star or brown dwarf with a spectral type later than M7V. Its proper motion was determined through comparison of Sky atlas Schmidt plates, scanned by the MAMA microdensitometer, with the DENIS images. At 1.52 yr −1 it primarily attests the closeness of DENIS 1048−39 and hence its dwarf status. These characteristics make it an obvious target for further detailed studies.

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“…As for amplitudes, we have plotted the standard deviation, σ, of the photometric data for each object in Fig. 15 (data compiled from Martín et al , 2000Martín et al , 2001Zapatero Osorio et al 1996Delfosse et al 1999;Terndrup et al 1999;Bailer-Jones & Mundt 1999, 2001aKirkpatrick et al 1999Kirkpatrick et al , 2000Reid et al 2000;Gelino et al 2002;Clarke et al 2002a,b). Amplitudes do not scale with the strength of Hα emission.…”

Section: Rotationmentioning

confidence: 99%

Photometric variability of a young, low-mass brown dwarf

Osorio

Caballero

Béjar

et al. 2003

A&A

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Abstract. We report differential I-band and J-band photometry of S Ori 45, a cool (spectral type M8.5), young (1-8 Myr) brown dwarf of the σ Orionis cluster with a likely mass estimated at around 20 times the mass of Jupiter. We detect variability (amplitudes ranging from 34 to 81 mmag) and observe a modulation at a period of 2.5-3.6 h in both optical and near-infrared light curves. The most recent optical data set, however, presents a modulation at the very short period of 46.4 ± 1.5 min, which remains a mystery. The origin of the 2.5-3.6 h modulation is analyzed in terms of various scenarios: inhomogeneous features (dust clouds or magnetically induced dark spots) co-rotating with the object's surface, and presence of an unseen very low-mass companion that is steadily transferring mass to the primary. Because of the very young age of the object and its persistent strong Hα emission, the possible presence of an accreting disk is also discussed. If the period of a few hours is related to rotation, our results suggest that σ Orionis low-mass brown dwarfs are rotating faster than more massive cluster brown dwarfs at a rate consistent with their theoretically inferred masses and radii, implying that all of these objects have undergone similar angular momentum evolution.

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Searching for very low-mass stars and brown dwarfs with DENIS

Cited by 98 publications

References 29 publications

Radio Observations of a Large Sample of Late M, L, and T Dwarfs: The Distribution of Magnetic Field Strengths

Radio Observations of a Large Sample of Late M, L, and T Dwarfs: The Distribution of Magnetic Field Strengths

New neighbours: II. An M9 dwarf at ${\vec d}\sim$ 4 pc, DENIS-P J104814.7-395606.1

Photometric variability of a young, low-mass brown dwarf

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