Untitled - Laboratoire d'Astrophysique de l'Observatoire de Grenoble

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Figure 6.8: Distribution of separations for multiple M-dwarfs of the Solar neighbourhood, compared with the distribution of solar-type multiples. one that produces a flat mass ratio distribution over a broad period range, and a second that only forms short period binaries with nearly equal masses. The multiplicity of L dwarfs Where do free-floating brown dwarfs come from? Are they ejected stellar embryos (Reipurth & Clarke 2001, AJ, 122, 432), or do they form like “isolated” stars, by fragmentation of molecular cores? Searching for companions around L dwarfs is the logical next step to get a complete view of multiplicity accross the mass spectrum and answer these questions. To search for companions to L dwarfs, a part of the DENIS sample of ultracool dwarfs (Delfosse et al. 2003) was observed with HST/WFPC2 (Bouy et al. 2003). 15 new ultracool binaries are reported and statistical elements determined. The observed frequency of ultracool binaries is lower than that of binaries with G-type primaries in the separation range from 0.42 AU to 80 AU. There is also a clear deficit of ultracool binaries with separations wider than 15 AU and a tendency for the ultracool binaries to have mass ratios near unity. Noteworthy, this astrometric work lead to the first determination of the orbit and dynamical masses of a binary brown dwarfs: the L dwarf 2MASSW J0746425+2000321 (Bouy et al. 2004), mentioned before in this report. The deficit of wide ultracool dwarfs binaries reported above by Bouy et al. (2003), but also in Close et al. (2003, ApJ, 598, 1265) and Gizis et al. (2003, AJ, 125, 3302), is frequently presented as an argument in favour of the embryo-ejection scenario for the formation of brown dwarfs. To test this scenario, we obtained infrared images of a very large sample of ultracool dwarfs (250 DENIS late-M and L dwarfs) to detect companion at separation larger than 1arcsec. We detected the first wide binary for this range of mass (Billères et al. 2005, see Fig. 6.9), which is clearly not formed by the embryo-ejection scenario. One consequence of this discovery is that, although rare, low-mass pairs exist and brown dwarfs do not form solely by embryo ejection. Surveys for field brown dwarfs For the last 10 years we have used the DENIS survey to find very-late M- and L-dwarfs in the solar neighbourhood (see for example Crifo et al. 2005; Kendall et al. 2004; Phan-Bao et al. 2003; and Delfosse et al. 2003 for 94
Figure 6.9: Top panels: DENIS discovery images of D0551 in I- and J-band. In J-band the object is well visible with a magnitude J=15.3. Bottom Panels: SOFI images, with better resolution, revealing the binarity of D0551. the latest results). A large sample of 300 very late M- and L-dwarfs, identified over 5700 square degrees(!) of DENIS data, resulted. The sample is complete for objects redder than I-J=3.0 (M8) and brighter than I=18, and thus statistically well defined. It is an excellent basis for studies of the Galactic disk population of very low mass stars and brown dwarfs, allowing clean determinations of the luminosity function, mass function, and multiplicity fraction. Recently, we extended our study by including the CFHT-Legacy Survey data, with three main goals in mind: find ultracool brown dwarfs (T
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LABORATOIRE D’ASTROPHYSIQUE DE GR
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III Team ASTROMOL 41 2 Presentation
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8.1.3 Graduate Students . . . . . .
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VI Team SHERPA 145 15 Results 147 1
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Part I Foreword: Presentation of th
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Part II Executive Summary A 18th ce
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of CNRS for technicians and enginee
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Figure 1.3: New LAOG organigram (20
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heart attack. Manuel went back to t
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Figure 1.6: PhD student repartition
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• LAOG researchers (and publishin
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and published 95 papers in four yea
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• National astronomy programs. 4
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1.5 From dreams to reality: Human r
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and accretion disks with heavy nume
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emphasis on the chemistry of planet
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Part III TEAM ASTROMOL Sub-arcsecon
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Table 15.1: List of the permanent S
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15.4 Transport phenomena in accreti
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Figure 15.2: Spectral energy distri
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states, combining a still powerful
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Excitation of turbulence by Cosmic
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Table 15.2: Former PhD students of
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Chapter 16 Perspectives The distinc
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Ray background. The second project
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164
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- Ceccarelli Cecilia (AT) - Delfoss
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Among the various areas of expertis
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-responsable du groupe ”logiciel
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Chef de l’ Equipe ASTROMOL du LAO
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jury de concours: 1 concours IR CNR
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Chapter 20 Appendix 4: The Jean Mar
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20.7 Production informatique ¡¢£
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20.10 Formation des utilisateurs La
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20.13 Darwin ¡¢£¤¥¦§¨©�
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