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Post Info TOPIC: Two TW Hydrae Association Brown Dwarfs


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Posts: 131433
Date:
L dwarfs
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Title: L dwarfs in the Hyades
Authors: E. Hogan (1), R. F. Jameson (1), S. L. Casewell (1), S. L. Osbourne (1), N. C. Hambly (2) ((1) Department of Physics and Astronomy, University of Leicester, (2) Scottish Universities' Physics Alliance (SUPA), Institute for Astronomy, School of Physics, University of Edinburgh)

We present the results of a proper motion survey of the Hyades to search for brown dwarfs, based on UKIDSS and 2MASS data. This survey covers ~275 square degrees to depth of K~15 mag, equivalent to a mass of 0.05 solar masses assuming a cluster age of 625 Myr. The discovery of 12 L dwarf Hyades members is reported. These members are also brown dwarfs, with masses between 0.05 < M < 0.075 solar masses. A high proportion of these L dwarfs appear to be photometric binaries.

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Posts: 131433
Date:
DENIS J124514.1-442907
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Title: Discovery of an M9.5 Candidate Brown Dwarf in the TW Hydrae Association - DENIS J124514.1-442907
Authors: Dagny L. Looper (UH/IfA), Adam J. Burgasser (MIT), J. Davy Kirkpatrick (Caltech/IPAC), Brandon J. Swift (UH/IfA; U Arizona)
(Version v3)

We report the discovery of a fifth candidate substellar system in the ~5-10 Myr TW Hydrae Association - DENIS J124514.1-442907. This object has a NIR spectrum remarkably similar to that of 2MASS J1139511-315921, a known TW Hydrae brown dwarf, with low surface gravity features such as a triangular-shaped H-band, deep H2O absorption, weak alkali lines, and weak hydride bands. We find an optical spectral type of M9.5 and estimate a mass of <24 M_Jup, assuming an age of ~5-10 Myr. While the measured proper motion for DENIS J124514.1-442907 is inconclusive as a test for membership, its position in the sky is coincident with the TW Hydrae Association. A more accurate proper motion measurement, higher resolution spectroscopy for radial velocity, and a parallax measurement are needed to derive the true space motion and to confirm its membership.

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Posts: 131433
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Title: Discovery of an M9.5 Candidate Brown Dwarf in the TW Hydrae Association - DENIS J124514.1-442907
Authors: Dagny L. Looper (UH/IfA), Adam J. Burgasser (MIT), J. Davy Kirkpatrick (Caltech/IPAC), Brandon J. Swift (UH/IfA; U Arizona)
(Version v2)

We report the discovery of a fifth candidate substellar system in the ~5-10 Myr TW Hydrae Association - DENIS J124514.1-442907. This object has a NIR spectrum remarkably similar to that of 2MASS J1139511-315921, a known TW Hydrae brown dwarf, with low surface gravity features such as a triangular-shaped H-band, deep H2O absorption, weak alkali lines, and weak hydride bands. We find an optical spectral type of M9.5 and estimate a mass of <24 M_Jup, assuming an age of ~5-10 Myr. While the measured proper motion for DENIS J124514.1-442907 is inconclusive as a test for membership, its position in the sky is coincident with the TW Hydrae Association. A more accurate proper motion measurement, higher resolution spectroscopy for radial velocity, and a parallax measurement are needed to derive the true space motion and to confirm its membership.

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Posts: 131433
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RE: Two TW Hydrae Association Brown Dwarfs
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Title: The Trigonometric Parallax of the Brown Dwarf Planetary System 2MASSW J1207334-393254
Authors: John E. Gizis, Wei-Chun Jao, John P. Subasavage, Todd J. Henry

We have measured a trigonometric parallax to the young brown dwarf 2MASSW J1207334-393254. The distance [54.0 (+3.2,-2.8) pc] and space motion confirm membership in the TW Hydrae Association. The primary is a ~25 M_jup brown dwarf. We discuss the "planetary mass" secondary, which is certainly below the deuterium-burning limit but whose colours and absolute magnitudes pose challenges to our current understanding of planetary-mass objects.

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Posts: 131433
Date:
2M1207
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Title: HST NICMOS Imaging of the Planetary-mass Companion to the Young Brown Dwarf 2MASS J1207334-393254
Authors: Inseok Song, G. Schneider, B. Zuckerman, J. Farihi, E. E. Becklin, M. S. Bessell, P. Lowrance, B. A. Macintosh

Multi-band (0.9 to 1.6 um) images of the TW Hydrae Association (TWA) brown dwarf, 2MASS J1207334-393254 (also known as 2M1207), and its candidate planetary mass companion (2M1207b) were obtained on 2004 Aug 28 and 2005 Apr 26 with HST/NICMOS. The images from these two epochs unequivocally confirm the two objects as a common proper motion pair (16.0 sigma confidence). A new measurement of the proper motion of 2M1207 implies a distance to the system of 597 pc and a projected separation of 465 AU. The NICMOS and previously published VLT photometry of 2M1207b, extending overall from 0.9 to 3.8 um, are fully consistent with an object of a few Jupiter masses at the canonical age of a TWA member (~8 Myr) based on evolutionary models of young giant planets. These observations provide information on the physical nature of 2M1207b and unambiguously establish that the first direct image of a planetary mass companion in orbit around a self-luminous body, other than our Sun, has been secured.

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Posts: 131433
Date:
Two TW Hydrae Association Brown Dwarfs
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Title: Spitzer Observations of two TW Hydrae Association Brown Dwarfs
Authors: Basmah Riaz, John E. Gizis, Abraham Hmiel

Researchers present Spitzer Space Telescope observations of two TW Hydrae Association brown dwarfs, 2MASSW J1207334-393254 and 2MASSW J1139511-315921, in the IRAC and MIPS 24 micron bands. Based on their IRAC colours, they have classified them as Classical and Weak-line T Tauri stars, respectively.
For 2MASSW J1207334-393254, they find that a flat disk model fits the data very well. This brown dwarf shows the presence of warm (T > 100 K) circumstellar dust close (R < 0.2 AU) to it, and does not display any signs of cleansing of dust within several AU of the star.
In comparison with other TWA members that show excess in IR, they suggest that there exists a different disk evolution/dust processing mechanism for stellar and sub-stellar objects. 2MASSW J1139511-315921 does not show any significant excess in any of the IRAC bands, but a small one at 24 micron, which is not significant enough to suggest the presence of warm dust around this star. It shows signs of dust cleansing in the inner several AU, similar to most of the other TWA members.

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