AB Doradus C: age,spectral type,orbit, and comparison to evolutionary models     

E. L. Nielsen  L. M. Close  J. C. Guirado  B. A. Biller  R. Lenzen  W. Brandner  M. Hartung  C. Lidman 《Astronomische Nachrichten》2005,326(10):1033-1039

  相似文献   

A study of the young open cluster Collinder 359     

N. Lodieu 《Astronomische Nachrichten》2005,326(10):1001-1006

We present the first deep, optical, wide‐field imaging survey of the young open cluster Collinder 359, complemented by near‐infrared follow‐up observations. This study is part of a large programme aimed at examining the dependence of the mass function on environment and time. We have surveyed 1.6 square degree in the cluster in the I and z filters with the CFH12K camera on the Canada‐France‐Hawaii 3.6m telescope down to completeness and detection limits in both filters of 22.0m and 24.0m, respectively. Based on their location in the optical (I‐z ,I ) colour‐magnitude diagram, we have extracted new cluster member candidates in Collinder 359 spanning 1.3‐0.04 M_⊙, assuming an age of 100 Myr and a distance of 450 pc for the cluster.We have used the 2MASS database as well as our own near‐infrared photometry to confirm the membership of the optically‐selected cluster candidates. Additionally, we have obtained optical spectroscopy and employed chromospheric activity as a further criterion to assess the membership of candidates. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

New stellar and substellar candidate members of the Coma Berenices open star cluster     

S. L. Casewell  R. F. Jameson  P. D. Dobbie 《Astronomische Nachrichten》2005,326(10):991-995

We present the results of a survey of the open star cluster Melotte 111 in Coma Berenices, undertaken using the USNO‐B1.0 and 2MASS Point Source catalogues. On the basis of their astrometric and photometric properties, we have identified 60 new candidate members with masses in the range 1.007 < M < 0.269 M_⊙. We estimate a membership probability for each by extracting control clusters from the proper motion vector diagram. All 60 are found to have greater than 60 per cent probability of being cluster members, which if they are confirmed as members, more than doubles the number of known cluster members. We also have I and Z photometry for 100 low mass candidate members of the cluster, 13 of which we suggest may be brown dwarfs. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

A coronagraphic search for brown dwarfs and planets around nearby stars     

T. Nakajima  J.‐I. Morino  T. Tsuji  H. Suto  M. Ishii  M. Tamura  M. Fukagawa  K. Murakawa  S. Miyama  H. Takami  N. Takato  S. Oya  S. Hayashi  T. Kudo  Y. Itoh  Y. Oasa  B. R. Oppenheimer 《Astronomische Nachrichten》2005,326(10):952-957

  相似文献   

Ultra‐cool dwarf variability     

B. Goldman 《Astronomische Nachrichten》2005,326(10):1059-1064

Ultra‐cool dwarf variability studies have matured into a multi‐wavelength, multi‐method probe of ultra‐cool atmospheres. They have the unique potential to address the question of heterogeneity on the ultra‐cool dwarf surface. The constraints on the models that we can gain though time‐sensitive observations are however hampered by the weak signal detected so far, and the limitations of current atmospheric models, otherwise quite successful, to predict dynamical, or even static 2‐D atmosphere characteristics. Here I review the situation of the ultra‐cool dwarf variability studies: possible sources of variability; methods, their limitations and their results; tentative interpretation and prospects. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

The lower mass function of young open clusters: clues to (sub)stellar formation     

E. Moraux  J. Bouvier  C. Clarke 《Astronomische Nachrichten》2005,326(10):985-990

We report the present day mass functions (PDMFs) of 4 young open clusters over a mass range from 30 Jupiter masses to 3M_ . Three of these clusters have been chosen to have a similar age of ∼100 Myr. Their PDMFs are remarkably similar and are comparable to the field mass function. This suggests little impact of initial conditions (stellar density, metallicity) on the mass distribution and raises some issues concerning the currently debated star and brown dwarf formation theories. The fourth cluster is older (600 Myr) which allow us to investigate the effect of the cluster dynamical evolution on the shape of the mass function. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Lithium depletion in the brown dwarf binary GJ 569Bab     

M. R. Zapatero Osorio  E. L. Martín  B. F. Lane  Ya. Pavlenko  H. Bouy  I. Baraffe  G. Basri 《Astronomische Nachrichten》2005,326(10):848-851

GJ 569Bab is the first brown dwarf binary for which the mass of each component has been derived by solving the astrometric and spectroscopic orbit of the pair, i.e., independently of any theoretical assumption. This allows us to test the predictions of the various evolutionary models available in the literature. Particularly interesting are the predictions of lithium depletion for the mass (0.08–0.05M_⊙) and likely age (300–800 Myr) of the substellar components. High‐resolution optical spectra of GJ 569B (the pair is not resolved) obtained with HIRES at the Keck telescope show that there has been significant lithium depletion in both components. We will compare these results to state‐of‐the‐art theoretical calculations. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

New brown dwarf companions to dM(e) stars     

A. Seifahrt  M. Mugrauer  M. Wiese  R. Neuhuser  E. W. Guenther 《Astronomische Nachrichten》2005,326(10):974-976

We present new astrometric and spectroscopic data to confirm two new M/L dwarf systems, G124‐62 and LHS5166, and discuss the nature of a third system (LP261‐75). Age and thus mass determinations of the L dwarf companions are discussed based on various activity‐age relationships of the M dwarf primaries. This publication will update the list of widely separated substellar companions to nearby stars. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Two nearby M dwarf binaries from the Two Micron All Sky Survey     

John E. Gizis  David G. Monet  I. Neill Reid  J. Davy Kirkpatrick  Adam J. Burgasser 《Monthly notices of the Royal Astronomical Society》2000,311(2):385-388

We report the discovery of two binary M dwarf systems in the immediate solar neighbourhood using the Two Micron All Sky Survey (2MASS). The first is an M6.5 companion to the nearby G star HD 86728 (Gl 376). The known properties of HD 86728 indicate that the M dwarf (Gl 376B) is old, metal-rich and only 14.9 parsec away. The M dwarf is highly active, with both H α and X-ray emission. Thus, Gl 376B offers the opportunity to study an old, bright, active M dwarf with known metallicity, age and luminosity. We show that it is probable that Gl 376B is itself an unresolved pair. The other system consists of an M6.5 and an M8 dwarf with 14.5 arcsec separation. We estimate a distance of ∼16 parsec for this very low-mass pair. Stronger activity is observed in the M6.5 dwarf, supporting evidence that chromospheric activity is weakening near the hydrogen-burning limit.  相似文献   

A population of very young brown dwarfs and free-floating planets in Orion     

P. W. Lucas  P. F. Roche 《Monthly notices of the Royal Astronomical Society》2000,314(4):858-864

We describe the results of a very deep imaging survey of the Trapezium cluster in the IJH bands, using the UKIRT high-resolution camera UFTI. Approximately 32 per cent of the 515 point sources detected are brown dwarf candidates, including several free-floating objects with masses below the deuterium-burning (planetary) threshold at 0.013 M_⊙, which are detectable because of their extreme youth. We have confidence that almost all the sources detected are cluster members, since foreground contamination is minimal in the 33-arcmin² area surveyed, and the dense backdrop of OMC-1 obscures all background stars at these wavelengths. Extinction is calculated from the ( J − H ) colours, permitting accurate luminosity estimates, and temperatures are derived from the dereddened ( I − J ) colours. There is some evidence for a cut-off in the luminosity function below the level corresponding to several Jupiter masses, which may represent the bottom end of the initial mass function . Since star formation is complete in the Trapezium, this limit could have wide significance, if confirmed. However, it could well be an effect of the dispersal of the molecular cloud by the central O-type stars, a process for which the time-scale will vary between star formation regions.  相似文献