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Dwarf Candidates (dwarf + candidate)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Discovery of new nearby L and late-M dwarfs at low Galactic latitude from the DENIS data base

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008
N. Phan-Bao
ABSTRACT We report on new nearby L and late-M dwarfs (dphot, 30 pc) discovered in our search for nearby ultracool dwarfs (I,J, 3.0, later than M8.0) at low Galactic latitude (|b| < 15°) over 4800 deg2 in the Deep Near Infrared Survey of the Southern Sky (DENIS) data base. We used late-M (, M8.0), L and T dwarfs with accurate trigonometric parallaxes to calibrate the MJ versus I,J colour,luminosity relation. The resulting photometric distances have standard errors of ,15 per cent, which we used to select candidates dphot, 30 pc. We measured proper motions from multi-epoch images found in the public archives ALADIN, DSS, 2MASS and DENIS, with at least three distinct epochs and time baselines of 10,21 yr. We then used a maximum reduced proper motion cut-off to select 28 candidates as ultracool dwarfs (M8.0,L8.0) and to reject one as a distant red star. No T dwarf candidates were found in this search, which required an object to be detected in all three DENIS bands. Our low-resolution optical spectra confirmed that 26 were indeed ultracool dwarfs, with spectral types from M8.0 to L5.5. Two contaminants and one rejected by the maximum reduced proper motion cut-off were all reddened F,K main sequence stars. 20 of these 26 ultracool dwarfs are new nearby ultracool dwarf members, three L dwarfs within 15 pc with one L3.5 at only ,10 pc. We determine a stellar density of dwarfs pc,3 mag,1 over 11.1 ,MJ, 13.1 based on this sample of M8,L3.5 ultracool dwarfs. Our ultracool dwarf density value is in good agreement with the measurement by Cruz et al. of the ultracool dwarf density at high Galactic latitude. [source]

The lithium depletion boundary and the age of NGC 2547

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2003
J. M. Oliveira
ABSTRACT We present the results of a photometric and spectroscopic survey of cool M dwarf candidates in the young open cluster NGC 2547. Using the 2dF fibre spectrograph, we have searched for the luminosity at which lithium remains unburned in an attempt to constrain the cluster age. The lack of a population of individual lithium-rich objects towards the faint end of our sample places a very strong lower limit to the cluster age of 35 Myr. However, the detection of lithium in the averaged spectra of our faintest targets suggests that the lithium depletion boundary lies at 9.5 < MI < 10.0 and that the cluster age is <54 Myr. The age of NGC 2547 judged from fitting isochrones to low-mass pre-main-sequence stars in colour,magnitude diagrams is 20,35 Myr using the same evolutionary models. The sense and size of the discrepancy in age determined by these two techniques is similar to that found in another young cluster, IC 2391, and in the low-mass pre-main-sequence binary system, GJ 871.1AB. We suggest that the inclusion of rotation or dynamo-generated magnetic fields in the evolutionary models could reconcile the two age determinations, but only at the expense of increasing the cluster ages beyond that currently indicated by the lithium depletion. Alternatively, some mechanism is required that increases the rate of lithium depletion in young, very low-mass fully convective stars. [source]

New brown dwarf candidates in the Pleiades,,

ASTRONOMISCHE NACHRICHTEN, Issue 5 2009
T. Eisenbeiss
Abstract We have performed deep, wide-field imaging on a ,0.4 deg2 field in the Pleiades (Melotte 22). The selected field was not yet target of a deep search for low mass stars and brown dwarfs. Our limiting magnitudes are R , 22 mag and I , 20 mag, sufficient to detect brown dwarf candidates down to 40 MJ. We found 197 objects, whose location in the (I, R , I) color magnitude diagram is consistent with the age and the distance of the Pleiades. Using CTK R and I as well as JHK photometry from our data and the 2MASS survey we were able to identify 7 new brown dwarf candidates. We present our data reduction technique, which enables us to resample, calibrate, and co-add many images by just two steps. We estimate the interstellar extinction and the spectral type from our optical and the NIR data using a two-dimensional ,2 fitting (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Brown dwarf candidates in the Serpens cloud core,

ASTRONOMISCHE NACHRICHTEN, Issue 1 2006
C. Eiroa
Abstract The Serpens cloud core is populated by a young, low-mass stellar cluster with members in many different evolutionary stages. We revisit the near-IR properties of the cluster in this contribution. A total of 188 near-IR sources are identified, including new members suggested in this work. Near-IR colour-magnitude and colour-colour diagrams allow us to suggest 42 objects among the cluster members as brown dwarf candidates. A considerable fraction of them present near-IR excesses which indicates that many of these very low mass objects are still surrounded by prominent dust accretion disks. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]