A. C. Katsiyannis

Publications (2)0 Total impact

• Source

  Available from: Federico Marocco

  Article: Discovery of the benchmark metal poor T8 dwarf BD+01 2920B

  D. J. Pinfield, B. Burningham, N. Lodieu, S. K. Leggett, C. G. Tinney, L. van Spaandonk, F. Marocco, R. Smart, J. Gomes, L. Smith, [......], A. C. Katsiyannis, S. Catalan, C. Cardoso, J. R. A. Clarke, S. Folkes, M. C. Galvez-Ortiz, D. Homeier, J. S. Jenkins, H. R. A. Jones, Z. H. Zhang
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  ABSTRACT: We have searched the WISE first data release for widely separated (<10,000AU) late T dwarf companions to Hipparcos and Gliese stars. We have discovered a new binary system containing a K-band suppressed T8p dwarf WISEP J1423+0116 and the mildly metal poor ([Fe/H]=-0.38+-0.06) primary BD+01 2920 (Hip 70319), a G1 dwarf at a distance of 17.2pc. This new benchmark has Teff=680+-55K and a mass of 20-50 Mjup. Its spectral properties are well modelled except for known discrepancies in the Y and K bands. Based on the well determined metallicity of its companion, the properties of BD+01 2920B imply that the currently known T dwarfs are dominated by young low-mass objects. We also present an accurate proper motion for the T8.5 dwarf WISEP J075003.84+272544.8.
  01/2012;
• Source

  Available from: arxiv.org

  Article: Brown dwarfs and low-mass stars in the Pleiades and Praesepe:- Membership and binarity

  D. J. Pinfield, P. D. Dobbie, R. F. Jameson, I. A. Steele, H. R. A. Jones, A. C. Katsiyannis
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  ABSTRACT: We present near infrared J-, H- and K-band photometry and optical spectroscopy of low-mass star and brown dwarf (BD) candidates in the Pleiades and Praesepe open clusters. We find that Pleiades stars with K=10.5--13 are rather redder than the NextGen isochrones. We also identify this effect amongst alphaPer sources from the literature, but find no evidence of it for field stars from the literature. It is possible that the I-K colour of youthful stars is affected by the presence of magnetic activity. In the 2-colour diagram we find no colour change across the "M dwarf gap" (which would be indicative of dust formation). For Teff=2800--3150K, the colours of Praesepe and Pleiades sources differ, which may result from gravity sensitive molecular opacities. Praesepe sources cooler than 2500K agree with the dusty models, but Pleiades sources agree with the NextGen models down to 2000K. It is possible that dust formation does not begin until lower Teffs in sources with lower surface gravities. We also identify unresolved binaries in both clusters, and estimate mass ratios (q) for Pleiades BDs. Most of these have q>0.7, however, 3/18 appear to have lower q values. We determine the binary fraction (BF) for numerous mass ranges in each cluster, and find that it is generally rising towards lower masses. We find a BD BF of 50(+11/-10)%. We also find some evidence suggesting that the BF-q distribution is flat for 0.5-0.35Mo, in contrast to solar type stars. Comment: (updated version) 22 pages, 11 figures, accepted for publication in MNRAS
  03/2003;