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J/A+A/290/609       Be stars near-IR excess                   (Dougherty+, 1994)
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Near-IR excess of Be stars
      Dougherty S.M., Waters L.B.F.M., Burki G., Cote J., Cramer N.,
      van Kerkwijk M.H., Taylor A.R.
     <Astron. Astrophys. 290, 609 (1994)>
     =1994A&A...290..609D      (SIMBAD/NED Reference)
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ADC_Keywords: Stars, Be; Reddening
Keywords: stars: emission-line, Be - infrared

Abstract:
    The near-IR excess emission of 144 Be stars is derived from visual and 
    near-IR observations. The quasi-simultaneous nature of the observations 
    provide colour excesses that are independent of temporal variations. 
    Colour-colour diagrams are used to identify stars with excess colours 
    markedly different from the bulk of the sample stars. The near-IR emission
    of four stars that have markedly different colours is attributed to the 
    presence of a binary companion or thermal dust emission. The percentage of
    stars with a significant excess increases with wavelength. The excess 
    emission increases with wavelength and the largest excesses occur in stars
    of earlier spectral type. The near-IR excess colours are examined and 
    compared to theoretical excess colours calculated from a simple 
    bremsstrahlung emitting disc model with a radial density distribution of 
    the form {rho}{prop.to}r^-{beta}^. The effect of model parameters on the 
    excess colours is discussed. The observed excesses for the bulk of the 
    stars are well fit by circumstellar discs with radii greater than 
    ~10R_*_ and with a density index {beta}, in the range 2.0-5.0. This is very
    similar to the range of values previously determined by Waters et al. from
    IRAS far-IR observations. A small number of stars cannot be reconciled with
    discs with a constant density index out to 10R_*_. It is argued that the 
    circumstellar plasma around these stars has a change in structure at 
    ~2-10R_*_. The possibilities of disc truncation or a change in the density
    index as the cause of the structure change are discussed. 

File Summary:
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 FileName    Lrecl    Records    Explanations
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ReadMe          80          .    This file
table1          83        144    Excess colours of 144 Be stars
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Byte-by-byte Description of file: table1
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   Bytes Format  Units   Label    Explanations
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   2-  5  I4     ---     HR       []? HR number
   7- 12  I6     ---     HD       HD number
  15- 28  A14    ---     Source   Source name
  30- 43  A14    ---     Sp       Spectral type (from the Bright Star Catalogue)
  45- 49  F5.2   mag   E[B-V]1    Excess [B-V] colour
                                   (calculated from spectral type)
  51- 54  F4.2   mag   E[B-V]2    []? Excess [B-V] colour from the 2175 angstrom
                                   interstellar absorption feature (Beeckmans
                                   and Hubert-Delplace (1980)) and converted
                                   using E(B-V) = 0.84E[B-V] (Cramer, 1984)
  56- 60  F5.2   mag   E[V-J]     Excess [V-J] colour
  62- 66  F5.2   mag   E[V-H]     []? Excess [V-H] colour
  68- 72  F5.2   mag   E[V-K]     []? Excess [V-K] colour
  74- 78  F5.2   mag   E[V-L]     []? excess [V-L] colour
      80  A1     ---     Ref      Comment for the source of the observations:
                                   a) Dougherty et al., 1991
                                   b) Dachs et al., 1988
                                   c) Burki et al., in preparation
                                   Visual observations from Burki et al.
                                   (in preparation) except when n_Ref. = 5
      82  A1     ---   n_Ref      If n_Ref = 5, the visual observations are
                                    taken from the catalogue of Rufener (1988)
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References:
  Beeckmans, F., Hubert-Delplace, A.M. 1980, A&A  86, 72
  Cramer, N. 1984, A&A 132, 283
  Dachs, J., Engels, D., Kiehling, R. 1988, A&A 194, 167
  Dougherty, S.M., Taylor, A.R., Clark, T.A. 1991a, AJ 102, 1753
  Rufener, F. 1988, Catalogue of stars measured in the Geneva Observatory
   photometric system, 4th edn., Observatoire de Geneve
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(End)                                         Patricia Bauer [CDS]   30-May-1994