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J/A+A/304/406    Photometry and radial velocities of 16 Lac  (Chapellier+, 1995)
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Pulsation and binarity in Beta Cephei Stars. II. 16 Lac
    Chapellier E., Le Contel J.M., Le Contel D., Sareyan J.P., Valtier J.C.
   <Astron. Astrophys. 304, 406 (1995)>
   =1995A&A...304..406C      (SIMBAD/NED BibCode)
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ADC_Keywords: Stars, variable; Radial velocities; Photometry
Keywords: stars: variables: other - stars: pulsation -
          stars: binaries: close - stars: individual: 16 Lac

Description:
    Photometric and spectroscopic observations of the {beta} Cephei star
    16 Lacertae obtained in 1983 and 1984 are presented and analysed.
    Using all the published maxima we have computed ephemerides for each
    of the three pulsational modes. No period variation is detected from
    1950 to 1983. In order to identify the pulsational modes corresponding
    to the three main periods of 16 Lac we have applied different methods
    based on photometric and radial velocity variations. All give the same
    results: the mode corresponding to the largest amplitude P_1_
    (016917d) is radial, P_2_ (017079d) is a nonradial mode of degree l=2.
    For P_3_ (018171d) the results are more dubious, but P_3_ is probably
    a l=1 nonradial mode. We have also studied the interaction between
    pulsation and binarity in 16 Lac. We confirm the existence of a
    resonance phenomenon between the radial and nonradial modes: the
    ratios between the beat frequencies of the pulsational modes and the
    orbital frequency are close but significantly different from simple
    rational numbers. According to Kato (1974) that means that the
    nonradial modes might be excited or at least enhanced by tidal
    effects. They would have been selected among all the possible modes
    because their ability to be resonant with the radial mode.

    The photometric amplitude of P_3_ in both filters appears to be
    variable from night to night in correlation with the orbital phase but
    despite its rapid and irregular fluctuations, the P_3_ amplitude
    stayed in constant average over 80 years. The present observations
    confirm the decrease of P_1_ and P_2_ amplitudes since 1950 but an
    analysis of older radial velocity data shows that the amplitude of the
    P_1_ mode went through a maximum around the middle of the century
    before the observed decrease of the last thirty years.

Objects:
    ---------------------------------------------------
       RA   (2000)  DE     Name(s)
    ---------------------------------------------------
    22 56 23.5 +41 36 14   16 Lac = HR 8725 = HD 216916
    ---------------------------------------------------

File Summary:
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  FileName      Lrecl  Records   Explanations
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ReadMe             80        .   This file
photo              50     1200   Photometric data
velo               22       47   Radial velocity data
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Byte-by-byte Description of file: photo
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   Bytes Format  Units      Label    Explanations
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   5- 12  A8    "DD/MM/YY"  Date      Date
      15  I1     ---        Filter    [4,5] Filter (1)
  19- 31  F13.5  d          JD        Julian day
  43- 50  F8.5   mag        DMag      Magnitude difference between 16 Lac
                                      and 2 And
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Note (1): filter 4 (UV): Lambda= 3513 A, DeltaLambda= 94 A
          filter 5 (blue): Lambda= 4766 A, DeltaLambda= 112 A;
          Sareyan et al. 1976.
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Byte-by-byte Description of file: velo
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   Bytes Format  Units   Label    Explanations
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   1- 13  F13.5  d       JD       Julian day
  17- 22  F6.2   km/s    RV       Radial velocity of 16 Lac.
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References: 
  Sareyan J.P., Le Contel J.-M., Valtier J.C.    =1976A&AS...25..129S
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(End)                                             Simona Mei [CDS]   07-Jun-1995