J/A+A/304/406 Photometry and radial velocities of 16 Lac (Chapellier+, 1995)
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 1995A&A...304..406C (SIMBAD/NED BibCode)
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 β 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 P1
(016917d) is radial, P2 (017079d) is a nonradial mode of degree l=2.
For P3 (018171d) the results are more dubious, but P3 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 P3 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 P3 amplitude
stayed in constant average over 80 years. The present observations
confirm the decrease of P1 and P2 amplitudes since 1950 but an
analysis of older radial velocity data shows that the amplitude of the
P1 mode went through a maximum around the middle of the century
before the observed decrease of the last thirty years.
Objects concerned:
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RA (2000) DE Name(s)
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22 56 23.5 +41 36 14 16 Lac = HR 8725 = HD 216916
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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 1976A&AS...25..129S
(End) Simona Mei [CDS] 07-Jun-1995