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J/A+A/294/135 Rapid variations of Eta Cen (Stefl+, 1995)
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Simultaneous photometric and spectroscopic monitoring of rapid variations
of the Be star Eta Centauri
Stefl S., Baade D., Harmanec P., Balona L.A.
<Astron. Astrophys. 294, 135 (1995)>
=1995A&A...294..135S (SIMBAD/NED Reference)
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ADC_Keywords: Stars, variable; Stars, Be; Spectroscopy; Photometry, uvby, beta
Keywords: stars: Be - stars: activity - stars: individual: Eta Cen
Abstract:
Results of the simultaneous monitoring of line-profile and light and
colour variations of the bright southern Be star {eta}Cen in May-June 1992
are reported. The new data were analyzed along with numerous earlier b and
uvby observations of the star, secured between 1987 and 1991. The
brightness of {eta}Cen varies on three distinct time scales but only rapid
variations on a time scale of hours to days are analyzed here. They can be
described as a superposition of a periodic component with period
0.6424241d, which is secularly stable over the whole six-year interval
covered by our data, and systematic but obviously aperiodic cycle-to-cycle
disturbances. The 0.6424-d light curve is slightly non-sinusoidal (light
minima occur 0.64^P^ after light maxima) and has an average peak-to-peak
amplitude of 0.05mag in y, b and v and about 0.10mag in u. The u-b and 1
indices also vary with the same period, with full amplitudes of 0.04mag
and 0.03mag, respectively, while the variations of b-y and .1mag - if
present - are within 0.01mag only. During light maximum, the star is
bluest in u-b. The radial velocity of Si III 455.26nm as measured in the
outer wings of the profile exhibits a nearly sinusoidal variation with the
0.6424-d period and definitively excludes the triple-wave photometric
period of 1.927d considered earlier. For variations of other line-profile
parameters of the Si III 455.26 nm line, the most significant periods
differ by up to +/-5% from the 0.6424-d period. More extended spectroscopic
material will be needed to confirm our preliminary conclusion that this
disparity is of stochastic nature only and that the entire line-profile
variability may be reconciled with the photometric period. The exactly
simultaneous monitoring shows that radial velocity, first moment,
equivalent width, and line depth of the Si III 455.26nm line increase when
the star is getting brighter and bluer. Very pronounced higher-order
line-profile variations of the Si III line were also detected. They have
the character of apparent absorption or emission bumps, which move across
the line profile from blue to red. Most of them disappear close to the
line center. The analysis of their radial velocities leads to a
super-period, which is close to the photometric one. Occurrence and
strength of the bumps also seem to follow the same period. The light,
colour, radial-velocity and equivalent-width variations can only be due to
the low-order line profile variations or duplicity. The observed
radial-velocity amplitude seems to be larger than expected for the
rotational modulation and nonradial pulsation models. The equivalent-width
variation cannot be understood unless a phase-dependent microturbulent
velocity is assumed in both models. Available data cannot also exclude a
model of a contact binary with 0.6-day orbital period.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1 79 86 Quantitative parameters measured in the
Si III 455.26 nm line profiles of Eta Cen
table3 38 111 Photometric observations of Eta Cen obtained at
the La Silla observatory in May-June, 1992
table4 38 82 Photometric observations of Eta Cen obtained at
the SAAO in May, 1992
tables.tex 105 322 LaTeX version of the tables
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Byte-by-byte Description of file: table1
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Bytes Format Units Label Explanations
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1- 12 F12.4 d HJD Heliocentric Julian day
14- 18 F5.1 km/s RV Stellar radial velocity
20- 24 F5.1 km/s <v> First line moment (in the heliocentric
wavelength scale)
27- 31 F5.1 km/s <v>c First line moment (in the heliocentric
wavelength scale corrected for the radial
velocity RV
33- 37 F5.1 km/s FWHM Full width at half maximum
39- 43 F5.1 --- LD Difference of central depth of the line with
respect to the mean profile
(in units of 10^-3^ x continuum)
45- 49 F5.3 0.01nm EW Equivalent width
51- 55 F5.3 mag ymag []? Stroemgren y magnitude
57- 61 F5.3 mag bmag []? Stroemgren b magnitude
63- 67 F5.3 mag vmag []? Stroemgren v magnitude
69- 73 F5.3 mag umag []? Stroemgren u magnitude
75- 79 F5.3 mag c1 []? Stroemgren c1 colour index
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Byte-by-byte Description of file: table3 table4
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Bytes Format Units Label Explanations
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1- 12 F12.4 d HJD Heliocentric Julian day
14- 18 F5.3 mag ymag Stroemgren y magnitude
20- 24 F5.3 mag bmag Stroemgren b magnitude
27- 31 F5.3 mag vmag Stroemgren v magnitude
33- 37 F5.3 mag umag Stroemgren u magnitude
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(End) Patricia Bauer [CDS] 31-Aug-1994