COMMISSION 27 OF THE I. A. U.
INFORMATION BULLETIN ON VARIABLE STARS
Number 1764
Konkoly Observatory
Budapest
1980 March 31
6 IOTA TRIANGULI: A NEW VARIABLE STAR
The bright star 6 iota Trianguli is the visual binary ADS 1697. The brighter
component (V=5.5m) is an SB2 of spectral type G5III and orbital period
14.732d. The fainter component (V=6.7m), about 4 arcseconds away, is also
an SB2, of spectral type F5V and orbital period 2.2365d. Because the former
is a known RS CVn binary (Young and Koniges 1977), we obtained photoelectric
photometry to see if it showed the ~ 0.1m distortion wave characteristic of so
many binaries of this type. We did find 6 iota Tri varying by about 0.05m but
probably due to the combined effect of ellipticity and differential reflection.
We observed 6 iota Tri differentially with respect to the comparison star HD
14373 on a total of 34 nights from 2,443,741.8 to 2,444,256.7 at four different
observatories. Needless to say, we all included both components of ADS 1697 in
our photometry. The individual differential observations, generally three on
each night, were corrected for differential atmospheric extinction with mean
extinction coefficients and transformed to V of the UBV system with known
transformation coefficients and a mean color difference of Delta(B-V)=-0.42m.
Here and elsewhere Delta is in the sense variable minus comparison.
The Delta V magnitudes plotted versus phase, computed with the
spectroscopically determined orbital period 14.732 of Harper (1921), showed two
maxima, of roughly equal height, and two minima, of discernably unequal depth.
This suggested we might be seeing a superposition of the ellipticity effect and
either the differential reflection effect or a distortion wave. Although the
value 14.732d was sufficiently precise to use for the 1.4-year span of our
observations, it was not sufficiently precise to carry the initial epoch of
Harper forward from 1919 to the present. Therefore we used Fourier analysis to
determine the phases of the two conjunctions, as indicated by the coefficients
of the terms in 2Theta. At this point we were not certain whether the terms in
Theta were produced by the differential reflection effect or by a distortion
wave. We are persuaded to believe reflection was responsible, because the
terms in Theta place their minimum very near one of the two conjunctions, not
at a random phase somewhere between. Assuming reflection is the agent, we
selected the conjunction at the deeper minimum as the conjunction with the
hotter star behind. The time of this conjunction (we chose the one just before
our observations began in 1978) is 2,443,729.8+-0.3d.
Then we redid the Fourier analysis, expressing the light as
1 = A_0+A_1cosTheta+A_2cos2Theta+B_1sinTheta,
where unit light corresponds to delta V=-1.550m and phase angle is computed
with our new ephemeris for conjunction
JD = 2,443,729.8+14.732d n.
The resulting coefficients are A_0=1.001+-0.001, A_1=-0.016+-0.002,
A_2=-0.014+-0.002, and B_1=+0.007+-0.002. If the A_1 and B_1 coefficients were
attributed to a distortion wave, then its full amplitude would be Delta
V=0.037m+-0.004m and its minimum would occur at 0.94p+-0.02p. We are,
however, believing that this minimum so close to conjunction (which itself is
uncertain by +-0.02p) probably results from differential reflection.
Work on 6 iota Tri is not finished. The light curve should be redetermined to
see if the minimum given by terms in Theta remains near conjunction
(confirming reflection effect) or migrates to a different phase (indicating
distortion wave). A later determination of a time of conjunction, either
photometrically as we have done or spectroscopically as Harper did, is needed
to refine the orbital period. Because residuals from our Fourier fit, when
plotted versus Julian date, gave a hint of systematic secular variations in
light on a time scale of ~100 days, future photometry should include secure
observations of a check star, something we confess not having done.
D.S.H. is happy to acknowledge that part of this work was supported by
N.A.S.A. research grant NSG-7543. G.W.H. was a Guest Investigator at Kitt
Peak National Observatory, which is operated by the Association of Universities
for Research in Astronomy, under contract with the National Science Foundation.
The others wish to thank the A.A.V.S.O. for help with instrumentation provided
through the Photoelectric Committee, currently chaired by Howard J. Landis.
DOUGLAS S. HALL
GREGORY W. HENRY
Dyer Observatory
Vanderbilt University
Nashville, Tennessee 37235
HOWARD LOUTH
2199 Hathaway Road
Sedro Woolley, Washington 98284
LARRY P. LOVELL
CHRISTOPHER STEPHAN
Hickox Observatory
18410 Munn Road
Chagrin Falls, Ohio 44022
References:
Harper, W. E. 1921, P.D.A.O. 2, 129. [BIBCODE 1921PDAO....2..129H ]
Young, A. and Koniges, A. 1977, Ap.J. 211, 836. [BIBCODE 1977ApJ...211..836Y ]