uvby photometry of the mCP stars HD 35298, 19 Lyrae, HD 192678, and HR 8216
Astron. Astrophys. Suppl. Ser.
uvby photometry of the mCP stars HD 35298, 19 Lyrae, HD 192678, and HR 8216?
S.J. Adelman 0
R.H. Rice 0
0 Department of Physics , The Citadel, 171 Moultrie Street, Charleston SC 29409 , U.S.A
Di erential Str¨omgren uvby observations from the Four College Automated Photoelectric Telescope are presented for the mCP stars HD 35298, 19 Lyr, HD 192678, and HR 8216. The period for HD 35298 of 1.85457 days is a revision of North's value while that for 19 Lyr of 7.0980 days is alias of that found by Winzer. HD 192678 is found to be a small amplitude photometric variable with the 6.4186 day period proposed by Leroy from polarization measurements. For HR 8216, observations taken between 1995 and 1998 con rm that the star has remained constant at least since 1990.
stars; individual; HD 35298; 19 Lyr; HD 192678; HR 8216 | stars; chemically peculiar
-
1. Introduction
This paper presents di erential Stro¨mgren uvby
observations of four magnetic Chemically Peculiar (mCP) stars
HD 35298, 19 Lyr, HD 192678, and HR 8216. Studies
of the mCP stars using data from the Four College
Automated Photoelectric Telescope (FCAPT) have both
improved our knowledge of their rotational periods and
better de ned the shapes of their light curves
(see,
e.g. Adelman & Brunhouse 1998 and references therein)
.
These results can be used to better relate observations
taken at di erent times and to study the period
distribution of mCP stars. Their variable light curves provide
information concerning the uniformity of the surface
abundances. Hydrodynamical processes including di usion and
gravitational settling in radiative atmospheres with strong
Send o print requests to: S.J. Adelman
? Tables 2, 3, 4 and 6 are only available in
electronic form at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.ustrasbg.fr/Abstract.html
v
c
ch
v
c
ch
v
c
ch
v
c
ch
magnetic elds most likely produce the anomalous
photospheric abundances of the mCP stars. Their abundance
distributions are patchy and a ect the emergent flux
distribution. As their magnetic and rotational axes are not
aligned, a distant observer will see photometric, magnetic,
and spectrum variability as the stars rotate (Michaud &
Pro tt 1993 and references therein).
The FCAPT operated on Mt. Hopkins, AZ between
September 1990 and July 1996 and since then on nearby
Washington Camp, AZ. After the dark count, the
telescope measures the sky{ch{c{v{c{v{c{v{c{ch{sky in each
lter where sky is a reading of the sky, ch that of the
check star, c that of the comparison star, and v that of
the variable star. Table 1 contains group (a variable along
with two supposedly non-variable stars, the comparison
and check, against which the brightness of the variable is
compared) information
(Ho eit 1982; Ho eit et al. 1993)
.
Corrections were not made for neutral density lter
differences among the stars of each group. The comparison
and check stars were chosen from supposedly non-variable
stars in the vicinity of the variable on the sky that had
0.79
0.80
0.81
0.82
-)c 0.83
v
(u 0.84
0.85
0.86
0.87
0.88
1.15
1.16
1.17
1.19
1.20
1.21
-)c 1.18
v
(
v
0.92
0.93
0.94
similar V magnitudes and B − V colors.
Adelman (1998)
checked their stability using Hipparcos photometry (ESA
1997). We used the Scargle periodogram
(Scargle 1982;
Horne & Baliunas 1986)
and the clean algorithm (Roberts
et al. 1987) in nding periods.
North (1984)
derived a period of 1.85336 0.00116 days
for the Helium weak star HD 35298 (= V1156 Ori = BD
+1 996), a member of the Ori OB1 association. This star
exhibits a double-wave light curve with all colors varying
in phase. The amplitude is as large as 0.07 mag in the
Geneva photometric system.
Borra (1981)
measured the
magnetic eld with essentially this period.
We have 100 di erential uvby observations, 56 from the
1995-96 and 44 from the 1996-97 observing seasons. A
periodogram analysis resulted in a period close to one-half
of North's period. But when we plotted the observations,
there were two values for each phase indicating that the
period was twice that. To have North's V values properly
rezeroed best overlay our y values we had to adjust his
period slightly. The zero epoch is better taken for maximum
light in u. Thus
HJD (umax) = 2444973.886 0.006 + (1.85457 0.00001)
E.
0.79
)
-cv 0.80
(
u
Figure 1 shows our FCAPT photometry (+ signs) and
North's V values (solid diamonds) on our y magnitude
scale plotted with our ephemeris. The amplitudes are
0.08 mag for u, 0.05 mag for v and b, and 0.037 mag for y.
The light curves are in phase with two minima and a
primary and secondary maxima. Some light curves especially
u and v show additional structure as the star begins the
primary minimum. The relative depths of the two minima
are more discrepant for u than for v, b, and y. We are
probably seeing most of the photosphere including both
polar regions during the cycle. North's U light curve has
an amplitude similar to ours, but some of the details near
phase 0.5 are not seen probably due to a lesser number of
values. Likewise his B light curve is similar to our b.
period. Winzer's zero epoch appeared to be satisfactory.
Thus
HJD (light maximum) = 2441449.99 0.01 + (7.0980
0.0001) E.
Figure 2 shows the FCAPT values as + signs and Winzer's
and Burke & Barr's V data rezeroed to our y scale as solid
diamonds and circles, respectively. The variations in u, v,
b, and y are in phase. The curves suggest possible
incipient structure. The amplitudes are 0.045 mag, 0.025 mag,
0.030 mag, and 0.025 mag for u, v, b, and y, respectively.
There is a sharp primary maximum with a weaker
secondary maximum whose prominence decreases with
increasing wavelength. Two approximately equal strength
minima are symmetrically located with respect to the
secondary maximum.
3. 19 Lyr
4. HD 192678
Winzer (1974)
discovered the light variations of 19 Lyr
(= HR 7283 = HD 179527 = V471 Lyrae) of 0.04 mag in
Leroy (1995)
found the time variations of the Stokes
paU with smaller B and V amplitudes. His tentative period rameters of HD 192678 (= V1372 Cyg = BD +53 2368)
of 1.1608 days was based upon very limited data. Burke could be described as
& Barr (1981) obtained additional U BV photometry and JD (magnetic maximum) = 2444890.17 + 6.4186 E.
con rmed Winzer's period.
Mathys & Lanz (1992)
demonstrated that the
determi
We obtained di erential uvby observations of 19 Lyr: nation of its period by
Stepien (1968)
of order 18 days
18 in the 1995-96 observing season, 40 in 1996-97, and was incorrect.
Wade et al. (1996)
presented a magnetic
66 in 1997-98. The periodogram contains several possible model consisting of an oblique rotating dipole with
modiperiods of which one near 7.10 days, which is an alias of ed eld line inclinations. The dipole has = 173 and =
Winzer's period, is the most likely and consistent with the 120 . Their ephemeris uses the same period, but a slightly
v sin i value of
Abt & Morrell (1995)
, 20 km s−1. Using di erent zero point. Essentially the surface magnetic eld
the V data of Winzer and of Burke & Barr, we re ned the is strongest near phase 0.00 and weakest near phase 0.50.
We obtained 77 di erential uvby observations of 1991-94 vs. 1996-97 show small o sets in u, v, b, and y,
reHD 192678, 45 during the 1995-96 and 32 during the 1996- spectively of 0.004, 0.000, 0.007, and 0.004 mag. Although
97 observing season (Table 4). As our analyses revealed a these di erences are suggestive of possible long term
variperiod close to that of Leroy's, we adopted his ephemeris ability, observations in additional years are needed for
and found that it was adequate to describe our obser- con rmation.
vations. To improve the period requires photometry for Acknowledgements. This work was supported in part by NSF
this star over a longer period of time. Figure 3 shows the grants AST-9115114 and 9528506 and in part by grants from
uvby photometry as a function of phase. HD 192678 is The Citadel Development Foundation. We appreciate the
conbrightest in u when the surface magnetic eld strength is tinuing e orts of Louis J. Boyd, Robert J., Dukes Jr., and
weakest. The amplitude in u is 0.017 mag and in b is about George P. McCook to keep the FCAPT operating properly.
0.010 mag while this star is essentially constant in v and
y. The light curves for u and b are shifted by about 0.15
in phase with u reaching its maximum before b. This be- References
havior is consistent with the need for a complex magnetic
model such as that of
Wade et al. (1996)
.
Adelman et al. (1994)
presented di erential uvby
photometry of the mCP ultra-sharp lined star HR 8216
(= HD 204411) obtained between 1990 and 1994. The
data for the three observing seasons with many
observations showed that this star was constant and values
in the literature indicate that this has been the case for
many additional years. Its constancy has been con rmed
also by Hipparcos photometry
(ESA 1997)
. Any evidence
of variability can lead to an estimate of its rotational
period. Table 5 summarizes the FCAPT photometry. For
three of the eight observing seasons, there are only a few
observations and di erences in ch − c values between
these and other years are probably due to their poorer
statistics. The 1996-97 and 1997-98 seasons have su cient
observations to clearly show that HR 8216 was constant
(Table 6). The telescope being moved just before the start
of observing in the fall of 1996 and the order 0.01 mag
changes in ch − c values seen between the last two and
rst 6 observing seasons might simply reflect small errors
in the extinction. The o set seen in the ch − c values of b
is currently unexplained. Comparison of the v−c values for
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