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\IBVShead{4467}{14 April 1997}

\title{Sorting Out W Bootis and Its Comparison Stars}

\begintext

W Bootis (HR\,5490, HD\,129712, V $\sim$ 4.81, SpT M3 III) is a bright example
of a small-amplitude red variable.  Percy \& Desjardins (1996) recently
reported that W Boo had changed period in about 1990, from 25 days
to 50 days, and suggested that W Boo had switched pulsation mode.
Unfortunately, the check star (HD 130446) used in the differential photometry
appeared to be slightly variable.  A second check star
(HR 5524, HD 130603) was adopted, but it too appeared to be slightly
variable.  We therefore decided to observe all three stars in 1996,
relative to the original comparison star, and a new check star.
We report the results here.

The comparison star was HR\,5534 (HD\,130948, V = +5.85, B$-$V = +0.56, SpT G0-2 V)
and the new check star was HR\,5454 (HD\,128402, V = +6.41, B$-$V = +1.1, SpT K0).
Five observers (Beresky, Luedeke, Smith, Thompson, Wood) carried out the
measurements as part of the American Association of Variable Star
Observers (AAVSO) photoelectric photometry program (Landis et al. 1992).
The observations were made and reduced as described there, and in
Percy \& Desjardins (1996).

We have a total of 48 V observations of W Boo (and its comparison and
new check star), 23 observations of HD\,130446, and 25 observations of
HR\,5524.  The standard deviation of the (new check -- comparison) magnitudes
is $\sigma$ = 0.011, which is the expected error of the observations,
especially considering that they were made by five different observers.
These stars therefore appear to be constant.  The $\sigma$ of the
(HR\,5524 -- comparison) magnitudes is 0.010, which suggests that this star
is also constant. 

The $\sigma$ of the (HD\,130446 -- comparison)
magnitudes is 0.020, which suggests that this star may be slightly
variable.  It is also possible that the larger scatter is due to the
faintness (V = 7.6) of the star.
The power spectrum of the previous observations of this
star (Percy \& Desjardins 1996) showed a peak at 0.1277 cycle/day, but
this peak does not appear in the power spectrum of the present
observations, nor does it produce a reasonable phase diagram.
There are several peaks in the
power spectrum of the present observations, none of which is very
conspicuous.  The star is K0 III type, so the variability, if real,
could be due to star spots.  Hatzes \& Cochran (1996) have recently
reported short-term radial velocity variations in K giants, which
they attribute to pulsation.

The 1996 light curve of W Boo (Figure 1) is very interesting.  The
cycle count period is 24 days (very similar to the period of W Boo
before 1990), but it is strongly modulated, and there is some
evidence for long-term variations.  The light curve can be well represented
as the superposition of two periods - 25 and 33 days.  Periods of 25, 35
and 50 days were found by Percy \& Desjardins (1996), and interpreted
as adjacent radial modes.  The new 25- and 33-day periods were determined
independently of the previously-known periods.  The mode switching in W Boo is
rather similar to that recently reported in RR UMi by Lloyd \& West
(1996).  This star switched between periods of 34 and 61 days, with strong
modulation of the amplitude.
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Figure 1. The 1996 V light curve of W Boo, relative to the comparison
star HR\,5534.  The time axis is (JD - 2450000).
Note the modulation in the amplitude of the pulsation; the
light curve can be represented as the superposition of 25- and 33-day
periods
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\large

\vskip 2mm

{\it Acknowledgements.}  A. Desjardins and M. Marinova were participants in the
University of Toronto Mentorship Program, which enables outstanding
senior high school students to take part in research projects at the
university.  JRP acknowledges a research grant from NSERC Canada,
and thanks the AAVSO for the infrastructure within which this project
was carried out.

\vskip .5cm

\beginauthors
JOHN R. PERCY
ADRIEN DESJARDINS
MARGARITA MARINOVA
Department of Astronomy and
Erindale College
University of Toronto
Mississauga, Ontario
Canada  L5L 1C6
e-mail: jpercy@erin.utoronto.ca
\vskip 2mm
TED BERESKY
1833 S. Virginia Avenue,
Springfield MO 65807-7101, USA
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\authorsrightcol
KENNETH LUEDEKE
9624 Giddings Avenue NE
Albuquerque NM 87109, USA
\vskip 2mm
MICHAEL S. SMITH
6715 N. Table Mountain Rd.
Tucson AZ 85718, USA
\vskip 2mm
RAYMOND R. THOMPSON
7 Welton Street
Maple, Ontario
Canada  L6A 1R8
\vskip 2mm
JAMES E. WOOD
15101 David Court
Bakersfield CA 93312, USA
\endauthors
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\references

Hatzes, A.P. \& Cochran, W.D., 1996, {\it ASP Conf.
   Ser.}, {\bf 109}, 527, in Cool Stars, Stellar Systems,
   and the Sun, ed. R. Pallavicini \& A.K. Dupree
%Changed: Wed Jun  1 16:26:15 MEST 2005

Landis, H.J., Mattei, J.A. \& Percy, J.R., 1992, {\it IBVS} No. 3739

Lloyd, C. \& West, K.W., 1996, {\it IBVS}, No. 4335

Percy, J.R. \& Desjardins, A. 1996, {\it PASP}, {\bf 108}, 847

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