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\IBVShead{4114}{16 November 1994}                      % Use it with dummy or empty arguments

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\title{APT OBSERVATIONS OF SMALL-AMPLITUDE RED VARIABLES}

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           Small-amplitude red variables (SARVs) are M giants which are pulsating with small
amplitudes ($<$2.5 mag) and with periods of 20 to 200 days.  SARVs are believed to be part of a
sequence of red variables extending from the so-called $\sigma$ Librae stars (periods 10 - 20 days,
V amplitudes typically 0.1 mag) to the Mira stars.  Along this sequence of red variables, the
incidence of variability, and the period and amplitude of variability, tend to increase with later
spectral type, but the correlation is not an exact one.

           There are 164 known and 136 suspected variables among the approximately 500 M giants
in the Yale Catalogue of Bright Stars.  In order to clarify the variability status of these 500 M
giants, one of us (JRP) has been conducting a search for SARVs using the 0.4 m ``teaching
telescope" of the University of Toronto (Percy and Fleming 1992; Percy and Shepherd 1992), and
using the American Association of Variable Star Observers (AAVSO) network of photoelectric
photometrists (Percy et al. 1994).  Several SARVs which had not been assigned to a student
observer or to the AAVSO observers were monitored for one season with an automatic
photoelectric telescope (APT).

           The seven SARVs listed in Table 1 were monitored automatically with the Phoenix~10
0.25 m reflector through the APT Service of the Fairborn Observatory, exactly as described by
Percy (1993).  Table 1 lists the program (P), comparison (C) and check (K) stars, their properties,
the standard deviations à of the differential U, B and V magnitudes of the program and check
stars relative to the comparison stars, and the assessment of the variability of each star.  A few
observations were omitted for a priori reasons, e.g. if there was a large internal standard error, if
the APT quality control information indicated that the night was a poor one, and/or if the
observation was incomplete.  The standard deviations of the constant stars (0.005 to 0.01 in B
and V, 0.01 to 0.02 in U) are typical for observations of cool stars with this telescope.

           In addition to the results given in Table 1, there are the following notes on individual
stars; sample light curves are given for three stars:

           HR\,5123.  VAR? (YCBS).  The variability is marginal, at best.

           HR\,5150.  VAR? (YCBS).  The star varies on time scales of  $\sim$20 and $>$100 days
(Figure 1); there is also a distinct peak in the power spectrum at  $\sim$6 days.

           HR\,5154.  NSV 06389; V = 4.63 - 4.73 (NSV).  We find a similar range.  The variability
is irregular, with a characteristic time scale of 20 days (Figure 2).  The highest peak in the power
spectrum is at 18 days.

           HR\,5215.  VAR? (YCBS).  The most obvious variability is on a time scale of  $\sim$100 days,
but there is some evidence for more rapid variability as well (Figure 3).
 
           HR\,5226.  CV Dra; V = 4.46 - 4.94 (YCBS).  Our observations show a much smaller
range (but over a limited time interval).  The power spectrum shows no dominant peak.

           HR\,5299.  BY Boo;  Lb? V = 5.1 - 5.28 (YCBS).  The dominant peak in the power
spectrum is at 30 days.
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\centerline{Table 1.  APT Observations of Small-Amplitude Red Variables.}
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\hline
Star (HR)&SpT&V&$\sigma$(U)&$\sigma$(B)&$\sigma$(V)&Result&$\Delta$V&Period (days)\\
\hline
\\
P\,5123&M2\,III&5.74&0.0204&0.0096&0.0093&constant?&0.04& \\
C\,5102&G8\,III&6.11&--&--&--&constant& & \\
K\,5149&G9\,III&5.62&0.0091&0.0057&0.0047&constant& & \\
\\
P\,5150&M2\,III&5.01&0.0546&0.0321&0.0262&variable&0.09&6+longer\\
C\,5111&G6\,III&5.73&--&--&--&constant?& & \\
K\,5178&K5\,III&6.05&0.0373&0.0091&0.0108&constant?& & \\
\\
P\,5154&M2\,III&4.66&0.0155&0.0170&0.0204&variable&0.08&18?\\
C\,5177&F7\,IV-V&6.50&--&--&--&constant& & \\
K\,5142&A3\,Vn&5.46&0.0075&0.0068&0.0061&constant& & \\
\\
P\,5215&M2\,III&5.87&0.0307&0.0198&0.0207&variable&0.07&$\sim$100?+shorter\\
C\,5195&K0\,III&5.62&--&--&--&constant& & \\
K\,5161&G5\,III&5.98&0.0117&0.0048&0.0085&constant& & \\
\\
P\,5226&M3.5\,III&4.65&0.0248&0.0352&0.0317&variable&0.10& \\
C\,5256&K3\,V&6.37&--&--&--&constant& & \\
K\,5213&G3\,V&5.96&0.0080&0.0058&0.0045&constant& & \\
\\
P\,5299&M4\,III&5.27&0.0329&0.0510&0.0547&variable&0.17&30\\
C\,5335&gK3&6.24&--&--&--&constant& & \\
K\,5271&K2\,III&6.27&0.0232&0.0120&0.0063&constant& & \\
\\
P\,5300&M1.5\,III&5.25&0.0308&0.0228&0.0230&variable&0.10&19\\
C\,5271&K2\,III&6.27&--&--&--&constant?& & \\
K\,5280&A2\,V&6.15&0.0199&0.0074&0.0136&constant?& & \\
\hline
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\centerline{Figure 1. The V light curve HR\,5150 relative to HR\,5111.}
\centerline{The standard error of the measurements is 0.010.}
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\centerline{Figure 2. The V light curve of HR\,5154 relative to HR\,5177.}
\centerline{The standard error of the measurements it 0.006.}
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\centerline{Figure 3. The V light curve of HR\,5215 relative to HR\,5195.}
\centerline{The standard error of the measurements is 0.008.}
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           HR\,5300.  CF Boo;  m$_{pg}$ = 7.0 - 7.13 (YCBS).  The dominant peak in the power spectrum
is at 19 days.

           Because of the limited span of the observations, it is not possible to derive precise
information about the amplitude and time scales of the variability.  The observations have,
however, given estimates of the amplitude of short-term (days to months) variability which are
useful for statistical purposes.  Most of these stars are early M giants, and the amplitudes are
relatively small, and the time scales short.  HR 5150, for instance, shows some evidence of very
short time scale variability.  A few of the stars show conspicuous time scales of variability of
order weeks.  At least two show variability on a time scale $\geq$100 days.  The origin of these 
long-term variations is not known.  In general, the incidence, amplitude and time scales of variability,
as a function of spectral type, are consistent with previous results.

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\centerline{4}
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Acknowledgements.  JRP thanks Michael Seeds for his excellent work as Principal Astronomer
for the APT Service, and the Natural Sciences and Engineering Research Council of Canada for a
research grant.  Winnie Au was a participant in the University of Toronto Mentorship Program,
which enables outstanding senior high school students to work on research projects at the
university.
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% Call for macros \authors - \authorsrightcol - \endauthors
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John R. PERCY
Winnie AU
Erindale Campus
University of Toronto
Mississauga, Ontario
Canada  L5L 1C6
\endauthors

% Call for macro \references
\references

Kholopov, P.N. ed., 1982, New Catalog of Suspected Variable Stars (Moscow, Nauka)

Percy, J.R., 1993, {\it PASP}, {\bf 105}, 1422

Percy, J.R. and Fleming, D.E.B., 1992, {\it PASP}, {\bf 104}, 96

Percy, J.R. and Shepherd, C., 1992, {\it IAU Inf. Bull. Var. Stars}, No.\,3792

Percy, J.R. et al., 1994, {\it PASP}, {\bf 106}, 611


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