Taylor (1982, 1984) claimed that the bright A0 V star 109 Vir (= HR 5511 = HD 130109) which has been used as a spectrophotometric standard and as a primary four-color uvby standard (Crawford & Barnes 1970) is variable. However, numerous observations have been published of this star which indicate consistency, see, example, four-color observations by Olsen (1983, 1993) and Philip & Hayes (1984) and spectrophotometry in the later paper. These results might not be in conflict if 109 Vir is only occasionally variable with a few episodes a year. Such behavior has been seen in some rapid rotators.
To gain some insight on the stability of the FCAPT values, observations were
also made of the nearby spectrophotometric standard 
Vir (= HR 4963
= HD 114330) which is a binary composed of an A1 IVs and an Am star. For 109
Vir the comparison and check stars were 108 Vir (= HR 5501 = HD 129956,
spectral type B9.5 V) and 16 Lib (= HR 5570 = HD 132052, spectral type F0 V),
respectively, while for Vir they were HR 5163 (= HD 119537, spectral
type A1 V) and 66 Vir (= HR 5050 = HD 116568, spectral type F3-4 Vs),
respectively. FCAPT differential Strömgren uvby observations were made
during years 2 through 5. On some nights during years 4 and 5 observations of
Vir alternated with those of 109 Vir for several hours.
Table 2 contains 231 observations of Vir with 16, 33, 84, and 98 in
years 2, 3, 4, and 5, respectively. The data for years 4 and 5 are quite
consistent. The worst offset is in the c-ch values for u which is 0.004
mag or about 0.5 
of the mean. The year 2 and 3 values show some
minor differences, most notably slightly offset b v-c and ch-c and v
ch-c
values, but these are less than 1 . The observations obtained in years
2 and 3 total only about one-half of that in either of the other two years
so such differences may be partially due to statistics.
Another way to examine the possible variability of Vir is to study the
data obtained on single nights. At the end of Table 2, I selected the data
for those nights on which Vir was observed five or six times (these
all occurred in years 4 and 5). Within a given observing season or night
Vir is not variable. But the slight offsets 0.003 mag in v-c values
for b and y seen in the averages of all values are also seen in the averages
based only on the data taken on nights with 5 or more observations/night.
Their origin is unknown, but could well be due to slight differences in the
nightly extinction. The reduction used extinction coefficients which were
consistent with several years of data. In summary within any given season of
observation Vir is a constant star and the small differences between
yearly means are not necessarily significant.
The 380 observations for 109 Vir are given in Table 3 with 28, 43, 143, and
166 in years 2, 3, 4, and 5, respectively. As for Vir, the data for
years 4 and 5 are very consistent. The largest average offsets in v-c are
0.001 mag, which implies constancy. Years 2 and 3 exhibit much larger
offsets. Offsets in v-c and ch-c are of similar size which suggests we are
seeing extinction produced differences. Further previous observers did not
report such offsets. The much greater number of observations in years 4 and
5 also means that the results for these years are much more certain. At the
end of Table 3, I selected the data for those nights on which 109 Vir was
observed at least 5 times (these occur only in years 4 and 5). For each the
averages for these nights are similar to those for the year. There is not a
night which exhibits any variability episode in agreement with
Philip & Hayes
(1984). Thus the apparent variability episodes for 109 Vir at best are
rarer than originally claimed.