The following discussion is intended to draw attention to some special technical circumstances or special features in the light-curve behavior of our program stars but is not supposed to be a summary of all relevant literature data. For previously published photometry we refer to Table 5 (click here) but will try to comment on the most relevant and most recent papers in the text. For a complete listing of all available literature on a particular star we recommend to consult the SIMBAD data base at CDS Strasbourg.
HD 12545 (XX Tri). This is the RS CVn star with the previously largest light-curve amplitude (0.60 mag; Nolthenius 1991). Consequently, it attracted several follow-up studies (see Table 5 (click here)) although its light variability was already known since 1985 (Skiff & Nations 1991) and independently since 1986 (Hooten & Hall 1990). A preliminary orbit with a period of 24 days had already been entered into the tables of the CABS catalog and a definite orbit was published in the meantime by Bopp et al. (1993).
The y magnitudes of the Strömgren photometry of Skiff & Nations
(1991) have been converted to Johnson V magnitudes with the
relation given in Olsen (1983): V=y+0.015(b-y)-0.003 and are
plotted in Fig. 2 (click here). Ten years of V data suggest that the
light-curve amplitude varies more or less systematically showing a small
amplitude every 
years and a large amplitude shifted in time by
about one half of that period. If periodic we expect to see the next minimum
at
around JD 2 450 500 (
). The maximum amplitude in our new data
was 0.48 mag in V, 0.12 mag in V-I, and 0.06 mag in B-V in December
1995 but only 
mag in V and 0.04 mag in V-I and 0.02 mag in
B-V one and a half years
earlier while the light and color curves showed two minima at that time.
The seasonal period continuously
increased between 1988 and 1992 but changed inconsistently thereafter and do
not seem to relate with the light-curve amplitude. Periodograms of the
full data set and the 1995/96 observing season are compared in Fig. 1 (click here).
HD 17433 (VY Ari). An extensive multiwavelength study of this star was
presented by Bopp et al. (1989), finding it to be one of the
most active binaries yet observed. The relatively sharp lines (
kms-1) allowed the detection of a 2 kG magnetic field with a filling
factor of 66%.
Photometry from 1974 through 1991 was discussed in Strassmeier & Bopp
(1992) and a new value for the rotation period of 16.42 days was
found. Since the orbit of HD 17433 is nearly circular and the orbital and
rotational periods differ by approximately 30%, HD 17433 represents the case
of an asynchronously rotating star. Time-series starspot modeling of the
1988/89 and 1989/90 photometry revealed emergence and decay timescales for
individual spots that likely scale with the area of the spots - as is the
case with sunspots.
Our new data cover five seasons from 1991/92 on and, together with the
literature data cited in Table 5 (click here), now span over 22 years (Fig. 3 (click here)). However,
there is a big data gap between 1975 and 1985, but the trend in the more
recent V light curves suggests a sinusoidal long-term brightness variation
possibly periodic with minimum light occuring at around 1994.0 and maximum
light at around 1987.0 (
years). The seasonal periods are
plotted in the lower panel of Fig. w" (click here) and exhibit
variations exceeding the 3-
level but - as for HD 12545 -
do not indicate a long-term relation with the overall system brightness. The
present data density does not allow a conclusive statement whether the
photometric period is related to the amount of the rotationally modulated
amplitude (see the lower panel in Fig. 3 (click here)). The seasonal phase curves are
plotted in Fig. 27 (click here) and show the maximum amplitude of 0.18 mag in V and
0.04 mag in B-V in 1993/94.
HD 26337 (EI Eri). EI Eri has been a prime target for Doppler
imaging since the first application of this technique to spotted late-type
stars in 1982. Doppler images can be found in Hatzes & Vogt
(1992),
Strassmeier et al. (1991), and Strassmeier (1990). All
of these images show a cool polar spot whose appendages
cause a significant part of the light-curve variability and, if
real, has been present since observations commenced in 1982 by Vogt and
collaborators. The photometric period of EI Eri is close to
2 days (1.95) and observations from a single ground-based site take
30 days to cover all rotational phases. This is doubly
unfortunate because a continuous IUE-FES light curves for 85 hours obtained
by J. Neff (see Strassmeier et al. 1989b) showed clear
variations of the shape of the light curve, i.e. within two consecutive
stellar rotation cycles.
Our new data are from seven observing seasons starting in late 1989 and
the long-term plot in Fig. 4 (click here) now covers the past 16 years. Seasonal phase
plots are shown in Fig. 28 (click here) and give an impression of how rapidly the
light-curve shapes may change from cycle to cycle. The largest amplitude was
observed in 1993/94 and reached 0.15 mag in V and 0.03 mag in B-V by the
end of the season. Most remarkably, however, is the sinusoidal long-term
brightness variation with a likely period of around 
year and an
average V amplitude of 0.1 mag. Once
again, the seasonal periods indicate no clear relation with the long-term
brightness variation.
HD 283518 (V410 Tau). Despite its relative faintness of 11th mag this
star is the most well observed weak-line T Tauri star in the sky. Extensive
photometry exists from various sources (see Table 5 (click here)) and recently has been
entered into a publicly available photometric data base for T Tauri stars
by Herbst et al. (1994). This service is gratefully
acknowledged here!
The most recent photometric period determination, and probably the best
so far, has been that of Petrov et al. (1994) who found
days. V410 Tau is also a prime target for Doppler
imaging and four maps exist to date (Strassmeier et al.
1994d;
Joncour et al. 1994; Hatzes 1995;
Rice & Strassmeier 1996). From a photometrists point of view it is especially
interesting to note that our Doppler images
reveal hot and cool spots coexisting
on the photospheric surface. A fit to a light curve with a simple
geometric two-spot model with only cool spots would, therefore, result in
very uncertain if not completely spurious spot longitudes and areas.
It seems that spot distributions in general are much more complicated than
what is suggested from continuum light curves alone.
Our new data are from two observing seasons 1994-1996 and bring up the
total time coverage to 34 years (Fig. 5 (click here)). The seasonal phase plots are
shown in Fig. 29 (click here). We emphasize that our observations in 1994-95 caught
V410 Tau with an amplitude of 
in V. This is the largest amplitude
ever observed on any spotted star and the corresponding surface
feature must
cover almost an entire hemisphere. This could even affect the star's
hydrostatic equilibrium in the outer regions because simple energy
redistribution within the convection zone might not be sufficient any more
to store away the "missing flux'' blocked by such a huge spot. Since the
accompanying V-I color curve also shows the enormous amplitude of 
and is in phase with the V light curve we believe that the amplitudes are
indeed due to temperature inhomogeneities on the stellar surface.
The long-term trend in Fig. 5 (click here) is very similar to that observed for HD 12545,
now being the second largest amplitude star with a maximum V amplitude of
. Both stars' average light level remain more or less constant and
V410 Tauri also shows the same - possibly cyclic - change of the lightcurve
amplitude but with a period between 6-7 years compared to 2.7 yr
for HD 12545. Again, there is an obvious lack of correlation between the
seasonal photometric period and the overall light-curve amplitude.
HD 283750 (V833 Tau). Oláh & Pettersen (1991) and
Guinan
& McCook (1991) have been observing this star since around 1983
and Eggen (1994) discovered its light variability from observations in
1962. The long-term variability was discovered by Hartmann et al.
(1981) who found a very distinct cycle with a period of
60 years and an amplitude of around 
0.7 mag.
Recently,
Bondar (1995) extended the database with additional archival
photographic magnitudes to a time range from 1899 to 1990 and confirmed
the earlier cycle period.
In November 1993 Guinan (1996) detected a huge flare in all five
Johnson bandpasses that reached an amplitude of 0.5 mag in U and was
still visible in I. Earlier, Oláh & Pettersen (1991) suggested
the existence of a long-lived polar spot due to the low inclination of
the rotation axis of 20
and the continuous light-curve
variations on all accessable time scales.
Three seasons of photometric data and part of a third were obtained so far. These data are compared with other photoelectric data from the literature in Fig. 6 (click here). V833 Tau shows a long-term variation of 0.25 mag between 1988 and 1996 which is at least twice as large as the amplitude due to rotational modulation. Therefore, periodogram analysis of the whole data set was carried out from prewhitened data by removing all frequencies longer than 270 days. The best period found was 1.791601 days (Table 4 (click here)) very close to the orbital period of 1.788 days. Figure 30 (click here) shows the seasonal plots.
HD 282624 (SU Aur). SU Aurigae seems to be an intermediate case between
a weak-lined T Tauri star and a classical T Tauri star because its
photospheric spectrum is clearly seen but still slightly veiled (e.g.
Giampapa et al.
1993; Basri et al. 1995). Despite the veiling,
Petrov et
al. (1995) presented a photospheric Doppler image that shows
predominantly cool spots along the stellar equator. The true rotation period
of SU Aur has been -
most unusual - determined from H
line profile variations and is
days (Giampapa et al. 1993). We note that
Petrov et
al. (1995) used a period of 3.094 days for phasing their
spectroscopic data because earlier photometry by Herbst et al.
(1987)
caught the star in a stage when the light curve was
double-humped and thus the best-fit period (1.55 days) was only one-half
the true rotation period. Further photometry from various sources, partially
even unpublished, is available from the T-Tauri data base of Herbst et al.
(1994).
We have only one observing season of photometry of SU Aur. Figure 7 (click here) shows all available V-band photometry over the past 20 years. Periodogram analysis of seasons with sufficient data coverage yields periods between 2.51 and 3.32 days (see Fig. 7 (click here) and Table 4 (click here)). The best period from all data between 1974 and 1994 is 2.7 days while the range in brightness is 0.8 mag. This large range is due to the low brightness of the 1982 data of Herbst et al. (1983).
HD 31738 (V1198 Ori). Balona (1987) presented 28 radial
velocities in the range of +10 and 
but judged these
variations not as significant and listed HD 31738 as a single star.
Fekel et al. (1996) found asymmetric
absorption lines and concluded that the star is a double-lined spectroscopic
binary. They also found a weak, sometimes even apparently absent, H
line as well as strong CaII H & K emission that was confirmed by
Strassmeier et al.
(1990). The light variability was discovered by Hall et al.
(1986) but they concluded that the comparison star was the variable.
Later, Strassmeier et al. (1989a) reexamined the same data set and
found that HD 31738 was the variable and not the comparison star. Their
periodogram from two years of data between 1984 and 1986
gave similarly good fits at 3.70 and 4.51 days in the first season and 4.59
days in the second. No orbital period is known to date. Cutispoto
(1995) observed HD 31738 in December 1989 and found the star to be
constant to within 0.005 mag.
We have acquired photometry of HD 31738 since 1993 covering three full
observing seasons (Fig. 8 (click here), upper panel). Combining these data with
previous Vanderbilt APT observations (Hall 1996) as well as data
from sources listed in Table 4 (click here) we find a sinusoidal long-term
variation with an amplitude of 0.1 mag and possibly with a period
of around 15 years. However, no clear periodic variability
within an observing season is detected, in agreement with Cutispoto's
(1995) observations from 1989. Thus, the 4.5-day period claimed
earlier by Strassmeier et al. (1989a) remains to be verified.
The lower panel in Fig. 8 (click here) shows the check-minus-comparison V data
(HD 32263 minus HD 31594) between 1987 and 1995 and verify the long-term
constancy of the comparison star although it is not clear from our data
that there are no short-term variations. Clearly, higher precision is needed
to solve the puzzle of HD 31738. Our periodogram analysis from prewhitened
data shows one frequency at 0.214 d-1 (4.667 days), however, its
resulting amplitude
is barely 2- above the noise level and has an amplitude of just
0.015 mag. We nevertheless use this period, despite that it is likely
spurious, and phase the seasonal data with it. The resulting plots are given
in Fig. 32 (click here). We note that if we adopt a stellar radius of 3 
from
the G5IV spectral classification, an inclination of the stellar rotation
axis of 45 then the measured 
would imply a rotation period
of around 5.6 days.
HD 31993 (V1192 Ori). Fekel et al. (1986) observed the star
spectroscopically and gave a value for of 31 kms-1 that
prompted further attention. From an independent study Balona (1987)
found the star to be constant in radial velocity and thus HD 31993 seems
to be a single star. The spectral classification of K2III is originally from
Bidelman & MacConnell (1973) and has been confirmed by
Fekel et al. (1986). Ultraviolet IUE data and a high lithium
abundance were reported by Fekel & Balachandran (1993).
The light variability was first mentioned by Lloyd-Evans & Koen
(1987) from data taken in 1980. They also found a period of
6.78 days with a very small amplitude of
just 0.03-0.05 mag in V. Several seasons of photometry were analyzed by
Hooten & Hall (1990), including data from as early as 1978,
but their period analysis allowed various photometric periods between 4.8 and
29 days.
We present data from three full seasons and part of a fourth. The long-term
plot is shown in Fig. 9 (click here). Clear variability is only seen in two of these
seasons but verify that the 28-day period is the correct one. The
and the 28-day period interpreted as the rotation period result
in a minimum radius of 17 , which is still consistent with the
K2III classification if the inclination of the stellar rotation axis is
close to 90 . Seasonal light curves are shown in Fig. 33 (click here).
HD 39576. Buckley et al. (1987) drew attention to this star
when they found it to be a variable X-ray emission source with moderately
strong CaII H and K emission lines. Houk (1982) had assigned
a spectral type of G1V. Buckley et al. already noted that the star is likely
a spectroscopic binary but no orbital elements are available to date.
Strassmeier et al. (1992) discovered the light variability from
data taken at ESO in 1992 and showed that the star is a very small amplitude
variable with an amplitude of 0.036 mag in Strömgren y and a preliminary
period of 2.7 days. Their
measure of 
kms-1 from a high-resolution spectrum
superseded the 65 kms-1 value derived by Buckley et al. (1987)
and agrees with the spectral classification of Houk (1982).
We have three full seasons of photometry and part of a fourth (Fig. 10 (click here)).
Periodogram analysis of each individual season gives the best period at
around 2.27 days (Table 4 (click here)). This is similar but still different by almost
20% to the period from the 1992 ESO data but supersedes that value.
Interpreting it as the rotation period and using the of
Strassmeier et al. (1992) we find a minimum radius of 0.90
, in agreement with the G1V classification of Houck. The seasonal
plots are shown in Fig. 34 (click here).
HD 81410 (IL Hya). Eggen (1973) discovered the light
variability of HD 81410 and Raveendran et al.
(1981, 1992)
published the first orbital solution for this single-lined spectroscopic
binary. Balona (1987) confirmed that finding using radial-velocity
data from 1979 and 1980.
Recently, Weber (1996) obtained a Doppler image of HD 81410
from KPNO spectra from 1994 showing the star with a weak polar spot. He
also redetermined the spectroscopic orbit with a slightly revised period of
days but in good agreement with Balona's orbit.
We have four seasons of new data of HD 81410, which brings the total
baseline in time to 26 years of V data (Fig. 11 (click here)). The long-term average
photometric period is 12.786 days and is very close to the orbital period.
Figure 11 (click here) shows a more or less continuous increase in brightness since the
discovery of its light variability until 1988.0 and a stagnation thereafter.
The maximum V amplitude from the rotationally modulated part is
mag from 1971, but a more typical and more recent value is
0.2 mag (e.g. between 1990-1996). The long-term variation's amplitude of
the average brightness is 0.4 mag between 1971 and 1989. The
seasonal plots from our new data are shown in Fig. 35 (click here).
HD 82443. In a recent paper Henry et al. (1995a) summarized
the observational history of this single K0V star and we refer the reader
to this paper. They were also the first to unambiguously determine (and
publish) the photometric rotation period of 
days.
However, we point out that the photospheric light-curve variability was
already known at the time of Henry et al.'s APT observations and had been
discovered by Guinan & McCook (1991). Just recently,
Messina
& Guinan (1996) presented UBV photometry of HD 82443 with
the Phoenix-10 APT from February to May 1989. They found a photometric
period of 
from 67 nights of observations.
Our new data are from 1994 and 1996 (Fig. 12 (click here)) and braket the data of
Henry et al. (1995a) from 1994/95. Differential measures
were converted to absolute values by using the V magnitude of our
comparison star of 
mag (Rufener 1988). Its zero
point is thus somewhat uncertain but should be good to, say, 0.01 mag.
Together with the data of Messina & Guinan (1996) we see a clear
downward trend in the overall brightness of HD 82443 of 0.1 mag between 1989
and 1996, which likely indicates the existence of a decade-long spot cycle.
The scatter in the seasonal plots in Fig. 36 (click here) indicates significant variations
of the light curve shape on relatively short time scales.
HD 82558 (LQ Hya). LQ Hydrae is a rapidly rotating, single K2 dwarf star that probably just arrived on the zero-age main sequence (Fekel et al. 1986), while Vilhu et al. (1991) even suggested it to be a pre-main sequence object. Its light variability was discovered independently by Eggen (1984) and Fekel et al. (1986) from data taken in late 1982. A first Doppler map was presented by Strassmeier et al. (1993b) that showed a high-latitude spot straddling the rotational pole but not a polar spot as seen on several evolved RS CVn binaries and was confirmed by Saar et al. (1994) who presented further maps for 1991 and 1993.
We present four new seasons of photometric data and have now 14 years of continuous V data. Figure 13 (click here) shows the long-term behavior of LQ Hya and possibly detects a sinusoidal light variation with a period of around 7 years. The seasonal light and color curves in Fig. 37 (click here) indicate a changing light curve shape with V amplitudes between 0.03 mag in 1995/96 and 0.15 mag in 1994/95.
HD 106225 (HU Vir). Bidelman (1981) and
Fekel et al.
(1984, 1986) were the first who drew attention to
this star and Fekel et al. also discovered its light and spectrum
variability. Strassmeier (1994) presented an extensive
spectroscopic and photometric study and proposed a single, large
coronal loop to explain their photospheric and chromospheric Doppler images
as well as the complex H line-profile variations. Although
follow-up observations with ROSAT did not result in the proposed
rotational modulation of the X-ray flux but, instead, discovered a huge
X-ray flare lasting for about two days (Endl et al. 1995).
Hudec & Stepan (1995) used archival photographic plates to
search whether HD 106225 is the optical counterpart of the luminous
gamma-ray source GRB 930103. However, they did not find any variations
exceeding their detection limit of 0.3 mag within a monitoring interval of
180 hours nor 0.8 mag within an interval of 420 hours, respectively.
We have six full seasons of new photometry for HD 106225 bringing the total
time coverage to 14 years (Fig. 14 (click here)). Most notable in Fig. 14 (click here) is the
continuous increase of the maximum system brightness since a pronounced
minimum in 1992. These variations might proceed periodically with a
sawtooth-like shape. The most
recent data from 1996 indicate a reverse of the light increase (see Fig. 14 (click here))
and, if real, a period of around 4-5 years could be expected. The seasonal
light curves for our data from 1990 through 1996 are plotted in Fig. 38 (click here) while
the seasonal periods are plotted in the lower panel of Fig. 14 (click here). The light
curve shows mostly two minima except in 1995/96 where a single but
asymmetric
minimum is seen, indicating the long-term presence of two spotted regions.
The V amplitude remains more or less the same during our time coverage
and is 0.2 mag and 0.04 mag in V-I.
HD 111812 (31 Com). 31 Comae is a rapidly rotating, active, single G0 giant located in the Hertzsprung gap of the HRD and as such very similar to the FK Comae type stars (e.g. Bopp et al. 1988). Its early spectral type, however, probably prevents it from being a heavily spotted star, in agreement with its low (predicted) Rossby number (Hall 1994) but despite the existence of strong CaII H&K emission-line fluxes similar to the most active RS CVn's (Strassmeier et al. 1990). No photometric variations were detected so far (Strassmeier & Hall 1988a; Lockwood et al. 1993) but Strassmeier et al. (1994c) claimed to have seen line-profile variations in high-resolution spectra of photospheric absorption lines that would indicate starspots. Lockwood et al. (1993) obtained an rms error from eight years of Strömgren data of as small as 0.0029 mag but mentioned that 31 Comae is variable on a seasonal timescale.
Three seasons of new UBV data of 31 Comae from the Phoenix-10 and T7 APTs
are available and are plotted together with previous data from the Phoenix-10
as well as V data from the Vanderbilt/TSU APT (Hall 1988)
in Fig. 15 (click here). Our periodogram analysis does not reveal any significant period.
However, the range of the observed V magnitudes within individual
observing seasons is somewhat larger than what is expected from the
Phoenix-10 data quality. Also, Fig. 15 (click here) shows a continuous downward trend of
the average V brightness from 4.927 mag in 1984 to 4.950 mag in 1996. If
real, it probably indicates the existence of a long-term activity cycle but
without measurable rotational modulation. We note that the
of 31 Comae is 
. A value that is too large if the
star were seen pole on. Adopting an inclination of 45 and a radius of
we would expect a rotation period of around 4 days.
HD 112313 (IN Com). Despite extensive observational efforts it is
still not fully clear what IN Comae really is (see e.g. Jasniewicz et al.
1987, 1996). Here we treat it as a
G5III-IV RS CVn-type binary star but note that IN Comae is
related with one of the hottest stars known, an O subdwarf with
K, with which it forms together the central
binary system of the planetary nebula LoTr-5 (see the CABS catalog
for further references). Its light variability was discovered by
Schnell & Purgathofer (1983) and several, mostly spurious,
periods were found. Two very different periodicities
were published thereafter: one with 0.25 days (Kuszawska & Mikolajewski
1993),
and the other with either 1.2 or 5.9 days (one is the alias of the other,
see references in Table 5 (click here)). One
of the latter periods is interpreted as the rotation period of the G5III-IV
star. It is still unknown where the 0.25-day period - if real - comes from.
Neither Jasniewicz et al. (1996) nor Schnell
(1996) could confirm the short-period variations despite intensive
monitoring in spring 1994 and 1983, respectively.
Hubl & Strassmeier (1995) presented Doppler maps with
both the 1.2 and the 5.9-day period and concluded that the longer period
is the more likely one. In either case the maps do not show the big,
cool polar spot typical for RS CVn stars but mostly spots at low latitudes.
In this paper we also present unpublished BV photometry obtained by A. Schnell at Vienna Observatory (Schnell 1996) from 1983 through 1988. New APT photometry has been obtained for four full seasons between 1993 and 1996. Figure 16 (click here) shows all available V data since the discovery of the light variability in 1983. Periodogram analysis of the entire data set shows the strongest peak at 5.9345 days. Its 1-f alias is also present but significantly weaker and we therefore believe that the 5.9-day period is the rotation period of IN Comae. Figure 40 (click here) shows the seasonal data phased with the long-term average photometric period.
HD 113816. Buckley et al. (1987) discovered the star to be a
strong X-ray source and identified it as a chromospherically active binary
star. Dadonas (1996) computed a single-lined spectroscopic
orbit with a period of 23.7 days. The light variability was long suspected
and recently discovered by Henry et al. (1995a) with a 23.5-day
modulation, making the star a synchronous rotator. Still significant
differences exist in the published values for HD 113816, from the
30 kms-1 value of Buckley et al. (1987) from relatively
low-resolution spectra to 10 kms-1 in Randich et al. (1994)
and 
kms-1 in Henry et al. (1995a) from spectra of
comparable resolution and quality than Randich et al.'s. The spectrum has
been classified as
K0III by Henry et al. (1995a) and as K2III-IV from multi-color
photometry (Buckley et al. 1987). The resulting minimum radius
depends linearly on the measure and is either 2.3 or 4.6
whether the 5 or the 10-kms-1 value is adopted. The former would
suggest a very low inclination of the stellar rotation axis of just
11. Because the V-light curve amplitude was only 0.04 mag
in 1994 (Fig. 26 (click here) in Henry et al. 1995a) such a low amplitude would
be in general agreement with a low inclination.
We have four full seasons of new photometry of HD 113816 from 1993 through 1996 (Fig. 17 (click here)). Periodogram analysis for each observing season gives consistent periods around 23.7 days, in good agreement with the period found by Henry et al. (1995a) from their data in 1994. The long-term light curve in Fig. 17 (click here) shows the unusually faint brightness level in that season compared to the other seasons. The average seasonal difference in V was 0.075 mag compared to 1993 and 0.035 mag compared to 1995. Figure 41 (click here) presents the individual seasons together with the phase plots.
Henry et al. (1995a) mentioned that their comparison star
HD 113449 exhibited long-term brightness variations of about 0.02 mag
in V. Our T7 check-comp data (SAO 
113449 in our case) from
four seasons (1993-1996) gave following average differential V magnitudes:
, 
, 
, and 
mag,
respectively. The four-year averages in 
, 
, and
are 
, 
, and 
mag,
respectively. Their standard deviations are
close to or even within the respective long-term external precision
and we are thus unable to confirm whether HD 113449 is a low-lamplitude
long-term variable and consequently still use the comparison star for
the differential magnitudes for HD 113816.
HD 116544 (IN Vir). The light variability of this EXOSAT X-ray source
was discovered by Cutispoto (1992, 1994).
Tagliaferri et al.
(1994)
included IN Vir in their lithium study and found a weak-to-moderate Li
abundance. A recent Doppler-imaging study by
Strassmeier (1997)
brought the following results: IN Virginis is a moderately rapid rotating K2-3
subgiant in a 8.2-day binary system. No secondary star is visible in the
optical
spectrum. Despite its relatively low of 24.0 kms-1 and a
photometric rotation period of 8.2 days it shows very strong emission
lines in all five optical CaII lines as well as in H
.
H appears as a complicated two-component line with a sharp and
variable absorption feature and a blue-shifted emission component - both
reminiscent of a strong, inhomogeneous stellar wind. Doppler images show
a polar spot with one large appendage and a temperature difference of about
1000 K.
Three seasons of photometric data of IN Vir have been obtained and are plotted along with Cutispoto's discovery data in Fig. 18 (click here). Periodogram analysis verifies the 8.2-day period. The seasonal plots in Fig. 42 (click here) reveal significant changes from season to season.
HD 117555 (FK Com). FK Comae is the prototype of a class of
rapidly-rotating single giants with the strongest, non-thermal emissions
encountered within stellar objects.
As can be seen from the references in Table 5 (click here) FK Comae attracts a long
list of interested astronomers. Probably the most comprehensive paper on its
spot and flare activity is that by Jetsu et al. (1993) where they
also discovered the light curve's "flip-flop" behavior and give an
improved photometric rotation period of 2.400247 days. The
BVRI photometry of Petreshock et al. (1995) has been
significantly updated for this paper (Petreshock 1996) and will be
published in a forthcoming
paper by Petreshock and colleagues. Spectroscopic
studies mainly concentrated on H and other chromospheric-activity
indicators (e.g. Walter & Basri 1982) but
only to a smaller degree on its photospheric spectrum.
This is simply due to the large rotational broadening of
160 kms-1 that makes absorption lines rather shallow and hard to
measure. Nevertheless, a Doppler image was obtained by Piskunov et al.
(1994) and shows cool spots mainly along the stellar equator.
We present three seasons of new data of FK Comae and plot them in Fig. 19 (click here)
along with data cited in Table 5 (click here). The seasonal plots are shown in
Fig. 43 (click here). Note that unpublished 
data from Oláh & Jurcsik
(1996) is included in our plots. Jetsu et al. (1994)
presented a collection of photometric data of FK Com from various sources
up to 1990 (not separated in Fig. 19 (click here)) that we also use in the analysis.
(Note that the data
of Huenemoerder et al. (1993) were included in the Jetsu et al.
paper but not the data of Eaton (1985),
and also that the data of Dorren et al. (1984) are H
narrow-band photometry and could not be used in our long-term study.)
Periodogram analysis of the whole data set from 1966 to 1996 gives a period
of 
days (see also Fig. 1 (click here)). This period is derived
without any further fine tuning like the elimination of the flip-flop
phase behavior discovered by Jetsu et al. (1993).
HD 129333 (EK Dra). According to Dorren & Guinan (1994) EK Draconis is the most active "solar twin" known. Its G1-2V spectral classification, strong radio and X-ray emission (Guedel 1995), and a rotation period of 2.70 days (Dorren & Guinan 1994) places it among a group of young stars that probably just arrived on the main sequence.
We present two full seasons of data plus part of a third between
1994 and 1996.
Previously unpublished Strömgren y data from Guinan (1996) were
converted to Johnson V with the relation given by Olsen (1983)
and are plotted along with our own data in Fig. 20 (click here). The seasonal phase
plots are given in Fig. 44 (click here). There seems to be a continuous decrease of the
average V light level of HD 129333 between 1994 and 1996 of approximately
0.05 mag. Periodogram analysis yields an average photometric period from
the three seasons of 2.605 days, that we interpret to be the rotation period
of HD 129333.
BD-08 3999 (UZ Lib). This RS CVn binary has been shown to display
photometric variations of up to 0.35 mag in V, has the spectrum of a K0
class-III giant,
and rotationally broadened lines with 
kms-1 (Bopp et
al. 1984). Grewing et al. (1989) discovered a hot companion
star in the ultraviolet spectrum and concluded that the system is a highly
evolved binary. Recently, Strassmeier (1996) derived improved
orbital elements with a period of 
days and zero
eccentricity that, together with the photometric period of Grewing et al.
(1989) of 
days, suggests UZ Lib to be a
synchronous rotator. A Doppler image shows very high latitude spots as well
as equatorial features but not a cap-like polar spot as seen on other RS CVn
binaries (Strassmeier 1996).
We have four full seasons of new photometric data of UZ Librae which we plot in Fig. 21 (click here) along with data cited in Table 5 (click here). Note that the data of Hoffmann (1980) were taken only in Johnson B and are thus not included in our long-term V plot. UZ Lib expierences a continuous brightness increase since 1972 with a full range of 0.5 mag. Its maximum V amplitude due to rotational modulation was around 0.3 mag in 1995 when the light curve appears with a single minimum (Fig. 45 (click here)). The V-I color variations are always in phase with the light curve and reach amplitudes of up to 0.07 mag.
HD 195040 (AT Cap). The light variability of this single-lined
spectroscopic binary was discovered by Lloyd-Evans & Koen (1987)
with a photometric period of 23.21 days and a maximum amplitude of 0.23 mag
in V. Hooten & Hall
(1990) listed the star in their program but did not obtain new
data. The spectral classification of K2III
is originally from Bidelman & MacConnell (1973) and was confirmed
by Fekel et al. (1986) who also determined the of 24
kms-1. Balona (1987) computed orbital elements with a
period of 23.206 days.
We have new photometric data of HD 195040 from three observing seasons (Fig. 22 (click here)), which show the star with a double-humped light curve. Periodogram analysis yields seasonal periods of around 11.6 days, very close to 1/2 the orbital period. Some of the light variations might be due to an ellipticity effect in case the orbital eccentricity is indeed different from zero. However, the light curve maximum at around phase 0.6 in Fig. 46 (click here) is fainter than the one at phase 0.1 in 1995 and in 1996 but equal if not brighter in 1994 and completely absent in 1993. This indicates that the light curve variation is governed by changing starspots and that twice the photometric period is the rotation period of HD 195040.
HD 202077 (BM Mic). Lloyd-Evans & Koen (1987) presented
extensive photometry for the observing period 1979-81 and found the star to
be variable with a period of 14.6 days and a V amplitude of
around 0.2 mag. Strassmeier et al. (1994b) obtained additional data
on 15 nights in mid 1994 and confirmed the period of Lloyd-Evans & Koen
with 
days and a V amplitude of 0.06 mag. No B-V nor U-B
color variations were seen in this data set.
We present new photometry from the four observing seasons between 1993 and 1996 (Fig. 23 (click here)). Periodograms show a clear period at 14.7 days with seasonal deviations of up to 0.6 days. The individual seasons were phased with that period and are shown in Fig. 47 (click here). The scatter in the seasonal phase plots indicates both light and color changes on relatively short timescales.
HD 216489 (IM Peg). IM Pegasi is one of the more well-observed systems in the RS CVn class and appeared already in the first RS CVn list of Hall (1976). Previous photometry is summarized in Table 5 (click here) and for earlier (photometric) references we refer the reader to the papers by Poe & Eaton (1985) and Strassmeier et al. (1989a). Here we just note that the light curve variability was originally discovered by W. Herbst in 1971 and later presented in Percy & Welch (1982). From a preliminary study, Dempsey et al. (1994) tentatively identified a solar-like spot cycle from 15 years of photometry. For references on visual and ultraviolet spectroscopy we refer to the most recent paper on IM Peg by Dempsey et al. (1996).
We have three full seasons of observations as well as unpublished
data from Oláh (1996) from 1991/92. Figure 24 (click here) is the corresponding
long-term plot covering 25 years of photometry. The V amplitude due to
rotational modulation reached an all-time maximum of almost 0.3 mag in mid
1995/96 while, at the same time, IM Pegasi's brightness is at an all-time
low with the faintest V-light minimum ever observed at around 6.1 mag
(compared to a maximum value of 5.64 mag in 1986). We do not see
indications for a periodic long-term behavior as suggested by Dempsey
et al. (1994) but long-term light variations are clearly present.
Note that our check star for the T7 observations was the semi-regular S-type giant HR Pegasi (HD 216672 = HR 8714, e.g. Eggen 1992) and, since our comparison star is indeed constant, we present a complete light curve for HR Peg in Fig. 25 (click here).
All new APT data presented in this paper is available at CDS from
http://cdsweb.u-strasbg.fr/Abstract.html
and from the ASTROSERVERVIENNA under following URL
(then click on "publications'')
http://www.ast.univie.ac.at/kgs/StellarActivity.html
Acknowledgements
Research with automated photometry at the University of Vienna is supported by a governmental grant to the Institute for Astronomy and by the Joint Research Initiative on stellar astrophysics of the Austrian Fond zur Förderung der wissenschaftlichen Forschung (FWF). Within this initiative KGS acknowledges the support through grant S7301-AST, and grant OWP-40 from the Austrian Academy of Sciences via their East-West program. Stellar activity research at Catania Observatory is supported by the Italian Ministry for Scientific Research and Technology, the Italian National Council for Research ("Gruppo Nazionale di Astronomia'') and the Sicilian Regional Government. GC acknowledges the hospitality at Vienna Observatory through grant S-7300-AST. Besides the cash flow, it is also a great pleasure to thank Lou Boyd and Don Epand of Fairborn Observatory for their continuous operation of and help with the T7 APT and its data reduction. Thanks also go to Mike Seeds of Franklin & Marshall College for keeping the Phoenix-10 APT busy and to the whole TSU-Center of Excellence group for continuous collaboration. Following colleagues allowed us to use their data prior to publication: D.S. Hall, W. Barksdale, B. Skiff and H. Nations, K. Oláh and H. Jurcsik, J. Petreshock, and A. Schnell, we gratefully acknowledge their generousity. This research has greatly benefited from use of the SIMBAD data base, operated at CDS in Strasbourg, France.
Figure 25: HD216672 = HR Peg. This star was the check star for our APT
observations of IM Pegasii. It exhibits semiregular light variations not
related to starspots
Figure 26: HD12545 = XX Tri
Figure 27: HD17433 = VY Ari
Figure 28: HD26337 = EI Eri
Figure 29: V410 Tau
Figure 30: HD283750 = V833 Tau
Figure 31: SU Aur
Figure 32: HD31738 = V1198 Ori
Figure 33: HD31993 = V1192 Ori
Figure 34: HD39576
Figure 35: HD81410 = IL Hya
Figure 36: HD82443
Figure 37: HD82558 = LQ Hya
Figure 38: HD106225= HU Vir
Figure 39: HD111812 = 31 Com
Figure 40: HD112313 = IN Com
Figure 41: HD113816
Figure 42: HD116544 = IN Vir
Figure 43: HD117555 = FK Com
Figure 44: HD129333 = EK Dra
Figure 45: UZ Lib
Figure 46: HD195040 = AT Cap
Figure 47: HD202077 = BM Mic
Figure 48: HD216489 = IM Peg
