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\IBVShead{4110}{4 November 1994}                      % Use it with dummy or empty arguments

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\centerline{\ft  THE SPOTTED YOUNG SUN -- HD\,129333 (= EK Dra)}
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    HD 129333 (= EK Dra) is a young, single, solar-type star with a
rotational period of approximately 2\fd 7.  Its U, V, W space velocity
components (+3, $-$29, $-$17) (km/s) are very close to those of the
Pleiades cluster (+9, $-$27 $-$12), making it a probable member of the
Pleiades moving group of young stars with an age of $\approx 70$ Myr
(Soderblom \& Clements, 1987).  This star is part of a program being
carried out at Villanova University called {\it The Sun in Time}.  The
program involves multiwavelength observations of single G0-G5 V stars
with ages ranging from $\approx$ 70 Myr to $\approx$ 9 Gyr.  These stars
are suitable proxies for the sun at several stages of its life history
from the zero age main sequence (ZAMS) to the very late (terminal)
main-sequence (TAMS) phase (Dorren \& Guinan, 1994a).

  HD\,129333 (dG0,
B$-$V = +0.61, T$_{eff}$ = 5930 K, age $\approx$ 70 Myr) provides a look
at the sun shortly after it arrived on the main-sequence (Dorren \&
Guinan, 1994b).  It has a very active chromosphere and transition
region, which are consistent with its youth and rapid rotation.
Furthermore, in 1991, HD 129333 was detected as an X-ray source during
ROSAT pointed observations, with an X-ray luminosity of L$_{x}$ (0.2-2.4
keV)$\sim 9\times 10^{29}$ erg/s, or about 300 times stronger
than the Sun (Dorren \& Guinan, 1992).  The X-ray emission probably
originates from the stellar corona, while the UV emission features are
associated with the chromosphere-corona transition region of the star
(Dorren \& Guinan, 1994b).  The best fit to the X-ray energy
distribution indicates a two-temperature component corona with T$_{1} =
1.3\times10^{6}$ K and T$_{2} = 9.6\times10^{6}$ K (Dorren, G\"{u}del \&
Guinan 1994).

In 1983 this star was discovered to have low amplitude
(Amp(V) $\approx$ 0.05) light variations with a period of $\sim$ 2\fd 7 (Dorren
\& Guinan, 1994b).  These periodic 2\fd 7 variations increase in amplitude
with a decrease in wavelength and are assumed to be rotational
modulation due to the presence of cool starspots.  In that case, the
photometric period ($\sim$ 2\fd 7) represents the stellar rotational period.  
HD\,129333 now has a variable star designation of EK Draconis (Kazarovets,
Samus \& Goranskij, 1993).

Photoelectric photometry was obtained from
1990/91 to the present for HD\,129333 in {\it UBV}, {\it ubvy} and H$\alpha$ {\it wide} and
{\it narrow} bandpasses with Automatic Photoelectric Telescopes (APTs) located
at Mt.Hopkins, Arizona.  The data presented in this report has come from
the Four College Consortium (FCC) 0.8m APT.  The photoelectric
observations were carried out relative to the nearby comparison star HD
129390 (V = +7.5; B$-$V = +0.4; F2) and check star HD 127821 (V = +6.09;
B$-$V = +0.41; F4\,IV) and followed the usual pattern of
{\it sky-comparison-check-variable-comparison-sky}, with each measure lasting
10 seconds.  The effects of differential atmospheric extinction were
removed using extinction coefficients determined from the observation of
standard stars.  Normal points were computed for the observations of
each night.  Typically, each normal consists of 4-5 individual 10 sec
measurements.
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\centerline{2}
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{\centerline{Figure 1: Photometric variations of HD 129333 versus phase. Each}
{\centerline{filter was fit with a model (solid lines on figure) using Binary Maker 2.0.}
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\centerline{Table 1. Spot Parameters for HD\,129333}
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%Table to accompany article on HD129333
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\begin{tabular}{lcccc}
%\multicolumn{5}{c}{\bf Table 1: Spot Parameters for HD129333}\\ [0.1in]\hline\hline
& & & &\\
\multicolumn{5}{c}{\it Assumed Quantities}\\
\multicolumn{5}{c}{Inclination $i = 60^{\circ}$}\\
\multicolumn{5}{c}{P$_{rotation} = 2.74$d}\\
\multicolumn{5}{c}{T$_{photosphere} = 5930$ K$^{a}$}\\ [0.1in]
\multicolumn{5}{c}{\it  Limb-Darkening Coefficients$^{b}$}\\
\multicolumn{5}{c}{ x($\lambda 3700$) = 0.76}\\
\multicolumn{5}{c}{ x($\lambda 5500$) = 0.62}\\[0.1in]
\multicolumn{5}{c}{\it Determined Quantities}\\
        &  Temperature  &  Radius &      Longitude  &     Latitude\\
         & (K) & & &\\[0.1in]
 Spot 1  &  $5470\pm40$ &$ 20.5^{\circ}\pm1.5^{\circ}$& $ 240^{\circ}\pm5^{\circ}$&$ +40^{\circ}\pm5^{\circ}$\\
 Spot 2  &  $5470\pm40$ &$ 24.5^{\circ}\pm1.5^{\circ}$&$100^{\circ}\pm5^{\circ}$&$+38^{\circ}\pm5^{\circ}$\\[0.1in]
\multicolumn{5}{c}{\bf  Total Spotted Area$^{c} = 7.4\%\pm 0.5\%$} \\[0.1in]\hline\hline
\end{tabular}
\end{center}

\hspace*{1.2in}$^{a}$ From dG0 spectral type.

\hspace*{1.2in}$^{b}$Al-Naimiy (1978).

\hspace*{1.2in}$^{c}$In terms of the total surface area of the star.



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\centerline{3}
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The data discussed here represents 15 nights over the
period 1994 January 24 UT through 1994 February 26 UT.  Nightly means
were calculated and phases were computed using an arbitrary starting
heliocentric Julian Date and a period of 2\fd 74.  The data were then
normalized to intensity units and plotted in intensity versus phase.


Figure 1 shows the nightly mean differential magnitudes for the $y$-band
(5500 \AA) and the u-band (3600 \AA).  The differential yellow light curve
has a broad primary minimum extending from $\approx$ 0.10P to $\approx$
0.60P.  The light amplitude of the yellow curve is $\simeq 0.040$ mag.  For the
{\it u}-filter ($\lambda 3600$), the shape is very similar to the yellow curve but the
light amplitude is greater ($\simeq 0.062$ mag).  The intermediate filters
(violet 4100 \AA\ and blue 4400 \AA) have similar shapes and amplitudes which
fall between the yellow and ultra-violet curves.

 The fits for HD\,129333
were done using Binary Maker 2.0, a synthetic modeler for binary star
systems (Bradstreet, 1993), with the second component essentially {\em
turned off} (given a very low mass and temperature) in order to model a
single rotating star.  The model consists of two large, mid-latitude
spots separated by $140^{\circ}$ in longitude.  The total area spotted is about
7.4\% of the stellar surface area.  The spots were assumed to be
circular and to have the same temperature.  Table 1 gives a summary of
the spot parameters used in the model.

The temperature difference
between the spots and the photosphere was determined to be 460 ($\pm$40)
K. The model was fit for several different starspot temperatures and
radii in the {\it y}-band (5500 \AA) and then compared with the {\it u}-band (3600 \AA)
to cover the full range of wavelength dependence in the data.  The
models that best fit to both colors were in the range 420-500 K. This
solution was found to fit the other light curves at the intermediate
wavelengths.  The uncertainty in the value results from the scatter in
the data and ambiguities in the model.
\bigskip


% Call for macros \authors - \authorsrightcol - \endauthors
\beginauthors
\authorsrightcol
Maureen P. SCHEIBLE
Edward F. GUINAN   
Dept. of Astronomy and 
Astrophysics 
Villanova University     
Villanova, PA 19085 U.S.A.
\endauthors

% Call for macro \references
\references

Al-Naimiy, H.M., 1978, {\it Astrophys. Space Sci.}, {\bf 53}, 181

Bradstreet, D.H., 1993, {\it Binary Maker 2.0: Light Curve Synthesis
         Program}, (Contact Software, Norristown, PA)

Dorren, J.D. \& Guinan, E.F., 1992, {\it BAAS}, {\bf 24}, 1205

Dorren, J.D., G\"{u}del, M. \& Guinan, E.F., 1994, {\it ApJ} (submitted)

Dorren, J.D., \& Guinan, E.F., 1994a, {\it The Sun as a Variable Star:
        Solar and Stellar Irradiance Variations}, ed. J.M. Pap 
         (Cambridge Univ. Press), p.206

Dorren, J.D., \& Guinan, E.F., 1994b, {\it ApJ}, {\bf 428}, 805

Kazarovets, E.V., Samus, N.N., \& Goranskij, V.P., 1993, {\it IBVS}, No.\,3840

Soderblom, D.R., \& Clements, S.D., 1987, {\it AJ}, {\bf 93}, 920

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