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\IBVShead{5073}{11 May 2001}

\IBVStitle{Period Determination for V576 Herculis and V1116 Cygni}

\IBVSauth{Yoshinaga, M.; Benson, P. J.}

\IBVSinsto{Wellesley College, Whitin Observatory, 106 Central Street, Wellesley, MA 02481, USA \\ \indent e-mail:  myoshinag@wellesley.edu, pbenson@wellesley.edu}

\SIMBADobj{V576 Her}
\SIMBADobj{V1116 Cyg}

\IBVStyp{ RR }
\IBVSkey{photometry}

\begintext

V576 Herculis and V1116 Cygni are suspected RR Lyrae stars listed in
the General Catalog of Variable Stars (GCVS) without periods.  Both
stars were observed with the 24-inch Cassegrain reflecting telescope
and Tektronics $1024 \times 1024$ CCD camera at Wellesley College
between May 1999 and September 2000. During each night of observation,
we took twilight flats in each filter, dark and bias images, and
several variable star images in each of the $R$ and $V$ filters.
Images were processed with standard techniques in IRAF\@.  We did
differential photometry on each variable compared to several comparison
stars in the field and between all pairs of comparisons.  We chose the
most stable pair of comparisons as the primary comparison and check
star.  After an approximate period was determined with least square
fitting following the prescription of Horne and Baliunas (1986), we made
phase diagrams and refined the period visually.  When the period is
changed by the listed uncertainty, the phase diagram data from the
earliest cycle is definitely out of alignment with the data from the
oldest cycle.

We note that the position of both stars in the GCVS is incorrect.  A
recent SIMBAD search turned up two papers by Kato (1999) which confirm
the positions we found. V576 Herculis is GSC 2105-1084; the comparison
we used is GSC 2105-274 and the check is GSC 2105-70. Neither V1116
Cygni nor its comparison and check stars have a Guide Star catalog
number, so we give a finder chart in Figure~1.

V1116 Cygni was observed on 17 different nights with a total of 85
images in each filter.  We have determined an ephemeris  of:
\begin{equation}
\begin{array}{r@{}r@{}r}
{\rm Max = HJD}~2451809.589 & {} + 0\fday53854 & {} \times E. \\
{} \pm4 & {} \pm 5 & \\
\end{array}
\end{equation}
The phase diagram for the $V$ filter is given in Figure~2.  The $V$ filter
amplitude is 1.2 magnitudes, and the $R$ filter amplitude is
approximately one magnitude.

V576 Herculis was observed on 14 different nights with a total of 112
images in each filter.  We have determined an ephemeris of:
\begin{equation}
\begin{array}{r@{}r@{}r}
{\rm Max = HJD}~2451802.649 & {} + 0\fday40378 & {} \times E. \\
{} \pm4 & {} \pm 5 & \\
\end{array}
\end{equation}
The phase diagram for the $V$ filter is given in Figure~3.  The $V$ filter
amplitude is about 1.25 magnitudes, and the $R$ filter amplitude is about
one magnitude.

\IBVSfig{10cm}{5073-f1.ps}{A finder chart for V1116 Cygni.  Each side is about 15\arcs}

\IBVSfig{10cm}{5073-f2.ps}{The $V$ filter phase diagram for V576 Herculis using ephemeris (1)}

\IBVSfig{10cm}{5073-f3.ps}{The $V$ filter phase diagram for V1116 Cygni using ephemeris (2)}

We have thus confirmed that V576 Herculis and V1116 Cygni are RR Lyrae
stars; the amplitude and the rapid increase in brightness indicates
that both stars are probably of the the RRab type.

{\it Acknowledgements:} MY thanks Massachusetts Space Grant for funding
a summer research fellowship.  We thank Keck Northeast Astronomy
Consortium for supporting Astronomy research at Wellesley College, and
NSF Grant AST9417359 and Wellesley College Brachman Hoffman Research
funds for support of this research. This research has made use of the
Simbad database operated at CDS, Strasbourg, France.

\references

Horne, J. H. \& Baliunas, S. L., 1986, {\it Astrophys.\ J.}, {\bf 302}, 757

Kato, T., 1999, {\it Inf.\ Bull.\ Var.\ Stars}, No.\ 4762

Kato, T., 1999, {\it Inf.\ Bull.\ Var.\ Stars}, No.\ 4764

Kholopov, P. N., 1985, {\it General Catalog of Variable Stars}, Moscow

Space Telescope Science Institute, 1992, {\it The Guide Star Catalog}, Baltimore

\endreferences

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