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\begin{document}
\IBVShead{5012}{15 January 2001}
\IBVStitle{NSV 24505: A Semiregular Variable}

\IBVSauth{Lloyd, C.$^1$; Collins, M.J.$^2$; Takamizawa, K.$^3$; Haseda, K.$^4$}
\IBVSinst{Space Science \& Technology Department, Rutherford Appleton
Laboratory, Chilton, Didcot,\\ \indent Oxon.\ OX11 0QX, UK,
e-mail: {\tt cl@astro1.bnsc.rl.ac.uk}}
\IBVSinst{12 The Lawns, Everton, Bedfordshire SG19 2LB, UK,
e-mail: {\tt 101763.3365@compuserve.com}}
\IBVSinst{65-1 Oohinata, Saku-machi, Minami-Saku-gun, Nagano-ken 384-0502,
Japan,
e-mail: {\tt GHA07243@nifty.ne.jp}}
\IBVSinst{2-7-10 Fujimidai, Toyohashi-shi, Aichi-ken 441-8135, Japan,
e-mail: {\tt haseda@mxs.mesh.ne.jp}}

\SIMBADobj{NSV 24505}
\IBVStyp{ SRV }
\IBVSkey{SR variables}
\IBVSabs{Photographic observations of NSV 24505 show it to be a semiregular}
\IBVSabs{variable with a range of about 1.5 magnitudes. From ten years data}
\IBVSabs{a persistent period of 163 day emerges but the star also shows rapid}
\IBVSabs{variations and periods of lower activity.}


\begintext

NSV 24505 (GSC 1578-1162, 18\hr33\mm47\fsec58, +19\deg02\arcm14\farcs7,
$V=11.2$) was found to be variable during the photographic survey
conducted by Collins (1992) as part of the UK Nova Search Programme, and
reported under the name TAV 1831+19, assigned by {\it The Astronomer\/}
group. It is not recorded on the True Visual Magnitude Photographic Star
Atlas but does appear on the Atlas Stellarum. The NSV designation was
given in the recent supplement (Kazarovets et al.\ 1998) on the basis of
Collins' report covering the first three years of observations.
Photographic observations have continued up to the present time and an
analysis of these, together with additional observations by Takamizawa
and Haseda, is presented here.

The variable is the northern component of a close ($\sim 5\arcs$) N-S pair
with the slightly fainter star, GSC 1578-1746 ($V=12.1$). The GSC and
USNO A1.0 catalogues give similar positions but the pair does not appear in
USNO A2.0. The variable is also identified with the weak infrared source
FSC 18315+1859.
%\IBVSindexobj{GSC 1578-1746}

Collins' observations were made with a 135-mm fl $f/2.8$ lens and recorded
on gas hypered Kodak TechPan 2415 film. Takamizawa and Haseda's
observations were both made with 10-cm $f/4$ twin patrol cameras using
Kodak T-Max 400 film. The band pass of all the systems giving
$m_{\rm pv}$ is very broad. The magnitude of the variable was determined by visual
inspection of the films, relative to nearby stars with GSC magnitudes.

The data were analysed using a least-squares sine periodogram, which is
shown in Figure~1. The only significant peaks appear at a period of 163
days and its 1-year and 1-day aliases. A fit to the data with this
period gives an amplitude, $\Delta m \sim 0\fmm7$ which is not
unexpected for a semiregular variable. The phase diagram for this
period is shown in Figure~2. After subtracting this variation from the
data a search for secondary periods revealed nothing. The quantity of
data merits a closer look at the light curve, which is shown in some
detail in Figure~3. Different types of behaviour are clearly visible at
different times. A strong cyclical, pattern consistent with the 163 day
period can be seen (JD $\sim $ 2447600, 2449000) but there are also very
rapid variations, where the whole magnitude range is covered in $\sim
30$ days (JD $\sim $ 2448350, 2449850), and cycles with only marginal
variation (JD $\sim $ 2448000, 2451300).  Recent visual observations
discussed by Collins et al.\ (2001) suggest more rapid variations,
although their extent is difficult to assess.

\IBVSfig{8cm}{5012-f1.eps}{The least-squares sine periodogram of all the
photographic data, showing the relative standard deviation with frequency.
The main feature lies at a period of 163 days, while the second feature is
the 1-year alias. Other than the 1-day aliases there are no significant
features above 0.1 cycles\,day$^{-1}$}

\IBVSfig{8cm}{5012-f2.eps}{The phase diagram of the photographic data folded
with a period of 163 days, with the data of Collins (filled circles and
upper limits), Takamizawa (filled squares) and Haseda (filled triangles)
identified}

\IBVSfig{18cm}{5012-f3.eps}{Light curve of NSV 24505 for 1989--2000,
from the photographic observations. The same symbols are used as in
Figure~2.  Each panel shows 1200 days and the different phases of
cyclical, marginal and rapid variation can be seen. The mean light
curve from Figure~2 has been over plotted}

NSV 24505 is shown to be a semiregular variable with a basic period of
163 days, which has remained viable through over ten years of data.
Significant additional variation in the form of larger and more rapid
variations are superimposed together with periods of reduced activity.
There do not appear to be any significant secondary periodicities.

\references

Collins, M.J., 1992, {\it The Astronomer}, {\bf 29}, No.\ 341, 115

Collins, M.J., Lloyd, C., Jones, C., Takamizawa, K., Haseda, K., 2001, {\it The
Astronomer}, in press

Kazarovets, E.V., Durlevich, O.V., Samus, N.N., 1998,
{\it New Catalogue of Suspected Variable Stars. Supplement -- Version 1.0},
Institute of Astronomy of the
Russian Acad\-emy of Sciences and Sternberg Astronomical Institute

\end{document}

