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\IBVShead{5297}{9 July 2002}

\IBVStitle{The RR Lyrae variable CH O\lowercase{ph} and a new Mira in its field}

\IBVSauth{PASTUKHOVA, E.N.$^1$; SAMUS, N.N.$^{1,2}$; HAZEN, M.L.$^3$}

\IBVSinst{Institute of Astronomy, Russian Academy of Sciences,
48, Pyatnitskaya Str., Moscow 119017, Russia, \\
e-mail: samus@sai.msu.ru}

\IBVSinst{Sternberg Astronomical Institute, 13, University Ave.,
Moscow 119992, Russia}

\IBVSinst{Harvard College Observatory, 60 Garden Str., Cambridge,
MA 02138, USA, \\
e-mail: mhazen@cfa.harvard.edu}

\SIMBADobj{CH Oph} 

\IBVSkey{photometry}


\begintext

The variable star CH Oph was discovered by Swope (1928). Later
the discoverer published a low-quality photographic finding chart
(Swope 1932). The star was never studied in detail, the GCVS
(Kholopov 1985) gives no type for the star and only the
variability range (15.5 to fainter than 16.5 pg).

In our current effort to provide identifications and accurate
coordinates for all stars of the GCVS (cf. Samus et al., 2002),
we are now working on the constellations of the GCVS Volume II.
The variable CH~Oph could not be readily found from its published
coordinates and the finding chart. An attempt to recover the
variable using archive images provided by the US Naval
Observatory Flagstaff Station revealed a variable object not far
from the GCVS position of CH~Oph. However, the positional
difference was larger than usual for variables discovered by
H.H.~Swope in 1920ies. A check in the Harvard plate stacks has
shown that our variable object is not identical with the real
CH~Oph, which was also identified beyond doubt. Figure~1 presents
the finding chart for both variables. The coordinates of the two
stars from the Guide Star Catalogue, Version 2.2.01, are:
$${\rm CH\ Oph} \ \ \ \ 16\hr54\mm03\fsec5, \ \
-27\deg14\arcm45\arcs, \ \ 2000.0;$$
$${\rm New\ var.} \ \ \  16\hr54\mm05\fsec9,  \ \
-27\deg16\arcm47\arcs, \ \ 2000.0.$$

We estimated the brightness of the two variables on 88 plates of
the Moscow collection taken with the 40~cm astrograph in Crimea
(JD~2437109--2448454). We used comparison stars from the Tycho2
and USNO A2.0 catalogs.

CH Oph is an RR~Lyrae (RRAB) star with the elements
$${\rm Max\ Hel}=2447264.573+0\fday561375\times E.$$
It varies between 14\fmm5 and 16\fmm0 $B$. Note that, for this
southern region, the limiting magnitude of our plate collection
is usually between 15\fmm5 and 16\fmm5, so the star is a
difficult object for our plates. Its light curve (Fig.~2) shows a
considerable scatter near minimum.

Our new variable is a Mira, with the variability range from
12\fmm3 to fainter than 16\fmm5~$B$ (Fig.~3). It can be identified with
IRAS~PSC~16509--2711. The star's light elements are
$${\rm Max}=2447740+349\fday4\times E.$$

The GCVS work is supported, in part, by grants from the Russian
Foundation for Basic Research (02-02-16069), the Federal
Scientific and Technological Program ``Astronomy'', and the
program of support for leading scientific schools of Russia
(00-15-96627). The Digitized Sky Survey images are provided by
the Hubble Space Telescope Science Institute under support from
grant NAG W-2166 of the USA Government. Thanks are due to
Dr.~S.V.~Antipin for his assistance during the preparation of the
manuscript.

\vspace*{1cm}

\IBVSfig{7.5cm}{5297-f1.eps}{The finding chart for CH~Oph and the new
Mira variable. The size of the chart is $3\farcm5\times
3\farcm5$. This is a red image of the second Digitized Sky
Survey.}

\vspace*{-0.7cm}

\IBVSfig{7.5cm}{5297-f2.eps}{The $B$ light curve of CH~Oph.}

\IBVSfig{7.5cm}{5297-f3.eps}{The $B$ light curve of the new Mira variable in the field of CH Oph. Triangles are bright limits.}

\references

Kholopov, P.N. (ed.), 1985, {\it The General Catalogue of
Variable Stars}, 4th Edition, {\bf II}

Samus, N.N., Goranskii, V.P., Durlevich, O.V., Zharova, A.V.,
Kazarovets, E.V., Pastukhova, E.N., Hazen, M.L., \& Tsvetkova,
T.M., 2002, {\it Astronomy Letters}, {\bf 28}, 174

Swope, H.H., 1928, {\it Harvard Observatory Bulletin}, {\bf No. 857}

Swope, H.H., 1932, {\it Harvard Observatory Bulletin}, {\bf No. 887}



\endreferences


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