\documentstyle[epsf,twoside]{article}

\input ibvs2.sty

\begin{document}

\IBVShead{4820}{22 December 1999}

\IBVStitle{Photometry of the HD 187123 Field} 

\IBVSauth{Robb, R.M.$^1$; Cardinal, R.D.; Wagg, J.; Berndsen, A.; Desroches, L.}

\IBVSinst{Guest User, Canadian Astronomy Data Centre, which is operated by
the Herzberg Institute of Astrophysics, National Research Council of
Canada}

\IBVSinsto{Climenhaga Observatory, Dept.\ of Physics and Astronomy, 
University of Victoria, Victoria, BC, Canada, V8W 3P6, 
Internet: robb@uvic.ca}

\IBVSabs{Although HD 187123 has an orbiting planet there are no transits.}
\IBVSabs{We have discovered IRAS19450+3416 to be a new very red long period}
\IBVSabs{variable star.}

\SIMBADobjAlias{HD 187123}{BD +34 3708}
\SIMBADobj{IRAS19450+3416}

\IBVStyp{ cst }
\IBVStyp{ SRA }

\IBVSkey{ stars: individual (HD 187123)}
\IBVSkey{ stars: individual (USNO 1200-13176787)}
\IBVSkey{ stars: individual (IRAS19450+3416)}

\begintext

The star HD 187123 = GSC\,2664\_550 was found to have an orbiting planet
with a period of 3\fday097 and a semi-amplitude of 72 m/s (Butler et al.\ 1998). Anticipating that the star might experience transits of the planet we began photometric observations. The star IRAS\,19450+3416 (Beichman et al.\ 1988) = USNO\,1200--13176787 (Monet et al.\ 1996) was also in the field.

\IBVSfig{6.5cm}{4820-f1.ps}{Finder chart labeled with the GSC
numbers and an `$\ast$' for IRAS19450+3416}

\vskip-22pt
Plotted in Figure~1 is the field of stars observed with the automated 0.5-m
telescope and reduced in a fashion nearly identical to that described in
Robb and Greimel (1999). Due to the brightness of HD 187123 the telescope
was left slightly out of focus and 8 arc second star apertures were used. 
During the 47 nights a total of 8323 frames were observed each with an
exposure time of 42 seconds.

Tabulated in Table~1 are the stars' identification numbers, coordinates
(J2000) and magnitudes from the Hubble Space Telescope Guide Star Catalog
(GSC) (Jenkner et al.\ 1990). The most precise photometry requires that
all parameters be kept constant during a night, from night to night, from
run to run and from year to year. Our data divide naturally into three
runs, fall 1998, summer 1999 and fall 1999. A different flat field was
used for each run and it was found that there were constant offsets from
run to run of about 0.01 magnitudes. Due to this offset we present in
Table 1 the results for the fall 1998 data, which had a smaller standard
deviation from night to night but a larger standard deviation during each
night. Our differential $\Delta R$ magnitudes are calculated in the sense
of the star minus GSC\,2664\_1334. Brightness variations during a night
were measured by the standard deviation of the differential magnitudes
during a night. The best night is tabulated in Table 1 as ``Std Dev
Within". For each star the mean of the nightly means is shown as $\Delta R$
in Table 1. The standard deviation of the nightly means is a measure of
the night to night variations and is called ``Std Dev Between" in Table 1. 
The star IRAS\,19450+3416 had obvious variations from night to night and
is therefore a new variable star.

\begin{table}
\caption{Stars observed in the field of HD 187123 in 1998}
\begin{center}
\begin{tabular}{ccccccc}
\hline
\lower6pt\hbox{GSC No.} & R.A. & Dec. & GSC & $\Delta R$ & Std Dev & Std Dev \\[-3pt]
 & J2000 & J2000 & Mag. & Mag. & Between & Within \\
\hline
2664\_550 & $19\hr46\mm58\sec$ & $+34\deg$25\arcm12\arcs & 7.5 & $-2.137$ & 0.001 & 0.002\\ 
2664\_1334 & $19\hr47\mm08\sec$ & $+34\deg$27\arcm43\arcs & 9.6 & --- & --- & --- \\
2664\_1028 & $19\hr47\mm02\sec$ & $+34\deg$26\arcm30\arcs & 10.1 & 0.415 & 0.003 & 0.003\\
2664\_974 & $19\hr47\mm20\sec$ & $+34\deg$23\arcm55\arcs & 10.8 & 0.947 & 0.002 & 0.004\\
2664\_299 & $19\hr47\mm12\sec$ & $+34\deg$24\arcm11\arcs & 11.8 & 2.488 & 0.002 & 0.008\\
2664\_529 & $19\hr47\mm04\sec$ & $+34\deg$24\arcm43\arcs & 11.9 & 2.070 & 0.003 & 0.008\\
2664\_141 & $19\hr47\mm06\sec$ & $+34\deg$23\arcm42\arcs & 11.8 & 2.506 & 0.003 & 0.010\\
IRAS\,19450+3416 & $19\hr46\mm55\sec$ & $+34\deg$23\arcm35\arcs & 12.7 & 2.209 & 0.052 & 0.008\\
2664\_906 & $19\hr46\mm48\sec$ & $+34\deg$24\arcm18\arcs & 11.9 & 2.335 & 0.004 & 0.009\\
\hline
\end{tabular}
\end{center}
\end{table}

Since star spots or pulsations could cause the observed velocity
variations, we initially observed HD 187123 at all orbital phases.
From Table 1 and the 1999 data we can
see that any such variations must be less than a millimagnitude
and are not likely to be significant.

During some of the nights there remained a trend of about 0.01 magnitudes
from sunset to sunrise, which we attribute to the telescope focus changing
as a function of hour angle. The trend was removed by subtracting a
straight line fit from that night's data. To increase clarity of the light
curve, nine points were then averaged to make a normal point. In Figure 2 we have plotted the normal points near the expected phase of transit with
their errors in the mean and the phases calculated from the period
3\fday096571 and and epoch of Julian Date 2451268.76416 (Marcy 1999). A
line has been added to show the approximate phase, depth and duration of a
transit of a planet of the expected radius. From this plot we can see that
there is no transit of a depth greater than about 0.002 magnitudes,
depending on the assumed duration and phase of the transit. Thus the
orbital inclination must be less than 84\deg, which does not
significantly restrict the estimate of the planet's mass.

\IBVSfig{8cm}{4820-f2.ps}{$R$ band normal points of HD 187123 showing
a prediction of a planetary transit}

\IBVSfig{8cm}{4820-f3.ps}{Nightly means of $R$ band differential magnitudes of star IRAS\,19450+3416}

\vskip-22pt
The variations of the star IRAS\,19450+3416 were not evident during a 
night so the data were combined into nightly means. Since we observed
only three maxima, there is a little ambiguity in the determination of a
photometric period of IRAS\,19450+3416, but the best light curve
as estimated by eye was found using the ephemeris:
$$ {\rm HJD~of~Maxima} = 2451006\fday(5) + 118\fday(5) \times E. $$
An estimate of the uncertainties in the final digit are given in
brackets.

The differential (IRAS\,19450+3416${} - {}$GSC\,2664\_1334) $R$ magnitudes phased at this period are plotted in Figure 3 with +'s and $\ast$'s for 1998 and $\times$'s for the 1999 data. The small run offsets have been ignored for this plot.

The USNO Catalog (Monet et al.\ 1996) gives a $(b-r)=2.3$ for
IRAS\,19450+3416 suggesting that this is a very cool star. On one night a
few frames of this field were observed through the $V$ and $I$ filters. 
Assuming that HD 187123 has $V=7.925$ and $V-I= 0.72$ (ESA 1997), the star
IRAS\,19450+3416 has a $V=14.3$, $(V-R)_c=2.3$ and a $(V-I)_c=4.5$ with an
uncertainty of 0.1 from photon counting errors and as a consequence of the
star's extreme redness at least 0.5 magnitudes for transformation errors.
Ignoring reddening these colors do not match a dwarf star but are correct
for an M8 giant (Th\'{e} et al.\ 1990) at a distance of 3600~pc. Garnavich et al.\ (1994) find $M_I\simeq -2.7$ for M giants of about solar metallicity, giving a distance of $3100\pm1000$~pc.

The star HD 187123 is a star constant in brightness. IRAS\,19450+3416 is
a late-type variable star with a period of 118 days and an amplitude of
0.13 magnitudes. Its very red color, small amplitude, short period and low
galactic latitude hint that it could be a very interesting star. 
Spectroscopic classification and photometric observations would be
valuable to learn the temperature and to look for variations in the period
and morphology of the light curve.

NSERC grants to Ann Gower, David Hartwick and Don VandenBerg provided
partial support for this work.

\references

Beichman, C. A., Neugebauer, G., Habing, H. J., Clegg, P. E., Chester, T.
J., 1988, IRAS Catalogs and Atlases, Version 2. Explanatory Supplement
NASA Ref.\ Publ., 1190 

Butler, R. P., Marcy, G.W., Vogt, S.S., and Apps, K., 1998, PASP, {\bf110}, 1389

ESA, 1997, The Hipparcos and Tycho Catalogues, ESA SP-1200

Garnavich, P., VandenBerg, D., Zurek, D., Hesser, J., 1994, {\it AJ},
{\bf107}, 1097

Jenkner, H., Lasker, B., Sturch, C., McLean, B., Shara, M., Russell, J.,
1990, {\it AJ}, {\bf 99}, 2082

Marcy, G., 1999, private communication.

Monet, D., Bird, A., Canzian, B., Harris, H., Reid, N., Rhodes, A., Sell,
S., Ables, H., Dahn, C., Guetter, H., Henden, A., Leggett, S., Levison,
H., Luginbuhl, C., Martini, J., Monet, A., Pier, J., Riepe, B., Stone, R.,
Vrba, F., Walker, R., 1996, USNO-A1.0, (U.S. Naval Observatory, Washington
DC).

Robb, R.M., Greimel, R., 1999, {\it ASP Conf. Ser.}, {\bf 189}, 198,
CCD Precision Photometry Workshop, ed.\ Craine, E., Tucker, R., and Barnes, J.,
(San Francisco: ASP)
%Changed: Fri Jun  3 09:45:45 MEST 2005

Th\'{e}, P., Thomas, D., Christensen, C., and Westerlund, B., 1990, PASP,
{\bf 102}, 565


\end{document}
