\documentstyle {article}
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\IBVShead{4065}{11 August 1994}
\title{Photometry of Stars in the Field of V431 Orionis}
\begintext

     V431 Orionis (= BD+11\degr 755) is a cool carbon star that varies over a 
range of about two magnitudes, becoming as bright as visual mag. 9.  The 
variability was discovered by Morgenroth (1933), who suggested it was a Mira 
variable.  In contrast, observations by Olivier (1959) showed the variations 
to have a period of only 122 days.  He suggested, however, that this period 
is approximate only, and that the variations may be irregular.  I observed a 
number of stars in the field as a check on the existing AAVSO comparison 
sequence, which is based on Olivier's.

     The position of the variable given by Morgenroth is slightly in error.
The star does not appear in astrometric catalogues, but more accurate 
positions can be found in the IRAS catalogue and in the Guide Star Catalogue;
the GSC position is listed in Table 2 below.

     I observed the variable and comparison stars using the Lowell 53cm 
telescope on 30 January and 1 March 1994 UT.  Str\"{o}mgren $y$ and $b$ 
filters were used through a 29-arcsec diaphragm.  Each observation consisted
of at least three 10s integrations on `star' and two 10s integrations on 
`sky', with more integrations for stars fainter than about mag. 9.0.

     The values for the primary and secondary standard stars were taken mostly
from the work of E. H. Olsen, supplemented by the sources listed in Table 1.
Dr. Olsen has supplied revised values for the primary four-color standards
(marked with * by the star name) derived from the original standard-star list
of Crawford \& Barnes (1970).  The ``Lowell'' secondary standards were 
observed on about thirty nights each over several seasons with the 53cm 
telescope directly against primary standards.  Table 1 shows the adopted and 
observed mean V and {\it b--y}, the number of observations `n', and the source
for the standard values.  The stars are sorted in RA order for equinox 2000.
The data in parentheses were omitted from the transformations, mostly involving 
the slightly variable red stars, which are not primary standards.  The mean 
deviations of the observed averages from the assumed values in this group of 
data are:  V = +0.001 $\pm$ 0.006; {\it b--y} = +0.002 $\pm$ 0.006.

     Results for the stars near V431 Orionis are shown in Table 2, sorted in
order of decreasing brightness.  The individual observations of V431 Ori are 
given in the first entry.  The stars are identified by HD, BD, or GSC number;
positions come from the PPM and Carlsberg Meridian Circle astrometric
catalogues or the GSC; spectral types were retrieved from the literature via 
SIMBAD.  The standard deviations of the mean values are given in the second 
line of each entry.  For the single measure of the faintest star, the 
uncertainties (in parentheses) are merely the internal {\it rms} errors on the
batches of integrations and the errors in the fit to the standards taken in 
quadrature.


\vfill\eject
\begin{center}
{Table 1.  Standard Star Observations}\\
\bigskip
\begin{tabular}{lrrcrrcl}
\hline
Name& \multicolumn{1}{c}{V}& \multicolumn{1}{c}{\it b--y}&&  \multicolumn{1}{c}V&  \multicolumn{1}{c}{\it b--y}& n& source\\& \multicolumn{2}{c}{(std)}& &\multicolumn{2}{c}{(obs)}&&\\
\hline
          &       &        &&        &        &   &             \\
HD 11577  & 7.707 &  0.112 &&  7.710 &  0.108 & 1 &  O83        \\
HD 16802  & 7.236 &  0.701 &&  7.235 & (0.720)& 1 &  O83        \\
HD 23324* & 5.665 & -0.022 &&  5.665 & -0.017 & 1 &  O83/CB70   \\
HD 24357* & 5.970 &  0.221 &&  5.973 &  0.225 & 1 &  Nic/CB70   \\
HD 24482  & 8.184 &  1.256 && (8.208)&  1.267 & 3 &  Lowell     \\
HD 26546  & 6.085 &  0.658 &&  6.089 &  0.660 & 1 &  Lowell     \\
HD 27749* & 5.632 &  0.179 &&  5.638 &  0.180 & 1 &  POC/CB70   \\
HD 33021* & 6.165 &  0.397 &&  6.172 &  0.398 & 3 &  POC/O83    \\
HD 35299  & 5.701 & -0.092 &&  5.715 & -0.098 & 1 &  GO76       \\
HD 41143  & 7.757 &  0.720 &&  7.763 &  0.732 & 1 &  GO91       \\
HD 42131  & 7.059 &  0.614 &&  7.061 &  0.620 & 1 &  GO91       \\
HD 42049  & 5.929 &  1.044 && (5.951)&  1.057 & 1 &  HO87/Lowell\\
HD 42398  & 5.821 &  0.683 &&  5.815 &  0.686 & 1 &  Lowell     \\
HD 42824  & 6.627 &  0.019 &&  6.621 &  0.029 & 2 &  GO76/C72   \\
HD 43358* & 6.363 &  0.296 &&  6.368 &  0.298 & 1 &  POC/O83    \\
HD 44974  & 6.524 &  0.571 &&  6.524 &  0.570 & 1 &  Lowell     \\
HD 48805  & 6.497 &  0.543 &&  6.497 & (0.528)& 1 &  O93        \\
HD 52533  & 7.702 &  0.006 &&  7.693 &  0.000 & 1 &  L83/Lowell \\
HD 57006* & 5.915 &  0.339 &&  5.914 &  0.333 & 1 &  GOS/O83    \\
HD 58580  & 6.781 & -0.003 &&  6.780 & -0.008 & 1 &  O83        \\
HD 60803* & 5.902 &  0.376 &&  5.902 &  0.378 & 2 &  O83        \\
HD 73665  & 6.391 &  0.603 &&  6.386 &  0.598 & 3 &  O93/CB69   \\
HD 73666  & 6.619 &  0.005 &&  6.609 &  0.005 & 2 &  \dag /CB69 \\
HD 74721  & 8.715 &  0.029 &&  8.713 &  0.026 & 2 &  AT91/S91   \\
HD 79248  & 6.480 &  0.017 &&  6.490 &  0.017 & 1 &  Nic/C72    \\
HD 85217* & 6.236 &  0.305 &&  6.234 &  0.307 & 1 &  GOS/O83    \\
HD 86238  & 7.272 &  0.815 &&  7.268 & (0.803)& 1 &  Lowell     \\
\hline
\end{tabular}
\end{center}
\smallskip
\dag  V is weighted mean of Sowell \& Wilson (1993) and S91.
\bigskip


     The color of V431 Orionis is extremely far outside the range of the
standards.  The results are thus subject to both `reduction errors' from 
extrapolating the calibrations defined by the standards, and especially 
`conformity errors' from the mismatch of the carbon star spectrum to the
ordinary stars comprising the standards ({\it cf}. Manfroid \& Sterken 1992).
Much of the scatter in {\it b--y} between the two observations arises simply 
from photon-statistical errors in $b$, since the star is nearly mag. 15 in 
that filter.  On the other hand, we are extrapolating the system {\it three 
magnitudes} beyond the reddest standard!

\vfill\eject
\begin{center}
{Table 2.  Photometry of Stars in the Field of V431 Orionis}\\
\bigskip
\begin{tabular}{lcccrrclc}
\hline
Name& \multicolumn{2}{c}{RA  (2000)  Dec}&& \multicolumn{1}{c}{V}& \multicolumn{1}{c}{\it b--y}& n &spec& Remarks \\
\hline
               &           &           &&        &        &    &      &      \\
V431 Ori       & 5\fh15\fmm57\fss7& +11\degr58\farcmm40\farcss&& 10.595 &  4.317 &    & C5,5 &   (1)\\
               &           &           && 10.536 &  4.415 &    &      &   (2)\\
HD 34203       & 5~16~04.1 & +11~20~29 &&  5.535 & -0.002 &  2 & A0V  &   (3)\\
               &           &           &&   .004 &   .001 &    &      &      \\
HD242171       & 5~16~15.4 & +12~12~12 &&  9.080 &  0.314 &  2 & G0   &      \\
               &           &           &&   .002 &   .004 &    &      &      \\
HD242111       & 5~15~51.3 & +12~02~08 &&  9.565 &  0.312 &  3 & A0   &   (4)\\
               &           &           &&   .005 &   .008 &    &      &      \\
BD+11\degr 758 & 5~16~15.1 & +11~50~18 &&  9.619 &  1.414 &  2 &      &   (5)\\
               &           &           &&   .004 &   .008 &    &      &      \\
HD242126       & 5~15~57.7 & +12~02~42 && 10.391 &  0.341 &  2 & F8   &   (6)\\
               &           &           &&   .006 &   .016 &    &      &      \\
GSC 0707-1121  & 5~15~54.0 & +12~05~43 && 12.233 &  1.176 &  1 &      &      \\
               &           &           &&  (.024)&  (.037)&    &      &      \\
\hline
\end{tabular}
\end{center}
\medskip

Remarks:

(1) - = BD+11\degr 755. observation on 30 Jan 1994 UT.

(2) - observation on 1 Mar 1994 UT.

(3) - = HR 1718 = 18 Ori.  V = 5.56 (Oja 1983), {\it b--y} = -0.004 (Crawford 
      et al. 1972).

(4) - = GSC 0707-1127.

(5) - = IRAS 05134+1137 = GSC 0707-1711.

(6) - = GSC 0707-1121.
\bigskip

     For the convenience of observers, a chart derived from the GSC is shown
in Figure 1.  The comparison stars are indicated by their V magnitudes rounded
to the nearest tenth (decimal point omitted) in the style of visual 
variable-star charts.
\smallskip

     Preparation of this report was facilitated by the use of SIMBAD, 
maintained by the Centre de Donn\'{e}es astronomiques, Strasbourg, France.
I appreciate the efforts of Jeff Hall and Doug Loucks in helping me negotiate
the minefield of \LaTeX\ gobbledygook.
\bigskip
\bigskip

\beginauthors
\authorsrightcol
Brian A. Skiff
Lowell Observatory
1400 West Mars Hill Road
Flagstaff  AZ  86001-4499
Internet:  bas@lowell.edu
\endauthors
\bigskip

\references

Anthony-Twarog, B. J., Laird, J. B. , Payne, D., and Twarog, B. A.  1991, 
     {\it Astron. J.}, {\bf 101}, 1902 [AT91].

Crawford, D. L., and Barnes, J. V.  1969, {\it Astron. J.}, {\bf 74}, 
     818 [CB69].

Crawford, D. L., and Barnes, J. V.  1970, {\it Astron. J.}, {\bf 75}, 
     978 [CB70].

Crawford, D. L., Barnes, J. V., Gibson, J., Golson, J. C., Perry, C. L., and
     Crawford, M. L.  1972, {\it Astron. Astrophys., Suppl. Ser.}, 
     {\bf 5}, 109 [C72].

Gray, R. O., and Olsen, E. H.  1991, {\it Astron. Astrophys., Suppl. Ser.},
     {\bf 87}, 541 [GO91].

Gr{\o}nbech, B., and Olsen, E. H.  1976, {\it Astron. Astrophys., Suppl. Ser.},
     {\bf 25}, 213; with revisions from Olsen (priv. comm.) [GO76].

Gr{\o}nbech, B., Olsen, E. H., and Str\"{o}mgren, B.  1976, {\it Astron. 
     Astrophys., Suppl. Ser.}, {\bf 26}, 155 [GOS].

H\"{a}ggkvist, L., and Oja, T.  1987, {\it Astron. Astrophys., Suppl. Ser.},
     {\bf 68}, 269 [HO87].

Landolt, A. U.  1983, {\it Astron. J.}, {\bf 88}, 439 [L83].

Manfroid, J., and Sterken, C.  1992, {\it Astron. Astrophys.}, {\bf 258}, 600.

Morgenroth, O.  1933, {\it Astron. Nachr.}, {\bf 250}, 75.

Nicolet, B.  1978, {\it Astron. Astrophys., Suppl. Ser.}, {\bf 34}, 1 [Nic].

Oja, T.  1983, {\it Astron. Astrophys., Suppl. Ser.}, {\bf 52}, 131.

Olivier, C. P.  1959, {\it Astron. Nachr.}, {\bf 285}, 148.

Olsen, E. H.  1983, {\it Astron. Astrophys., Suppl. Ser.}, {\bf 54}, 55 [O83].

Olsen, E. H.  1993, {\it Astron. Astrophys., Suppl. Ser.}, {\bf 102}, 89 [O93].

Perry, C. L., Olsen, E. H., and Crawford, D. L.  1987, {\it Publ. Astron. 
     Soc. Pac.}, {\bf 99}, 1184 [POC].

Sowell, J. R., and Wilson, J. W.  1993, {\it Publ. Astron. Soc. Pac}., 
     {\bf 105}, 36.

Stetson, P. B.  1991, {\it Astron. J.}, {\bf 102}, 589 [S91].

\vskip2.0cm

Figure caption:
\medskip

Figure 1.  The field of V431 Orionis showing stars from the GSC.  V magnitudes
are indicated to the nearest tenth with the decimal point omitted.
\end{document}
