COMMISSION 27 OF THE I.A.U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                             Number 3225

                                                        Konkoly Observatory
                                                        Budapest
                                                        5 August 1988

                                                        HU ISSN 0374 - 0676


                 Photoelectric Observations of HR 4047

HR 4047 (HD 89343, Sp.T. A7n, V=5.80) was chosen as a comparison star
for VY UMa in the American Association of Variable Star Observers (AAVSO)
photoelectric photometry program. However, it was found in 1986 to be variable
by a few hundredths of a magnitude by Don Pray (Cranston, Rhode Island), and
this result was confirmed in 1987 by Howard J. Landis (Locust Grove, Georgia).
The spectral type and amplitude of the star suggest that it is most likely a
Delta Scuti star.
   An observation program of HR 4047 was therefore undertaken in the summer of
1987 and May of 1988. HR 4215 (Sp. T. A1V, V=6.39) was used as the comparison
star. The use of HR 4021 as a check star was discontinued when the task of
isolating it from a nearby star in the field proved difficult at best. Also
included in the program were the stars HR 4026 and HR 4108 which, on the basis
of their spectral types, might also be Delta Scuti stars but so far have been
found to have little or no short-term variability.
   The observations were taken differentially in the V filter only, with the
University of Toronto's 0.4m reflector, located on the 16th floor of the
McLennan Physical Laboratories in downtown Toronto. The DC photometer used an
EMI 6094 photomultiplier tube which was operated at 1300 volts supplied by a
Keithley Instruments 242 Regulated High Voltage Supply. The signal from the
photometer was amplified by a Keithley Instruments DC Amplifier and the
output was fed into a Vidar 240 Voltage to Frequency Converter. The 10
second integrations were performed by a NOVA computer which also displayed the
results on screen and printed them on paper.
   In all, 22 observations on 5 nights were obtained in 1987 and 64 points on
5 nights in 1988. These will be deposited in the IAU Commission 27 Archive
for Unpublished Photoelectric Photometry (Breger 1988). The precision of the
observations is estimated at > ~0.007 magnitude. This value is the standard
deviation of the HR 4026 and HR 4108 measurements taken on the night of HJD
2447307 and excludes 3 points which lie more than 4sigma from the mean. Of
course, in using the HR 4026 and HR 4108 data, we make the possibly false
assumption that these two stars are non-variable. However, based upon the


                            [FIGURE 1]

 Figure 1. Light curve of HR 4047 for one night of data only.


                            [FIGURE 2]

 Figure 2. Power spectrum of HR 4047 utilizing all 64 points from 1988.


data so far received, this assumption appears reasonable. A value of ~0.007
magnitude is consistent with the precision obtained in other photometric
programs using the same telescope.
   Preliminary analysis of the light curve (e.g. figure 1) and the power
spectrum (e.g. figure 2) of HR 4047 has yielded an amplitude of
approximately 0.05 magnitude and a dominant period somewhere around 0.11 to
0.14 days. However, as can be seen in figure 2, the power spectrum is fairly
complicated and seems to indicate the presence of at least two periods. The
power spectrum was obtained using Scargle's method (Scargle 1982).
   Power spectra of the comparison star have shown a maximum realistic signal
to noise ratio of about 0.4 at a frequency of 12.24, negligible when compared
to HR 4047's maximum peak of 9.416 at a frequency of 9.16 (see figure 2). A
sine wave of frequency 12.24 was fit to the HR 4215 data by the method of least
squares and has given an amplitude of 0.00459. This translates into a maximum
variation of about 0.009 magnitude. Therefore, it appears that HR 4215 is not
variable and any small peaks seen in its power spectrum can be attributed to
noisy data.
   Clearly there is a danger of over-interpreting the results obtained from so
few points. It will probably take many closely-spaced nights of observations
(preferably from observatories at widely-spaced longitudes) to disentangle
the periods in this star.
   Acknowledgments: We thank the Natural Sciences and Engineering Research
Council of Canada for financial support in the form of an Undergraduate Student
Research Award to R.P. and an Operating Grant to J.R.P. We also thank AAVSO
photoelectric observers Don Pray and Howard J. Landis for informing us of the
results of their observations, and Alex Fullerton for providing the power
spectrum program.


                 RENE PLUME, JOHN R. PERCY

                     Dept. of Astronomy
                    University of Toronto
                     60 St. George street
                       Toronto, Ontario
                       CANADA, M5S 1A7



References:

Breger, M., 1988, Publ. Ast. Soc. Pacific, 100, 751. [BIBCODE 1988PASP..100..751B ]
Scargle, J.D., 1982, Astrophys. J., 263, 835. [BIBCODE 1982ApJ...263..835S ]


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