COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1618

                                     Konkoly Observatory
                                     Budapest
                                     1979 June 5



	COMPARISON STAR ADJUSTMENTS FOR THE CEPHEID EU Tau


  EU Tau has become well studied after Guinan (1966) showed that it was
a classical, short period cepheid of type Is. UBV observations include 28
by Szabados (1977), 45 by Wachmann (1976), 139 by Sanwal and Parthasarthy
(1974), and 342 by Guinan (1972). However, the mean V magnitudes of all
four sets of data disagree, in some cases by 0.13m. In addition, Guinan's
results should have one day added to all dates due to an error in his computer
program. Because of the low amplitude of this variable, disagreements of
more than +- 0.02m are obvious when data is combined.      
  The source of error in the mean values stems from magnitude determinations 
for the three common comparison stars. However, no single
comparison star was measured by all four observers. For this reason, all
three comparisons were reobserved, in the course of a survey of short
period cepheids (Henden 1979a), with the 41 cm cassegrain telescope of the
Morgan-Monroe State Forest site of Goethe Link Observatory. Results
were obtained on three nights and were computed differentially with respect
to four standard stars from the Arizona-Tonantzintla catalog (Iriarte, et. al.
1965) : HR 1908, HR 1946, HR 2010, and HR 2047, which spatially bracket
the variable and its comparison stars. The new and previous measures
for the comparison stars are presented in Table 1. By comparison of the
derived magnitudes, the adjustments for each observer have been calculated
and are given in Table 2.

            Table 1.   Comparison Star Magnitudes
           
             BD +18d939                 BD +18d959            BD +18d966

Observer   V      B-V     U-B        V      B-V   U-B       V     B-V     U-B
Guinan     -      -       -          7.72   0.42  0.11    7.90    1.02    0.93
Wachmann   -      -       -          7.60   0.446 0.105   -       -       -
Sanwal     8.41   0.35    0.09       -      - -           7.77    1.09    0.90
Szabados   -      -       -          7.53   0.44  0.17    7.79    1.10    1.04
Henden     8.41   0.339   0.144      7.58   0.460 0.130   7.76    1.084   0.942
(p. e.)    0.02   0.01    0.01       0.02   0.02  0.01    0.02    0.01    0.02


                             [FIGURE 1]

  Figure 1:  EU Tau data after zero point corrections have been made.


Table 2. Corrections to existing Data

Observer   V       B-V     U-B

  Guinan -0.14    +0.05   +0.01
Wachmann -0.02    +0.01   +0.02
  Sanwal +0.00    -0.01   +0.05
Szabados -0.04    -0.01   -0.07


   The combined light curve after adjustments were made is shown in
Figure 1. All data by Henden (1979b), Szabados and Wachmann are included,
along with a random sample of 25 observations each by Sanwal and Parthasarthy
and Guinan. The data is phased according to the light curve elements.

        T_max   = J. D. 2441324.22 + 2.10248d E
         
The scatter has now been reduced to observational error limitations.



                ARNE A. HENDEN
                Department of Astronomy
                Swain West 319
                Indiana University
                Bloomington, Indiana 47401 USA



References:

Guinan, E. F. 1966, Inf. Bull. Var. Stars, n. 170.
	      1972, Publ. astr. Soc. Pacific 84, 56. [BIBCODE 1972PASP...84...56G ]
Henden, A. A. 1979a, Mon. Not. Roy.  astr. Soc. (in press).
	      1979b, in preparation.
Iriarte, B., Johnson, H. L., Mitchell, R. I. and W. K. Wisniewski 1965,
	Sky Tel. 30, 21. [BIBCODE 1965S&T....30...21I ]
Sanwal, N. B. and M. Parthasarathy 1974, Astr.  Astrophys. Suppl. 13, 91. [BIBCODE 1974A&AS...13...91S ]
Szabados, L. 1977, Mitt. Stern. Ungarisch.  Akad. Wiss.,
	Budapest-Szabadsaghegy, n. 70. [BIBCODE 1977CoKon..70....1S ]
					[CoKon No. 70]
Wachmann, A. A. 1976, Astr. Astrophys Suppl.  23, 249. [BIBCODE 1976A&AS...23..249W ]