COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                       Number 2738

                                       Konkoly Observatory
                                       Budapest
                                       30 May 1985

                                       HU ISSN 0374 - 0676





                  IS HD 23878 A MILD CP STAR?


 In a systematic study of rotation and metallicism among early A stars, Conti (1%5) suggested
that HD 23878 (= HR 1181= tau7 Eri, A2V) might be an Am star or a mild CP 
star, according
to its anomalous (low) ratio Sc II lambda 4246/ Sr II lambda 4215. To our knowledge, there have been no
other spectroscopic studies of this star since then, so that its classification could not be secured.
However, Heck (1977) observed the star photometrically and pointed out that, in his sample,
it showed the largest discrepancy in the Stromgren index c1 (0.058) with respect to the value
given by Hauck and Mermilliod (1975). Heck and Manfroid (1980) were subsequently unable to
definitely decide about the suspected photometric variability.
 Yet HD 23878 had been used as a comparison star for the study of photometric variations
in the Stromgren uvby system of the CP star HD 25267 (= tau9 Eri). The 
data, which had been
obtained during two runs at the ESO Danish 50 cm telescope in December 1975 (35 points)
and November 1977 (44 points), were recently reanalysed (Manfroid et al., 1985). 
New careful
reductions of the observations, using the PHOT2 algorithm (Manfroid and Heck, 1983) allowed
to confirm the variability of HD 23878. Nevertheless, in view of its low amplitude (about 0.012
mag peak-to-peak in u, 0.008 in the three other colours) it was kept as a comparison by Manfroid
et al., since the second comparison of HD 25267, HD 24587, was also variable.
 We analysed the data with our programme of period determination based on least-squares
fitting (Manfroid and Mathys, 1985). First, we traced the periodogram for 
each run separately
and then for both together. A periodicity is obviously present and the most likely frequencies
that we derive are:

             f = 0.13945 +/- 0.00015 + n0.00144 d^(-1).

The alias frequencies (1 + f) cannot be definitely ruled out but seem much less probable; 
furthermore, the low projected rotational velocity (v sin i = 30km.s^(-1), 
Uesugi and Fukuda, 1981)
also favours the longer period. In spite of the very low amplitude, we believe that the variations
that we observe are real, because the same frequency appears in all three periodograms.


Another argument is that HD 24587 (for which HD 23878 was used as a comparison) is the only
CP-like variable in Mathys et al.'s recent study (1985) for which the standard deviation of the
least-squares fit is significantly larger than the estimated accuracy of the measurements.
  In conclusion, HD 23878 appears to be a low amplitude variable with a period of about 7.17 d.
As far as one can judge for such small variations, these seem to be similar to those of CP stars.
A new spectroscopic study of this star would thus be very desirable in order to confirm Conti's
suggestion that it is a mild CP star.



                          G. MATHYS
                          Institut fur Astronomie
                          ETH-Zentrum
                          CH-802 Zurich
                          Switzerland


                          J. MANFROID
                          Institut d'Astrophysique
                          5, avenue de Cointe
                          B-4200 Cointe-Ougree
                          Belgium


                          A. HECK
                          Observatoire Astronomique
                          11, rue de l'Universite
                          F-67000 Strasbourg
                          France





References:

Conti, P.S., 1965, Astrophys. J. 142, 1594 [BIBCODE 1965ApJ...142.1594C ]
Hauck, B. and Mermilliod, J.C., 1975 Astron. Astrophys. Suppl. 22, 235 [BIBCODE 1975A&AS...22..235H ]
Heck, A., 1977, Astron. Astrophys. Suppl. 27, 47 [BIBCODE 1977A&AS...27...47H ]
Heck, A. and Manfroid, J., 1980, Astron. Astrophys. Suppl. 42, 311 [BIBCODE 1980A&AS...42..311H ]
Manfroid, J. and Heck, A., 1983, Astron. Astrophys. 120, 302 [BIBCODE 1983A&A...120..302M ]
Manfroid, J. and Mathys, G., 1985, Astron. Astrophys. Suppl. 59, 429 [BIBCODE 1985A&AS...59..429M ]
Manfroid, J., Mathys, G. and Heck, A., 1985, Astron. Astrophys. 144, 251 [BIBCODE 1985A&A...144..251M ]
Mathys, G., Manfroid, J. and Renson, P., 1985, submitted to Astron. Astrophys. Suppl.
Uesugi, A. and Fukuda, L., 1981, Revised Catalogue of Stellar Rotational Velocities [BIBCODE 1981rcsr.book.....U ]