COMMISSION 27 OF THE I. A. U.
                  INFORMATION BULLETIN ON VARIABLE STARS
                              Number 2460

                                                      Konkoly Observatory
                                                      Budapest
                                                      16 January 1984

                                                      HU ISSN 0374-0676




           ON THE delta Sct-LIKE VARIABILITY OF THE Ap STAR HD 10088



  The Ap star HD 10088 (BD +21d224, SAO 74848, sp = A0, m_v = 7.9) was found
by Weiss (1983) to exhibit light variations characteristic of delta Sct variables.
This group of Ap stars with delta Sct characteristics is described by Kurtz
(1982 a). Weiss found a period of about 1d29m and an amplitude of about
0.03m in Stromgren v on two nights. Efforts were undertaken to obtain additional
photometry.
  Photometry was carried out on several nights using Lowell Observatory's
1.1 m and 0.8 m telescopes, employing either a single-channel or dual-channel
photometer and electronically cooled EMI tubes. Three integrations of either
10 or 15 sec were obtained on the program star, followed by an equivalent
number on the comparison star. This produced an equal number of observations
for each star. The comparison star used was HD 9985 (BD +20d261, SAO 74837),
which is classified in the SAO catalog as sp = A0, m_v = 8.0, and lies only
about 1d from HD 10088. The means of the data triplets were first formed. The
differential photometry was obtained by subtracting from HD 10088 the 
interpolated values from a spline fit through the HD 9985 data. The resulting
values are plotted in relative differential magnitudes, as shown in the
Figure. No corrections were made to heliocentric time.
  There appears to be no evidence of variability in any of the data sets.
However, it is perhaps not entirely surprising, as the coming and going of
variability in delta Sct stars has been well known for some time (Danziger and
Dickens, 1967), and may be due to destructive interference of two or more
frequencies (Wehlau and Leung, 1964, Fitch and Wehlau 1965). To see a similar
phenomenon in an Ap star would strongly support Kurtz' assertion that at least
some of the Ap stars showing short-period variability might be delta Sct stars
(Kurtz, 1982 a, 1982 b). HD 10088 might be just on the edge of the instability
strip, and may, therefore, only occasionally show pulsational instability.

                             [FIGURE 1]

         Figure 1   Differential mag. (HD 10088 - HD 9985)

 Additional monitoring of HD 10088 is desirable to see over what time spans
variability _is_ present. If this star pulsates infrequently, a great deal of
effort may be necessary to detect it in an active state.



                 TOBIAS J. KREIDL

                Lowell Observatory
                P.O. Box 1269
                Flagstaff, AZ 86002
                U.S.A.

References:

Danziger, I.J. and Dickens, R.J. (1967) Ap. J. 149, 55 [BIBCODE 1967ApJ...149...55D ]
Fitch, W.S. and Wehlau, W. (1965) Ap. J. 142, 1616 [BIBCODE 1965ApJ...142.1616F ]
Kurtz, D.W. (1982 a) MNRAS 200, 503 [BIBCODE 1982MNRAS.200..807K ]
Kurtz, D.W. (1982 b) MNRAS 200, 807 [BIBCODE 1982MNRAS.200..503K ]
Wehlau, W. and Leung, K-C. (1964) Ap. J. 139, 843 [BIBCODE 1964ApJ...139..843W ]
Weiss, W.W. (1983) Astron. and Astrophys. 128, 152 [BIBCODE 1983A&A...128..152W ]