COMMISSIONS 27 AND 42 OF THE IAU
               INFORMATION BULLETIN ON VARIABLE STARS
                            Number 4068

                                                Konkoly Observatory
                                                Budapest
                                                16 August 1994

                                                HU ISSN 0374 - 0676


               DETECTION OF VARIABILITY IN HD 168947

 We obtained two nights of differential photometry of HD 168947. The observations
were done at the 70cm Swiss-telescope at ESO, La Silla. The observers were P. North
and E. Paunzen. The measurements are in the Geneva photometric system (Rufener
and Nicolet, 1988) and the integration time was 3 minutes. In one night (30.06./01.07.)
we observed one comparison star (C1, HD 168287, m_V=7.3, A3m), in the second night
(10.07./11.07.) we observed an additional comparison star (C2, HD 170149, m_V=7.6,
F5IV). Both comparison stars proved to be constant within an upper limit of 0.003 mag
in Geneva-V.
  HD 168947 is a binary star with a B type companion in a distance of 5.5 arcminutes
(Eggen, 1982). Eggen gives a spectral type of A3 II/III. The following calibrations have
been adopted by Stromgren indices (Moon & Dworetsky, 1985):

            T_eff = 7500 K, log g = 3.6, delta m_0 = 0.064

Because of the decreased metallicity and the classification as luminosity-class II/III star,
HD 168947 is a candidate for the lambda Bootis group (Gray,1991) which contains metal weak
A type stars with broad and shallow hydrogen lines. The properties of this group are
described in Weiss et al. (1994). The spectrum of HD 168947 shows a weak lambda 4481 MgII
line, but otherwise the characteristics are normal for early A type stars (Gray, 1994).
Further observations have to prove the membership to the lambda Bootis group.
  The evolutionary status of this group is not clear. In one scenario these stars are at
the end of the ZAMS, in another they are just arriving at the ZAMS. In the first case
diffusion would be the mechanism determining the peculiar abundance pattern, in the
other it would be accretion and/or mass-loss. It is interesting that Eggen suggested that
this star has not yet arrived at the ZAMS.


                             [FIGURE 1]

  Figure 1. The light curve for HD 168947, C1 and C2 for the second night in Geneva V

                             [FIGURE 2]

  Figure 2. Amplitude spectrum for the differential data of HD 168947 and
  HD 168287, the spectral window is inserted


 With the tools of asteroseismology it should be possible to derive the evolutionary
status of stars. We started therefore a survey for pulsation among lambda Bootis stars. Up to
now we found 6 new pulsating stars. For HD 168947 we observed a period of 17.2 c/d (84
minutes) and an amplitude of about 0.026 mag in Geneva-V (see Figure 2). This period is
consistent with an expected period of an A type star arriving at the ZAMS (Stellingwerf,
1979). Figure 1 shows the light curve for the second night for all three measured stars.

Acknowledgement: This research was supported by the Hochschuljubilaumsstiftung der
Stadt Wien.


   E. PAUNZEN
   W.W. WEISS
   Institut fur Astronomie
   Turkenschanzstr. 17
   A-1180 Wien, Austria
   E-mail: PAUNZEN@ASTRO.AST.UNIVIE.AC.AT

   PIERRE NORTH
   Institut d'astronomie de l'Universite de Lausanne
   CH-1290 Chavannes-des-Bois, Switzerland



References:

Eggen, O.J., 1982, ApJ, 258, 605 [BIBCODE 1982ApJ...258..605E ]
Gray, R., 1991, Precision Photometry, ed. Philip, page 309 [BIBCODE 1991ppag.proc..309G ]
Gray, R., 1994, private communication
Moon, T.T., Dworetsky, M.M., 1985, MNRAS, 217, 305 [BIBCODE 1985MNRAS.217..305M ]
Rufener, F., Nicolet, B., 1988, A&A, 206, 357 [BIBCODE 1988A&A...206..357R ]
Stellingwerf, R., 1979, ApJ, 227, 935 [BIBCODE 1979ApJ...227..935S ]
Weiss, W.W., Paunzen, E., Kuschnig, R., Schneider, H., 1994, A&A, 281, 797 [BIBCODE 1994A&A...281..797W ]