COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                        Number 3452

                                          Konkoly Observatory
                                          Budapest
                                          18 April 1990

                                          HU ISSN 0374 - 0676


            TV Nor, ANOTHER ECLIPSING Ap STAR

   In a previous paper (Renson and Mathys 1984) the attention of
the spectroscopists has been drawn to a few Ap stars known as 
eclipsing variables. The study of the changes undergone by their spectra
during the eclipses may establish the existence of inhomogeneous
physical and chemical conditions over their surfaces, thus providing
a valuable test of the oblique rotator model. Indeed according to
this model the variations exhibited by an Ap star are explained by
the presence of patches with various chemical abundances and different 
values of the physical parameters, which appear successively
when the star rotates.
   However there is an eclipsing Ap star that was not quoted in
that paper (nor in Renson 1984), i.e. HD 143654. Its Ap nature has
been discovered by N. Houk (1978), who gives for the observed spectral 
type (with quality 1) Ap Eu Cr Sr. But it was already known
as an eclipsing binary long ago. Its variability has been discovered 
by H. van Gent (Kruytbosch 1930). Because its luminosity was
almost always at its maximum value, it was immediately believed
to be an eclipsing variable. By examining this object on hundreds
of plates, E. Hertzsprung (1937) established that the period is

              8.524406 d +/- 0.000017 d.

The data are the following ones, in the same order as in I.B.V.S.
2522, i.e. HD number (A) and other identifications (B), variable
star name (C), coordinates for the epoch 1950 (D and E), magnitude
(F), spectral type (G), period in days (H), depth of the primary
and secondary minima (I and J):

 A           B         C         D        E      F       G          H     I     J
143654  CoD-51 9739  TV Nor  16h00.4m  -51 24'  8.9:  A0 EuCrSr  8.5244  0.6:  0.2:
       =CpD-51 8888

This star is somewhat brighter than the other eclipsing binaries
quoted by Renson and Mathys (1984) and Renson (1984) except 17 Aur.
But 17 Aur belongs to the group of Mn-Hg stars, the spectral 
variations of which are always very small, which implies that there
are no large inhomogeneities over their surfaces. Thus TV Nor is
probably the more suited star for the above mentioned purpose.
  Therefore observers are called on to study in detail this star
and especially the evolution of its spectrum during the eclipses.


                          P. RENSON
                          Institut d'Astrophysique
                          de l'Universite de Liege
                          Avenue de Cointe, 5
                          B-4200 Ougree (Belgium)


References :

Hertzsprung, E., 1937, Bull.Astr.Netherl. 8, 168 [BIBCODE 1937BAN.....8R.168H ]
Houk, N., 1978, "Michigan Catalogue of two-dimensional spectral
           Types for the HD Stars", Vol.2 [BIBCODE 1978mcts.book.....H ]
Kruytbosch, W.E., 1930, Bull.Astr.Netherl. 6, 15 [BIBCODE 1930BAN.....6...15K ]
Renson, P., 1984, Inform.Bull.Var.Stars No. 2559
Renson, P., and Mathys, G., 1984, Inform.Bull.Var.Stars No. 2522