COMMISSION 27 OF THE I.A.U.
               INFORMATION BULLETIN ON VARIABLE STARS
                            Number 1490

                                                      Konkoly Observatory
                                                      Budapest
                                                      1978 October 18


      VARIABILITY AMONG STARS OF SPECTRAL CLASS S!

Stephenson's (1976) "A Catalogue of S Stars" includes 24
that have been classified as S! by either Stephenson (21 stars)
or Sanduleak (3 stars). The comment was made that probably all
stars so classified are variable. Among the 24, eight had 
already been confirmed as variable: 4 Mira, 3 Lb and one SRa. Two
others are contained in the Catalogue of Suspected Variables,
CSV 1356 and CSV 1482. For the regions of two of these not previously
suspected of variability, Nos. 557 and 566 in Stephenson's Catalogue,
plates are available at the Maria Mitchell Observatory. Both stars
prove to be typical Mira type variables.
   For 557 at 18h21m17s -14d45'17", 110 plates spanned the 
interval JD 26889 - 43697, while the only earlier plate on the
region, taken JD 22611, showed the star at maximum. The range of
magnitude is provisionally 13.0 to 15.0 pg. The observations are
satisfied by

              Max = JD2442940 + 398E.


   Star 566 at 18h29m21s -22d42'51" I had some difficulty in
identifying in the crowded Sagittarius field. Dr. Stephenson
therefore kindly supplied me with a finder chart. The star marked
a in Figure 1 appeared to vary slightly but this could have been

                     [FIGURE 1]

 Figure 1. Finder charts, approximately 10' x 10', for Stephenson's
 S! stars, Nos. 557 (left) and 566 (right). The variable star 566
 is a companion about 0.3' north preceding star a. A is BD -14d5054,
 and B is BD -22d4793.

a deceptive effect of the overlapping of adjacent images. The
better of the available plates revealed a companion about 0'.3 N
which was intermittently as bright as a. This normally faint 
companion is presumably the star with the S-type spectrum. Its 
magnitude appears to vary from 14.3 to 15.5 pg. The average color
index for those S! stars for which Stephenson listed both 
photographic arid visual magnitudes is 2.7. Hence the difference between
my photographic magnitude and his visual is reasonable. Among the
600 plates of the region, only 90 showed unblended images. These
observations are represented by

      Max = JD 2443000 + 369E.

Table I. lists the other S! stars which remain to be discovered 
as variable. The visual magnitudes listed are from Stephenson's
Catalogue.


                       Table I

Stars with S!-Type Spectra to be Investigated for Variability.

Stephenson        R.A. (1900) Dec.    m_vis
 Cat. No.
    10          0h38m44s    +63d13'6   12.0
   123          5 52 43     +35 07.5    9.9:
   139          6 08 02     +28 09.6   10.7
   223          7 15 57     - 7 37.2   11.3
   297          8 08 13     -30 56.3   11.8
   359          9 18 27     -42 13.0   12.4
   397         10 22 18     -51 59.2   12.6
   408         10 35 58     -52 41.1   11.6
   489         14 50 53     -63 00.9   11.0
   519         17 13 44     -24 49.0   11.8
   687         21 28 04     +61 07.0   11.8:
   727         23 10 48     +49 46.2   10.6:

   Another star, No. 576 with spectral class S4,2 and identified
as CoD -23d14695, 11.0 mv (CoD mag. 9.6) has been examined on
Nantucket plates without success. The star I have taken to be
CoD -23d14695 is photographically bright, about 11.5 pg. Plates
of better resolving power are required to detect if this star
has a red companion possibly fainter than 13 pg.
   This work was carried out under NSF Grant AST78-07405.


                                DORRIT HOFFLEIT

                                Maria Mitchell Observatory
                                Nantucket, Mass. 02554 U.S.A.



Reference:

Stephenson, C.B. 1976, Pub. Warner and Swasey Obs. Vol. 2 No. 2 [BIBCODE 1976PW&SO...2...21S ]