COMMISSION 27 OF THE I. A. U
       INFORMATION BULLETIN ON VARIABLE STARS
                    NUMBER 248

                                     Konkoly Observatory
                                     Budapest
                                     1968 January 15


                      DH CARINAE


The first known flare star, DH Carinae, was discovered by E. Hertzsprung in
1924 (1), when a flare of 1.^m8 was observed. Further flares of this star have
not been observed. The spectral type of the star is undetermined. At the
suggestion of A.H. Joy, a direct red plate of the star was taken by M. Bester
at the ADH telescope of the Boyden Observatory using 103a-E emulsion and W25A
filter, in order to estimate its colour. Identification from Hertzsprung's
chart is difficult owing to the presence of a nearby companion which is not
indicated by him and which is photographically brighter. The Boyden red plate
shows, however, that the more northerly star of the pair is much redder, and
undoubtedly this is Hertzsprung's star since all confirmed flare stars are red
dwarfs earlier than about K0. Blue and ultraviolet plates were also taken at
Boyden and an approximate B and U sequence was transferred to the region of DH
Carinae from H. Schmidt and G. Diaz Santanilla's sequences in NGC 3590 and Tr
18 (2). See Fig. 1.


                              [FIGURE 1]

         B          U
a      13.^m15    14.^m85
b      14.95      15.55
c      15.05      15.25
d      15.30      15.55
e      15.50      15.60
f      15.55      15.55
g      16.20      16.15
DH     16.00      16.10

The observed redness is in accordance with the colour index (2.^m7) from Joy's
visual magnitude for the star of 12.2 (3) and the photographic magnitude of
14.9 in the Kukarkin-Parenago Catalogue of Variable Stars. Judging from all
the plates the southerly companion (star f) is approximately of type A
(U-B~0.^m0), whilst DH Carinae itself appears to show a large ultraviolet
excess for such a red star (U-B~0.^m1). This conforms, however, with
observations of several flare stars by E. Mendoza an the Orion I Association
(4) and not with those in the solar neighbourhood. It will be noticed that DH
Carinae appears one magnitude fainter in the standard B system than the
photographic magnitude, and this is probably partly accounted for by the strong
ultraviolet excess of the star and the ultraviolet cut-off of the B filter.
Accurate multicolour photometry and proper motion studies would be interesting
for this star.


Armagh Observatory,
January 4, 1968
                                              A.D. ANDREWS

References

1) E. Hertzsprung, B.A.N. Vol.2, 87 (1924). [BIBCODE 1924BAN.....2...87H ]
2) H. Schmidt and G. Diaz Santanilla, Veroff. Ast. Inst. Univ. Bonn Nr. 71
   (1964). [BIBCODE 1964VeBon..71....1S ]
3) A.H. Joy, Stars and Stellar Systems Vol.6, 667 (Univ. Chicago Press, 1960).
4) E. Mendoza, Astroph. Journ. Vol.143, 1010 (1966). [BIBCODE 1966ApJ...143.1010M ]