COMMISSION 27 OF THE I. A. U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                             Number 3557

                                                        Konkoly Observatory
                                                        Budapest
                                                        18 January 1991

                                                        HU ISSN 0374 - 0676



                   MISCLASSIFIED RV TAURI STARS

   An RV Tauri variable, according to the definition given in the GCVS
(Kholopov 1985) is a giant or supergiant, and it should have (1) a maximum and
minimum spectral type of F-G and K-M, respectively, (2) a formal period between
30 and 150 days, and (3) its light curve is supposed to show alternating deep
and shallow minima. It is interesting to know if the stars classified as RV
(or RV:) satisfy these conditions.
   Since numerous RV Tau variables have no published photometry or light curve
only the first two conditions (spectral type and period) are considered here.
Table I lists those stars whose spectra, as given in the GCVS, are M-type.
   The extensive spectroscopic surveys of Rosino (1951) and Joy (1952) show
that RV Tau stars have spectral types between F and K (from maximum to
minimum). This result was confirmed later by Preston et al. (1963). There
are, however, two stars with conflicting spectral types: for DY Aql and RV Tau
Joy (1952) gave G5-K0 and G4-K1, respectively, while Preston et al. (1963)
classified them, at certain phases, as M.
   Table II lists those stars whose period is greater than 150 days. The real
upper limit (if there is such) of the periods of RV Tau stars is clearly not
150 days, so stars like QV Aql, RU Hyi, or HZ Sgr could belong to this class.
   There are four stars common in both Tables:  BI Cep, V609 Oph, V794 Sgr, and
LU Sct. These stars are almost certainly not RV Tau variables (Lovell (1989)
published photographic light curves of V794 Sgr showing equal minima but
unequal maxima).
   In conclusion, apart from QV Aql, RU Hyi, and HZ Sgr, all stars listed in
Table I and Table II are probably not RV Tau variables. Since a lot of RV Tau
stars have no period and spectral type given in the GCVS, the number of
misclassifications is certainly higher.


                          Table I

  Star       Spectral type       Star           Spectral type

BI Cep       M5eII               V1541 Sgr      M5
CU Del       M3II                V2342 Sgr      M:
V609 Oph     M6II                V3808 Sgr      M5
V794 Sgr     M3eIa-M4Ia          V3829 Sgr      M3
V1377 Sgr    M2                  GK Sct         M
V1462 Sgr    M5                  KT Sct         M3
V1472 Sgr    M6                  LU Sct         M4
V1486 Sgr    M3


                          Table II

Star         Period              Star           Period
             (day)                              (day)

QV Aql       169.5               CK Lac         279
V786 Ara     200:                KW Lyr         260
BI Cep       212                 V581 Oph       352
EI Cyg       287.6               V609 Oph       195
V1690 Cyg    285                 HZ Sgr         163:
OR Her       210                 V794 Sgr       175.2
RU Hyi       157                 LU Sct         375:




                                         E. ZSOLDOS
                                         Konkoly Observatory
                                         Budapest XII. P.O. Box 67
                                         1525 HUNGARY



References:

Joy, A.H. 1952, Astrophys. J. 115, 25 [BIBCODE 1952ApJ...115...25J ]
Kholopov, P.N. 1985, General Catalogue of Variable Stars (4th ed.), Vol. 1,
      Nauka Publ., Moscow
Lovell, A.J. 1989, J. AAVSO 18, 45 [BIBCODE 1989JAVSO..18...45L ]
Preston, G.W.; Krzeminski, W.; Smak, J.; Williams, J.A. 1963, Astrophys. J.
      137, 401 [BIBCODE 1963ApJ...137..401P ]
Rosino, L. 1951, Astrophys. J. 113, 60 [BIBCODE 1951ApJ...113...60R ]