DW Cnc and others

(vsnet-chat 209)

Tonny Vanmunster wrote in [vsnet-chat 208]:

>>Selected CCD results:
>>0000+00      DW CNC     2450523.3243   1997-03-15   0.8243      14.4, is
>>this an outburst ?
>It probably is. The star is catalogued as an UG cataclysmic variable with
>a magnitude range of 15v - 17.5v. Past outburst observations list maximum
>magnitudes around mag 14.5 (CCD unfiltered). Recurrence time of this
>poorly studied object seems to be rather short, although I have not been
>able to derive an exact value. Maybe Taichi Kato has more information on
>DW Cnc (discovery paper, ...) ?

DW Cnc (=SVS 2424) was discovered by J. A. Stepanian (Perem. Zvezdy 21, 691, 1982) in the course of a search for UV-bright galaxies at Byurakan. The follow-up spectroscopic study revealed the presence of doubly peaked emission lines of hydrogen, HeI, HeII and CaII. Photometrically, following estimates were listed.

    2440920   17.5
      41003   17
      42804   15
      43222   16.5
      43607   16
      43608   15.5
      43637   17.5
      43952   16.5
      43956   16
      43961   15.5
      43963   15

The star was then studied by I. M. Kopylov et al. (Astrophysics 28, 168, 1988). In the description of DW Cnc = FBS 0756+164 they wrote: "The lines of the hydrogen series are moderately broad. The Balmer decrement is very gentle. The line He II 4686 is rather weak, about twice as weak as He I 4471 and about ten times weaker then H beta. The line Ca II (K) is observed in emission. Numerous weak shell lines of low excitation (Fe II et al.) are observed. The object may be classified as adwarf nova."

Makoto Iida (VSOLJ) once communicated that he suspected this star to be a Z Cam star based on his CCD measurements.

This article by I. M. Kopylov et al. is interesting in that this FBS survey includes both famous and neglected CVs. Examples:

                (1950.0)    mag      their classification    present
FBS 0022-021  002224 -0210  15       dwarf nova
FBS 0107-082  010706 -0814  15       novalike
FBS 0756+164  075606 +1625  15-17.5  dwarf nova
FBS 0948+343  094842 +3421  14-17    A5-A7V           = RZ LMi, peculiar DN
FBS 1031+590  103100 +5903  14.5-15  polar            = DW UMa, NLAD+E
FBS 2320+181  232036 +0108  13-18.5  dwarf nova, IP Peg
FBS 2351+228  235118 +2252  15-16    recurrent nova? (*1)

(*1) FBS 2351+228 shows both TiO bands (M-type spectrum) and H alpha in emission. The authors state the spectrum resembles T CrB and RS Oph at minimum.

Taichi Kato

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