COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                         Number 3684

                                                 Konkoly Observatory
                                                 Budapest
                                                 28 November 1991

                                                 HU ISSN 0374 - 0676


          Spectral changes in the probable SB 60 Cygni ^1


The probable spectroscopic binary 60 Cyg (=HD 200310) has long been known as a
variable Be star*. Copeland and Heard (1963) mention a double emission at
H beta and H gamma in 1946. According to Hubert-Delplace and Hubert (1979),
the H alpha emission, which remained weak between 1955 and 1958, increased up
to the year 1964. Occasionally, Fe II emissions are seen. Harmanec et al.
(1986), both from light and radial-velocity curves find a most probable period
of 2.48257 days. The energy distribution between 0.33 and 1.06 micrometer is
given by Gunn and Stryker (1983). At that time (most likely in the early
eighties) H alpha is a moderately bright line and the blue part of the spectrum
looks like a rotationally broadened early B-type. The star is classified as
B1.5 IV-Vne by Schmidt-Kaler (1967). Beyond H alpha, observations are very
scarce but on our spectrum obtained in 1965 (Andrillat and Houziaux, 1967),
the double emission at H alpha is the only bright line up to 8800 angstrom;
Paschen lines appear as broad and shallow absorption features. Andrillat et
al. (1988) publish a 1982 spectrum in the same region, which displays "filled
in" Paschen lines.

The spectrum still seemed very stable when we secured a CCD spectrum at 1
angstrom resolution around 1 micrometer in August 1991. However, by the end of
October, the Hydrogen Paschen 7 photospheric absorption line at 1.0049
micrometer had been replaced by an asymmetric double emission (Fig. 1), and
the 0.99978 micrometer Fe II line appeared with the same type of structure.
Further observations in the 0.7 to 0.74 micrometers to 0.878 micrometers
ranges showed the higher members of the Paschen series to exhibit a similar
line profile, i.e. a rather ill-defined double peaked emission (with a ~ 6
angstrom separation), not inconsistent with a ring-shaped emitting region. The
P18 line is severely blended with the neighbouring O I line at 0.8446
micrometer, the maximum of which peaks at 35 percent above the local continuum.
We can also identify neutral nitrogen emission lines at 8629, 8683-86, 8704 and
8714 angstrom, belonging to multiplets 1 and 8. (see Fig. 2). A thirty
minute exposure further to the infrared (1.05 to 1.09 micrometer) did not
reveal any structure either in absorption or emission at the location of the
HeI 1.083 micrometer line.

                               [FIGURE 1]

 Fig. 1. Changes in the 1 micrometer region between August and October 1991.
 Note the strength of the Fe II line at 9997A. The circles denote 
 atmospheric features. 


While such features make the near-infrared spectrum rather unusual, there is
nothing in the blue-violet region (0.39 to 0.5258 micrometer) that distinguishes
the star's spectrum from a bona fide B1.5 type. The He I lines are
strong and rotationally broadened at 4009, 4026, 4121, 4144, 4388, 4471, 4713,
4922, 5015 and 7065 angstrom. Both the triplet and the singlet systems are
well represented and it is quite likely that the undetected first line of the
2s - 2p series is filled-in with emission. However, the presence of Si III, O
II, N II and C II absorption lines in the visible spectrum seems to indicate a
higher luminosity class than the one mentioned by Schmidt-Kaler. The
equivalent width of H gamma points to the same direction. Its value of 3.7
angstrom would better suit to a B 1.5 III-IV star rather than to a
main-sequence object. If such is actually the case, the usually admitted v sin
i value of 320 km/s seems indeed somewhat high.


                                 [FIGURE 2]

 Fig. 2. Spectrum of 60 Cyg in the region of the higher members of the 
 Paschen series. Intensity is on a linear scale. One intensity unit 
 corresponds to 1.42 10^-12 erg cm^-2 s^-1 A^-1


In conclusion, it seems that 60 Cygni has started some time after August a new
emission episode which develops at a rate that has not yet been observed.
Therefore this object deserves a continuing interest from Be star observers,
both photometrically and spectroscopically, especially in the red and in the
infrared.


                  Y. ANDRILLAT, L. HOUZIAUX
                  Observatoire de Haute-Provence

References

ANDRILLAT Y., HOUZIAUX L. 1967 J. Observateurs, 50, 107 [BIBCODE 1967JO.....50..107A ]
ANDRILLAT Y., JASCHEK M., JASCHEK C. 1988 Astron. Astrophys.
   Suppl. Ser. 72, 129 [BIBCODE 1988A&AS...72..129A ]
COPELAND E, HEARD J.F. 1963 Publ. David Dunlap Obs. 2, 11
GUNN J.E., STRYKER L.L. 1983 Astrophys.J. Suppl. Ser. 52, 121 [BIBCODE 1983ApJS...52..121G ]
HARMANEC P., HORN J., KOUBSKY P., BOZIC H. 1986 I.B.V.S. 2912
HUBERT-DELPLACE A.-M., HUBERT H. 1979 Un atlas des etoiles Be, Obs.
   Paris-Meudon
SCHMIDT-KALER TH. 1967 Publ. Astron. Soc. Pacific, 79, 181 [BIBCODE 1967PASP...79..181S ]

1 Based on observations obtained at Observatoire de Haute-Provence (CNRS,
France)
* Its variable star name is V1931 Cyg (the Editor).