COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 1716

                                    Konkoly Observatory
                                    Budapest
                                    1979 December 14


              THE NATURE OF V986 OPHIUCHI


The photometric variability of the early type star V986 Ophiuchi (HD 165174, HR
6747, 18 02 05 + 01 55 (1950), Sp O9.5III) is well documented (Jerzykiewicz,
1975) although its true nature and interpretation remain elusive. Photometry
has revealed a dominant variation of amplitude 0.014m in both B and V with a
period of 0.2907m. The amplitude is not constant and whilst its behaviour is
reminiscent of the beat phenomenon seen in some beta Cephei variables,
Jerzykiewicz (1975) was unable to account satisfactorily for his observations
in this way.

In 1978 we obtained both photometric and spectroscopic observations of V986
Ophiuchi. The photometric data are rather sparse but from them we conclude
that the amplitudes of the 0.2907d variation on JD 2443729 in the Stromgren
system were Delta u=0.021m, Delta v=0.017m, Delta b=0.017m and Delta y=
0.015m (each +-0.002m) although the data do not cover a full period. There
are indications that the data obtained on JD 2443732 and 2443733 would require
a period nearer 0.4d.

During seven nights we obtained 53 spectra at a reciprocal dispersion of 15
A/mm using the coude spectrograph of the 1.9 metre reflector at the South
African Astronomical Observatory. The high rotational velocity of this star (v
sin i ~290 km/s, Watson 1972) which is apparent in Figure 1 makes accurate
radial velocity determination difficult. However highly broadened systems have
been successfully investigated (cf Pike. et al. 1978 for investigation of alpha
Trianguli).

                          [FIGURE 1]

   Fig. 1  Part of the spectrum of V986 Ophiuchi. This plot is the intensity
                    summation of nine spectra.

The spectra were measured on a PDS microdensitometer and analysed using the
techniques described by Pike (1977). Fifteen lines including interstellar Ca II
H and K were measured in each spectrum by fitting parabolae to density scans of
the line profiles. The standard error of a single plate using 13 stellar lines
is on average 15 km/s although the error on each nightly mean velocity is
always < 2 km/s. The radial velocities of the interstellar lines are equally
consistent. The errors on individual plates might be expected to mask any
velocity variations associated with the 0.2907d period. However on JD 2443732
a downward trend in the velocities was observed. A free-hand attempt to
reconcile this with a sinusoidal variation of 10 km/s full amplitude and period
of 0.2907d yields a date for the downward crossing of zero relative 
velocity
as JD 2443732.33+-0.01. Photometry was also obtained on this night and shows
maximum light also occurring at JD 2443732.33+-0.01. This follows the
known-relationship between photometric and radial velocity variations of beta
Cephei stars. The velocities on other nights show no significant trends. On
the two other nights for which we have photometry the star was on the
descending branch of the light curve and therefore by the relationship
mentioned above no significant velocity variations would be expected.

                        [FIGURE 2]

   Fig. 2  The nightly mean velocities of V986 Ophiuchi.

We have calculated the nightly mean velocities of V986 Ophiuchi and plotted
these in Figure 2. Radial velocities of this star published by Plaskett and
Pearce (1931) show a very similar range. We conclude that V986 Ophiuchi is
contained in a binary system with a period of approximately 20 days and a total
amplitude 2K ~40 km/s. This interpretation may account for the complicated
light curve by providing for tidally induced effects as described by Fitch
(1969). At this stage our conclusions are tentative but we intend to pursue
the matter in the forthcoming observing season. It is clear that much would be
gained by having observations that cover a longer continuous period than is
possible from one site. We would therefore be pleased to hear from anyone able
to obtain data at a different longitude and who would be willing to collaborate
in observing this star.


C.D. PIKE and C. LLOYD
Royal Greenwich Observatory
Herstmonceux Castle
Hailsham
East Sussex.

References :

Fitch, W.S., 1969 Astrophys. J. 158, 269. [BIBCODE 1969ApJ...158..269F ]
Jerzykiewicz, M., 1975. Acta Astronomica 25, 81. [BIBCODE 1975AcA....25...81J ]
Pike C.D., 1977. Mon Not. R. ast Soc. 184, 265. [BIBCODE 1978MNRAS.184..265P ]
Pike C.D., Lloyd C. and Stickland, D.J. 1978. Acta Astronomica 28, 235. [BIBCODE 1978AcA....28..235P ]
Plaskett, J.S. and Pearce, J.A., 1931. Publ. Dom. Astrophys. Obs. Victoria, 5. 1.  [BIBCODE 1931PDAO....5....1P ]
Watson, R.D., 1972. Astrophys. J. Suppl. 24, 167. [BIBCODE 1972ApJS...24..167W ]