COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 3278 Konkoly Observatory Budapest 30 December 1988 HU ISSN 0374 - 0676 PHOTOMETRIC FLUCTUATIONS IN THE LIGHT CURVES OF R ARAE The southern peculiar bright binary system R Arae (HD 149730A = HJ 4866A, Mv= ~6.5, RA = 16h35m6s; Dec = -56d54' (1950) ) has received more attention in recent years (Nield et al. (1986), Kondo et al. (1985), McClusky et al. (1983), Wolf and Kern (1983). Nield reported some discrepancies in earlier quoted values of the period while pointing out some definite increase of the orbital cycle since the epoch of Hertzsprung (1942). We obtained a new time of primary mid-minimum of HJD 2447386.1200. Again this minimum occurs somewhat later than Hertzsprung's period would predict and a period value of 4.42522 days best describes the interval between Nield's and our current data. Here we wish to call attention to some clear indications of two types of small-scale optical broad-band (Johnson UBV) photometric variations which seem to persist through all phases and times of observations. These were previously discussed by Nield (1987) and are confirmed here. In figure 1, an extensive series of measurements of a check star (HD 150745), against the comparison star (HD 147977) used in our differential photometry is plotted with R Arae using Hertzsprung's ephemeris. This data was collected at the Black Birch outstation of Carter Observatory (New Zealand) over the period April 1986 to September 1988. Some recent improvements to the photometric equipment and its control and data acquisition system have been described by Forbes (1989). Clearly the variations of R Arae are larger than the 'noise' in the check star and so can be confidently considered intrinsic variations of R Arae and not due to atmospheric or instrumental fluctuations. Similar results are also found in the U and B filter measurements. Figure 2 shows R Arae in more detail, with the data from various nights plotted separately. The two types of fluctuations are; a) a variation throughout most nights of ~0.08 mag and on a timescale of order 10 hours (most clearly visible in the out of eclipse regions) b) a fluctuation in the average magnitude level on different nights (corresponding to the same phase) of ~0.15 mag These variations correspond to ~3.5x10^27 Watts and ~6.6 x 10^27 Watts respectively at the source. R Arae is thought to be an interactive eclipsing binary with a (~3.6M_sun) B9 primary and an (~1.4M_sun) F type secondary (cf. Budding (1984). In this picture, the primary is surrounded by some accretion structure formed from material 'falling' from the secondary which is undergoing Roche Lobe OverFlow. The average-period increase since Hertzsprung's Epoch would require a mass transfer rate of ~2x10^-7 M_sun yr^-1 (cf. Nield (1987). An order of magnitude estimate of the power available from this infall gives ~3x10^27 Watts. It is feasible, therefore that the short timescale variations of light level might be associated with irregularities in the rate of infall, perhaps some instability of the flow or accretion structure. [FIGURE 1] [FIGURE 2] The larger scale variation (night to night) cannot however be explained by a RLOF effect. A point to be kept in mind concerning this is the presence of the visual companion (HD 149730B), only 3.6 arc secs away. All photometry hitherto has included this companion but efforts to measure it's relative contribution have been rather error prone. Nield gave an estimate of 30% +- 10%, though a rather lower figure (16%) is quoted in the General Catalogue of Variable Stars (Kholopov (1985), see also Jeffers et al. (1963). The question arises as to whether this companion might be the source of this ~0.15 mag variation. Clearly the proportional effects would have to be large and seem to rule out the possibility of any Alpha2 CVn type variability. No binarity of the companion has been reported, nor does the variability clearly indicate such. Hence the undoubted peculiarities of R Arae remain rather mysterious and we can only urge further observational attention to help resolve some of these problems. MURRAY FORBES Victoria University of Wellington New Zealand and EDWIN BUDDING and JOHN PRIESTLEY Carter Observatory, Wellington New Zealand References: Budding, E., 1984, CDS Bulletin, 27, 91 [BIBCODE 1984BICDS..27...91B ] Forbes, M.C., 1989, M.Sc. Thesis, Victoria University of Wellington (unpub.) Hertzsprung, E., 1942, Bull. Astr. Inst. Netherlands, 9, 277 [BIBCODE 1942BAN.....9..275H ] Jeffers, H.M., van dan Bos, W.H. and Greeby, F.M., 1963, Index Catalogue of Visual Double Stars 1961.0, Part 2, University of California, Publications of the Lick Observatory, 21, 804 [BIBCODE 1963icvd.book.....J ] Kholopov, P.N., 1985, General Catalogue of Variable Stars, "Nauka", Moscow Kondo, Y., McCluskey, G.E., and Parsons, S.B., 1985, The Astrophysical Journal 295, 580 [BIBCODE 1985ApJ...295..580K ] McCluskey, G.E. and Kondo, Y., 1983, The Astrophysical Journal, 266, 755 [BIBCODE 1983ApJ...266..755M ] Nield, K.M., Priestley, J., and Budding, E., 1986, IBVS No. 2941 Nield, K.M., 1987, M.Sc. Thesis, University of Waikato (unpublished) Wolf, G.W., and Kern, J.T., 1983, The Astrophysical Journal Supplement Series 52, 429 [BIBCODE 1983ApJS...52..429W ]