COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1672 Konkoly Observatory Budapest 1979 September 14 SH 2-71: NEW VARIABLE CENTRAL STAR OF A POSSIBLE PLANETARY NEBULA Nebula Sh 2-71 (36-1d1) was discovered by Minkowski (1946) who classified it as a diffuse or peculiar nebulosity. Sharpless (1959) included this object ( AR_1950 = 18h59m28.0s, D_1950 = +2d04'56" - Milne, 1973) in his catalogue of H II regions and considered it as a possible planetary nebula. Our UBV photoelectric photometry from 1977, 1978 and 1979 shows the nucleus of this very little known nebula to be variable with an amplitude of at least 0.7 mag. [FIGURE 1] Fig. 1 Finding chart for the central star of Sh 2-71 (V) and for comparison stars a, b, c Our measurements of the planetary central star during eight nights are presented in Table 1. We observed in 1977 with the 1 m-telescope and a pulse counting photometer (RCA 8850 photomultiplier) of the Wise Observatory at Mitzpe Ramon, Table 1 UBV observations of Sh 2-71 in 1977-1979 JD V B U Dia. m 2443000+ (arcsec) pg 364.2986 13.96 14.71 15.09 14.5 14.66 .3070 13.89 14.67 15.06 21.8 14.68 .3143 13.95 14.74 15.08 14.5 14.69 .3229 13.93 14.69 14.99 21.8 14.70 365.3140 13.92 14.74 15.10 14.5 14.69 .3238 13.81 14.63 15.00 21.8 14.64 .3321 13.92 14.73 15.04 14.5 14.68 .3488 13.80 14.56 14.96 21.8 14.57 607.8724 13.24 14.03 14.40 22 14.04 .8771 13.27 14.09 14.44 16 14.04 608.8700 13.38 14.20 14.61 22 14.21 .8750 13.39 14.24 14.64 16 14.19 609.8381 13.45 14.22 14.63 22 14.23 .8404 13.43 14.22 14.61 22 14.23 .8454 13.45 14.26 14.72 16 14.21 .8829 13.51 14.31 14.80 22 14.32 .9034 13.45 14.29 14.74 16 14.24 963.8831 13.73 14.55 14.85 22 14.56 .8906 13.77 14.59 14.92 16 14.54 964.8806 13.77 14.55 14.94 22 14.56 .8892 13.81 14.61 14.99 16 14.56 965.8898 13.82 14.62 14.96 22 14.63 .8992 13.84 14.67 15.09 16 14.62 Israel. In 1978 and 1979 we used the 1 m-telescope and a pulse counting photometer (EMI 6256) of the European Southern Observatory at La Silla, Chile. As photometric standards we measured in 1977 the stars near IC 4665 (Johnson, 1954) and in several open clusters (Hoag et al., 1961), and in 1978-79 stars in E-regions (Cousins, 1973). The following standard deviation can be expected for the individual magnitudes given in Table 1: sigma_V = 0.03m, sigma_B = 0.03m, sigma_U = 0.04m. Several local standards in the vicinity of Sh 2-71 were observed in order to investigate the interstellar extinction in this region. The photometrical results will be published in a separate paper in more detail. In Table 2 we give the magnitudes and their r.m.s. errors of three comparison stars together with the average UBV magnitudes of the central star of Sh 2-71 for 1977, 1978 and 1979. Whereas the stellar magnitudes in Table 1 were affected by the nebula, the data in Table 2 represent the brightness of the central star only. We have eliminated the contribution of the nebula by comparing the stellar + nebular brightness Table 2 Mean UBV magnitudes of the central star of Sh 2-71 and of three comparison stars Star V B-V U-B n Sh 2-71 in 1977 13.95 +0.82 +0.36 8 +-2 +-1 +-1 m.e. 1978 13.45 +0.85 +0.41 9 +-3 +-1 +-2 m.e. 1979 13.85 +0.84 +0.36 6 +-1 +-1 +-2 m.e. Comparison a 11.400 +0.747 +0.239 4 +-2 +-2 +-5 m.e. b 13.169 +0.921 +0.630 10 +-9 +-5 +-15 m.e. c 13.944 +0.799 +0.222 4 +-10 +-3 +-8 m.e. in two different diaphragms assuming that the nebula was homogeneous near the central star. The variability of the nucleus of Sh 2-71 was confirmed on 28 plates (1897 - 1947) found in the plate files of the Harvard Observatory. Table 3 gives the visual estimates of the Table 3 Photographic magnitudes of the central star of Sh 2-71 from Harvard plates Plate No. JD m_pg Plate No. JD mpg 2400000+ 2400000+ A 2572 14129.626 14.36 MC 21990 24686.756 14.10 A 2573 14129.658 14.30 MC 22525 25009.827 14.30 A 4443 15179.661 14.46 MC 22558 25037.759 14.32 A 10451 19241.696 13.96 MC 22649 25110.585 14.44 A 10460 19249.709 14.38 MC 22702 25147.526 14.00 MC 1226 19268.588 14.52 MC 23442 25408.771 13.96 A 10488 19292.584 13.82 MC 23500 25443.656 14.63 MC 1265 19293.541 13.82 MC 23596 25479.575 13.88 A 10493 19299.580 14.24 MC 24328 25796.753 14.63 MC 5706 20301.763 14.44 MC 24391 25826.629 14.10 MC 6407 20397.525 13.99 MC 24990 26155.713 14.29 MC 8861 20696.694 14.63 MC 35473 32379.773 14.33 A 13526 24404.619 13.90 MC 35477 32380.750 14.36 MC 21956 24670.753 13.84 MC 35493 32387.745 14.63 photographic magnitudes of this star: the internal error of one estimate lies between +-0.05 and 0.1 mag. In order to compare the values from Table 3 with the photoelectric observations from 1977-1979 we transformed our observed B magnitudes into m_pg (see last column in Table 1): m_pg = B_* - 0.11, where B_*=B + 0.06 was found for observations made through diaphragm 14.5 and 16 arcsec, and B_* = B + 0.12 for dia. 21.8 and 22 arcsec. The following conclusions can be made concerning the variability of the central star of Sh 2-71: 1) The extreme values of mpg from Harvard plates, 13.82 and 14.63, suggest an amplitude of about 0.8 mag. The UBV data from 1977-1979 show a value somewhat lower (about 0.7 mag),but very probably they do not cover the whole light-curve. 2) The existing data do not allow to describe the shape of the light-curve. Nevertheless, the distribution of the individual values of Table 3 favours a smooth sine-like curve. 3) According to the UBV data the period should exceed two days substantially as only a change of about 0.2 mag has been recorded within two days. We could estimate P between 17 and 22 days from the photographic data. Our observations, however, cannot exclude short periods between about 0.5 and 1 day. 4) There is no evidence for a secular change in the brightness of the central star. The mean value of its photographic magnitude was 14.24 from 1897-1915, and 14.23 from 1925-1947. In 1977-1979 we observed mpg = 14.46, but this lower mean brightness can be explained by an unequal distribution of the observed data. The observed central star of Sh 2-71 cannot be responsible for the radiation of the surrounding nebula. The nebula is of very high-excitation (Glushkov et al., 1975) and the presence of He II lambda4686 emission line in its spectrum requires a radiation source of T_* >~ 60000degK. On the other hand, the mean colours of the central star, B-V = 0.84, U-B = 0.38, lead to spectral type B8 (and to visual interstellar absorption AV = 3.2 EB-V = 3.0). This contradiction can be explained, as in case of some other planetary nebulae (NGC 1514, NGC 2346, NGC 3132, He 2-36), using a binary hypothesis for the central star: the visible B8 star should be accompanied by a hot sub- dwarf. The observed light changes of Sh 2-71 support this consideration. This study is only preliminary. More photometric observations are planned in order to obtain the complete light-curve of Sh 2-71. I acknowledge the Wise Observatory of Tel Aviv University and the Smithsonian Research Foundation Grant SFC-0-3005 for the use of their facilities at Mitzpe Ramon, Israel. A part of the observations has been collected at the European Southern Observatory., La Silla, Chile. My thanks are also due to the Directorate of the Smithsonian Astrophysical Observatory, Cambridge, Mass. for the possibility to investigate Harvard plates, and to Dr. Martha Liller for her valuable help. L. KOHOUTEK* Hamburger Sternwarte D-2050 Hamburg 80 BR Deutschland * Visiting astronomer, The Florence and George Wise Observatory, Tel Aviv University, Israel Visiting astronomer, European Southern Observatory, La Silla, Chile References: Cousins, A.W.J., 1973, Mem.Roy.Astron.Soc. 77, 223 [BIBCODE 1973MmRAS..77..223C ] Glushkov, Y.I., Denisyuk, E.K., Karyagina, Z.V., 1975, Astron. Tsirk. USSR No. 852 [BIBCODE 1975ATsir.852....3G ] Hoag, A.A., Johnson, H.L., Iriarte, B., Mitchell, R.I., Hallam, K.L., Sharpless, S., 1961, Publ. US Naval Obs. Second Ser., Vol. XVII, Part VII [BIBCODE 1961PUSNO..17....1H ] Johnson, H.L., 1954, Astrophys.J. 119, 181 [BIBCODE 1954ApJ...119..181J ] Milne, D.K., 1973, Astron.J. 78, 239 [BIBCODE 1973AJ.....78..239M ] Minkowski, R., 1946, Publ.Astron.Soc.Pacific 58, 305 [BIBCODE 1946PASP...58..305M ] Sharpless, S., 1959, Astrophys.J. Suppl. 4, 257 [BIBCODE 1959ApJS....4..257S ]