COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 4052 Konkoly Observatory Budapest 25 July 1994 HU ISSN 0374 - 0676 THE PERIOD OF AG PHOENICIS HAS DECREASED This study is based upon the photographic times of minimum from the epoch of discovery of the light variation of this system (Strohmeier, 1972) and on the photoelectric times of minimum derived by the author in two observational seasons at CTIO^1 in Chile, during 1979 and 1984 in the UBV and VRI systems, respectively (Cerruti, 1980; 1993). The 'history' of the system comprises about 10000 cycles. The bisection-of-chords method was used for the determination of the UBV times of minima while Kwee and Van Woerden's (1956) algorithm was used with the VRI observations. Standard deviations were assigned to the photographic minima based in the displayed values of the residuals by an unweighted linear least squares fit of these minima. The dispersion used for the photoelectric minima was that of the output of the applied method. In Table 1 are displayed the residuals (O-C) and (O-C)' from two linear least squares solutions between the three epochs of observation. The derived ephemerides are: Min I = HJD 2444170.79581d + 0.75534298d x E (1) +/-0.0048d+/-0.00000051d m.e. Min I = HJD 2444170.79505d + 0.75533906d x E' (2) +/-0.00013d+/-0.00000011d m.e. Figure 1 depicts the behaviour of the residuals for the two solutions. The period decreased by DeltaP/P = -5.2 x 10^-6 in 21 years leading to Pdot/P= -2.47 x 10^-7 per year and an associated time scale of period changes of 4.0 x 10^6 years. ^1 NOAO, operated by AURA Inc. under cooperative agreement with the NSF [FIGURE 1] Figure 1. Behaviour of the O-C residuals for AG Phe form the ephemeris T=HJD 38309.332+0.7553426xE. Filled circles stand for primary minima. Table 1. Times of minima and residuals for AG Phe HJD (sigma) Ref. Min. Band E (O-C) (O-C)' 2400000+ 1 I pg. 38309.3650(0.0300) -7760.0 0.0307 1 I pg. 38315.3690(0.0100) -7752.0 -0.0080 1 I pg. 38318.3690(0.0300) -7748.0 -0.0294 1 I pg. 38340.2920(0.0100) -7719.0 -0.0113 1 I pg. 38614.5280(0.0400) -7356.0 0.0352 1 I pg. 38642.4460(0.0100) -7319.0 0.0055 1 I pg. 38670.3740(0.0200) -7282.0 -0.0142 1 I pg. 38695.3400(0.0300) -7249.0 0.0255 1 I pg. 39053.3500(0.0100) -6775.0 0.0029 1 I pg. 39361.4900(0.0400) -6367.0 -0.0370 1 I pg. 39383.4180(0.0100) -6338.0 -0.0140 1 I pg. 40415.2330(0.0100) -4972.0 0.0025 1 I pg. 40526.3020(0.0400) -4825.0 0.0361 1 I pg. 40823.0930(0.0200) -4432.0 -0.0227 2 I U 43778.7756(0.0003) -519.0 0.0028 0.0015 2 I B 43778.7745(0.0003) -519.0 0.0017 0.0004 2 I V 43778.7749(0.0004) -519.0 0.0021 0.0008 2 I U 43781.7956(0.0009) -515.0 0.0014 0.0002 2 I B 43781.7954(0.0004) -515.0 0.0012 0.0000 2 I V 43781.7957(0.0003) -515.0 0.0015 0.0003 2 I U 43902.6483(0.0010) -355.0 -0.0008 -0.0014 2 I B 43902.6487(0.0003) -355.0 -0.0004 -0.0010 2 I V 43902.6494(0.0003) -355.0 0.0003 -0.0003 2 I U 44170.7948(0.0003) 0.0 -0.0010 -0.0003 2 I B 44170.7949(0.0004) 0.0 -0.0009 -0.0002 2 I V 44170.7951(0.0008) 0.0 -0.0007 0.0000 2 I U 44171.5501(0.0003) 1.0 -0.0011 -0.0003 2 I B 44171.5507(0.0007) 1.0 -0.0005 0.0003 2 I V 44171.5509(0.0003) 1.0 -0.0003 0.0005 2 I U 44173.8144(0.0009) 4.0 -0.0028 -0.0020 2 I B 44173.8157(0.0004) 4.0 -0.0015 -0.0007 2 I V 44173.8161(0.0004) 4.0 -0.0011 -0.0003 2 I U 44174.5721(0.0008) 5.0 -0.0004 0.0004 2 I B 44174.5717(0.0003) 5.0 -0.0008 0.0000 2 I V 44174.5715(0.0004) 5.0 -0.0010 -0.0002 3 I V 45986.6300(0.0004) 2404.0 -0.0002 3 I R 45986.6299(0.0006) 2404.0 -0.0003 3 I I 45986.6297(0.0006) 2404.0 -0.0005 3 I V 45988.8961(0.0006) 2407.0 -0.0001 3 I R 45988.8963(0.0003) 2407.0 0.0001 3 I I 45988.8963(0.0004) 2407.0 0.0001 3 II V 45990.7840(0.0011) 2409.5 -0.0005 3 II R 45990.7855(0.0011) 2409.5 0.0010 3 II I 45990.7861(0.0009) 2409.5 0.0016 1) Strohmeier (1972); 2) 1979 minima; 3) 1984 minima. Because the system is believed to be in an almost semidetached configuration (Cerruti, in preparation) with the less massive component near filling its Roche lobe, the interpretation of this decrease in terms of pure conservative mass transfer is prohibited by theory. For illustrative purposes the term that accounts for a monotonic decrease is dP/dE = -(4.46 +/- 0.58) x 10^-10 obtained from a parabolic least squares fit to the minima. Excluding third body effects the variation might be caused by mass and angular momentum loss from the system, perhaps by stellar wind from the low mass component or by a mechanism to account for alternate period changes in the system (Tout and Hall, 1991; Hall, 1989). Miguel Angel CERRUTI I.A.F.E. CC 67 Suc. 28 1428 Buenos Aires, Argentina miguelangel @ iafe.edu.ar References Cerruti, M.A., 1980, IAU Inf. Bull. Var. Stars, No. 1830 Cerruti, M.A., 1993, IAU Inf. Bull. Var. Stars, No. 3948 Hall, D.S., 1989, Space Science Reviews, 50, 219 [BIBCODE 1989SSRv...50..219H ] Kwee, K.K., Van Woerden, H., 1956, Bull. astr. Inst. Csl., 12, 327 [BIBCODE 1956BAN....12..327K ] [Bull. astr. Inst. Neth.] Strohmeier, W., 1972, IAU Inf. Bull. Var. Stars, No. 610 Tout, C.A., Hall, D.S., 1991, Mon. Not. Royal astr. Soc., 253, 9 [BIBCODE 1991MNRAS.253....9T ]