COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 590 Konkoly Observatory Budapest 1971 October 26 NOTE ON LMC VARIABLE STARS Paul W. Hodge and Frances W. Wright September 1971 Smithsonian Institution Astrophysical Observatory Cambridge, Massachusetts 02138 NOTE ON LMC VARIABLE STARS Of the 53 LMC variables studied by us in Region 35 (Hodge and Wright 1969, Paper 1; Wright and Hodge 1971, Paper 2), 36 have also appeared in the massive study published by Payne-Gaposchkin (1971). It is unusual to have so many stars common to different studies in the Magellanic Clouds, and it is particularly important, therefore, that a comparison be made so that previous suspicions of systematic errors - those due, for example, to selection effects - be checked. This note compares results and draws what conclusions seem reasonable. 1. Cepheids ----------- Periods. Table 1 compares data for the 24 Cepheids common to the two surveys and gives period differences, which are quite small except for 3 cases (Fig. 1). The differences are probably due primarily to the fact that our study includes additional, more recent series of plates, the 1958-59 AHD and the 1969 CTIO series. Furthermore, we had plates in two colors, which provided additional aid in the photometry. The differences (Fig. 1) have a mean of 0.043 X 10^-3; three-quarters of the cases are less than this mean value. Three others are less than twice this value, while three have a larger difference. In the case of HV 5684, Wright and Hodge (1971) could obtain a fit of all observations only with a changing period. Amplitudes. The differences in amplitudes for the Cepheids are plotted in Fig. 2. There is a tendency for our data to show larger amplitudes than do the Payne-Gaposchkin data, by as much as 0.5 mag for a few cases. The reason apparently lies in the methods of measurement and reduction. An amplitude that is too small can result from a slightly incorrect period from less precise measurements or from an averaging interval that is too large; an amplitude that is too large can result from an averaging interval that is too small. Future photoelectric measures will surely demonstrate which of these factors is responsible for the differences. In the meantime, it is clear that amplitudes from either survey should be used with reservation. Mean magnitudes. Fig. 3 shows the differences found in the mean B magnitudes for the Cepheids. To transfer our magnitudes to the Payne-Gaposchkin system, we have applied her absorption corrections before plotting our data in Fig. 3. The differences show no significant systematic trends and are not inconsistent with the quoted absolute photometric uncertainties of the two studies. There is some indication of her magnitudes being somewhat (~ 0.1 mag) fainter at the faint end (around 16.5) and brighter for the two brightest variables (around mag 13). 2. Other Variables ------------------ For four of the non-Cepheid variables, our conclusions were significantly different. We have assembled these in Table 2. We reported HV 2379 as "semiregular," while Payne-Gaposchkin termed it a long- period variable at 355 days. We have reviewed our 524 measures of this variable and still classify it as semiregular. As we noticed previously, it does show cyclic variation over 200 or 300 days, with irregularity. Its (B) - (V) of ~ 3.7 indicates an N variable typical of the semiregular type. It might even be classified as irregular. It in certain that 355 days does not fit all our observations reasonably. No period was given by Payne-Gaposchkin for HV 5715. Our period of 421 days fits our observations well, although there is more scatter in magnitude than usual; a slightly longer period, of 422.9 days, fits all the earlier observations more exactly. Hence, there seems to be some irregularity, either in period or in magnitude. The mean light curve is shown in Wright and Hodge (1971, Fig. 12). Classified as red irregular by Payne-Gaposchkin, HV 5654 is, according to our analysis, a V Hydrae-type variable, with one period around 2400 days and another of about 400 to 600 days. Individual observations are shown in Fig. 13 of Wright and Hodge (1971). For HV 2360, our observations and analysis show more irregularity than indicated by Payne-Gaposchkin in her classification "long period of 790 days." Except for one instance where the interval between successive maxima is 500 days (from JD 2423000 to 2433000), the period of HV 2360 varies between 600 and 900 days, with an accompanying variation in range, as shown in our individual observations (Wright and Hodge 1971, Fig. 14). For the W Virginis variable HV 2351, we have a changing period (Hodge and Wright 1969), while Payne-Gaposchkin has a constant one. For the R Coronae Borealis variable HV 5637, there is reasonable agreement in magnitude. Finally, for the four eclipsing stars common to the two studies, the period differences (listed at the end of Table 1 and shown graphically in Fig. 1 by triangles) are extremely small. Paul W. Hodge University of Washington Seattle, Washington and Smithsonian Astrophysical Observatory Cambridge, Massachusetts and Frances W. Wright Smithsonian Astrophysical Observatory and Harvard College Observatory Cambridge, Massachusetts References: Hodge, P. W., Wright, F. W. 1969, Studies of the Large Magellanic Cloud. X. Photometry of variable stars, Astrophys. J. Suppl. Ser. 153, 17, 467-490. [BIBCODE 1969ApJS...17..467H ] Payne-Gaposchkin, C. H. 1971, The variable stars of the Large Magellanic Clouds, Smithsonian Contr. Astrophys., No. 13, 41 pp. [BIBCODE 1971SCoA...13.....P ] Wright, F. W., Hodge, P. W. 1971, Further studies of variable stars of the Large Magellanic Cloud, Astr. J., 76 (in press). [BIBCODE 1971AJ.....76.1003W ] Table 1 Differences in period ------------------------------------------------------------ Period Differences (to 3 decimal (Hodge and Wright - Differences HV places) Payne-Gaposchkin) as % of period no. (days) (X 10^-6) (X 10^-3) ------------------------------------------------------------ 24 Cepheids --------------- 2315 2.413 +125 +0.052 2391 2.482 00 000 5684 2.788 ~ +360 +0.129 5567 2.794 - 27 -0.010 W48 3.113 - 13 -0.004 12972 3.165 + 02 +0.001 W47 3.193 + 32 +0.010 2355 3.622 - 26 -0.007 2375 3.636 - 63 -0.017 11987 3.665 + 51 +0.014 5656 3.727 00 000 2287 3.784 - 29 -0.008 5591 3.968 + 55 +0.014 5643 4.112 - 01 -0.000 5586 4.317 +373 +0.086 5579 4.461 - 63 -0.014 12979 4.510 + 21 +0.005 12974 4.654 - 83 -0.018 2420 9.035 + 10 +0.001 5543 9.048 + 50 +0.006 2299 12.063 - 60 -0.005 5594 17.202 -1180 -0.069 2294 36.536 +5000 +0.137 2369 48.287 +20020 +0.415 4 Eclipsing Stars ----------------------- 2374 28.494 0 000 2401 2.945 + 4 +0.001 2403 1.312 + 6 +0.012 5549 6.066 -73 -0.012 ---------------------------------------------------------- Table 2 Four non-Cepheid variables ---------------------------------------------------------------------------------------------------- Payne- Hodge and Wright Gaposchkin Payne- Payne- period period Hodge and Wright Gaposchkin Hodge and Wright Gaposchkin HV no. (days) (days) amplitude amplitude average B mag. range in mag. ---------------------------------------------------------------------------------------------------- 5715 ~ 421 omitted 1.13 16.90 2379 Semiregular 355 ~ 3+? 2.56 17.4? 15.89 with cyclic long period or -18.45 variation over fainter 200-300 days, with irregularity 5654 V Hydrae type; very red 1.4 1.99 14.9 14.44 ~2400 irregular deepest -16.43 ~400-600 min. 2360 600-900 790 2.88 3.26 ~15.5 13.85 long period -17.11 --------------------------------------------------------------------------------------------------- [FIGURE 1] Fig. 1. Comparison of periods. [FIGURE 2] Fig. 2. Comparison of amplitudes for Cepheids. [FIGURE 3] Fig. 3. Comparison of B magnitudes for the Cepheids.