RED GIANT STARS OF M3 ABSTRACT Photographic observations of seven red giant stars of M3 (CI>=1.3m) are presented. The star v.Z.1397 was found to be variable with the period of 31.395 or 215.8 days. Two other stars, v.Z.238 and 837 previously known as variables, show constant light within the observational error. It seems that only the two reddest stars in M3, i.e. v.Z.1397, CI=1.58m and v.Z.318 = V95, CI=1.60m, are variable. INTRODUCTION The investigation of red giant variable stars in globular clusters is of great importance especially from the theoretical point of view. These stars lie at the tip of the red giant branch in the HRD and are at an interesting stage of their evolution. It can be supposed that from a given colour index all the redder giant stars show light variation (see e.g. Osborn and Fuenmayor, 1977). For this reason much work has been done on the red giants of various clusters. In addition, a number of studies have already been published on some red giants of M3 (see for example Walker, 1955; Russev, 1971). Here we present a photographic study of red giant stars of M3 covering the time interval 1938-1962. OBSERVATIONS The red giant stars of M3 redder than CI=1.3m (see Sandage, 1953) were selected in order to investigate their possible light variations. Recent photoelectric B-V observations (Cohen et al., 1978) show no substantial difference from the values observed by Sandage for the three stars v.Z.238, 1392 and 1397, but for v.Z. 205 the B-V colour index measured by Cohen et al. is about 0.1m redder than Sandage's value (detailed remarks on this star are included). From the selected ten stars the following six have been measured: v.Z.238, 297, 837, 1392, 1397 and I-I-109 (designation after Sandage, 1953) whereas v.Z.490, 612, 752 and 1053 proved to be unmeasurable in our photographic plates because of their position near the centre of the cluster. As comparisons, v.Z.216, 237, 334, 740 and 1402 were used (selected from Sandage's paper). The detailed description of the observational material can be found in Szeidl's paper (Szeidl, 1965). The measurements were carried out with both the Becker and the Cuffey iris photometer of the Konkoly Observatory. Every plate was measured twice using the two photometers. No difference were found between the observational errors of the two sets of measurements. The mean values of the two measured magnitudes are given in Table 2. The mean error of one single measurement is +-0.061m, nevertheless, the standard deviations of the measurements of different stars vary depending on their positions. In Table 1 the mean of all magnitudes, the standard deviations and the numbers of observations are given for each measured star. Table 1 star mean(m_pg) standard number of deviation observations v.Z. 205 14.094 0.059 200 238 14.235 0.061 205 297 14.287 0.058 204 837 14.171 0.071 201 1392 14.373 0.053 189 1397 14.295 0.094 195 I-I-109 14.029 0.104 165 REMARKS ON INDIVIDUAL STARS v.Z.205 = I-III-28 This star was originally chosen as a comparison, but has never fitted the calibration curve. Therefore, the star was added to the other variable candidates. The mean of the observed magnitudes (14.09m) was found to be 0.1m fainter than Sandage's result (13.99m). According to Cohen et al.'s observations the star seems to be about 0.1m redder than previously thought. As 68% of the measured values are within a +-0.06m interval around the mean, we can say that the star does not vary at least with an amplitude larger than 0.12m (Figure 1).
Figure 1: Histogram of the measured magnitudes of v.Z.205 with
0.03m wide intervals. The normal distribution curve was calculated with
the estimated mean: 14.094 and standard deviation: 0.059
v.Z.238 = AA
v.Z.238 was supposed by Russev (Russev, 1971) to be variable
with 80.98d period and 0.24m amplitude. The mean brightness of the
star given by him differs from our result by only 0.02m (14.26m and
14.24m respectively) but the scatter of Russev's values is much
wider than ours.
Figure 2: Histogram of the measured magnitudes of v.Z.238 with
0.03m wide intervals. The normal distribution curve was calculated with
the estimated mean: 14.235 and standard deviation: 0.061
Concerning our observations, no light variation was found for
this star, 73% of the measured magnitudes are within a range of
+-0.06m around the mean (Figure 2).
v.Z.297
According to our measurements, this star does not show any
light variation. 76% of the obtained magnitudes lie in the region
14.29m +-0.06m (Figure 3).
Figure 3: Histogram of the measured magnitudes of v.Z.297 with
0.03 wide intervals. The normal distribution curve was calculated with
the estimated mean: 14.287 and standard deviation: 0.058.
v.Z.837 = I-II-46
For this star, Russev found light variation with a period of
89.59d and an amplitude of 0.33m. There is no great difference
between the mean brightness given by him (14.11m) and our result
(14.17m) but as with v.Z.238, the scatter of his magnitudes is
considerably wider.
The distribution of the measured values is close to the normal
one (Figure 4) and from all the data 74% take place within
+-0.07m around the mean. Therefore we can claim that this star also
does not vary with an amplitude greater than 0.14m.
Figure 4: Histogram of the measured magnitudes of v.Z.837 with
0.03 wide intervals. The normal distribution curve was calculated with
the estimated mean: 14.171 and standard deviation: 0.071
v.Z.1392 = I-I-21
This star does not show light variation; 78% of the measured values
fall within the range of 0.06m around the mean (Figure 5).
Figure 5: Histogram of the measured magnitudes of v.Z.1392 with
0.03 wide intervals. The normal distribution curve was calculated with
the estimated mean: 14.373 and standard deviation: 0.053
v.Z.1397
The distribution of the measured magnitudes of this star does
not follow a normal distribution (Figure 6). Two peaks are visible
in the histogram which is characteristic of the histograms of
variable stars. The standard deviation of the values obtained is
definitely larger (+-0.094m) than the average standard deviation of
the other non-variable stars. As well as the others, this star
lies in a very good measurable place far from the centre.
A modified Lafler-Kinman method was used to search for period
with trial periods from 30 to 350 days. As a result, two almost
equally well acceptable periods were received: 31.395d (Figure 7)
and 215.8d (Figure 8).
Figure 6: Histogram of the measured magnitudes of v.Z.1397 with
0.03 wide intervals. The normal distribution curve was calculated with
the estimated mean: 14.295 and standard deviation: 0.094
I-I-109
The scatter of the measurements of this star is relatively
wide, because of its close companion and dense surroundings. The
histogram of the measured values does not follow a normal distribution
but the shape of it is not similar to a variable star's
histogram (Figure 9).
In this case the search for period was unsuccessful, no suitable
period has been found. The wide scatter is very probably due
to the above mentioned effects.
Figure 7: Light curve of v.Z.1397 with the period of 31.395 day
Figure 8: Light curve of v.Z.1397 with the period of 215.8 days
Figure 9: Histogram of the measured magnitudes of I-I-109 with
0.03 wide intervals. The normal distribution curve was calculated with
the estimated mean: 14.029 and standard deviation: 0.104
Figure 10: Composite distribution of all measured magnitudes of
v.Z.205, 238, 297, 837 and 1392. The means were placed at the 0 point.
The estimated standard deviation of the normal distribution curve is
0.061.
CONCLUSION
The results of the present investigation seem to confirm the
idea that from a given colour index all redder giant stars are
variable in globular clusters.
v.Z.1397 is the reddest star (CI=1.58m) in our sample and
shows small amplitude light variation. There exists one redder
giant star in M3, namely v.Z.318 = V95 (CI=1.60m), the only known
red variable of the cluster with large amplitude.
Our photographic observations do not preclude the possibility
of the very small amplitude (less than 0.15m) light variations
among the red giant stars measured. Precise photoelectric observations
are necessary for making the final decision on the variability
of these stars.
I gratefully acknowledge the many helpful discussions with
Dr. B. Szeidl and thank him for his continuous encouragement.
Mr. B. Kálmán Jr. is thanked for his valuable assistance with the
instruments.
REFERENCES
Cohen, J.G., Frogel, J.A. and Persson, S.E., 1978, Astroph. J. 222. 165
Osborn, W. and Fuenmayor, F., 1977, Astron. Journal 82. 395
Russev, R.M., 1971, Per. Zvezdy 18. 171
Sandage, A., 1953, Astron. Journal 58. 61
Szeidl, B., 1965, Budapest Mitt. Nr. 58 CoKon58
1973, Budapest Mitt. Nr. 63 CoKon63
Walker, M.F., 1955, Astron. Journal 60. 197
von Zeipel, M.H., 1908, Ann. obs. Paris 25. F
Table 2
Photographic observations
(m-10)
J.D. 205 238 297 837 1392 1397 I-I-109
2428963.487 4.17 4.21 4.27 4.28 4.25 - 3.98
28991.403 4.20 4.28 4.32 4.33 4.36 4.24 4.06
.416 4.12 4.20 - 4.23 4.33 4.23 4.01
.430 4.13 4.21 4.19 4.37 4.35 4.20 4.03
.522 4.12 4.28 4.35 4.32 4.31 4.29 4.04
.542 4.18 4.27 4.34 4.29 4.31 4.22 4.02
29346.376 4.09 4.24 4.14 4.26 4.30 4.18 4.03
.392 4.10 4.21 4.12 4.18 4.23 4.22 3.94
29719.549 4.20 4.32 4.25 4.09 4.44 4.36 4.02
.560 4.12 4.28 4.29 4.19 4.36 4.42 3.93
29720.546 - 4.28 4.32 4.33 - - 3.95
.558 - 4.31 4.34 4.30 - - 4.01
29774.405 4.08 4.21 4.25 - - 4.27 3.97
.417 4.16 - 4.27 4.25 - 4.37 3.92
29775.403 4.10 4.27 4.35 4.16 4.41 4.37 4.05
.415 4.18 4.31 4.27 4.11 4.40 4.30 3.94
.426 4.19 4.23 4.29 4.20 - 4.35 3.97
.437 4.21 4.27 4.30 4.21 - 4.37 4.04
.447 - 4.34 4.28 4.24 - 4.36 4.09
30052.462 4.02 4.31 4.34 4.10 4.30 4.28 3.92
.474 3.99 4.36 4.28 - 4.26 4.19 3.94
.489 4.09 - 4.30 4.24 4.47 4.31 -
.501 3.96 4.24 4.30 4.05 4.34 4.32 3.96
30078.418 3.98 4.17 4.34 4.12 4.37 4.33 3.92
.434 3.99 4.25 4.42 4.13 4.28 4.21 -
.470 3.92 4.26 4.30 4.04 4.30 4.35 -
.483 4.02 4.24 4.28 4.20 4.39 4.20 3.85
.498 4.08 4.30 4.41 4.12 4.33 4.29 3.95
.509 4.02 4.19 4.38 4.16 4.29 4.20 3.82
.521 4.06 4.30 4.33 4.16 4.33 4.24 3.93
.536 4.03 4.24 4.32 4.14 4.33 4.23 3.84
.548 4.07 4.16 4.39 4.07 4.37 4.29 3.91
33390.497 4.11 4.26 4.28 4.24 4.31 4.43 4.24
.534 4.15 4.24 4.28 4.27 4.44 4.43 -
.545 4.14 4.21 4.29 4.18 - 4.37 4.19
.558 4.13 4.23 4.33 4.25 4.44 4.42 4.17
.570 4.15 4.20 4.30 4.20 4.38 4.34 4.21
.586 4.08 4.21 4.25 4.26 4.32 4.36 4.18
33420.424 4.10 4.20 4.18 4.16 4.44 4.38 4.15
.438 4.06 4.15 4.15 4.17 4.41 4.45 4.10
.450 4.13 4.18 4.25 4.12 4.41 4.38 4.13
.476 4.10 4.27 4.24 4.16 4.43 4.40 4.13
.487 4.08 4.22 4.14 4.16 4.35 4.40 4.07
.498 4.12 4.23 4.26 4.12 4.47 4.40 4.14
.510 4.14 4.27 4.23 4.14 4.44 4.43 4.08
.523 4.11 4.29 4.20 4.12 4.30 4.33 4.09
33421.385 4.18 4.34 4.33 4.13 4.44 4.49 4.07
.442 4.10 4.20 4.26 4.08 4.35 4.37 4.05
.454 4.11 4.26 4.27 4.04 4.37 4.42 4.04
.465 4.08 4.24 4.28 4.08 4.37 4.39 3.97
.475 4.10 4.27 4.33 4.06 4.38 4.45 4.05
Table 2 (continued)
J.D. 205 238 297 837 1392 1397 I-I-109
2433421.486 4.08 4.19 4.25 4.01 4.35 4.38 3.98
.497 4.13 4.27 4.39 - 4.32 4.46 4.00
.535 4.17 4.24 4.30 4.07 4.38 4.40 4.05
.548 4.12 4.24 4.26 4.00 4.30 4.41 4.03
33422.398 4.18 4.28 4.21 4.21 4.44 4.40 4.18
.431 4.11 4.19 4.17 4.20 4.50 4.51 4.14
.442 4.04 4.24 - 4.14 4.41 4.38 4.16
.452 4.10 4.23 4.17 4.20 4.48 - -
.472 4.17 4.23 4.24 4.14 4.34 4.38 4.11
.483 4.15 4.29 4.27 4.24 - 4.46 4.16
.493 4.14 4.29 4.21 4.16 4.44 4.42 4.06
.508 4.08 - 4.19 - 4.40 4.36 4.04
.520 4.06 4.20 4.22 4.15 4.41 4.43 4.14
33763.406 4.12 4.25 4.32 4.12 4.37 4.39 4.12
.420 4.06 4.24 4.25 4.08 4.33 4.34 4.12
.442 4.18 4.31 4.33 4.20 4.38 4.38 4.18
.455 4.12 4.21 4.31 4.13 4.44 4.37 -
.464 4.08 4.24 4.26 4.10 4.40 4.34 4.20
.483 4.16 4.29 4.22 4.18 4.43 4.43 4.20
.494 4.18 4.31 4.24 4.17 4.40 4.36 4.15
.504 4.07 4.30 4.30 4.18 4.42 4.34 4.16
.514 4.09 4.21 4.29 4.12 4.39 4.33 4.16
.525 4.06 4.20 4.30 4.08 - 4.31 4.14
34118.355 - 4.28 4.35 - - - -
.372 - 4.21 4.36 4.19 4.36 4.12 4.09
.428 - 4.10 4.34 4.02 - - 3.84
.443 4.02 4.02 4.21 3.99 4.25 4.05 3.92
.470 - 4.21 4.33 4.24 - 4.17 -
.485 4.03 4.11 4.38 4.05 - 4.04 3.95
.499 4.13 4.22 4.30 4.14 4.35 4.12 3.98
.513 4.08 4.07 4.29 4.04 - 4.02 3.96
.540 4.05 4.15 4.37 - 4.20 4.15 -
34120.471 4.07 4.11 4.29 4.15 4.38 4.19 3.92
.484 4.10 4.11 4.30 4.21 4.38 4.21 3.92
.497 4.07 4.17 4.36 4.17 4.42 4.19 3.94
.510 4.09 4.21 4.26 4.19 4.41 4.24 3.93
.523 4.12 4.13 4.25 4.13 4.33 4.16 3.93
.536 4.17 4.20 4.34 4.11 4.40 4.18 3.89
.551 4.11 4.21 4.30 4.10 4.34 - 3.92
.564 4.21 4.20 4.31 4.24 4.36 4.29 4.03
.579 4.19 4.22 4.31 4.24 4.35 4.20 3.87
34121.401 4.06 4.14 4.27 4.12 4.36 4.17 4.04
.412 4.16 4.19 4.33 4.17 4.35 4.25 4.05
.422 4.13 4.23 4.28 4.21 4.40 4.22 4.05
.431 4.17 4.23 4.35 4.16 4.36 4.22 3.99
.441 4.13 4.13 4.28 4.14 4.32 - 3.91
.484 4.17 4.17 4.29 4.20 4.40 4.23 4.01
.495 4.10 4.14 4.26 4.17 4.37 4.18 3.99
.505 4.15 4.15 4.36 4.23 4.49 - 4.02
.517 4.07 4.14 4.26 4.13 4.36 4.14 -
.528 4.04 4.09 4.37 4.15 4.39 4.27 3.89
.539 4.04 4.09 4.29 4.17 4.40 4.15 4.02
.552 4.18 4.11 4.35 4.23 4.41 4.22 4.05
Table 2 (continued)
J.D. 205 238 297 837 1392 1397 I-I-109
2434121.562 4.15 4.16 4.31 4.15 4.42 4.23 4.05
.594 - 4.20 4.34 4.25 - 4.28 3.94
.605 4.16 4.20 4.28 4.21 - 4.21 -
34122.404 4.02 4.21 4.32 4.13 4.39 4.23 3.97
.416 4.07 4.17 4.36 4.18 4.35 4.29 3.93
.431 4.10 4.09 4.32 4.16 4.43 4.19 -
34126.433 4.07 4.19 4.33 4.13 4.27 4.21 4.07
34131.415 4.14 4.26 4.24 4.20 4.39 - 4.13
34487.347 4.06 4.23 4.28 4.25 4.35 - -
.367 4.11 4.26 4.36 4.39 - 4.45 4.21
.385 4.12 4.28 4.27 4.36 4.40 4.36 -
.397 4.10 4.26 4.34 4.33 4.41 4.37 4.23
.410 4.14 4.20 4.31 4.32 4.40 4.31 4.21
.428 4.14 4.28 4.37 4.31 4.39 4.40 -
.438 4.13 4.22 4.27 4.30 4.42 4.38 4.24
.449 4.16 4.18 4.27 4.34 4.33 4.34 4.18
.460 4.13 4.30 4.32 4.27 4.43 4.46 4.24
.474 4.12 4.25 4.30 4.25 4.30 4.37 -
.483 - 4.22 4.33 4.26 4.33 4.33 4.23
.494 4.14 4.23 4.24 4.28 4.41 4.36 4.22
.508 4.08 4.29 4.31 4.26 4.38 4.37 4.16
.518 4.07 4.20 4.29 4.26 4.38 4.33 4.22
34488.530 4.09 4.26 4.25 4.24 4.42 4.45 4.19
.540 4.04 4.21 4.38 4.15 4.36 4.49 4.15
34567.388 4.02 4.29 4.25 4.11 4.39 4.23 4.09
35223.415 3.97 4.21 4.31 4.21 4.43 4.26 3.92
.428 4.07 4.28 4.27 4.14 4.42 4.26 3.86
.441 4.06 4.30 4.25 4.10 4.40 4.27 3.90
.467 4.11 4.31 4.26 4.14 4.39 4.26 3.94
.490 4.07 4.24 4.34 4.12 4.41 4.21 3.90
.503 4.05 4.27 4.33 4.15 4.40 4.21 3.95
.517 4.05 4.24 4.27 4.17 4.35 4.14 3.95
.530 3.97 4.25 4.32 4.15 4.29 4.24 3.97
.546 4.01 4.29 4.24 4.22 4.45 4.24 3.98
.573 4.05 4.27 4.21 4.15 4.37 4.22 3.94
35224.454 3.98 4.29 4.25 4.11 4.34 4.19 3.90
.472 4.07 4.28 4.25 4.18 4.42 4.24 3.91
.485 4.00 4.27 4.27 4.11 4.31 4.19 3.91
.499 4.07 4.32 4.31 4.17 4.32 4.26 3.99
.512 4.00 4.30 4.23 4.15 4.34 4.22 3.93
.524 4.07 4.34 4.32 4.19 4.37 4.19 4.01
.542 4.04 4.29 4.25 4.09 4.40 4.20 4.01
.556 3.99 4.28 4.37 4.11 4.41 4.18 3.98
.569 4.08 4.27 4.30 4.11 4.39 4.20 3.93
.583 4.01 - - 4.07 4.28 4.14 3.93
35227.534 3.99 4.24 - 4.17 4.44 4.06 4.01
.547 4.11 4.23 4.17 4.18 4.37 4.16 4.08
.560 4.04 4.19 4.10 4.21 4.33 - 4.08
.573 4.13 4.30 4.19 4.17 4.31 4.13 4.10
.586 4.00 4.26 4.22 4.19 4.31 4.16 3.93
35598.507 4.03 4.23 4.23 4.19 4.31 4.30 4.10
.524 4.01 4.30 4.15 4.17 4.41 4.28 4.09
.537 4.14 4.34 4.25 4.20 4.39 4.28 4.19
Table 2 (continued)
J.D. 205 238 297 837 1392 1397 I-I-109
2435600.363 4.10 4.24 4.31 4.12 4.32 4.26 4.06
.378 4.10 4.33 4.20 4.23 4.39 4.27 4.11
.391 4.10 4.28 4.24 4.17 4.27 4.28 4.15
.405 4.04 4.31 4.32 4.19 4.47 4.36 4.05
.421 4.16 4.34 4.23 4.15 4.36 4.39 4.15
.434 4.15 4.32 4.22 - 4.44 4.23 4.11
.446 4.03 4.20 4.22 4.19 4.41 4.21 4.05
.501 4.10 4.22 4.18 4.17 4.25 4.24 4.07
.525 4.16 4.25 4.20 4.16 4.38 4.23 4.07
35603.369 4.13 4.31 4.35 4.22 4.38 4.27 4.03
.381 4.04 4.24 4.25 - - 4.24 3.90
.397 4.07 4.31 4.40 4.23 4.40 4.32 3.92
.408 4.11 4.27 4.23 4.16 4.38 4.29 -
.419 4.03 4.18 4.31 4.15 4.39 4.33 3.97
.431 4.17 4.26 4.29 4.25 4.39 4.30 4.01
.446 4.06 4.18 4.31 4.25 4.30 4.26 -
.457 4.02 4.21 4.24 4.15 - 4.26 3.94
.468 4.13 4.29 4.33 4.22 4.45 4.29 4.05
.491 4.01 4.26 4.19 4.14 4.29 4.24 3.98
.507 4.11 4.31 4.26 4.20 4.35 4.33 3.92
36991.457 4.17 4.27 4.26 4.13 4.42 4.37 4.05
.470 4.16 4.26 - 4.09 4.40 4.36 -
.485 4.18 4.28 4.36 4.08 4.43 4.33 3.94
37016.470 4.18 4.37 4.34 4.22 4.43 4.25 -
.483 4.16 4.34 - 4.18 4.40 - -
.496 4.14 4.33 4.32 4.10 - - -
.510 4.00 4.24 4.27 4.16 4.36 4.32 -
.523 4.04 4.22 4.28 4.10 4.44 4.43 -
.537 4.00 4.22 4.33 4.13 4.40 - -
.550 4.14 4.29 4.35 4.19 4.32 4.33 -
.577 4.08 4.23 4.30 4.14 4.40 4.34 -
.609 4.06 4.31 4.28 4.10 4.31 4.27 -
.623 4.09 4.29 4.35 4.22 4.38 4.40 -
.637 4.01 4.26 4.27 4.15 4.32 4.35 -
37057.539 4.09 4.21 4.34 4.12 4.37 4.39 -
.552 3.97 4.16 4.33 4.08 4.37 4.38 -
.578 4.06 4.20 4.22 4.06 4.31 4.34 -
37058.529 - 4.14 4.21 4.07 4.43 4.32 -
.580 4.10 4.19 4.29 4.19 4.29 4.26 -
37757.598 4.19 4.27 4.40 4.13 4.47 4.40 -
37791.365 4.07 4.15 4.30 - 4.33 4.35 -
.380 4.13 4.17 4.33 4.18 4.35 4.37 -
.394 4.17 4.24 4.34 4.20 4.43 4.33 -
.424 4.18 4.24 4.27 4.22 4.41 4.21 -
.439 4.11 4.16 4.34 4.17 4.39 4.29 -
.454 4.04 4.13 4.29 4.14 4.39 4.27 -
.469 4.08 4.20 4.33 4.13 4.34 4.33 -
.483 4.07 4.15 4.35 4.11 4.41 4.24 3.88
.497 4.15 4.23 4.39 4.18 4.42 4.31 -
.519 4.17 4.26 4.31 4.14 4.43 4.34 3.90
.533 4.16 4.21 4.35 4.20 4.37 4.37 -
.549 4.05 4.19 4.30 4.11 4.37 4.32 3.86
.563 4.09 - 4.25 4.19 4.34 4.25 3.88