NGC 7089

NGC 7089, which is also called M2, is a globular cluster located in the constellation Aquarius.

NGC 7089
Observation data: 2000.0 epoch
Constellation	Aquarius
Right ascension	21h33.5m
Declination	-00o49'
Type	Globular cluster
Apparent dimensions	12.9
Apparent magnitude	6.5
Other designations	M 2

Scientific research

• Wehave presented BV photometry for 30 RR Lyrae variables, including 13 newly discovered variables, in the Oosterhoff type II globular cluster M2. The methods of searching for periods and new variables were discussed. We have derived pulsational parameters for RR Lyrae variables. With the discovery of new RR Lyrae variables, the mean periods of the RRab and RRc variables are 〈Pab〉 = 0.69 ± 0.02 days and 〈Pc〉 = 0.33 ± 0.01 days, respectively. The number ratio of the RRc type variables to the total number of the RR Lyrae type variables is n(c)/n(ab + c) = 0.40. A comparison with the model instability boundaries shows general agreement, although the detailed comparison is somewhat uncertain in the theoretical fundamental red edge given by Bono et al. (1995b). The RR Lyrae pulsational mode transition occurs between the fundamental period of 0.528 days and 0.556 days. From the star counts along the horizontal branch, two HB color distribution indices have been derived, (B-R)/(B + V + R) = 0.92 and B2/(B + V + R) = 0.46. Our analysis of the secular period-change rates from six RRab variables shows a general agreement with the canonical synthetic HB model predictions by Lee (1991). Finally, the HB star distribution shows that there are no significant blue HB gaps in M2.