Table of Variable Stars in M55 (update October 2010)

Notes and References

All the data listed for 001-015 are from Olech et al. (1999, AJ 118, 442). The data for 016-042 are from the discovery paper by Pych et al. (2001, A&A 367, 148). They classified 016-030 as single-mode SX Phe variables and 031-042 as double-mode SX Phe variables. For all of the double-mode stars (except 041), one of the modes is considered to be non-radial in origin. The periods listed for 031-042 in the above table are the longer of the stars' two periods and the amplitudes are the amplitudes associated with these longer periods (except in the case of 038).

Notes on individual stars 009, 010, 012: Olech et al. (1999, AJ 118, 442) found evidence for non-radial pulsations in these three variables.

038: The period listed is the longer period, but the amplitude corresponds to the shorter period.

041: Pych et al. (2001) tentatively concluded that this star is pulsating in the first and second radial overtone modes.

043: This is the star CV1 announced by Kaluzny et al. (2005, MNRAS 359, 677). The data in the table are from their paper.

Discovery of the variable stars in M55:

001-002 Bailey (1902, Harvard Annals 38, 1) with x,y coordinates (page 243) and an ID chart (plate XII: Fig 1, page 252.23, description on page 251)

003-006 King (1951, Harvard Bulletin 920, 16) with x,y coordinates. No finding chart was provided, but in a later paper (King & Bruzual, 1976, A&A 50, 459) he pointed out that Figures 2 and 3 in a paper by Alcaino (1975, A&A Suppl 22, 193) serve as convenient finding charts. V1-V6 are equivalent to Alcaino #59, 366, 96, 433, 592, and 456, respectively.

007-015 Olech et al. (1999, AJ 118, 442) with RA, dec and findng charts.

016-042 Pych et al. (2001, A&A 367, 148) with RA, dec and finding charts

043 = CV1 (a dwarf nova) Kaluzny et al. (2005, MNRAS 359, 677) with RA, dec and finding chart. These authors also detected a blue variable (M55-B1) that they concluded might be a candidate quasar. The extragalactic nature of this source was confirmed by Webb et al. (2006, A&A 445, 155). It was their X-ray source #39.

Additional candidate variables:

Webb et al. (2006, A&A 445, 155) identified 47 X-ray sources in the vicinity of M55 with XMM-Newton, four within the core radius (2.83 arcmin) and one at the half mass radius (2.89 arcmin). In their Table 7, they classified the sources that might be related to M55. They concluded that their source #30 was the Kaluzny et al. dwarf nova. In their Table 6, they listed sources that had varied since Rosat observations obtained in 1993.

Bassa et al. (2008, A&A 488, 921) identified 16 X-ray sources within the half mass radius, based on Chandra data. They expected about half of these to be background sources. Their CX1 was the dwarf nova announced by Kaluzny et al. They concluded that their source CX2 could be a faint cataclysmic variable and CX7, CX10 and CX16 might be associated with active binaries.

Color-magnitude diagrams of the M55

References: The Astronomical Journal Volume 112, Number 4 - October 1996 "A Study of the Globular Cluster M55" G. Mandushev, G. Fahlman and B. Richer