NGC 6522 / C1800-300 (Updated May 2016) RA: 18:03:34.08 DEC: -30:02:02.3 (J2000) ============================================================ Bytes Format Explanation 1-8 A8 Star ID 10-32 A11,1x,A11 Position 34-35 A2 Units for position R0 denotes RA, DEC in the J2000 coordinates R5 denotes RA, DEC in the 1950 coordinates XA denotes X, Y in arcseconds XP denotes X, Y in pixels 37-44 F8.4 Period (days) 46-51 F6.3 Mean magnitude (or maximum magnitude if "max" is indicated in the remarks column) 53-57 F5.3 Light amplitude (range of variability) 59 A1 Colour for mean magnitude and amplitude e.g. B, V, R, I, J, K or P (for photographic). 61-65 A5 Type of variable (draft 2006 GCVS classifications) CST denotes non variable stars previously designated as variables 67-80 A19 Notes and Remarks (f denotes field star) "--" or "----" indicates no data available ========================================================================= ID Position Period ampl C Type Notes/ RA/X Dec/Y Units Remarks ========================================================================= 1 18:03:29.99 -30:01:30.1 R0 0.2700 15.928 0.313 I RR1 2 18:03:35.23 -30:01:24.9 R0 0.4741 15.691 0.575 I RR0 3 18:03:36.32 -30:01:27.5 R0 0.2887 15.912 0.283 I RR1 4 18:03:37.29 -30:01:55.9 R0 0.5638 17.808 0.450 I RR0 Note 5 18:03:40.26 -30:02:47.5 R0 0.2868 15.955 0.278 I RR1 6 18:03:42.57 -30:01:34.1 R0 0.1613 16.40 0.30 I DSCT f;Note 7 18:03:31.21 -30:01:01.8 R0 ---- 17.32 0.59 P L? f?;Note 8 18:03:33.63 -30:01:14.9 R0 1.7480 14.430 0.769 I CW Note 9 18:03:33.64 -30:03:09.2 R0 0.2987 15.348 0.261 I RR1 10 18:03:35.16 -30:02:00.1 R0 0.5574 15.130 0.274 I RR0 11 18:03:35.15 -30:02:02.2 R0 0.6158 15.887 0.483 I RR0 12 18:03:29.89 -30:01:56.5 R0 0.2569 15.780 0.152 I RR1 13 18:03:34.29 -30:01:44.8 R0 0.6360 15.560 0.456 I RR0 14 18:03:35.40 -30:01:55.2 R0 0.3281 15.452 0.140 I RR1 15 18:03:36.10 -30:01:51.9 R0 1.7972 14.365 0.719 I CW Note PSR ================================================================== Supplementary Notes The field around NGC 6522 was observed by Baade (1946, 1951) in his investigations to characterize the nature of the nucleus of the Milky Way galaxy and to determine its distance from the Sun. He used the Mount Wilson 100-inch telescope to study the field within 16 arcminutes of the cluster and discovered 285 variable stars. Their elements were later published by Gaposchkin (1955). This field is now known as "Baade's window" because it is an area with relatively low absorption near the Galactic centre and has been the subject of many studies. NGC 6522 is a core collapsed cluster with 0.05 arcminute core radius, 1.0 arcminute half-light radius and [Fe/H] = -1.34 according to the 2010 update to the Harris (1996) catalogue. Soszynski et al. (2011a) listed a cluster radius of 4.7 arcminutes. Since the cluster is located in a very rich field, only variables that lie less than 2 arcminutes of the cluster centre have been included in the above table. Some of these (e.g. V6) are probably field stars, while some stars beyond 2 arcminutes might be cluster members. A proper motion study by Terndrup et al. (1998) showed that most stars up to 2.2 arcminutes from the cluster centre are probable members. However, some stars less than 1 arcminute from the centre may belong to the field. The data for the RR Lyrae variables are from the Ogle IV survey (Soszynski et al. 2014) where V1 = OGLE-BLG-RRLYR-12073 V2 = OGLE-BLG-RRLYR-12117 V3 = OGLE-BLG-RRLYR-12127 V4 = OGLE-BLG-RRLYR-12132 V5 = OGLE-BLG-RRLYR-12154 V9 = OGLE-BLG-RRLYR-12099 = V1438 Sgr V10 = OGLE-BLG-RRLYR-12115 V11 = OGLE-BLG-RRLYR-12114 V12 = OGLE-BLG-RRLYR-12072 = V4113 Sgr V13 = OGLE-BLG-RRLYR-12108 V14 = OGLE-BLG-RRLYR-33606 The sources for variables, V6, V7, V8, and V15 are indicated in the notes on individual stars. ================================================================= Notes on individual stars V4: There has been confusion about the variability status of V4 because of an identification error. It was one of the variables discovered by Baade (1946, 1951) and its elements were later published by Gaposchkin (1955) who listed the star as #170. Unfortunately, the star was incorrectly labelled on his 1955 plate. V4 is located about 20 arcsecs southwest of the star he labelled as G#170. As a result, subsequent investigators (Clube 1965, Blanco 1984, Walker & Mack 1986) did not detect the variability of "V4" because it was in a crowded field and they were looking at the wrong star. In a later paper, Gaposchkin (1956) published a hand-drawn finder chart that showed the correct position for G#170 relative to nearby stars within approximately 15 arcseconds. Unfortunately, the star he identified as #170 in the earlier paper did not appear on the chart and this made his chart hard to decipher. In the meantime, Clube (1965) announced a new RR Lyrae variable which he numbered V7 and identified on a plate obtained with the Radcliffe 74-inch reflector. Sawyer Hogg (1973) designated this "new" variable as V10 in her 3rd catalogue. However, it turns out that Clube's new variable was Baade's original V4. Its location matches the position published on Gaposchkin's (1956) finder chart and the (Baade) x,y coordinates that Sawyer (1955) listed for V4. Furthermore, the period Clube derived for his new variable, 0.564 days, agrees with 0.56383 days, the period that Gaposchkin (1955) published for his star #170. V4 has also been observed by the Ogle group (Soszynski et al. 2014) who listed it as OGLE-BLG-RRLYR-12132 and derived a perod of 0.56383333 days. V6: This star is Gaposchkin (1955) #247, Blanco (1984) #64 and BWC V82 of Udalski et al. (1994). According to McNamara et al. (2000), BWC V82 is a high amplitude Delta Scuti variable (HADS) in the Galactic bulge. Its period is too long for an SX Phe variable and thus it is unlikely that it belongs to the cluster. All of the data listed in the above table are from Udalski et al. (1994). Walker & Mack (1986) also observed this star and derived a period of 0.16282 days and =17.51 mag. V7: This star is Gaposchkin #172 (V3900 Sgr). The RA and dec are from Samus et al. (2009). The remaining data are from Gaposchkin (1955). Sawyer (1955) stated that Baade considered V7 to be a field star and as a result, it was designated as V3900 Sgr in the Moscow GCVS. It is located at a distance of about 1.2 arcminutes from the cluster centre. The variability of V7 has not been confirmed in the OGLE study of long period variables in the Galactic Bulge (Soszynski 2013). However, according to Alard et al. (2001), the MACHO collaboration detected a semi-regular variable at J180331.3-300101 which is less than 2 arcsec from the published position of V7. V8, V15: The data for these stars are from the Ogle III Catalogue of Type II Cepheids in the Galactic Bulge (Soszynski et al. 2011b) where they are listed as OGLE-BLG-T2CEP-283 and 284 respectively. V8 (= Gaposchkin #27 = V1437 Sgr) was also observed by Walker & Mack (1986) who derived a mean V magnitude (15.60) and V amplitude (1.1 mag). ============================================================ Discovery of the variable stars in NGC 6522: V1-9 = Gaposchkin # 222, 133, 44, [170?*], 37, 247, 172, 27, 232 labelled on a photograph published by Gaposhkin (1955) who also listed their 1900 RA and dec. Sawyer (1955) assigned the numbers V1-9 and published x,y coordinates in consultation with Baade (private correspondence). In his correspondence with Sawyer (1955), Baade also indicated that V7, V8 and V9 were field stars. Therefore they are listed in the GCVS as V3900, V1437, V1438 Sgr respectively. However, these three stars are now considered to be probable cluster members. *Gaposchkin #170 (V4): Sawyer (1955, 1973) published the correct x,y coordinates for this star. However, it was incorrectly labelled on Gaposchkin's (1955) plate and this caused confusion in subsequent studies. Authors assumed that the star labelled as #170 by Gaposchkin (1955) was V4. He labelled the star correctly in a later paper (Gaposchkin 1956), on a hand drawn finder chart, but the chart was difficult to decipher. V10-11 = OGLE-BLG-RRLYR-12115, OGLE-BLG-RRLYR-12114 identified by RA and dec in the Ogle III survey (Soszynski et al. 2011a) who assigned the numbers V10-11. V12 = Blanco (1984) #54 = V4113 Sgr = OGLE-BLG-RRLYR-12072 Blanco published RA and dec (Epoch 1950) and an ID plate. The number V12 has been assigned in this catalogue. V13 = OGLE-BLG-RRLYR-12108 identified by RA and dec in the Ogle III survey (Soszynski et al. 2011a). The number V13 has been assigned in this catalogue. V14 = OGLE-BLG-RRLYR-33606 identified by RA and dec in the Ogle IV survey (Soszynski et al. 2014). The number V14 has been assigned in this catalogue. ---------------------------------- There are 5 additional RR Lyrae that have V and I magnitudes appropriate for cluster membership and are located beyond 2 arcminutes and within 4 arcminutes of the cluster centre: OGLE-BLG-RRLYR-11972 = V1416 Sgr = Gaposchkin #46 (r=3.9') OGLE-BLG-RRLYR-11993 = V1418 Sgr = Gaposchkin #50 (r=3.4') OGLE-BLG-RRLYR-12032 = V1426 Sgr = Gaposchkin #45 (r=2.4') OGLE-BLG-RRLYR-12044 = V1427 Sgr = Gaposchkin #51 (r=3.8') OGLE-BLG-RRLYR-12185 (r=2.9') OGLE-BLG-RRLYR-33568 (r=3.8') --------------------------------------- V15 = OGLE-BLG-T2CEP-284 identified by RA and dec in the OGLE III Catalogue of Type II Cepheids in the Galactic Bulge (Soszynski et al. 2011b) The number V15 has been assigned in this catalogue. ---------------------------------------------------------------------- In the OGLE III survey of Long period Variables in the Galactic Bulge, Soszynski et al. (2013) identified eight long period variables within 2 arcminutes of the cluster centre and with less than 14.5 mag. Some of these might be cluster members: OGLE-BLG-LPV-193749 (r=1.31') SRV =V5466 Sgr OGLE-BLG-LPV-194243 (r=0.13') OSARG OGLE-BLG-LPV-194274 (r=0.23') OSARG OGLE-BLG-LPV-194290 (r=0.23') OSARG OGLE-BLG-LPV-194311 (r=0.29') OSARG OGLE-BLG-LPV-194316 (r=1.02') OSARG OGLE-BLG-LPV-194544 (r=0.84') OSARG OGLE-BLG-LPV-194566 (r=1.49') OSARG -------------------------------------------------------------------- PSR: According to Paulo Freire's website, there are 3 millisecond pulsars in NGC 6522. (www.naic.edu/~pfreire/GCpsr.html) ================================================================== References Alard, C., Blommaert, A. A. D. L., Cesarsky, C., Epchtein, N., Felli, M., Fouque, P., Ganesh, S. and 34 coauthors, (The ISOGAL Collaboration and The MACHO Collaboration) 2001, ApJ, 552, 289 Baade, W. 1946, PASP, 58, 249 Baade, W. 1951, Pub. Obs. 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