J/ApJ/705/1481 Spectroscopy of stars in 6 globular clusters (Da Costa+, 2009)
M22: an [Fe/H] abundance range revealed. Da Costa G.S., Held E.V., Saviane I., Gullieuszik M. <Astrophys. J., 705, 1481-1491 (2009)> =2009ApJ...705.1481D
ADC_Keywords: Abundances ; Clusters, globular ; Stars, giant ; Spectroscopy ; Equivalent widths ; Radial velocities Keywords: globular clusters: general - globular clusters: individual (M22) - stars: abundances Abstract: Intermediate resolution spectra at the CaII triplet have been obtained for 55 candidate red giants in the field of the globular cluster M22 with the VLT/FORS2 instrument. Spectra were also obtained for a number of red giants in standard globular clusters to provide a calibration of the observed line strengths with overall abundance [Fe/H]. For the 41 M22 member stars that lie within the V-VHB bounds of the calibration, we find an abundance distribution that is substantially broader than that expected from the observed errors alone. We argue that this broad distribution cannot be the result of differential reddening. Instead, we conclude that, as has long been suspected, M22 is similar to ω Cen in having an intrinsic dispersion in heavy element abundance. The observed M22 abundance distribution rises sharply to a peak at [Fe/H]~-1.9 with a broad tail to higher abundances: the highest abundance star in our sample has [Fe/H] ~-1.45dex. If the unusual properties of ω Cen have their origin in a scenario in which the cluster is the remnant nucleus of a disrupted dwarf galaxy, then such a scenario likely also applies to M22. Description: Short and "long" exposures of each cluster in the program were first obtained in service time with the FORS2 instrument in imaging mode at the Cassegrain focus of the VLT-UT1 telescope in the V and I bands. The 6.8'x6.8' field of view (FOV) was centered on the cluster for the sparser or more distant systems, but was offset from the centers for the nearer and richer clusters, including the "standard" clusters. These latter clusters were taken from the compilation of Pritzl et al. (2005, Cat. J/AJ/130/2140). The spectroscopic observations were then carried out in visitor mode with the FORS2 instrument in MOS-mode during a two night run at the end of May in 2006 with a spectral coverage of ∼7700-9500Å at a scale of 0.85Å per (binned) pixel. The number of stars observed in each cluster per configuration varied from ∼10 to the maximum of 19, depending on the density of likely members within the FOV. The M22 field was centered to the east of the cluster center. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 78 73 Standard globular cluster data (superseded by table3 of Saviane et al., 2012, Cat. J/A+A/540/A27) table2.dat 78 51 *M22 member data (superseded by data of table4 of Saviane et al., 2012, Cat. J/A+A/540/A27)
Note on table2.dat: For the 55 stars in the M22 field with reduced spectra, 51 have velocities compatible with cluster membership. The mean velocity of these stars is -150±2km/s. Only 41 M22 members with V-VHB≤0.2 were included in the fit with a slope of -0.51Å/mag (see figure 4).
See also: J/ApJ/698/2048 : Abundances of red giants in ω Cen (Johnson+, 2009) J/ApJ/681/1505 : Abundances of red giants in ω Cen (Johnson+, 2008) J/ApJ/682/1217 : Abundances in red giants in 7 globular clusters (Kirby+, 2008) J/AJ/130/2140 : Abundances and velocities in globular clusters (Pritzl+, 2005) J/MNRAS/349/1278 : BVI photometry of M22 (Monaco+, 2004) J/A+A/373/899 : New variables in M22 globular cluster (Kaluzny+, 2001) J/ApJS/99/637 : Equivalent widths for 54 red giants (Norris+ 1995) J/PASP/107/32 : uvby-hk photometry in M22 (Anthony-Twarog+ 1995) J/ApJ/420/612 : Proper motions + radial velocities in M22 (Peterson+ 1994) J/A+A/540/A27 : RV & EWCAII of Galactic globular clusters (Saviane+, 2012) Byte-by-byte Description of file: table.dat
Bytes Format Units Label Explanations
1- 8 A8 --- Cluster Cluster name (1) 10- 16 A7 --- Name Source identification (N_NNNNN) (2) 18- 19 I2 h RAh Hour of Right Ascension (J2000) 21- 22 I2 min RAm Minute of Right Ascension (J2000) 24- 27 F4.1 s RAs Second of Right Ascension (J2000) 29 A1 --- DE- Sign of the Declination (J2000) 30- 31 I2 deg DEd Degree of Declination (J2000) 33- 34 I2 arcmin DEm Arcminute of Declination (J2000) 36- 37 I2 arcsec DEs Arcsecond of Declination (J2000) 39- 42 I4 km/s HRV Heliocentric radial velocity 44- 48 F5.2 mag DelV Differential magnitude from horizontal branch (V-VHB) 50- 53 F4.2 0.1nm W8542 Equivalent width of CaII 8542AA line (3) 55- 58 F4.2 0.1nm e_W8542 Uncertainty in W8542 (3) 60- 63 F4.2 0.1nm W8662 Equivalent width of CaII 8662AA line (3) 65- 68 F4.2 0.1nm e_W8662 Uncertainty in W8662 (3) 70- 73 F4.2 0.1nm W(Ca) Sum of W8542 and W8662 (3) 75- 78 F4.2 0.1nm e_W(Ca) Uncertainty in W(Ca) (3)
Note (1): In table 1, the clusters are M4, M10, NGC 6397, M71 and M15. Note (2): Note that for each cluster the data sets from the two detectors in the camera were treated separately: stars falling on CCD1 are labeled as "1_" followed by a running number and those falling on CCD2 as "2_"Note (3): In units of Angstroms (Å). Note (3): In units of Angstroms (Å).
History: * 03-Jan-2012: From electronic version of the journal * 20-Mar-2012: All data superseded by those of Saviane et al., 2012, Cat. J/A+A/540/A27
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 07-Dec-2011
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