J/ApJS/219/7 Ca,by photometry in globular clusters. I. M22 (Lee, 2015)
Multiple stellar populations of globular clusters from homogeneous Ca
by photometry.
I. M22 (NGC 6656).
Lee J.-W.
<Astrophys. J. Suppl. Ser., 219, 7 (2015)>
=2015ApJS..219....7L 2015ApJS..219....7L
ADC_Keywords: Clusters, globular ; Photometry, uvby ; Stars, giant
Keywords: globular clusters: individual: M22: NGC 6656;
Hertzsprung-Russell and C-M diagrams; stars: abundances
Abstract:
We investigate the multiple stellar populations in one of the peculiar
globular clusters (GCs), M22, using new ground-based wide-field Ca by
and Hubble Space Telescope Wide-Field Camera 3 photometry with
equivalent passbands, confirming our previous result that M22 has a
distinctive red giant branch (RGB) split mainly due to the difference
in metal abundances. We also make use of radial velocity measurements
by others of the large number of cluster membership stars. Our main
results are the following. (1) The RGB and the subgiant branch number
ratios show that the calcium-weak (Ca-w) group is the dominant
population of the cluster. However, an irreconcilable difference can
be seen in the rather simple classification into two horizontal
branches by others. (2) Each group has its own CN-CH anticorrelation.
However, the alleged CN-CH positive correlation is likely illusory.
(3) The location of the RGB bump of the calcium-strong (Ca-s) group is
significantly fainter, which may pose a challenge to the helium
enhancement scenario in the Ca-s group. (4) The positions of the
centers are similar. (5) The Ca-w group is slightly more centrally
concentrated, whereas the Ca-s is more elongated at larger radii. (6)
The mean radial velocities for both groups are similar, but the Ca-s
group has a larger velocity dispersion. (7) The Ca-s group rotates
faster. The plausible scenario for the formation of M22 is that it
formed via a merger of two GCs in a dwarf galaxy environment and
accreted later to our Galaxy.
Description:
New Ca by observations for M22 were made over 44 nights, 23 of which
were photometric, in 10 runs from 2011 March to 2014 May using the
CTIO 1.0 and 0.9m telescopes. The total exposure times for M22 were
90900, 20930, and 9145s for our new Ca and Stromgren b and y,
respectively.
We also carried out the HST WFC3 photometry for the central part of
M22. In Figure 10, we show the preliminary results from HST WFC3
observations of the cluster (PI: J.-W.Lee and PID: 12193) using the
similar passbands that we used in our ground-based observations.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 50 144632 Color-magnitude diagram data
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
J/ApJ/804/71 : HST/WFC3 observations of stars in M15 (Larsen+, 2015)
J/ApJS/216/19 : Spectroscopic HK' index for 3 globular clusters (Lim+, 2015)
J/MNRAS/442/3044 : Photometry and abundances of NGC1851 stars (Marino+, 2014)
J/A+A/563/A80 : Wide field imagers ground-based astrometry (Libralato+, 2014)
J/A+A/563/A76 : CaII triplet equivalent widths in 30 globulars (Mauro+, 2014)
J/A+A/563/A13 : Horizontal branch stars in M22 (Gratton+, 2014)
J/MNRAS/437/1609 : NGC 2808 HB stars abundances (Marino+, 2014)
J/ApJ/778/L13 : Subaru new Ca filter transmission function (Lee+, 2013)
J/MNRAS/431/1995 : Deep uVI photometry of NGC2419 (Beccari+, 2013)
J/A+A/541/A15 : Abundances of M22 subgiants (Marino+, 2012)
J/A+A/540/A27 : Spectroscopy in Galactic globular clusters (Saviane+, 2012)
J/ApJ/742/37 : Abundances of six RGB stars in M22 (Roederer+, 2011)
J/AJ/142/126 : CN & CH in SDSS Galactic globular clusters (Smolinski+, 2011)
J/A+A/533/A69 : Spectroscopy of 124 RGB stars in NGC 1851 (Carretta+, 2011)
J/A+A/526/A136 : Hot HB stars in ω Cen (Moehler+, 2011)
J/A+A/524/A44 : CN and CH line strengths in 12 globulars (Pancino+, 2010)
J/ApJ/705/1481 : Spectroscopy of stars in 6 globular clusters (Da Costa+, 2009)
J/A+A/505/117 : Abundances of red giants in 15 GCs (Carretta+, 2009)
J/A+A/486/437 : CN and CH line strengths in 8 Galactic GlCl (Kayser+, 2008)
J/ApJ/654/915 : Deep FORS1 BR photometry of omega Cen (Sollima+, 2007)
J/AJ/130/873 : Properties of BQS objects in the SDSS DR3 area (Jester+, 2005)
J/MNRAS/349/1278 : BVI photometry of M22 (Monaco+, 2004)
J/AJ/125/197 : CN abundances of the 47 Tuc main sequence (Harbeck+, 2003)
J/A+A/373/899 : New variables in M22 globular cluster (Kaluzny+, 2001)
J/AJ/116/1922 : CaII H and K filter photometry III. (Anthony-Twarog+, 1998)
J/AJ/109/2828 : CaII H and K filter photometry II. (Twarog+ 1995)
J/PASP/107/32 : uvby-hk photometry in M22 (Anthony-Twarog+ 1995)
J/AJ/109/218 : Catalogue of globular cluster profiles (Trager+ 1995)
J/ApJS/99/637 : Equivalent widths for 54 red giants (Norris+ 1995)
J/ApJ/420/612 : Proper motions + radial velocities in M22 (Peterson+ 1994)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- ID [1/591556] Stellar identifier
8- 17 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000)
19- 28 F10.6 deg DEdeg Declination in decimal degrees (J2000)
30- 35 F6.3 mag Vmag [8.6/19] The V band magnitude
37- 42 F6.3 mag b-y [-4.7/8.3]?=99.999 The Stromgren (b-y)
color index
44- 50 F7.3 mag hk [-11.4/13.6]?=99.999 The hk index (1)
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Note (1): The hk index of RGB stars is a measure of the CaII H&K absorption
strength (Anthony-Twarog et al. 1991AJ....101.1902A 1991AJ....101.1902A). It is
equal to [(Ca-b)-(b-y)] where Ca is the Ca filter
(λc≃397nm, FWHM≃9nm)
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 02-Sep-2015