J/ApJS/216/19 Spectroscopic HK' index for 3 globular clusters (Lim+, 2015)
Low-resolution spectroscopy for the globular clusters with signs of supernova
enrichment: M22, NGC 1851, and NGC 288.
Lim D., Han S.-I., Lee Y.-W., Roh D.-G., Sohn Y.-J., Chun S.-H., Lee J.-W.,
Johnson C.I.
<Astrophys. J. Suppl. Ser., 216, 19 (2015)>
=2015ApJS..216...19L 2015ApJS..216...19L
ADC_Keywords: Clusters, globular ; Abundances ; Spectroscopy
Keywords: Galaxy: formation; globular clusters: general; stars: abundances;
globular clusters: individual: M22, NGC 1851, NGC 288, NGC 6397
Abstract:
There is increasing evidence for the presence of multiple red giant
branches (RGBs) in the color-magnitude diagrams of massive globular
clusters (GCs). In order to investigate the origin of this split on
the RGB, we have performed new narrow-band Ca photometry and
low-resolution spectroscopy for M22, NGC 1851, and NGC 288. We find
significant differences (more than 4σ) in calcium abundance from
the spectroscopic HK' index for M22 and NGC 1851. We also find more
than 8σ differences in CN-band strength between the Ca-strong
and Ca-weak subpopulations for these GCs. For NGC 288, however, a
large difference is detected only in the CN strength. The calcium
abundances of RGB stars in this GC are identical to within the errors.
This is consistent with the conclusion from our new Ca photometry
where the RGB splits are confirmed in M22 and NGC 1851, but not in NGC
288. We also find interesting differences in the CN-CH correlations
among these GCs. While CN and CH are anti-correlated in NGC 288, they
show a positive correlation in M22. NGC 1851, however, shows no
difference in CH between the two groups of stars with different CN
strengths. We suggest that all of these systematic differences would
be best explained by how strongly Type II supernovae enrichment has
contributed to the chemical evolution of these GCs.
Description:
Our photometry with the new Ca filter on the du Pont 2.5m telescope at
Las Campanas Observatory (LCO) was conducted during the nights from
2011 to 2013. In order to compare with the data obtained from new Ca
filter, we have also reduced the Ca+CN filter data from the CTIO 4m
telescope (2009 Jul 28-30).
The spectral data were taken from the multi-object spectroscopic mode
with the Wide Field Reimaging CCD Camera (WFCCD) mounted on the du
Pont telescope. The observations were carried out during four
observing runs of 2011 July 7-13, 2011 September 16-19, 2012 February
19-22, and 2013 June 15-21. The spectral coverage depends on the
location of a slit on the mask, but the calcium II H and K lines, and
the CN and CH bands (3700Å∼4500Å) are covered for all sample
stars.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 108 186 Index measurements for the sample stars in M22
and NGC 288
table4.dat 108 65 Index measurements for the sample stars in NGC 1851
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See also:
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
J/A+A/563/A13 : Horizontal branch stars in M22 (Gratton+, 2014)
J/A+A/559/A101 : NGC6656 spectroscopy of 71 blue HB stars (Salgado+, 2013)
J/A+A/541/A15 : Abundances of M22 subgiants (Marino+, 2012)
J/A+A/539/A19 : Horizontal branch stars in NGC 1851 (Gratton+, 2012)
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/ApJ/742/37 : Abundances of six RGB stars in M22 (Roederer+, 2011)
J/A+A/524/A44 : CN and CH line strengths in 12 globulars (Pancino+, 2010)
J/MNRAS/405/839 : Spectroscopic obs. of globular clusters (Sharina+, 2010)
J/ApJ/705/1481 : Spectro. of stars in 6 globular clusters (Da Costa+, 2009)
J/A+A/505/139 : Abundances of red giants in 17 GCs (Carretta+, 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 GC (Kayser+, 2008)
J/ApJS/99/637 : Equivalent widths for 54 red giants (Norris+ 1995)
J/PASP/107/32 : uvby-hk photometry in M22 (Anthony-Twarog+ 1995)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- GC Globular cluster name (M22 or N288)
5 A1 --- --- [-]
6- 9 I4 --- Seq Star identifier
(<[LHL2015] {GC}-NNNN> in Simbad)
11- 19 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000)
21- 29 F9.5 deg DEdeg Declination in decimal degrees (J2000)
31- 35 F5.2 mag y [11.8/17.8] The Stroemgren y band magnitude
37- 41 F5.3 mag hk [0.4/1.3] The hk index (1)
43- 48 F6.4 mag HK' [0.18/0.61] The HK' index (G1)
50- 55 F6.4 mag e_HK' Error in HK'
57- 63 F7.4 mag dHK' The δHK' index (deviation from fit)
65- 71 F7.4 mag CN [-0.5/0.6] The CN index
73- 78 F6.4 mag e_CN Error in CN
80- 86 F7.4 mag dCN The δCN index (deviation from fit)
88- 93 F6.4 mag CH [0.8/1.4] The CH index
95-100 F6.4 mag e_CH Error in CH
102-108 F7.4 mag dCH The δCH index (deviation from fit)
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Note (1): The hk index, following Anthony-Twarog et al. (1991AJ....101.1902A 1991AJ....101.1902A),
is defined as hk=(Ca-b)-(b-y). See section 2.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- GC Globular cluster name (N1851)
6 A1 --- --- [-]
7- 10 I4 --- Seq Star identifier
(<[LHL2015] N1851-NNNN> in Simbad)
12- 19 F8.5 deg RAdeg Right Ascension in decimal degrees (J2000)
21- 29 F9.5 deg DEdeg Declination in decimal degrees (J2000)
31- 35 F5.2 mag Vmag [14.5/17.6] The V band magnitude
37- 41 F5.3 mag U-I The (U-I) color index
43- 48 F6.4 mag HK' [0.34/0.67] The HK' index (G1)
50- 55 F6.4 mag e_HK' Error in HK'
57- 63 F7.4 mag dHK' The δHK' index (deviation from fit)
65- 71 F7.4 mag CN [-0.4/0.8] The CN index
73- 78 F6.4 mag e_CN Error in CN
80- 86 F7.4 mag dCN The δCN index (deviation from fit)
88- 93 F6.4 mag CH [0.9/1.3] The CH index
95-100 F6.4 mag e_CH Error in CH
102-108 F7.4 mag dCH The δCH index (deviation from fit)
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Global notes:
Note (G1): We defined a new calcium index (HK'), which is analogous
to A(Ca) index except the width of blue side continuum band.
The definition of this index is:
HK'=-2.5log(F3916-3985)/(2F3894-3911+F3990-4025)
where F3916-3985, for example, is the integrated flux
from 3916 to 3985Å. See section 3.2.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 13-Feb-2015