J/AJ/134/321 Hδ line in globular clusters (Prochaska+, 2007)
Hδ in the integrated light of galaxies: what are we actually measuring?
Prochaska L.C., Rose J.A., Caldwell N., Castilho B.V., Concannon K.,
Harding P., Morrison H., Schiavon R.P.
<Astron. J., 134, 321-333 (2007)>
=2007AJ....134..321P 2007AJ....134..321P (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Spectroscopy ; Abundances
Keywords: galaxies: abundances - galaxies: evolution - galaxies: stellar content
Abstract:
We present a cautionary study exploring the reliability of the
Hδ line in the integrated spectra of galaxies for determining
galaxy ages. Our database consists of the observed integrated spectra
of ∼120 early-type galaxies, 7 metal-rich globular clusters in M31 and
the Galactic globular cluster 47 Tuc, and the open cluster M67. We
have measured Hδ using index definitions designed to assess
contamination from the CN molecule in and around Hδ by choosing
combinations of bandpasses that both avoid and include a region of CN
molecular lines redward of Hδ. We find systematic differences in
the ages derived from Hδ measurements among the various
definitions when extracting ages from Hδ in old stellar
populations with enhanced CN bands due to nonsolar abundance ratios.
We propose that neighboring CN lines have a strong effect on
pseudocontinuum and central bandpass levels. For stellar populations
that have nonsolar abundance ratios in C and/or N, population
synthesis models that do not account for abundance ratio variations
cannot accurately reproduce the CN 4216Å band, which leads to a
corresponding inaccuracy in reproducing the various Hδ indices.
Hence, caution must be used when extracting galaxy ages from the
Hδ line in old stellar populations with significant nonsolar
abundance ratios.
Description:
The observational data used in this paper consist of integrated
spectra of 119 early-type galaxies, 7 metal-rich globular clusters in
M31, the open cluster M67, and the Galactic globular cluster 47
Tucanae.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 76 16 Index definitions
table2.dat 121 128 Index measurements and error
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See also:
J/ApJS/94/687 : Old stellar populations. V. (Worthey+, 1994)
J/ApJS/111/377 : Hγ + Hδ absorption features (Worthey+ 1997)
J/A+A/326/1069 : Abundances in globular clusters (Russell 1997)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Index Abbreviated index name
8- 20 A13 --- Name Index name
22- 29 F8.3 0.1nm bp1 Lower bound of central bandpass
30 A1 --- --- [-]
31- 38 F8.3 0.1nm bp2 Upper bound of central bandpass
40- 47 F8.3 0.1nm cont1 Lower bound of pseudo-continuum
48 A1 --- --- [-]
49- 56 F8.3 0.1nm cont2 Upper bound of pseudo-continuum
59- 66 F8.3 0.1nm Bcont1 ? Lower bound of second pseudo-continuum
67 A1 --- --- [-]
68- 75 F8.3 0.1nm Bcont2 ? Upper bound of second pseudo-continuum
76 A1 --- Ref [ab] Reference of index (1)
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Note (1): Note as follows:
a = Bandpass definitions are from Worthey & Ottaviani, 1997,
Cat. J/ApJS/111/377
b = Bandpass definitions are from Worthey et al., 1994, Cat. J/ApJS/94/687
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Type Source location (1)
7- 15 A9 --- Name Source name
17- 21 F5.2 --- HdAb HδAb index (2)
23- 26 F4.2 --- e_HdAb 1σ error in hdAb
28- 32 F5.2 --- HdA HδA index (2)
34- 37 F4.2 --- e_HdA 1σ error in HdA
39- 43 F5.2 --- HdAr HδAr index (2)
45- 48 F4.2 --- e_HdAr 1σ error in HdAr
50- 54 F5.2 --- HdFb HδFb index (2)
56- 59 F4.2 --- e_HdFb 1σ error in HdFb
61- 65 F5.2 --- HdF HδF index (2)
67- 70 F4.2 --- e_HdF 1σ error in HdF
72- 76 F5.2 --- HdFr HδFr index (2)
78- 81 F4.2 --- e_HdFr 1σ error in HdFr
83- 86 F4.2 --- Hbb Hβb index (2)
88- 91 F4.2 --- e_Hbb 1σ error in Hbb
93- 96 F4.2 --- Hb Hβ index (2)
98-101 F4.2 --- e_Hb 1σ error in Hb
103-106 F4.2 --- Hbr Hβr index (2)
108-111 F4.2 --- e_Hbr 1σ error in Hbr
113-116 F4.2 --- Fe4383 Fe4383 index (2)
118-121 F4.2 --- e_Fe4383 1σ error in Fe4383
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Note (1): Source location is abbreviated as:
Gal = Milky Way
M31 = M31 Globular Clusters
CRC03 = Early Type Galaxies in Caldwell, Rose, & Concannon
(2003AJ....125.2891C 2003AJ....125.2891C)
Note (2): as defined in table1
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 26-Aug-2009