Prospects of measuring a metallicity trend and spread in globular clusters from low-resolution spectroscopy

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Table 2.

Mean iron abundance, errors, dispersion, and trend obtained from different setups, compared with H16 and J20.

Lib.	[α/Fe]	λλ (nm)	I	⟨[Fe/H]⟩	ϵ(T_eff)	ϵ([Fe/H])	σ([Fe/H])	τ([Fe/H])
(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)
Husser et al. (2016)

GSL	0	475 − 930	C	−1.995	46	0.080	0.103	0.21

Jain et al. (2020)

MIL	SN	475 − 740	P	−2.086	56	0.078	0.095	−0.05

GSL	0.4	475 − 930	L	−1.966	41	0.060	0.081	0.15
			Q	−1.942	40	0.063	0.084	0.17
			C	−1.945	41	0.059	0.082	0.18

GSL	0.4	475 − 740	L	−2.186	50	0.131	0.137	0.28
			Q	−2.180	50	0.134	0.142	0.28
			C	−2.167	51	0.133	0.139	0.25

GSL	0.4	475 − 580	L	−2.224	56	0.146	0.159	0.33
			Q	−2.218	55	0.147	0.164	0.33
			C	−2.203	57	0.149	0.165	0.31

GSL	0	475 − 930	L	−1.727	42	0.063	0.086	0.19
			Q	−1.704	42	0.061	0.082	0.16
			C	−1.712	42	0.061	0.082	0.16

GSL	0	475 − 740	L	−2.066	48	0.130	0.135	0.22
			Q	−2.055	48	0.133	0.143	0.23
			C	−2.047	48	0.125	0.131	0.21

GSL	0	475 − 580	L	−2.129	56	0.151	0.168	0.34
			Q	−2.123	56	0.154	0.174	0.34
			C	−2.109	56	0.154	0.171	0.33

AP18	0.5	475 − 930	L	−2.031	41	0.055	0.079	0.20
			Q	−2.015	40	0.052	0.075	0.21
			C	−2.014	41	0.052	0.075	0.21

AP18	0.5	475 − 740	L	−1.945	48	0.086	0.113	0.46
			Q	−1.928	47	0.086	0.112	0.46
			C	−1.925	47	0.084	0.111	0.46

AP18	0.5	475 − 580	L	−2.092	61	0.129	0.137	0.39
			Q	−2.074	62	0.128	0.134	0.40
			C	−2.073	62	0.127	0.134	0.41

AP18	0	475 − 930	L	−1.650	42	0.058	0.081	0.24
			Q	−1.636	41	0.056	0.079	0.25
			C	−1.635	42	0.056	0.079	0.25

AP18	0	475 − 740	L	−1.758	50	0.089	0.120	0.47
			Q	−1.744	50	0.091	0.122	0.47
			C	−1.741	50	0.091	0.121	0.47

AP18	0	475 − 580	L	−1.925	62	0.145	0.148	0.42
			Q	−1.908	63	0.143	0.147	0.44
			C	−1.907	63	0.143	0.146	0.45

APC	0.5	475 − 930	L	−2.068	42	0.061	0.083	0.20
			Q	−2.023	41	0.055	0.077	0.20
			C	−2.013	40	0.051	0.074	0.22

Notes. (1) Grid or library; MIL stands for the MILES library (Sánchez-Blázquez et al. 2006) used in J20, and APC for the AP18 coarse grid. (2) [α/Fe] value; SN stands for solar neighbourhood, as the abundance pattern of the empirical library used by J20 is made of stars from this environment. (3) Wavelength range in nm. (4) Interpolation schema; L: linear, Q: quadratic, C: cubic, P: polynomial approximation; the cubic splines used in H16 are different from the cubic Beziér interpolation of FERRE used in our analyses. (5) ⟨[Fe/H]⟩ is the average of the mean iron abundance determined in five T_eff bins of 250 K, for 5100 < T_eff < 6350 K. (6) ϵ(T_eff) is the mean uncertainty on T_eff estimated from pairs of repeated observations, averaged in the five T_eff bins. (7) ϵ([Fe/H]) is the mean uncertainty on [Fe/H]_e estimated from pairs of repeated observations and computed in the same way as ϵ(T_eff). (8) σ([Fe/H]) is the square root of the mean variance of [Fe/H]_e in the same five bins. (9) τ([Fe/H]) is the equivalent iron abundance trend, computed as the difference of mean [Fe/H]_e in the first and last bin.

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