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Table 7.

Slope of the metallicity gradient from selected literature papers.

Reference Sample d[Fe/H]/dRgc N OCs Comment
Friel et al. (2002) Low-res optical spectra −0.059 ± 0.010 39 7 < Rgc < 16 kpc, All ages (a)
Reddy et al. (2016) High-res optical spectra −0.052 ± 0.011 67 6 < Rgc < 12 kpc and |z|< 500 pc
−0.015 ± 0.007 12 12 < Rgc > 24 kpc (b)
Carrera et al. (2019) APOGEE DR14, GALAH DR2 −0.052 ± 0.003 46 6 < Rgc < 13 kpc (c)
−0.077 ± 0.007 6 < Rgc < 11 kpc (c)
0.018 ± 0.009 11 < Rgc < 13 kpc (c)
Casamiquela et al. (2019) High-res optical spectra −0.056 ± 0.011 18 Rgc < 12 kpc, All ages (d)
Donor et al. (2020) APOGEE DR16 −0.068±0.004 68 Rgc< 13.9 kpc, all ages(e)
−0.009 ± 0.011 3 Rgc > 13.9 kpc, All ages

Notes.

(a)

The slope is also given in different age ranges, with a gradient steepening for increased age: −0.023, −0.053, −0.075 for age < 2, 2–4, and > 4 Gyr, respectively (a similar result was found by Andreuzzi et al. (2011) using [Fe/H] from high resolution spectroscopy, who found values of −0.07 and −0.15 for age lower and larger than 4 Gyr, respectively).

(b)

They do not consider it representative of the disc midplane (their Sect. 5).

(c)

The first value is obtained for OCs where at least 4 stars were measured, the second and third to the whole sample. The gradient in the outer bin becomes −0.04 ± 0.01 if the two low metallicity OCs close to Rgc11 kpc are excluded.

(d)

No significant difference in the age ranges covered.

(e)

Also divided for age: −0.50 (13 OCs, age < 0.4 Gyr), −0.073 (16 OCs, 0.4–9,7 Gyr), −0.066 (27 OCs, 0.8–2 Gyr), and −0.094 (12 OCs, > 2 Gyr).

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