Table A.1: Column densities $N({\rm CO^+})$ and fractional abundances $x({\rm CO^+})$ calculated with Eq. (A.1) assuming $T_{\rm ex}({\rm CO^+}) = 20$ K. The upper limits correspond to $3\sigma$ in line flux.
Source $N({\rm CO^+})$ $x({\rm CO^+})$

10¹² cm^-2

AFGL 2591 1.0 $1.0\times 10^{-11}$

W3 IRS 5 1.7 $2.5\times 10^{-12}$

IRAS 16293 0.6 $3.9\times 10^{-13}$

N1333-I2 0.2 $3.3\times 10^{-13}$

N1333-I4A <0.1 < $6.0\times 10^{-14}$

L1448-C <0.1 < $6.0\times 10^{-13}$

L483 <0.1 < $9.0\times 10^{-14}$

L723 <0.1 < $3.0\times 10^{-13}$

SMM4 <0.1 < $9.0\times 10^{-14}$

V1057 Cyg <0.1 < $2.0\times 10^{-12}$

**Table A.1:** Column densities $N({\rm CO^+})$ and fractional abundances $x({\rm CO^+})$ calculated with Eq. (A.1) assuming $T_{\rm ex}({\rm CO^+}) = 20$ K. The upper limits correspond to $3\sigma$ in line flux.
Source	$N({\rm CO^+})$	$x({\rm CO^+})$
	10¹² cm^-2
AFGL 2591	1.0	$1.0\times 10^{-11}$
W3 IRS 5	1.7	$2.5\times 10^{-12}$
IRAS 16293	0.6	$3.9\times 10^{-13}$
N1333-I2	0.2	$3.3\times 10^{-13}$
N1333-I4A	<0.1	< $6.0\times 10^{-14}$
L1448-C	<0.1	< $6.0\times 10^{-13}$
L483	<0.1	< $9.0\times 10^{-14}$
L723	<0.1	< $3.0\times 10^{-13}$
SMM4	<0.1	< $9.0\times 10^{-14}$
V1057 Cyg	<0.1	< $2.0\times 10^{-12}$

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