We analyze space- and ground-based data for the old ( 7.0 \pm 0.3 Gyr ) solar analogs 16 Cyg A and B .
The stars were observed with the Cosmic Origins UV Spectrographs on the Hubble Space Telescope ( HST ) on 23 October 2015 and 3 February 2016 respectively , and with the Chandra X-ray Observatory on 7 February 2016 .
Time-series data in \ion Ca2 data are used to place the UV data in context .
The UV spectra of 18 Sco ( 3.7 \pm 0.5 Gyr ) , the Sun ( 4.6 \pm 0.04 Gyr ) and \alpha Cen A ( 5.4 _ { \mathrm { -0.2 } } ^ { +1.2 } Gyr ) , appear remarkably similar , pointing to a convergence of magnetic heating rates for G2 main-sequence stars older than \approx 2 - 4 Gyr .
But the B component ’ s X-ray ( 0.3-2.5 keV ) flux lies 20 \times below a well-known minimum level reported by Schmitt .
As reported for \alpha Cen A , the coronal temperature probably lies below that detectable in soft X-rays .
No solar UV flux spectra of comparable resolution to stellar data exist , but they are badly needed for comparison with stellar data .
Center-to-limb ( C-L ) variations are re-evaluated for lines such as \ion Ca2 through to X-rays , with important consequences for observing activity cycles in such features .
We also call into question work that has mixed solar intensity-intensity statistics with flux-flux relations of stars .