Representation of the five first PCs obtained on the chunk-by-chunk RVs of HD 192310. Top: PC_j(t) length-projected onto the RV(t) time series. The date(s) of ThAr lamp replacement(s) are displayed as vertical red dashed line(s). Middle: corresponding Generalised Least Squares (GLS) periodogram of the PCs. Bottom: projection of the α_i,j coefficients (converted to Z-scores, i.e. normalised to zero mean and unit variance) into the physical detector space (pixel, λ). The separation between the two detectors of HARPS around λ = 5250 Å is indicated by the horizontal dashed line. The colour scale was set between Z = −2 and Z = 2, the direction being irrelevant since signs of the PCs are free to change. PC₁(t) is clearly related to ThAr lamp ageing as highlighted by the discontinuity of 100 cm s⁻¹ visible in the time-domain that matches the date of the lamp’s replacement. PC₂(t) shows some smooth modulation in the physical detector space, whereas PC₃(t) and PC₄(t) exhibit power at a period of 1-yr in the GLS.