Dear PIs of HARPS program,

This letter is to inform you that since May 18th until June 10th 2026 we had a major upgrade of the HARPS instrument.

This included:

• a new, monolithic detector (same number of pixels and same size as before);
• new control electronics;
• new cooling strategy (Stirling cooler rather than liquid Nitrogen);
• a new pipeline (same "familiy" as the ESPRESSO & NIRPS one), available from this link;
• a new fiber link is installed for the HAM mode
• refocus of the instrument.

The fiber-link exchange was due to a detected drop in throughput of the HAM fibers.

We are closely monitoring the EGGS fibers as well to determine whether an exchange is necessary also for this fiber-link.

As a consequence of all these delicate changes, we expect a constant offset to be introduced in the radial velocity measurements
taken after the fiber exchange (June 4th). The instrument and its pipeline are not yet fully operational, we are working
on the optimization of the data-reduction and on the determination of this offset as accurately as possible with the goal
to assure best precision and long-term continuity to all programs, especially to the ones spanning pre- and post-upgrade observing time.

Be informed that we are preparing a detailed report and the main results will be published in the December edition of the ESO Messenger.

In the meantime, do not hesitate to contact us for additional information.

Best regards,
        
    Gaspare Lo Curto