Observing the Sun with stellar radial-velocity instruments: new approaches for weighing Earth analogues.

With the launch of the PLATO mission only a few years away, the exoplanet
detection community is working hard on new approaches to extreme-precision
radial-velocity (EPRV) measurements. Candidate Earth analogues detected by PLATO will have orbital
periods of order hundreds of days, and reflex orbital-motion signals with amplitudes of order
10 cm/s. In this talk I will discuss some of the instrumental and data-analysis capabilities
needed to detect the reflex orbital motion of such planets’ host stars, in order to meaure
the planets’ masses. High instrumental throughput and long-term thermal stability,
precise wavelength calibration and drift monitoring, and efficient mitigation
of telluric absorption are mandatory. New instruments are already approaching
the necessary precision. The stars themselves present the most formidable
remaining challenge, as p-mode oscillations, granular convection and magnetic
effects on surface brightness and velocity fields alter the shapes and relative
strengths of spectral lines on time scales from minutes to years. To connect
these to known surface features on the Sun, I will present data from stellar EPRV
instruments which now observe the Sun all day, every day via fibre feeds from
small, disc-integrating telescopes. The Sun’s own reflex motion about the
solar-system barycentre reminds us that the radial-velocity signal  of a true Earth
analogue will have to be disentangled from the reflex motions of other non-transiting planets
in the same system.