Day 1663

Thursday, Friday.

2001.10575

Starshade formation flying I: optical sensing

Bottom, et al

A key challenge for starshades is formation flying. To successfully image exoplanets, the telescope boresight and starshade must be aligned to ~1 m at separations of tens of thousands of kilometers. This challenge has two parts: first, the relative position of the starshade with respect to the telescope must be sensed; and second, sensor measurements must be combined with a control law to keep the two spacecraft aligned in the presence of gravitational and other disturbances. In this work, we present an optical sensing approach using a pupil imaging camera in a 2.4-m telescope that can measure the relative spacecraft bearing to a few centimeters in 1 s, much faster than any relevant dynamical disturbances. A companion paper will describe how this sensor can be combined with a control law to keep the two spacecraft aligned with minimal interruptions to science observations.

2001.11044

Testing low-redshift cosmic acceleration with large-scale sturcture

Nadathur, Percival, Beutler, Winther

We examine the cosmological implications of measurements of the void-galaxy cross-correlation at redshift $z=0.57$ combined with baryon acoustic oscillation (BAO) data at $0.1<z<2.4$. We find direct evidence of the late-time acceleration due to dark energy at $>10\sigma$ significance from these data alone, independent of the cosmic microwave background and supernovae. Using a nucleosynthesis prior on $\Omega_bh^2$, we measure the Hubble constant to be $H_0=72.3\pm1.9$ kms$^{-1}$Mpc$^{-1}$ from BAO+voids at $z<2$, and $H_0=69.0\pm1.2$ kms$^{-1}$Mpc$^{-1}$ when adding Lyman-$\alpha$ BAO at $z=2.34$, both independent of the CMB. Adding voids to CMB, BAO and supernova data greatly improves measurement of the dark energy equation of state, increasing the Figure of Merit by >40%, but remaining consistent with flat $\Lambda$CDM.