Faint objects in motion: the new frontier of high precision astrometry

Abstract

Sky survey telescopes and powerful targeted telescopes play complementary roles in astronomy. In order to investigate the nature and characteristics of the motions of very faint objects, a flexibly-pointed instrument capable of high astrometric accuracy is an ideal complement to current astrometric surveys and a unique tool for precision astrophysics. Such a space-based mission will push the frontier of precision astrometry from evidence of Earth-mass habitable worlds around the nearest stars, to distant Milky Way objects, and out to the Local Group of galaxies. As we enter the era of the James Webb Space Telescope and the new ground-based, adaptive-optics-enabled giant telescopes, by obtaining these high precision measurements on key objects that Gaia could not reach, a mission that focuses on high precision astrometry science can consolidate our theoretical understanding of the local Universe, enable extrapolation of physical processes to remote redshifts, and derive a much more consistent picture of cosmological evolution and the likely fate of our cosmos. Already several missions have been proposed to address the science case of faint objects in motion using high precision astrometry missions: NEAT proposed for the ESA M3 opportunity, micro-NEAT for the S1 opportunity, and Theia for the M4 and M5 opportunities. Additional new mission configurations adapted with technological innovations could be envisioned to pursue accurate measurements of these extremely small motions. The goal of this White Paper is to address the fundamental science questions that are at stake when we focus on the motions of faint sky objects and to briefly review instrumentation and mission profiles.

The proper motion of stars in dwarf galaxies: distinguishing central density cusps from cores

“…At the distance of Draco, ∼ 76 kpc (e.g., McConnachie 2012), the uncertainty 𝜎 𝑣 = 1.0 km s −1 implies an uncertainty ∼ 4 𝜇as yr −1 on the proper motion of a star. This uncertainty is comparable to the precision of a few 𝜇as yr −1 expected for Theia-like astrometric missions (Malbet et al 2019;Malbet et al 2021).…”

“…These parameters correspond to Draco galaxy. We adopt this dwarf as a working example of the possible targets of future Theia-like astrometric missions (Malbet et al 2016;The Theia Collaboration et al 2017;Malbet et al 2019;Malbet et al 2021).…”

“…We create mock data sets mirroring the generic expected observational limitations of future space-borne astrometric missions to determine the minimum number of stars and the maximum uncertainty on the proper motions that are required to effectively solve the CCP. As a benchmark, we adopt a future Theia-like mission (Malbet et al 2016;The Theia Collaboration et al 2017;Malbet et al 2019;Malbet et al 2021) designed to achieve an end-of-mission uncertainty on proper motions of a few 𝜇as yr −1 , namely ∼ 100 times smaller than the uncertainty of Gaia (Gaia Collaboration 2016; Gaia Collaboration et al 2016aCollaboration et al ,b, 2018bCollaboration et al ,a, 2021. A Theia-like mission is thus expected to be able to measure the proper motions of stars in nearby dwarf galaxies, and thus solve the CCP through an accurate determination of the DM density profile.…”

From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity

“…This subtle effect might be detectable with the proposed Theia mission [844] or something similar [845]. Due to the low temperature of Proxima Centauri, the prospects are somewhat better if using near-infrared wavelengths [846]. After a decade of observations, there would be a difference in RV of 0.52 cm/s between the models, while that in sky position would be 7.18 µas.…”

From galactic bars to the Hubble tension: weighing up the astrophysical evidence for Milgromian gravity

“…This subtle effect might be detectable with the proposed Theia mission (Theia Collaboration 2017) or something similar (Hobbs et al 2021). Due to the low temperature of Proxima Centauri, the prospects are somewhat better if using near-infrared wavelengths (Malbet et al 2021). After a decade of there would be a difference in RV of 0.52 cm/s between the models, while that in sky position would be 7.18 µas.…”