Peering through the dust of the Milky Way to obtain a dense sampling of the phase space is necessary to properly study the bulge, bar, bar-disc interface and spiral arms. NIR astrometry (and simultaneous photometry) is crucial for penetrating obscured regions and for observing intrinsically red objects when implemented with sufficient accuracy. Key topics are focused on what dark matter is and how is it distributed, how the Milky Way was formed and how has it been impacted by mergers and collisions? How do stars form and how does stellar feedback affect star formation what are the properties of stars, particularly those shrouded in dust, and small Solar System bodies how are they distributed and what is their motion? How many co-planar systems like ours (with Earth-sized and giant planets) are there and what fraction have planets with long period orbits? To answer these questions there are three main science challenges for a new all-sky astrometry mission: Nevertheless, the metrology systems explored may find application in improving a future all-sky mission.Ī new all-sky NIR astrometric mission will expand and improve on the science cases of Gaia using basic astrometry. Other mission proposals have tried to avoid this by employing long focal lengths and advanced metrology systems for ultra-accurate narrow field proposals, like SIM, NEAT and Theia, but these missions were focused on answering important specific science cases and did not aim to do a broad all-sky astrometric survey. minimum angular separation) R ∝ λ/ D at a fixed wavelength λ is very costly. Gaia was designed very well and only just fitted in the available launchers so improving the telescope’s angular resolution (i.e. An obvious question to ask is – can a more accurate all-sky mission than Gaia be done? Clearly the answer is yes, if we can build a space telescope with a larger aperture ( D) but in practice it is very difficult to do this without greatly inflating the cost of the mission. In this White Paper we argue that rather than improving on the accuracy to answer specific science questions, a greater overall science return can be achieved by going deeper than Gaia and by expanding the wavelength range to the NIR. However, one could argue that this uncertainty is a key science case in itself that cannot be resolved by Gaia alone A note of caution, the estimation of the star count ratio between Gaia and GaiaNIR is uncertain due to the uncertainty in the extinction model used (older models gave a lower ratio of around 3), mainly towards the centre of the Galaxy. SMC and LMC) is similar to GDR2mock (using Galaxia with the extinction map of ) but only 0.1% of the stars are sampled explaining the noise in low density regions. ![]() The underlying Milky Way model (which does not include clusters or external galaxies, e.g. In the bottom figure we show the corresponding H-band number densities. Crowding is not taken into account here and will limit the increase in numbers in the densest areas. In total 5 times more stars could be observed, especially in the disc where extinction is highest, by GaiaNIR for the H-band limit of 20th mag (top figure) and 6 times more stars could be observed by including the K-band limit of 20th mag. Instead, it is extremely broad, answering key science questions in nearly every branch of astronomy while also providing a dense and accurate visible-NIR reference frame needed for future astronomy facilities.Īll-sky projection in Galactic coordinates of the star count ratio per square degree between GaiaNIR and Gaia (G-band limit of 20.7th mag giving 1.5 billion Gaia sources). ![]() All-sky visible and Near-InfraRed (NIR) astrometry with a wavelength cutoff in the K-band is not just focused on a single or small number of key science cases. Why is accurate astrometry so important? The answer is that it provides fundamental data which underpin much of modern observational astronomy as will be detailed in this White Paper. Its final catalogue to be released \(\sim \) 2027, will provide astrometry for \(\sim \) 2 billion sources, with astrometric precisions reaching 10 microarcsec. Gaia has just completed its nominal 5-year mission (July 2019), but is expected to continue in operations for an extended period of an additional 5 years through to mid 2024. The second Gaia data release contained astrometric data for almost 1.7 billion sources with tens of microarcsec (or microarcsec per year) accuracy in a vast volume of the Milky Way and future data releases will further improve on this. ![]() Hipparcos has now been superseded by the results of the Gaia mission. The era of all-sky space astrometry began with the Hipparcos mission in 1989 and provided the first very accurate catalogue of apparent magnitudes, positions, parallaxes and proper motions of 120 000 bright stars at the milliarcsec (or milliarcsec per year) accuracy level.
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