LSST Cadence Optimization White Papers

Enabling Deep All-Sky Searches of Outer Solar System Objects

Jurić et al. - PDF

Abstract: A foundational goal of the Large Synoptic Survey Telescope (LSST) is to map the Solar System small body populations that provide key windows into understanding of its formation and evolution (Ivezi ́c et al., 2008; LSST Science Collaboration et al., 2009). This is especially true of the populations of the Outer Solar System – objects at the orbit of Neptune r > 30 AU and beyond. In this whitepaper, we propose a minimal change to the LSST cadence that can greatly enhance LSST’s ability to discover faint distant Solar System objects across the entire wide-fast-deep (WFD) survey area. Specifically, we propose that the WFD cadence be constrained so as to deliver least one sequence of 􏰀 10 visits per year taken in a ∼ 10 day period in any combination of g, r, and i bands. Combined with advanced shift-and-stack algorithms (e.g. Whidden et al., 2018) this modification would enable a nearly complete census of the outer Solar System to ∼ 25.5 magnitude, yielding 4 − 8x more KBO discoveries than with single-epoch baseline, and enabling rapid identification and follow-up of unusual distant Solar System objects in 􏰀 5x greater volume of space. These increases would enhance the science cases discussed in Schwamb et al. 2018 whitepaper, including probing Neptune’s past migration history as well as discovering hypothesized planet(s) beyond the orbit of Neptune (or at least placing significant constraints on their existence).

A Big Sky Approach to Cadence Diplomacy

Olsen et al. - Arxiv link

Abstract: The LSST survey was designed to deliver transformative results for four primary objectives: constraining dark energy and dark matter, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. While the LSST Wide-Fast-Deep survey and accompanying Deep Drilling and mini-surveys will be ground-breaking for each of these areas, there remain competing demands on the survey area, depth, and temporal coverage amid a desire to maximize all three. In this white paper, we seek to address a principal source of tension between the different LSST science collaborations, that of the survey area and depth that they each need in the parts of the sky that they care about. We present simple tools which can be used to explore trades between the area surveyed by LSST and the number of visits available per field and then use these tools to propose a change to the baseline survey strategy. Specifically, we propose to reconfigure the WFD footprint to consist of low-extinction regions (limited by galactic latitude), with the number of visits per field in WFD limited by the LSST Science Requirements Document (SRD) design goal, and suggest assignment of the remaining LSST visits to the full visible LSST sky. This proposal addresses concerns with the WFD footprint raised by the DESC (as 25 percent of the current baseline WFD region is not usable for dark energy science due to MW dust extinction), eases the time required for the NES and SCP mini-surveys (since in our proposal they would partially fall into the modified WFD footprint), raises the number of visits previously assigned to the GP region, and increases the overlap with DESI and other Northern hemisphere follow-up facilities. This proposal alleviates many of the current concerns of Science Collaborations that represent the four scientific pillars of LSST and provides a Big Sky approach to cadence diplomacy.

A Northern Ecliptic Survey for Solar System Science

Schwamb et al. - Arxiv link

Abstract: Making an inventory of the Solar System is one of the four fundamental science requirements for the Large Synoptic Survey Telescope (LSST). The current baseline footprint for LSST's main Wide-Fast-Deep (WFD) Survey observes the sky below 0∘ declination, which includes only half of the ecliptic plane. Critically, key Solar System populations are asymmetrically distributed on the sky: they will be entirely missed, or only partially mapped, if only the WFD occurs. We propose a Northern Ecliptic Spur (NES) mini survey, observing the northern sky up to +10∘ ecliptic latitude, to maximize Solar System science with LSST. The mini survey comprises a total area of ∼5800 deg2/604 fields, with 255 observations/field over the decade, split between g,r, and z bands. Our proposed survey will 1) obtain a census of main-belt comets; 2) probe Neptune's past migration history, by exploring the resonant structure of the Kuiper belt and the Neptune Trojan population; 3) explore the origin of Inner Oort cloud objects and place significant constraints on the existence of a hypothesized planet beyond Neptune; and 4) enable precise predictions of KBO stellar occultations. These high-ranked science goals of the Solar System Science Collaboration are only achievable with this proposed northern survey.

A near-Sun Solar System Twilight Survey with LSST

Seaman et al. - Arxiv link

Abstract: We propose a LSST Solar System near-Sun Survey, to be implemented during twilight hours, that extends the seasonal reach of LSST to its maximum as fresh sky is uncovered at about 50 square degrees per night (1500 sq. deg. per lunation) in the morning eastern sky, and surveyable sky is lost at the same rate to the western evening sky due to the Earth's synodic motion. By establishing near-horizon fence post picket lines to the far west and far east we address Solar System science use cases (including Near Earth Objects, Interior Earth Objects, Potentially Hazardous Asteroids, Earth Trojans, near-Sun asteroids, sun-grazing comets, and dormant comets) as well as provide the first look and last look that LSST will have at the transient and variable objects within each survey field. This proposed near-Sun Survey will also maximize the overlap with the field of regard of the proposed NEOCam spacecraft that will be stationed at the Earth's L1 Lagrange point and survey near quadrature with the Sun. This will allow LSST to incidently follow-up NEOCam targets and vice-versa (as well as targets from missions such as Euclid), and will roughly correspond to the Earth's L4 and L5 regions.

Simultaneous LSST and Euclid observations - advantages for Solar System Objects

Snodgrass et al. - Arxiv link

Abstract: The ESA Euclid mission is a space telescope that will survey ~15,000 square degrees of the sky, primarily to study the distant universe (constraining cosmological parameters through the lensing of galaxies). It is also expected to observe ~150,000 Solar System Objects (SSOs), primarily in poorly understood high inclination populations, as it will mostly avoid +/-15 degrees from the ecliptic plane. With a launch date of 2022 and a 6 year survey, Euclid and LSST will operate at the same time, and have complementary capabilities. We propose a LSST mini-survey to coordinate quasi-simultaneous observations between these two powerful observatories, when possible, with the primary aim of greatly improving the orbits of SSOs discovered by these facilities. As Euclid will operate from a halo orbit around the Sun-Earth L2 Lagrangian point, there will be significant parallax between observations from Earth and Euclid (0.01 AU). This means that simultaneous observations will give an independent distance measurement to SSOs, giving additional constraints on orbits compared to single Euclid visits.

The Diverse Science Return from a Wide-Area Survey of the Galactic Plane

Street et al. - Arxiv link

Abstract: The overwhelming majority of objects visible to LSST lie within the Galactic Plane. Though many previous surveys have avoided this region for fear of stellar crowding, LSST's spatial resolution combined with its state-of-the-art Difference Image Analysis mean that it can conduct a high cadence survey of most of the Galaxy for the first time. Here we outline the many areas of science that would greatly benefit from an LSST survey that included the Galactic Plane, Magellanic Clouds and Bulge at a cadence of 2-3 d. Particular highlights include measuring the mass spectrum of black holes, and mapping the population of exoplanets in the Galaxy in relation to variations in star forming environments. But the same survey data will provide a goldmine for a wide range of science, and we explore possible survey strategies which maximize the scientific return for a number of fields including young stellar objects, cataclysmic variables and Neptune Trojans.

Deep Drilling Fields for Solar System Science

Trilling et al. - Arxiv link

Abstract: We propose an ecliptic Deep Drilling Field that will discover some 10,000 small and faint Kuiper Belt Objects (KBOs) — primitive rocky/icy bodies that orbit at the outside of our Solar System and uniquely record the processes of planetary system formation and evolution. The primary goals are to measure the KBO size and shape distributions down to 25 km, a size that probes both the early and ongoing evolution of this population. These goals can be met with around 10 hours total of on-sky time (five separate fields that are observed for 2.1 hours each). Additional science will result from downstream observations that provide colors and orbit refinement, for a total time request of 40 hours over the ten year LSST main survey.

The Effects of Filter Choice on Outer Solar System Science with LSST

Volk et al. - Arxiv link

Abstract: Making an inventory of the Solar System is one of the four pillars that the requirements for the Large Synoptic Survey Telescope (LSST) are built upon. The choice between same-filter nightly pairs or different-filter nightly pairs in the Wide-Fast-Deep (WFD) Survey will have a dramatic effect on the ability of the Moving Object Pipeline System (MOPS) to detect certain classes of Solar System objects; many of the possible filter pairings would result in significant (∼50% or more) loss of Solar System object detections. In particular, outer Solar System populations can be significantly redder than those in the inner Solar System, and nightly pairs in r-band will result in the deepest survey for the outer Solar System. To maximize the potential for outer Solar System science, we thus advocate for ensuring that the WFD survey contains a sufficient number of r-r nightly pairs for each field during a discovery season to ensure detection and linking using MOPS. We also advocate for adding additional spectral energy distributions (SEDs) that more accurately model outer Solar System populations to the pipeline for evaluating the outputs of the LSST operations simulator. This will enable a better estimate of how many Solar System population detections are lost or gained for different filter choices in the WFD survey.