The Resonance Hopping Effect in the Neptune-planet Nine SystemKhain, T.; Becker, J. C.; Adams, F. C.
doi: 10.1088/1538-3873/abbd8apmid: N/A
The observed physical clustering of the orbits of small bodies in the distant Kuiper Belt (TNOs) has recently prompted the prediction of an additional planet in the outer solar system. Since the initial posing of the hypothesis, the effects of Planet Nine on the dynamics of the main cluster of TNOs—the objects anti-aligned with its orbit—have been well-studied. In particular, numerical simulations have revealed a fascinating phenomenon, referred to as “resonance hopping,” in which these objects abruptly transition between different mean-motion commensurabilities with Planet Nine. In this work, we explore this effect in greater detail, with the goal of understanding what mechanism prompts the hopping events to occur. In the process, we elucidate the often underestimated role of Neptune scattering interactions, which leads to diffusion in the semimajor axes of these distant TNOs. In addition, we demonstrate that although some resonant interactions with Planet Nine do occur, the anti-aligned objects are able to survive without the resonances, confirming that the dynamics of the TNOs are predominantly driven by secular, rather than resonant, interactions with Planet Nine.
Research Output Between 1965 and 2019 from the Use of Telescopes at Lick ObservatorySmith, Graeme H.; Shetrone, Matthew
doi: 10.1088/1538-3873/abc022pmid: N/A
The productivity of Lick Observatory (LO) is reviewed over the years from 1965 to 2019, a 55 yr period which commences with the Shane 3 m telescope being the second-largest astronomical reflector in the world, but transitions into the era of 10 m ground-based optical telescopes. The metric of productivity used here is the annual number of refereed papers within which are presented results that are based at least in part on observations made with the telescopes of LO on Mount Hamilton. Criteria are set forth that have guided the counting of this metric. A bibliography of papers pertinent to observations from Lick Observatory has been compiled, and is made available through a NASA ADS library. The overall productivity of the observatory, counting all telescopes, went through a broad maximum between the years 1975 and 1982. This period also corresponds to a maximum in productivity of the Shane 3 m telescope. An author network shows that this period is attended by the introduction of digital detector systems at LO, particularly at the Shane telescope. Following 1983 the overall productivity of LO shows a net long-term decrease but with two other lesser peaks superimposed on that decrease. A slightly smaller peak occurs around 1996 and is associated with programs taking advantage of CCD spectrometers at both cassegrain and coudé foci of the Shane telescope. A third lesser peak around 2012 can be attributed to a rise in extragalactic supernova studies originating out of UC Berkeley. Author networks serve to document the UC astronomical communities that were using LO telescopes at these peak times. Institutional affiliations of first authors are documented.
Validation of the WRF Model for Estimating Precipitable Water Vapor at the Ali Observatory on the Tibetan PlateauQian, Xuan; Yao, Yongqiang; Wang, Hongshuai; Zou, Lei; Li, Yao; Yin, Jia
doi: 10.1088/1538-3873/abc22dpmid: N/A
In this study, we assess the validity of the Weather Research and Forecasting (WRF) numerical model for estimating precipitable water vapor (PWV) at the Ali observatory, located in the southwestern part of the Tibetan Plateau. We have run WRF in three nested domains with different horizontal resolutions, centered at the Ali observatory, and the ability of the WRF model on estimating PWV conditions at an astronomical observatory on the Tibetan Plateau with complex terrain has been discussed. In the validation, we make use of a verification sample of 1 yr of radiosonde data set obtained directly at the Ali radiosonde station in 2016, which is about 25 km north of the observatory. The results from model with the highest horizontal resolution of 1 km and the temporal resolution of 0.5 hr in domain 03 are presented in this article. On the Tibetan Plateau, it should be noted that the WRF model slightly overestimates the PWV, while there are high correlation coefficients between the PWV from model and that from observation. In summary, the WRF model shows an excellent performance in estimating PWV at the observatory, and a good agreement between model simulation and radiosonde observation has been found, including for the extremely low value of the PWV (≤1 mm), thus allowing it to complement the PWV estimation above the Tibetan Plateau.
Seeing-limited Imaging Sky Surveys—Small versus Large TelescopesOfek, E. O.; Ben-Ami, S.
doi: 10.1088/1538-3873/abc14cpmid: N/A
Typically large telescope construction and operation costs scale up faster than their collecting area. This slows scientific progress, making it expensive and complicated to increase telescope size. We review the argument that a metric that represents the capability of an imaging survey telescopes, and that captures a wide range of science objectives, is the telescope grasp—the amount of volume of space in which a standard candle is detectable per unit time. We show that in a homogeneous Euclidean universe, and in the background-noise dominated limit, the grasp is: , where Ω is the telescope field of view, Aeff is the effective collecting area of the telescope, σ is the instrumental or atmospheric seeing or the pixel-size, whichever dominates, tE is the exposure time, and tD is the dead time. In this case, the optimal exposure time is three times the dead time. We also introduce a related metric we call the information-content grasp, which summarizes the variance of all sources observed by the telescope per unit time. We show that, in the background-noise dominated regime, the information-content grasp scales like the grasp. For seeing-dominated sky surveys, in terms of grasp, étendue, or collecting-area optimization, recent technological advancements make it more cost effective to construct multiple small telescopes rather than a single large telescope with a similar grasp or étendue. Among these key advancements are the availability of large-format back-side illuminated CMOS detectors with ≲4 μm pixels, well suited to sample standard seeing conditions given typical focal lengths of small fast telescopes. We also discuss the possible use of multiple small telescopes for spectroscopy and intensity interferometers. We argue that if all the obstacles to implementing cost-effective wide-field imaging and multi-object spectrographs using multiple small telescopes are removed, then the motivation to build new single large-aperture (≳1 m) visible-light telescopes which are seeing-dominated, will be weakened. These ideas have led to the concept of the, currently under construction, Large-Array Survey Telescope.
Searching for RR Lyrae Stars by Imbalanced LearningZhang, Jingyi
doi: 10.1088/1538-3873/abc734pmid: N/A
As standard candles, RR Lyrae stars are taken as distance markers and age indicators, which is helpful to estimate the distance and age of globular clusters as well as galactic and extragalactic (Local Group) locations. At the same time, as tracers, they reveal the structure, chemical and dynamic evolution of the galaxy, as well as the substructure of the halo. However, the number of RR stars is very small compared with other types of stars in nature. With the development and operation of large-scale sky survey projects, they have made a qualitative leap in number. Compared with other types of stars, RR Lyrae stars are still not enough in number. Therefore, separating RR Lyrae stars from stars belongs to an imbalanced learning problem. It may be solved by popular imbalanced learning methods.