KELT-21b: A Hot Jupiter Transiting The Rapidly Rotating Metal-Poor Late-A Primary Of A Likely Hierarchical Triple System

We present the discovery of KELT-21b, a hot Jupiter transiting the V = 10.5 A8V star HD 332124. The planet has an orbital period of P = 3.6127647 ± 0.0000033 days and a radius of 1.586 (+0.039)/(-0.040) RJ. We set an upper limit on the planetary mass of MP \u3c 3.91 MJ at 3σ confidence. We confirmed the planetary nature of the transiting companion using this mass limit and Doppler tomographic observations to verify that the companion transits HD 332124. These data also demonstrate that the planetary orbit is well-aligned with the stellar spin, with a sky-projected spin–orbit misalignment of λ = -5.6(+1.7o)/(-1.9). The star has Teff = 7598 (+81)/(-84) K, M* = 1.458 (+0.029)/(-0.028) M⊙, R* = 1.638 ± 0.034 R⊙, and v sin I* = 146 km s⁻¹, the highest projected rotation velocity of any star known to host a transiting hot Jupiter. The star also appears to be somewhat metal poor and α-enhanced, with [Fe/H] = -0.405 (+0.032)/(-0.033) and [α/Fe] = 0.145 ± 0.053; these abundances are unusual, but not extraordinary, for a young star with thin-disk kinematics like KELT-21. High-resolution imaging observations revealed the presence of a pair of stellar companions to KELT-21, located at a separation of 1farcs2 and with a combined contrast of ΔKS = 6.39 ± 0.06 with respect to the primary. Although these companions are most likely physically associated with KELT-21, we cannot confirm this with our current data. If associated, the candidate companions KELT-21 B and C would each have masses of ∼0.12 M⊙, a projected mutual separation of ∼20 au, and a projected separation of ∼500 au from KELT-21. KELT-21b may be one of only a handful of known transiting planets in hierarchical triple stellar systems

Investigation of clay and neutron absorbers’ roles in the genesis and evolution of Oklo natural nuclear reactors

International audienceSince their discovery, the Oklo natural nuclear reactors were subject of many detailed field studies, sample analysis and criticality simulations. The present article is dedicated to advanced simulations of Oklo cores using a custom Python code to generalize and automate MCNP criticality calculations. The impacts of both the initial neutron absorbers and the clay fraction, which define the initial and evolving mineralogical environment, were studied by means of parametric simulations

Aligning and Labeling Genomes Under the Duplication-Loss Model

Abstract. In this paper we investigate the complexity of two combinatorial problems related to genome alignment, a recent approach to genome comparison based on a duplication-loss model of evolution. The first combinatorial problem, Duplication-Loss Alignment, aims to align two genomes and to explain the unaligned part of the genomes as duplications and losses. The problem has been recently shown to be NP-hard, even when each gene has at most five occurrences in each genome. Here, we improve this result by showing that Duplication-Loss Alignment is APX-hard even if the number of occurrences of a gene inside a genome is bounded by 2. Then we consider a second combinatorial problem, Minimum Relabeling Alignment, and we show that it is equivalent to Minimum Feedback Vertex Set on Direct Graph, hence implying that the problem is APX-hard, is fixed-parameter tractable and approximable within factor O(log|X|loglog|X|), where X is the aligned genome considered by Minimum Relabeling Alignment.