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Realistic observing scenarios for the next decade of early warning detection of binary neutron stars
No full textWe describe realistic observing scenarios for early warning detection of binary neutron star mergers with the current generation of ground-based gravitational-wave detectors as these approach design sensitivity. Using Fisher analysis, we estimate that Advanced LIGO and Advanced Virgo will detect one signal before merger in their fourth observing run provided they maintain a 70% duty cycle. 60% of all observations and 8% of those detectable 20 seconds before merger will be localized to ≲ 100 deg². If KAGRA is able to achieve a 25 Mpc horizon, these prospects increase to ≲2 early detections with 70% of all BNS localized to ≲ 100 deg² by merger. As the AHKLV network approaches design sensitivity over the next ∼10 years, we expect up to 1 (14) detections made 100 (10) seconds before merger. Although adding detectors to the HLV network impacts the detection rate at ≲ 50% level, it improves localization prospects and increases the completeness of compact binary surveys. Given uncertainties in sensitivities, participating detectors, and duty cycles, we consider 103 future detector configurations so electromagnetic observers can tailor preparations towards their preferred models
Monitoring Inner Regions in the RY Tau Jet
No full textWe present multiepoch observations of the RY Tau jet for Hα and [Fe ii] 1.644 μm emission lines obtained with the Subaru Coronagraphic Extreme-AO and Visible Aperture Masking Polarimetric Imager for Resolved Exoplanetary Structures (VAMPIRES), Gemini Near-infrared Integral Field Spectrograph, and Keck/OSIRIS in 2019–2021. These data show a series of four knots within 1″ consistent with the proper motion of ∼0.″3 yr⁻¹, analogous to the jets associated with another few active T Tauri stars. However, the spatial intervals between the knots suggest the time intervals of the ejections of about 1.2, 0.7, and 0.7 yr, significantly shorter than those estimated for the other stars. These Hα images contrast with the archival Very Large Telescope Spectro-Polarimetric High-contrast Exoplanet Research and Zurich IMaging POLarimeter (ZIMPOL) observations from 2015, which showed only a single knot-like feature at ∼0.″25. The difference between the 2015 and 2019–2021 epochs suggests an irregular ejection interval within the six-year range. Such variations of the jet ejection may be related to a short-term (α emissions with the ZIMPOL data taken in 2015, showing the brighter profile at the base (<0.″3) than the 2020–2021 VAMPIRES profiles due to time-variable mass ejection rates or the heating–cooling balance in the jet. The observed jet knot structures may be alternatively attributed to stationary shocks, but a higher angular resolution is required to confirm its detailed origin
Current Algebra Approach to 2d Chiral Metals
No full textWe reinterpret Balents and Fisher's free 2d chiral metal [Phys. Rev. Lett. 76, 2782 (1996)] as a chiral U(N) Wess-Zumino-Witten model at level k=1. Here, the U(N) symmetry relates the N→∞ low-energy excitations about the chiral Fermi surface. We obtain non-Fermi liquid generalizations of the free chiral metal that maintain the U(N) symmetry of the k=1 theory by taking the level to be a positive integer k>1. We calculate two-point correlation functions of the U(1) number density and current operators in these theories for general k. We find k to provide an overall rescaling of the amplitude of these correlation functions. This construction illustrates the ersatz Fermi liquid proposal of Else, Thorgren, and Senthil [Phys. Rev. X 11, 021005 (2021)]
Measuring Optical Extinction Towards Young Stellar Objects Using Diffuse Interstellar Bands
No full textLine-of-sight extinction estimates to well-studied young T Tauri and Herbig Ae/Be stars are based on many different measurements and analysis methods. This has resulted in wide scatter among the published A_V values for the same star. In this work, we discuss the challenges in measuring extinction to actively accreting and especially outbursting young stellar objects (YSOs), and explore a method not previously applied to young stars, utilizing diffuse interstellar bands (DIBs). In early-type stars, narrow correlations exist between DIB equivalent widths and the column density of interstellar material, and therefore the line-of-sight extinction. Here, we measure equivalent widths of the 5780 Å and 6614 Å DIB features in a sample of actively accreting YSOs, and apply established DIB--reddening calibrations to derive reddening, and subsequently extinction. We also compare the DIBs-inferred optical line-of-sight extinction values with previous extinction estimates for our sample stars
The TESS-Keck Survey. XI. Mass Measurements for Four Transiting Sub-Neptunes Orbiting K Dwarf TOI–1246
No full textMultiplanet systems are valuable arenas for investigating exoplanet architectures and comparing planetary siblings. TOI-1246 is one such system, with a moderately bright K dwarf (V = 11.6, K = 9.9) and four transiting sub-Neptunes identified by TESS with orbital periods of 4.31, 5.90, 18.66, and 37.92 days. We collected 130 radial velocity observations with Keck/HIRES and TNG/HARPS-N to measure planet masses. We refit the 14 sectors of TESS photometry to refine planet radii (2.97 ± 0.06 R_⊕, 2.47 ± 0.08 R_⊕, 3.46 ± 0.09 R_⊕, and 3.72 ± 0.16 R_⊕) and confirm the four planets. We find that TOI-1246 e is substantially more massive than the three inner planets (8.1 ± 1.1 M_⊕, 8.8 ± 1.2 M_⊕, 5.3 ± 1.7 M_⊕, and 14.8 ± 2.3 M_⊕). The two outer planets, TOI-1246 d and TOI-1246 e, lie near to the 2:1 resonance (P_e/P_d = 2.03) and exhibit transit-timing variations. TOI-1246 is one of the brightest four-planet systems, making it amenable for continued observations. It is one of only five systems with measured masses and radii for all four transiting planets. The planet densities range from 0.70 ± 0.24 to 3.21 ± 0.44 g cm⁻¹, implying a range of bulk and atmospheric compositions. We also report a fifth planet candidate found in the RV data with a minimum mass of 25.6 ± 3.6 M_⊕. This planet candidate is exterior to TOI-1246 e, with a candidate period of 93.8 days, and we discuss the implications if it is confirmed to be planetary in nature
Threshold constraints on the size, shape and stability of alluvial rivers
No full textThe geometry of alluvial river channels both controls and adjusts to the flow of water and sediment within them. This feedback between flow and form modulates flood risk, and the impacts of climate and land-use change. Considering widely varying hydro-climates, sediment supply, geology and vegetation, it is surprising that rivers follow remarkably consistent hydraulic geometry scaling relations. In this Perspective, we explore the factors governing river channel geometry, specifically how the threshold of sediment motion constrains the size and shape of channels. We highlight the utility of the near-threshold channel model as a suitable framework to explain the average size and stability of river channels, and show how deviations relate to complex higher-order behaviours. Further characterization of the sediment transport threshold and channel adjustment timescales, coupled with probabilistic descriptions of river geometry, promise the development of future models capable of capturing rivers’ natural complexity
Ab initio development of generalized Lennard-Jones (Mie) force fields for predictions of thermodynamic properties in advanced molecular-based SAFT equations of state
No full textA methodology for obtaining molecular parameters of a modified statistical associating fluid theory for variable-range interactions of Mie form (SAFT-VR Mie) equation of state (EoS) from ab initio calculations is proposed for non-associative species that can be modeled as single spherical segments. The methodology provides a strategy to map interatomic or intermolecular potentials obtained from ab initio quantum-chemistry calculations to the corresponding Mie potentials that can be used within the SAFT-VR Mie EoS. The inclusion of corrections for quantum and many-body effects allows for an excellent, fully predictive description of the vapor–liquid envelope and other bulk thermodynamic properties of noble gases; this description is of similar or superior quality to that obtained using SAFT-VR Mie with parameters regressed in the traditional way using experimental thermodynamic-property data. The methodology is extended to an anisotropic species, methane, where similar levels of accuracy are obtained. The efficacy of using less-accurate quantum-chemistry methods in this methodology is explored, showing that these methods do not provide satisfactory results, although we note that the description is nevertheless substantially better than those obtained using the conductor-like screening model for describing real solvents (COSMO-RS), the only other fully predictive ab initio method currently available. Overall, the reliance on thermophysical data is completely dispensed with, providing the first extensible, wholly predictive SAFT-type EoSs
Efficient querying of genomic reference databases with gget
No full textA recurring challenge in interpreting genomic data is the assessment of results in the context of existing reference databases. Currently, there is no tool implementing automated, easy programmatic access to curated reference information stored in a diverse collection of large, public genomic databases. gget is a free and open-source command-line tool and Python package that enables efficient querying of genomic reference databases, such as Ensembl. gget consists of a collection of separate but interoperable modules, each designed to facilitate one type of database querying required for genomic data analysis in a single line of code. The manual and source code are available at https://github.com/pachterlab/gget
Ir-Catalyzed Asymmetric Allylic Alkylation of Dialkyl Malonates Enabling the Construction of Enantioenriched All-Carbon Quaternary Centers
No full textAn enantioselective iridium-catalyzed allylic alkylation of malonates with trisubstituted allylic electrophiles to form all-carbon quaternary stereocenters is reported. This reaction proceeds at ambient temperature and enables the preparation of a wide range of enantioenriched products in up to 93% yield and 97% ee. The quaternary products can be readily converted to several valuable building blocks such as vicinal quaternary products and β-quaternary acids
Spanning the Gap from Bulk to Bin: A Novel Spectral Microphysics Method
No full textMicrophysics methods for climate models typically track one, two, or three moments of a droplet size distribution for various categories of liquid, ice, and aerosol. Such methods rely on conversion parameters between these categories, which introduces uncertainty into predictions. While higher-resolution options such as bin and Lagrangian schemes exist, they require too many degrees of freedom for climate modeling applications and introduce numerical challenges. Here we introduce a flexible spectral microphysics method based on collocation of basis functions. This method generalizes to a linear bulk scheme at low resolution and a smoothed bin scheme at high resolution. Tested in an idealized box setting, the method improves spectral accuracy for droplet collision-coalescence and improves precipitation predictions relative to bulk methods; furthermore, it generalizes well to multimodal distributions with less complexity than a bin method. The potential to extend this collocation representation to multiple hydrometeor classes suggests a path forward to unify liquid, ice, and aerosol microphysics in a single, flexible, computational framework for climate modeling