Numerical computation of second order vacuum perturbations of Kerr black holes

Motivated by the desire to understand the leading order nonlinear gravitational wave interactions around arbitrarily rapidly rotating Kerr black holes, we describe a numerical code designed to compute second order vacuum perturbations on such spacetimes. A general discussion of the formalism we use is presented in (arXiv:2008.11770); here we show how we numerically implement that formalism with a particular choice of coordinates and tetrad conditions, and give example results for black holes with dimensionless spin parameters $a=0.7$ and $a=0.998$. We first solve the Teukolsky equation for the linearly perturbed Weyl scalar $\Psi_4^{(1)}$, followed by direct reconstruction of the spacetime metric from $\Psi_4^{(1)}$, and then solve for the dynamics of the second order perturbed Weyl scalar $\Psi_4^{(2)}$. This code is a first step toward a more general purpose second order code, and we outline how our basic approach could be further developed to address current questions of interest, including extending the analysis of ringdown in black hole mergers to before the linear regime, exploring gravitational wave "turbulence" around near-extremal Kerr black holes, and studying the physics of extreme mass ratio inspiral.Comment: Comments welcom

Perceived coercion in psychiatric hospital admission: validation of the French-language version of the MacArthur Admission Experience Survey.

The MacArthur Admission Experience Survey (AES) is a widely used tool to evaluate the level of perceived coercion experienced at psychiatric hospital admission. The French-language AES was prepared using a translation/back-translation procedure. It consists of 16 items and 3 subscores (perceived coercion, negative pressures and voice). This study aimed to assess the psychometric properties of the French-language AES. 152 inpatients were evaluated. Reliability was estimated using internal consistency coefficients and a test-retest procedure. Internal validity was assessed using a two-parameter logistic item response model. Convergent validity was estimated using correlations between the AES scores and the Coercion Ladder (CL), the Coercion Experience Scale (CES) and the Global Assessment of Functioning (GAF) scale. Discriminatory power was evaluated by comparing the scores of patients undergoing voluntary or compulsory admission. The French-language AES showed good internal consistency and test-retest reliability. Internal validity of the three-factor model was excellent. Correlations between AES and CL, CES and GAF scores suggested good convergent validity. AES scores were significantly higher among patients subject to compulsory psychiatric hospital admission than among those admitted voluntarily. Overall, the French-language version of the AES demonstrated very good psychometric proprieties

New M, L, and T Dwarf Companions to Nearby Stars from the Wide-field Infrared Survey Explorer

We present 11 candidate late-type companions to nearby stars identified with data from the Wide-field Infrared Survey Explorer (WISE) and the Two Micron All Sky Survey (2MASS). Eight of the candidates are likely to be companions based on their common proper motions with the primaries. The remaining three objects are rejected as companions, one of which is a free-floating T7 dwarf. Spectral types are available for five of the companions, which consist of M2V, M8.5V, L5, T8, and T8. Based on their photometry, the unclassified companions are probably two mid-M dwarfs and one late-M/early-L dwarf. One of the T8 companions, WISE J142320.84+011638.0, has already been reported by Pinfield and coworkers. The other T8 companion, ULAS J095047.28+011734.3, was discovered by Burningham and coworkers through the United Kingdom Infrared Telescope Infrared Deep Sky Survey, but its companionship has not been previously recognized in the literature. The L5 companion, 2MASS J17430860+8526594, is a new member of a class of L dwarfs that exhibit unusually blue near-IR colors. Among the possible mechanisms that have been previously proposed for the peculiar colors of these L dwarfs, low metallicity does not appear to be a viable explanation for 2MASS J17430860+8526594 since our spectrum of the primary suggests that its metallicity is not significantly subsolar

Discovery of a Companion at the L/T Transition with the Wide-field Infrared Survey Explorer

We report the discovery of a substellar companion to the nearby solar-type star HD 46588 (F7V, 17.9 pc, ~3 Gyr). HD 46588 B was found through a survey for common proper motion companions to nearby stars using data from the Wide-field Infrared Survey Explorer and the Two-Micron All-Sky Survey. It has an angular separation of 79.2" from its primary, which corresponds to a projected physical separation of 1420 AU. We have measured a spectral type of L9 for this object based on near-infrared spectroscopy performed with TripleSpec at Palomar Observatory. We estimate a mass of 0.064+0.008/-0.019 Msun from a comparison of its luminosity to the values predicted by theoretical evolutionary models for the age of the primary. Because of its companionship to a well-studied star, HD 46588 B is one of the few known brown dwarfs at the L/T transition for which both age and distance estimates are available. Thus, it offers new constraints on the properties of brown dwarfs during this brief evolutionary phase. The discovery of HD 46588 B also illustrates the value of the Wide-field Infrared Survey Explorer for identifying brown dwarfs in the solar neighborhood via their proper motions.Comment: Astrophysical Journal, in pres

Second-order perturbations of Kerr black holes: Formalism and reconstruction of the first-order metric

Motivated by gravitational wave observations of binary black hole mergers, we present a procedure to compute the leading-order nonlinear gravitational wave interactions around a Kerr black hole. We describe the formalism used to derive the equations for second-order perturbations. We develop a procedure that allows us to reconstruct the first-order metric perturbation solely from knowledge of the solution to the first-order Teukolsky equation, without the need of Hertz potentials. Finally, we illustrate this metric reconstruction procedure in the asymptotic limit for the first-order quasinormal modes of Kerr. In a companion paper [J. L. Ripley et al., Phys. Rev. D 103, 104018 (2021)] we present a numerical implementation of these ideas