Astronomical Informant

2022-06-03 20:09:15 NASA Invites Media to Learn About Mission Studying Thunderstorms
http://www.nasa.gov/press-release/nasa-invites-media-to-learn-about-mission-studying-thunderstorms

NASA will host a media teleconference at 10 a.m. CDT Tuesday, June 7, to discuss research about intense summer thunderstorms over the central United States and their effects on Earth’s atmosphere and climate change. Aprire / Come

2022-06-03 17:39:09 Apollo 1 Monument Dedication
http://www.nasa.gov/image-feature/apollo-1-monument-dedication

The Apollo 1 monument at Arlington National Cemetery was dedicated on Thursday, June 2, 2022, in Arlington, Va. Aprire / Come

2022-06-03 05:36:34 arXiv:We study the scattering of gravitational waves by a Schwarzschild black hole and its perturbed siblings to investigate influences of proposed spectral instability of quasinormal modes on the ringdown signal. Our results indicate that information of dominant ringdown signals, which are ascribed to the fundamental (i.e., least damping) quasinormal mode of unperturbed Schwarzschild black holes, is imprinted in the phase shift defined from the transmission amplitude (1/A_{in} in our notation). This approximately parallels the fact that the resonance of quantum systems is imprinted in the phase shift of the S-matrix. The phase shift around the oscillation frequency of the fundamental mode is modified only perturbatively even if the quasinormal-mode spectrum is destabilized by a perturbative bump at a distant location, signifying the stability of the ringdown signal. At the same time, the phase shift at low frequencies is modulated substantially reflecting the late-time excitation of echo signals associated with the quasinormal-mode spectrum after destabilization.

via astro-ph updates on arXiv.org https://ift.tt/LwiXFo4 Aprire / Come

2022-06-03 05:36:33 arXiv:We measure the 3PCF of 300 halo catalogs from the Minerva simulations covering a total volume of $~1000 h^{-3} \mathrm{Gpc}^3$. Each 3PCF measurement includes all possible triangular configurations with sides between 20 and $130h^{-1}\mathrm{Gpc}$. First, we test different estimates of the covariance matrix, a crucial aspect of the analysis. We compare the covariance computed numerically from the limited but accurate benchmark simulations set to the one obtained from $10000$ approximate halo catalogs generated with the Pinocchio code. We demonstrate that the two numerically-estimated covariance matrices largely match, confirming the validity of approximate methods based on Lagrangian Perturbation Theory for generating mocks suitable for covariance estimation. We also compare the numerical covariance with a theoretical prediction in the Gaussian approximation. We find a good match between the two for separations above 40 $h^{-1} \mathrm{Gpc}$. We test the 3PCF tree-level model in Perturbation Theory. The model is adopted in a likelihood analysis aimed at the determination of bias parameters. We find that, for our sample of halos at redshift $z=1$, the tree-level model performs well for separations $r \geq 40 \, h^{-1}\mathrm{Gpc}$. Results obtained with this scale cut are robust against different choices of covariance matrix. We compare to the analogous analysis of the halo bispectrum already presented in a previous publication, finding a remarkable agreement between the two statistics. We then test different assumptions to build the model defining a robust combination of hypotheses that lead to unbiased parameter estimates. Our results confirm the importance of 3PCF, supplying a solid recipe for its inclusion in likelihood analyses. Moreover, it opens the path for further improvements, especially in modelling, to extract information from non-linear regimes

via astro-ph updates on arXiv.org https://ift.tt/vMriSKe Aprire / Come

2022-06-02 05:36:38 arXiv:The Oort cloud and the scattered disk are the two primary reservoirs for long-period and short-period comets, respectively. In this review, we assess the known observational constraints on these reservoirs' properties and their formation. In addition, we discuss how the early orbital evolution of the giant planets generated the modern scattered disk from the early, massive planetesimal disk and how $\sim$5\% of this material was captured into the Oort cloud. We review how the Sun's birth environment and dynamical history within the Milky Way alters the formation and modern structure of the Oort cloud. Finally, we assess how the coming decade's anticipated observing campaigns may provide new insights into the formation and properties of the Oort cloud and scattered disk.

via astro-ph updates on arXiv.org https://ift.tt/5z3gatW Aprire / Come

2022-06-02 05:36:37 arXiv:Convection is ubiquitous in stars and occurs under many different conditions. Here we explore convection in main-sequence stars through two lenses: dimensionless parameters arising from stellar structure and parameters which emerge from the application of mixing length theory. We first define each quantity in terms familiar both to the 1D stellar evolution community and the hydrodynamics community. We then explore the variation of these quantities across different convection zones, different masses, and different stages of main-sequence evolution. We find immense diversity across stellar convection zones. Convection occurs in thin shells, deep envelopes, and nearly-spherical cores; it can be efficient of inefficient, rotationally constrained or not, transsonic or deeply subsonic. This atlas serves as a guide for future theoretical and observational investigations by indicating which regimes of convection are active in a given star, and by describing appropriate model assumptions for numerical simulations.

via astro-ph updates on arXiv.org https://ift.tt/SDuB0i6 Aprire / Come

2022-05-27 17:11:32 Hubble Captures Pair of Star-Forming Spirals
http://www.nasa.gov/image-feature/goddard/2022/hubble-captures-pair-of-star-forming-spirals

This new image from NASA’s Hubble Space Telescope looks at two spiral galaxies, collectively known as Arp 303. Aprire / Come

2022-05-27 17:04:41 ATel 15401: Aql X-1: indicators of optical outburst in 2022
https://www.astronomerstelegram.org/?read=15401

Our team informs about presence of new outburst indicator for the Soft X-ray Transient (SXT) Aql X-1. Most of our data were taken with the 1-m SAO RAS optical telescope, some additional measurements were performed with our 0.5-m RC reflector. ... Aprire / Come

2022-05-25 06:36:17 arXiv:We report on three-dimensional direct numerical simulation of wave turbulence on the free surface of a magnetic fluid subjected to an external horizontal magnetic field. A transition from capillarywave turbulence to anisotropic magneto-capillary wave turbulence is observed for an increasing field. At high enough field, wave turbulence becomes highly anisotropic, cascading mainly perpendicularly to the field direction, in good agreement with the prediction of a phenomenological model, and with anisotropic Alfv{\'e}n wave turbulence. Although surface waves on a magnetic fluid are different from Alfv{\'e}n waves in plasma, a strong analogy is found with similar wave spectrum scalings and similar magnetic-field dependent dispersionless wave velocities.

via astro-ph updates on arXiv.org https://ift.tt/rRcu3hz Aprire / Come

2022-05-22 01:29:12 ATel 15390: Optical follow-up of Mrk421
https://www.astronomerstelegram.org/?read=15390

After the announcement in ATel #15389 of a flaring activity in Gamma rays of Mrk 421 I observed the source on May 21 2021 with the 30cm telescope of the Foligno Observatory (K56) in the B and V (Johnson) bands. ... Aprire / Come