Earth, Sun, and Venus

Theoretical models based on spherical geometries have long provided essential insights into the directional behavior of sound sources such as loudspeakers and human speech. Because commonly applied models predict omnidirectional radiation at low frequencies and increasing directionality at higher frequencies, they fail to predict the directional characteristics of certain sources with different source geometries. These sources include violins and open-back guitar amplifiers that have openings or ports connecting a cavity or enclosure to the exterior domain. This work presents the low-frequency radiation from a vibrating cap on a rigid spherical shell with a circular aperture to study the directional characteristics of such sources. The proposed model predicts dipolar radiation at very low frequencies, monopolar radiation near the Helmholtz resonance, and increasing directionality at higher frequencies. Experimental results based on measuring the sound field of an open-back spherical loudspeaker validate the theoretical model and highlight its utility in predicting directional behavior.

Aims. The origin and maintenance of spiral structure in galaxies, the correlation between different types of spiral structure and several proposed mechanisms for their generation, and the evolution of spiral arms of galaxies with time are questions that are still controversial. In this note we study the spiral structure in a sample of distant galaxies in order to infer the evolution of spiral arm characteristics with redshift.

Methods. We considered a sample of 171 face-on spiral galaxies in the Hubble Space Telescope COSMOS (The Cosmic Evolution Survey) field. The galaxies are distributed up to z approximate to 1 with a mean value of 0.44. For all galaxies, we determined the pitch angles of the spiral arms and analysed their dependence on redshift; a total of 359 arms were measured.

Results. Analyses of our measurements combined with the literature data suggest a possible evolution of the pitch angles of spiral galaxies: by the modern epoch the spiral pattern, on average, becomes more tightly wound. This may be a consequence of the general evolution of the structure of galaxies as galaxies become more massive over time and their bulges grow. In addition, the distribution of the cotangent of pitch angle of galaxies indicates the possibility that the dominant mechanism of spiral pattern generation changes over time.

The approximation of real non-spherical scatterers by spheroids is used in various applications. It often requires fast massive calculations of the optical properties of spheroids. The most powerful approach to that is known to be a field expansion in terms of spheroidal wave functions, in particular, in the way suggested by Farafonov over 30 years ago. We improve the main shortcomings of such an approach. Our solution is formulated in terms of normalised spheroidal functions, and firstly for their definition given by Meixner & Schafke, which is computationally favourable and is required by the unique subroutines recently created to compute these functions. By means of T-matrix transformations we solve a long-standing major problem of Farafonov's version, namely the accuracy and time losses for one kind (TE mode) of the incident wave polarisation. Apart from this and other improvements of this solution, for the first time we relate its single particle spheroidal T-matrix to the standard spherical one which is widely employed for particle ensembles. The constructed algorithm has been extensively numerically tested. It is found to be very accurate for dielectric spheroids with the aspect ratio a/b reaching 100 and the diffraction (size) parameter xa = 2za/angstrom as large as 300, where a and b are the major and minor semi-axes, respectively, angstrom is the wavelength. The algorithm is supplied with a program interface to the free package CosTuuM to perform parallel computations of various optical properties for ensembles of spheroids with different distributions over orientation (alignment) and shape.

We present 0.'' 22-resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO(2-1) emission from the circumnuclear gas disk in the red nugget relic galaxy PGC 11179. The disk shows regular rotation, with projected velocities near the center of 400 km s-1. We assume the CO emission originates from a dynamically cold, thin disk and fit gas-dynamical models directly to the ALMA data. In addition, we explore systematic uncertainties by testing the impacts of various model assumptions on our results. The supermassive black hole (BH) mass (M BH) is measured to be M BH = (1.91 +/- 0.04 [1 sigma statistical] -0.51+0.11 [systematic]) x 109 M circle dot, and the H-band stellar mass-to-light ratio M/L H = 1.620 +/- 0.004 [1 sigma statistical] -0.107+0.211 [systematic] M circle dot/L circle dot. This M BH is consistent with the BH mass-stellar velocity dispersion relation but over-massive compared to the BH mass-bulge luminosity relation by a factor of 3.7. PGC 11179 is part of a sample of local compact early-type galaxies that are plausible relics of z similar to 2 red nuggets, and its behavior relative to the scaling relations echoes that of three relic galaxy BHs previously measured with stellar dynamics. These over-massive BHs could suggest that BHs gain most of their mass before their host galaxies do. However, our results could also be explained by greater intrinsic scatter at the high-mass end of the scaling relations, or by systematic differences in gas- and stellar-dynamical methods. Additional M BH measurements in the sample, including independent cross-checks between molecular gas- and stellar-dynamical methods, will advance our understanding of the co-evolution of BHs and their host galaxies.

The AGN STORM 2 campaign is a large, multiwavelength reverberation mapping project designed to trace out the structure of Mrk 817 from the inner accretion disk to the broad emission line region and out to the dusty torus. As part of this campaign, Swift performed daily monitoring of Mrk 817 for approximately 15 months, obtaining observations in X-rays and six UV/optical filters. The X-ray monitoring shows that Mrk 817 was in a significantly fainter state than in previous observations, with only a brief flare where it reached prior flux levels. The X-ray spectrum is heavily obscured. The UV/optical light curves show significant variability throughout the campaign and are well correlated with one another, but uncorrelated with the X-rays. Combining the Swift UV/optical light curves with Hubble Space Telescope UV continuum light curves, we measure interband continuum lags, tau(lambda), that increase with increasing wavelength roughly following tau(lambda) proportional to lambda 4/3, the dependence expected for a geometrically thin, optically thick, centrally illuminated disk. Modeling of the light curves reveals a period at the beginning of the campaign where the response of the continuum is suppressed compared to later in the light curve-the light curves are not simple shifted and scaled versions of each other. The interval of suppressed response corresponds to a period of high UV line and X-ray absorption, and reduced emission line variability amplitudes. We suggest that this indicates a significant contribution to the continuum from the broad-line region gas that sees an absorbed ionizing continuum.

To improve acoustical models of super heavy-lift launch vehicles, this Letter reports Space Launch System's (SLS's) overall sound power level (OAPWL) and compares it to NASA's past lunar rocket, the Saturn V. Measurements made 1.4–1.8 km from the launchpad indicate that SLS produced an OAPWL of 202.4 (⁠ 

0.5) dB re 1 pW and acoustic efficiency of about 0.33%. Adjustment of a static-fire sound power spectrum for launch conditions implies Saturn V was at least 2 dB louder than SLS with approximately twice the acoustic efficiency.