Thermal Models of Asteroids with Two-band Combinations of Wide-field Infrared Survey Explorer Cryogenic Data

We used the reparameterized Near-Earth Asteroid Thermal Model to model observations of a curated set of over 4000 asteroids from the Wide-field Infrared Survey Explorer in two wavelength bands (W2-3 or W3-4) and compared the results to previous results from all four wavelength bands (W1-4). This comparison was done with the goal of elucidating unique aspects of modeling two-band observations so that any potential biases or shortcomings for planned two-band surveys (e.g., the NASA Near-Earth Object Surveyor Mission) can be anticipated and quantified. The W2-3 two-band fits usually yielded slightly smaller diameters than the four-band fits, with a median diameter difference of -10%, with the 5% and 95% quantiles of the distribution at -32% and -1.5%, respectively. We conducted similar comparisons for W3-4, in part because the longest wavelength bands are expected to provide the best two-band results. We found that the W3-4 two-band diameters are slightly larger than the four-band results, with a median diameter difference of 11% and the 5% and 95% quantiles of the distribution at -2.1% and 26%, respectively. The diameter uncertainty, obtained with bootstrap analysis, is larger by 30% and 35% (median values) for the W2-3 and W3-4 fits, respectively, than for the corresponding four-band fits. Using 23 high-quality stellar occultation diameters as a benchmark, we found that the median errors of W2-3 and W3-4 diameter estimates are -15% and +12%, respectively, whereas the median error of the four-band fits is 9.3%. Although the W2-3 and W3-4 diameters appear to have greater systematic errors and uncertainties than their four-band counterparts, two-band estimates remain useful because they improve upon diameter estimates obtained from visible photometry alone.Comment: 18 pages, 21 figure

Semiaquatic adaptations in a giant predatory dinosaur

Mysterious dinosaur a swimmer? Dinosaurs are often appreciated for their size and oddity. In this regard, the North African carnivorous theropod Spinosaurus , with its huge dorsal sail and a body larger than Tyrannosaurus rex , has long stood out. This species also stands out because of its history. The unfortunate loss of the type specimen during World War II left much of what we know about Spinosaurus to be divined through speculation and reconstruction. Ibrahim et al. now describe new fossils of this unusual species. They conclude it was, at least partly, aquatic, a first for dinosaurs. Science , this issue p. 1613 </jats:p

A thermal instability for positive brane cosmological constant in the Randall-Sundrum cosmologies

We describe a novel dynamical mechanism to radiate away a positive four dimensional cosmological constant, in the Randall-Sundrum cosmological scenario. We show that there are modes of the bulk gravitational field for which the brane is effectively a mirror. This will generally give rise to an emission of thermal radiation from the brane into the bulk. The temperature turns out to be nonvanishing only if the effective four dimensional cosmological constant is positive. In any theory where the four dimensional vacuum energy is a function of physical degrees of freedom, there is then a mechanism that radiates away any positive four dimensional cosmological constant.Comment: 14 pages. The discussion on the relation between temperature and effective 4d cosmological constant is changed. References are adde

A Search for Technosignatures Around 11,680 Stars with the Green Bank Telescope at 1.15-1.73 GHz

We conducted a search for narrowband radio signals over four observing sessions in 2020-2023 with the L-band receiver (1.15-1.73 GHz) of the 100 m diameter Green Bank Telescope. We pointed the telescope in the directions of 62 TESS Objects of Interest, capturing radio emissions from a total of ~11,680 stars and planetary systems in the ~9 arcminute beam of the telescope. All detections were either automatically rejected or visually inspected and confirmed to be of anthropogenic nature. In this work, we also quantified the end-to-end efficiency of radio SETI pipelines with a signal injection and recovery analysis. The UCLA SETI pipeline recovers 94.0% of the injected signals over the usable frequency range of the receiver and 98.7% of the injections when regions of dense RFI are excluded. In another pipeline that uses incoherent sums of 51 consecutive spectra, the recovery rate is ~15 times smaller at ~6%. The pipeline efficiency affects calculations of transmitter prevalence and SETI search volume. Accordingly, we developed an improved Drake Figure of Merit and a formalism to place upper limits on transmitter prevalence that take the pipeline efficiency and transmitter duty cycle into account. Based on our observations, we can state at the 95% confidence level that fewer than 6.6% of stars within 100 pc host a transmitter that is detectable in our search (EIRP > 1e13 W). For stars within 20,000 ly, the fraction of stars with detectable transmitters (EIRP > 5e16 W) is at most 3e-4. Finally, we showed that the UCLA SETI pipeline natively detects the signals detected with AI techniques by Ma et al. (2023).Comment: 22 pages, 9 figures, submitted to AJ, revise