2005.07707
Effects of supernova redshift uncertainties on the determination of cosmological parameters
Steinhardt, Sneppen, Sen
Redshifts used in current cosmological supernova samples are measured using two primary techniques, one based on well-measured host galaxy spectral lines and the other based on supernova-dominated spectra. Here, we construct an updated Pantheon catalog with revised redshifts, redshift sources and estimated uncertainties for the entire sample to investigate whether these two techniques yield consistent results. The best-fit cosmological parameters using these two measurement techniques disagree, and we explore several possible sources of bias which could result from using the lower-precision supernova-dominated redshifts. In a pilot study, we show that using a host redshift-only subsample of the Pantheon catalog will result in lower $\Omega_m$ and matter density $\Omega_m h^2$ and slightly higher $H_0$ than previous analysis which, among other possibilities, could result in supernova and CMB measurements agreeing on $\Omega_m h^2$ despite tension in $H_0$. To obtain rigorous results, though, the Pantheon catalog should be improved by obtaining host spectra for supernova that have faded and future surveys should be designed to use host galaxy redshifts rather than lower-precision methods.
Effects of supernova redshift uncertainties on the determination of cosmological parameters
Steinhardt, Sneppen, Sen
Redshifts used in current cosmological supernova samples are measured using two primary techniques, one based on well-measured host galaxy spectral lines and the other based on supernova-dominated spectra. Here, we construct an updated Pantheon catalog with revised redshifts, redshift sources and estimated uncertainties for the entire sample to investigate whether these two techniques yield consistent results. The best-fit cosmological parameters using these two measurement techniques disagree, and we explore several possible sources of bias which could result from using the lower-precision supernova-dominated redshifts. In a pilot study, we show that using a host redshift-only subsample of the Pantheon catalog will result in lower $\Omega_m$ and matter density $\Omega_m h^2$ and slightly higher $H_0$ than previous analysis which, among other possibilities, could result in supernova and CMB measurements agreeing on $\Omega_m h^2$ despite tension in $H_0$. To obtain rigorous results, though, the Pantheon catalog should be improved by obtaining host spectra for supernova that have faded and future surveys should be designed to use host galaxy redshifts rather than lower-precision methods.
2005.07831
Science merit function for the KEPLER mission
Borucki
The Kepler Mission was a NASA Discovery-class mission designed to continuously monitor the brightness of at least 100,000 stars to determine the frequency of Earth-size and larger planets orbiting other stars. Once the Kepler proposal was chosen for a flight opportunity, it was necessary to optimize the design to accomplish the ambitious goals specified in the proposal and still stay within the available resources. To maximize the science return from the mission, a merit function (MF) was constructed that relates the science value (as determined by the PI and the Science Team) to the chosen mission characteristics and to models of the planetary and stellar systems. This MF served several purposes; prediction of the science results of the proposed mission, effects of varying the values of the mission parameters to increase the science product or to reduce the mission costs, and assessment of risks. The Merit Function was also valuable for the purposes of advocating the Mission by illustrating its expected capability. Later, it was used to keep management informed of the changing mission capability as trade-offs and mission down-sizing occurred. The MF consisted of models of the stellar environment, assumed exoplanet characteristics and distributions, parameter values for the mission point-design, and equations that related the science value to the predicted number and distributions of detected exoplanets. A description of the MF model and representative results are presented.
2005.08252
Gravitational focusing of low-velocity dark matter on the Earth's surface
Sofue
We show that the Earth acts as a high-efficiency gravitational collector of low-velocity flow of dark matter (DM). The focal point appears on the Earth's surface, when the DM flow speed is about 17 km s$^{-1}$ with respect to the geo-center. We discuss diurnal modulation of the local DM density influenced by the Earth's gravity. We also touch upon similar effects on galactic and solar system objects.
2005.08330
Formation of giant planet satellites
Batygin, Morbidelli
Recent analyses have shown that the concluding stages of giant planet formation are accompanied by the development of large-scale meridional flow of gas inside the planetary Hill sphere. This circulation feeds a circumplanetary disk that viscously expels gaseous material back into the parent nebula, maintaining the system in a quasi-steady state. Here we investigate the formation of natural satellites of Jupiter and Saturn within the framework of this newly outlined picture. We begin by considering the long-term evolution of solid material, and demonstrate that the circumplanetary disk can act as a global dust trap, where $s_{\bullet}\sim0.1-10\,$mm grains achieve a hydrodynamical equilibrium, facilitated by a balance between radial updraft and aerodynamic drag. This process leads to a gradual increase in the system's metallicity, and eventually culminates in the gravitational fragmentation of the outer regions of the solid sub-disk into $\mathcal{R}\sim100\,$km satellitesimals. Subsequently, satellite conglomeration ensues via pairwise collisions, but is terminated when disk-driven orbital migration removes the growing objects from the satellitesimal feeding zone. The resulting satellite formation cycle can repeat multiple times, until it is brought to an end by photo-evaporation of the parent nebula. Numerical simulations of the envisioned formation scenario yield satisfactory agreement between our model and the known properties of the Jovian and Saturnian moons.
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