Day 1614

Tuesday.

1908.06100
Gravitational waves, CMB polarization, and the Hubble tension
Jeong, Kamionkowski

The discrepancy between the Hubble parameter inferred from local measurements and that from the cosmic microwave background (CMB) has motivated careful scrutiny of the assumptions that enter both analyses. Here we point out that the location of the recombination peak in the CMB B-mode power spectrum is determined by the light horizon at the surface of last scatter and thus provides an alternative early-Universe standard ruler. It can thus be used as a cross-check for the standard ruler inferred from the acoustic peaks in the CMB temperature power spectrum and to test various explanations for the Hubble tension. The measurement can potentially be carried out with a precision of $\lesssim2\%$ with stage-IV B-mode experiments. The measurement can also be used to measure the propagation speed of gravitational waves in the early Universe.

1908.06102

The impact of stars stripped in binaries on the integrated spectra of stellar populations

Götberg, et al

Stars stripped of their envelopes from interaction with a binary companion emit a significant fraction of their radiation as ionizing photons. They are potentially important stellar sources of ionizing radiation, however, they are still often neglected in spectral synthesis simulations or simulations of stellar feedback. We modeled the radiative contribution from stripped stars by using detailed evolutionary and spectral models. We estimated their impact on the integrated spectra and specifically on the emission rates of HI-, HeI-, and HeII-ionizing photons from stellar populations. We find that stripped stars have the largest impact on the ionizing spectrum of a population in which star formation halted several Myr ago. In such stellar populations, stripped stars dominate the emission of ionizing photons, mimicking a younger stellar population in which massive stars are still present. Our models also suggest that stripped stars have harder ionizing spectra than massive stars. The additional ionizing radiation affects observable properties that are related to the ionizing emission from stellar populations. In co-eval stellar populations, the ionizing radiation from stripped stars increases the ionization parameter and the production efficiency of HI-ionizing photons. They also cause high values for these parameters for about ten times longer than what is predicted for massive stars. The hard ionizing radiation from stripped stars likely introduces a characteristic ionization structure of the nebula, which leads to the emission of highly ionized elements such as O$^{2+}$ and C$^{3+}$. We, therefore, expect that the presence of stripped stars affects the location in the BPT diagram and the diagnostic ratio of OIII to OII nebular emission lines. Our models are publicly available through CDS database and on the Starburst99 website.

1908.06469

Predictive model of persistence in H2RG detectors

Tulloch, George

Infrared hybridized detectors are widely used in astronomy, and their performance can be degraded by image persistence. This results in remnant images that can persist in the detector for many hours, contaminating any subsequent low-background observations. A different but related problem is reciprocity failure whereby the detector is less sensitive to low flux observations. It is demonstrated that both of these problems can be explained by trapping and detrapping currents that move charge back and forward across the depletion region boundary of the photodiodes within each pixel. These traps have been characterized in one 2.5 $\mu$m and two 5.3 $\mu$m cutoff wavelength Teledyne H2RG detectors. We have developed a behaviour model of these traps using a 5-pole Infinite Impulse Response digital filter. This model allows the trapped charge in a detector to be constantly calculated for arbitrary exposure histories, providing a near real-time correction for image persistence.

1908.06768

A low-profile, self-contained system for atmospheric monitoring and mid-flight collection of viable microbiological samples at high altitude

Singam

The prevalence of bacteria in the atmosphere has been well established in relevant literature, suggesting that airborne bacteria can influence atmospheric characteristics including the development of clouds. Studies have also demonstrated that the atmospheric biological profile is influenced by the underlying terrestrial biomes. An understanding of the complex interplay of factors that can influence the atmospheric biological profile, not to mention developing a biological census of the atmosphere, requires a cost-effective experimental system capable of generating reproducible results with reliable data. However, as has been demonstrated by payloads launched by space agencies such as NASA and JAXA, these payloads are both complex and cost prohibitive. This paper discusses the design and implementation of a biologically oriented experimental payload for high-altitude ballooning that is within the means of most student-run experimental programs. The payload highlighted in this presentation, PHANTOM (Probe for High Altitude Numeration and Tracking of Microorganisms, which has the goal of capturing aerial microorganisms at multiple altitudes in order to characterize the biological composition of the upper atmosphere), has undergone a number of successful flight trials, and serves to highlight the feasibility and utility of interdisciplinary projects between aerospace and the biological sciences.