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Context. Radio pulsars can be used for many studies, including the investigation of the ionized interstellar medium and the solar wind via their dispersive effects. These phenomena affect the high-precision timing of pulsars and are among the main sources of noise in experiments searching for low-frequency gravitational waves in pulsar data. Aims. In this paper, we compare the functionality and reliability of three commonly used schemes to measure temporal variations in interstellar propagation effects in pulsar timing data. Methods. We carried out extensive simulations at low observing frequencies (100–200 MHz) by injecting long-term correlated noise processes with power-law spectra and white noise, to evaluate the robustness, accuracy, and precision of the following three mitigation methods: epoch-wise (EW) measurements of interstellar dispersion; the DMX method of simultaneous, piece-wise fits to interstellar dispersion; and DM GP, which models dispersion variations through Gaussian processes using a Bayesian analysis method. We then evaluated how reliably the input signals were reconstructed and how the various methods reacted to the presence of achromatic long-period noise. Results. All the methods perform well, provided the achromatic long-period noise is modeled for DMX and DM GP. The most precise method is DM GP, followed by DMX and EW, while the most accurate is EW, followed by DMX and DM GP. We also tested different scenarios including simulations ofL-band times of arrival and realistic DM injection, with no significant variation in the obtained results. Conclusions. Given the nature of our simulations and our scope, we deem that EW is the most reliable method to study the Galactic ionized media. Follow-up works should be conducted to confirm this result via more realistic simulations. We note that DM GP and DMX seem to be the best-performing techniques in removing long-term correlated noise, and hence for gravitational wave studies. However, full simulations of pulsar timing array experiments are needed to support this interpretation. 

Exoplanets in the ultra-hot Jupiter regime provide an excellent laboratory for testing the impact of stellar irradiation on the dynamics and chemical composition of gas giant atmospheres. In this study, we observed two transits of the ultra-hot Jupiter WASP-189 b with MAROON-X/Gemini-North to probe its high-altitude atmospheric layers, using strong absorption lines. We derived posterior probability distributions for the planetary and stellar parameters by calculating the stellar spectrum behind the planet at every orbital phase during the transit. This was used to correct the Rossiter–McLaughlin imprint on the transmission spectra. Using differential transmission spectroscopy, we detect strong absorption lines of Ca⁺, Ba⁺, Na, Hα, Mg, Fe, and Fe⁺, providing an unprecedented and detailed view of the atmospheric chemical composition. Ca⁺absorption is particularly well suited for analysis through time-resolved narrow-band spectroscopy, owing to its transition lines formed in high-altitude layers. The spectral absorption lines show no significant blueshifts that would indicate high-altitude day-to-night winds, and further analysis is needed to investigate the implications for atmospheric dynamics. These high signal-to-noise observations provide a benchmark data set for testing high-resolution retrievals and the assumptions of atmospheric models. We also simulate observations of WASP-189 b with ANDES/ELT, and show that ANDES will be highly sensitive to the individual absorption lines of a myriad of elements and molecules, including TiO and CO. 

Abstract While observations of many high-precision radio pulsars of order ≲1 μ s across the sky are needed for the detection and characterization of a stochastic background of low-frequency gravitational waves (GWs), sensitivity to single sources of GWs requires even higher timing precision. The Argentine Institute of Radio Astronomy (IAR; Instituto Argentino de Radioastronomía) has begun observations of the brightest known millisecond pulsar, J0437−4715. Even though the two antennas are smaller than other single-dish telescopes previously used for pulsar timing array (PTA) science, the IAR’s capability to monitor this pulsar daily, coupled with the pulsar’s brightness, allows for high-precision measurements of pulse-arrival time. While upgrades of the facility are currently underway, we show that modest improvements beyond current plans will provide IAR with unparalleled sensitivity to this pulsar. The most stringent upper limits on single GW sources come from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). Observations of PSR J0437−4715 will provide a significant sensitivity increase in NANOGrav’s “blind spot” in the sky where fewer pulsars are currently being observed. With state-of-the-art instrumentation installed, we estimate the array’s sensitivity will improve by a factor of ≈2–4 over 10 yr for 20% of the sky with the inclusion of this pulsar, as compared to a static version of the PTA used in NANOGrav’s most recent limits. More modest instrumentation results in factors of ≈1.4–3. We identify four other candidate pulsars as suitable for inclusion in PTA efforts. International PTA efforts will also benefit from inclusion of these data, given the potential achievable sensitivity.