4 results
Search Results
Now showing 1 - 4 of 4
- ItemBayesian approach for auroral oval reconstruction from ground-based observations(Amsterdam [u.a.] : Elsevier Science, 2022) Wagner, D.; Neuhäuser, R.; Arlt, R.Naked eye observations of aurorae might be used to obtain information on the large-scale magnetic field of the Earth at historic times. Their abundance may also help bridge gaps in observational time-series of proxies for solar activity such as the sunspot number or cosmogenic isotopes. With information derived from aurora observations like observing site, time of aurora sighting and position on the sky we can reconstruct the auroral oval. Since aurorae are correlated with geomagnetic indices like the Kp index, it is possible to obtain information about the terrestrial magnetic field in the form of the position of the magnetic poles as well as the magnetic disturbance level. Here we present a Bayesian approach to reconstruct the auroral oval from ground-based observations by using two different auroral oval models. With this method we can estimate the position of the magnetic poles in corrected geomagnetic coordinates as well as the Kp index. The method is first validated on synthetic observations before it is applied to four modern geomagnetic storms between 2003 and 2017 where ground-based reports and photographs were used to obtain the necessary information. Based on the four modern geomagnetic storms we have shown, that we are able to reconstruct the pole location with an average accuracy of ≈2° in latitude and ≈11° in longitude. The Kp index can be inferred with a precision of one class. The future goal is to employ the method to historical storms, where we expect somewhat higher uncertainties, since observations may be less accurate or not favorably distributed.
- ItemThe Abundance of S-Process Elements: Temporal and Spatial Trends from Open Cluster Observations(Basel : MDPI, 2022) Magrini, Laura; Vázquez, Carlos Viscasillas; Casali, Giada; Baratella, Martina; D’Orazi, Valentina; Spina, Lorenzo; Randich, Sofia; Cristallo, Sergio; Vescovi, DiegoSpectroscopic observations of stars belonging to open clusters, with well-determined ages and distances, are a unique tool for constraining stellar evolution, nucleosynthesis, mixing processes, and, ultimately, Galactic chemical evolution. Abundances of slow (s) process neutron capture elements in stars that retain their initial surface composition open a window into the processes that generated them. In particular, they give us information on their main site of production, i.e., the low-and intermediate-mass Asymptotic Giant Branch (AGB) stars. In the present work, we review some observational results obtained during the last decade that contributed to a better understanding of the AGB phase: the growth of s-process abundances at recent epochs, i.e., in the youngest stellar populations; the different relations between age and [s/Fe] in distinct regions of the disc; and finally the use of s-process abundances combined with those of α elements, [s/α], to estimate stellar ages. We revise some implications that these observations had both on stellar and Galactic evolution, and on our ability to infer stellar ages.
- ItemReflectivity of Venus’s Dayside Disk During the 2020 Observation Campaign: Outcomes and Future Perspectives([Bristol] : IOP Publishing, 2022) Lee, Yeon Joo; García Muñoz, Antonio; Yamazaki, Atsushi; Quémerais, Eric; Mottola, Stefano; Hellmich, Stephan; Granzer, Thomas; Bergond, Gilles; Roth, Martin; Gallego-Cano, Eulalia; Chaufray, Jean-Yves; Robidel, Rozenn; Murakami, Go; Masunaga, Kei; Kaplan, Murat; Erece, Orhan; Hueso, Ricardo; Kabáth, Petr; Špoková, Magdaléna; Sánchez-Lavega, Agustín; Kim, Myung-Jin; Mangano, Valeria; Jessup, Kandis-Lea; Widemann, Thomas; Sugiyama, Ko-ichiro; Watanabe, Shigeto; Yamada, Manabu; Satoh, Takehiko; Nakamura, Masato; Imai, Masataka; Cabrera, JuanWe performed a unique Venus observation campaign to measure the disk brightness of Venus over a broad range of wavelengths in 2020 August and September. The primary goal of the campaign was to investigate the absorption properties of the unknown absorber in the clouds. The secondary goal was to extract a disk mean SO2 gas abundance, whose absorption spectral feature is entangled with that of the unknown absorber at ultraviolet wavelengths. A total of three spacecraft and six ground-based telescopes participated in this campaign, covering the 52–1700 nm wavelength range. After careful evaluation of the observational data, we focused on the data sets acquired by four facilities. We accomplished our primary goal by analyzing the reflectivity spectrum of the Venus disk over the 283–800 nm wavelengths. Considerable absorption is present in the 350–450 nm range, for which we retrieved the corresponding optical depth of the unknown absorber. The result shows the consistent wavelength dependence of the relative optical depth with that at low latitudes, during the Venus flyby by MESSENGER in 2007, which was expected because the overall disk reflectivity is dominated by low latitudes. Last, we summarize the experience that we obtained during this first campaign, which should enable us to accomplish our second goal in future campaigns.
- ItemThe Complex Behaviour of s-Process Element Abundances at Young Ages(Basel : MDPI, 2022) D’Orazi, Valentina; Baratella, Martina; Lugaro, Maria; Magrini, Laura; Pignatari, MarcoOpen clusters appear as simple objects in many respects, with a high degree of homogeneity in their (initial) chemical composition, and the typical solar-scaled abundance pattern that they exhibit for the majority of the chemical species. The striking singularity is represented by heavy elements produced from the slow process of the neutron-capture reactions. In particular, young open clusters (ages less than a few hundred Myr) give rise to the so-called barium puzzle: that is an extreme enhancement in their [Be/Fe] ratios, up to a factor of four of the solar value, which is not followed by other nearby s-process elements (e.g., lanthanum and cerium). The definite explanation for such a peculiar trend is still wanting, as many different solutions have been envisaged. We review the status of this field and present our new results on young open clusters and the pre-main sequence star RZ Piscium.