Chemical Abundances of Planetary Nebulae in the Sagittarius Dwarf Elliptical Galaxy

Spectrophotometry and imaging of the two planetary nebulae He2-436 and Wray16-423, recently discovered to be in the Sagittarius dwarf elliptical galaxy, are presented. Wray16-423 is a high excitation planetary nebula (PN) with a hot central star. In contrast He2-436 is a high density PN with a cooler central star and evidence of local dust, the extinction exceeding that for Wray16-423 by E(B-V)=0.28. The extinction to Wray16-423, (E(B-V)=0.14), is consistent with the extinction to the Sagittarius (Sgr) Dwarf. Both PN show Wolf-Rayet features in their spectra, although the lines are weak in Wray16-423. Images in [O III] and H-alpha+[N II], although affected by poor seeing, yield a diameter of 1.2'' for Wray16-423 after deconvolution; He~2-436 was unresolved. He2-436 has a luminosity about twice that of Wray16-423 and its size and high density suggest a younger PN. In order to reconcile the differing luminosity and nebular properties of the two PN with similar age progenitor stars, it is suggested that they are on He burning tracks The abundance pattern is very similar in both nebulae and shows an oxygen depletion of -0.4 dex with respect to the mean O abundance of Galactic PN and [O/H] = -0.6. The Sgr PN progenitor stars are representative of the higher metallicity tail of the Sgr population. The pattern of abundance depletion is similar to that in the only other PN in a dwarf galaxy companion of the Milky Way, that in Fornax, for which new spectra are presented. However the abundances are larger than for Galactic halo PN suggesting a later formation age. The O abundance of the Sgr galaxy deduced from its PN, shows similarities with that of dwarf ellipticals around M31, suggesting that this galaxy was a dwarf elliptical before its interaction with the Milky Way.Comment: 24 pages, Latex (aas2pp4.sty) including 5 postscript figures. To appear in Ap

Global ecological predictors of the soil priming effect

Identifying the global drivers of soil priming is essential to understanding C cycling in terrestrial ecosystems. We conducted a survey of soils across 86 globally-distributed locations, spanning a wide range of climates, biotic communities, and soil conditions, and evaluated the apparent soil priming effect using 13C-glucose labeling. Here we show that the magnitude of the positive apparent priming effect (increase in CO2 release through accelerated microbial biomass turnover) was negatively associated with SOC content and microbial respiration rates. Our statistical modeling suggests that apparent priming effects tend to be negative in more mesic sites associated with higher SOC contents. In contrast, a single-input of labile C causes positive apparent priming effects in more arid locations with low SOC contents. Our results provide solid evidence that SOC content plays a critical role in regulating apparent priming effects, with important implications for the improvement of C cycling models under global change scenarios

Arrival Directions of Cosmic Rays above 32 EeV from Phase One of the Pierre Auger Observatory

A promising energy range to look for angular correlations between cosmic rays of extragalactic origin and their sources is at the highest energies, above a few tens of EeV (1 EeV equivalent to 10^(18) eV). Despite the flux of these particles being extremely low, the area of similar to 3000 km^(2) covered at the Pierre Auger Observatory, and the 17 yr data-taking period of the Phase 1 of its operations, have enabled us to measure the arrival directions of more than 2600 ultra-high-energy cosmic rays above 32 EeV. We publish this data set, the largest available at such energies from an integrated exposure of 122,000 km^(2) sr yr, and search it for anisotropies over the 3.4 pi steradians covered with the Observatory. Evidence for a deviation in excess of isotropy at intermediate angular scales, with similar to 15 degrees Gaussian spread or similar to 25 degrees top-hat radius, is obtained at the 4 sigma significance level for cosmic-ray energies above similar to 40 EeV

The energy spectrum of cosmic rays beyond the turn-down around 10^17 eV as measured with the surface detector of the Pierre Auger Observatory

We present a measurement of the cosmic-ray spectrum above 100 PeV using the part of the surface detector of the Pierre Auger Observatory that has a spacing of 750 m. An inflection of the spectrum is observed, confirming the presence of the so-called second-knee feature. The spectrum is then combined with that of the 1500 m array to produce a single measurement of the flux, linking this spectral feature with the three additional breaks at the highest energies. The combined spectrum, with an energy scale set calorimetrically via fluorescence telescopes and using a single detector type, results in the most statistically and systematically precise measurement of spectral breaks yet obtained. These measurements are critical for furthering our understanding of the highest energy cosmic rays

Status and performance of the underground muon detector of the Pierre Auger Observatory

The Auger Muons and Infill for the Ground Array (AMIGA) is an enhancement of the Pierre Auger Observatory, whose purpose is to lower the energy threshold of the observatory down to 1016.5 eV, and to measure the muonic content of air showers directly. These measurements will significantly contribute to the determination of primary particle masses in the range between the second knee and the ankle, to the study of hadronic interaction models with air showers, and, in turn, to the understanding of the muon puzzle. The underground muon detector of AMIGA is concomitant to two triangular grids of water-Cherenkov stations with spacings of 433 and 750 m; each grid position is equipped with a 30 m2 plastic scintillator buried at 2.3 m depth. After the engineering array completion in early 2018 and general improvements to the design, the production phase commenced. In this work, we report on the status of the underground muon detector, the progress of its deployment, and the performance achieved after two years of operation. The detector construction is foreseen to finish by mid-2022

Performance of the 433 m surface array of the Pierre Auger Observatory

The Pierre Auger Observatory, located in western Argentina, is the world’s largest cosmic-ray observatory. While it was originally built to study the cosmic-ray flux above 1018.5 eV, several enhancements have reduced this energy threshold. One such enhancement is a surface array composed of a triangular grid of 19 water-Cherenkov detectors separated by 433 m (SD-433) to explore the energies down to about 1016 eV. We are developing two research lines employing the SD-433. Firstly, we will measure the energy spectrum in a region where previous experiments have shown evidence of the second knee. Secondly, we will search for ultra-high energy photons to study PeV cosmic-ray sources residing in the Galactic center. In this work, we introduce the SD-433 and we show that it is fully efficient above 5×1016 eV for hadronic primaries with θ < 45°. Using seven years of data, we present the parametrization of the lateral distribution function of measured signals. Finally, we show that an angular resolution of 1.8° (0.5°) can be attained at the lowest (highest) primary energies. Our study lays the goundmark for measurements in the energy range above 1016 eV by utilizing the SD-433 and thus expanding the scientific output of the Auger surface detector

Outreach activities at the Pierre Auger Observatory

The Pierre Auger Observatory, sited in Malargüe, Argentina, is the largest observatory available for measuring ultra-high-energy cosmic rays (UHECR). The Auger Collaboration has measured and analysed an unprecedented number of UHECRs. Along with making important scientific discoveries, for example, the demonstration that cosmic rays above 8 EeV are of extragalactic origin and the observation of a new feature in the energy spectrum at around 13 EeV, outreach work has been carried out across the 18 participating countries and online. This program ranges from talks to a varied audience, to the creation of a local Visitor Center, which attracts 8000 visitors annually, to initiating masterclasses. Permanent and temporary exhibitions have been prepared both in reality and virtually. Science fairs for elementary- and high-school students have been organised, together with activities associated with interesting phenomena such as eclipses. In addition, we participate in international events such as the International Cosmic Day, Frontiers from H2020, and the International Day of Women and Girls in Science. Part of the Collaboration website is aimed at the general public. Here the most recent articles published are summarised. Thus the Collaboration informs people about work in our field, which may seem remote from everyday life. Furthermore, the Auger Observatory has been a seed for scientific and technological activities in and around Malargüe. Different outreach ventures that already have been implemented and others which are foreseen will be described

Satellite Data for Atmospheric Monitoring at the Pierre Auger Observatory

Atmospheric monitoring over the 3000 km2 of the Pierre Auger Observatory can be supplemented by satellite data. Methods for night-time cloud detection and aerosol cross-checking were created using the GOES-16 and Aeolus satellites, respectively. The geostationary GOES-16 satellite provides a 100% up-time view of the cloud cover over the observatory. GOES-13 was used until the end of 2017 for cloud monitoring, but with its retirement a method based on GOES-16 data was developed. The GOES-16 cloud detection method matches the observatory’s vertical laser cloud detection method at a rate of ∼90%. The Aeolus satellite crosses the Pierre Auger Observatory several times throughout the year firing UV-laser shots. The laser beams leave a track of scattered light in the atmosphere that can be observed by the light sensors of the observatory fluorescence telescopes. Using a parametric model of the aerosol concentration, the laser shots can be reconstructed with different combinations of the aerosol parameters. A minimization procedure then yields the parameter set that best describes the aerosol attenuation. Furthermore, the possibility of studying horizontal homogeneity of aerosols across the array is being investigated

Energy spectrum of cosmic rays measured using the Pierre Auger Observatory

We present the energy spectrum of cosmic rays measured at the Pierre Auger Observatory from 6 × 1015 eV up to the most extreme energies where the accumulated exposure reaches about 80 000 km2 sr yr. The wide energy range is covered with five different data sets: events detected by the surface detector (with separate reconstruction methods for zenith angles below and above 60◦), those collected by a denser array, a set of hybrid events simultaneously recorded by the surface and fluorescence detectors, and those events in which the signal is dominated by Cherenkov light registered by the high-elevation telescopes. In this contribution, we report updates of the analysis techniques and present the spectrum obtained by combining the five different measurements. Spectral features occurring in the wide energy range covered by the Observatory are discussed

Search for upward-going showers with the Fluorescence Detector of the Pierre Auger Observatory

Given its operation time and wide field of view, the Fluorescence Detector (FD) of the Pierre Auger Observatory is sufficiently sensitive to detect upward-going events when used in monocular mode. Upward-going air showers are a possible interpretation of the recent events reported by the ANITA Collaboration in the energy range above 1017 eV. The Pierre Auger FD data can be used to support or constrain this interpretation. If confirmed, it would require either new phenomena or significant modifications to the standard model of particle physics. To prepare this search, a set of quality selection criteria was defined by using 10% of the available FD data from 14 years of operation. This subset was mainly used to clean the data from improperly labelled laser events that had been used to monitor the quality of the atmosphere. The potential background for this search consists of cosmic-ray induced air showers with specific geometric configurations which, in a monocular reconstruction, can be reconstructed erroneously as upward-going events. To distinguish candidates from these false positives, to calculate the exposure, and to estimate the expected background, dedicated simulations for signal (upward-going events) and background (downward-going events) have been performed. The detector exposure is large enough to strongly constrain the interpretation of ANITA anomalous events. Preliminary results of the analysis after unblinding the data set are presented