Search

Since the earliest space‐based observations of Earth's atmosphere, ultraviolet (UV) airglow has proven a useful resource for remote sensing of the ionosphere and thermosphere. The NASA Ionospheric Connection Explorer (ICON) spacecraft, whose mission is to explore the connections between ionosphere and thermosphere utilizes UV airglow in the typical way: an extreme‐UV (EUV) spectrometer uses dayglow between 54 and 88 nm to measure the density of O+, and a far‐UV spectrograph uses the O 135.6 nm doublet and N2Lyman‐Birge‐Hopfield band dayglow to measure the column ratio of O to N2in the upper thermosphere. Two EUV emission features, O+61.6 and 83.4 nm, are used for the O+retrieval; however, many other features are captured along the EUV instrument's spectral dimension. In this study, we examine the other dayglow features observed by ICON EUV and demonstrate that it measures a nitrogen feature around 87.8 nm which can be used to observe the neutral thermosphere. The ionosphere is a region of near‐Earth space made up of plasma. NASA's Ionospheric Connection Explorer (ICON) mission seeks explore the factors influencing formation of the ionosphere and how it interacts with Earth and its atmosphere. One of the ways ICON does this is by measuring airglow: light released by the air in the upper atmosphere. This occurs with visible light, with the same shades seen in the aurora; it also occurs in the ultraviolet range, invisible to the human eye but visible to ICON instruments. An imager is included on ICON to measure extreme‐ultraviolet light, almost as energetic as X‐rays. Certain atoms and molecules in the atmosphere are known to glow at specific wavelengths. By measuring the brightness of airglow at certain wavelengths, ICON is able see the structure of ionospheric oxygen. The instrument also measures dimmer emissions at other wavelengths, some of which are known to come from certain atmospheric species and others which are unknown or uncertain. Here we look at the other wavelengths and attempt to find their origins. We find that most are likely coming from oxygen. Interestingly, we find one that we think comes from nitrogen. This could be useful for measuring the abundance of molecular nitrogen in the upper atmosphere, a task currently performed by another instrument on the ICON spacecraft. We make a case for the practicality of this approach. A comprehensive introduction to the Ionospheric Connection Explorer Extreme ultraviolet dayglow observations is presentedSome dim emission features are identified as originating from O+from similarity to known featuresEmission near 87.8 nm follows N2and, combined with 61.6 nm data, contains information about ΣO/N2 A comprehensive introduction to the Ionospheric Connection Explorer Extreme ultraviolet dayglow observations is presented Some dim emission features are identified as originating from O+from similarity to known features Emission near 87.8 nm follows N2and, combined with 61.6 nm data, contains information about ΣO/N2

The Galactic Arecibo L-band Feed Array H I (GALFA-H I) survey is mapping the entire Arecibo sky at 21 cm, over a velocity range of -700 to +700 km s-1 (LSR), at a velocity resolution of 0.18 km s-1, and a spatial resolution of 3.5 arcmin. The unprecedented resolution and sensitivity of the GALFA-H I survey have resulted in the detection of numerous isolated, very compact H I clouds at low Galactic velocities, which are distinctly separated from the H I disk emission. In the limited area of [?]4600 deg2 surveyed so far, we have detected 96 such compact clouds. The detected clouds are cold with a median T k,max (the kinetic temperature in the case in which there is no non-thermal broadening) of 300 K. Moreover, these clouds are quite compact and faint, with median values of 5 arcmin in angular size, 0.75 K in peak brightness temperature, and 5 x 1018 cm-2 in H I column density. Most of the clouds deviate from Galactic rotation at the 20-30 km s-1 level, and a significant fraction show evidence for a multiphase medium and velocity gradients. No counterparts for these clouds were found in other wave bands. From the modeling of spatial and velocity distributions of the whole compact cloud population, we find that the bulk of the compact clouds are related to the Galactic disk, and their distances are likely to be in the range of 0.1 to a few kpc. We discuss various possible scenarios for the formation and maintenance of this cloud population and its significance for Galactic interstellar medium studies.

We used the FUSE (Far Ultraviolet Spectroscopic Explorer ) satellite to observe O VI emission along two sight lines toward the edge of the interaction zone (IZ) between the Loop I superbubble and the Local Bubble. One sight line was chosen because material in the interaction zone blocks distant X-ray emission, and should thus do the same for nonlocal O VI emission. We measured an O VI intensity of Ishad = 2750 +- 550 photons cm[?]2 s[?]1 sr[?]1 along this "shadowed" sight line, and Iunshad = 10,800 +- 1200 photons cm[?]2 s[?]1 sr[?]1 along the other sight line. Given these results, very little ([?] 800 photons cm[?]2 s[?]1 sr[?]1) of the emission arises from the near side of the interaction zone, which likely has an H I column density of about 4 x 1020 cm[?]2 along the "shadowed" sight line. The O VI emission arising within Loop I (~104 photons cm[?]2 s[?]1 sr[?]1) is probably associated with gas of ne [?] 0.1 cm[?]3 and an emitting path length of ~2.5 pc, suggesting it arises at interfaces rather than from gas filling Loop I. In contrast, the C III emission is similar along both sight lines, indicating that much of the emission likely arises on the near side of the interaction zone.

We present far-ultraviolet observations of the Antlia supernova remnant obtained with Far-Ultraviolet Imaging Spectrograph (FIMS, also called SPEAR). The strongest lines observed are C IV ll1548, 1551 and C III l977. The C IV emission of this mixed-morphology supernova remnant shows a clumpy distribution, and the line intensity is nearly constant with radius. The C III l977 line, although too weak to be mapped over the whole remnant, is shown to vary radially. The line intensity peaks at about half the radius and drops at the edge of the remnant. Both the clumpy distribution of C IV and the rise in the C IV to C III ratio toward the edge suggest that central emission is from evaporating cloudlets rather than thermal conduction in a more uniform, dense medium.

Observations with the Extreme Ultraviolet Explorer (EUVE) have shown the Coma Cluster to be a source of EUV emission in excess of that produced by X-ray gas in the cluster. We have reexamined the EUVE data on this cluster in an attempt to obtain clues as to the origin of this emission. We find two important new results. First, the ratio between the azimuthally averaged EUV excess emission and the ROSAT hard X-ray flux is constant as a function of distance from the cluster center outward. Second, a correlation analysis between the EUV excess emission and the X-ray emission shows that on a detailed level the EUV excess is spatially closely related to the X-ray emission. These findings contradict previous suggestions as to the underlying source of the diffuse EUV emission in Coma and provide important information in regard to the true source of this emission. We propose a new explanation for the source of this emission: inverse Compton scattering of microwave background photons by secondary electrons and positrons. We explore this possibility in some detail and show that it is consistent with all of the available observational evidence. The parent cosmic-ray protons may have been produced by any of a number of sources, including supernovae, active galaxies, galactic winds, and cluster formation shocks, but we believe that the most likely source is cluster formation shocks. If the EUV emission in the Coma Cluster is, in fact, the result of secondary electrons, this may be the only direct evidence for secondary electrons in the intracluster medium of a cluster of galaxies, since recent work suggests that secondary electrons may not be the cause of radio halos.

In near‐Earth space, variations in thermospheric composition have important implications for thermosphere‐ionosphere coupling. The ratio of O to N2is often measured using far‐UV airglow observations. Taking such airglow observations from space, looking below the Earth's limb allows for the total column of O and N2in the ionosphere to be determined. While these observations have enabled many previous studies, determining the impact of nonmigrating tides on thermospheric composition has proved difficult, owing to a small contamination of the signal by recombination of ionospheric O+. New ICON observations of far‐UV are presented here, and their general characteristics are shown. Using these, along with other observations and a global circulation model, we show that during the morning hours and at latitudes away from the peak of the equatorial ionospheric anomaly, the impact of nonmigrating tides on thermospheric composition can be observed. During March–April 2020, the column O/N2ratio was seen to vary by 3–4% of the zonal mean. By comparing the amplitude of the variation observed with that in the model, both the utility of these observations and a pathway to enable future studies is shown. At high altitude in the atmosphere, mixing of the gas via turbulence becomes less important, and mix of atmospheric species begins to vary with altitude, depending on the mass of the atom or molecule. At these altitudes, the composition of the atmosphere can vary greatly with location and time in a manner not seen in the lower levels of the atmosphere. This same high‐altitude region overlaps with the charged particle environment known as the Earth's ionosphere. How the atmosphere and ionosphere interact is in‐part determined by the composition of the atmosphere. Measuring this composition is therefore important and is done regularly using observations in the far‐ultraviolet. These reveal much of the compositional variation, but a small contaminating signal from the ionosphere has made detecting some small changes produced by waves in the atmosphere a challenge. Here, new observations in the far‐UV are introduced and their general properties shown. By selecting a specific location and time and utilizing supporting data and a global model, we are able to show the change in the composition produced by a certain class of wave in the atmosphere. This demonstrates the utility of these new observations and provides a pathway to futures studies. An initial overview of the Ionospheric Connection Explorer‐far‐ultraviolet sublimb observations and derived column O/N2ratios is presentedIn the morning, away from the equatorial ionosphere, the impact of nonmigrating tides on O/N2is shown clearly for the first timeComparison of the tidal signature with the TIEGCM highlights basic agreement, with possible discrepancy in tidal vertical wavelength An initial overview of the Ionospheric Connection Explorer‐far‐ultraviolet sublimb observations and derived column O/N2ratios is presented In the morning, away from the equatorial ionosphere, the impact of nonmigrating tides on O/N2is shown clearly for the first time Comparison of the tidal signature with the TIEGCM highlights basic agreement, with possible discrepancy in tidal vertical wavelength

We report on spectral observations of the night sky in the band around 900 A where the emission line in the Sciama model of radiatively decaying massive neutrinos would be present. The data were obtained with a high-resolution, high-sensitivity spectrometer flown on the Spanish satellite MINISAT. The observed emission is far less intense than that expected in the Sciama model.

We report new EUV data on the cluster of galaxies Abell 1795. These data were taken well away from a detector defect which could have compromised earlier results on this cluster. Our new observations confirm the validity of the original data set. However, we find our results are strongly influenced by the variation of the telescope sensitivity over the field of view and upon the details of the subtraction of the EUV emission from the X-ray plasma. We investigate these effects using our new data and archival data on Abell 1795, Abell 2199, and the Coma Cluster. When we use the appropriate correction factors, we find there is no evidence for any excess EUV emission in Abell 1795 or Abell 2199. However, we do find extended EUV emission in the Coma Cluster using our new analysis procedures, confirming that in at least this cluster some as yet unidentified process is operative.

One of the keys to interpreting the character and evolution of interstellar matter in the Galaxy is understanding the distribution of the low-density hot (105-106K) phase of the interstellar medium (ISM). This phase is much more difficult to observe than the cooler high-density components of the ISM because of its low density and lack of easily observable tracers. Because gas of this temperature emits mainly in the far-ultraviolet (FUV) (912-1800 Å) and extreme-ultraviolet (EUV) (80-912 Å), and (for gas hotter than 106K) X-rays, observations in these bands can provide important constraints to the distribution of this gas. Because of interstellar opacity at EUV wavelengths, only FUV and X-ray observations can provide clues to the properties of hot gas from distant regions. We present results from a search for FUV emission from the diffuse ISM conducted with an orbital FUV spectrometer, DUVE, which was launched in 1992 July. The DUVE spectrometer, which covers the band from 950 to 1080 Å with 3.2 Å resolution, observed a region of low neutral hydrogen column density near the south Galactic pole for a total effective integration time of 1583 s. The only emission line detected was a geocoronal hydrogen line at 1025 Å. We are able to place upper limits to several expected emission features that provide constraints on interstellar plasma parameters. We are also able to place limits on the continuum emission throughout the bandpass. We compare these limits and other diffuse observations with several models of the structure of the ISM and discuss the ramifications.

Breakthrough Listenis the most comprehensive and sensitive search for extraterrestrial intelligence (SETI) to date, employing a collection of international observational facilities including both radio and optical telescopes. During the first three years of the Listenprogram, thousands of targets have been observed with the Green Bank Telescope (GBT), Parkes Telescope and Automated Planet Finder. At GBT and Parkes, observations have been performed ranging from 700 MHz to 26 GHz, with raw data volumes averaging over 1 PB day?1. A pseudo-real time software spectroscopy suite is used to produce multi-resolution spectrograms amounting to approximately 400 GB h?1GHz?1beam?1. For certain targets, raw baseband voltage data is also preserved. Observations with the Automated Planet Finder produce both two-dimensional and one-dimensional high-resolution (R? 105) echelle spectral data. Although the primary purpose of Listendata acquisition is for SETI, a range of secondary science has also been performed with these data, including studies of fast radio bursts. Other current and potential research topics include spectral line studies, searches for certain kinds of dark matter, probes of interstellar scattering, pulsar searches, radio transient searches and investigations of stellar activity. Listendata are also being used in the development of algorithms, including machine-learning approaches to modulation scheme classification and outlier detection, that have wide applicability not just for astronomical research but for a broad range of science and engineering. In this paper, we describe the hardware and software pipeline used for collection, reduction, archival, and public dissemination of Listendata. We describe the data formats and tools, and present Breakthrough Listen Data Release 1.0 (BLDR 1.0), a defined set of publicly available raw and reduced data totaling 1 PB.