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Role of Low-Energy (<20 eV) Secondary Electrons in the Extraterrestrial Synthesis of Prebiotic Molecules
Get PDFWe demonstrate for the first time that Galactic cosmic rays with energies as high as ∼1010 eV can trigger a cascade of low-energy (<20 eV) secondary electrons that could be a significant contributor to the interstellar synthesis of prebiotic molecules whose delivery by comets, meteorites, and interplanetary dust particles may have kick-started life on Earth. For the energetic processing of interstellar ice mantles inside dark, dense molecular clouds, we explore the relative importance of low-energy (<20 eV) secondary electrons─agents of radiation chemistry─and low-energy (<10 eV), nonionizing photons─instigators of photochemistry. Our calculations indicate fluxes of ∼102 electrons cm-2 s-1 for low-energy secondary electrons produced within interstellar ices due to attenuated Galactic cosmic-ray protons. Consequently, in certain star-forming regions where internal high-energy radiation sources produce ionization rates that are observed to be a thousand times greater than the typical interstellar Galactic ionization rate, the flux of low-energy secondary electrons should far exceed that of nonionizing photons. Because reaction cross sections can be several orders of magnitude larger for electrons than for photons, even in the absence of such enhancement, our calculations indicate that secondary low-energy (<20 eV) electrons are at least as significant as low-energy (<10 eV) nonionizing photons in the interstellar synthesis of prebiotic molecules. Most importantly, our results demonstrate the pressing need for explicitly incorporating low-energy electrons in current and future astrochemical simulations of cosmic ices. Such models are critically important for interpreting James Webb Space Telescope infrared measurements, which are currently being used to probe the origins of life by studying complex organic molecules found in ices near star-forming regions
Ultraviolet H2 luminescence in molecular clouds induced by cosmic rays
Get PDFContext. Galactic cosmic rays (CRs) play a crucial role in ionisation, dissociation, and excitation processes within dense cloud regions where UV radiation is absorbed by dust grains and gas species. CRs regulate the abundance of ions and radicals, leading to the formation of more and more complex molecular species, and determine the charge distribution on dust grains. A quantitative analysis of these effects is essential for understanding the dynamical and chemical evolution of star-forming regions.
Aims: The CR-induced photon flux has a significant impact on the evolution of the dense molecular medium in its gas and dust components. This study evaluates the flux of UV photons generated by CRs to calculate the photon-induced dissociation and ionisation rates of a vast number of atomic and molecular species, as well as the integrated UV photon flux.
Methods: To achieve these goals, we took advantage of recent developments in the determination of the spectra of secondary electrons, in the calculation of state-resolved excitation cross sections of H2 by electron impact, and of photodissociation and photoionisation cross sections.
Results: We calculated the H2 level population of each rovibrational level of the X, B, C, B′, D, B″, D′, and a states. We then computed the UV photon spectrum of H2 in its line and continuum components between 72 and 700 nm, with unprecedented accuracy, as a function of the CR spectrum incident on a molecular cloud, the H2 column density, the isomeric H2 composition, and the dust properties. The resulting photodissociation and photoionisation rates are, on average, lower than previous determinations by a factor of about 2, with deviations of up to a factor of 5 for the photodissociation of species such as AlH, C2H2, C2H3, C3H3, LiH, N2, NaCl, NaH, O2+, S2, SiH, l-C4, and l-C5H. A special focus is given to the photoionisation rates of H2, HF, and N2, as well as to the photodissociation of H2, which we find to be orders of magnitude higher than previous estimates. We give parameterisations for both the photorates and the integrated UV photon flux as a function of the CR ionisation rate, which implicitly depends on the H2 column density, as well as the dust properties
Implementazione di un software di supporto per le osservazioni con lo strumento TANDEM all’Osservatorio di Loiano
Get PDFNel 2023, presso l’Osservatorio Cassini di Loiano, e’ stato installato lo strumento TANDEM (Telescope Array eNabling DEbries Monitoring, https://www.oas.inaf.it/it/progetti/tandem-it/ ), realizzato da ADS (https://www.ads-int.com/astronomy) e pensato principalmente per eseguire osservazioni di supporto nell’ambito delle attivita’ europee di sorveglianza spaziale (https://www.eusst.eu/). Questo strumento condivide la montatura equatoriale inglese e sfrutta il movimento in angolo orario del telescopio Cassini, mentre utilizza dei propri attuatori per gli spostamenti in declinazione. Avendo sistemi di controllo diversi tra loro, i due strumenti sono per il momento indipendenti. In questo rapporto tecnico descrivo brevemente l’implementazione ed i principali comandi di funzionamento di una nuova interfaccia utente, utile per ottimizzare le osservazioni notturne, con cui il TANDEM ed il Cassini possono operare in concerto
Thermalization of a SQUID Chip at Cryogenic Temperature: Thermal Conductance Measurement for GE 7031 Varnish Glue, Apiezon N Grease and Rubber Cement Between 20 and 200 mK
Get PDFIn the context of the ATHENA X-IFU Cryogenic AntiCoincidence detector (CryoAC) development, we have studied the thermalization properties of a 2 × 2 mm SQUID chip. The chip is glued on a front-end PCB and operated on the cold stage of a dilution refrigerator (TBASE < 20 mK). We performed thermal conductance measurements by using different materials to glue the SQUID chip on the PCB. These have been repeated in subsequent cryostat runs, to highlight degradation effects due to thermal cycles. Here, we present the results obtained by glues and greases widely used in cryogenic environments, i.e., GE 7031 Varnish Glue, Apiezon N Grease and Rubber Cement
La generazione e distribuzione dei riferimenti di tempo e frequenza della Stazione Radioastronomica di Medicina.
Get PDFSi ringrazia il Ing. ORLATI Andrea per aver svolto la funzione di revisore.In occasione dell’attuale ricambio generazionale è importante richiamare in estrema
sintesi i principi motivanti la progettazione, costruzione ed operatività del laboratorio
Tempo e Frequenza (T&F), nato concomitante alla parabola VLBI di Medicina.R. Ambrosini, M. Roma, C. Bortolotti, “H-maser i74 acts good wine!”
Technical Report IRA 523/19
R. Ambrosini, M. Roma, C. Bortolotti, “Hardware/Software configuration of the
Time & Frequency laboratory at the Medicina Observatory”, Rapporto Interno
IRA 517-18
Un metodo originale di misura delle instabilità di fase a lungo termine”
R. Ambrosini, M. Caporaloni, M. Roma; IRA 99/87
”Il sistema di controllo remoto della stazione T&F per uso VLBI”
R. Ambrosini, M. Roma; IRA 120/89
”Sessione di misure della Varianza di ALLAN per la caratterizzazione della
stabilità di fase del modulo SBT, per il progetto Cassini”
R. Ambrosini, M. Roma; IRA 195/95
”Long and Short term PHASE Stability measurements of microwave
Synthesizers for VLBI and RADIO SCIENCE with Cassini”
R. Ambrosini, M. Roma, S. Mariotti; IRA 237/97
”Extremely accurate timing with a new interface for the Motorola GPS
modules”,
R. Ambrosini, G. Maccaferri, M. Roma, A. Maccaferri, A. Scalambra
IRA 273/99
Hydrogen MASER Frequency Standard – EFOS – “Part 2 maintenence and
repair manual”
Manuale presente nella vetrina del Lab. T&F
Manuale dei Rb FS725 della Stanford Research Systems (SRS)
https://www.thinksrs.com/downloads/pdfs/manuals/FS725m.pdf
e presente nella vetrina del Lab. T&F
LIFT (The Italian Link for Time and Frequency)
Published in: 2013 Joint European Frequency and Time Forum & International
Frequency Control Symposium (EFTF/IFC)
21-25 July 2013
Date Added to IEEE Xplore: 09 January 2014 Publisher: IEEE
ISBN Information:
Electronic ISBN:978-1-4799-0342-9
DVD ISBN:978-1-4799-0341-2
DOI: 10.1109/EFTF-IFC.2013.6702195
Very Long Baseline Interferometry
J. Campbell
Geodetic Institute University of Bonn.
https://cds.cern.ch/record/611415/files/375.pdf
DOI 10.5170/CERN-1987-001.37
Eruptive events with exceptionally bright emission in H i Ly-α observed by the Metis coronagraph
Get PDFContext. Ultraviolet (UV) emission from coronal mass ejections can provide information on the evolution of plasma dynamics, temperature, and elemental composition, as demonstrated by the UV Coronagraph Spectrometer (UVCS) on board the SOlar and Heliospheric Observatory (SOHO). Metis, the coronagraph on board Solar Orbiter, provides for the first time coronagraphic imaging in the UV H i Ly-α line and, simultaneously, in polarized visible light, thus providing a host of information on the properties of coronal mass ejections and solar eruptions such as their overall dynamics, time evolution, mass content, and outflow propagation velocity in the expanding corona. Aims. For this work, we analyzed six coronal mass ejections observed by Metis between April and October 2021, which are characterized by a very strong H i Ly-α emission. We studied in particular the morphology, kinematics, and the temporal and radial evolution of the emission of such events, focusing on the brightest UV features. Methods. The kinematics of the eruptive events under consideration were studied by determining the height-time profiles of the brightest parts on the Metis plane of the sky. Furthermore, the 3D positions in the heliosphere of the coronal mass ejections were determined by employing co-temporal images, when available, from two other coronagraphs: LASCO/C2 on board SOHO, and COR2 on board STEREO-A. In three cases, the most likely source region on the solar surface could be identified. Finally, the radiometrically calibrated Metis images of the bright UV features were analyzed to provide estimates of their volume and density. From the kinematics and radiometric analysis, we obtained indications of the temperatures of the bright UV cores of these events. These results were then compared with previous studies with the UVCS spectrocoronagraph. Results. The analysis of these strong UV-emitting features associated with coronal mass ejections demonstrates the capabilities of the current constellation of space coronagraphs, Metis, LASCO/C2, and COR2, in providing a complete characterization of the structure and dynamics of eruptive events in their propagation phase from their inception up to several solar radii. Furthermore, we show how the unique capabilities of the Metis instrument to observe these events in both the H i Ly-α line and polarized VL radiation allow plasma diagnostics on the thermal state of these events
L'evoluzione delle stelle in realtà virtuale
Get PDFIl progetto 3DMAPVR: un nuovo metodo di indagine per rendere visibile l'invisibil
Hydrogen Epoch of Reionization Array (HERA) Phase II Deployment and Commissioning
Get PDFThis paper presents the design and deployment of the Hydrogen Epoch of Reionization Array (HERA) phase II system. HERA is designed as a staged experiment targeting 21 cm emission measurements of the Epoch of Reionization. First results from the phase I array are published as of early 2022, and deployment of the phase II system is nearing completion. We describe the design of the phase II system and discuss progress on commissioning and future upgrades. As HERA is a designated Square Kilometre Array pathfinder instrument, we also show a number of “case studies” that investigate systematics seen while commissioning the phase II system, which may be of use in the design and operation of future arrays. Common pathologies are likely to manifest in similar ways across instruments, and many of these sources of contamination can be mitigated once the source is identified
LOFAR Deep Fields: Probing the sub-mJy regime of polarized extragalactic sources in ELAIS-N1: I. The catalog
Get PDFContext. Quantifying the number density and physical characteristics of extragalactic polarized sources is important for the successful planning of future studies based on Faraday rotation measure (RM) grids of polarized sources to probe foreground Galactic and intergalactic magnetic fields. However, it is proving very hard to detect polarized signal from the population of very faint (sub-mJy) polarized sources at low radio frequencies, and their properties are mostly unknown. LOFAR can play an important role in such studies thanks to its sensitivity and angular resolution, combined with the precision on the inferred RM values that can be achieved through low-frequency broad-band polarimetry.
Aims: The aim of this study is to probe the sub-mJy polarized source population with LOFAR. In this first paper, we present the method used to stack LOFAR polarization datasets, the resulting catalog of polarized sources, and the derived polarized source counts.
Methods: The European Large Area ISO Survey-North 1 (ELAIS-N1) field, one of the deepest of the LOFAR Two-Metre Sky Survey (LoTSS) Deep Fields so far, was selected for a polarimetric study at 114.9-177.4 MHz. A total area of 25 deg2 was imaged at 6″-resolution in the Stokes Q and U parameters. Alignment of polarization angles was done both in frequency and in Faraday space before stacking datasets from 19 eight-hour-long epochs taken in two different LOFAR observing cycles. A search for polarized sources was carried out in the final, stacked dataset, and the properties of the detected sources were examined. The depolarization level of sources known to be polarized at 1.4 GHz was quantified.
Results: A one-sigma noise level, σQU, of 19 µJy beam−1 was reached in the central part of the field after stacking. Twenty-five polarized sources were detected above 8σQU, five of which had not been detected in polarization at any other radio frequencies before. Seven additional polarized components were found by lowering the threshold to 6σQU at positions corresponding to sources known to be polarized at 1.4 GHz. In two radio galaxies, polarization was detected from both radio lobes, so the final number of associated radio continuum sources is 31. The detected sources are weakly polarized, with a median degree of polarization of 1.75% for the sample of sources detected in polarized emission. For the 10 polarized sources previously identified in a pilot LOFAR study of the ELAIS-N1 field at 20″-resolution, the RM values are consistent but the degrees of polarization are higher in the 6″-resolution data. The sources previously detected in polarization at 1.4 GHz are significantly depolarized at 150 MHz. The catalog is used to derive the polarized source counts at 150 MHz.
Conclusions: This is the deepest and highest-resolution polarization study at 150 MHz to date. A full characterization of the sources and an analysis of the catalog will be presented in Paper II
The Physalis system: discovery of ORC-like radio shells around a massive pair of interacting early-type galaxies with offset X-ray emission
Get PDFWe present the discovery of large radio shells around a massive pair of interacting galaxies and extended diffuse X-ray emission within the shells. The radio data were obtained with the Australian Square Kilometre Array Pathfinder (ASKAP) in two frequency bands centred at 944 MHz and 1.4 GHz, respectively, while the X-ray data are from the XMM-Newton observatory. The host galaxy pair, which consists of the early-type galaxies ESO 184-G042 and LEDA 418116, is part of a loose group at a distance of only 75 Mpc (redshift ). The observed outer radio shells (diameter 145 kpc) and ridge-like central emission of the system, ASKAP J1914-5433 (Physalis), are likely associated with merger shocks during the formation of the central galaxy (ESO 184-G042) and resemble the new class of odd radio circles (ORCs). This is supported by the brightest X-ray emission found offset from the centre of the Physalis system, instead centred at the less massive galaxy, LEDA 418116. The host galaxy pair is embedded in an irregular envelope of diffuse light, highlighting ongoing interactions. We complement our combined radio and X-ray study with high-resolution simulations of the circumgalactic medium (CGM) around galaxy mergers from the Magneticum project to analyse the evolutionary state of the Physalis system. We argue that ORCs/radio shells could be produced by a combination of energy release from the central active galactic nucleus and subsequent lightening up in radio emission by merger shocks travelling through the CGM of these systems