Since the middle 1950s, neutron monitors have provided a continuous record of the intensity of secondary atmospheric particles produced by the primary cosmic radiation above the atmosphere. The ...number of counts due to these secondary particles is related to the primary spectrum above the atmosphere through the so‐called atmospheric yield function. This yield function includes the secondary particles produced in the atmosphere, as well as inside the particular detector. In this paper the primary focus is to recalculate the yield function for neutron monitors. The motivation for this study is that the quality of the experimental observations has increased to such an extent that it has become possible to reduce uncertainties in the yield function down to approximately 10%. It thus becomes possible to refine our knowledge of the atmospheric cascade process considerably. We parameterize the yield functions in a simple way; we also make reference to the yield and response functions of muon, Cherenkov and stratospheric balloon detectors, and we compare their response to that of the neutron monitors.
Key Points
A parameterization of the neutron monitor yield, spectrum and response is shown
The response functions in the atmosphere for different detectors are compared
The neutron monitor response to solar energetic particle events is shown
The force field approximation to the transport equation which describes cosmic ray modulation in the heliosphere is a widely used tool. It is popular because it provides an easy to use, ...quasi‐analytical method to describe the level of modulation with a single parameter. A simple numerical solution of the one‐dimensional cosmic ray transport equation is used to show that this is a good approximation for galactic cosmic rays in the inner heliosphere but that its accuracy decreases toward the outer heliosphere. On the other hand, the even simpler convection‐diffusion approximation improves with radial distance. The reason for the complementary behavior of these two approximations is that energy losses are relatively important in the inner heliosphere but not in the outer heliosphere. The force field approximation is worse for anomalous cosmic rays at all radial distances due to the exponential cutoff of these spectra at high energies. The ranges of validity are quantified. Since both approximations have their limitations, a simple numerical solution of the one‐dimensional transport equation is provided for general use.
In this work, we analyze the long-term cosmic-ray modulation observed by the Hermanus neutron monitor, which is the detector with the longest cosmic-ray record, from 1957 July. For our study we use ...the force-field approximation to the cosmic-ray transport equation, and the newest results on the mean free paths from the scattering theory. We compare the modulation parameter (φ) with different rigidity (P) dependences: P, P2, and P2/3. We correlate them with solar and interplanetary parameters. We found that (1) these rigidity dependences properly describe the modulation, (2) long-term cosmic-ray variations are better correlated with the magnitude of the heliospheric magnetic field (HMF) than the sunspot number, solar wind speed, and tilt angle of the HMF, and (3) the theoretical dependence of the parallel mean free path on the magnetic field variance is in agreement with the modulation parameter and therefore with the neutron monitor record. We also found that the force-field approximation is not able to take into account the effects of three-dimensional particle transport, showing a poor correlation with the perpendicular mean free path.
The present study estimates the yield and response functions of the mini neutron monitor (miniNM). This relatively new cosmic ray detector is the mobile version of the standard NM64. It can be use ...not only to calibrate the NM64 but also to study the modulation processes. Due to its portability, the miniNM can be easily placed in a suitable location to measure secondary particles, which give information about the intensity variations of galactic and solar cosmic rays. In order to perform these modulation studies with miniNMs, it is crucial to know their sensitivity to detect secondary cosmic ray flux, i.e., we must know their yield function. A previous study found that miniNM and NM64 have slightly different response functions. This work analyzes the observed counting rate ratio (miniNM to NM64) and gives for the first time an useful expression for the yield function of the miniNM. The results found here will allow to interpret the new measurements with this mobile neutron monitor. For comparison, a brief summary of the NM64 yield functions reported by other authors is presented.
Key Points
Yield function estimation for the mini neutron monitor
Response of the mini neutron monitor
Useful expression for analysis of new measurements
H II regions in galaxies are the sites of star formation, so they are special places for understanding the build-up of stellar mass in the universe. The line ratios of this ionized gas are frequently ...used to characterize the ionization conditions. We explore the connections between the ionization conditions and the properties of the overall underlying stellar population in H II regions, in order to uncover the actual physical connection between them. We use the H II regions catalog from the CALIFA survey, which is the largest in existence with more than 5000 H II regions, to explore their distribution across the classical OIII lambda5007/Hbeta vs. NII lambda6583/Halpha diagnostic diagram, and the way it depends on the oxygen abundance, ionization parameter, electron density, and dust attenuation. The results indicate that although H II regions are short-lived events, they are affected by the total underlying stellar population.
Barnard's star is a red dwarf, and has the largest proper motion (apparent motion across the sky) of all known stars. At a distance of 1.8 parsecs
, it is the closest single star to the Sun; only the ...three stars in the α Centauri system are closer. Barnard's star is also among the least magnetically active red dwarfs known
and has an estimated age older than the Solar System. Its properties make it a prime target for planetary searches; various techniques with different sensitivity limits have been used previously, including radial-velocity imaging
, astrometry
and direct imaging
, but all ultimately led to negative or null results. Here we combine numerous measurements from high-precision radial-velocity instruments, revealing the presence of a low-amplitude periodic signal with a period of 233 days. Independent photometric and spectroscopic monitoring, as well as an analysis of instrumental systematic effects, suggest that this signal is best explained as arising from a planetary companion. The candidate planet around Barnard's star is a cold super-Earth, with a minimum mass of 3.2 times that of Earth, orbiting near its snow line (the minimum distance from the star at which volatile compounds could condense). The combination of all radial-velocity datasets spanning 20 years of measurements additionally reveals a long-term modulation that could arise from a stellar magnetic-activity cycle or from a more distant planetary object. Because of its proximity to the Sun, the candidate planet has a maximum angular separation of 220 milliarcseconds from Barnard's star, making it an excellent target for direct imaging and astrometric observations in the future.
In this work, we analyze the spectrum of solar cosmic rays flux during ground-level enhancements using the pair of lead-free and standard neutron monitors in the South Pole station. Using both ...monitor data, effects due to anisotropy are considerably reduced. We assume a power-law form for the solar particle spectrum at the top of the atmosphere. The spectral index was computed during all events for which data were available, regardless of the duration or the intensity of the GLE. Seventeen events were analyzed. In this paper, we show the efficiency of the method used, as well as a clear tendency of the spectral index behavior to the ratio between the observed increases in both monitors. It is also shown that the method can be used to calculate the solar cosmic ray spectrum at any required stage of the event. Our results show that the spectral index estimation depends on the choice of the yield function. For the three yield functions used in the analysis, the spectral index changes by about 10%.
For the first time, we used computer simulations to study lift forces on two static disks placed side-by-side within a two-dimensional granular flow and found them to be either repulsive or ...attractive depending on the flow velocity and separation between the disks. Our simulations results reveal that differences in the flow velocity between the disks and outside of that region are closely correlated with the lift force. We propose an empirical function for the lift force based on this correlation and our dimensional analysis. The specific region where the measured velocity exhibits this correlation suggests that attractive lift is not a Bernoulli-like effect. Instead, we speculate that it might be explained by a force balance based on Coulomb’s theory of passive failure in a Mohr–Coulomb material. Our results confirm that repulsive lift is due to the jamming of particles flowing between the disks.
Aims.
We present the photometric calibration of the twelve optical passbands for the Javalambre Photometric Local Universe Survey (J-PLUS) second data release (DR2), comprising 1088 pointings of two ...square degrees, and study the systematic impact of metallicity on the stellar locus technique.
Methods.
The Fe/H metallicity from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) for 146 184 high-quality calibration stars, defined with signal-to-noise ratio larger than ten in J-PLUS passbands and larger than three in
Gaia
parallax, was used to compute the metallicity-dependent stellar locus (ZSL). The initial homogenization of J-PLUS photometry, performed with a unique stellar locus, was refined by including the metallicity effect in colors via the ZSL.
Results.
The variation of the average metallicity along the Milky Way produces a systematic offset in J-PLUS calibration. This effect is well above 1% for the bluer passbands and amounts 0.07, 0.07, 0.05, 0.03, and 0.02 mag in
u
,
J
0378,
J
0395,
J
0410, and
J
0430, respectively. We modeled this effect with the Milky Way location of the J-PLUS pointing, also providing an updated calibration for those observations without LAMOST information. The estimated accuracy in the calibration after including the metallicity effect is at 1% for the bluer J-PLUS passbands and below for the rest.
Conclusions.
Photometric calibration with the stellar locus technique is prone to significant systematic bias in the Milky Way for passbands bluer than
λ
= 4500 Å. The calibration method for J-PLUS DR2 reaches 1–2% precision and 1% accuracy for 12 optical filters within an area of 2176 square degrees.
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