- ID:
- ivo://CDS.VizieR/J/ApJ/737/L35
- Title:
- Pulsed Alfven waves in the solar wind
- Short Name:
- J/ApJ/737/L35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using 3s plasma and magnetic field data from the Wind spacecraft located in the solar wind well upstream from Earth, we report observations of isolated, pulse-like Alfvenic disturbances in the solar wind. These isolated events are characterized by roughly plane-polarized rotations in the solar wind magnetic field and velocity vectors away from the directions of the underlying field and velocity and then back again. They pass over Wind on timescales ranging from seconds to several minutes. These isolated, pulsed Alfven waves are pervasive; we have identified 175 such events over the full range of solar wind speeds (320-550km/s) observed in a randomly chosen 10 day interval.
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- ID:
- ivo://CDS.VizieR/J/ApJ/833/284
- Title:
- Quasi-periodic pulsations in solar flares
- Short Name:
- J/ApJ/833/284
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nature of quasi-periodic pulsations (QPP) in solar flares is poorly constrained, and critically the general prevalence of such signals in solar flares is unknown. Therefore, we perform a large-scale search for evidence of signals consistent with QPP in solar flares, focusing on the 1-300s timescale. We analyze 675 M- and X-class flares observed by the Geostationary Operational Environmental Satellite (GOES) series in 1-8 A soft X-rays between 2011 February 1 and 2015 December 31. Additionally, over the same era we analyze Fermi/Gamma-ray Burst Monitor (GBM) 15-25keV X-ray data for each of these flares associated with a Fermi/GBM solar flare trigger, a total of 261 events. Using a model comparison method, we determine whether there is evidence for a substantial enhancement in the Fourier power spectrum that may be consistent with a QPP signature, based on three tested models; a power-law plus a constant, a broken power-law plus constant, and a power-law-plus-constant with an additional QPP signature component. From this, we determine that ~30% of GOES events and ~8% of Fermi/GBM events show strong signatures consistent with classical interpretations of QPP. For the remaining events either two or more tested models cannot be strongly distinguished from each other, or the events are well-described by single power-law or broken power-law Fourier power spectra. For both instruments, a preferred characteristic timescale of ~5-30s was found in the QPP-like events, with no dependence on flare magnitude in either GOES or GBM data. We also show that individual events in the sample show similar characteristic timescales in both GBM and GOES data sets. We discuss the implications of these results for our understanding of solar flares and possible QPP mechanisms.
- ID:
- ivo://CDS.VizieR/J/A+A/644/A109
- Title:
- Quiet-sun hydrogen Lyman-alpha line profile
- Short Name:
- J/A+A/644/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The solar radiation in the Lyman-alpha spectral line of hydrogen plays a significant role in the illumination of chromospheric and coronal structures, such as prominences, spicules, chromospheric fibrils, cores of coronal mass ejections, and solar wind. Moreover, it is important for the investigation of the heliosphere, Earth's ionosphere, and the atmospheres of planets, moons, and comets. We derive a reference quiet-Sun Lyman-alpha spectral profile that is representative of the Lyman-alpha radiation from the solar disk during a minimum of solar activity. This profile can serve as an incident radiation boundary condition for the radiative transfer modelling of chromospheric and coronal structures. Because the solar radiation in the Lyman lines is not constant over time but varies significantly with the solar cycle, we provide a method for the adaptation of the incident radiation Lyman line profiles (Lyman-alpha and higher lines) to a specific date. Moreover, we analyse how the change in the incident radiation influences the synthetic spectra produced by the radiative transfer modelling. We used SOHO/SUMER Lyman-alpha raster scans obtained without the use of the attenuator in various quiet-Sun regions on the solar disk. The observations were performed on three consecutive days (June 24, 25, and 26, 2008) during a period of minimum solar activity. The reference Lyman-alpha profile was obtained as a spatial average over eight available raster scans. To take into account the Lyman-alpha variation with the solar cycle, we used the LISIRD composite Lyman-alpha index. To estimate the influence of the change in the incident radiation in the Lyman lines on the results of radiative transfer models, we used a 2D prominence fine structure model. We present the reference quiet-Sun Lyman-alpha profile and a table of coefficients describing the variation of the Lyman lines with the solar cycle throughout the lifetime of SOHO. The analysis of the influence of the change in the incident radiation shows that the synthetic spectra are strongly affected by the modification of the incident radiation boundary condition. The most pronounced impact is on the central and integrated intensities of the Lyman lines. There, the change in the synthetic spectra can often have the same amplitude as the change in the incident radiation itself. The impact on the specific intensities in the peaks of reversed Lyman-line profiles is smaller but still significant. The hydrogen Halpha line can also be considerably affected, despite the fact that the Halpha radiation from the solar disk does not vary with the solar cycle.
- ID:
- ivo://CDS.VizieR/J/ApJS/255/16
- Title:
- Quiet-Sun MgII h & k line profiles from IRIS
- Short Name:
- J/ApJS/255/16
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- We derived high-precision reference profiles of the MgII h and k lines that represent the quiet Sun during a minimum of the solar activity. To do so, we used the broad catalog of full-Sun mosaics obtained by the Interface Region Imaging Spectrograph (IRIS). To minimize the influence of the local variations due to the on-disk solar features and to achieve low levels of uncertainties, we used 12 IRIS full-Sun mosaics without sunspots or other significant signs of solar activity. These mosaics were obtained between 2019 April and 2020 September in the near-ultraviolet spectral range. In this paper, we present the disk-averaged reference profiles of MgII h and MgII k lines, together with a series of reference profiles spanning the distance between the disk center and the solar limb. These series of profiles offer a detailed representation of the center-to-limb variation of both MgII h and MgII k lines. The reference MgII h and k line profiles provided in this paper can be used as the incident radiation boundary condition for radiative-transfer modeling of prominences, spicules, and other coronal and chromospheric structures.
- ID:
- ivo://CDS.VizieR/J/ApJS/182/80
- Title:
- Rare earth abundances
- Short Name:
- J/ApJS/182/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived new abundances of the rare earth elements Pr, Dy, Tm, Yb, and Lu for the solar photosphere and for five very metal-poor, neutron-capture r-process-rich giant stars. The photospheric values for all five elements are in good agreement with meteoritic abundances. For the low-metallicity sample, these abundances have been combined with new Ce abundances from a companion paper, and reconsideration of a few other elements in individual stars, to produce internally consistent Ba, rare earth, and Hf(56<=Z<=72) element distributions. These have been used in a critical comparison between stellar and solar r-process abundance mixes.
- ID:
- ivo://CDS.VizieR/J/A+A/615/A93
- Title:
- Reconstructed decadal sunspot numbers
- Short Name:
- J/A+A/615/A93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The solar activity in the past millennia can only be reconstructed from cosmogenic radionuclide proxy records in terrestrial archives. However, because of the diversity of the proxy archives, it is difficult to build a homogeneous reconstruction. All previous studies were based on individual, sometimes statistically averaged, proxy datasets. Here we aim to provide a new consistent multiproxy reconstruction of the solar activity over the last 9000 years, using all available long-span datasets of ^10^Be and ^14^C in terrestrial archives. A new method, based on a Bayesian approach, was applied for the first time to solar activity reconstruction. A Monte Carlo search (using the x2 statistic) for the most probable value of the modulation potential was performed to match data from different datasets for a given time. This provides a straightforward estimate of the related uncertainties. We used six ^10^Be series of different lengths (from 500-10000 years) from Greenland and Antarctica, and the global ^14^C production series. The 10Be series were resampled to match wiggles related to the grand minima in the ^14^C reference dataset. The stability of the long data series was tested. Results. The Greenland Ice-core Project (GRIP) and the Antarctic EDML (EPICA Dronning Maud Land) ^10^Be series diverge from each other during the second half of the Holocene, while the ^14^C series lies in between them. A likely reason for the discrepancy is the insufficiently precise beryllium transport and deposition model for Greenland, which leads to an undercorrection of the GRIP series for the geomagnetic shielding effect. A slow 6-7-millennia variability with lows at ca. 5500 BC and 1500 AD in the longterm evolution of solar activity is found. Two components of solar activity can be statistically distinguished: the main component, corresponding to the 'normal' moderate level, and a component corresponding to grand minima. A possible existence of a component representing grand maxima is indicated, but it cannot be separated from the main component in a statistically significant manner. A new consistent reconstruction of solar activity over the last nine millennia is presented with the most probable values of decadal sunspot numbers and their realistic uncertainties. Independent components of solar activity corresponding to the main moderate activity and the grand-minimum state are identified; they may be related to different operation modes of the dynamo.
- ID:
- ivo://CDS.VizieR/J/ApJS/220/2
- Title:
- Rosseland opacities with the OPAS model
- Short Name:
- J/ApJS/220/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The OPAS opacity model has been used to calculate the radiative opacity of stellar plasmas in local thermodynamic equilibrium. According to the recent chemical composition revision of the solar photosphere, opacities have been computed for various hydrogen and metallic element mass fractions. Calculations have been performed toward solar interior modeling for temperatures between log[T(K)]=6 and log[T(K)]=7.2, and for electron densities between 10^20^ and 10^26^cm^-3^. We discuss possible sources of uncertainty in the calculations. We also compare Rosseland opacities to OPAL and OP data.
- ID:
- ivo://CDS.VizieR/J/A+A/595/A104
- Title:
- Scheiner drawing sunspot areas and tilt angles
- Short Name:
- J/A+A/595/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Digital images of observations printed in the books Rosa Ursina sive solis and Prodromus pro Sole mobili by Christoph Scheiner, as well as the drawings from Scheiner's letters to Marcus Welser, are analysed to obtain information on the positions and sizes of sunspots that appeared before the Maunder minimum. In most cases, the given orientation of the ecliptic is used to set up the heliographic coordinate system for the drawings. Positions and sizes are measured manually on screen. Very early drawings have no indication of their orientation. A rotational matching using common spots of adjacent days is used in some cases, while in other cases, the assumption that images were aligned with a zenith-horizon coordinate system appeared to be the most probable.
- ID:
- ivo://CDS.VizieR/J/A+A/634/A117
- Title:
- Screening potential and continuum lowering
- Short Name:
- J/A+A/634/A117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An accurate description of the screening potential induced by a hot, dense plasma is a fundamental problem in atomic physics and plasma physics, and it plays a pivotal role in the investigation of microscopic atomic processes and the determination of macroscopic physical properties, such as opacities and equations of state as well as nuclear fusion cross sections. Recent experimental studies show that currently available analytical models of plasma screening have difficulty in accurately describing the ionization-potential depression, which is directly determined by the screening potential. Here, we propose a consistent approach to determine the screening potential in dense plasmas under solar-interior conditions from the free-electron micro-space distribution. It is assumed that the screening potential for an ion embedded in a dense plasma is predominately determined by the free electrons in the plasma. The free-electron density is obtained by solving the ionization-equilibrium equation for an average-atom model to obtain the average degree of ionization of the plasma. The proposed model was validated by comparing the theoretically predicted ionization-potential depression of a solid-density Si plasma with recent experiments. Our approach was applied to investigate the screening potential and ionization-potential depression of Si plasmas under solar-interior conditions over a temperature range of 150-500eV and an electron-density range of 5.88x10^22^-3.25x10^24^cm^-3^. It can be easily incorporated into atomic-structure codes and used to investigate basic atomic processes, such as photoionization, electron-ion collisional excitation and ionization, and Auger decay, in a dense plasma.
- ID:
- ivo://CDS.VizieR/J/ApJ/869/66
- Title:
- Search for extraterrestrial intelligence with ATA
- Short Name:
- J/ApJ/869/66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report a novel radio autocorrelation search for extraterrestrial intelligence. For selected frequencies across the terrestrial microwave window (1-10GHz), observations were conducted at the Allen Telescope Array to identify artificial non-sinusoidal periodic signals with radio bandwidths greater than 4Hz, which are capable of carrying substantial messages with symbol rates from 4 to 10^6^Hz. Out of 243 observations, about half (101) were directed toward sources with known continuum flux >~1Jy over the sampled bandwidth (quasars, pulsars, supernova remnants, and masers), based on the hypothesis that they might harbor heretofore undiscovered natural or artificial repetitive, phase or frequency modulation. The rest of the observations were directed mostly toward exoplanet stars with no previously discovered continuum flux. No signals attributable to extraterrestrial technology were found in this study. We conclude that the maximum probability that future observations like the ones described here will reveal repetitively modulated emissions is less than 5% for continuum sources and exoplanets alike. The paper concludes by describing a new approach to expanding this survey to many more targets and much greater sensitivity using archived data from interferometers all over the world.
