- ID:
- ivo://CDS.VizieR/J/A+AS/143/265
- Title:
- Solar diameter observations in 1998-1999
- Short Name:
- J/A+AS/143/265
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In January 1997, at the Observatsrio Nacional (ON), Rio de Janeiro, Brazil, digital CCD observations of the solar diameter began with a Danjon astrolabe adapted for solar observations and equipped with a variable angle reflecting prism. The prism enables observations of the Sun several times per day and all year round at the southern latitude {phi}=-22{deg} 54'. As of June 1999, about 9000 observations have been made. The mean value of the apparent semi-diameter is 959.13"+/-0.01". Here we report on the results obtained between July 1998 and June 1999. In 162 days 4276 observations were made. For this period the mean apparent semi-diameter is 959.07"+/-0.02". No significant difference between the apparent semi-diameters is found as observed on the East and West sides of the meridian.
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- ID:
- ivo://CDS.VizieR/J/A+AS/135/227
- Title:
- Solar diameter observations in 1997-1998
- Short Name:
- J/A+AS/135/227
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In January 1997, at the Observatsrio Nacional (ON), Rio de Janeiro, Brazil, CCD observations of the solar diameter with a Danjon astrolabe equipped with a variable angle reflecting prism began. This prism is operated manually and enables to observe the Sun many times per day and all year round on the Southern latitude {phi}=-22{deg}54'. Thanks to this and owing to a large number of sunny days at Rio de Janeiro, a high density of observations was achieved - 2900 East and 1730 West observations during the first 18 months.
- ID:
- ivo://CDS.VizieR/J/A+AS/126/281
- Title:
- Solar disk spectrum (660-1175A)
- Short Name:
- J/A+AS/126/281
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The near-limb quiet-Sun spectrum recorded on January 25, 1996 near the solar North pole is presented in tabular form and in graphical form. Table 1 - the line list - lists all lines found in the spectrum providing absolute peak intensities, measured and literature wavelengths, identification, and classification of the transition. Fig. 4 is a display the composite spectrum. The most prominent lines are labelled. In this figure intensities are given in instrumental units and logarithmic scale.
- ID:
- ivo://CDS.VizieR/J/ApJ/759/69
- Title:
- Solar electron events from 1995 to 2005 with WIND/3DP
- Short Name:
- J/ApJ/759/69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We survey the statistical properties of 1191 solar electron events observed by the WIND 3DP instrument from <1keV to >~300keV for a solar cycle (1995 through 2005). After taking into account times of high background, the corrected occurrence frequency of solar electron events versus peak flux exhibits a power-law distribution over three orders of magnitude with exponents between -1.0 and -1.6 for different years, comparable to the frequency distribution of solar proton events, microflares, and coronal mass ejections (CMEs), but significantly flatter than that of soft X-ray (SXR) flares. At 40keV (2.8keV), the integrated occurrence rate above ~0.29 (~330)/cm2/s.sr^-1^/keV near 1 AU is ~1000/year (~600/year) at solar maximum and ~35/year (~25/year) at solar minimum, about an order of magnitude larger than the observed occurrence rate. We find these events typically extend over ~45{deg} in longitude, implying the occurrence rate over the whole Sun is ~10^4^/year near solar maximum. The observed solar electron events have a 98.75% association with type III radio bursts, suggesting all type III bursts may be associated with a solar electron event. They have a close (~76%) association with the presence of low-energy (~0.02-2MeV/nucleon), ^3^He-rich (^3^He/^4^He>=0.01) ion emissions measured by the ACE ULEIS instrument. For these electron events, only ~35% are associated with a reported GOES SXR flare, but ~60% appear to be associated with a CME, with ~50% of these CMEs being narrow. These electrons are often detected down to below 1keV, indicating a source high in the corona.
- ID:
- ivo://CDS.VizieR/J/A+A/422/337
- Title:
- Solar EUV Post-Eruptive Arcades
- Short Name:
- J/A+A/422/337
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Extreme ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) spacecraft provides unique observations of dynamic processes in the low corona. The EIT 195{AA} data taken from 1997 to the end of 2002 were investigated to study the basic physical properties of post-eruptive arcades (PEAs) and their relationship with coronal mass ejections (CMEs) as detected by SOHO/LASCO (Large Angle Spectrometric Coronagraph). Over the investigated time period, 236 PEA events have been identified in total. For each PEA, its EUV lifetime as derived from the emission time at 195{AA}, its heliographic position and length, and its corresponding photospheric source region inferred from SOHO/MDI (Michelson Doppler Imager) data has been studied, as well as the variation of these parameters over the investigated phase of solar cycle 23.
- ID:
- ivo://CDS.VizieR/J/A+A/655/A51
- Title:
- Solar evolutionary and structure models
- Short Name:
- J/A+A/655/A51
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- In protoplanetary disks, the growth and inward drift of dust lead to the generation of a temporal "pebble wave" of increased metallicity. This phase must be followed by a phase in which the exhaustion of the pebbles in the disk and the formation of planets lead to the accretion of metal-poor gas. At the same time, disk winds may lead to the selective removal of hydrogen and helium from the disk. Hence, stars grow by accreting gas that has an evolving composition. In this work, we investigated how the formation of the Solar System may have affected the composition and structure of the Sun, and whether it plays any role in solving the so-called solar-abundance problem, that is, the fact that standard models with up-to-date lower-metallicity abundances reproduce helioseismic constraints significantly more poorly than those with old higher-metallicity abundances. We simulated the evolution of the Sun from the protostellar phase to the present age and attempted to reproduce spectroscopic and helioseismic constraints. We performed chi-squared tests to optimize our input parameters, which we extended by adding secondary parameters. These additional parameters accounted for the variations in the composition of the accreted material and an increase in the opacities. We confirmed that, for realistic models, planet formation occurs when the solar convective zone is still massive; thus, the overall changes due to planet formation are too small to significantly improve the chi-square fits. We found that solar models with up-to-date abundances require an opacity increase of 12% to 18% centered at T=10^6.4^K to reproduce the available observational constraints. This is slightly higher than, but is qualitatively in good agreement with, recent measurements of higher Fe opacities. These models result in better fits to the observations than those using old abundances; therefore, they are a promising solution to the solar abundance problem. Using these improved models, we found that planet formation processes leave a small imprint in the solar core, whose metallicity is enhanced by up to 5%. This result can be tested by accurately measuring the solar neutrino flux. In the improved models, the protosolar molecular cloud core is characterized by a primordial metallicity in the range Zproto=0.0127-0.0157 and a helium mass fraction in the range Yproto=0.268-0.274.
- ID:
- ivo://CDS.VizieR/J/ApJ/757/94
- Title:
- Solar flares observed with GOES and AIA
- Short Name:
- J/ApJ/757/94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore the spatio-temporal evolution of solar flares by fitting a radial expansion model r(t) that consists of an exponentially growing acceleration phase, followed by a deceleration phase that is parameterized by the generalized diffusion function r(t){prop.to}{kappa}(t-t_1_)^{beta}/2^, which includes the logistic growth limit ({beta}=0), sub-diffusion ({beta}=0-1), classical diffusion ({beta}=1), super-diffusion ({beta}=1-2), and the linear expansion limit ({beta}=2). We analyze all M- and X-class flares observed with Geostationary Operational Environmental Satellite and Atmospheric Imaging Assembly/Solar Dynamics Observatory (SDO) during the first two years of the SDO mission, amounting to 155 events. We find that most flares operate in the sub-diffusive regime ({beta}=0.53+/-0.27), which we interpret in terms of anisotropic chain reactions of intermittent magnetic reconnection episodes in a low plasma-{beta} corona. We find a mean propagation speed of v=15+/-12km/s, with maximum speeds of v_max_=80+/-85km/s per flare, which is substantially slower than the sonic speeds expected for thermal diffusion of flare plasmas. The diffusive characteristics established here (for the first time for solar flares) is consistent with the fractal-diffusive self-organized criticality model, which predicted diffusive transport merely based on cellular automaton simulations.
- ID:
- ivo://CDS.VizieR/J/ApJ/774/L27
- Title:
- Solar flares predictors
- Short Name:
- J/ApJ/774/L27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on several magnetic nonpotentiality parameters obtained from the vector photospheric active region magnetograms obtained with the Solar Magnetic Field Telescope at the Huairou Solar Observing Station over two solar cycles, a machine learning model has been constructed to predict the occurrence of flares in the corresponding active region within a certain time window. The Support Vector Classifier, a widely used general classifier, is applied to build and test the prediction models. Several classical verification measures are adopted to assess the quality of the predictions. We investigate different flare levels within various time windows, and thus it is possible to estimate the rough classes and erupting times of flares for particular active regions. Several combinations of predictors have been tested in the experiments. The True Skill Statistics are higher than 0.36 in 97% of cases and the Heidke Skill Scores range from 0.23 to 0.48. The predictors derived from longitudinal magnetic fields do perform well, however, they are less sensitive in predicting large flares. Employing the nonpotentiality predictors from vector fields improves the performance of predicting large flares of magnitude >=M5.0 and >=X1.0.
- ID:
- ivo://CDS.VizieR/J/ApJ/747/L41
- Title:
- Solar flares probabilities
- Short Name:
- J/ApJ/747/L41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Solar flares occur in complex sunspot groups, but it remains unclear how the probability of producing a flare of a given magnitude relates to the characteristics of the sunspot group. Here, we use Geostationary Operational Environmental Satellite X-ray flares and McIntosh group classifications from solar cycles 21 and 22 to calculate average flare rates for each McIntosh class and use these to determine Poisson probabilities for different flare magnitudes. Forecast verification measures are studied to find optimum thresholds to convert Poisson flare probabilities into yes/no predictions of cycle 23 flares. A case is presented to adopt the true skill statistic (TSS) as a standard for forecast comparison over the commonly used Heidke skill score (HSS). In predicting flares over 24 hr, the maximum values of TSS achieved are 0.44 (C-class), 0.53 (M-class), 0.74 (X-class), 0.54 (>=M1.0), and 0.46 (>=C1.0). The maximum values of HSS are 0.38 (C-class), 0.27 (M-class), 0.14 (X-class), 0.28 (>=M1.0), and 0.41 (>=C1.0). These show that Poisson probabilities perform comparably to some more complex prediction systems, but the overall inaccuracy highlights the problem with using average values to represent flaring rate distributions.
- ID:
- ivo://CDS.VizieR/J/ApJS/253/29
- Title:
- Solar flare variability from GOES-15 Ly{alpha} obs.
- Short Name:
- J/ApJS/253/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Lyman-alpha (Ly{alpha}) line of neutral hydrogen at 121.6nm is by far the brightest emission line in the vacuum ultraviolet spectral range of the Sun. The emission at this line could be a major energy input to the upper layers of the Earth's atmosphere, strongly impacting the geospace environment. The Geostationary Operational Environmental Satellite (GOES) series, starting with GOES-13, began to carry a multichannel Extreme UltraViolet Sensor (EUVS) with one channel (E-channel) targeting the Ly{alpha} line. In the present work, we produce a Ly{alpha} flare catalog from the GOES-15/EUVS-E data between 2010 April 8 and 2016 June 6 with an automatic flare detection algorithm. This algorithm is designed to search events at various scales and find their real start and end times. Based on the obtained flare list, statistics on the temporal behavior such as the duration, rise, and decay times, and the event asymmetries of Ly{alpha} flares is presented. On average (defined by the median of the distributions), the duration, rise and decay times of the flares were estimated to be 20.8 minutes, 5.6 minutes, and 14.2 minutes, respectively. We also discuss the frequency distributions of the peak flux and the fluence of Ly{alpha} flares, both of which reveal power-law behaviors with power-law indices of 2.71+/-0.06 and 2.42+/-0.06, respectively, implying that more flares are accumulated at small scales and these small-scale events play an important role in explaining the violent solar energy release.
