Caius Lucius Selhorst

New Jersey Institute of Technology | NJIT

Aims. The present solar cycle is particular in many aspects: it had a delayed rising phase, it is the weakest of the last 100 years, and it presents two peaks separated by more than one year. To understand the impact of these characteristics on the solar chromosphere and coronal dynamics, images from a wide wavelength range are needed. In this work...

Solar type II radio bursts are produced by plasma oscillations in the solar corona as a result of shock waves. The relationship between type II bursts and coronal shocks is well evidenced by observations since the 1960s. However, the drivers of the shocks associated with type II events at metric wavelengths remain as a controversial issue among sol...

We investigate the physical conditions of the sources of two metric Type-II bursts associated with CME expansions with the aim of verifying the relationship between the shocks and the CMEs, comparing the heights of the radio sources and the heights of the EUV waves associated with the CMEs. The heights of the EUV waves associated with the events we...

We report the statistics of the number of active regions (NAR) observed at 17 GHz with the Nobeyama Radioheliograph between 1992, near the maximum of cycle 22, and 2013, that also includes the maximum of cycle 24, and we compare with other activity indexes. We find that NAR minima are shorter than those of the sunspot number (SSN) and radio flux at...

Planetary transits are commonly observed at visible wavelengths. Here we investigate the shape of a planetary transit observed at radio wavelengths. Solar maps at 17 GHz are used as a proxy for the stellar eclipse by several sizes of planets from super-Earths to hot Jupiters. The relative depth at mid-transit is the same as observed at visible wave...

Aims. This study investigates and compares the physical properties, such as intensity and area, of coronal bright points (CBPs) inside and outside of coronal holes (CHs) using the Atacama Large Millimeter/submillimeter Array (ALMA) and Solar Dynamics Observatory (SDO) observations. Methods. The CBPs were analysed using the single-dish ALMA Band 6 o...

This study investigates and compares brightness and area of coronal bright points (CBPs) inside and outside of coronal holes (CHs) using the single-dish Band 6 observations by the Atacama Large Millimeter/submillimeter Array (ALMA), combined with extreme-ultraviolet (EUV) 193 $\overset{\circ}{\mathrm{A}}$ filtergrams obtained by the Atmospheric Ima...

In recent decades our understanding of solar active regions (ARs) has improved substantially due to observations made with better angular resolution and wider spectral coverage. While prior AR observations have shown that these structures were always brighter than the quiet Sun at centimeter wavelengths, recent observations at millimeter and submil...

In recent decades our understanding of solar active regions (ARs) has improved substantially due to observations made with better angular resolution and wider spectral coverage. While prior AR observations have shown that these structures were always brighter than the quiet Sun at centimeter wavelengths, recent observations at millimeter and submil...

Supra-arcade downflows (SADs) are infrequent, wiggly, and low-emission structures observed to descend through the solar corona, mostly in EUV and soft X-ray frequencies. Based on their physical characteristics, SADs have been interpreted as low-density bubbles and are related to magnetic reconnection processes during long-term erupting flares. In t...

Supra-arcade downflows (SADs) are infrequent, wiggly opaque structures observed to descend through the solar corona, mostly in EUV and soft X-ray frequencies. From their physical characteristics, SADs have been interpreted as voided (subdense) bubbles and are related to magnetic reconnection processes during long-term erupting flares. In this work...

Measurements of the radius and limb brightening of the Sun provide important information about the solar atmosphere structure and temperature. The solar radius increases as the observation at radio frequency decreases, indicating that each emission originates higher in the atmosphere. Thus, different layers of the solar atmosphere can be probed by...

Measurements of the radius and limb brightening of the Sun provide important information about the solar atmosphere structure and temperature. The solar radius increases as the observation at radio frequency decreases, indicating that each emission originates higher in the atmosphere. Thus, different layers of the solar atmosphere can be probed by...

Aims. The main aim of the present analysis is to decipher (i) the small-scale bright features in solar images of the quiet Sun and active regions obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) and (ii) the ALMA correspondence of various known chromospheric structures visible in the H-alpha images of the Sun. Methods. Small-sc...

Aims. The main aim of the present analysis is to decipher (i) the small-scale bright features in solar images of the quiet Sun and active regions obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) and (ii) the ALMA correspondence of various known chromospheric structures visible in the H α images of the Sun. Methods. Small-scale...

At subterahertz frequencies—i.e., millimeter and submillimeter wavelengths—there is a gap in measurements of the solar radius, as well as other parameters of the solar atmosphere. As the observational wavelength changes, the radius varies because the altitude of the dominant electromagnetic radiation is produced at different heights in the solar at...

At subterahertz frequencies -- \textit{i.e.}, millimeter and submillimeter wavelengths -- there is a gap of measurements of the solar radius as well as other parameters of the solar atmosphere. As the observational wavelength changes, the radius varies because the altitude of the dominant electromagnetic radiation is produced at different heights i...

Active regions were observed with different instruments covering the spectral band from 17 to 405 GHz. The observations were made with the Nobeyama Radioheliograph (17 GHz), the Atacama Large Millimetre Array (107 and 238 GHz), and the Solar Submillimeter Telescope (212 and 405 GHz). A procedure was developed that allows the comparison between obse...

We report the temporal evolution of the excess brightness temperature ΔTb above solar active regions (ARs) observed with the Solar Submillimeter Telescope (SST) at 212 (λ = 1.4 mm) and 405 GHz (λ = 0.7 mm) during Cycles 23 and 24. Comparison with the sunspot number (SSN) yields a Pearson's correlation coefficient R = 0.88 and 0.74 for 212 and 405 G...

We report the temporal evolution of the excess brightness temperature above solar active regions (ARs) observed with the Solar Submillimeter Telescope (SST) at 212 ({\lambda} = 1.4 mm) and 405 GHz ({\lambda} = 0.7 mm) during Cycles 23 and 24. Comparison with the sunspot number (SSN) yields a Pearson's correlation coefficient R = 0.88 and 0.74 for 2...

The behavior of sunspots is governed by the magnetic dynamo acting deep within the convection zone of the Sun. Therefore, knowledge of sunspot physical characteristics and how they evolve in time during a solar cycle can help to improve our understanding of the solar magnetic behavior. This work analyzes the physical characteristics of sunspots dur...

When a planet transits in front of its host star, a fraction of its light is blocked, decreasing the observed flux from the star. The same is expected to occur when observing the stellar radio flux. However, at radio wavelengths, the planet also radiates, depending on its temperature, and thus modifies the transit depths. We explore this scenario s...

When a planet transits in front of its host star, a fraction of its light is blocked, decreasing the observed flux from the star. The same is expected to occur when observing the stellar radio flux. However, at radio wavelengths, the planet also radiates, depending on its temperature, and thus modifies the transit depths. We explore this scenario s...

To better understand the influence of the activity cycle on the solar atmosphere, we report the time variation of the radius observed at 37 GHz (λ = 8.1 mm) obtained by the Metsähovi Radio Observatory (MRO) through Solar Cycles 22 to 24 (1989-2015). Almost 5800 maps were analyzed, however, due to instrumental setups changes the data set showed four...

To better understand the influence of the activity cycle on the solar atmosphere, we report the time variation of the radius observed at 37 GHz ($\lambda$=8.1 mm) obtained by the Mets\"ahovi Radio Observatory (MRO) through Solar Cycles 22 to 24 (1989-2015). Almost 5800 maps were analyzed, however, due to instrumental setups changes the data set sho...

In this work we use solar observations with the ALMA radio telescope at the wavelength of 1.21 mm. The aim of the analysis is to improve understanding of the solar chromosphere, a dynamic layer in the solar atmosphere between the photosphere and corona. The study has an observational and a modeling part. In the observational part full-disc solar im...

Polar brightening of the Sun at radio frequencies has been studied for almost fifty years and yet a disagreement persists between solar atmospheric models and observations. Some observations reported brightening values much smaller than the expected values obtained from the models, with discrepancies being particularly large at millimeter wavelengt...

Polar brightening of the Sun at radio frequencies has been studied for almost fifty years and yet a disagreement persists between solar atmospheric models and observations. Some observations reported brightening values much smaller than the expected values obtained from the models, with discrepancies being particularly large at millimeter wavelengt...

Aims. We report on a well-defined EUV wave observed by the Extreme Ultraviolet Imager (EUVI) on board the Solar Terrestrial Relations Observatory (STEREO) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The event was accompanied by a shock wave driven by a halo CME observed by the Large Angle and Spectromet...

Radio-bright regions near the solar poles are frequently observed in Nobeyama Radioheliograph (NoRH) maps at 17 GHz, and often in association with coronal holes. However, the origin of these polar brightening has not been established yet. We propose that small magnetic loops are the source of these bright patches, and present modeling results that...

An exoplanet transiting in front of the disk of its parent star may hide a dark starspot causing a detectable change in the light curve, that allows to infer physical characteristics of the spot such as size and intensity. We have analysed the Kepler Space Telescope observations of the star Kepler-71 in order to search for variabilities in 28 trans...

Here we simulate the shape of a planetary transit observed at radio wavelengths. The simulations use a light curve of the K4 star HAT-P-11 and its hot Jupiter companion as proxy. From the HAT-P-11 optical light curve, a prominent spot was identified (1.10 Rp and 0.6 Ic). On the radio regime, the limb brighting of 30% was simulated by a quadratic fu...

In this work, we analysed the physical parameters of the spotless actives regions observed during solar minimum 23 - 24 (2007 - 2010). The study was based on radio maps at 17~GHz obtained by the Nobeyama Radioheliograph (NoRH) and magnetograms provided by the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO). The...

This document was created by the Solar Simulations for the Atacama Large Millimeter Observatory Network (SSALMON) in preparation of the first regular observations of the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA), which are anticipated to start in ALMA Cycle 4 in October 2016. The science cases presented here demonstrate that...

It is well established that solar Type-II radio bursts are signatures of MHD shock waves propagating outward through the solar corona. Nevertheless, there are long-standing controversies about how such shocks are formed, being solar flares and the coronal mass ejections (CMEs) their most likely drivers. We present the results of the analysis of fou...

Atribuídas a ondas de choque e a ejeções de plasmoide, as emissões solares tipo II são ondaseletromagnéticas geradas a partir de oscilações do plasma coronal. A origem dos choques associados a essasemissões é ainda uma questão em aberto da física solar. Enquanto alguns trabalhos sugerem os flares solarescomo seus acionadores, outros fornecem indíci...

The main objective of the present investigation has been to compare the ionospheric parameters (NmF2 and hmF2) observed by two ground-based ionospheric sounders (one at PALMAS- located near the magnetic equator and the other at Sao Jose dos Campos-located in the low-latitude region) in the Brazilian sector with that by the satellite FORMOSAT-3/COSM...

This work brings out the outcomes of investigation of two solar type II radio bursts observed on October 16, 2010 (19:12:54 UT) and on February 14, 2011 (15:27:05 UT) by CALLISTO-BR (Compound Astronomical Low frequency Low Cost Instrument for Spectroscopy and Transportable Observatory) spectrometer operating in the frequency range of 45-870 MHz. Th...

Resumo This study presents the analysis of a solar split-band type II radio burst observed on November 3, 2010 (∼ 10:17:14 UT) by CALLISTO-BR (Compound Astronomical Low frequency Low Cost Instrument for Spectroscopy and Transportable Observatory) spectrometer operating in the frequency range of 45-870 MHz. Among the physical parameters determined...

The current solar minimum has surprised the entire solar community because the spotless period is presently almost 2–3 years longer than the usual minima. To better understand this, we studied the variation of the solar radius and the polar limb brightening at 17 GHz, comparing the results from the minimum at the end of cycle XXIII with those of th...

We present a new numerical model called "Pakal" intended to solve the radiative transfer equation in a three-dimensional (3D) geometry, using the approximation for a locally plane-parallel atmosphere. Pakal uses pre-calculated radial profiles of density and temperature (based on hydrostatic, hydrodynamic, or MHD models) to compute the emission from...

In this work, we analyze observations of the solar radius at 22 and 43 GHz obtained with the 13.7 m antenna of the Itapetinga Radio Observatory (Atibaia, Brazil) and at submillimeter-wave frequencies, 212 and 405 GHz, obtained by the Solar Submillimeter-wave Telescope (SST) (El Leoncito, San Juan, Argentina). The radius is defined as the limb posit...

The actual solar minimum has surprised all the solar community, since the spotless period is presently almost 2 years longer than the usual minima. In this work we studied the variation of the solar radius and the polar limb brightening at 17 GHz, comparing this minimum with the previous one. Daily maps obtained by the Nobeyama Radioheliograph (NoR...

There is one suggestion that solar activity and climate are linked by cloud formation. Clouds are formed by water vapor condensing onto small particles called aerosols. Cosmic rays can interact with the atmosphere through various chemical reactions that can create aerosols and hence help the formation of clouds. Cosmic rays consist mainly of proton...

Aims: We correlate the polar limb brightening time evolution observed with pass-band filters centered at the EUV 17.1 nm (Fe ix,x) and 30.4 nm (He ii) lines with radio continuum images obtained at 17 GHz (~1.76 cm) during solar cycle 23. Methods: We determine the limb brightening in units of the quiet Sun from daily maps at 17.1 and 30.4 nm obtaine...

To reproduce the radio observations at 17 GHz from Nobeyama Radioheliograph (NoRH), a 3-D solar atmospheric model was constructed considering the thermal bremsstrahlung and gyro-resonance emission mechanisms. To estimate the magnetic field structure in the solar atmosphere, we have extrapolated photospheric magnetograms from MDI considering potenti...

We have determined the solar transition region and coronal radius at EUV wavelengths and its time evolution during Solar Cycle XXIII using daily 30.4 and 17.1 nm images obtained by the Extreme Ultraviolet Imager (EIT) aboard the SoHO satellite. The radius was obtained by fitting a circle to the limb brightness ring. The weighted mean of the tempora...

Aims. We construct a 3D solar atmospheric model to reproduce active region brightness temperature of radio observations.Methods. A 3D solar atmospheric model was developed to reproduce the radio observations at 17 and 34 GHz from the Nobeyama Radioheliograph. The model included bremsstrahlung and gyro-resonance emission mechanisms. Both potential a...

Aims. To determine the solar transition region and coronal radius at EUV wavelengths and its time evolution during Solar Cycle XXIII. Methods. We use daily 30.4 and 17.1 nm images obtained by the Extreme Ultraviolet Imager (EIT) aboard the SoHO satellite and derive the solar radius by fitting a circle to the limb brightness ring. Results. The weigh...

In this work we present the results of our 3D atmospheric model over solar active regions. Our model considers the temperature and density distributions with height, as well the local magnetic 3D structure. To obtain the positions and intensities of magnetic field lines in the solar atmosphere, we made force-free extrapolations of the magnetic fiel...

We present here the first results of our 3-D solar atmospheric model over active regions based on radio observations. Intense magnetic fields take place in active regions, which may result in a gyro-resonance emission contribution to the brightness temperature observed at radio frequencies. This model considers the temperature and densities (electr...

We present a statistical study of the evolution of active regions observed at microwave wavelengths during the 23rd solar cycle (1992-2004). Active regions are sites of increased magnetic fields, thus the radio emission at microwave wavelengths is mostly due to gyro-resonance of thermal electrons around relatively strong magnetic fields. We analyze...

In order to explain the bright patches of emission near the poles of 17 GHz solar maps, we have applied a previously developed atmospheric model based on radio observations. This 2-D model, which includes spicules, yields results in good agreement with brightness temperature values at the disk center, radius, and limb brightening 17 GHz observation...

An atmospheric model was constructed in order to reproduce quantitatively the observations at 17 GHz from Nobeyama Radio Heliograph, namely the brightness temperature at disk center (from 1.4 to 400 GHz), center-to-limb brightening distribution, and radius derived from 17 GHz solar maps. The two dimensional solar atmospheric model, that takes into...

We report the analysis of solar radius determination for more than 3800 maps at 17 GHz from the Nobeyama Radioheliograph (NoRH) over a solar cycle (1992-2003). The aim of this work is to determine the radius dependence on solar activity at 17 GHz. This study was divided into two parts: (i) the mean solar radius calculated using the coordinates arou...

O estudo das variações do raio solar durante o ciclo de atividades do Sol e das diferenças em relação à sua distribuição angular nos fornece informações importantes sobre as mudanças na estrutura da atmosfera solar. Neste trabalho foram analisados mais de 3600 mapas do Sol em 17 GHz obtidos pelo Rádio Heliógrafo de Nobeyama (NoRH), durante 1 ciclo...

A medição acurada do raio solar em qualquer banda do espectro eletromagnético é de relevância na formulação e calibração de modelos da estrutura e atmosfera solar. Esses modelos atribuem emissão do contínuo do Sol calmo em microondas à mesma região da linha Ha do Hell. Apresentamos a medição do raio solar em UV com imagens do EIT (Extreme Ultraviol...

In order to better understand the atmosphere structure of the Sun, we have analyzed over 3000 daily maps of the Sun taken at 17 GHz from the Nobeyama Radioheliograph (NoRH) from 1992 through 2001, focusing on the excess brightness temperature observed near the limb. The purpose of this work is to characterize the limb brightness in two ways: (i) st...