Shocked Wind Research Articles

Realistic modelling of wind and supernovae shocks in star clusters: addressing 22Ne/20Ne and other problems in Galactic cosmic rays

ABSTRACT Cosmic ray (CR) sources leave signatures in the isotopic abundances of CRs. Current models of Galactic CRs that consider supernovae (SNe) shocks as the main sites of particle acceleration cannot satisfactorily explain the higher 22Ne/20Ne ratio in CRs compared to the interstellar medium. Although stellar winds from massive stars have been invoked, their contribution relative to SNe ejecta has been taken as a free parameter. Here, we present a theoretical calculation of the relative contributions of wind termination shocks (WTSs) and SNe shocks in superbubbles, based on the hydrodynamics of winds in clusters, the standard stellar mass function, and stellar evolution theory. We find that the contribution of WTSs towards the total CR production is at least $25{{\ \rm per\ cent}}$, which rises to $\gtrsim 50{{\ \rm per\ cent}}$ for young (≲10 Myr) clusters, and explains the observed 22Ne/20Ne ratio. We argue that since the progenitors of apparently isolated supernovae remnants (SNRs) are born in massive star clusters, both WTS and SNe shocks can be integrated into a combined scenario of CRs being accelerated in massive clusters. This scenario is consistent with the observed ratio of SNRs to γ-ray bright (Lγ ≳ 1035 erg s−1) star clusters, as predicted by star cluster mass function. Moreover, WTSs can accelerate CRs to PeV energies, and solve other long-standing problems of the standard SN paradigm of CR acceleration.

A new method for force prediction in an accelerometer force balance system using support vector regression

The accurate prediction of force is very important in the present scenario of aerodynamic force measurement. The high accuracy of force prediction during calibration facilitates a better accuracy of force measurement in aerodynamic facilities like shock tunnels and wind tunnels. The present study describes the force prediction in an accelerometer force balance system using support vector regression (SVR). The comparison of SVR with the existing force prediction techniques namely, adaptive neuro-fuzzy inference system (ANFIS) and artificial neural network (ANN) has also been carried out. The accelerometer force balance used in the current experimentation consists of a tri-axial accelerometer to measure the response on an aluminium hemispherical model on the application of force. The impulse forces were applied along the axial, normal and azimuthal directions. The forces were predicted using the accelerations obtained from the tri-axial accelerometer. SVR method was able to predict the forces quite accurately as compared to ANFIS and ANN. However, SVR has the advantage over ANFIS and ANN in that it is independent of the magnitude of the training and testing data. It is capable of an accurate prediction of forces with any magnitude of training and testing data, unlike ANFIS and ANN.

Effect of Görtler-like vortices of various intensity on heat transfer in supersonic compression corner flows

Experiments on heat transfer over Mach 8, 15° compression corner flow affected by Görtler-like reattachment vortices of controllable intensity are carried out in the shock wind tunnel UT-1 M (TsAGI). Experiments cover two Reynolds numbers Re∞,L=(1.75±0.08) × 105 and Re∞,L=(3.90±0.15) × 105 based on the sharp flat plate length at which the reattachment flow is close to laminar or beginning transitional, respectively. The effect of streamwise vortices of different intensity on spanwise variations of the heat flux and its spanwise-averaged level at the reattachment region is investigated. The intensity of the vortices is varied by accurate controlling the height of a spanwise rake of cylindrical pins (seeding elements) placed on the plate ahead of the separation bubble.

DETERMINATION OF MAGNETIC RECONNECTION IN A LOW AND A HIGH ACTIVITY YEAR

When there is a temporary disturbance of earth's magnetosphere, then a geomagnetic storm (or solar storm) has occurred. It is caused by a solar wind shock wave and/or cloud of a magnetic field that interacts with the Earth's magnetic fields. The interaction of Interplanetary Magnetic Fields (IMF) of the sun [1] with the earth's magnetic fields in opposite directions is known as magnetic reconnection. Magnetic reconnection (often referred as is the breaking and reconnecting of oppositely directed magnetic field lines in plasma at a neutral point which leads to converting the magnetic field energy into plasma kinetic and thermal energy. It occurs either in the daytime (day reconnection) where the sunward convection near the polar cusps allows energized particles to be transmitted earthward or night-time (tail reconnection) where particles are injected into the magnetosphere, thus releasing stored energy in the form of auroral substorms. A geostorm can be determined by changes in the Disturbance-storm time (Dst) Sokolov [2]. However not all geomagnetic storms have an initial phase and not all sudden increases in Dst Original Research Article Ojerheghan and Adimula; IAARJ, 2(4): 30-47, 2020; Article no.IAARJ.62999 31 or SYM-H are followed by a geomagnetic storm. This paper attempts to determine when the magnetic reconnection occurs in the solar cycle 24 considering a low activity year 2009 and a high activity year 2012. We analysed 39 and 202 geomagnetic storms in 2009 and 2012 respectively considering the Dst indices and IMF Bz values of each month obtained from the OMNIWeb database. Our results showed that storms were frequent and intense at high levels of solar activity due to the frequent occurrence of CMEs and ICMEs in the year 2012 than in the year 2009 which occurred in 10% and 45% of days in the year 2009 and 2012 respectively. This study also revealed that negative Bz occurrences were 47.54% and 52.18% of Bz occurrences in 2009 and 2012 respectively. Thus, the more intense the geostorms, the more Bz would go south and the more magnetic reconnection and subsequently auroral substorms which can increase radiation doses for occupants of transpolar flights, disruption of shortwave radio communications, distortion of compass readings in polar regions, failure of electrical transmission lines, increased corrosion in long pipelines, anomalies in the operations of communications satellites, and potentially lethal doses of radiation for astronauts in interplanetary spacecraft.

SN2018kzr: A Rapidly Declining Transient from the Destruction of a White Dwarf

Abstract We present SN2018kzr, the fastest declining supernova-like transient, second only to the kilonova, AT2017gfo. SN2018kzr is characterized by a peak magnitude of M r = −17.98, a peak bolometric luminosity of ∼1.4 × 1043 erg s−1, and a rapid decline rate of 0.48 ± 0.03 mag day−1 in the r band. The bolometric luminosity evolves too quickly to be explained by pure 56Ni heating, necessitating the inclusion of an alternative powering source. Incorporating the spin-down of a magnetized neutron star adequately describes the lightcurve and we estimate a small ejecta mass of M ej = 0.10 ± 0.05 M ⊙. Our spectral modeling suggests the ejecta is composed of intermediate mass elements including O, Si, and Mg and trace amounts of Fe-peak elements, which disfavors a binary neutron star merger. We discuss three explosion scenarios for SN2018kzr, given the low ejecta mass, intermediate mass element composition, and high likelihood of additional powering—the core collapse of an ultra-stripped progenitor, the accretion induced collapse (AIC) of a white dwarf, and the merger of a white dwarf and neutron star. The requirement for an alternative input energy source favors either the AIC with magnetar powering or a white dwarf–neutron star merger with energy from disk wind shocks.

Modelling the interaction between relativistic and non-relativistic winds in binary pulsar systems: strong magnetization of the pulsar wind

ABSTRACT We present a numerical study of the properties of the flow produced by the collision of a magnetized anisotropic pulsar wind with the circumbinary environment. We focus on studying the impact of the high wind magnetization on the geometrical structure of the shocked flow. This work is an extension of our earlier studies that focused on a purely hydrodynamic interaction and weak wind magnetization. We consider the collision in the axisymmetric approximation, i.e. the pulsar rotation axis is assumed to be oriented along the line between the pulsar and the optical star. The increase of the magnetization results in the expansion of the opening cone in which the shocked pulsar wind propagates. This effect is explained in the frameworks of the conventional theory of collimation of magnetized winds. This finding has a direct implication for scenarios that involve Doppler boosting as the primary mechanism behind the GeV flares detected with the Fermi Large Area Telescope from PSR B1259−63/LS 2883. The maximum enhancement of the apparent emission is determined by the ratio of 4$\pi$ to the solid in which the shocked pulsar wind propagates. Our simulations suggest that this enhancement factor is decreased by the impact of the magnetic field.

The Source, Significance, and Magnetospheric Impact of Periodic Density Structures Within Stream Interaction Regions

AbstractWe present several examples of magnetospheric ultralow frequency pulsations associated with stream interaction regions and demonstrate that the observed magnetospheric pulsations were also present in the solar wind number density. The distance of the solar wind monitor ranged from just upstream of Earth's bow shock to 261 RE, with a propagation time delay of up to 90 min. The number density oscillations far upstream of Earth are offset from similar oscillations observed within the magnetosphere by the advection timescale, suggesting that the periodic dynamic pressure enhancements were time stationary structures, passively advecting with the ambient solar wind. The density structures are larger than Earth's magnetosphere and slowly altered the dynamic pressure enveloping Earth, leading to a quasi‐static and globally coherent “forced‐breathing” of Earth's dayside magnetospheric cavity. The impact of these periodic solar wind density structures was observed in both magnetospheric magnetic field and energetic particle data. We further show that the structures were initially smaller‐amplitude, spatially larger, structures in the upstream slow solar wind and that the higher‐speed wind compressed and amplified these preexisting structures leading to a series of quasiperiodic density structures with periods typically near 20 min. Similar periodic density structures have been observed previously at L1 and in remote images, but never in the context of solar wind shocks and discontinuities. The existence of periodic density structures within stream interaction regions may play an important role in magnetospheric particle acceleration, loss, and transport, particularly for outer zone electrons that are highly responsive to ultralow frequency wave activity.

Analysis of the X-ray emission of OB stars II: B stars

This paper is the second part of an investigation into the mechanism for the origin of X-rays in early-type stars. Archival X-ray observations of 25 B stars, obtained by the XMM-Newton satellite, are analysed. We check two hypotheses on the origin of X-ray emission: the Magnetically Confined Wind Shock Model (MCWS) and Pollock’s paradigm. For all studied stars, the mean ratio of the half widths at half maximum to the terminal velocities appears to be in contradiction to Pollock’s hypothesis that . We checked three possible consequences of the MCWS model: correlations between the hardness of the X-ray spectra for B stars and terminal wind velocities, mass loss rates and magnetic fields. It was shown that such correlations are marginal or even absent both for magnetic and non-magnetic B stars.

Observational limits on the X-ray emission from the bubble nebula surrounding Ho IX X-1

ABSTRACT Optical and radio observations of shock-ionized bubble nebulae surrounding ultraluminous X-ray sources (ULXs) suggest that they are powered by jets or supercritical outflows presumably launched from the ULX accretion disc. Recent simulations of these systems have shown that the shocked wind can emit thermal X-rays with estimated luminosities ≲1036 erg s−1. In this work, we investigated whether it is possible to detect and spatially resolve the X-ray emission from these systems using archival Chandra observations of the ULX Holmberg IX X-1 (Ho IX X-1). This source is an ideal target to study for two reasons: it is surrounded by an optical bubble nebula with a large spatial extent (∼400 pc) that can easily be resolved with Chandra. Further, it has a hard X-ray continuum that is easily distinguishable from the expected soft thermal emission from the nebula. However, a spectral and photometric analysis on stacked Chandra observations of the source reveals that there is no strong evidence for an X-ray bubble associated with it, to a limiting luminosity of ∼2 × 1036 erg s−1. The detection of such X-ray nebulae may be possible with future X-ray missions such as Advanced Telescope for High ENergy Astrophysics(ATHENA), which would provide useful constraints on the kinematics of the outflow. Finally, our observations also emphasize that the nebular emission does not contribute significantly to the residuals in the X-ray spectrum of the source, which are more likely to be linked to processes localized to the ULX.

Modelling multiwavelength emissions from PSR B1259–63/LS 2883: Effects of the stellar disc on shock radiations

PSR B1259–63/LS 2883 is an elliptical pulsar/Be star binary that emits broadband emissions from radio to TeVγ-rays. The massive star possesses an equatorial disc that is inclined with the orbital plane of the pulsar. Non-thermal emission from the system is believed to be produced by pulsar wind shock and double-peak profiles in the X-ray, and TeVγ-ray light curves are related to the phases of the pulsar passing through the disc region of the star. In this paper, we investigate the interactions between the pulsar wind and stellar outflows, especially with the presence of the disc, and present a multiwavelength modelling of the emission from this system. We show that the double-peak profiles of X-ray and TeVγ-ray light curves are caused by the enhancements of the magnetic field and soft photons at the shock during the disc passages. As the pulsar is passing through the equatorial disc, the additional pressure of the disc pushes the shock surface closer to the pulsar, which causes the enhancement of magnetic field in the shock, and thus increases the synchrotron luminosity. The TeVγ-rays due to the inverse-Compton (IC) scattering of shocked electrons with seed photons from the star are expected to peak around periastron, which is inconsistent with observations. However, the shock heating of the stellar disc could provide additional seed photons for IC scattering during the disc passages, and thus produces the double-peak profiles as observed in the TeVγ-ray light curve. Our model can possibly be examined and applied to other similar gamma-ray binaries, such as PSR J2032+4127/MT91 213, HESS J0632+057, and LS I+61°303.

Local fading accelerator and the origin of TeV cosmic ray electrons

The total cosmic ray electron spectrum (electrons plus positrons) exhibits a break at a particle energy of $\sim 1\rm~TeV$ and extends without any attenuation up to $\rm \sim 20~ TeV $. Synchrotron and inverse Compton energy losses strongly constrain both the age and the distance of the potential sources of TeV and multi-TeV electrons to $\rm\approx 10^5~yr$ and $\rm \approx 100-500~pc$, depending on both the absolute value and energy dependence of the cosmic ray diffusion coefficient. This suggests that only a few, or just one nearby discrete source may explain the observed spectrum of high energy electrons. On the other hand the measured positron fraction, after initially increasing with particle energy, saturates at a level well below 0.5 and likely drops above $\sim 400-500$ GeV. This means that the local source(s) of TeV electrons should not produce positrons in equal amount, ruling out scenarios involving pulsars/pulsar winds as the main sources of high energy leptons. In this paper we show that a single, local, and fading source can naturally account for the entire spectrum of cosmic ray electrons in the TeV domain. Even though the nature of such source remains unclear, we discuss known cosmic ray accelerators, such as supernova remnant and stellar wind shocks, which are believed to accelerate preferentially electrons rather than positrons.

Long-term soft and hard X-ray investigation of the colliding wind WN+O binary WR 25

ABSTRACT We investigated the long-term behaviour in X-rays of the colliding wind binary WR 25, using archival data obtained with Suzaku, Swift, XMM–Newton, and NuSTAR spanning over ∼16 yr. Our analysis reveals phase-locked variations repeating consistently over many consecutive orbits, in agreement with an X-ray emission fully explained by thermal emission from the colliding winds in the 208-d orbit. We report on a significant deviation of the X-ray flux with respect to the 1/D trend (expected for adiabatic shocked winds) close to periastron passage. The absence of a drop in post-shock plasma temperature close to periastron suggests this break in trend cannot be explained in terms of reduced pre-shock velocities in this part of the orbit. Finally, NuSTAR data reveal a lack of hard X-ray emission (above 10.0 keV) above the background level. Upper limits on a putative non-thermal emission strongly suggest that the sensitivity of present hard X-ray observatories is not sufficient to detect non-thermal emission from massive binaries above 10 keV, unless the wind kinetic power is large enough to significantly feed particle acceleration in the wind–wind interaction.

Using a Numerical MHD Model to Improve Solar Wind Time Shifting

AbstractWe present three solar wind shock events that all occurred at times when Advanced Composition Explorer was near L1 and WIND was in front of the bow shock. We use a 1.5‐D MHD (magnetohydrodynamic) numerical model and the well known MVAB‐0 time‐shifting algorithm to propagate these events from Advanced Composition Explorer to the location of WIND. The results of these two methods are compared to WIND observations. We find that the 1.5‐D numerical model reproduces some important features in the WIND data that are not reflected in the time‐shifted results. We believe that 1.5‐D numerical simulations could supplement traditional time‐shifting methods in some circumstances for time‐shifting solar wind data to the bow shock.

GeV–TeV Cosmic-Ray Leptons in the Solar System from the Bow Shock Wind Nebula of the Nearest Millisecond Pulsar J0437–4715

Abstract We consider the acceleration of leptons up to GeV–TeV energies in the bow shock wind nebula of PSR J0437–4715 and their subsequent diffusion through the interstellar magnetic fields. The leptons accelerated at the pulsar wind termination surface are injected into re-acceleration in colliding shock flows. Modeled spectra of synchrotron emission from the accelerated electrons and positrons are consistent with the far-ultraviolet and X-ray observations of the nebula carried out with the Hubble Space Telescope and Chandra X-ray Observatory. These observations are employed to constrain the absolute fluxes of relativistic leptons, which are escaping from the nebula and eventually reaching the solar system after energy-dependent diffusion through the local interstellar medium accompanied by synchrotron and Compton losses. It is shown that accelerated leptons from the nebula of PSR J0437–4715 can be responsible both for the enhancement of the positron fraction above a few GeV detected by PAMELA and AMS-02 spectrometers and for the TeV range lepton fluxes observed with H.E.S.S., VERITAS, Fermi, CALET, and DAMPE.

Using Mutual Information to Determine Geoeffectiveness of Solar Wind Phase Fronts With Different Front Orientations

AbstractThe geoeffectiveness of solar wind shocks depends on angle with respect to the Sun‐Earth line, with highly angled solar wind shocks being less geoeffective than nearly frontal solar wind shocks. However, it is unclear whether this holds for the orientation of structures in nonshocked solar wind. In this paper, we perform a mutual information analysis of 18 years of in situ solar wind and ground magnetometer data in order to investigate the effects of solar wind phase front orientation on solar wind geoeffectiveness (indicated by SuperMAG SME, the SuperMAG enhanced version of the AE index). Since geomagnetic response is strongly influenced by interplanetary magnetic field (IMF) Bz, and IMF Bz affects phase front orientation, we use conditional mutual information to account for the effect of Bz on geomagnetic activity. In contrast to what has been found for solar wind shocks, we find that during times of IMF Bz > 0, phase fronts aligned with the average Parker spiral direction (45° azimuth, 0° inclination) tend to be associated with higher geomagnetic activity (SME > 500 nT) than would be expected if IMF Bz and phase front orientation quantities were unrelated. During times of IMF Bz < 0, there is no connection between solar wind phase front orientation and geomagnetic activity (SME). We believe that Parker spiral‐aligned phase fronts being associated with higher geomagnetic activity during times of IMF Bz > 0 is due to constant phase front orientation allowing for more efficient energy transfer either through viscous interaction or high‐latitude reconnection.

Dispersion surface and electromagnetic responses of the magnetosonic/whistler mode in the high-β collisionless plasmas

Near-parallel and highly oblique magnetosonic/whistler (M/W) mode waves are frequently observed in solar wind and interplanetary shocks. These observed waves are usually analyzed by the plasma kinetic and fluid theories. This study compares the dispersion surface and electromagnetic responses of the M/W mode wave under both kinetic and fluid theories in the plasmas with βp = βe ≃ 1 in detail. In comparison with the kinetic theory, it proposes that the hot fluid theory is suitable to obtain the dispersion relation, the ratio of the parallel to perpendicular magnetic fluctuation Bz/B⊥, and the ratio of the electric to magnetic fluctuation E/B. Except the near-parallel low-frequency M/W mode, the hot fluid theory would be used to calculate the ratio between two magnetic fluctuations perpendicular to the wave vector B1/B2, the magnetic helicity σ, and the ratio of the parallel to perpendicular electric fluctuation Ez/E⊥ of the M/W mode waves. The cold fluid theory is good at describing the magnetic responses including Bz/B⊥, B1/B2, and σ, but it underestimates ω, E/B, and Ez/E⊥ for the obliquely propagating M/W mode wave. Furthermore, both hot and cold fluid theories can obtain the ratio of the longitudinal to transverse electric fluctuation relative to the wave vector EL/EP of the obliquely propagating low-frequency M/W mode. These results provide an indicator about how to choose the adequate theory to analyze the observations of the M/W mode waves in the solar wind and interplanetary shocks. Besides, from the dispersion surface in kinetic theory, it shows that the relative weak damping arises for the low-frequency branch at the angle around 0°, 60°, and 90° and for the high-frequency branch with ω ∼ [ωcp, 300ωcp] at the normal angle smaller than 60°, which indicates the possible angle and frequency of the freely propagating M/W mode waves.

The Orion Region: Evidence of enhanced cosmic-ray density in a stellar wind forward shock interaction with a high density shell

Context. In recent years, an in-depth γ-ray analysis of the Orion region has been carried out by the AGILE and Fermi/LAT (Large Area Telescope) teams with the aim of estimating the H2–CO conversion factor, XCO. The comparison of the data from both satellites with models of diffuse γ-ray Galactic emission unveiled an excess at (l, b)=[213.9, −19.5], in a region at a short angular distance from the OB star κ-Ori. Possible explanations of this excess are scattering of the so-called “dark gas”, non-linearity in the H2–CO relation, or cosmic-ray (CR) energization at the κ-Ori wind shock. Aims. Concerning this last hypothesis, we want to verify whether cosmic-ray acceleration or re-acceleration could be triggered at the κ-Ori forward shock, which we suppose to be interacting with a star-forming shell detected in several wavebands and probably triggered by high energy particles. Methods. Starting from the AGILE spectrum of the detected γ-ray excess, showed here for the first time, we developed a valid physical model for cosmic-ray energization, taking into account re-acceleration, acceleration, energy losses, and secondary electron contribution. Results. Despite the characteristic low velocity of an OB star forward shock during its “snowplow” expansion phase, we find that the Orion γ-ray excess could be explained by re-acceleration of pre-existing cosmic rays in the interaction between the forward shock of κ-Ori and the CO-detected, star-forming shell swept-up by the star expansion. According to our calculations, a possible contribution from freshly accelerated particles is sub-dominant with respect the re-acceleration contribution. However, a simple adiabatic compression of the shell could also explain the detected γ-ray emission. Futher GeV and TeV observations of this region are highly recommended in order to correctly identify the real physical scenario.

3D dynamics and morphology of bow-shock pulsar wind nebulae

Bow-shock pulsar wind nebulae (PWNe) show a variety of morphological shapes. We attribute this diversity to the geometrical factors: relative orientations of the pulsar rotation axis, proper velocity, and the line of sight (magnetic inclination angle may also have a certain influence on the morphology). We identify three basic types of bow-shock nebulae: (i) a "Rifle Bullet" (pulsar spin axis and proper velocity are aligned); (ii) a "Frisbee" (pulsar spin axis and proper velocity are orthogonal with the spin axis lying in the plane of the sky), and (iii) a Cart Wheel" (like frisbee but the spin axis is perpendicular to the plane of the sky). Using 3D RMHD simulations, as well as analytical calculations, we reproduce the key morphological features of the bow-shock PWNe, as well as variations, are seen across different systems. magnetic stresses within the shocked pulsar wind affect the overall structure strongly, producing "whiskers", "tails", "filled-in" and "mushroom" shapes, as well as non-symmetric morphologies. On the other hand, the interstellar medium inhomogeneities and the anisotropy of the energy flux in the pulsar wind have only a mild impact of the PWN morphology. In a few cases, when we clearly identify specific morphological structures, our results do not favor alignment of the pulsar spin axis and proper velocity. Our calculations of the underlying emission processes explain the low synchrotron X-ray efficiency (in terms of the spin-down luminosity) and imply an energetical subdominant contribution of the inverse Compton process.

Chandra Observations of the Massive Star-forming Region Onsala 2

Abstract Previous radio and infrared observations have revealed an obscured region of high-mass star formation in Cygnus known as Onsala 2 (ON2). Within this region lies the optically revealed young stellar cluster Berkeley 87, which contains several OB stars and the rare oxygen-type Wolf–Rayet star WR 142. Previous radio studies of ON2 have also discovered masers and several H ii regions excited by embedded OB stars. Radio and Gaia parallaxes have now shown that the H ii regions are more distant than Berkeley 87. We summarize two Chandra X-ray observations of ON2, which detected more than 300 X-ray sources. Several optically identified stars in Berkeley 87 were detected, including massive OB stars and WR 142, the latter being a faint hard source whose X-ray emission likely arises in hot thermal plasma. Intense X-ray emission was detected near the compact H ii regions G75.77+0.34 and G75.84+0.40, consisting of numerous point sources and diffuse emission. Heavily absorbed X-ray sources and their near-IR counterparts that may be associated with the exciting OB stars of the H ii regions are identified. Shocked winds from embedded massive stars offer a plausible explanation of the diffuse emission. Young stellar object candidates in the ON2 region are identified using near-IR colors, but surprisingly few counterparts of X-ray sources have near-IR excesses typical of classical T Tauri stars.

The risk markup of intermittent renewable supply in German electricity forward markets

Renewable energy sources such as wind or solar power currently make up a large share of the total German electricity supply as a result of the German energy transition. This paper presents an empirical analysis of how power shocks resulting from intermittent renewables affect the forecast error of the forward premium in German electricity markets. We extend the existing literature by investigating determinants of forward premiums, focusing on both wind and solar power. We find positive monthly wind shock effects on forecast errors, ie, a specific risk markup on forward prices. These findings underline the need to introduce wind power futures at the European Energy Exchange (EEX) in order to reduce the risk markup for participants in forward markets. No daily wind shock or solar shock effects are found. One explanation for this could be the almost perfect approximations of the expected spot price. This is in line with the EEX’s strategy, which does not create wind power futures for contracts with maturities of days. The wind shock effect on monthly peak-load premium is larger than that on base-load premiums. This is likely due to higher differences in marginal costs on the right-hand side of the merit order curve.