K2-79b and K2-222b: Mass Measurements of Two Small Exoplanets with Periods beyond 10 days that Overlap with Periodic Magnetic Activity Signals

We present mass and radius measurements of K2-79b and K2-222b, two transiting exoplanets orbiting active G-type stars observed with HARPS-N and K2. Their respective 10.99 day and 15.39 day orbital periods fall near periods of signals induced by stellar magnetic activity. The two signals might therefore interfere and lead to an inaccurate estimate of exoplanet mass. We present a method to mitigate these effects when radial velocity (RV) and activity-indicator observations are available over multiple observing seasons and the orbital period of the exoplanet is known. We perform correlation and periodogram analyses on subsets composed of each target's two observing seasons, in addition to the full data sets. For both targets, these analyses reveal an optimal season with little to no interference at the orbital period of the known exoplanet. We make a confident mass detection of each exoplanet by confirming agreement between fits to the full RV set and the optimal season. For K2-79b, we measure a mass of 11.8 ± 3.6 M ⊕ and a radius of 4.09 ± 0.17 R ⊕. For K2-222b, we measure a mass of 8.0 ± 1.8 M ⊕ and a radius of 2.35 ± 0.08 R ⊕. According to model predictions, K2-79b is a highly irradiated Uranus analog and K2-222b hosts significant amounts of water ice. We also present a RV solution for a candidate second companion orbiting K2-222 at 147.5 days.

What Seismic Minimum Reveals about Solar Magnetism below the Surface

The Sun’s magnetic field varies on multiple timescales. Observations show that the minimum between cycles 24 and 25 was the second consecutive minimum that was deeper and wider than several earlier minima. Since the active regions observed at the Sun’s surface are manifestations of the magnetic field generated in the interior, it is crucial to investigate/understand the dynamics below the surface. In this context, we report by probing the solar interior with helioseismic techniques applied to long-term oscillations data from the Global Oscillation Network Group, that the seismic minima in deeper layers have been occurring about a year earlier than that at the surface for the last two consecutive solar cycles. Our findings also demonstrate a decrease in strong magnetic fields at the base of the convection zone, the primary driver of the surface magnetic activity. We conclude that the magnetic fields located in the core and near-surface shear layers, in addition to the tachocline fields, play an important role in modifying the oscillation frequencies. This further strengthens the existence of a relic magnetic field in the Sun’s core.

WHISTLER-TRIGGERED VLF EMISSIONS RECORDED AT JAMMU DURING DAY TIME

Whistler-triggered VLF emissions recorded at low latitude station Jammu (Geomagnetic latitude = 220 26/ N; L = 1.17) during day time period on 19th February 1999 at 14:35 hrs. IST. The recorded data have been analyzed. Based on whistler-triggered VLF emissions spectrum, the VLF waves propagate along the path with L – values lying between L = 4.4 and 4.38. During the observation period, magnetic activity was very high. Mostly these types of emissions recorded at mid latitudes. These whistler-triggered emission waves propagate along the geomagnetic field lines either in a ducted mode or in a pro-longitudinal mode. Relative amplitude of whistlers waves is almost equal to relative amplitude of triggered emissions. The proposed generation mechanism explains through the dynamic spectra of the whistler-triggered emissions.

Solar Wind Parameters and Its Geoefficiency During Minimums of Four Solar Cycles

Recently a number of publications have appeared on the long and deep minimum in cycle 23 of solar activity. This interest is due to the fact that it turned out to be the longest and deepest in terms of the number of sunspots in the entire era of space exploration. The features of the minimum of cycle 23 of solar activity and the beginning of cycle 24 made it possible to assume that in the coming decades, a minimum of solar activity similar to the Dalton or Maunder minimum, leading to a global change in the earth's climate, may occur. Such assumptions make a detailed study of the influence of the minimum of solar cycle 23 on the parameters of the solar wind and the interplanetary magnetic field, as well as a comparison of this influence with similar manifestations in the three previous cycles very urgent. The work carried out statistical processing and analysis of data available in print and on the Internet on the indices of solar activity (W and F10.7), on geomagnetic activity, as well as on the parameters of the solar wind and interplanetary field. In contrast to other similar studies, when choosing time intervals for all cycles, only one — 12 months was used, which made it possible to exclude annual and semi-annual variations in solar wind parameters. For the considered minima of solar activity, the geoeffectiveness of the disturbed fluxes ICME, CIR, and Sheath was considered. A monotonic and very significant decrease in the geoeffectiveness of the ICME streams was found. Data processing on the hourly average values of the solar wind parameters at the minima of geomagnetic activity for 4 cycles confirmed the significant difference between cycle 23 and the previous ones in the behavior of the magnetic field. The cycle-by-cycle decrease in the geoeffectiveness of coronal ejections discussed in the press deserves a more detailed analysis using extensive data on magnetic activity indices.

Statistical Study of Ionospheric Equivalent Slab Thickness at Guam Magnetic Equatorial Location

The ionospheric equivalent slab thickness (τ) is defined as the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), and it is a significant parameter representative of the ionosphere. In this paper, a comprehensive statistical analysis of the diurnal, seasonal, solar, and magnetic activity variations in the τ at Guam (144.86°E, 13.62°N, 5.54°N dip lat), which is located near the magnetic equator, is presented using the GPS-TEC and ionosonde NmF2 data during the years 2012–2017. It is found that, for geomagnetically quiet days, the τ reaches its maximum value in the noontime, and the peak value in winter and at the equinox are larger than that in summer. Moreover, there is a post-sunset peak observed in the winter and equinox, and the τ during the post-midnight period is smallest in equinox. The mainly diurnal and seasonal variation of τ can be explained within the framework of relative variation of TEC and NmF2 during different seasonal local time. The dependence of τ on the solar activity shows positive correlation during the daytime, and the opposite situation applies for the nighttime. Specifically, the disturbance index (DI), which can visually assess the relationship between instantaneous τ values and the median, is introduced in the paper to quantitatively describe the overall pattern of the geomagnetic storm effect on the τ variation. The results show that the geomagnetic storm seems to have positive effect on the τ during most of the storm-time period at Guam. An example, on the 1 June 2013, is also presented to analyze the physical mechanism. During the positive storms, the penetration electric field, along with storm time equator-ward neutral wind, tends to increase upward drift and uplift F region, causing the large increase in TEC, accompanied by a relatively small increase in NmF2. On the other hand, an enhanced equatorward wind tends to push more plasma, at low latitudes, into the topside ionosphere in the equatorial region, resulting in the TEC not undergoing severe depletion, as with NmF2, during the negative storms. The results would complement the analysis of τ behavior during quiet and disturbed conditions at equatorial latitudes in East Asia.

A Pilot Radio Search for Magnetic Activity in Directly Imaged Exoplanets

We present the first systematic search for GHz frequency radio emission from directly imaged exoplanets using Very Large Array observations of sufficient angular resolution to separate the planets from their host stars. We obtained results for five systems and eight exoplanets located at ≲50 pc through new observations (Ross 458, GU Psc, and 51 Eri) and archival data (GJ 504 and HR 8799). We do not detect radio emission from any of the exoplanets, with 3σ luminosity upper limits of (0.9–23) × 1021 erg s−1. These limits are comparable to the level of radio emission detected in several ultracool dwarfs, including T dwarfs, whose masses are only a factor of two times higher than those of the directly imaged exoplanets. Despite the lack of detections in this pilot study, we highlight the need for continued GHz frequency radio observations of nearby exoplanets at μJy-level sensitivity.

GRASS: Distinguishing Planet-induced Doppler Signatures from Granulation with a Synthetic Spectra Generator

Owing to recent advances in radial-velocity instrumentation and observation techniques, the detection of Earth-mass planets around Sun-like stars may soon be primarily limited by intrinsic stellar variability. Several processes contribute to this variability, including starspots, pulsations, and granulation. Although many previous studies have focused on techniques to mitigate signals from pulsations and other types of magnetic activity, granulation noise has to date only been partially addressed by empirically motivated observation strategies and magnetohydrodynamic simulations. To address this deficit, we present the GRanulation And Spectrum Simulator (GRASS), a new tool designed to create time-series synthetic spectra with granulation-driven variability from spatially and temporally resolved observations of solar absorption lines. In this work, we present GRASS, detail its methodology, and validate its model against disk-integrated solar observations. As a first-of-its-kind empirical model for spectral variability due to granulation in a star with perfectly known center-of-mass radial-velocity behavior, GRASS is an important tool for testing new methods of disentangling granular line-shape changes from true Doppler shifts.

A software-computational neural network tool for predicting the electromagnetic state of the polar magnetosphere, taking into account the process that simulates its slow loading by the kinetic energy of the solar wind

The auroral activity indices AU, AL, AE, introduced into geophysics at the beginning of the space era, although they have certain drawbacks, are still widely used to monitor geomagnetic activity at high latitudes. The AU index reflects the intensity of the eastern electric jet, while the AL index is determined by the intensity of the western electric jet. There are many regression relationships linking the indices of magnetic activity with a wide range of phenomena observed in the Earth's magnetosphere and atmosphere. These relationships determine the importance of monitoring and predicting geomagnetic activity for research in various areas of solar-terrestrial physics. The most dramatic phenomena in the magnetosphere and high-latitude ionosphere occur during periods of magnetospheric substorms, a sensitive indicator of which is the time variation and value of the AL index. Currently, AL index forecasting is carried out by various methods using both dynamic systems and artificial intelligence. Forecasting is based on the close relationship between the state of the magnetosphere and the parameters of the solar wind and the interplanetary magnetic field (IMF). This application proposes an algorithm for describing the process of substorm formation using an instrument in the form of an Elman-type ANN by reconstructing the AL index using the dynamics of the new integral parameter we introduced. The use of an integral parameter at the input of the ANN makes it possible to simulate the structure and intellectual properties of the biological nervous system, since in this way an additional realization of the memory of the prehistory of the modeled process is provided.