Session 8 - Solar/stellar magnetic activity and its influence on planetary bodies

Conveners: James Mason (GSFC), Marc DeRosa (LMSAL)
Thursday 1/11, 12:00 - 16:30

Host stars are the major, if not the main, energy input for their surrounding planetary bodies. The star's magnetic fields can vary dramatically, resulting in significant changes to the form and amount of energy inserted into planetary atmospheres and magnetospheres. Continuous observations of the Sun with SDO, and other complementary observatories, provide detailed information regarding the only star that can be studied up close. Data from planetary missions, such as MAVEN, can be used to study the planetary response. CoRoT, Kepler, and -- soon -- TESS, provide data about cool stars of various ages, masses, rotation rates, and activity characteristics that place the Sun in context. Topics include, but are not limited to: magnetic activity on cool stars (including the sun), insights provided by stellar flares, atmospheric escape driven by solar/stellar activity, impacts of solar eruptive events on planetary bodies, and solar wind and cosmic ray modulation.

Plenary speaker: Allison Youngblood (NASA Goddard)

Talks

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Thursday November 1, 12:00 - 12:30

12:00	The Solar-Stellar-Exoplanet Connection	Youngblood, A	Invited Oral
	Allison Youngblood
	NASA Goddard Space Flight Center
	Cooperation between solar and stellar astrophysicists opens new research avenues for both fields as well as planetary and exoplanetary science. Stellar astrophysics leverages detailed information about the Sun to add some resolution to a usually spatially-unresolved stellar picture, and observations of sun-like stars spanning the stellar lifetime inform the evolutionary history and future of the Sun. Since 2010, the Kepler/K2 satellite’s ultra-precise long-baseline photometry has greatly renewed interest in Sun-as-a-star observations via the discovery of thousands of exoplanets, superflares on Sun-like stars, unique starspot distributions, asteroseismic oscillations, and rotation periods for stars of a wide range of mass and age. Scientific resources worldwide are concentrated on finding and characterizing even more exoplanets, and as the necessary techniques and technologies are pushed to their current limits, information about stars is desperately desired with many researchers turning to solar physics for answers on topics like the origin of radial velocity jitter and the transit light source effect. Additionally, solar and planetary science provide information on phenomena that are important for exoplanet habitability and atmosphere evolution that either cannot currently be observed or are very challenging to observe from other stars. Examples include EUV radiation, CMEs, stellar winds, and multiwavelength flare energy partitions, which all could greatly impact atmospheric heating and chemistry, potentially resulting in catastrophic mass loss. In this overview, I will discuss some of the stellar and exoplanet communities’ needs from the solar community, and I will present some recent results that highlight how extreme the environments around stars other than Sun can be.

Thursday November 1, 15:00 - 16:30

15:00	Stellar flares observed in long cadence data from the Kepler mission	Van doorsselaere, T	Oral
	Tom Van Doorsselaere[1], Hoda Shariati[2], Jonas Debosscher[2,3]
	[1]Centre for mathematical Plasma Asytrophysics, Mathematics Department, KU~Leuven, Celestijnenlaan 200B bus 2400, 3001 Leuven, Belgium, [2]Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium, [3]Royal Belgian Institute for Space Aeronomy, Ringlaan-3-Avenue Circulaire, B-1180 Brussels, Belgium
	We have performed a statistical study of stellar flares observed by Kepler. We want to study the flare amplitude, duration, energy and occurrence rates, and how they are related to the spectral type and rotation period. To that end, we have developed an automated flare detection and characterisation algorithm. We have harvested the stellar parameters from the Kepler input catalogue and the rotation periods from McQuillan et al. (2014). We find several new candidate A stars showing flaring activity. Moreover, we find 653 giants with flares. From the statistical distribution of flare properties, we find that the flare amplitude distribution has a similar behaviour between F+G-types and K+M-types. The flare duration and flare energy seem to be grouped between G+K+M-types vs. F-types and giants. We also detect a tail of stars with high flare occurrence rates across all spectral types (but most prominent in the late spectral types), and this is compatible with the existence of ``flare stars''. Finally, we have found a strong correlation of the flare occurrence rate and the flare amplitude with the stellar rotation period: a quickly rotating star is more likely to flare often, and has a higher chance to generate large flares.
15:15	Probability of Impact of CMEs from Active Stars with Terrestrial Exoplanets	Kay, C	Oral
	Christina Kay[1,2], Vladimir Airapetian[2,3], Theresa Lueftinger[4]
	[1]The Catholic University of America, [2]NASA Goddard Space Flight Center/SEEC, [3]American University, [4]University of Vienna
	Coronal mass ejections drive the most extreme space weather events in our solar system. Recent Kepler observations suggest that a large population of exoplanets in our galaxy may be impacted by severe space weather. Here, we consider the effects of stellar CME deflection and rotation (changes in the latitude and longitude or orientation as a CME propagates outward) on the frequency of impacts on an exoplanet.  Observations and our simulations show that solar CMEs tend to deflect to the Heliospheric Current Sheet, the surface where the solar magnetic field reverses its radial direction, which corresponds to the minimum in the magnetic energy.  Using our analytic model for the magnetic deflection and rotation of solar CMEs, ForeCAT (Kay et al. 2015), we simulate the propagation of CMEs erupting from k1 Ceti, an active solar-type star and a close proxy for the young Sun.  The surface magnetic field has been reconstructed from spectropolarimetric observations at two epochs that suggest that significant magnetic flux evolution occurs over less than a year.  Our ForeCAT simulations show that k1 Ceti CMEs deflect toward its Astrospheric Current Sheet (ACS) during both epochs, with the average distance from the ACS decreasing by roughly a factor of two.  This causes an increase in the likelihood of impact for any exoplanet orbiting near the ACS, which we quantify with a simple probabilistic model.  This model depends on the initial CME latitude distribution and the inclination of the ACS, which are expected to vary over the stellar cycle.  We find that variations in the CME latitude distribution and HCS inclination can yield a 10% change in the probability of impact.
15:30	Energetic Particle Events from Active Stars	Li, G	Oral
	Gang Li[1], Vladimir Airapetian [2], Junxiang Hu [1], Gary Zank [1]
	[1] UAH, Huntsville, AL [2] NASA/GSFC/SEEC & American University, DC
	In large Solar Energetic Particle events, ions and electrons can be accelerated to very high energies by large solar flares and fast coronal mass ejections (CMEs). Often large flares and fast CMEs occur together and it is generally believed that acceleration at the CME-driven shocks are responsible for the major phase of gradual SEP events. Flares and Coronal Mass Ejections also occur in active stars. These stars differ from our Sun in magnetic field, rotation speed, star wind temperature, star wind speed and activity level. Nevertheless, we believe the fundamental process of magnetic reconnection and the resulting coronal mass ejection are similar to our own Sun. It is an interesting question to ask how the enviroment of energetic particles are different in active stars? Using the recently extended 2D improved Particle Acceleration and Transport in the Heliosphere (iPATH) model, we model particle acceleration at a CME-driven shock with shock parameters appropriate for a range of active stars. Protons and ions that are energized via the diffusive shock acceleration (DSA) mechanism are followed at a 2D CME- driven shock where the shock geometry varies across the shock front. The subsequent transport of energetic particles, including cross-field diffusion, is modeled by a Monte-Carlo code which is based on a stochastic differential equation method. Time intensity profiles and particle spectra at multiple locations and different radial distances, separated in longitudes, are presented. Our results may shed some lights on the habitability near other active stars.
15:45	Initiation of Superflares and Super-CMEs in Active Solar-type Stars	Lynch, B	Oral
	B. J. Lynch[1], V. S. Airapetian[2,3], M. D. Kazachenko[1,4], T. Lueftinger[5], C. R. DeVore[2], and W. P. Abbett[1]
	[1] Space Science Laboratory, Univ. of California-Berkeley, Berkeley, CA, USA, [2] NASA Goddard Space Flight Center, Greenbelt, MD, USA, [3] Dept. of Physics, American University, Washington, DC, USA [4] Laboratory Atmospheric Space Physics, Univ. of Colorado, Boulder, CO, USA, [5] Dept. of Astrophysics, Univ. of Vienna, Vienna, Austria
	Recent Kepler observations reveal frequent superflares on young active solar-like stars. We present preliminary simulation results for a global eruptive flare from the young-Sun analog Kappa-1 Cet. Our simulation magnetic field initialization is based on a low-order PFSS representation of the observed stellar magnetogram that provides a non-trivial dipolar magnetic field configuration with a significantly warped helmet streamer belt. We use a standard Parker [1958] isothermal solar wind for the coronal atmosphere and energize the closed-field stellar corona with idealized shearing flows parallel to the radial field polarity inversion line. We examine the energy evolution of the global superflare showing a release of 7.1e+33 erg of magnetic free energy over the course of ~10 hours while the maximum kinetic energy increase of the CME eruption reaches 2.8e+33 erg, i.e. approximately the strength of the famous 1859 Carrington Event. We use a flare-ribbon geometric proxy to calculate a total unsigned flare reconnection flux of 2.2e+23 Mx and a peak reconnection rate of 8.0e+18 Mx/s. We examine various proxy measures of synthetic emission during the flare and discuss the potential for extreme space weather impacts on the early Earth associated with the CME-driven shock and the CME/ICME flux rope field structure and orientation.
16:00	Linking stellar flares to CMEs: energy partition and modeling	Moschou, S	Oral
	S. P. Moschou [1], D. Borovikov [2], O. Cohen [3], J. J. Drake [1], I. Sokolov [4], C. Garraffo [1], J.D. Alvarado-Gomez [1]
	[1] Harvard-Smithsonian Center for Astrophysics, [2] University of New Hampshire, [3] UMASS Lowell, [4] University of Michigan
	The large number of verified exoplanetary discoveries has created the need for moving beyond the purely temperature-based definition of the “habitable zone” and account for stellar activity. In the solar paradigm, energetic flares are associated with massive and fast CMEs. If the energy partition remains the same for the stellar regime then we expect that monster CMEs will be a common phenomenon in active stars. Unlike stellar flares, direct imaging of stellar CMEs is beyond our current technological capabilities. Based on a number of indirect observational methods currently available, we present the most probable stellar CME candidates up to date. However, these methods have high uncertainty levels. Thus, computational methods need to be employed to examine the energy partition between flares and CMEs in Sun-like and more active stellar cases. The problem is intrinsically multi-scale and multi-physical and for that we are using the state-of-the-art code BATS-R-US for both MHD and the kinetic modeling, to study the CME-flare connection.
16:15	Evolution of a coronal mass ejection from the Sun to Saturn	Palmerio, E	Oral
	Erika Palmerio[1], Emilia Kilpua[1], Andrei Zhukov[2,3], David Barnes[4], Marilena Mierla[2,5], Olivier Witasse[6], Teresa Nieves-Chinchilla[7,8], Beatriz Sánchez-Cano[9], Christian Möstl[10], Luciano Rodriguez[2], Elias Roussos[11], Jingnan Guo[12], Adam Masters[13], Gabrielle Provan[9], Alexey Isavnin[14], Neel Savani[7,15], Lucile Turc[1]
	[1] University of Helsinki, [2] Royal Observatory of Belgium, [3] Moscow State University, [4] RAL Space, [5] Institute of Geodynamics of the Romanian Academy, [6] ESA ESTEC, [7] NASA GSFC, [8] The Catholic University of America, [9] University of Leicester, [10] Space Research Institute, Austrian Academy of Science, [11] Max Planck Institute for Solar System Research, [12] Christian-Albrechts-University, [13] Imperial College London, [14] KU Leuven, [15] University of Maryland Baltimore County
	The prediction of the magnetic structure, arrival time, and arrival speed of coronal mass ejections (CMEs) at different locations in the heliosphere is a subject of intense study and great importance for understanding how CMEs evolve after they erupt. The magnetic structure of CMEs at the time of their eruption can be inferred through indirect proxies based on remote-sensing observations of the CME source region. However, the knowledge of the magnetic structure of CMEs at the Sun does not always imply a successful prediction of the magnetic structure at Earth, or in general in interplanetary space. This is because CMEs can change their orientation and shape due to deflections, rotations, and/or deformations. We present a case study of a filament eruption and related CME that took place in May 2012, aiming at estimating how the knowledge of the CME magnetic structure at the Sun can be used in the case of CMEs that are associated with rotating filaments. We aim at comparing the magnetic structure of the CME at the Sun with observations from multiple vantage points through the heliosphere, in order to describe how the CME evolves as it travels away from the Sun. We use remote-sensing observations of the solar disc, the corona, and the inner heliosphere, and in situ measurements taken at Venus, at Earth, at Mars, and at Saturn.

Posters

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e-Posters

Astrospheric Space Weather as a Factor of (Exo)Planetary Habitability	Airapetian, V
Airapetian, Vladimir S.
NASA GSFC/SEEC & American Unibversity
Recent Kepler discoveries of exoplanets located around main-sequence stars have dramatically changed the landscape of exoplanetary science. Specifically, the Kepler mission has helped to detect and characterize thousands of transit candidates and hundreds of confirmed exoplanets around K-M dwarf stars and a few planets within their habitable zones (HZ). Kepler also revealed thousands of superflares on hundreds of solar-type stars, which suggests that planet hosting stars could have profound effects on the physical and chemical evolution of exoplanetary atmospheres. What do we know about the impact of space weather on our own planet? How can we apply lessons learned from the largest solar space weather events to understand how exoplanets are affected by their host stars? In this brief review, I present our team’s recent results on how current heliophysics tools can be applied for reconstruction of astrospheric space weather (ASW) from active stars (both theory & observations) and evaluation of positive and negative ASW impacts on habitable environments of rocky exoplanets. They include the ASW effects on atmospheric erosion, chemistry and surface dosages of ionizing radiation.

p-Posters

Latitudinal variability of Total electron content over low, mid and high latitudes during solar maximum and its comparison with IRI-2012 and IRI-2016 model	Atulkar, R
Roshni Atulkar[1],P.K. Purohit[2]
National Institute of Technical Teachers' Training and Research, Bhopal, 462002,MP, India.[1],National Institute of Technical Teachers' Training and Research, Bhopal, 462002,MP, India.[2]
Total electron content (TEC) is a key of ionospheric parameters which is defined as the total number of electrons present within a cross-section 1 m2 along the integrated path from the satellite to the receiver. TEC describes the major impact of the ionosphere on the propagation of radio waves which is crucial for terrestrial and Earth space communication including Global Positioning System (GPS). For this analysis we used dual frequency GPS observations at low, mid and high latitude stations IISC, Bangalore, India (13.02_N, 77.57_E), GUAO, Urumqi, China (43.82_N, 87.60_E) and NYAL, NY-Alesund, Norway (78.92_N, 11.86_E) respectively; we used one year of data for a high solar activity period of 24th solar cycle, i.e. during January 2012 to December 2012.From our analysis we observed that GPS-TEC achieves its highest values during the months of October and March at low latitude, during the months of April and May at mid latitude and during September and March at high latitude while the lowest values of TEC were recorded at all the stations in December. Almost a linear relationship between ionospheric GPS-TEC with IRI-2012 and IRI-2016 was observed at low and mid latitude stations; however, high latitude TEC does not show any significant relation to IRI 2012 and IRI 2016 TEC. This research obtains a practical approach to study the ionospheric variability at low, mid, and high latitude and compares with the latest IRI-2012 and IRI-2016 models during the high solar activity period 2012.
Stellar activity effects on high energy exoplanet transits	Llama, J
Joe Llama[1], Evgenya Shkolnik[2]
[1]Lowell Observatory, [2] Arizona State Univeristy
High energy (X-ray / UV) observations of transiting exoplanets have revealed the presence of extended atmospheres around a number of systems. At such high energies, stellar radiation is absorbed high up in the planetary atmosphere, making X-ray and UV observations a potential tool for investigating the upper atmospheres of exoplanets. At these high energies, stellar activity can dramatically impact the observations. At short wavelengths, the stellar disk appears limb-brightened, and active regions appear as extended bright features that evolve on a much shorter timescale than in the optical. These features impact both the transit depth and shape, affecting our ability to measure the true planet-to-star radius ratio. In this presentation, I will show results of simulated exoplanet transit light curves using Solar data obtained in the soft X-ray and UV by the Atmospheric Imaging Assembly onboard NASA's Solar Dynamics Observatory to investigate the impact of stellar activity at these wavelengths. By using a limb-brightened transit model coupled with disk resolved Solar images in the X-ray, extreme- and far-UV I will show how both occulted and unocculted active regions can mimic an inflated planetary atmosphere by changing the depth and shape of the transit profile. I will also show how the disk-integrated Lyman-alpha Solar irradiance varies on both short and long timescales and how this variability can impact our ability to recover the true radius ratio of a transiting exoplanet. Finally, I will present techniques on how to overcome these effects to determine the true planet-to-star radius in X-ray and UV observations.