General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. ABSTRACTThe habitability of an exoplanet depends on many factors. One such factor is the impact of stellar eruptive events on nearby exoplanets. Currently this is poorly constrained due to heavy reliance on solar scaling relationships and a lack of experimental evidence. Potential impacts of coronal mass ejections (CMEs), which are the large eruption of magnetic field and plasma from a star, are space weather and atmospheric stripping. A method for observing CMEs as they travel though the stellar atmosphere is the type II radio burst, and the new Low Frequency Array (LOFAR) provides a means of detection. We report on 15 hr of observation of YZ Canis Minoris (YZ CMi), a nearby M dwarf flare star, taken in LOFAR's beam-formed observation mode for the purposes of measuring transient frequency-dependent low-frequency radio emission. The observations utilized the Low Band Antenna (10-90 MHz) or High Band Antenna (110-190 MHz) for five three-hour observation periods. In this data set, there were no confirmed type II events in this frequency range. We explore the range of parameter space for type II bursts constrained by our observations. Assuming the rate of shocks is a lower limit to the rate at which CMEs occur, no detections in a total of 15 hr of observation places a limit of n < 0.0667 type II shocks/hrν CME for YZ CMi due to the stochastic nature of the events and the limits of observational sensitivity. We propose a methodology to interpret jointly observed flares and CMEs which will provide greater constraints to CMEs and test the applicability of solar scaling relations.

Stellar coronal mass ejections remain experimentally unconstrained, unlike their stellar flare counterparts which are observed ubiquitously across the electromagnetic spectrum. Low frequency radio bursts in the form of a type II burst offer the best means of identifying and constraining the rate and properties of stellar CMEs. CME properties can be further improved through the use of proposed solar-stellar scaling relations and multi-wavelength observations of CMEs through the use of type II bursts and the associated flare expected to occur occur alongside. We report on 20 hours of observation of the nearby, magnetically active, and well characterized M dwarf star EQ Peg. The observations are simultaneously observed with the Jansky Very Large Array at their P-band (230-470 MHz) and at the Apache Point observatory in the SDSS u' filter (λ = 3557Å).Dynamic spectra of the P band data, constructed to search for signals in the frequency-time domains, did not reveal evidence for drifting radio bursts that could be ascribed to type II bursts. Given the sensitivity of our observations, we are able to place limits on the brightness temperature and source size of any bursts which may have occurred. Using solar scaling rations on four observed stellar flares, we predict CME parameters. Given the constraints on coronal density and photospheric field strength, our models suggest that the observed flares would have been insufficient to produce detectable type II bursts at our observed frequencies. We consider the implications of these results, and other recent findings, on stellar mass loss.

Stellar coronal mass ejections (CMEs) remain observationally elusive, but could have important implications for exoplanet habitability. Low-frequency radio bursts, known as Type IIs in the solar context, offer the best means to identify stellar CMEs, determine their occurrence rates, and characterize their properties. We report on 44 hr of observation of the nearby, magnetically active, and well-characterized M-dwarf star binary EQ Peg. The observations are taken with the Jansky Very Large Array’s P-band (230–470 MHz) receiver in both its B and C configurations. Two radio transient events were detected, one in each configuration. Both bursts lasted on the order of 20 minutes between 275 and 350 MHz, had a median polarization of ∼30%, and have a frequency drift rate of ∼10 kHz. These two events are likely not type II bursts as their properties do not match expected parameters based on coronal models for each star. This work and the work of Crosley & Osten represent a combined 64 hr for the longest timescale search of a single star for radio transients at low frequencies to date, and casts serious doubt on the assumption that a high flaring rate corresponds to a high rate of CMEs.

Low frequency dynamic spectra of radio bursts from nearby stars offer the best chance to directly detect the stellar signature of transient mass loss on low mass stars. Crosley et al. (2016) proposes a multi-wavelength methodology to determine coronal mass ejection parameters, such as Coronal Mass Ejection (CME) speed, mass, and kinetic energy.We test the validity and accuracy of the results derived from the methodology by using Geostationary Operational Environmental Satellite X-ray observations and Bruny Island Radio Spectrometer radio observations. These are analogous observations to those which would be found in the stellar studies. Derived results from these observations are compared to direct white light measurements of the Large Angle and Spectrometric Coronagraph.We find that, when a pre-event temperature can be determined, that the accuracy of CME speeds are within a few hundred km/s, and are reliable when specific criteria has been met. CME mass and kinetic energies are only useful in determining approximate order of magnitude measurements when considering the large errors associated to them. These results will be directly applicable to interpretation of any detected stellar events and derivation of stellar CME properties.