| 1. |
- Broeg, C., et al.
(författare)
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CHEOPS: A transit photometry mission for ESA's small mission programme
- 2013
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. - 9782759809851 ; 47
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Konferensbidrag (refereegranskat)abstract
- Ground based radial velocity (RV) searches continue to discover exoplanets below Neptune mass down to Earth mass. Furthermore, ground based transit searches now reach milli-mag photometric precision and can discover Neptune size planets around bright stars. These searches will find exoplanets around bright stars anywhere on the sky, their discoveries representing prime science targets for further study due to the proximity and brightness of their host stars. A mission for transit follow-up measurements of these prime targets is currently lacking. The first ESA S-class mission CHEOPS (CHaracterizing ExoPlanet Satellite) will fill this gap. It will perform ultra-high precision photometric monitoring of selected bright target stars almost anywhere on the sky with sufficient precision to detect Earth sized transits. It will be able to detect transits of RV-planets by photometric monitoring if the geometric configuration results in a transit. For Hot Neptunes discovered from the ground, CHEOPS will be able to improve the transit light curve so that the radius can be determined precisely. Because of the host stars' brightness, high precision RV measurements will be possible for all targets. All planets observed in transit by CHEOPS will be validated and their masses will be known. This will provide valuable data for constraining the mass-radius relation of exoplanets, especially in the Neptune-mass regime. During the planned 3.5 year mission, about 500 targets will be observed. There will be 20% of open time available for the community to develop new science programmes.
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| 2. |
- Nakamura, R., et al.
(författare)
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Flow bouncing and electron injection observed by Cluster
- 2013
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Ingår i: Journal of Geophysical Research-Space Physics. - : American Geophysical Union (AGU). - 2169-9380. ; 118:5, s. 2055-2072
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Tidskriftsartikel (refereegranskat)abstract
- Characteristics of particles and fields in the flow-bouncing region are studied based on multipoint observations from Cluster located at 13-15R(E) downtail during a substorm event around 12:50 UT on 7 September 2007. The Cluster spacecraft were separated by a distance of up to 10,000 km and allowed to determine the mesoscale evolution of the current sheet as well as the development of the dipolarization front. We show that the flow bouncing took place associated with a tailward-directed j x B force in a disturbed current sheet in addition to an enhanced tailward pressure gradient force. Multiple Earthward propagating dipolarization fronts accompanied by enhanced flux of energetic electrons were observed before the flow bouncing. The sequence of events started with a localized dipolarization front and ended with a large scale (>10R(E)) dipolarization front accompanied by a major increase in energetic electrons at all spacecraft and immediately followed by flow bouncing. Multiple dipolarization fronts result in the formation of compressed magnetic field with a plasma bulge bounded by thin ion-scale current layers, a favorable condition for flow bouncing. These observations suggest that to understand the flow bouncing and related acceleration of plasma in the near-Earth tail, both the large-scale MHD properties and the transient and small-scale effect of the plasma interaction with the Earth-dipole field need to be taken into account.
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| 3. |
- Tao, J. B., et al.
(författare)
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A model of electromagnetic electron phase-space holes and its application
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. A11213-
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Tidskriftsartikel (refereegranskat)abstract
- Electron phase-space holes (EHs) are indicators of nonlinear activities in space plasmas. Most often they are observed as electrostatic signals, but recently Andersson et al. [2009] reported electromagnetic EHs observed by the THEMIS mission in the Earth's plasma sheet. As a follow-up to Andersson et al. [2009], this paper presents a model of electromagnetic EHs where the delta E x B(0) drift of electrons creates a net current. The model is examined with test-particle simulations and compared to the electromagnetic EHs reported by Andersson et al. [2009]. As an application of the model, we introduce a more accurate method than the simplified Lorentz transformation of Andersson et al. [2009] to derive EH velocity (v(EH)). The sizes and potentials of EHs are derived from v(EH), so an accurate derivation of v(EH) is important in analyzing EHs. In general, our results are qualitatively consistent with those of Andersson et al. [2009] but generally with smaller velocities and sizes.
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| 4. |
- Tao, J. B., et al.
(författare)
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Kinetic instabilities in the lunar wake : ARTEMIS observations
- 2012
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. A03106-
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Tidskriftsartikel (refereegranskat)abstract
- The Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission is a new two-probe lunar mission derived from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. On 13 February 2010, one of the two probes, ARTEMIS P1 (formerly THEMIS-B), made the first lunar wake flyby of the mission. We present detailed analysis of the electrostatic waves observed on the outbound side of the flyby that were associated with electron beams. Halekas et al. (2011) derived a net potential across the lunar wake from observations and suggested that the net potential generated the observed electron beams and the electron beams in turn excited the observed electrostatic waves due to kinetic instabilities. The wavelengths and velocities of the electrostatic waves are estimated, using high-resolution electric field instrument data with cross-spectrum analysis and cross-correlation analysis. In general, the estimated wavelengths vary from a few hundred meters to a couple of thousand meters. The estimated phase velocities are on the order of 1000 km s(-1). In addition, we perform 1-D Vlasov simulations to help identify the mode of the observed electrostatic waves. We conclude that the observed electrostatic waves are likely on the electron beam mode branch.
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