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Propagation of the 7 January 2014 CME and Resulting Geomagnetic Non-event
Thompson, B. J.; Möstl, C.; Jian, L. K. +9 more
On 2014 January 7 an X1.2 flare and coronal mass ejection (CME) with a radial speed ≈2500 km s-1 was observed from near an active region close to disk center. This led many forecasters to estimate a rapid arrival at Earth (≈36 hr) and predict a strong geomagnetic storm. However, only a glancing CME arrival was observed at Earth with a t…
Predicting the Arrival Time of Coronal Mass Ejections with the Graduated Cylindrical Shell and Drag Force Model
Zhang, Jie; Ding, Mingde; Cheng, Xin +3 more
Accurately predicting the arrival of coronal mass ejections (CMEs) to the Earth based on remote images is of critical significance for the study of space weather. In this paper, we make a statistical study of 21 Earth-directed CMEs, specifically exploring the relationship between CME initial speeds and transit times. The initial speed of a CME is …
Revealing the X-ray variability of AGN with principal component analysis
Fabian, A. C.; Brenneman, L.; Matt, G. +7 more
We analyse a sample of 26 active galactic nuclei (AGN) with deep XMM-Newton observations, using principal component analysis (PCA) to find model-independent spectra of the different variable components. In total, we identify at least 12 qualitatively different patterns of spectral variability, involving several different mechanisms, including five…
The 1.4-GHz radio properties of hard X-ray-selected AGN
Bird, A. J.; Ubertini, P.; Malizia, A. +7 more
We have analysed the NRAO Very Large Array Sky Survey and Sydney University Molonglo Sky Survey data at 1.4 GHz and 843 MHz for a well-defined complete sample of hard X-ray AGN observed by INTEGRAL. A large number (70/79) of sources are detected in the radio band, showing a wide range of radio morphologies, from unresolved or slightly resolved cor…
Benchmark stars for Gaia Fundamental properties of the Population II star HD 140283 from interferometric, spectroscopic, and photometric data
Morel, P.; Berio, P.; Meilland, A. +18 more
Metal-poor halo stars are important astrophysical laboratories that allow us to unravel details about many aspects of astrophysics, including the chemical conditions at the formation of our Galaxy, understanding the processes of diffusion in stellar interiors, and determining precise effective temperatures and calibration of colour-effective tempe…
Properties of solar energetic particle events inferred from their associated radio emission
Valtonen, E.; Hillaris, A.; Malandraki, O. +6 more
Aims: We study selected properties of solar energetic particle (SEP) events as inferred from their associated radio emissions.
Methods: We used a catalogue of 115 SEP events, which consists of entries of proton intensity enhancements at one AU, with complete coverage over solar cycle 23 based on high-energy (~68 MeV) protons from SOHO/ER…
Cooling of the Martian thermosphere by CO2 radiation and gravity waves: An intercomparison study with two general circulation models
Medvedev, Alexander S.; Yiǧit, Erdal; Hartogh, Paul +3 more
Observations show that the lower thermosphere of Mars (∼100-140 km) is up to 40 K colder than the current general circulation models (GCMs) can reproduce. Possible candidates for physical processes missing in the models are larger abundances of atomic oxygen facilitating stronger CO2 radiative cooling and thermal effects of gravity wave…
Six years of Venus winds at the upper cloud level from UV, visible and near infrared observations from VIRTIS on Venus Express
Hueso, R.; Sánchez-Lavega, A.; Peralta, J. +2 more
The Venus Express mission has provided a long-term monitoring of Venus atmosphere including the morphology and motions of its upper clouds. Several works have focused on the dynamics of the upper cloud visible on the day-side in ultraviolet images sensitive to the 65-70 km altitude and in the lower cloud level (50 km height) observable in the nigh…
Dust devil height and spacing with relation to the martian planetary boundary layer thickness
Fenton, Lori K.; Lorenz, Ralph
In most remote and unmonitored places, little is known about the characteristics of daytime turbulent activity. Few processes render the optically transparent atmospheres of Earth and Mars visible; put more plainly, without clever instruments it is difficult to "see the unseen". To address this, we present a pilot study of images of martian dust d…
An Ultrasoft X-Ray Flare from 3XMM J152130.7+074916: A Tidal Disruption Event Candidate
Gwyn, Stephen D. J.; Komossa, S.; Lin, Dacheng +6 more
We report on the discovery of an ultrasoft X-ray transient source, 3XMM J152130.7+074916. It was serendipitously detected in an XMM-Newton observation on 2000 August 23, and its location is consistent with the center of the galaxy SDSS J152130.72+074916.5 (z = 0.17901 and dL = 866 Mpc). The high-quality X-ray spectrum can be fitted with…