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Optimized Trajectories to the Nearest Stars Using Lightweight High-velocity Photon Sails
Heller, René; Hippke, Michael; Kervella, Pierre
New means of interstellar travel are now being considered by various research teams, assuming lightweight spaceships to be accelerated via either laser or solar radiation to a significant fraction of the speed of light (c). We recently showed that gravitational assists can be combined with the stellar photon pressure to decelerate an incoming ligh…
An artificial neural network to discover hypervelocity stars: candidates in Gaia DR1/TGAS
Rossi, E. M.; Brown, A. G. A.; Kordopatis, G. +5 more
The paucity of hypervelocity stars (HVSs) known to date has severely hampered their potential to investigate the stellar population of the Galactic Centre and the Galactic potential. The first Gaia data release (DR1, 2016 September 14) gives an opportunity to increase the current sample. The challenge is the disparity between the expected number o…
A Helioseismic Perspective on the Depth of the Minimum Between Solar Cycles 23 and 24
Broomhall, A. -M.
The minimum in the solar-activity cycle observed between Cycles 23 and 24 is generally regarded as being unusually deep and long. This minimum is being followed by a cycle with one of the smallest amplitudes in recent history. We perform an in-depth analysis of this minimum with helioseismology. We use Global Oscillation Network Group (GONG) data …
Polyaromatic disordered carbon grains as carriers of the UV bump: Far-UV to mid-IR spectroscopy of laboratory analogs
Dartois, E.; Giuliani, A.; Pino, T. +3 more
Context. A multiwavelength study of laboratory carbons with varying degrees of hydrogenation and sp2 hybridization is required to characterize the structure of the carbonaceous carriers of interstellar and circumstellar extinction.
Aims: We study the spectral properties of carbonaceous dust analogs from the far-ultraviolet to the m…
Comparison between the Logotropic and ΛCDM models at the cosmological scale
Kumar, Suresh; Chavanis, Pierre-Henri
We perform a detailed comparison between the Logotropic model [P.H. Chavanis, Eur. Phys. J. Plus, 130 (2015)] and the ΛCDM model. These two models behave similarly at large (cosmological) scales up to the present. Differences will appear only in the far future, in about 25 Gyrs, when the Logotropic Universe becomes phantom while the ΛCDM Universe …
Reaching the peak of the quasar spectral energy distribution - II. Exploring the accretion disc, dusty torus and host galaxy
Done, Chris; Elvis, Martin; McDowell, Jonathan C. +3 more
We continue our study of the spectral energy distributions (SEDs) of 11 active galactic nuclei (AGN) at 1.5 < z < 2.2, with optical-near-infrared (NIR) spectra, X-ray data and mid-IR photometry. In a previous paper, we presented the observations and models; in this paper, we explore the parameter space of these models. We first quantify unce…
Observations and Modelling of the Pre-flare Period of the 29 March 2014 X1 Flare
Long, D. M.; Harra, L. K.; Matthews, S. A. +3 more
On 29 March 2014, NOAA Active Region (AR) 12017 produced an X1 flare that was simultaneously observed by an unprecedented number of observatories. We have investigated the pre-flare period of this flare from 14:00 UT until 19:00 UT using joint observations made by the Interface Region Imaging Spectrometer (IRIS) and the Hinode Extreme Ultraviolet …
Recovering galaxy cluster gas density profiles with XMM-Newton and Chandra
Arnaud, M.; Pointecouteau, E.; Pratt, G. W. +6 more
We examined the reconstruction of galaxy cluster radial density profiles obtained from Chandra and XMM-Newton X-ray observations, using high quality data for a sample of twelve objects covering a range of morphologies and redshifts. By comparing the results obtained from the two observatories and by varying key aspects of the analysis procedure, w…
Witnessing the reionization history using Cosmic Microwave Background observation from Planck
Hazra, Dhiraj Kumar; Smoot, George F.
We constrain the history of reionization using the data from Planck 2015 Cosmic Microwave Background (CMB) temperature and polarization anisotropy observations. We also use prior constraints on the reionization history at redshifts ~7-8 obtained from Lyman-α emission observations. Using the free electron fractions at different redshifts as free pa…
The Mars diffuse aurora: A model of ultraviolet and visible emissions
Gérard, J. -C.; Soret, L.; Shematovich, V. I. +2 more
A new type of Martian aurora, characterized by an extended spatial distribution, an altitude lower than the discrete aurora and electron precipitation up to 200 keV has been observed following solar activity on several occasions from the MAVEN spacecraft. We describe the results of Monte Carlo simulations of the production of several ultraviolet a…