First detections of the cataclysmic variable AE Aquarii in the near to far infrared with ISO and IRAS: Investigating the various possible thermal and non-thermal contributions

We have used ISO to observe the Magnetic Cataclysmic Variable AE Aquarii in the previously unexplored range from 4.8 $\mu$m up to 170 $\mu$m in the framework of a coordinated multi-wavelength campaign from the radio to optical wavelengths. We have obtained for the first time a spectrum between 4.8 and 7.3 $\mu$m with ISOCAM and ISOPHOT-P: the major contribution comes from the secondary star spectrum, with some thermal emission from the accretion stream, and possibly some additional cyclotron radiation from the post-shock accretion material close to the magnetised white dwarf. Having reprocessed ISOPHOT-C data, we confirm AE Aqr detection at $90~\mu$m and we have re-estimated its upper limit at 170 $\mu$m. In addition, having re-processed IRAS data, we have detected AE Aqr at 60 $\mu$m and we have estimated its upper limits at 12, 25, and 100 $\mu$m. The literature shows that the time-averaged spectrum of AE Aqr increases roughly with frequency from the radio wavelengths up to ${\sim} 761~ \mu$m; our results indicate that it seems to be approximately flat between ~761 and ${\sim} 90 ~\mu$m, at the same level as the 3$\sigma$ upper limit at 170 $\mu$m; and it then decreases from ${\sim} 90 ~\mu$m to ${\sim} 7~ \mu$m. Thermal emission from dust grains or from a circum-binary disc seems to be very unlikely in AE Aqr, unless such a disc has properties substantially different from those predicted recently. Since various measurements and the usual assumptions on the source size suggest a brightness temperature below 109 K at $\lambda \leq 3.4$ mm, we have reconsidered also the possible mechanisms explaining the emission already known from the submillimetre to the radio. The complex average spectrum measured from ${\sim} 7~ \mu$m to the radio must be explained by emission from a plasma composed of more than one "pure" non-thermal electron energy distribution (usually assumed to be a power-law): either a very large volume (diameter $\geq$ 80 times the binary separation) could be the source of thermal bremsstrahlung which would dominate from ${\sim} 10 ~\mu$m to the ~millimetre, with, inside, a non-thermal source of synchrotron which dominates in radio; or, more probably, an initially small infrared source composed of several distributions (possibly both thermal, and non-thermal, mildly relativistic electrons) radiates gyro-synchrotron and expands moderately: it requires to be re-energised in order to lead to the observed, larger, radio source of highly relativistic electrons (in the form of several non-thermal distributions) which produce synchrotron

Analysis and modeling of high temporal resolution spectroscopic observations of flares on AD Leo

We report the results of a high temporal resolution spectroscopic monitoring of the flare star AD Leo. During 4 nights, more than 600 spectra were taken in the optical range using the Isaac Newton Telescope (INT) and the Intermediate Dispersion Spectrograph (IDS). We have observed a large number of short and weak flares occurring very frequently (flare activity > 0.71 hours-1). This is in favour of the very important role that flares can play in stellar coronal heating. The detected flares are non white-light flares and, though most of solar flares belong to this kind, very few such events had been previously observed on stars. The behaviour of different chromospheric lines (Balmer series from H_alpha to H_11, Ca II H & K, Na I D_1 & D_2, He I 4026 AA and He I D_3) has been studied in detail for a total of 14 flares. We have also estimated the physical parameters of the flaring plasma by using a procedure which assumes a simplified slab model of flares. All the obtained physical parameters are consistent with previously derived values for stellar flares, and the areas - less than 2.3% of the stellar surface - are comparable with the size inferred for other solar and stellar flares. Finally, we have studied the relationships between the physical parameters and the area, duration, maximum flux and energy released during the detected flares.Comment: Latex file with 17 pages, 11 figures. Available at http://www.ucm.es/info/Astrof/invest/actividad/actividad_pub.html Accepted for publication in: Astronomy & Astrophysics (A&A

On the origin of Jovian decametric radio bursts

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Far-UV FUSE spectra of peculiar magnetic cataclysmic variables

We present far-UV spectra of the three magnetic cataclysmic variables (MCVs) BY Cam, V1309 Ori and AE Aqr obtained with the FUSE satellite. These MCVs have revealed strongly unusual NV and CIV UV resonance lines. The FUSE spectra exhibit broad OVI lines as well as a strong NIII line at 991A, while the CIII 1175A line is nearly absent, supporting non-solar CNO abundances of the accreting matter in these sources. The spectrum of BY Cam shows molecular H2 lines which might be of circumstellar nature. The flaring activity of AE Aqr is also observed in the far-UV range. The radial velocities of the broad OVI components in AE Aqr are orbitally modulated and would indicate an emission region close to the magnetosphere.Comment: 7pages, 4 figures, To appear in `Magnetic Cataclysmic Variables', IAU Col. 190, Capetown, Eds.: M. Cropper & S. Vrielmann, uses newpasp.st

Searching for CU Vir-type cyclotron maser from \sigma Ori E: The role of the magnetic quadrupole component

In this paper we present new and archive radio measurements obtained with the Very Large Array of the magnetic chemically peculiar (MCP) star \sigma Ori E. The radio data have been obtained at different frequencies and are well distributed along the rotational phases. We analyze in detail the radio emission from \sigma Ori E with the aim to search evidence of circularly polarized radio pulses. Up to now, among the MCP stars only CU Virginis shows 100% polarized time-stable radio pulses, explained as highly directive electron cyclotron maser emission, visible from Earth at particular rotational phases, like a pulsar. Our analysis shows that there is no hint of coherent emission at frequencies below 15 GHz. We conclude that the presence of a quadrupolar component of the magnetic field, dominant within few stellar radii from the star, where the maser emission should be generated, inhibits the onset of the cyclotron maser instability in \sigma Ori E.Comment: 10 pages, 5 figures, accepted for publication in MNRA

Excess mid-IR emission in Cataclysmic Variables

We present a search for excess mid-IR emission due to circumbinary material in the orbital plane of cataclysmic variables (CVs). Our motivation stems from the fact that the strong braking exerted by a circumbinary (CB) disc on the binary system could explain several puzzles in our current understanding of CV evolution. Since theoretical estimates predict that the emission from a CB disc can dominate the spectral energy distribution (SED) of the system at wavelengths > 5 microns, we obtained simultaneous visible to mid-IR SEDs for eight systems. We report detections of SS Cyg at 11.7 microns and AE Aqr at 17.6 microns, both in excess of the contribution from the secondary star. In AE Aqr, the IR likely originates from synchrotron-emitting clouds propelled by the white dwarf. In SS Cyg, we argue that the observed mid-IR variability is difficult to reconcile with simple models of CB discs and we consider free-free emission from a wind. In the other systems, our mid-IR upper limits place strong constraints on the maximum temperature of a putative CB disc. The results show that if any sizeable CB disc are present in these systems, they must be self-shadowed or perhaps dust-free, with the peak thermal emission shifted to far-IR wavelengths.Comment: 14 pages, 6 figures, accepted for publication in MNRA

AE Aquarii represents a new subclass of Cataclysmic Variables

We analyze properties of the unique nova-like star AE Aquarii identified with a close binary system containing a red dwarf and a very fast rotating magnetized white dwarf. It cannot be assigned to any of the three commonly adopted sub-classes of Cataclysmic Variables: Polars, Intermediate Polars, and Accreting non-magnetized White Dwarfs. Our study has shown that the white dwarf in AE Aqr is in the ejector state and its dipole magnetic moment is $\mu ~ 1.5 \times 10^{34} G cm^3$. It switched into this state due to intensive mass exchange between the system components during a previous epoch. A high rate of disk accretion onto the white dwarf surface resulted in temporary screening of its magnetic field and spin-up of the white dwarf to its present spin period. Transition of the white dwarf to the ejector state had occurred at a final stage of the spin-up epoch as its magnetic field emerged from the accreted plasma due to diffusion. In the frame of this scenario AE Aqr represents a missing link in the chain of Polars evolution and the white dwarf resembles a recycled pulsar.Comment: accepted for publication in Astronomy Reports (July 2012

FCC Physics Opportunities: Future Circular Collider Conceptual Design Report Volume 1

We review the physics opportunities of the Future Circular Collider, covering its e+e-, pp, ep and heavy ion programmes. We describe the measurement capabilities of each FCC component, addressing the study of electroweak, Higgs and strong interactions, the top quark and flavour, as well as phenomena beyond the Standard Model. We highlight the synergy and complementarity of the different colliders, which will contribute to a uniquely coherent and ambitious research programme, providing an unmatchable combination of precision and sensitivity to new physics