Search results for " Solar"
showing 10 items of 958 documents
Hydrodynamic simulations of the interaction of supernova shock waves with a clumpy environment: the case of the RX J0852.0-4622 (Vela Jr.) supernova …
2013
Observations in all electromagnetic bands show that many supernova remnants (SNRs) have a very aspherical shape. This can be the result of asymmetries in the supernova explosion or a clumpy circumstellar medium. We study the generation of inhomogeneities and the mixing of elements arising from these two sources in multidimensional hydrodynamic simulations of the propagation of a supernova blast wave into a cloudy environment. We model a specific SNR, Vela Jr (RX J0852.0-4622). By comparing our results with recent observations, we can constrain the properties of the explosion. We find that a very energetic explosion of several 10^{51} erg occurring roughly about 800 years ago is consistent w…
Magnetohydrodynamic Modeling of the Accretion Shocks in Classical T Tauri Stars: The Role of Local Absorption in the X-Ray Emission
2014
We investigate the properties of X-ray emission from accretion shocks in classical T Tauri stars (CTTSs), generated where the infalling material impacts the stellar surface. Both observations and models of the accretion process reveal several aspects that are still unclear: the observed X-ray luminosity in accretion shocks is below the predicted value, and the density versus temperature structure of the shocked plasma, with increasing densities at higher temperature, deduced from the observations, is at odds with that proposed in the current picture of accretion shocks. To address these open issues we investigate whether a correct treatment of the local absorption by the surrounding medium …
An idealized mechanism for the orbital migration of protoplanets
1993
We report here how the action of radiation forces on small solid particles in a circumstellar disc could induce a suitable mechanism for orbital migration of protoplanets. The ratio of radiation-to-gravitational forces acting on a particle depends on its physical and chemical properties. As a consequence of this fact, we show that different particles following the same trajectory would move with different velocities. Sufficiently large bodies, insensitive to radiation forces, would accrete dust particles that are moving more slowly, thus spiralling towards the central star and transporting mass and angular momentum from the outer to the inner parts of the circumstellar disc. In the case of …
SOLAR DYNAMICS OBSERVATORY DISCOVERS THIN HIGH TEMPERATURE STRANDS IN CORONAL ACTIVE REGIONS
2011
One scenario proposed to explain the million degrees solar corona is a finely-stranded corona where each strand is heated by a rapid pulse. However, such fine structure has neither been resolved through direct imaging observations nor conclusively shown through indirect observations of extended superhot plasma. Recently it has been shown that the observed difference in appearance of cool and warm coronal loops (~1 MK, ~2-3 MK, respectively) -- warm loops appearing "fuzzier" than cool loops -- can be explained by models of loops composed of subarcsecond strands, which are impulsively heated up to ~10 MK. That work predicts that images of hot coronal loops (>~6 MK) should again show fine s…
SphinX: The Solar Photometer in X-Rays
2012
Solar Photometer in X-rays (SphinX) was a spectrophotometer developed to observe the Sun in soft X-rays. The instrument observed in the energy range ≈ 1 – 15 keV with resolution ≈ 0.4 keV. SphinX was flown on the Russian CORONAS–PHOTON satellite placed inside the TESIS EUV and X telescope assembly. The spacecraft launch took place on 30 January 2009 at 13:30 UT at the Plesetsk Cosmodrome in Russia. The SphinX experiment mission began a couple of weeks later on 20 February 2009 when the first telemetry dumps were received. The mission ended nine months later on 29 November 2009 when data transmission was terminated. SphinX provided an excellent set of observations during very low solar activ…
First results of an Hα based search of classical Be stars in the Perseus Arm and beyond
2013
We investigate a region of the Galactic plane, between 120 <= l <= 140 and -1 <= b <= +4, and uncover a population of moderately reddened (E(B-V) \sim 1) classical Be stars within and beyond the Perseus and Outer Arms. 370 candidate emission line stars (13 <= r <= 16) selected from the INT Photometric H-alpha Survey of the Northern Galactic plane (IPHAS) have been followed up spectroscopically. A subset of these, 67 stars with properties consistent with those of classical Be stars, have been observed at sufficient spectral resolution (Delta_lambda \sim 2 - 4 Angstrom) at blue wavelengths to narrow down their spectral types. We determine these to a precision estimated to be…
Solar Neutrino Spectroscopy
2017
More than forty years after the first detection of neutrinos from the Sun, the spectroscopy of solar neutrinos has proven to be an on-going success story. The long-standing puzzle about the observed solar neutrino deficit has been resolved by the discovery of neutrino flavor oscillations. Today's experiments have been able to solidify the standard MSW-LMA oscillation scenario by performing precise measurements over the whole energy range of the solar neutrino spectrum. This article reviews the enabling experimental technologies: On the one hand mutli-kiloton-scale water Cherenkov detectors performing measurements in the high-energy regime of the spectrum, on the other end ultrapure liquid-s…
Correlated optical and X-ray variability in CTTS
2010
Optical and X-ray emission from classical T Tauri stars (CTTSs) has long been known to be highly variable. Our long, uninterrupted optical observation of the NGC2264 region with CoRoT allows the optical variability in CTTS to be studied with unprecedented accuracy and time coverage. Two short Chandra observations obtained during the CoRoT pointing with a separation of 16 days allow us to study whether there is a correlation between optical and X-ray variability on this timescale, thus probing the physical mechanisms driving the variability in both bands. We have computed the optical and X-ray fractional variability between the two 30 ks duration windows covered by both the Chandra and CoRoT…
Results from DROXO. II. - [Ne II] and X-ray emission from Rho Ophiuchi young stellar objects
2009
The infrared [Ne II] and [Ne III] fine structure lines at 12.81um and 15.55um are predicted to trace the circumstellar disk gas subject to X-ray heating and ionization. We investigate the origin of these lines by comparing observations with models of X-ray irradiated disks and by searching for empirical correlations between the line luminosities and stellar and circumstellar parameters. We measure neon line fluxes and X-ray luminosities for 28 young stellar objects in the Rho Ophiuchi star formation region for which good quality infrared spectra and X-ray data have been obtained, the former with the Spitzer IRS and the latter with the Deep Rho Ophiuchi XMM-Newton Observation. We detect the …
Comparison of Hinode/XRT and RHESSI detection of hot plasma in the non-flaring solar corona
2009
We compare observations of the non-flaring solar corona made simultaneously with Hinode/XRT and with RHESSI. The analyzed corona is dominated by a single active region on 12 November 2006. The comparison is made on emission measures. We derive emission measure distributions vs temperature of the entire active region from multifilter XRT data. We check the compatibility with the total emission measure values estimated from the flux measured with RHESSI if the emission come from isothermal plasma. We find that RHESSI and XRT data analyses consistently point to the presence of a minor emission measure component peaking at log T ~ 6.8-6.9. The discrepancy between XRT and RHESSI results is withi…