Search Publications
Large-Amplitude Velocity Fluctuations in Coronal Loops: Flare Drivers?
Veltri, P.; Malara, F.; Nigro, G.
Recent space observations of coronal lines broadening during a flare occurrence suggest that unresolved nonthermal velocity rises well above the background level before the start of the flare, defined as the start of hard X-ray emission. Using a new shell model to describe the Alfvénic turbulence inside a coronal loop, it is shown that the occurre…
Nonthermal Velocities in Different Temperature Regions of the Solar Lower Transition Region
Doschek, G. A.; Mariska, J. T.; Akiyama, S.
We analyze the relationship between nonthermal velocities derived from spectral lines of ions formed at different temperatures in the solar lower transition region, using spectra from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on board the Solar and Heliospheric Observatory (SOHO). We find a high degree of correla…
Oxygen Abundance in Coronal Streamers
Raymond, John C.; Vásquez, Alberto M.
In a previous work we developed a stationary proton-electron MHD model of the solar corona, suitable for the minimum-activity epochs. In the present work, we use empirically derived information from the past solar minimum for the oxygen parameters (temperatures and outflow velocity) to develop an oxygen model in the frame of our previous model. So…
Spatial Evidence for Transition Radiation in a Solar Radio Burst
Fleishman, Gregory D.; Nita, Gelu M.; Gary, Dale E.
Microturbulence, i.e., enhanced fluctuations of plasma density and electric and magnetic fields, is of great interest in astrophysical plasmas, but occurs on spatial scales far too small to resolve by remote sensing, e.g., at ~1-100 cm in the solar corona. This Letter reports spatially resolved observations that offer strong support for the presen…
Proper Motion of the Irradiated Jet HH 399 in the Trifid Nebula
Yusef-Zadeh, F.; Wardle, M.; Biretta, J.
HH 399 is one of the first Herbig-Haro flows recognized to be irradiated by the UV radiation of the massive O7.5 star in the Trifid Nebula. We present the proper motion of the first irradiated jet, based on two epochs of Hubble Space Telescope (HST) observations of HH 399 separated by nearly 5 yr, using Hα and [S II] line filters. High proper moti…
X-Ray and Infrared Observations of Embedded Young Stars in NGC 2264
Simon, Theodore; Dahm, S. E.
Images of the NGC 2264 star-forming region, which we have acquired with the XMM-Newton spacecraft, reveal strong X-ray emission from three deeply embedded (AV>=10 mag) young stellar objects in the vicinity of Allen's infrared source (AFGL 989 = IRS 1) and Castelaz & Grasdalen's infrared source (RNO-EW = IRS 2). Thermal plasma mod…
UV/Optical Nuclear Activity in the gE Galaxy NGC 1399
Crane, Jeffrey D.; O'Connell, Robert W.; Burstein, David +5 more
Using HST STIS, we have detected far-ultraviolet nuclear activity in the giant elliptical galaxy NGC 1399, the central and brightest galaxy in the Fornax I cluster. The source reached a maximum observed far-UV luminosity of ~1.2×1039 ergs s-1 in 1999 January. It was detectable in earlier HST archival images in 1996 (B band) b…
Swift, INTEGRAL, RXTE, and Spitzer Reveal IGR J16283-4838
Gehrels, N.; Rodriguez, J.; Mowlavi, N. +9 more
We present the first combined study of the recently discovered source IGR J16283-4838 with Swift, INTEGRAL, and RXTE. The source, discovered by INTEGRAL on 2005 April 7, shows a highly absorbed [variable NH=(0.4-1.7)×1023 cm-2] and flat (Γ~1) spectrum in the Swift XRT and RXTE PCA data. No optical counterpart is de…
A Study of the Near-Ultraviolet Spectrum of Vega
Hubeny, Ivan; Allende Prieto, Carlos; García López, Ramón J. +1 more
UV, optical, and near-IR spectra of Vega have been combined to test our understanding of stellar atmospheric opacities and to examine the possibility of constraining chemical abundances from low-resolution UV fluxes. We have carried out a detailed analysis assuming local thermodynamic equilibrium (LTE) to identify the most important contributors t…
Faint Blue Objects in the Hubble Deep Field-South Revealed: White Dwarfs, Subdwarfs, and Quasars
Winget, D. E.; Kilic, Mukremin; von Hippel, Ted +1 more
We explore the nature of the faint blue objects in the Hubble Deep Field-South. We have derived proper motions for the point sources in the Hubble Deep Field-South using a 3 yr baseline. Combining our proper-motion measurements with spectral energy distribution fitting enabled us to identify four quasars and 42 stars, including three white dwarf c…