Search Publications
The Off-Disk Thermal Structure of a Polar Coronal Hole
Landi, Enrico
The thermal structure of the coronal portion of coronal holes is a key factor in the modeling of the source regions and acceleration mechanisms of the fast solar wind. Studies aimed at this region are best carried out on observations outside the disk, where the chromosphere and transition region are not included in the line of sight. In the past, …
Stratification of Sunspot Umbral Dots from Inversion of Stokes Profiles Recorded by Hinode
Solanki, S. K.; Lagg, A.; Riethmüller, T. L.
This work aims to constrain the physical nature of umbral dots (UDs) using high-resolution spectropolarimetry. Full Stokes spectra recorded by the spectropolarimeter on Hinode of 51 UDs in a sunspot close to the disk center are analyzed. The height dependence of the temperature, magnetic field vector, and line-of-sight velocity across each UD is o…
Discovery of a Very Highly Extinguished Supernova in a Luminous Infrared Galaxy
Colina, L.; Kankare, E.; Efstathiou, A. +9 more
We report the discovery of a confirmed supernova (SN) and a supernova candidate in near-infrared images from the ALTAIR/NIRI adaptive optics system on the Gemini-North Telescope and NICMOS on the Hubble Space Telescope. The Gemini images were obtained as part of a near-infrared K-band search for highly obscured SNe in the nuclear regions of lumino…
The Extragalactic Distance Scale without Cepheids
Sakai, Shoko; Mould, Jeremy
Distances of galaxies in the Hubble Space Telescope Key Project are based on the Cepheid period-luminosity relation. An alternative basis is the tip of the red giant branch. Using archival HST data, we calibrate the infrared Tully-Fisher relation using 14 galaxies with tip of the red giant branch measurements. Compared with the Key Project, a high…
Novae as a Class of Transient X-Ray Sources
Mukai, K.; Della Valle, M.; Orio, M.
Motivated by the recently discovered class of faint (1034-1035 ergs s-1) X-ray transients in the Galactic center region, we investigate the 2-10 keV properties of classical and recurrent novae. Existing data are consistent with the idea that all classical novae are transient X-ray sources with durations of months t…
Limits on Hot Galactic Halo Gas from X-Ray Absorption Lines
Yao, Y.; Nowak, M. A.; Wang, Q. D. +2 more
Although the existence of large-scale hot gaseous halos around massive disk galaxies has been theorized for a long time, there is yet very little observational evidence. We report the Chandra and XMM-Newton grating spectral detection of O VII and Ne IX Kα absorption lines along the sight line of 4U 1957+11. The line absorption is consistent with t…
The ACS LCID Project: RR Lyrae Stars as Tracers of Old Population Gradients in the Isolated Dwarf Spheroidal Galaxy Tucana
Skillman, Evan D.; Cole, Andrew A.; Mateo, Mario +9 more
We present a study of the radial distribution of RR Lyrae variables, which present a range of photometric and pulsational properties, in the dwarf spheroidal galaxy Tucana. We find that the fainter RR Lyrae stars, having a shorter period, are more centrally concentrated than the more luminous, longer period RR Lyrae variables. Through comparison w…
Coronal Jet Observed by Hinode as the Source of a3He-rich Solar Energetic Particle Event
Krucker, Säm; Shibata, Kazunari; Nitta, Nariaki V. +5 more
We study the solar source of the 3He-rich solar energetic particle (SEP) event observed on 2006 November 18. The SEP event showed a clear velocity dispersion at energies below 1 MeV nucleon-1, indicating its solar origin. We associate the SEP event with a coronal jet in an active region at heliographic longitude of W50°, as o…
Weighing the Quiescent Central Black Hole in an Elliptical Galaxy with X-Ray-Emitting Gas
Gebhardt, Karl; Humphrey, Philip J.; Buote, David A. +2 more
We present a Chandra study of the hot interstellar medium (ISM) in the giant elliptical galaxy NGC 4649. In common with other group-centered ellipticals, its temperature profile rises with radius in the outer parts of the galaxy, from ~0.7 keV at 2 kpc to ~0.9 keV by 20 kpc. However, within the central ~2 kpc the trend reverses, and the temperatur…
Injection and Interplanetary Transport of Near-Relativistic Electrons: Modeling the Impulsive Event on 2000 May 1
Lario, D.; Vainio, R.; Sanahuja, B. +1 more
We present a Monte Carlo method to model the transport of solar near-relativistic electrons in the interplanetary medium, including adiabatic focusing, pitch-angle dependent scattering, and solar wind effects. By taking into account the angular response of the LEFS60 telescope of the EPAM instrument on board the ACE spacecraft, we transform the si…