Search Publications
EUV Emission and Scattered Light Diagnostics of Equatorial Coronal Holes as Seen by Hinode/EIS
Landi, Enrico; Wendeln, Carolyn
Spectroscopic diagnostics of solar coronal plasmas critically depends on the uncertainty in the measured line intensities. One of the main sources of uncertainty is instrumental scattered light, which is potentially most important in low-brightness areas. In the solar corona, such areas include polar and equatorial coronal holes, which are the sou…
A Changing Wind Collision
Corcoran, Michael F.; Hillier, D. John; Nazé, Yaël +4 more
We report on the first detection of a global change in the X-ray emitting properties of a wind-wind collision, thanks to XMM-Newton observations of the massive Small Magellenic Cloud (SMC) system HD 5980. While its light curve had remained unchanged between 2000 and 2005, the X-ray flux has now increased by a factor of ∼2.5, and slightly hardened.…
On Measuring the Variation of High-energy Cutoff in Active Galactic Nuclei
Wang, Jun-Xian; Zhang, Ji-Xian; Zhu, Fei-Fan
The variation in the high-energy cutoff, E c , in active galactic nuclei (AGNs) uniquely probes the corona physics. In this work, we show that the ratio of two NuSTAR spectra (analogous to the difference-imaging technique widely used in astronomy) is uniquely useful in studying E c variations. The spectra ratio could direc…
Strong Lensing Modeling in Galaxy Clusters as a Promising Method to Test Cosmography. I. Parametric Dark Energy Models
Jullo, Eric; Limousin, Marceau; Magaña, Juan +3 more
In this paper we probe five cosmological models for which the dark energy equation of state parameter, w(z), is parameterized as a function of redshift using strong lensing data in the galaxy cluster Abell 1689. We constrain the parameters of the w(z) functions by reconstructing the lens model under each one of these cosmologies with strong lensin…
Quiet-Sun and Coronal Hole in Mg II k Line as Observed by IRIS
Solanki, Sami K.; Peter, Hardi; Kayshap, Pradeep +1 more
Coronal hole (CH) regions are dark in comparison to the quiet Sun (QS) at coronal temperatures. However, at chromospheric and transition region temperatures, the QS and CHs are hardly distinguishable. In this study, we have used the Mg II 2796.35 Å spectral line recorded by the Interface Region Imaging Spectrometer (IRIS) to understand the similar…
Hubble Space Telescope Trigonometric Parallax of Polaris B, Companion of the Nearest Cepheid
Schaefer, Gail H.; Nelan, Edmund P.; Bond, Howard E. +2 more
Polaris, the nearest and brightest Cepheid, is a potential anchor point for the Leavitt period-luminosity relation. However, its distance is a matter of contention, with recent advocacy for a parallax of ∼10 mas, in contrast with the Hipparcos measurement of 7.54 ± 0.11 mas. We report an independent trigonometric parallax determination, using the …
High-frequency Spicule Oscillations Generated via Mode Conversion
Yokoyama, Takaaki; Shoda, Munehito
Spicule oscillations involve high-frequency components with a typical period approximately corresponding to 40-50 s. The typical timescale of the photospheric oscillation is a few minutes, and thus, the origin of this high-frequency component is not trivial. In this study, a one-dimensional numerical simulation is performed to demonstrate that the…
Spatially Offset Active Galactic Nuclei. III. Discovery of Late-stage Galaxy Mergers with the Hubble Space Telescope
Greene, Jenny E.; Comerford, Julia M.; Barrows, R. Scott
Galaxy pairs with separations of only a few kiloparsecs represent important stages in the merger-driven growth of supermassive black holes (SMBHs). However, such mergers are difficult to identify observationally due to the correspondingly small angular scales. In Paper I we presented a method of finding candidate kiloparsec-scale galaxy mergers th…
Dependence of Coronal Loop Temperature on Loop Length and Magnetic Field Strength
Velli, M.; Ugarte-Urra, I.; Dahlburg, R. B. +2 more
The temperature characteristics of solar coronal loops over a wide range of lengths and magnetic field strengths are investigated by means of numerical simulations. A very high correlation between magnetic field strength (B 0) and maximum temperature (T max) is found. Shorter loops rooted at stronger fields are those that rea…
Ensemble Properties of the White Dwarf Population of the Old, Solar Metallicity Open Star Cluster Messier 67
Kilic, Mukremin; Bellini, A.; Bolte, Michael +4 more
White dwarfs (WDs) are excellent forensic tools for studying end-of-life issues surrounding low- and intermediate-mass stars, and the old, solar metallicity open star cluster Messier 67 is a proven laboratory for the study of stellar evolution for solar-type stars. In this paper, we present a detailed spectroscopic study of brighter (M g