Search Publications
Imaging the Solar Tachocline by Time-Distance Helioseismology
Kosovichev, A. G.; Zhao, Junwei; Hartlep, Thomas +1 more
The solar tachocline at the bottom of the convection zone is an important region for the dynamics of the Sun and the solar dynamo. In this region, the sound speed inferred by global helioseismology exhibits a bump of approximately 0.4% relative to the standard solar model. Global helioseismology does not provide any information on possible latitud…
Convective bursty flows in the near-Earth magnetotail inside 13 RE
Dunlop, M. W.; Baumjohann, W.; Carr, C. +8 more
With the 4-s resolution data of the magnetometer and the ion plasma analyzer on Double Star TC-1 from June to November of each year during the period of 2004-2006, we statistically analyzed the occurrence rate of both convective and field-aligned bursty flows (FABFs). In the region -13 RE < X < -9 RE, |Y| < 10 R…
X-ray narrow line region variability as a geometry probe. The case of NGC 5548
Kaastra, J. S.; Detmers, R. G.; McHardy, I. M.
We study the long time scale variability of the gas responsible for the X-ray narrow emission lines in the Seyfert 1 galaxy NGC 5548, in order to constrain the location and geometry of the emitting gas. Using X-ray spectra taken with the Chandra-LETGS and HETGS instruments and with XMM-Newton RGS and combining them with long-term monitoring observ…
XMM-Newton and Optical Observations of Cataclysmic Variables from the Sloan Digital Sky Survey
Szkody, Paula; Schmidt, Gary D.; Mukadam, Anjum +3 more
We report on XMM-Newton and optical results for six cataclysmic variables that were selected from Sloan Digital Sky Survey (SDSS) spectra because they showed strong He II emission lines, indicative of being candidates for containing white dwarfs with strong magnetic fields. While high X-ray background rates prevented optimum results, we are able t…
The Unevolved Main Sequence of Nearby Field Stars and the Open Cluster Distance Scale
Twarog, Bruce A.; Anthony-Twarog, Barbara J.; Edgington-Giordano, Frederika
The slope and zero point of the unevolved main sequence as a function of metallicity are investigated using a homogeneous catalog of nearby field stars with absolute magnitudes defined with revised Hipparcos parallaxes, Tycho-2 photometry, and precise metallicities from high-dispersion spectroscopy. (B - V) -temperature relations are derived from …
Twist and turn: weak lensing image distortions to second order
Bacon, David J.; Schäfer, Björn Malte
We account for all the image distortions relevant to weak gravitational lensing to second order. Besides the familiar shear, convergence, rotation and flexions, we find a new image distortion with two distinct descriptions, the twist and the turn. Like rotation, this distortion is not activated gravitationally to first order, but will be activated…
Monitoring campaign of 1RXS J171824.2-402934, the low-mass X-ray binary with the lowest mass accretion rate
in't Zand, J. J. M.; Bassa, C. G.; Jonker, P. G. +2 more
An X-ray monitoring campaign with Chandra and Swift confirms that 1RXS J171824.2-402934 is accreting at the lowest rate among the known persistently accreting low-mass X-ray binaries. A thermonuclear X-ray burst was detected with the all-sky monitor on RXTE. This is only the second such burst seen in 1RXS J171824.2-402934 in more than 20 Ms of obs…
Two types of flare-associated coronal mass ejections
Michalek, G.
Aims: Here, we study the relationship between flares and CMEs.
Methods: For this purpose a statistical analysis of 578 flare-associated CMEs is presented. We considered two types of flare-associated CMEs: CMEs that follow and precede flare onset.
Results: We shown that both samples have quite different characteristics. The first type of CM…
A wave scattering theory of solar seismic power haloes
Hanasoge, S. M.
Spatial maps of the high-pass frequency filtered time-averaged root-mean-squared (RMS) Doppler velocities tend to show substantial decrements within regions of strong field and curiously, randomly distributed patches of enhancement in the vicinity. We propose that these haloes or enhancements are a consequence of magnetic-field-induced mode mixing…
Origin of Thermal and Non-Thermal Hard X-Ray Emission from the Galactic Center
Maeda, Yoshitomo; Kokubun, Motohide; Nakazawa, Kazuhiro +10 more
We analyse new results of Chandra and Suzaku Observatories which found a flux of hard X-ray emission from the compact region around Sgr A* (r ∼ 100 pc). We suppose that this emission is generated by accretion processes onto the central supermassive blackhole when an unbound part of captured stars obtains an additional momentum. As a res…