Search Publications
Reconnection and Energetics in Two-ribbon Flares: A Revisit of the Bastille-day Flare
Qiu, Jiong; Liu, WenJuan; Hill, Nicholas +1 more
We conduct a semi-quantitative analysis of two-ribbon flares to investigate the observational relationship between magnetic reconnection and energetics by revisiting the Bastille-day flare, particularly the UV and hard X-ray (HXR) observations. The analysis establishes that prominent UV emission is primarily produced by precipitating electrons tha…
High-excitation Emission Lines near Eta Carinae, and Its Likely Companion Star
Humphreys, Roberta M.; Davidson, Kris; Mehner, Andrea +1 more
In order to study the distribution of gas and ionizing radiation around η Car and their implications for its likely companion star, we have examined high-excitation emission lines of [Ne III], [Fe III], etc., in spectra obtained with the Hubble Space Telescope/Space Telescope Imaging Spectrograph instrument during 1998-2004. Our principal results,…
Characteristics of Solar Meridional Flows during Solar Cycle 23
Basu, Sarbani; Antia, H. M.
We have analyzed available full-disk data from the Michelson Doppler Imager on board SOHO using the "ring diagram" technique to determine the behavior of solar meridional flows over solar cycle 23 in the outer 2% of the solar radius. We find that the dominant component of meridional flows during solar maximum was much lower than that during the mi…
A High-resolution Mass Map of Galaxy Cluster Substructure: LensPerfect Analysis of A1689
Broadhurst, Tom; Coe, Dan; Benítez, Narciso +1 more
We present a strong lensing (SL) mass model of A1689 which resolves substructures an estimated 25 kpc across within the central ~400 kpc diameter. We achieve this resolution by perfectly reproducing the observed (strongly lensed) input positions of 168 multiple images of 55 knots residing within 135 images of 42 galaxies. Our model makes no assump…
Alfvén-wave Turbulence and Perpendicular Ion Temperatures in Coronal Holes
Chandran, Benjamin D. G.
Low-frequency Alfvén-wave turbulence causes ion trajectories to become chaotic, or "stochastic," when the turbulence amplitude is sufficiently large. Stochastic orbits enable ions to absorb energy from the turbulence, increasing the perpendicular ion temperature T bottomi even when the fluctuation frequencies are too small for a cyclotr…
Total Solar Eclipse Observations of Hot Prominence Shrouds
Rušin, V.; Druckmüller, M.; Morgan, H. +5 more
Using observations of the corona taken during the total solar eclipses of 2006 March 29 and 2008 August 1 in broadband white light and in narrow bandpass filters centered at Fe X 637.4 nm, Fe XI 789.2 nm, Fe XIII 1074.7 nm, and Fe XIV 530.3 nm, we show that prominences observed off the solar limb are enshrouded in hot plasmas within twisted magnet…
A Tidal Disruption Flare in A1689 from an Archival X-ray Survey of Galaxy Clusters
Eracleous, Michael; Maksym, W. Peter; Ulmer, M. P.
Theory suggests that a star making a close passage by a supermassive black hole at the center of a galaxy can under most circumstances be expected to emit a giant flare of radiation as it is disrupted and a portion of the resulting stream of shock-heated stellar debris falls back onto the black hole itself. We examine the first results of an ongoi…
Studying the Physical Diversity of Late-M Dwarfs with Dynamical Masses
Helling, Christiane; Cushing, Michael C.; Dupuy, Trent J. +4 more
We present a systematic study of the physical properties of late-M dwarfs based on high-quality dynamical mass measurements and near-infrared (NIR) spectroscopy. We use astrometry from Keck natural and laser guide star adaptive optics imaging to determine orbits for the late-M binaries LP 349 - 25AB (M7.5+M8), LHS 1901AB (M6.5+M6.5), and Gl 569Bab…
X-ray Variability and Evidence for Pulsations from the Unique Radio Pulsar/X-ray Binary Transition Object FIRST J102347.6+003841
Ransom, Scott M.; Kaspi, Victoria M.; Bogdanov, Slavko +4 more
We report on observations of the unusual neutron-star binary system FIRST J102347.6+003841 carried out using the XMM-Newton satellite. This system consists of a radio millisecond pulsar (PSR J1023+0038) in a 0.198 day orbit with a ~0.2 M sun Roche-lobe-filling companion and appears to have had an accretion disk in 2001. We observe a har…
Calibrating the Correlation Between Black Hole Mass and X-ray Variability Amplitude: X-ray Only Black Hole Mass Estimates for Active Galactic Nuclei and Ultra-luminous X-ray Sources
Zhang, Shuang-Nan; Zhou, Xin-Lin; Zhu, Ling +1 more
A calibration is made for the correlation between the X-ray Variability Amplitude (XVA) and black hole (BH) mass. The correlation for 21 reverberation-mapped Active Galactic Nuclei (AGNs) appears very tight, with an intrinsic dispersion of 0.20 dex. The intrinsic dispersion of 0.27 dex can be obtained if BH masses are estimated from the stellar ve…