Search Publications
3D Direct Simulation Monte Carlo Modelling of the Inner Gas Coma of Comet 67P/Churyumov–Gerasimenko: A Parameter Study
Kührt, E.; Keller, H. U.; Knollenberg, J. +9 more
Direct Simulation Monte Carlo (DSMC) is a powerful numerical method to study rarefied gas flows such as cometary comae and has been used by several authors over the past decade to study cometary outflow. However, the investigation of the parameter space in simulations can be time consuming since 3D DSMC is computationally highly intensive. For the…
Cool Subdwarf Investigations. III. Dynamical Masses of Low-metallicity Subdwarfs
Nelan, Edmund P.; Henry, Todd J.; Wasserman, Lawrence H. +2 more
We report dynamical mass measurements for the components of the previously known double-lined spectroscopic subdwarfs G 006-026 B and C using the Fine Guidance Sensors on the Hubble Space Telescope. To build the empirical mass-luminosity relation for low-metallicity subdwarfs, we collect four other subdwarf systems with dynamical masses that we co…
Exploring the crowded central region of ten Galactic globular clusters using EMCCDs. Variable star searches and new discoveries
Surdej, J.; Snodgrass, C.; Horne, K. +30 more
Aims: We aim to obtain time-series photometry of the very crowded central regions of Galactic globular clusters; to obtain better angular resolution thanhas been previously achieved with conventional CCDs on ground-based telescopes; and to complete, or improve, the census of the variable star population in those stellar systems.
Methods:…
Characteristics of field-aligned currents associated with magnetic flux ropes in the magnetotail: A statistical study
Zhao, Yan; Wang, Rongsheng; Du, Aimin
We present an investigation of 35 magnetic flux ropes encountered by Cluster in the Earth's magnetotail during the years between 2001 and 2004. The study shows that the parallel current dominates inside 86% of the identified flux ropes and 71% of the flux ropes are surrounded by the draping regions where the parallel current is comparable to the p…
Spectroscopic Confirmation of the Dwarf Spheroidal Galaxy d0994+71 as a Member of the M81 Group of Galaxies
Simon, Joshua D.; Chiboucas, Kristin; Guhathakurta, Puragra +3 more
We use Keck/DEIMOS spectroscopy to measure the first velocity and metallicity of a dwarf spheroidal (dSph) galaxy beyond the Local Group using resolved stars. Our target, d0944+71, is a faint dSph found in the halo of the massive spiral galaxy M81 by Chiboucas et al. We coadd the spectra of 27 individual stars and measure a heliocentric radial vel…
Asteroid orbits with Gaia using random-walk statistical ranging
Muinonen, Karri; Fedorets, Grigori; Pentikäinen, Hanna +10 more
We describe statistical inverse methods for the computation of initial asteroid orbits within the data processing and analysis pipeline of the ESA Gaia space mission. Given small numbers of astrometric observations across short time intervals, we put forward a random-walk ranging method, in which the orbital-element phase space is uniformly sample…
Andromeda IV, a solitary gas-rich dwarf galaxy
Rizzi, L.; Sharina, M. E.; Karachentsev, I. D. +4 more
Observations are presented of the isolated dwarf irregular galaxy And IV made with the Hubble Space Telescope Advanced Camera for Surveys and the Giant Metrewave Radio Telescope in the 21 cm H I line. We determine the galaxy distance of 7.17{±}0.31 Mpc using the Tip of Red Giant Branch method. The galaxy has a total blue absolute magnitude of -12.…
A global look at X-ray time lags in Seyfert galaxies
Kara, E.; Fabian, A.; Alston, W.
X-ray reverberation, where light-travel time delays map out the compact geometry around the inner accretion flow in supermassive black holes, has been discovered in several of the brightest, most variable and well-known bare Seyfert galaxies. In this work, we expand the study of X-ray time lags to all Seyfert galaxies in the XMM-Newton archive abo…
Spectroscopic Diagnostics of Solar Magnetic Flux Ropes Using Iron Forbidden Line
Cheng, X.; Ding, M. D.
In this Letter, we present Interface Region Imaging Spectrograph Fe xxi 1354.08 Å forbidden line emission of two magnetic flux ropes (MFRs) that caused two fast coronal mass ejections with velocities of ≥1000 km s-1 and strong flares (X1.6 and M6.5) on 2014 September 10 and 2015 June 22, respectively. The extreme-ultraviolet images at t…
Hot gas and magnetic arms of NGC 6946: Indications for reconnection heating?
Ehle, M.; Weżgowiec, M.; Beck, R.
Context. The grand-design face-on spiral galaxy
Aims:…