Search Publications
Evidence for Fresh Frost Layer on the Bare Nucleus of Comet Hale-Bopp at 32 AU Distance
Pál, András; Sárneczky, Krisztián; Juhász, Attila +4 more
Here, we report that the activity of comet Hale-Bopp ceased between late 2007 and 2009 March, at about 28 AU distance from the Sun. At that time, the comet resided at a distance from the Sun that exceeded the freeze-out distance of regular comets by an order of magnitude. A Herschel Space Observatory PACS scan was taken in mid-2010, in the already…
Ultraviolet Measurements of Interstellar C2
Federman, S. R.; Sheffer, Y.; Hupe, Ryan C.
We analyzed archival spectra acquired with the Hubble Space Telescope for a study of interstellar C2. Absorption from the electronic transitions, D 1Σ+ u - X 1Σ+ g (0,0) as well as F 1Πu - X 1Σ+ g (0,0) and (1,0), was…
New Evidence Supporting Cluster Membership for the Keystone Calibrator Delta Cephei
Gieren, W.; Turner, D.; Majaess, D.
New and existing UBVJHKs , spectroscopic, NOMAD, Hubble Space Telescope, and revised Hipparcos observations are employed to determine properties for δ Cep and its host star cluster. The multi-faceted approach ensured that uncertainties were mitigated (σ/d ~ 2%). The following fundamental parameters were inferred for δ Cep: E(B - V) = 0.…
Model Selection for Spectropolarimetric Inversions
Orozco Suárez, D.; Asensio Ramos, A.; Martínez González, M. J. +3 more
Inferring magnetic and thermodynamic information from spectropolarimetric observations relies on the assumption of a parameterized model atmosphere whose parameters are tuned by comparison with observations. Often, the choice of the underlying atmospheric model is based on subjective reasons. In other cases, complex models are chosen based on obje…
The Kinematics of HH 34 from HST Images with a Nine-year Time Baseline
Stapelfeldt, K. R.; Raga, A. C.; Lora, V. +3 more
We study archival HST [S II] 6716+30 and Hα images of the HH 34 outflow, taken in 1998.71 and in 2007.83. The ~9 yr time baseline and the high angular resolution of these observations allow us to carry out a detailed proper-motion study. We determine the proper motions of the substructure of the HH 34S bow shock (from the [S II] and Hα frames) and…
LBQS 0103-2753: A Binary Quasar in a Major Merger
Junkkarinen, V.; Shields, G. A.; Chapman, S. C. +3 more
We present Hubble Space Telescope (HST) and United Kingdom Infrared Telescope spectra and images of the 2 kpc (0farcs3) binary quasar LBQS 0103-2753 (z = 0.858). The HST images (V and I bands) show tidal features demonstrating that this system is a major galaxy merger in progress. A two-color composite image brings out knots of star formation alon…
Detection of Accretion X-Rays from QS Vir: Cataclysmic or a Lot of Hot Air?
Drake, Jeremy J.; Steeghs, Danny; Kashyap, Vinay +1 more
An XMM-Newton observation of the nearby "pre-cataclysmic" short-period (P orb = 3.62 hr) binary QS Vir (EC 13471-1258) revealed regular narrow X-ray eclipses when the white dwarf passed behind its M2-4 dwarf companion. The X-ray emission provides a clear signature of mass transfer and accretion onto the white dwarf. The low-resolution X…
Soft Coronal X-Rays from β Pictoris
Schmitt, J. H. M. M.; Robrade, J.; Günther, H. M. +3 more
A-type stars are expected to be X-ray dark, yet weak emission has been detected from several objects in this class. We present new Chandra/HRC-I observations of the A5 V star β Pictoris. It is clearly detected with a flux of (9 ± 2) × 10-4 counts s-1. In comparison with previous data this constrains the emission mechanism and…
Scattering of the f-mode by Small Magnetic Flux Elements from Observations and Numerical Simulations
Felipe, T.; Braun, D.; Crouch, A. +1 more
The scattering of f-modes by magnetic tubes is analyzed using three-dimensional numerical simulations. An f-mode wave packet is propagated through a solar atmosphere embedded with three different flux tube models that differ in radius and total magnetic flux. A quiet-Sun simulation without a tube present is also performed as a reference. Waves are…
Global Modeling of X-Ray Spectra Produced in O-type Star Winds
Nazé, Y.; Rauw, G.; Hervé, A. +1 more
High-resolution X-ray spectra of O-type stars revealed less wind absorption than expected from smooth winds with conventional mass-loss rates. Various solutions have been proposed, including porous winds, optically thick clumps, or an overall reduction of the mass-loss rates. The latter has a strong impact on the evolution of the star. Our final g…