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X-Ray Evidence for Flare Density Variations and Continual Chromospheric Evaporation in Proxima Centauri
Skinner, Stephen L.; Güdel, Manuel; Audard, Marc +1 more
Using the XMM-Newton X-ray observatory to monitor the nearest star to the Sun, Proxima Centauri, we recorded the weakest X-ray flares on a magnetically active star ever observed. Correlated X-ray and optical variability provide strong support for coronal energy and mass supply by a nearly continuous sequence of rapid explosive energy releases. Var…
The Origin of Water Vapor and Carbon Dioxide in Jupiter's Stratosphere
Lellouch, E.; Encrenaz, T.; Feuchtgruber, H. +6 more
Observations of H 2O rotational lines from the Infrared Space Observatory (ISO) and the Submillimeter Wave Astronomy Satellite (SWAS) and of the CO 2 ν 2 band by ISO are analyzed jointly to determine the origin of water vapor and carbon dioxide in Jupiter's stratosphere. Simultaneous modelling of ISO/LWS and ISO/SW…
Metal Abundances and Kinematics of Bright Metal-poor Giants Selected from the LSE Survey: Implications for the Metal-weak Thick Disk
Beers, Timothy C.; von Hippel, Ted; Rossi, Silvia +5 more
We report medium-resolution (1-2 Å) spectroscopy and broadband (UBV) photometry for a sample of 39 bright stars (the majority of which are likely to be giants) selected as metal-deficient candidates from an objective-prism survey concentrating on Galactic latitudes below |b|=30°, the Luminous Stars Extension (LSE) survey of Drilling & Bergeron…
Sungrazing Comets Discovered with the SOHO/LASCO Coronagraphs 1996-1998
Llebaria, A.; St. Cyr, O. C.; Lamy, P. +2 more
The Kreutz sungrazing family of comets is unique because of its small perihelion distance and because of the large number of known members of this family. SOHO/LASCO coronagraph observations beginning in 1996 have revealed an unprecedented number of Kreutz comets. These new coronagraph observations improve upon earlier observations because of a la…
Timing of magnetic reconnection initiation during a global magnetospheric substorm onset
Daly, P. W.; Dunlop, M. W.; Baker, D. N. +13 more
We have used a unique constellation of Earth-orbiting spacecraft and ground-based measurements in order to study a relatively isolated magnetospheric substorm event on August 27, 2001. Global ultraviolet images of the northern auroral region established the substorm expansion phase onset at 0408:19 (+/-1 min) UT. Concurrent measurements from the G…
Understanding the nature of FR II optical nuclei: A new diagnostic plane for radio galaxies
Capetti, A.; Chiaberge, M.; Celotti, A.
We extend our study of the nuclei of 3CR FR II radio galaxies through HST optical images up to z = 0.3. In the majority of them an unresolved nucleus (central compact core, CCC) is found. We analyze their position in the plane formed by the radio and optical nuclear luminosities in relation to their optical spectral properties. The broad-lined obj…
The Velocity Distribution of the Nearest Interstellar Gas
Welty, Daniel E.; Frisch, Priscilla C.; Grodnicki, Lauren
The bulk flow velocity for the cluster of interstellar cloudlets within ~30 pc of the Sun is determined from optical and ultraviolet absorption line data, after omitting from the sample stars with circumstellar disks or variable emission lines and the active variable HR 1099. A total of 96 velocity components toward the remaining 60 stars yield a …
On the Nature of Stars with Planets
Reid, I. Neill
We consider the metallicities and kinematics of nearby stars known to have planetary-mass companions in the general context of the overall properties of the local Galactic disk. We have used Strömgren photometry to determine abundances both for the extrasolar planet host stars and for a volume-limited sample of 486 F, G, and K stars selected from …
Transition from Gaseous Compounds to Aerosols in Titan's Atmosphere
McKay, Christopher P.; Lebonnois, Sébastien; Bakes, E. L. O.
We investigate the chemical transition of simple molecules like C 2H 2 and HCN into aerosol particles in the context of Titan's atmosphere. Experiments that synthesize analogs (tholins) for these aerosols can help illuminate and constrain these polymerization mechanisms. Using information available from these experiments, we …
Oscillations above sunspots: Evidence for propagating waves?
O'Shea, E.; Muglach, K.; Fleck, B.
We present results of an analysis of time series data observed in sunspot umbral regions. The data were obtained in the context of the SOHO Joint Observing Program (JOP) 97 in September 2000. This JOP included the Coronal Diagnostic Spectrometer (CDS) and the Michelson Doppler Imaging (MDI) instrument, both part of SOHO, the TRACE satellite and va…