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The EUV helium spectrum in the quiet Sun: A by-product of coronal emission?
Andretta, V.; Del Zanna, G.; Jordan, S. D.
In this paper we test one of the mechanisms proposed to explain the intensities and other observed properties of the solar helium spectrum, and in particular of its Extreme-Ultraviolet (EUV) resonance lines. The so-called Photoionisation-Recombination (P-R) mechanism involves photoionisation of helium atoms and ions by EUV coronal radiation, follo…
Abundant gas-phase H2O in absorption toward massive protostars
van Dishoeck, E. F.; Boonman, A. M. S.
We present infrared spectra of gas-phase H2O around 6 mu m toward 12 deeply embedded massive protostars obtained with the Short Wavelength Spectrometer on board the Infrared Space Observatory (ISO). The nu2 ro-vibrational band has been detected toward 7 of the sources and the excitation temperatures indicate an origin in the …
The recent X-ray history of NGC 5506
Perola, G. C.; Bianchi, S.; Guainazzi, M. +2 more
We present a detailed discussion of the spectral and spatial components of NGC 5506, based on XMM-Newton, Chandra and BeppoSAX observations. The overall picture consists of a nucleus absorbed by cold gas with column density of ~1022 cm-2 and surrounded by a Compton-thick torus, whose existence is inferred by a cold reflection…
A precise HST parallax of the cataclysmic variable EX Hydrae, its system parameters, and accretion rate
Gänsicke, B. T.; Beuermann, K.; McArthur, B. E. +2 more
Using the HST Fine Guidance Sensor, we have measured a high precision astrometric parallax of the cataclysmic variable EX Hydrae, π=15.50 +/- 0.29 mas. From the wavelength-integrated accretion-induced energy flux, we derive a quiescent accretion luminosity for EX Hya of Lacc =(2.6+/- 0.6)× 1032 erg s-1. The quiesce…
Ultraviolet and Optical Properties of Narrow-Line Seyfert 1 Galaxies
Shields, Joseph C.; Constantin, Anca
Narrow-line Seyfert 1 galaxies (NLS1s) are remarkable for their extreme continuum and emission-line properties, which are not well understood. New results bearing on the spectroscopic characteristics of these objects are presented here, with the aim of establishing their typical UV and optical spectral behavior. We employ Hubble Space Telescope ob…
The Tully-Fisher relation of cluster spirals at z= 0.83
Aragón-Salamanca, Alfonso; Hjorth, Jens; Milvang-Jensen, Bo +2 more
We present the rest-frame B-band Tully-Fisher relation for a sample of 8 cluster spiral galaxies at z= 0.83 and 19 field spirals at z= 0.15-0.90 based on Very Large Telescope (VLT) spectroscopy and Hubble Space Telescope (HST) photometry. No strong difference is detected between the cluster and the field galaxies, but we find some evidence that th…
Observational Evidence of a Magnetic Flux Rope Eruption Associated with the X3 Flare on 2002 July 15
Zhang, Hongqi; Liu, Yu; Wang, Haimin +2 more
We present the study of an eruption from the low solar atmosphere (photosphere/chromosphere) as seen in Transition Region and Coronal Explorer 1600 Å images and with the Solar and Heliospheric Observatory Michelson Doppler Imager. The eruption reached its maximum at 20:08 UT on 2002 July 15 in the NOAA Active Region 10030 (N19°, W01°), accompanied…
Cassini between Venus and Earth: Detection of interstellar dust
Dikarev, V.; Kempf, S.; Krüger, H. +5 more
We report the successful in situ measurement of interstellar dust particles inside the orbit of the Earth with the Cosmic Dust Analyzer (CDA) on the Cassini spacecraft. The impact ionization subsystem of the CDA is similar to the instruments on Ulysses and Galileo. As the heliocentric velocity and the direction of the interstellar dust flux are we…
On the Origin of the Basal Emission from Stellar Atmospheres: Analysis of Solar C II Lines
Judge, Philip G.; Carlsson, Mats; Stein, Robert F.
Combining a variety of data with radiation hydrodynamic simulations, we examine the heating of the Sun's internetwork chromosphere and the hypothesis that the chromospheric ``basal'' emission arises because of acoustic wave dissipation. We focus on the 2s2p22D-2s22p2Po multiplet of C II near 1…
The Sun and Heliosphere at Solar Maximum
Krupp, N.; Balogh, A.; Geiss, J. +9 more
Recent Ulysses observations from the Sun's equator to the poles reveal fundamental properties of the three-dimensional heliosphere at the maximum in solar activity. The heliospheric magnetic field originates from a magnetic dipole oriented nearly perpendicular to, instead of nearly parallel to, the Sun's rotation axis. Magnetic fields, solar wind,…