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  • 201.
    Davidsson, Björn
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Skorov, Yuri
    On the light-absorbing surface layer of cometary nuclei: II. Thermal modeling2002In: Icarus, ISSN 0019-1035, Vol. 159, no 1, p. 239-258Article in journal (Refereed)
    Abstract [en]

    The classical way to treat absorption of solar light in thermophysical modelling of cometary nuclei (and other ice-rich bodies such as jovian satellites), has been to assume complete opaqueness of the surface material. However, as shown by Davidsson and Skorov (2002), substantial light penetration can occur in porous ice even if it is very dusty, implying that gradual absorption of energy in a surface layer should be accounted for.

    We present a thorough comparison between a surface energy absorption model and a layer energy absorption model, for various combinations of heliocentric distances, conductivities, opacities, pore sizes and rotational periods relevant for cometary nuclei, by fully solving the coupled differential equations of heat transfer and gas diffusion. We find substantial differences between the models in terms of gas production rate, thermal lag angle, surface temperature, and the origin of coma molecules. For example, the surface energy absorption model overestimates the total gas production by a factor 2-7, underestimates the lag angle by a factor 2-3, and places the origin of coma molecules at the surface, instead of the near--surface interior.

  • 202. de Laverny, P.
    et al.
    Abia, C.
    Dominguez, I.
    Plez, B.
    Straniero, O.
    Wahlin, R.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Eriksson, K.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Jorgensen, U. G.
    Chemical analysis of carbon stars in the Local Group2006In: Astronomy and Astrophysics, Vol. 446, p. 1107-Article in journal (Refereed)
  • 203. de Laverny, P.
    et al.
    Abia, C.
    Dominguez, I
    Plez, B
    Straniero, O
    Wahlin, Rurik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Eriksson, Kjell
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Jorgensen, U.G.
    Abundances of s-elements in Extragalactic Carbon Stars2005In: From Lithium to Uranium: Elemental Tracers of Early Cosmic Evolution: IAU Symposium 228, 2005, p. p. 533-534Conference paper (Other scientific)
  • 204. De Ridder, J.
    et al.
    Telting, J. H.
    Balona, L. A.
    Handler, G.
    Briquet, M.
    Daszyńska-Daszkiewicz, J.
    Lefever, K.
    Korn, Andreas
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Heiter, Ulrike
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Aerts, C.
    Asteroseismology of the β Cephei star ν Eridani: III. Extended frequency analysis and mode identification2004In: Monthly Notices of the Royal Astronomical Society, Vol. 351, p. 324-Article in journal (Refereed)
  • 205. De Silva, G. M.
    et al.
    Freeman, K. C.
    Asplund, M.
    Bland-Hawthorn, J.
    Bessell, M. S.
    Collet, Remo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Chemical homogeneity in collinder 261 and implications for chemical tagging2007In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 133, no 3, p. 1161-1175Article in journal (Refereed)
    Abstract [en]

    This paper presents abundances for 12 red giants of the old open cluster Collinder 261 based on spectra from the Very Large Telescope UVES. Abundances were derived for Na, Mg, Si, Ca, Mn, Fe, Ni, Zr, and Ba. We find that the cluster has a solar-level metallicity of [Fe/H] = -0.03 dex. However, most alpha- and s-process elements were found to be enhanced. The star-to-star scatter was consistent with the expected measurement uncertainty for all elements. The observed rms scatter is as follows: Na = 0.07, Mg = 0.05, Si = 0.06, Ca = 0.05, Mn = 0.03, Fe = 0.02, Ni = 0.04, Zr = 0.12, and Ba = 0.03 dex. The intrinsic scatter was estimated to be less than 0.05 dex. Such high levels of homogeneity indicate that chemical information remains preserved in this old open cluster. We use the chemical homogeneity we have now established in Cr 261, the Hyades, and the HR 1614 moving group to examine the uniqueness of the individual cluster abundance patterns, i.e., chemical signatures. We demonstrate that the three studied clusters have unique chemical signatures and discuss how other such signatures may be searched for in the future. Our findings support the prospect of chemically tagging disk stars to common formation sites in order to unravel the dissipative history of the Galactic disk.

  • 206. de Val-Borro, M.
    et al.
    Edgar, R. G.
    Artymowicz, P.
    Ciecielag, P.
    Cresswell, P.
    D'Angelo, G.
    Delgado-Donate, E. J.
    Dirksen, G.
    Fromang, S.
    Gawryszczak, A.
    Klahr, H.
    Kley, W.
    Lyra, Wladimir
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Masset, F.
    Mellema, G.
    Nelson, R. P.
    Paardekooper, S. -J
    Peplinski, A.
    Pierens, A.
    Plewa, T.
    Rice, K.
    Schaefer, C.
    Speith, R.
    A comparative study of disc-planet interaction2006In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 370, no 2, p. 529-558Article in journal (Refereed)
    Abstract [en]

    We perform numerical simulations of a disc-planet system using various grid-based and smoothed particle hydrodynamics (SPH) codes. The tests are run for a simple setup where Jupiter and Neptune mass planets on a circular orbit open a gap in a protoplanetary disc during a few hundred orbital periods. We compare the surface density contours, potential vorticity and smoothed radial profiles at several times. The disc mass and gravitational torque time evolution are analysed with high temporal resolution. There is overall consistency between the codes. The density profiles agree within about 5 per cent for the Eulerian simulations. The SPH results predict the correct shape of the gap although have less resolution in the low-density regions and weaker planetary wakes. The disc masses after 200 orbital periods agree within 10 per cent. The spread is larger in the tidal torques acting on the planet which agree within a factor of 2 at the end of the simulation. In the Neptune case, the dispersion in the torques is greater than for Jupiter, possibly owing to the contribution from the not completely cleared region close to the planet.

  • 207. de Val-Borro, Miguel
    et al.
    Edgar, Richard
    Artymowicz, Pawel
    Ciecilag, P.
    Cresswell, P.
    D'Angelo, Genaro
    Delgado-Donate, Eduardo
    Dirksen, G.
    Fromang, Sebastien
    Gawryszczak, A.
    Klahr, Hubert
    Kley, Willy
    Lyra, Wladimir
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Theoretical Astrophysics.
    Masset, Frederic
    Mellema, Garrelt
    Nelson, Richard
    Paardekooper, Simje-Jan
    Peplinski, Adam
    Pierens, A.
    Plewa, T.
    Rice, Ken
    Schäfer, C.
    Speith, R.
    A comparative study of disk-planet interaction2006In: Monthly Notices of the Royal Astronomic Society, Vol. 370, no 529, p. 29-Article in journal (Refereed)
    Abstract [en]

    We perform numerical simulations of a disc–planet system using various grid-based and smoothed particle hydrodynamics (SPH) codes. The tests are run for a simple setup where Jupiter and Neptune mass planets on a circular orbit open a gap in a protoplanetary disc during a few hundred orbital periods. We compare the surface density contours, potential vorticity and smoothed radial profiles at several times. The disc mass and gravitational torque time evolution are analysed with high temporal resolution. There is overall consistency between the codes. The density profiles agree within about 5 per cent for the Eulerian simulations. The SPH results predict the correct shape of the gap although have less resolution in the low-density regions and weaker planetary wakes. The disc masses after 200 orbital periods agree within 10 per cent. The spread is larger in the tidal torques acting on the planet which agree within a factor of 2 at the end of the simulation. In the Neptune case, the dispersion in the torques is greater than for Jupiter, possibly owing to the contribution from the not completely cleared region close to the planet.

  • 208. Decin, L.
    et al.
    Blomme, L.
    Reyniers, M.
    Ryde, N.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Hinkle, K. H.
    de Koter, A.
    Probing the mass-loss history of the unusual Mira variable R Hydrae through its infrared CO wind2008In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 484, no 2, p. 401-U55Article in journal (Refereed)
    Abstract [en]

    Context. The unusual Mira variable R Hya is well known for its declining period between ad 1770 and 1950, which is possibly attributed to a recent thermal pulse. Aims. The goal of this study is to probe the circumstellar envelope (CSE) around R Hya and to check for a correlation between the derived density structure and the declining period. Methods. We investigate the CSE around R Hya by performing an in-depth analysis of (1.) the photospheric light scattered by three vibration-rotation transitions in the fundamental band of CO at 4.6 mu m; and (2.) the pure rotational CO J = 1-0 through 6-5 emission lines excited in the CSE. The vibrational-rotational lines trace the inner CSE within 3.5 '', whereas the pure rotational CO lines are sensitive probes of the cooler gas further out in the CSE. Results. The combined analysis bear evidence of a change in mass-loss rate some 220 yr ago (at similar to 150 R-* or similar to 1.9 arcsec from the star). While the mass-loss rate before ad 1770 is estimated to be similar to 2 x 10(-7) M-circle dot/yr, the present day mass-loss rate is a factor of similar to 20 lower. The derived mass-loss history nicely agrees with the mass-loss rate estimates by Zijlstra et al. (2002) on the basis of the period decline. Moreover, the recent detection of an AGB-ISM bow shock around R Hya at 100 arcsec to the west by Wareing et al. (2006) shows that the detached shell seen in the 60 mu m IRAS images can be explained by a slowing-down of the stellar wind by surrounding matter and that no extra mass-loss modulation around 1-2 arcmin needs to be invoked. Conclusions. Our results give empirical evidence to the thermal-pulse model, which is capable of explaining both the period evolution and the mass-loss history of R Hya.

  • 209.
    Decin, L.
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Vandenbussche, B.
    Waelkens, C.
    Decin, G.
    Eriksson, K.
    Gustafsson, B.
    Plez, B.
    Sauval, A. J.
    ISO-SWS calibration and the accurate modelling of cool-star atmospheres. IV. G9 to M2 stars2003In: Astronomy & Astrophysics, Vol. 400, p. 709-727Article in journal (Refereed)
  • 210.
    Decin, L.
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Vandenbussche, B.
    Waelkens, C.
    Eriksson, K.
    Gustafsson, B.
    Plez, B.
    Sauval, A. J.
    ISO-SWS calibration and the accurate modelling of cool-star atmospheres. III. A0 to G2 stars2003In: Astronomy & Astrophysics, Vol. 400, p. 695-708Article in journal (Refereed)
  • 211.
    Decin, L.
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Vandenbussche, B.
    Waelkens, C.
    Eriksson, K.
    Gustafsson, B.
    Plez, B.
    Sauval, A. J.
    Hinkle, K.
    ISO-SWS calibration and the accurate modelling of cool-star atmospheres. II. General results2003In: Astronomy & Astrophysics, Vol. 400, p. 679-694Article in journal (Refereed)
  • 212.
    Decin, L
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Waelkens, C
    Eriksson, K
    Gustafsson, B
    Plez, B
    Sauval, AJ
    Van, Assche W
    Vandenbussche, B
    ISO-SWS calibration and the accurate modelling of cool-star atmospheres - I. Method2000In: ASTRONOMY AND ASTROPHYSICS, ISSN 0004-6361, Vol. 364, no 1, p. 137-156Article in journal (Refereed)
    Abstract [en]

    A detailed spectroscopic study of the ISO-SWS data of the red giant alpha Tau is presented, which enables not only the accurate determination of the stellar parameters of alpha Tau, but also serves as a critical review of the ISO-SWS calibration. This stu

  • 213. Decin, Leen
    et al.
    Eriksson, Kjell
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Theoretical model atmosphere spectra used for the calibration of infrared instruments2007In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 472, no 3, p. 1041-1053Article in journal (Refereed)
    Abstract [en]

    Context: One of the key ingredients in establishing the relation between input signal and output flux from a spectrometer is accurate determination of the spectrophotometric calibration. In the case of spectrometers onboard satellites, the accuracy of this part of the calibration pedigree is ultimately linked to the accuracy of the set of reference spectral energy distributions (SEDs) that the spectrophotometric calibration is built on. Aims: In this paper, we deal with the spectrophotometric calibration of infrared (IR) spectrometers onboard satellites in the 2 to 200 μm wavelength range. We aim at comparing the different reference SEDs used for the IR spectrophotometric calibration. The emphasis is on the reference SEDs of stellar standards with spectral type later than A0, with special focus on the theoretical model atmosphere spectra. Methods: Using the MARCS model atmosphere code, spectral reference SEDs were constructed for a set of IR stellar standards (A dwarfs, solar analogs, G9-M0 giants). A detailed error analysis was performed to estimate proper uncertainties on the predicted flux values. Results: It is shown that the uncertainty on the predicted fluxes can be as high as 10%, but in case high-resolution observational optical or near-IR data are available, and IR excess can be excluded, the uncertainty on medium-resolution SEDs can be reduced to 1-2% in the near-IR, to ~3% in the mid-IR, and to ~5% in the far-IR. Moreover, it is argued that theoretical stellar atmosphere spectra are at the moment the best representations for the IR fluxes of cool stellar standards. Conclusions: When aiming at a determination of the spectrophotometric calibration of IR spectrometers better than 3%, effort should be put into constructing an appropriate set of stellar reference SEDs based on theoretical atmosphere spectra for some 15 standard stars with spectral types between A0 V and M0 III.

  • 214. DeKayser, J.
    et al.
    Gustafsson, Georg
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Space and Plasma Physics.
    Roth, M.
    Darrouzet, F.
    Dunlop, M.
    Rème, H.
    Fazakerley, A.
    Décréau, P.
    Cornilleau-Wehrling, N.
    Reconstruction of the magnetopause and low-latitude boundary layer topology using Cluster multi-point measurements2004In: Ann. Geophys., Vol. 22, p. 2381-2389Article in journal (Refereed)
  • 215.
    Delgado, DGA
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Olofsson, H
    Schwarz, HE
    Eriksson, K
    Gustafsson, B
    Imaging of detached shells around the carbon stars R Scl and U Ant through scattered stellar light2001In: ASTRONOMY & ASTROPHYSICS, ISSN 1432-0746, Vol. 372, no 3, p. 885-898Article in journal (Refereed)
    Abstract [en]

    We present the first optical images of scattered light from large, detached gas/dust shells around two carbon stars, R Scl and U Ant, obtained in narrow band filters centred on the resonance lines of neutral K and Na, and in a Stromgren b filter (only U A

  • 216. Derouich, M
    et al.
    Barklem, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Spin depolarizing effect in collisions with neutral hydrogen: II. Application to simple/complex ions in spherically symmetric states2007In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 462, no 3, p. 1171-1177Article in journal (Refereed)
    Abstract [en]

    Aims: We develop an accurate and general semi-classical formalism that deals with the definition and the calculation of the collisional depolarizing constants of the levels of simple and complex singly-ionized atoms in arbitrary s-states perturbed by collisions with hydrogen atoms. The case of ions with hyperfine structure is investigated fully. Methods: We obtain potential energy curves based on the MSMA exchange perturbation theory by employing the Unsöld approximation. These potentials enter the Schrödinger equation to determine the collisional T-matrix elements in a semi-classical description. We use the T-matrix elements for the calculation of the collisional depolarization rates of simple atoms. Then, we use these rates to calculate the collisional coefficients in cases of ions with hyperfine structure. Results: We evaluate the collisional depolarization and polarization transfer rates of the ground levels of the ionized alkaline earth metals Be II, Mg II, Ca II, Sr II, and Ba II. We study the variation of the collisional rates with effective principal quantum number n* characterizing an arbitrary s-state of a perturbed simple ion. We find that the collisional rates for simple ions obey simple power laws as a function of n^*. We present direct and indirect formulations of the problem of the calculation of the depolarization and polarization transfer rates of levels of complex atoms and hyperfine levels from those for simple atoms. In particular, the indirect method allows a quick and simple calculation with its simple power-law relations. For the state 4s ^2S{1/2} of Ca II, our computed rate of the destruction of orientation differs from existing quantum chemistry calculations by only 4% at T=5000 K.

  • 217. Derouich, M.
    et al.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Sahal-Bréchot, S.
    Spin depolarizing effect in collisions of simple/complex atoms in spherically symmetric states with neutral hydrogen2005In: Astronomy and Astrophysics, Vol. 441, p. 395-406Article in journal (Refereed)
  • 218. Derouich, M.
    et al.
    Sahal-Bréchot, S.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Collisional depolarization and transfer rates of spectral lines by atomic hydrogen. II. Application to d states of neutral atoms2003In: Astronomy & Astrophysics, Vol. 409, p. 369-373Article in journal (Refereed)
  • 219. Derouich, M.
    et al.
    Sahal-Bréchot, S.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Collisional depolarization and transfer rates of spectral lines by atomic hydrogen.: IV: Application to ionised atoms2004In: Astronomy and Astrophysics, Vol. 426, p. 707-715Article in journal (Refereed)
  • 220. Derouich, M.
    et al.
    Sahal-Bréchot, S.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Collisional depolarization of the lines of complex atoms/ions by neutral hydrogen2005In: Astronomy and Astrophysics, Vol. 434, p. 779-784Article in journal (Refereed)
  • 221. Derouich, M.
    et al.
    Sahal-Bréchot, S.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Depolarization rates of spectral lines of neutral and singly ionised atoms by isotropic collisions with hydrogen atoms2003In: SF2A-2003: Semaine de l'Astrophysique Française, meeting held in Bordeaux, France, June 16-20, 2003., 2003, p. p. 89-Conference paper (Other scientific)
  • 222. Derouich, M.
    et al.
    Sahal-Bréchot, S.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    On the collisional depolarization and transfer rates of spectral lines by atomic hydrogen.: III: Application to f states of neutral atoms2004In: Astronomy and Astrophysics, Vol. 414, p. 373-376Article in journal (Refereed)
  • 223. Derouich, M.
    et al.
    Sahal-Bréchot, S.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    O'Mara, B. J.
    Semi-classical theory of collisional depolarization of spectral lines by atomic hydrogen I. Application to p states of neutral atoms2003In: Astronomy & Astrophysics, Vol. 404, p. 763-773Article in journal (Refereed)
  • 224. Destree, Joshua D.
    et al.
    Snow, Theodore P.
    Eriksson, Kjell
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    The Presence of Diffuse Interstellar Bands in the Spectra of Cool Stars2007In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 664, no 2, p. 909-914Article in journal (Refereed)
    Abstract [en]

    Data from the Kitt Peak National Observatory (KPNO) coudé feed telescope were used to analyze the strength of three well-known diffuse interstellar bands (DIBs; 5780, 5797, and 6614 Å). Ten mid-A, mid-F, and mid-G stars with moderate reddening (EB-V=0.2-1.2) were observed, along with one reddened B0 dwarf for comparison. Synthetic spectra were calculated to remove the interference of stellar features. We report the detection of all three DIBs in A, F, and G stars. We also find the correlation of DIB strengths with E(B-V), in our sight lines, to be consistent with previous results from Herbig (1993), demonstrating that DIB strength is not dependent on the spectral type of the target star.

  • 225.
    Dhillon, R., Stocker, A., Warrington, E. and Eglitis, P.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    An experimentally based investigation on the refinement and development of mid-latitude trough models over Europe-description and initial measurements.2001In: Eleventh International Conference on Antennas and Propagation (IEE Conf. Publ.No.480), 2001, p. 155-Conference paper (Other scientific)
    Abstract [en]

    A new experiment to examine the propagation characteristics of radiowaves propagating through the mid-latitude ionospheric trough region has been described. The aim of this new investigation is (a) to determine experimentally the accuracy of the currently

  • 226. Donaldson Hanna, Kerri
    et al.
    Warell, Johan
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Mercury and the Moon: Initial Findings from Mid-Infrared Spectroscopic Measurements of the Surface2007Conference paper (Other (popular scientific, debate etc.))
    Abstract [en]

    Mid-infrared spectroscopic measurements from 8.2-12.7 μm of Mercury and the Moon obtained with MIRSI (Mid-Infrared Spectrometer and Imager) at the NASA Infrared Telescope Facility (IRTF) are presented

  • 227.
    Dorch, S.B.F
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Freytag, Bernd
    Does Betelgeuse have a Magnetic Field?2002In: Modelling of Stellar Atmospheres, IAU Symposium 210, San Francisco: The Astronomical Society of the Pacific , 2002Conference paper (Other scientific)
    Abstract [en]

    Betelgeuse (alpha Ori) is an example of a nearby cool super-giant (M1--2 Ia--Iab) that displays temporal brightness fluctuations and irregular surface structures. Recent numerical simulations by Freytag and collaborators of the entire star under realistic

  • 228. Drake, N.A.
    et al.
    Nesvacil, N.
    Hubrig, S.
    Kochukhov, Oleg
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    de la Reza, R.
    Polosukhina, N.
    Gonzales, J.F.
    Spectroscopic analysis of chemically peculiar stars: abundance determination of lithium and some rare earth elements2005In: IAUS 228, From Lithium to Uranium: Elemental Tracers of Early Cosmic Evolution, 2005, p. 89-Conference paper (Other scientific)
  • 229.
    Décréau, P.M.E. , Fergeau, P., Krasnosels'kikh, V., Le Guirriec, E., Lévêque , M., Martin, Ph. , Randriamboarison, O., Rauch, J. L., Sené, F. X., Séran, H. C., Trotignon, J.G. , Canu, P., Cornilleau, N., de Féraudy, H., Alleyne, H. , Yearby, K., Mögensen
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Early results from the Whisper instrument on Cluster: an overview.2001In: Annales Geophysicae, Vol. 19, no 10, p. . 1241-1258Article in journal (Refereed)
    Abstract [en]

    The Whisper instrument yields two data sets: (i) the electron density determined via the relaxation sounder, and (ii) the spectrum of natural plasma emissions in the frequency band 2-80 kHz. Both data sets allow for the three-dimensional exploration of th

  • 230.
    Edvardsson, Bengt
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Abundances in the Galactic Disk2002In: Cosmic chemical evolution. Proceedings of the 187th Symposium of the International Astronomical Union, Vol. 187, p. 91-96Article, book review (Other scientific)
    Abstract [en]

    I will constrain myself to discussion of abundances and abundance gradients in the local Galactic Disk and continue with the scatter in these abundances, presently and historically.

  • 231.
    Edvardsson, Bengt
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Faculty of Science and Technology, Astronomical observatory.
    Det kosmiska kretsloppet - om stjärnornas liv och atomernas historia2000Other (Other (popular scientific, debate etc.))
  • 232.
    Eliasson, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Outflow boundary conditions for the Fourier transformed one-dimensional Vlasov–Poisson system2001In: Journal of Scientific Computing, ISSN 0885-7474, E-ISSN 1573-7691, Vol. 16, p. 1-28Article in journal (Refereed)
  • 233.
    Eliasson, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Outflow boundary conditions for the Fourier transformed two-dimensional Vlasov equation2002In: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 181, p. 98-125Article in journal (Refereed)
  • 234.
    Emma, Olsson
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Theoretical Astrophysics.
    Haensel, P.
    Pethick, C.J.
    Static response of fermi liquids with tensor interactions2004In: PhRvC, Vol. 8Article in journal (Refereed)
  • 235.
    Engwall, Erik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Cold magnetospheric plasma flows: Properties and interaction with spacecraft2006Licentiate thesis, monograph (Other scientific)
  • 236.
    Engwall, Erik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Numerical Studies of Spacecraft-Plasma Interaction: Simulations of Wake Effects on the Cluster Electric Field Instrument EFW2003Report (Other scientific)
    Abstract [en]

    The Cluster satellites are designed for scientific exploration of fields, waves and particles in our space environment. Since their launch three years ago they have provided valuable information from different regions in space. The interpretation of the d

  • 237.
    Engwall, Erik
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Space Plasma Physics.
    Eriksson, Anders I.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Space Plasma Physics.
    Cold magnetospheric plasma flows and spacecraft wakes: PicUp3D simulations and Cluster data2005In: In Proceedings of the 9th International Spacecraft Science Technology Conference (SCTC-9), 2005, 2005Conference paper (Refereed)
  • 238.
    Engwall, Erik
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Space Plasma Physics.
    Eriksson, Anders I.
    Cold magnetospheric plasma flows and spacecraft wakes: PicUp3D simulations and Cluster data2005In: Proceedings of the 7th International Symposium for Space Simulations (ISSS-7), 2005, 2005Conference paper (Other scientific)
  • 239.
    Engwall, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Double-Probe Measurements in Cold Tenuous Space Plasma Flows2006In: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 34, no 5:2, p. 2071-2077Article in journal (Refereed)
    Abstract [en]

    Cold flowing tenuous plasmas are common in the terrestrial magnetosphere, particularly in the polar cap and tail lobe regions, which are filled by the supersonic plasma flow known as the polar wind. Electric field measurements with double-probe instruments in these regions suffer mainly from two error sources: 1) an apparent sunward electric field due to photoemission asymmetries in the probe-boom system and 2) an enhanced negatively charged wake forming behind the spacecraft, which will affect the probe measurements. The authors investigate these effects experimentally by Fourier analysis of the spin signature from the double-probe instrument Electric Fields and Waves (EFW) on the Cluster spacecraft. They show that while the signature due to photoemission asymmetry is very close to sinusoidal, the wake effect is characterized by a spectrum of spin harmonics. The Fourier decomposition can therefore be used for identifying wake effects in the data. As a spin-off, the analysis has also given information on the cold flowing ion population.

  • 240.
    Engwall, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Dandouras, Iannis
    Centre d’Etude Spatiale des Rayonnements, Centre National de la Recherche Scientifique, Toulouse, Toulouse, France.
    Paschmann, Goetz
    International Space Science Institute, Bern, Switzerland..
    Quinn, Jack
    Center for Space Physics, Boston University, Boston, Massachusetts, USA..
    Torkar, Klaus
    Space Research Institute of the Austrian Academy of Science, Graz, Austria..
    Low-energy (order 10 eV) ion flow in the magnetotail lobes inferred from spacecraft wake observations2006In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 33, p. L06110-1-L06110-4Article in journal (Refereed)
    Abstract [en]

    Cold ionospheric ions with eV energies are common inthe magnetosphere and can travel far out in the magnetotail.However, they are difficult to measure with conventional ionspectrometers mounted on spacecraft, since the potential of asunlit spacecraft often reaches several tens of volts. In thispaper we present two alternative methods of measuring thecold-ion flow with the Cluster spacecraft and apply them onone case in the magnetotail at 18 RE: 1. Ion spectrometer incombination with artificial spacecraft potential control;2. Deriving ion flow velocity (both perpendicular andparallel) from electric field instruments. The secondmethod takes advantage of the effect on the doubleprobeinstrument of the wake formed behind a spacecraftin a plasma flow. The results from the two methods showgood agreement and are also consistent with polar windmodels and previous measurements at lower altitudes,confirming the continuation of low-energy ion outflows.

  • 241.
    Engwall, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Forest, Julien
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wake formation behind positively charged spacecraft in flowing tenuous plasmas2006In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, no 6, article id 062904Article in journal (Refereed)
    Abstract [en]

    Spacecraft in tenuous plasmas become positively charged because of photoelectron emission. If the plasma is supersonically drifting with respect to the spacecraft, a wake forms behind it. When the kinetic energy of the positive ions in the plasma is not sufficient to overcome the electrostatic barrier of the spacecraft potential, they scatter on the potential structure from the spacecraft rather than get absorbed or scattered by the spacecraft body. For tenuous plasmas with Debye lengths much exceeding the spacecraft size, the potential structure extends far from the spacecraft, and consequently in this case the wake is of transverse dimensions much larger than the spacecraft. This enhanced wake formation process is demonstrated by theoretical analysis and computer simulations. Comparison to observations from the Cluster satellites shows good agreement.

  • 242.
    Engwall, Erik
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Eriksson, Anders I.
    Pedersen, A.
    Forest, J.
    Paschmann, G.
    Quinn, J.
    Torbert, R.
    Torkar, K.
    Wake effects on positively charged spacecraft in tenuous plasmas2004In: Proceedings of the 8th Space-craft Charging Technology Conference, 2004Conference paper (Other scientific)
  • 243.
    Engwall, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Eriksson, Anders
    Pedersen, Arne
    Forest, Julien
    Paschmann, Goetz
    Quinn, Jack
    Torbert, Roy
    Torkar, Klaus
    Wake effects on positively charged spacecraft in flowingtenuous plasmas: Cluster observations and modeling2003In: Proceedings of the 8th Spacecraft Charging Technology Conference, Huntsville, NASA , 2003Conference paper (Other academic)
    Abstract [en]

    Comparison between electric field measurements made by the double-probe and electron drift instruments on the Cluster satellites have revealed significant perturbations in the signals from the electrostatic probes when Cluster is on magnetic field lines a

  • 244.
    Erikson, A
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Mottola, S
    Lagerros, JSV
    Lindgren, M
    Piironen, J
    Oja, T
    Hahn, G
    Lagerkvist, CI
    Harris, AW
    Nathues, A
    Neukum, G
    The near-Earth objects follow-up program - III. 3 lightcurves for 12 objects from 1992 and 19952000In: ICARUS, ISSN 0019-1035, Vol. 147, no 2, p. 487-497Article in journal (Refereed)
    Abstract [en]

    In this paper we present lightcurves and physical parameters for nine near-Earth objects (NEOs) (433 Eros, 1917 Cuyo, 2368 Beltrovata, 3753 Cruithne, 4769 Castalia, 4953 1990 MU, 6491 1991 OA, 1995 EK1, and 1995 FJ) and three Mars crossers (5738 Billpicke

  • 245.
    Erikson, Anders
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Skoglöv, Erik
    Obliquity Evolution of a Planet in the 47 UMa Habitable Zone2003In: Planetenbildung: Das Sonnensystem und extrasolare Planeten, Weimar, 19-21 Feb., 2003, Thuringer Landessternwarte Tautenburg, 2003Conference proceedings (editor) (Other scientific)
  • 246.
    Erikson, Anders
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Skoglöv, Erik
    Planetary Obliquity Evolution in the 47 UMa Habitable Zone2003In: XXVIII General Assembly of the European Geophysical Society, Nice, France, 7-11 Apr., 2003, European Geophysical Society, 2003Conference proceedings (editor) (Other scientific)
  • 247.
    Erikson, Anders
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Skoglöv, Erik
    Planetary spin-axis evolution in the 47 UMa habitable zone2003In: Toward other Earths-Darwin/TPF and the search for Extrasolar Terrestrial Planets, Proceedings, April 22-25 2003, Heidelberg, Germany, MPI fur Astronomie and European Space Agency, 2003Conference proceedings (editor) (Other scientific)
  • 248.
    Eriksson, Anders
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Engwall, Erik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Prakash, R.
    Daldorff, Lars
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Torbert, R.
    Making use of spacecraft-plasma interactions: determining tenous plasma winds from wake observations and numerical simulations2007In: Proceedings of the 10th Spacecraft Charging Technology Conference, 2007Conference paper (Other scientific)
  • 249.
    Eriksson, Anders I.
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Space Plasma Physics.
    Wahlund, Jan-Erik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Space Plasma Physics.
    Charging of a conductive spacecraft in the auroral zone.2005In: Proceedings of the 9th International Spacecraft Charging Technology Conference (SCTC-9), 2005, 2005Conference paper (Other (popular scientific, debate etc.))
  • 250.
    Eriksson Hans G., Wahlberg Christer
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Effect of combined triangularity and ellipticity on the stability limit of the ideal internal kink mode in a tokamak2002In: PHYSICS OF PLASMAS, ISSN 1070-664X, Vol. 9, no 5, p. 1606-1621Article in journal (Refereed)
    Abstract [en]

    The effect of combined triangular and elliptical shaping of the plasma cross section on the stability limit of the ideal, internal kink mode in a tokamak is analyzed by means of a computer algebra expansion of the magnetohydrodynamic equations. The work e

2345678 201 - 250 of 1015
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