Search Publications
The classical stellar atmosphere problem.
Werner, K.; Dreizler, S.
The authors introduce the classical stellar atmosphere problem and describe in detail its numerical solution. The problem consists of the solution of the radiation transfer equations under the constraints of hydrostatic, radiative and statistical equilibrium (non-LTE). They outline the basic idea of the accelerated lambda iteration (ALI) technique…
The composition and nature of the dust shell surrounding the binary AFGL 4106
Waters, L. B. F. M.; van Loon, J. Th.; Henning, Th. +8 more
We present infrared spectroscopy and imaging of AFGL 4106. The 2.4-5 mu m ISO-SWS spectrum reveals the presence of a cool, luminous star (Teff ~ 3750 K) in addition to an almost equally luminous F star (Teff ~ 7250 K). The 5-195 mu m SWS and LWS spectra are dominated by strong emission from circumstellar dust. We find that th…
3-D magnetic configurations supporting prominences. III. Evolution of fine structures observed in a filament channel
van Driel-Gesztelyi, L.; Aulanier, G.; Schmieder, B. +3 more
On September 25() th 1996, a quiescent filament located near the center disc (S2, E5) was observed on the German VTT (Tenerife) with the MSDP instrument, in the Hα line center and wings. SOHO/MDI line-of-sight magnetograms were co-aligned with the MSDP images, showing the position and evolution of the lateral feet of the filament in the vicinity o…
The delta Scuti star FG Virginis. IV. Mode identifications and pulsation modelling
Garrido, R.; Pamyatnykh, A. A.; Breger, M. +1 more
This paper examines the mode identification and presents pulsation models for FG Vir, for which 24 frequencies have been detected. Histograms of the frequency spacings show peaks which are identified with adjacent radial orders and rotational splitting. Pulsational l values are deduced for eight modes by comparing the observed photometric phase la…
30 years of multi-wavelength observations of 3C 273
Bouchet, P.; Paltani, S.; Stevens, J. A. +14 more
We present a wide multi-wavelength database of most observations of the quasar 3C 273 obtained during the last 30 years. This database is the most complete set of observations available for an active galactic nucleus (AGN). It contains nearly 20 000 observations grouped together into 70 light curves covering 16 orders of magnitude in frequency fro…
Deriving star formation histories: inverting Hertzsprung-Russell diagrams through a variational calculus maximum likelihood method
Gilmore, Gerard; Valls-Gabaud, David; Hernandez, X.
We introduce a new method for solving maximum likelihood problems through variational calculus, and apply it to the case of recovering an unknown star formation history, SFR(t), from the resulting Hertzsprung-Russell (HR) diagram. This approach allows a totally non-parametric solution, which has the advantage of requiring no initial assumptions ab…
Detection of the Red Giant Branch Stars in M82 Using the Hubble Space Telescope
Madore, Barry F.; Sakai, Shoko
We present color-magnitude diagrams and luminosity functions of stars in two halo regions of the irregular galaxy in M82, based on F555W and F814W photometry taken with the Hubble Space Telescope (HST) and Wide Field Planetary Camera 2. The I-band luminosity function shows a sudden jump at I~23.95 mag, which is identified as the tip of the red gia…
Calibration of the Thickness of the Solar Tachocline
Gough, D. O.; Elliott, J. R.
Material circulation in the solar tachocline mixes the tachocline material with the convection zone, which causes the sound speed in and immediately beneath the tachocline to exceed what one would expect from current standard solar models. Calibration against a helioseismic determination of the sound speed from SOI/MDI data of a sequence of solar …
Hubble Space Telescope Fine Guidance Sensor Astrometric Parallaxesfor Three Dwarf Novae: SS Aurigae, SS Cygni, and U Geminorum
Harrison, Thomas E.; Benedict, G. F.; Szkody, Paula +4 more
We report astrometric parallaxes for three well-known dwarf novae obtained using the Fine Guidance Sensors on the Hubble Space Telescope (HST). We found a parallax for SS Aurigae of π=5.00+/-0.64 mas, for SS Cygni we found π=6.02+/-0.46 mas, and for U Geminorum we obtained π=10.37+/-0.50 mas. These represent the first true trigonometric parallaxes…
Infrared Spectroscopy of NGC 4151: Probing the Obscured Ionizing Active Galactic Nucleus Continuum
Lutz, Dieter; Netzer, Hagai; Alexander, Tal +3 more
The Infrared Space Observatory (ISO) Short-Wavelength Spectrometer4 (SWS) infrared spectroscopic observations of the nucleus of Seyfert galaxy NGC 4151, which are described in a companion paper, are used in conjunction with a compilation of UV to IR narrow emission line data to determine the spectral shape of the obscured extreme-UV continuum that…