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| last change Sat, 12 Mar 2011 11:52:50 GMT, U. Hanschur |
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Der älteste Braune Zwerg, 2MASS 1626+3925, auf einer der
Infrarot-Aufnahmen des 3.5-m-Teleskops, die am Calar-Alto-Observatorium im Laufe von mehreren Jahren für die direkte
(trigonometrische) Entfernungsmessung gewonnen wurden.
Quelle: Calar-Alto-Observatorium / ARI / AIP
[web size] [full size]
more at /highlight_archive/scholz_oldest_bd/ (image added 2009-02-12) |
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Amount of line asymmetry measured in the halo TO star HD 74000, for the mean of five Fe I lines having a stratification and a strength similar to the components of the doublet of the Lithium-7 resonance line.
Graph: R. Cayrel et al.
more at /highlight_archive/steffen_li/ (image added 2007-10-25) |
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3D hydrodynamical simulation of convection in the surface layers of a metal-poor star (Teff=6300 K, log g=4.0, [M/H]=-2, representative of HD 74000)). The top face of the rectangular box shows the stellar granulation pattern, as seen in continuum intensity, the side faces show the specific entropy.
Graph: R. Cayrel et al.
more at /highlight_archive/steffen_li/ (image added 2007-10-25) |
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Cepheid Period-Luminosity relation: the angular diameter of the Cepheid l Car determined interferometrically using the VLTI (black circles) and from our Baade-Wesselink method (red crosses). (Kervella et al. 2004)
[web size] [full size]
more at /People/jstorm/ (image added 2006-02-08) |
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Cepheid Period-Luminosity relation: the distances to individual Cepheids in the Large Magellanic Cloud using the old correction to the conversion factor between radial velocity and pulsational velocity. The unphysical difference in distance to short and long period stars is evident. (Gieren et al. 2005)
[web size] [full size]
more at /People/jstorm/ (image added 2006-02-08) |
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The observed photometric colour of UX Ari (dots) as function of its photometric magnitude. The straight lines connecting various plotting symbols represent model calculations. Filled symbols represent models where only dark spots are present on the surface of the primary component, whereas open symbols represent both spots and facular areas. The observations are thus in line with cool spots accompanied by faculae.
Vidar Aarum-Ulvås
more at http://www.aip.de/groups/activity/ (image added 2004-02-14) |
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Epsilon Indi Ba, Bb: the nearest binary brown dwarf
Such multiple brown dwarfs are particularly important because their physical parameters can be accurately determined, and they can serve as key templates in the understanding of sub-stellar sources. Unit Telescope 4 "Yepun" of the VLT on Cerro Paranal, Chile, was pointed to epsilon Indi B on August 13, 2003. NAOS/CONICA broad-band near-infrared adaptive optics images of the epsilon Indi Ba,Bb system. The images are taken in the J, H, and Ks bands, from left to right. Ks covers the longest wavelengths ("reddest") of the three, where adaptive optics works best. The angular resolution of the right image is 0.08 arc seconds which corresponds to resolving a head of a match 10 km away.
M. McCaughrean
more at http://www.aip.de/highlight_archive/mjm_eindi/ (image added 2003-11-20) |
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Epsilon Indi Ba, Bb: the nearest binary brown dwarf
Unit Telescope 4 "Yepun" of the VLT on Cerro Paranal, Chile, was pointed to epsilon Indi B on August 13, 2003. H band spectra of epsilon Indi Ba and Bb. Both objects show signatures of spectral class T which is associated with brown dwarfs. Combining the spectral classification of the sub-stars with their distance from us and the approximate age of the epsilon Indi system, surface temperatures and masses can be estimated. These are 1200-1300 K and 40-50 Jupiter masses for the brighter of the two and 800-900 K and 25-30 Jupiter masses for the fainter one.
M. McCaughrean
more at http://www.aip.de/highlight_archive/mjm_eindi/ (image added 2003-11-20) |
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Differential rotation is a key parameter controlling stellar activity. The figure compares observational and theoretical findings for the rotation frequency variation on the stellar surface as a function of the rotation period and spectral class. The symbols mark the observations for 8 active stars. The lines show theoretical predictions of a series of papers by Rüdiger, Kitchatinov, Küker, and Stix. The slopes of the theoretical lines change from K through G to F stars. Rapidly rotating, young F stars are predicted to possess much stronger differential rotation compared to later spectral classes.
K.G. Strassmeier, M. Weber, T. Granzer, G. Rüdiger, AIP
Zs. Kovari, K. Olah, Konkoly Observatory
J.B. Rice, Brandon University
more at http://www.aip.de/groups/activity/ (image added 2003-10-10) |
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Detection of weak solar-type differential rotation on a young star
We used time-dependent Doppler imaging to reconstruct the latitude dependency of surface rotation on an active star. We found that the equator is rotating faster than the poles with a lap time of ~280 days, i.e. the time the equator needs to lap the pole by one full rotation. As compared to the Sun, this implies a latitudinal shear that is roughly a factor of 3 weaker than on the Sun and at a rotation rate roughly 15 times higher than the Sun's.
K.G. Strassmeier, M. Weber, T. Granzer, G. Rüdiger, AIP
Zs. Kovari, K. Olah, Konkoly Observatory
J.B. Rice, Brandon University
more at http://www.aip.de/groups/activity/ (image added 2003-10-10) |
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We present the first Doppler image of a solar-type G dwarf in the Pleiades open cluster obtaine from high-resolution Gecko CFHT spectra. The star represents the Sun at an age of approximately 100~Myr and could be an important target for further progress in magnetic-braking and angular-momentum-transport theories.
Our image reconstructions were done from a full spectrum inversion with a total of 38 spectral lines simultaneously but we also present single-line inversions using the prominent Li I 6707-A line and the nearby Ca I 6717-A line. The maps reveal cool spots at or near the pole and within the equatorial regions, in contradiction to our predictions from flux-tube modelling that only medium-latitude spots should be seen. The maps also show several warm spots near the equatorial regions but their reality needs to be confirmed. A polar spot is recovered but likely consists of several smaller spots at very high latitudes touching the visible pole instead of a big cap-like spot as seen on some RS CVn binaries.
The image shows a Doppler image of HII 314 from a 20-A piece of spectrum including the Li I 6707A and the Ca I 6717A lines. Maps are plotted in a spherical projection at eight equidistant rotational phases. The temperature scale is indicated and is the same for all projections.
(credits: K.G. Strassmeier, AIP)
more at http://www.aip.de/groups/activity/DI/results.html (image added 2002-12-04) |
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A new neighbour of the Sun, LHS 2090, is discovered from the combination of old high proper motion catalogues with a new near-infrared sky survey (2MASS) and follow-up spectroscopy. The left picture shows the change in position of the newly discovered nearby star (Digitized Sky Surveys, Palomar Schmidt Telescope).
(credits: Scholz, Meusinger Jahreiss)
more at http://www.aip.de/groups/starplan/ (image added 2002-12-04) |
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A new neighbour of the Sun, LHS 2090, is discovered from the combination of old high proper motion catalogues with a new near-infrared sky survey (2MASS) and follow-up spectroscopy. The image shows the spectrum of LHS 2090 (obtained at Calar Alto observatory) in comparison with that of the well-known M6.5 dwarf GJ 1111.
The low-resolution spectrum of LHS 2090 and its large proper motion (0.79 arcsec/yr) classify this star as an M6.5 dwarf. The resulting spectroscopic distance estimate from comparing the infrared JHKs magnitudes of LHS2090 with absolute magnitudes of M6.5 dwarfs is 6.0 +- 1.1 pc assuming an uncertainty in absolute magnitude of +- 0.4 mag.
For more information we refer to our paper: Scholz, Meusinger, Jahreiss, A&A, 374 (2001), L12 ( credit: Scholz, Meusinger Jahreiss )
more at http://www.aip.de/groups/starplan/ (image added 2002-12-04) |
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Long-term photometry of EK Draconis
EK Dra (HD 129333) is a solar-type (G1.5V), but young single star
belonging to the Pleiades moving group (age <100 mill. yr). It rotates
ten times faster than the sun and is very active. Doppler imaging
revealed a persistent polar spot. A long-term photographic photometry
on 1400 scanned plates of the Sonneberg plate archive taken between
1958 and 1995 was performed.
The comparison stars (dashed lines) show no significant variations.
EK Draconis, however, shows a B-brightness fading of 0.006 magnitudes
per year after about 1975.
H.-E. Fröhlich, R. Tschäpe, G. Rüdiger, K.G. Strassmeier
more at http://www.aip.de/groups/activity/DI/maps/ (image added 2003-01-29) |
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