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  • 1
    Electronic Resource
    Electronic Resource
    Asteroid 45 Eugenia: Lightcurves and the pole orientation
    Amsterdam : Elsevier
    Icarus 73 (1988), S. 314-323 
    Details
    ISSN: 0019-1035
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0019-1035(88)90101-7
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  • 2
    Electronic Resource
    Electronic Resource
    Asteroid 532 Herculina: Lightcurves, pole orientation and a model
    Amsterdam : Elsevier
    Icarus 69 (1987), S. 354-369 
    Details
    ISSN: 0019-1035
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0019-1035(87)90111-4
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  • 3
    Electronic Resource
    Electronic Resource
    Discovery of a quadruply lensed quasar: the 'clover leaf H1413 + 117 (1988)
    [s.l.] : Nature Publishing Group
    Nature 334 (1988), S. 325-327 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] H1413 + 117, with a redshift of 2.55 and an apparent visual magnitude of 17, is one of the brightest members of the class of broad absorption line (BAL) quasars. The latter represent a few percent of the total number of quasars and display broad and deep absorptions on the short wavelength side of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/334325a0
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  • 4
    Electronic Resource
    Electronic Resource
    A new case of gravitational lensing (1987)
    [s.l.] : Nature Publishing Group
    Nature 329 (1987), S. 695-696 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Our optical search for gravitationally lensed highly luminous quasars (HLQs) is being performed with a charge-coupled device (CCD) camera at the Cassegrain focus of the ESO/MPI (Max-Planck Institut) 2.2-m telescope. The selected HLQs are first observed through narrow-band filters chosen to isolate ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/329695a0
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  • 5
    Electronic Resource
    Electronic Resource
    Formation of resonance doublet profiles in rapidly expanding envelopes (1980)
    Springer
    Astrophysics and space science 73 (1980), S. 101-158 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Generalization of the escape probability method introduced by Sobolev allows us to study the transfer of spectral line radiation for a resonance doublet in rapidly expanding envelopes. For the cases of outward-accelerating (or equivalently inward-decelerating) and outward-decelerating (or equivalently inward-accelerating) envelopes we derive, in the frame of a three-level atom model, the expressions for the spectral radiation fieldsJ 12 andJ 13, for the resulting radiative force FRE exerted per atom and for the resonance doublet profileE(X)/C c; we take into account the complex radiative coupling, in both resonance transitions 1⇌2 and 1⇌3, between distant parts of the atmosphere. For various physical and geometrical conditions prevailing in the expanding media, we illustrate and discuss the behaviours of those quantities as well as their dependence on the parameters of the model. Namely, we deduce criteria under which resonance doublet profiles formed in outward-accelerating and/or outward-decelerating envelopes would appear to be resolved into double P Cygni profiles. We also stress the importance of treating a resonance doublet as being formed by two distinct resonance transitions when evaluating the resulting radiative force FRE acting on an atom. It is indeed shown that if we use a two-level atom model to represent a resonance doublet-i.e., assigning to it an oscillator strength equal to the sum of the oscillator strengths of both resonance transitions-the amplitude of the resulting radiative force can be underestimated by factors reaching 100% and more in the regions of the expanding envelope which are optically thick to the spectral line radiation. In this context, it would be essential to revise the previous models of radiation-driven winds developed for early-type stars in which the lines belonging to any multiplet were treated as a single line.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642369
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  • 6
    Electronic Resource
    Electronic Resource
    A generalized method for deriving mass-loss rates: The first order moment of unsaturated P Cygni line profiles (1983)
    Springer
    Astrophysics and space science 90 (1983), S. 299-311 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract For the case of optically thin lines, we show that the relation existing between the first order momentW 1α∫ (E(λ)/E c −1)(λ−λ12)dλ of a P Cygni profile and the quantityMn(level), whereM is the mass-loss rate of the central star andn(level) the fractional abundance of the ion under study, is in fact independent of any Sobolev-type approximations used for the transfer of line radiation, contrary to what has been assumed in some previous works (Castoret al., 1981; Surdej, 1982). Consequently, all results established in the context of ‘very rapidly’ expanding atmospheres and mainly referring to the non-dependence ofW 1 vs various physical (underlying photospheric absorption line, limb darkening, etc.) and geometrical (velocity fieldv(r), etc.) effects remain unchanged for arbitrary (e.g non-Sobolev type) outward-accelerating velocity laws. Whenever applied with caution, Equation (50) thus provides a very powerful means of deriving mass-loss rates—with a total uncertainty less than 60 percent—from the measurementW 1 of unsaturated P Cygni profiles observed in the spectrum of early—as well as late—type stars, quasars, etc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00650064
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  • 7
    Electronic Resource
    Electronic Resource
    Determination of mass-loss rates from the first order momentW 1 of unsaturated P Cygni line profiles (1982)
    Springer
    Astrophysics and space science 88 (1982), S. 31-54 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The escape probability method introduced by Sobolev to treat the transfer of line photons is used in order to derive the expressions of thenth order momentW n ∝∫(E(λ)/E c −1)(λ−λ12) n ·d λ of a P Cygni profile formed in rapidly expanding envelopes around a central point-like source under various physical and geometrical conditions. With the only assumption that there is mass-conservation of the species in the flow, we state for the case of optically thin lines that the relation between the first order momentW 1 and the quantityM n (level), first established by Castoret al. (1981) under more restrictive conditions, is in fact independent of the type of velocity fieldv(r) and a fortiori of the distribution adopted for the radial opacity τ 12 r (X′). These results also remain unchanged when including collisions (ε≠0) and/or an additional rotational velocity fieldv ⊥(r) in the expanding atmosphere. We investigate the presence of an underlying photospheric absorption line and conclude that for realistic cases, neglecting this boundary condition to the radiative transfer leads to an underestimate of the mass-loss rate by a factor of about 20%. By means of a three-level atom model, we demonstrate that all results derived for a single line transition equally apply for an unresolved doublet profile providedW 1 andM n (level) are calculated with the weighted wavelength λ D and total oscillator strengthf D of the doublet. Considering the occultation and inclination effects caused by the finite size of the central core, we refine the value of the multiplicative constant fixing the ratio ofW 1 toM n (level). We show that this relation allows a determination of the mass-loss rate with an uncertainly less than 30%, irrespective of the sizeL max of the atmosphere and of the limb-darkening affecting the stellar core. Reviewing all possible sources of error, we finally conclude that this method of deriving a mass-loss rate from the analysis of an unsaturated P Cygni profile is very powerful. The total uncertainty affecting the determination ofM n (level) from the measurement ofW 1 should be smaller than 60%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00648988
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  • 8
    Electronic Resource
    Electronic Resource
    The use of gravitational microlensing to scan the structure of BAL QSOs (1994)
    Springer
    Astrophysics and space science 216 (1994), S. 361-365 
    Details
    ISSN: 1572-946X
    Keywords: BAL QSOs ; Gravitational lensing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Approximately 10% of the QSOs show broad absorption lines (BAL) in their spectra which, if interpreted in terms of Doppler velocities, reveal the presence of high velocity gas outflows. One of these BAL QSOs is known to be gravitationally lensed. It therefore constitutes a good candidate to search for microlensing effects, i.e. the selective amplification of different line forming regions. Considering current models for the BAL region, we have investigated the effects of moving microlenses on the line profiles, and we conclude that these effects strongly depend on the adopted model. A regular spectroscopic monitoring of lensed BAL QSOs would therefore be highly valuable to distinguish between the various models proposed so far to interpret the origin of broad absorption lines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00982519
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  • 9
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    Transits and starspots in the WASP-6 planetary system (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-30
    Description: We present updates to prism , a photometric transit-starspot model, and gemc , a hybrid optimization code combining MCMC and a genetic algorithm. We then present high-precision photometry of four transits in the WASP-6 planetary system, two of which contain a starspot anomaly. All four transits were modelled using prism and gemc , and the physical properties of the system calculated. We find the mass and radius of the host star to be 0.836 ± 0.063 M and 0.864 ± 0.024 R , respectively. For the planet, we find a mass of 0.485 ± 0.027 M Jup , a radius of 1.230 ± 0.035 R Jup and a density of 0.244 ± 0.014 Jup . These values are consistent with those found in the literature. In the likely hypothesis that the two spot anomalies are caused by the same starspot or starspot complex, we measure the stars rotation period and velocity to be 23.80 ± 0.15 d and 1.78 ± 0.20 km s –1 , respectively, at a colatitude of 75.8°. We find that the sky-projected angle between the stellar spin axis and the planetary orbital axis is  = 7.2° ± 3.7°, indicating axial alignment. Our results are consistent with and more precise than published spectroscopic measurements of the Rossiter–McLaughlin effect. These results suggest that WASP-6 b formed at a much greater distance from its host star and suffered orbital decay through tidal interactions with the protoplanetary disc.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Larger and faster: revised properties and a shorter orbital period for the WASP-57 planetary system from a pro-am collaboration (2015)
    Oxford University Press
    Details
    Publication Date: 2015-10-19
    Description: Transits in the WASP-57 planetary system have been found to occur half an hour earlier than expected. We present 10 transit light curves from amateur telescopes, on which this discovery was based, 13 transit light curves from professional facilities which confirm and refine this finding, and high-resolution imaging which show no evidence for nearby companions. We use these data to determine a new and precise orbital ephemeris, and measure the physical properties of the system. Our revised orbital period is 4.5 s shorter than found from the discovery data alone, which explains the early occurrence of the transits. We also find both the star and planet to be larger and less massive than previously thought. The measured mass and radius of the planet are now consistent with theoretical models of gas giants containing no heavy-element core, as expected for the subsolar metallicity of the host star. Two transits were observed simultaneously in four passbands. We use the resulting light curves to measure the planet's radius as a function of wavelength, finding that our data are sufficient in principle but not in practise to constrain its atmospheric properties. We conclude with a discussion of the current and future status of transmission photometry studies for probing the atmospheres of gas-giant transiting planets.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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