757 research outputs found
Magnetic chemically peculiar stars
Chemically peculiar (CP) stars are main-sequence A and B stars with
abnormally strong or weak lines for certain elements. They generally have
magnetic fields and all observables tend to vary with the same period.
Chemically peculiar stars provide a wealth of information; they are natural
atomic and magnetic laboratories. After a brief historical overview, we discuss
the general properties of the magnetic fields in CP stars, describe the oblique
rotator model, explain the dependence of the magnetic field strength on the
rotation, and concentrate at the end on HgMn stars.Comment: 9 pages, 4 figures, 2 tables, chapter in "Determination of
Atmospheric Parameters of B-, A-, F- and G-Type Stars", Springer (2014), eds.
E. Niemczura, B. Smalley, W. Pyc
Constraining the fundamental parameters of the O-type binary CPD-41degr7733
Using a set of high-resolution spectra, we studied the physical and orbital
properties of the O-type binary CPD-41 7733, located in the core of \ngc. We
report the unambiguous detection of the secondary spectral signature and we
derive the first SB2 orbital solution of the system. The period is 5.6815 +/-
0.0015 d and the orbit has no significant eccentricity. CPD-41 7733 probably
consists of stars of spectral types O8.5 and B3. As for other objects in the
cluster, we observe discrepant luminosity classifications while using
spectroscopic or brightness criteria. Still, the present analysis suggests that
both components display physical parameters close to those of typical O8.5 and
B3 dwarfs. We also analyze the X-ray light curves and spectra obtained during
six 30 ks XMM-Newton pointings spread over the 5.7 d period. We find no
significant variability between the different pointings, nor within the
individual observations. The CPD-41 7733 X-ray spectrum is well reproduced by a
three-temperature thermal mekal model with temperatures of 0.3, 0.8 and 2.4
keV. No X-ray overluminosity, resulting e.g. from a possible wind interaction,
is observed. The emission of CPD-41 7733 is thus very representative of typical
O-type star X-ray emission.Comment: Accepted by ApJ, 15 pages, 9 figure
The Core-Wing Anomaly of Cool Ap Stars: Abnormal Balmer Profiles
Paper by Cowley et al. The Core-Wing Anomaly Etc. The profiles of H
in a number of cool Ap stars are anomalous. Broad wings, indicative of
temperatures in the range 7000-8000K end abruptly in narrow cores. The widths
of these cores are compatible with those of dwarfs with temperatures of 6000K
or lower. This profile has been known for Przybylski's star, but it is seen in
other cool Ap's. The H profile in several of these stars shows a similar
core-wing anomaly (CWA). In Przybylski's star, the CWA is probably present at
higher Balmer members. We are unable to account for these profiles within the
context of LTE and normal dwarf atmospheres. We conclude that the atmospheres
of these stars are not ``normal.'' This is contrary to a notion that has long
been held.Comment: 4 Pages 5 Figures. Submitted to Astronomy and Astrophysics 4 Dec.
200
Zeevraag: Waarom staan windturbines op zee soms stil?
Windturbines op zee staan zelden stil, toch denken nogal wat mensen dat dit vaak het geval is. Wat is de verklaring hiervoor? Laten we eerst even naar de cijfers kijken
Pavlovian conditioning-induced hallucinations result from overweighting of perceptual priors
Some people hear voices that others do not, but only some of those people seek treatment. Using a Pavlovian learning task, we induced conditioned hallucinations in four groups of people who differed orthogonally in their voice-hearing and treatment-seeking statuses. People who hear voices were significantly more susceptible to the effect. Using functional neuroimaging and computational modeling of perception, we identified processes that differentiated voice-hearers from non-voice-hearers and treatment-seekers from non-treatment-seekers and characterized a brain circuit that mediated the conditioned hallucinations. These data demonstrate the profound and sometimes pathological impact of top-down cognitive processes on perception and may represent an objective means to discern people with a need for treatment from those without
Q-ary collision resolution algorithms in random-access systems with free or blocked channel access
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