670 research outputs found
Absolute Lineshifts - A new diagnostic for stellar hydrodynamics
For hydrodynamic model atmospheres, absolute lineshifts are becoming an
observable diagnostic tool beyond the classical ones of line-strength, -width,
-shape, and -asymmetry. This is the wavelength displacement of different types
of spectral lines away from the positions naively expected from the Doppler
shift caused by stellar radial motion. Caused mainly by correlated velocity and
brightness patterns in granular convection, such absolute lineshifts could in
the past be studied only for the Sun (since the relative Sun-Earth motion, and
the ensuing Doppler shift is known). For other stars, this is now becoming
possible thanks to three separate developments: (a) Astrometric determination
of stellar radial motion; (b) High-resolution spectrometers with accurate
wavelength calibration, and (c) Accurate laboratory wavelengths for several
atomic species. Absolute lineshifts offer a tool to segregate various 2- and
3-dimensional models, and to identify non-LTE effects in line formation.Comment: 13 pages, 9 figures; to appear in "Modelling of Stellar Atmospheres",
IAU Symp.210; N.E.Piskunov, W.W.Weiss, D.F.Gray (eds.
The Learning of Ancient Languages as\ud (super)Human Effort
Problems around teaching ancient languages are discussed. It is suggested to assume that\ud
learning and teaching of languages require some superhuman effort. Authorās experience of\ud
teaching ancient languages and producing electronic educational tools both for text version\ud
and for Internet in Faculty of Theology in University of Latvia is described. Problems around\ud
cognitive models of reasoning and place of languages there are discussed
Quanta Mathematica Instrumentalis!
Quanta mathematica instrumentalis, from Latin, might mean How much mathematics for physical applications. But we try to give this expression another meaning. \ud
We discuss how mathematics and its instrumental nature could serve as paradigm for other human activities and science in general. We introduce notions of higher observer and field of information. We discuss question why we are to study and develop mathematics more diligently than we do in natural way.\u
On building 4-critical plane and projective plane multiwheels from odd wheels
We build unbounded classes of plane and projective plane multiwheels that are
4-critical that are received summing odd wheels as edge sums modulo two. These
classes can be considered as ascending from single common graph that can be
received as edge sum modulo two of the octahedron graph O and the minimal wheel
W3. All graphs of these classes belong to 2n-2-edges-class of graphs, among
which are those that quadrangulate projective plane, i.e., graphs from
Gr\"otzsch class, received applying Mycielski's Construction to odd cycle.Comment: 10 page
The One Savior Paradigm
The one savior paradigm is discussed not only as doctrinal aspect of religious teachings but as one of mostly manifested aspect of our psychic that should be adequately investigated. We suggest simple idea that could serve as starting cognitive model for the one savior paradigm, that might give effect in considering global aspects of humanity, e.g., such as global economy and exact sciences in more friendly connection with religious thinking.religion, theology, science, art, cognition, society, global economy, noosphere, accessibility to information
Stellar intensity interferometry over kilometer baselines: Laboratory simulation of observations with the Cherenkov Telescope Array
A long-held astronomical vision is to realize diffraction-limited optical
aperture synthesis over kilometer baselines. This will enable imaging of
stellar surfaces and their environments, show their evolution over time, and
reveal interactions of stellar winds and gas flows in binary star systems. An
opportunity is now opening up with the large telescope arrays primarily erected
for measuring Cherenkov light in air induced by gamma rays. With suitable
software, such telescopes could be electronically connected and used also for
intensity interferometry. With no optical connection between the telescopes,
the error budget is set by the electronic time resolution of a few nanoseconds.
Corresponding light-travel distances are on the order of one meter, making the
method practically insensitive to atmospheric turbulence or optical
imperfections, permitting both very long baselines and observing at short
optical wavelengths. Theoretical modeling has shown how stellar surface images
can be retrieved from such observations and here we report on experimental
simulations. In an optical laboratory, artificial stars (single and double,
round and elliptic) are observed by an array of telescopes. Using high-speed
photon-counting solid-state detectors and real-time electronics, intensity
fluctuations are cross correlated between up to a hundred baselines between
pairs of telescopes, producing maps of the second-order spatial coherence
across the interferometric Fourier-transform plane. These experiments serve to
verify the concepts and to optimize the instrumentation and observing
procedures for future observations with (in particular) CTA, the Cherenkov
Telescope Array, aiming at order-of-magnitude improvements of the angular
resolution in optical astronomy.Comment: 18 pages, 11 figures; Presented at SPIE conference on Astronomical
Telescopes + Instrumentation in Montreal, Quebec, Canada, June 2014. To
appear in SPIE Proc.9146, Optical and Infrared Interferometry IV
(J.K.Rajagopal, M.J.Creech-Eakman, F.Malbet, eds.), 201
Astrometric radial velocities. I. Non-spectroscopic methods for measuring stellar radial velocity
High-accuracy astrometry permits the determination of not only stellar
tangential motion, but also the component along the line-of-sight. Such
non-spectroscopic (i.e. astrometric) radial velocities are independent of
stellar atmospheric dynamics, spectral complexity and variability, as well as
of gravitational redshift. Three methods are analysed: (1) changing annual
parallax, (2) changing proper motion and (3) changing angular extent of a
moving group of stars. All three have significant potential in planned
astrometric projects. Current accuracies are still inadequate for the first
method, while the second is marginally feasible and is here applied to 16
stars. The third method reaches high accuracy (<1 km/s) already with present
data, although for some clusters an accuracy limit is set by uncertainties in
the cluster expansion rate.Comment: 13 pages, 2 figures. Accepted for publication in Astronomy &
Astrophysics (main journal
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