Fotometrie [1-3] historicky náleží k části optiky věnované zkoumání světla z hlediska jeho účinku na lidské oko. K popisu tohoto působení proto zavádíme fotometrické veličiny, mezi které řadíme např. svítivost, světelný tok nebo osvětlení. Nejdříve se podíváme na základní jednotku SI svítivost, od níž si odvodíme další fotometrické veličiny. Závěrem si ukážeme fotometrii na příkladu našeho Slunce a různé metody fotometrie v astrofyzice., Photometry historically belongs to the part of optics which examines the effects of radiation on the human eye. To describe these effects we introduce photometric quantities amongst which are luminosity, luminous flux or illumination. First, we focus on the SI base unit luminosisty from which we deduce other photometric quantities. We show how our Sun emits energy and discuss different photometric methods used in astrophysics., Jan Janík., and Obsahuje seznam literatury
The azirnuthal distribution of planes containing e^i/e pairs from
high-energy photon materialization is reminiscent, through a quadrupole anisotropy, of the degree and position angle of linear polarization of the incident photons. Data on open pairs in the COS-B spark chamber are used in a search for such an effect in
> 50 MeV photons from bright sources, such as Vela, Crab, Geminga and a reference galactic plane region in Cygnus. After a description of the method and the related simulations and tests, the analysis of the available data shows no anisotropy for the other sources, but for the Vela pulsar a low-chance-probability effect is
found apparently implying a high (~ 100%) degree of linear polarization for the Vela photons. This is discussed in light of the physics of the production mechanisms as well as of their geometry.
Despite theoretical predictions on the existence of solar gravity oscillations (g modes), their detection is still marginal. The main reasons are their frequencies, ν<0.2 mHz, and amplitudes of
less than 10 cm/s. However, because these modes are extremely sensitive to the physical conditions in the very deep sun, they can give us detailed Information on the physics of the core. Using a resontant scattering spectrophotometer we measured the radial velocity of the Sun at the KI 769.9 nm. line with very high resolution and temporal stability. The observatíons carried out at Izaňa (Tenerife) continuously for the last three years, háve been used to search for solar g modes. Analysis of the whole lot of data as one single time series provides a spectral resolution of 12 nHz, and signal with amplitude above noise level, 1 cm/s. Several techniques are used in order to find.the signature of g modes and calculate the parameters Po and vr. Individua! peaks, well above noise level, are identified and their frequencies are likely to correspond with
g modes.
V568. Cyg has been observed photometrically, spectroscopically and photographically during a campaign on 0-B runaways. These may contain either postsupernova binaries or stars dynamically ejected. from young associations. Whereas even its variability was doubtful, we have recorded photometric minima deeper from V to U as well as strong inversion of colour indexes, the star becoming redder as the minimum gets deeper:
1986 (mean value) 1987 (mean value) July 30, 86 August 2,86
B-V - 0.26 - 0.23 + 1.74 + 1.62
U-B - 0.63 - 0.59 + 1.30 + 1.05
New transient Hα emission episodes have been observed. The equivalent widths of absorption lines of hydrogen, except Hα, change in a correlated way reaching their lowest value sometimes at photometric minima. Eclipse of a hot object with a possible disk, by a late type giant in an eccentric orbit, seems the most viable explanation. The ephemeris J.D. 2446641.5 + 152.12 days may help the search for further primary minima.
After reviewing the various aspects of solar-type magnetic activity, which occur in ttie atmospheres of late-type stars on time scales ranging from tens of seconds to years, the principal characterlstics
of inhomogeneous localized structures, such as starspots and plages, as derived from modelling the rotation-induced modulation of continuum or line fluxes and high-resolution UV emission line profiles of Mg II by the Doppler imaging technique, were critically presented by taking into account the present observational limits.
It was shown that the geometrical and energetic characteristics of magnetic activity phenomena on stars overcome by orders of magnitude the corresponding solar phenomena. However, stellar activity appears to be solar-like as far as it concerns its origin and evolution: active stars have deep convection zones and, possibly, differential rotation, so that solar-type dynamos can efficiently
operate. Nevertheless, in order to detect strictly solar activity signatures on stars, the photometric precision, the spectral - and time - resolutlon of stellar observations need to be improved by at least one order of magnitude. In partlcular, the time scales of stellar flares and the accurate timing smáli solar-type spot appearance on and disappearance from the visible disk of a rotating star were Indicated as priority observational objectives for the purpose of establishing the minimum flare duration and spot slze, which are important parameters to constrain theoretical models. The new generation of very large aperture ground-based telescopes (e.g., ESO-VLT) and space telescopes (e.g., Hubble Space Telescope), together with existing radio observatories (e.g. VLA, VLBI) will need to be used.