Fr.: catastrophe ultraviolette
A → paradox encountered in the classical theory of → thermal radiation (→ Rayleigh-Jeans law), whereby a → blackbody should radiate an infinite amount of energy at infinitely short wavelengths, in contradiction with what is observed. The problem was solved by Max Planck in 1900, who suggested that, rather than being continuous, the energy comes in discrete parcels called → quanta. The avoidance of the ultraviolet catastrophe was one of the first great achievements of → quantum mechanics.
havâsepehr-e zabarin, javv-e ~
Fr.: atmosphère supérieure
The general term applied to the atmosphere above the → troposphere.
Fr.: V2052 Oph
A hot star of → apparent visual magnitude V = 5.82 lying in the constellation → Ophiuchus, also known as HR 6684, HD 163472, and HIP 87812. V2052 Oph is of → subgiant → spectral type B2 IV-V and belongs to the family of magnetic → Beta Cephei → pulsators. It has a luminosity of 620 Lsol, a radius of 6.83 Rsol and lies about 830 → light-years away. Three stellar pulsation modes have been detected and studied from ground-based spectroscopy and multi-color photometry. Its magnetic field was deduced to be → dipolar dipolar with a strength of ~ 400 G, inclined 35° to the rotation axis. The star's → convective overshooting region is small, with no extra mixing in spite of the relatively large rotational velocity. This clearly illustrated the effect of the magnetic field: the inhibition of chemical mixing processes by the magnetic field. This result is in agreement with theoretical criteria, which predict that a surface magnetic field of ~ 70 G is sufficient to limit the overshooting in this star. V2052 Oph is now considered as a prime example of what magneto-asteroseismology can achieve (Neiner et al., 2012, A&A, 537, A148).
Fr.: photométrie de Walraven
A photometric system with five wavelength ranges that does not use filters. Instead it uses prisms and lenses (spectroscopy) to select the bands simultaneously. The wavelengths and the bandwidths are: W, 3250 and 140 Å; U, 3630 and 240 Å; L, 3840 and 230 Å; B, 4320 and 450 Å; and V, 5470 and 720 Å. The Walraven photometer was unique in design and remained literally unique as copies were never built. In addition, during its whole life the photometer was mounted permanently on the same telescope that had been built specifically for this instrument, the 91 cm Lightcollector' reflector, which started in 1958 at the Leiden Southern Station in Broederstroom, South-Africa. After 20 years in South-Africa the telescope and photometer were moved to the European Southern Observatory La Silla observatory in Chile. The photometric observations were resumed in March 1979 and continued for another 12 years until the decommissioning of the photometer in 1991.
After the inventors, the Dutch astronomer Theodore Walraven (1916-) and his wife Johanna Helena Walraven, née Terlinden (1920-89); → photometry.
Fr.: photomètre à coin
A photometer in which an → absorbing wedge is inserted in the brighter of two beams until the flux densities of the two light sources are equal.
Fr.: ζ Ophiuchi
A blue star, also called HD 149757 and HR 6175, which is the nearest, and probably the most widely studied, → massive star. It is variable in several wavelength bands and has a mean visual magnitude of V = 2.58, B - V = 0.01. It lies ~ 222 pc away and has a formal spectral type of O9.5 Ve and a luminosity of 105 Lsun. ζ Ophiuchi is a very rapid rotator with a v sin i ~ 400 km s-1, i.e. ~ 85% of the → break-up velocity. It is one of the earliest prototypes of the → Be phenomenon. Moreover, it shows episodes of Hα emission variability, a common feature of Be/Oe stars. It also shows periodic non-radial pulsations and UV → P Cygni profile variability, as is evident in the periodic behavior of → discrete absorption components (DACs). It has a → mass loss rate of 10-7 Msun yr-1 and a → terminal velocity of wind v∞ = 1550 km s-1. ζ Ophiuchi is a well-known → runaway star with a velocity of 30 km s-1. The interstellar → CH molecule and → CN molecule were first detected toward ζ Ophiuchi. It has been recognized for some time that this star lies close to the blue edge of the → beta Cephei instability strip.