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The amount of reddening is characterized by color excess, defined as the difference between the observed color index and the normal color index (or intrinsic color index), the hypothetical true color index of the star, unaffected by extinction. For example, in the UBV photometric system we can write it for the B−V color:
The apparent magnitudes of stars in the system are often used to determine the color indices B−V and U−B, the difference between the B and V magnitudes and the U and B magnitudes respectively. [1] The system is defined using a set of color optical filters in combination with an RMA 1P21 photomultiplier tube. [2]
A commonly adopted standardized photometric system is the Johnson-Morgan or UBV photometric system (1953). At present, there are more than 200 photometric systems. At present, there are more than 200 photometric systems.
Using B and V filters in the UBV system produces the B–V colour index. [20] For 51 Pegasi, the B–V = 6.16 – 5.46 = +0.70, suggesting a yellow coloured star that agrees with its G2IV spectral type. [21] [19] Knowing the B–V results determines the star's surface temperature, [22] finding an effective surface temperature of 5768±8 K. [23]
The latter is the theoretical value which it would have if unaffected by extinction. In the first system, the UBV photometric system devised in the 1950s and its most closely related successors, the object's color excess is related to the object's B−V color (calibrated blue minus calibrated visible) by:
The typical axes for infrared color–color diagrams have (H–K) on the horizontal axis and (J–H) on the vertical axis (see infrared astronomy for information on band color designations). On a diagram with these axes, stars which fall to the right of the main sequence and the reddening bands drawn are significantly brighter in the K band ...
An example of a UV-Vis readout. UV-Vis can be used to monitor structural changes in DNA. [8]UV-Vis spectroscopy is routinely used in analytical chemistry for the quantitative determination of diverse analytes or sample, such as transition metal ions, highly conjugated organic compounds, and biological macromolecules.
Standard refractive index measurements are taken at the "yellow doublet" sodium D line, with a wavelength (λ) of 589 nanometers. There are also weaker dependencies on temperature , pressure / stress , etc., as well on precise material compositions (presence of dopants , etc.); for many materials and typical conditions, however, these ...