UBV photometric system
The UBV photometric system (from Ultraviolet, Blue, Visual), also called the Johnson system (or Johnson-Morgan system), is a photometric system usually employed for classifying stars according to their colors. It was the first standardized photometric system. 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]
The choice of colors on the blue end of the spectrum was assisted by the bias that photographic film has for those colors. It was introduced in the 1950s by American astronomers Harold Lester Johnson and William Wilson Morgan. A Template:Cvt telescope and [[Otto Struve Telescope|the Template:Cvt telescope]] at McDonald Observatory were used to define the system.[1][3] The filters that Johnson and Morgan used were Corning 9 863 for U and 3 384 for V. The B filter used a combination of Corning 5 030 and Schott GG 13.[4]
The system has a key limit drawback. The short wavelength cutoff that is the shortest limit of the U filter is set by any given terrestrial atmosphere rather than the filter itself; thus, it (and observed magnitudes) varies chiefly with altitude and atmospheric water (humidity plus condensation into clouds).[5] However, many measurements have been made in this system, including thousands of the bright stars.[6]
Wavelengths and filters
The filters are selected so that the mean wavelengths of response functions (at which magnitudes are measured to mean precision) are 364 nm for U, 442 nm for B, 540 nm for V. Zero-points were calibrated in the B−V (B minus V) and U−B (U minus B) color indices selecting such A0 main sequence stars which are not affected by interstellar reddening.[1] These stars correspond with a mean effective temperature (Teff (K)) of between 9727 and 9790 Kelvin, the latter being stars with class A0[a]V (V meaning five)[b].
The following table shows the characteristics of each of the filters used (represented colors are only approximate):
Note: colors are only approximate and based on wavelength to sRGB representation (when possible).[7]UBV photometric system filter wavelengths U B V Peak wavelength (nm) 364 style="background-color: Template:Wavelength color; color:#ffffff; text-align:center;" | 442 style="background-color: Template:Wavelength color; color:#000000; text-align:center;" | 540
Extensions
The Johnson-Kron-Cousins UBVRI photometric system is a common extension of Johnson's original system that provides redder passbands.[8][9]
| U | B | V | R | I | |
|---|---|---|---|---|---|
| Peak wavelength (nm) | 343 | style="background-color: Template:Wavelength color; color:#ffffff; text-align:center;" | 425 | style="background-color: Template:Wavelength color; color:#000000; text-align:center;" | 547 | style="background-color: Template:Wavelength color; color:#000000; text-align:center;" |590 | 860-950 |
Note: colors are only approximate and based on wavelength to sRGB representation (when possible).[7]
See also
Notes
Page Template:Reflist/styles.css has no content.
- ^ 0 to 9 denotes temperature with 0 being the hottest
- ^ I to VII denotes the size of the star, and is found by calculating inherent luminosity; this is the Yerkes spectral classification. V corresponds to stars on the main sequence.
References
Lua error in mw.title.lua at line 404: bad argument #2 to 'title.new' (unrecognized namespace name 'Portal').
Page Template:Reflist/styles.css has no content.
- ^ a b c Page Module:Citation/CS1/styles.css has no content.Johnson, H. L.; Morgan, W. W. (1953). "Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas". The Astrophysical Journal. 117 (3): 313–352. Bibcode:1953ApJ...117..313J. doi:10.1086/145697.
- ^ Page Module:Citation/CS1/styles.css has no content.Johnson, H.L.; Morgan, W.W. (May 1953). "Fundamental stellar photometry for standards of spectral type on the Revised System of the Yerkes Spectral Atlas". Astrophysical Journal. 117 (3): 315. Bibcode:1953ApJ...117..313J. doi:10.1086/145697. Retrieved 22 July 2024.
- ^ Page Module:Citation/CS1/styles.css has no content.Hearnshaw, J. B. (1996). The Measurement of Starlight: Two Centuries of Astronomical Photometry. Cambridge University Press. p. 421. ISBN 9780521403931.
In the 1950–51 winter, Johnson had commenced photometry in three passbands (designated U, V, and Y) on the McDonald 13- and 82-inch reflectors [54].
- ^ Page Module:Citation/CS1/styles.css has no content.Johnson, H.L. (January 1955). "A Photometric System". Annales d'Astrophysique. 18: 292–316. Bibcode:1953ApJ...117..313J. doi:10.1086/145697.
- ^ Page Module:Citation/CS1/styles.css has no content.Hearnshaw, J. B. (1996). The Measurement of Starlight: Two Centuries of Astronomical Photometry. Cambridge University Press. p. 425. ISBN 9780521403931.
- ^ Page Module:Citation/CS1/styles.css has no content.Iriarte, Braulio; Johnson, Harold L; Mitchell, Richard I; Wisniewski, Wieslaw K (1965). "Five-Color Photometry of Bright Stars". Sky and Telescope. 30: 21. Bibcode:1965S&T....30...21I.
- ^ a b Page Module:Citation/CS1/styles.css has no content."Light wavelength to RGB Converter". www.johndcook.com. Retrieved 2023-07-28.
- ^ Page Module:Citation/CS1/styles.css has no content.Landolt, Arlo U (2009). "UBVRI Photometric Standard Stars Around the Celestial Equator: Updates and Additions". The Astronomical Journal. 137 (5): 4186–4269. arXiv:0904.0638. Bibcode:2009AJ....137.4186L. doi:10.1088/0004-6256/137/5/4186. S2CID 118627330.
- ^ a b Page Module:Citation/CS1/styles.css has no content.Landolt, Arlo U. (1992-07-01). "UBVRI Photometric Standard Stars in the Magnitude Range 11.5 < V < 16.0 Around the Celestial Equator". The Astronomical Journal. 104: 340. Bibcode:1992AJ....104..340L. doi:10.1086/116242. ISSN 0004-6256.
Lua error in package.lua at line 80: module 'Module:Navbox/configuration' not found.
