Violet stars are of two temperature ranges: those whose Planckian peak wavelength lies between 380 and 450 nm, or 6700-7900 K temperature and those above the violet range in the ultraviolet that appear violet to blue in color.

For example, A spectral type stars range in temperature from 7600 to 11,500 K. The violet stars are F3 (F3-F0) to A5 (A9-A5).

1 Centauri edit

Temperature (primary, F2 V) = 6898±235[1]

1 Centauri, or i Centauri,[2] is a yellow-white hued binary star[3] system in the southern constellation Centaurus. It can be seen with the naked eye, having an apparent visual magnitude of +4.23.[4] Based upon an annual parallax shift of 51.54 mas as seen from Earth's orbit, it is located 51.5 light years from the Sun. The system is moving closer to the Sun with a radial velocity of −21.5 km/s.[5]

Spectrographic images taken at the Cape Observatory between 1921 and 1923 showed this star has a variable radial velocity, which indicated this is a single-lined spectroscopic binary star system. The pair have an orbital period of 9.94 days and an orbital eccentricity of about 0.2.[3]

I Carinae edit

Temperature = 7017±239[1]

I Carinae is a single,[6] yellow-white hued star in the southern constellation Carina. It is a fourth[7] magnitude star that is visible to the naked eye. An annual stellar parallax of 61.64 mas provides a distance estimate of 62 light years and it is moving closer with a radial velocity of −5 km/s.[8] In an estimated 2.7 million years will pass within 24.3 ly (7.46 pc) of the Sun.[9] In the next 7500 years, the south Celestial pole will pass close to this star and Omega Carinae (5800 CE).[10]

This star is spectral type of F3 V.[11] It is younger than the Sun with an estimated age of 977[1] million years, and is spinning with a projected rotational velocity of 51.6 km/s.[12] The star has 1.4[1] times the mass of the Sun and is radiating 5.56[4] times the Sun's luminosity from its photosphere at an effective temperature of around 7,017 K.[1] It is a variable star and most likely (99.2% chance) the source of detected X-ray emission coming from these coordinates.[13]

Eta Carinae edit

This Hubble Space Telescope image shows excess violet light escaping along the equatorial plane between the bipolar lobes of the Eta Carinae Homunculus. Credit: Jon Morse (University of Colorado) & NASA Hubble Space Telescope.

"The “Purple Haze” is a diffuse blueish/purple glow within a few arcseconds of the central star in HST images of the Homunculus (Morse et al. 1998; Smith et al. 2000, 2004). This emission is seen in excess of violet starlight scattered by dust, and the strength of the excess increases into the far UV (Smith et al. 2004; hereafter Paper I)."[14]

Notation: let the symbol LH stand for the Little Homunculus.

"The LH has no outstanding correspondence with any of the clumps and filaments seen in scattered light in normal UV or visual-wavelength images of η Car, although it does match the spatial extent of the "Purple Haze"".[15] Bold added.

The Fe II emission line at 489.1 nm occurs in the Little Homunculus (Eta Carinae)[15]

Mass "loss at the η Carinae rate produces considerable changes of Teff on a human timescale. As an example, for the 120 Mʘ model, a change from about 20,000 K to 34,000 K was obtained over a time of 50 yr as a result of the secular bluewards evolution following the rapid ejection."[16]

RY Sagittarii edit

"Near minimum light, the spectra [of RY Sgr] display the same main features as those observed at a preceding minimum (Alexander et al. 1972) [including] three broad emission lines in the violet (Ca II and He I λ3888)".[17]

"The "broad bright lines" are displaced towards the red during the 1977 minimum, and they were displaced towards the violet during the 1967 minimum."[17]

"A possible interpretation of these differences is an unsymmetrical ejection of carbon clouds. An ejection mainly directed towards the observer would be linked with a deeper minimum and violet-shifted broad bright lines. An ejection mainly directed backwards would be linked with a less deep minimum and red-shifted lines."[17]

W UMa-type systems edit

“A W Ursae Majoris variable is a type of eclipsing binary variable star. These stars are close binaries of spectral types F, G, or K that share a common envelope of material and are thus in contact with one another. They are termed contact binaries because the two stars touch and transfer mass and energy through the connecting neck ... W Ursae Majoris variables are the most common variable stars in the present day Universe. About 1 percent of all stars belong to this group.”[18]

“[T]he violet and ultraviolet parts of the energy distributions in spectra of W UMa-type systems are abnormal with elevated ultraviolet fluxes for systems having the shortest periods at a given blue-visual colour.”[19]

NGC 5584 edit

This is a colour-composite of the barred spiral galaxy NGC 5584. Credit: ESO: observations by Susana Randall, Claudio Melo, Swetlana Hubrig; day astronomer Dominique Naef; Henri Boffin (ESO) processed the data and made the colour-composite, and Haennes Heyer (ESO) made the final adjustments.

"This image is a colour-composite of the barred spiral galaxy NGC 5584. It is based on data collected by the Paranal Science Team with the FORS1 instrument on Kueyen, the second 8.2-m Unit Telescope of ESO's Very Large Telescope. The supernova SN 2007af is the bright object seen slightly below and to the right of the galaxy's centre. The galaxy and its bright supernova were observed on the nights of 16, 19 and 22 March 2007 through a B, V, R, H-alpha and OII filter."[20]

The B filter is centered at 440 nm and the OII filter is centered at 372 nm.[20]

"Located about 75 million light years away towards the constellation Virgo ('the Virgin'), NGC 5584 is a galaxy slightly smaller than the Milky Way. It belongs, however, to the same category: both are barred spirals."[21]

"Spiral galaxies are composed of a 'bulge' and a flat disc. The bulge hosts old stars and usually a central supermassive black hole. Younger stars reside in the disc, forming the characteristic spiral structures from which the galaxies get their name. Barred spirals are crossed by a bright band of stars."[21]

"In this amazing new image of NGC 5584 two dominant spiral arms are clearly visible, while the others are deformed, probably due to interactions with other galaxies. Luminous patches are spread all over the disc, indicating that stars are being formed in this gigantic rose at a frantic pace."[21]

Quasars edit

As of 1979, "[m]ost astrophysicists seem to consider redshifts of quasars as being completely cosmological. ... In local models which involve expulsion of "quasars" from parent galaxies at distances of up to ~100 Mpc there must be objects with large violet shifts (Burbidge and Burbidge, 1967). ... [I]n the catalogue of quasars by Burbidge et al. (1977) among 633 quasars there are 57 objects which have only two lines in their spectra identified with C III 1909 and Mg II 2798. ... If local "quasars" do exist ... then objects with large violet shifts ... could be among those 57 quasars".[22]

See also edit

References edit

  1. 1.0 1.1 1.2 1.3 1.4 David, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal 804 (2): 146. doi:10.1088/0004-637X/804/2/146. 
  2. "1 Cen". Retrieved 2018-02-09.
  3. 3.0 3.1 Spencer Jones, Harold (1928). "Radial velocity determinations : including a spectroscopic determination of the constant of aberration, the orbits of 13 spectroscopic binary stars, and the radial velocities of 434 stars". Annals of the Cape Observatory 10: 246. 
  4. 4.0 4.1 Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. 
  5. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012). "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project". Astronomy & Astrophysics 546: 14. doi:10.1051/0004-6361/201219219. A61. 
  6. Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society 389 (2): 869–879. doi:10.1111/j.1365-2966.2008.13596.x. 
  7. Cousins, A. W. J.; Stoy, R. H. (1962). "Photoelectric magnitudes and colours of Southern stars.". Royal Observatory Bulletin 64. 
  8. Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system". Astronomy Letters 32 (11): 759–771. doi:10.1134/S1063773706110065. 
  9. Bailer-Jones, C. A. L. (March 2015). "Close encounters of the stellar kind". Astronomy & Astrophysics 575: 13. doi:10.1051/0004-6361/201425221. A35. 
  11. Gray, R. O.; Corbally, C. J.; Garrison, R. F.; McFadden, M. T.; Bubar, E. J.; McGahee, C. E.; O'Donoghue, A. A.; Knox, E. R. (July 2006). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample". The Astronomical Journal 132 (1): 161–170. doi:10.1086/504637. 
  12. Schröder, C. et al. (January 2009). "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo". Astronomy and Astrophysics 493 (3): 1099–1107. doi:10.1051/0004-6361:200810377. 
  13. Haakonsen, Christian Bernt; Rutledge, Robert E. (September 2009). "XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources". The Astrophysical Journal Supplement 184 (1): 138–151. doi:10.1088/0067-0049/184/1/138. 
  14. Nathan Smith; Jon A. Morse; Nicholas R. Collins; Theodore R. Gull (August 2004). "The Purple Haze of eta Carinae: Binary-induced Variability?". The Astrophysical Journal 610 (2): L105-8. doi:10.1086/423341. 
  15. 15.0 15.1 Nathan Smith (March 2005). "Doppler tomography of the Little Homunculus: High‐resolution spectra of [Fe II λ16 435 around Eta Carinae"]. Monthly Notices of the Royal Astronomical Society 357 (4): 1330-6. doi:10.1111/j.1365-2966.2005.08750.x. Retrieved 2012-02-27. 
  16. A. Maeder (April 1983). "Evolution of chemical abundances in massive stars. I - OB stars, Hubble-Sandage variables and Wolf-Rayet stars - Changes at stellar surfaces and galactic enrichment by stellar winds. II - Abundance anomalies in Wolf-Rayet stars in relation with cosmic rays and 22/Ne in meteorites". Astronomy and Astrophysics 120 (1): 113-35. Retrieved 2013-09-19. 
  17. 17.0 17.1 17.2 Monique Spite; François Spite (September 1979). "Spectra of the Variable Star RV Sgr Near Minimum Light". Messenger (18): 29-30. Retrieved 2013-03-27. 
  18. "W Ursae Majoris variable, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. March 28, 2012. Retrieved 2012-06-01.
  19. S. M. Rucinski (October 1983). "Violet and ultraviolet continua of W UMa systems on the basis of UVBY photometry observations". Astronomy and Astrophysics 127 (1): 84-92. 
  20. 20.0 20.1 Susana Randall; Claudio Melo; Swetlana Hubrig; Dominique Naef; Henri Boffin; Haennes Heyer (March 27, 2007). "The Spiral Galaxy NGC 5584 and SN 2007af". Kueyen: European Southern Observatory. Retrieved 2013-03-27.
  21. 21.0 21.1 21.2 Susana Randall; Claudio Melo; Swetlana Hubrig; Dominique Naef; Henri Boffin; Haennes Heyer (March 27, 2007). "The Purple Rose of Virgo". La Silla: European Southern Observatory. Retrieved 2013-03-27.
  22. S. A. Putsil'nik (1979). "Do They Observe Objects with Large Violet Shifts?". Astronomy and Astrophysics 78: 248-52. 

External links edit