Epoch J2000 Equinox
|Right ascension||17h 19m 49.330s|
|Declination||−39° 10′ 37.94″|
|Apparent magnitude (V)||13.1|
|Evolutionary stage||post-red supergiant|
|Spectral type||late B/early A|
|Apparent magnitude (K)||2.407|
|J−H color index||1.614|
|J−K color index||2.228|
|Proper motion (μ)||RA: 4.3 mas/yr
Dec.: −2.3 mas/yr
|Distance||3,600 - 4,700 pc|
|Radius||300 - 400 R☉|
|Temperature||7,500 - 10,000 K|
NSV 21444, GSC 07870-01348, IRSV 1716–3907, UCAC2 15112979, DENIS-P J171949.3-391037, Hen 3-1379, 2MASS J17194933-3910374, [NHO98] 17163-3907, GSC2 S2300121509, IRAS 17163-3907, MSX6C G348.5107–01.1199
IRAS 17163-3907 is a possible yellow hypergiant star located 13,000 light years from Earth in the constellation of Scorpius. The star is embedded in thick shells of expelled gases and dust, and owing to its appearance has been nicknamed by astronomers the "Fried Egg Nebula". Yellow hypergiants are in an extremely active phase of their evolution.
The star was discovered and catalogued as planetary nebula Hen 3-1379 in 1976, and classified as a proto-planetary nebular in 2003 after the 2.2 micron infrared sky survey. At the time of discovery, the star was thought to be much less massive and four times closer than it was discovered to be recently.
The picture of the star causing it to be dubbed the Fried Egg Nebula was taken in the mid infrared spectrum by the VISIR instrument in the Very Large Telescope in the Atacama Desert in northern Chile. The filters passed light of frequencies 12,810 nm (mapped to red in the image), 11,850 nm (mapped to green), and 8,590 nm (mapped to blue). The star is about 500,000 times the luminosity of the Sun. It is one of the brightest infrared sources in the sky, but intervening dust clouds mean the apparent visual magnitude is just 13.1. The photograph pictured is one of the best ever taken of a yellow hypergiant. The star is eventually expected to end its life in a supernova.
The star is characterized by two visible dusty shells. The inner shell is 4800 AUs in diameter and the outer shell is 12,000 AU wide. The source of materials for the shells is material ejected from the star during ejection events common in hypergiants. The time period between expulsion of materials causing the first and the second outer shells is estimated at 435 years and the total mass in the ejecta is around 4 M☉, of which about 1% is dust. At its most active star ejects materials equal to the mass of the Sun every few hundred years. The shells are also discovered to be rich in silicates and hence oxygen. The star may contain more outer shells but they were not detected by the VISIR instrument as the field of view of the instrument is insufficient. The outer shell it's estimated to contain 0.17 solar masses of dust and that it was produced in an outburst 17,000 years ago that expelled 7.1 solar masses of gas.
The properties of these shells are considered similar to those surrounding IRC+10420, also an evolved massive star suffering heavy mass loss as well as, for the outer one, of those around luminous blue variables, suggesting IRAS 17163-3907 is in a pre-LBV stage as well as that the ring nebulae that often surround those types of stars may have its origin on mass loss during the red supergiant stage.
A cautionary note
This star is described by the authors of the single paper that found such a high luminosity as "possibly belonging to the rare class of Yellow Hypergiants". Its position in the HR diagram, allowing for the margin of error in its known temperature, straddles the area where LBVs are found while in their active eruption phase. The lowest likely temperature for this star is at the high end of the range for yellow hypergiants. Yellow hypergiants are shown to vary on short timescales to considerably lower temperatures, which has not been seen for this star. Hence the designation of this star as a yellow hypergiant is tentative despite the rash of reports in popular media.
- Lagadec, E.; Zijlstra, A. A.; Oudmaijer, R. D.; Verhoelst, T.; Cox, N. L. J.; Szczerba, R.; Mékarnia, D.; Van Winckel, H. (2011). "A double detached shell around a post-red supergiant: IRAS 17163-3907, the Fried Egg nebula". Astronomy & Astrophysics 534: L10. arXiv:1109.5947. Bibcode:2011A&A...534L..10L. doi:10.1051/0004-6361/201117521.
- "Feast your Eyes on the Fried Egg Nebula". ESO Photo Release. 28 September 2011. Retrieved 28 September 2011.
- "Rare star resembles fried egg". Astronomy Now Online. Retrieved 2011-09-29.
- "'Fried Egg' nebula cracks open rare hypergiant star". The Sydney Morning Herald. 2011-09-29. Retrieved 2011-09-29.
- Hutsemékers, D.; Cox, N. L. J.; Vamvatira-Nakou, C. (2013). "A massive parsec-scale dust ring nebula around the yellow hypergiant Hen 3-1379". Astronomy & Astrophysics 552 (L6). arXiv:1303.4292. Bibcode:2013A&A...552L...6H. doi:10.1051/0004-6361/201321380.