IC 4997
Planetary nebula in the constellation Sagitta
From Wikipedia, the free encyclopedia
IC 4997 is a planetary nebula located in the constellation of Sagitta.[4] It was discovered in 1896 by Edward Charles Pickering and Williamina Fleming,[5] and independently by Gustav Gruss the same year.[6] This nebula is about 14,000 light-years from Earth.[2] It looks like an ordinary star in smaller telescopes, and only detailed study of its spectrum reveals its nebular characteristics.[7]
| Emission nebula | |
|---|---|
| Planetary nebula | |
| |
| Observation data: J2000 epoch | |
| Right ascension | 20h 20m 08.76s[1] |
| Declination | +16° 43′ 53.7″[1] |
| Distance | 14,090 (4,320 pc)[2] ly |
| Apparent magnitude (V) | 11.15[1] |
| Apparent dimensions (V) | 2.7″ x 1.4″ [3] |
| Constellation | Sagitta[4] |
| Physical characteristics | |
| Radius | 0.092 ly |
| Notable features | Bipolar outflow, Bipolar nebula |
| Designations | IC 4997 PNG 058.3-10.9 |
Physical characteristics
IC 4997 is very young and very dense with a very high nebular temperature of around 20,000 K,[8] which is twice those measured in most nebulae. The mean expansion velocity of the nebula seems to be slow at 20 km/s at the outer layer,[7] while it also reaches a maximum expansion velocity of 60 km/s relative to its central star.[8] Its central star has a magnitude of around 14m[7] and a temperature of around 47,000--59 000 K.[9]
The most characteristic feature of IC 4997 is its variability.[10] In the 1960s, there was a sudden change in its spectrum. Variability could be related to the nebula expansion[11] or an episodic smoothly changing stellar wind.[12]
