  | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Pegasus |
| Right ascension | 22h 53m 02.26608s[1] |
| Declination | +16° 50′ 28.2969″[1] |
| Apparent magnitude (V) | 5.55[2](5.60 – 5.85[3]) |
| Characteristics | |
| Spectral type | K2 III + dG[4] |
| Variable type | RS CVn[3] |
| Astrometry | |
| Radial velocity (Rv) | −14.43[5] km/s |
| Proper motion (μ) | RA: −20.73[1]mas/yr Dec.: −27.75[1]mas/yr |
| Parallax (π) | 11.17±0.33 mas[1] |
| Distance | 292 ± 9 ly (90 ± 3 pc) |
| Orbit[2] | |
| Period (P) | 24.64877±0.00003 d |
| Eccentricity (e) | 0.00 |
| Inclination (i) | 65° ≤ i ≤ 80°° |
| Semi-amplitude (K1) (primary) | 34.29±0.04 km/s |
| Semi-amplitude (K2) (secondary) | 62.31±0.06 km/s |
| Details[4] | |
| primary | |
| Mass | 1.8 ± 0.2 M☉ |
| Radius | 13.3 ± 0.6 R☉ |
| Luminosity | 54 ± 9 L☉ |
| Temperature | 4,550 ± 50 K |
| Rotation | 24.4936 days |
| secondary | |
| Mass | 1.0 ± 0.07 M☉ |
| Radius | 1.00 R☉ |
| Luminosity | 0.9 ± 0.3 L☉ |
| Temperature | 5,650 ± 200 K |
| Other designations | |
| IM Peg,HD 216489,HIP 112997,HR 8703,SAO 108231 | |
| Database references | |
| SIMBAD | data |
IM Pegasi is avariablebinary star system approximately 329light-years away in theconstellation ofPegasus. With anapparent magnitude of 5.7, it is visible to thenaked eye. Increased public awareness of it is due to its use as the guide star for theGravity Probe Bgeneral relativity experiment. It was chosen for this purpose because its microwave radio emissions are observable with a largeradio telescope network on the ground in such a manner that its precise position can be related byinterferometry to distantquasars.[6]
The two components of the binary system includes aK-type giant star and aG-type main sequence star. The primary star is estimated to be 1.8 times asmassive and 13 times thediameter of theSun. The secondary star is estimated to be similar to the Sun in size andmass. They orbit their commonbarycenter in a period precisely estimated to be 24.64877 days.
The variability of IM Pegasi is due to the active chromosphere of the giant primary star, which causes brightness changes of a few tenths of a magnitude as it rotates.
