HD 196917
Suspected variable star in Microscopium
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HD 196917 (HR 7909; 17 G. Microscopii; NSV 25227) is a solitary star[15] located in the southern constellation of Microscopium. It is faintly visible to the naked eye as a red-hued point of light with an apparent magnitude of 5.74.[3] Gaia DR3 parallax measurements imply a distance of 426 light-years and[2] it is rapidly approaching the Solar System with a heliocentric radial velocity of −97.3 km/s.[9] At its current distance, HD 196917's brightness is diminished by 0.13 magnitudes due to interstellar extinction[16] and it has an absolute magnitude of +0.04.[1]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Microscopium[1] |
| Right ascension | 20h 41m 23.65766s[2] |
| Declination | −31° 35′ 53.8334″[2] |
| Apparent magnitude (V) | 5.74[3] |
| Characteristics | |
| Evolutionary stage | AGB[4] |
| Spectral type | M1 III[5] or M0 III[6] |
| B−V color index | +1.53[7] |
| Variable type | suspected[8] |
| Astrometry | |
| Radial velocity (Rv) | −97.3±2.3[9] km/s |
| Proper motion (μ) | RA: +109.914 mas/yr[2] Dec.: −60.256 mas/yr[2] |
| Parallax (π) | 7.6563±0.0891 mas[2] |
| Distance | 426 ± 5 ly (131 ± 2 pc) |
| Absolute magnitude (MV) | +0.04[1] |
| Details | |
| Mass | 1.27[10] M☉ |
| Radius | 44.2±2.2[11] R☉ |
| Luminosity | 620+45 −20[2] L☉ |
| Surface gravity (log g) | 1.40[10] cgs |
| Temperature | 3,908±122[12] K |
| Metallicity [Fe/H] | −0.28[10] dex |
| Other designations | |
| 17 G. Microscopii[13], NSV 25227, CD−32°16130, CPD−32°6177, FK5 3652, GC 28808, HD 196917, HIP 102092, HR 7909, SAO 212345, TIC 441396067[14] | |
| Database references | |
| SIMBAD | data |
HD 196917 has a stellar classification of either M1 III[5] or M0 III,[6] indicating that it is an evolved M-type giant. It is currently on the asymptotic giant branch,[4] fusing hydrogen and helium shells around an inert carbon core. It has 1.27 times the mass of the Sun[10] but it has expanded to 44.2 times the radius of the Sun.[11] It radiates 620 times the luminosity of the Sun[2] from its enlarged photosphere at an effective temperature of 3,908 K.[12] HD 196917 is metal deficient with an iron abundance of [Fe/H] = −0.28 or 52.5% of the Sun's.[10]
The variability of the star was first detected in 1997 by the Hipparcos mission.[17] It found variations between 5.82 and 5.86 in the Hipparcos passband. Koen & Lyer (2002) observed visual variations from the star and found that HD 196917 varies by 0.009 magnitudes within 21.01 hours.[18] As of 2004, its variability has not been confirmed.[19]