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Suspected variable star in Microscopium From Wikipedia, the free encyclopedia
HD 196917 (HR 7909; 17 G. Microscopii; NSV 25227) is a solitary star[16] located in the southern constellation Microscopium. It is faintly visible to the naked eye as a red-hued point of light with an apparent magnitude of 5.74.[2] Gaia DR3 parallax measurements imply a distance of 426 light-years and[1] 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[17] and it has an absolute magnitude of +0.04.[10]
Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
---|---|
Constellation | Microscopium |
Right ascension | 20h 41m 23.65766s[1] |
Declination | −31° 35′ 53.8334″[1] |
Apparent magnitude (V) | 5.74[2] (5.75 - 5.76)[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[1] Dec.: −60.256 mas/yr[1] |
Parallax (π) | 7.6563 ± 0.0891 mas[1] |
Distance | 426 ± 5 ly (131 ± 2 pc) |
Absolute magnitude (MV) | +0.04[10] |
Details | |
Mass | 1.27[11] M☉ |
Radius | 44.2±2.2[12] R☉ |
Luminosity | 620+45 −20[1] L☉ |
Surface gravity (log g) | 1.40[11] cgs |
Temperature | 3,908±122[13] K |
Metallicity [Fe/H] | −0.28[11] dex |
Other designations | |
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[11] but it has expanded to 44.2 times the radius of the Sun.[12] It radiates 620 times the luminosity of the Sun[1] from its enlarged photosphere at an effective temperature of 3,908 K.[13] HD 196917 is metal deficient with an iron abundance of [Fe/H] = −0.28 or 52.5% of the Sun's.[11]
The variability of the star was first detected in 1997 by the Hipparcos mission.[18] 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.[19] As of 2004, its variability has not been confirmed.[20]
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