HD 161840
Star in the constellation Scorpius
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HD 161840 is a single,[8] blue-white hued star in the southern zodiac constellation of Scorpius. It is faintly visible to the naked eye with an apparent visual magnitude of 4.79.[1] With an annual parallax shift of 6.5 mas[2] it is located roughly 500 light years from the Sun. It is moving closer with a heliocentric radial velocity of −13 km/s.[1]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Scorpius[1] |
| Right ascension | 17h 48m 10.47559s[2] |
| Declination | −31° 42′ 11.5636″[2] |
| Apparent magnitude (V) | 4.79[1] |
| Characteristics | |
| Spectral type | B8 Ib/II[3] |
| B−V color index | −0.028±0.023[1] |
| Astrometry | |
| Radial velocity (Rv) | −13.3±2.8[1] km/s |
| Proper motion (μ) | RA: +6.845[2] mas/yr Dec.: −8.161[2] mas/yr |
| Parallax (π) | 6.5831±0.3618 mas[2] |
| Distance | 500 ± 30 ly (152 ± 8 pc) |
| Absolute magnitude (MV) | −1.37[1] |
| Details | |
| Mass | 3.93±0.08[4] M☉ |
| Radius | 3.2[5] R☉ |
| Luminosity | 565+59 −53[4] L☉ |
| Surface gravity (log g) | 3.38[6] cgs |
| Temperature | 11066+77 −76[4] K |
| Rotational velocity (v sin i) | 24[4] km/s |
| Other designations | |
| CD−31°14609, HD 161840, HIP 87220, HR 6628, SAO 209303[7] | |
| Database references | |
| SIMBAD | data |
There has been some uncertainty as to the classification of this stage. Houk (1979) lists a stellar class of B8 Ib/II for HD 161840,[3] which corresponds to a B-type bright giant/lesser supergiant mix. Multiple studies still use an older classification of B8 V,[8][6][4] suggesting instead this is a B-type main-sequence star. Garrison and Gray (1994) assigned it a class of B8 III-IV,[9] which would put it on the subgiant/giant star track. It has an estimated 3.93[4] times the mass of the Sun and 3.2[5] times the Sun's radius. The star is radiating 565[4] times the Sun's luminosity from its photosphere at an effective temperature of 11,066 K.[4]