HD 168625
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 21m 19.548s |
| Declination | −16° 22′ 16.0572″ |
| Apparent magnitude (V) | 8.44 |
| Characteristics | |
| Spectral type | B6Ia+(B2 - B8) |
| U−B color index | +0.37 |
| B−V color index | +1.41 |
| J−K color index | 0.599 |
| Variable type | alpha cygni |
| Astrometry | |
| Radial velocity (Rv) | -4.00 km/s |
| Proper motion (μ) |
RA: -0.71 ± 1.20 mas/yr Dec.: +0.01 ± 0.74 mas/yr |
| Parallax (π) | 2.52 ± 1.10mas |
| Distance | 2,800pc |
| Absolute magnitude (MV) | −8.39 |
| Details | |
| Luminosity | 380,000 L☉ |
| Surface gravity (log g) | 1.74 cgs |
| Temperature | 14,000 K |
| Rotational velocity (v sin i) | 60 km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
HD 168625 (V4030 Sgr) is a blue hypergiant and candidate luminous blue variable located in the constellation of Sagittarius easy to see with amateur telescopes. It forms a visual pair with the also blue hypergiant (and luminous blue variable) HD 168607 and is located to the south-east of M17, the Omega Nebula.
Its distance and association with that nebula and the mentioned star is dubious; while some authors think both stars are physically associated and belong to the stellar association Serpens OB1, at a distance to the Sun of 2.2 kiloparsecs (7.200 light years), others think HD 168625 is farther, at a distance estimated to be 2.8 kiloparsecs (9,100 light years) and unrelated to the former objects.
Assuming a distance of 2.2 kiloparsecs, HD 168625 is 220,000 times brighter than the Sun, having a surface temperature of 12,000 K. It is losing mass through a very strong stellar wind at a rate of roughly 1.46×10−6solar masses per year and observations realized in 2012 with the help of the VLT show it's actually a binary star, with the companion being around 4.5 magnitudes fainter than the primary.
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