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 |
| Astrometry | |
| Radial velocity (Rv) | -4 km/s |
| Proper motion (μ) | RA: -0.71 mas/yr Dec.: 0.01 mas/yr |
| Parallax (π) | 2.52 ± 1.10 mas |
| Distance | approx. 1,300 ly (approx. 400 pc) |
| Absolute magnitude (MV) | −7.85[1] |
| Characteristics | |
| Spectral type | B6Ia+[1] |
| U−B color index | 0.57 |
| B−V color index | 1.24 |
| J−K color index | 0.599 |
| Variable type | alpha cygni |
| Details | |
| Luminosity | 220,000[1] L☉ |
| Surface gravity (log g) | 1.5[1] cgs |
| Temperature | 12,000[1] K |
| Database references | |
| SIMBAD | data |
| Other designations | |
HD 168625 is a blue hypergiant and a variable star located in the constellation of Sagittarius easy to see with amateur telescopes. 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,[2] at a distance to the Sun of 2.2 kiloparsecs (7.200 light years),[3] 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.[4]
Physical characteristics
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.[3] It is losing mass through a very strong stellar wind at a rate of roughly 1.46×10−6 solar masses per year.[5]
However, its most notable characteristic is the presence of a nebula surrounding it that was discovered in 1994[6] and that has been studied with the help of several instruments and observatories and telescopes that include among others the Hubble Space Telescope[4] and the VLT.[5]
Said studies show that HD 168625 is actually surrounded by two nebulae: an inner one that has an elliptical shape and a very complex structure that includes arcs and filaments,[4] and a much larger outer one discovered with the help of the Spitzer Space Telescope that has a bipolar shape and that looks like a clone of the one surrounding Sanduleak -69° 202, the progenitor of the supernova 1987A in the Large Magellanic Cloud.[7] This suggests Sanduleak -69° 202 was also a luminous blue variable as well as the possibility of HD 168625 exploding as a Type II supernova in the near future.[7]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Bibcode: 1992A&A...264...88V
- ↑ Chentsov, E.L.; Gorda, E.S. (2004). "Spatial Closeness of the White Hypergiants HD 168607 and HD 168625". Astronomy Letters 30: 145–180. Bibcode:2004AstL...30..461C. doi:10.1134/1.1774398.
- ↑ 3.0 3.1 Nazé, Y.; Rauw, G.; Hutsemékers, D. (2012). "The first X-ray survey of Galactic luminous blue variables". Astronomy & Astrophysics 538. arXiv:1111.6375. Bibcode:2012A&A...538A..47N. doi:10.1051/0004-6361/201118040. A47.
- ↑ 4.0 4.1 4.2 Pasquali, A.; Nota, A.; Smith, L.J.; Akiyama, S.; Messineo, M.; Clampin, M. (2002). "Multiwavelength Study of the Nebula Associated with the Galactic LBV Candidate HD 168625". The Astronomical Journal 124 (3): 1625–1635. arXiv:astro-ph/0207613. Bibcode:2002AJ....124.1625P. doi:10.1086/341820.
- ↑ 5.0 5.1 Umana, G.; Buemi, C.S.; Trigilio, C.; Leto, P.; Hora, J.L. (2010). "Spitzer, Very Large Telescope, and Very Large Array Observations of the Galactic Luminous Blue Variable Candidate HD 168625". The Astrophysical Journal 718 (2): 1036–1045. Bibcode:2010ApJ...718.1036U. doi:10.1088/0004-637X/718/2/1036.
- ↑ Hutsemekers, D.; vanDrom, E.; Gosset, E.; Melnick, J. (1994). "A dusty nebula around the luminous blue variable candidate HD 168625". Astronomy and Astrophysics 2904: 906–914. Bibcode:1994A&A...290..906H.
- ↑ 7.0 7.1 Smith, Nathan (2007). "Discovery of a Nearby Twin of SN 1987A's Nebula around the Luminous Blue Variable HD 168625: Was Sk -69 202 an LBV?". The Astronomical Journal 133 (3): 1034–1040. arXiv:astro-ph/0611544. Bibcode:2007AJ....133.1034S. doi:10.1086/510838.
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