Summary
HD 168625 (V4030 Sagittarii) is a blue hypergiant star 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.
 HD 168625 is the left star of the pair below the Omega Nebula. The other is the hypergiant HD 168607. | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 21m 19.548s[1] |
| Declination | −16° 22′ 16.0572″[1] |
| Apparent magnitude (V) | 8.30–8.41[2] |
| Characteristics | |
| Spectral type | B6Ia+[3] (B2—B8[4]) May be B60 due to hypergiant designation |
| U−B color index | +0.37[5] |
| B−V color index | +1.41[5] |
| J−K color index | 0.599 |
| Variable type | α Cygni[6] |
| Astrometry | |
| Radial velocity (Rv) | −4.00[7] km/s |
| Proper motion (μ) | RA: −0.71±1.20[1] mas/yr Dec.: +0.01±0.74[1] mas/yr |
| Parallax (π) | 0.6212 ± 0.0640 mas[8] |
| Distance | approx. 5,300 ly (approx. 1,600 pc) |
| Absolute magnitude (MV) | −8.39[4] |
| Details[4] | |
| Radius | 105 R☉ |
| 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 |
Distance edit
The distance of HD 168625 and its association with the Omega Nebula and HD 168607 is in doubt; while some authors think both stars are physically associated and belong to the stellar association Serpens OB1,[9] at a distance to the Sun of 2.2 kiloparsecs (7,200 ly),[10] or for both per Gaia Data Release 2 about 1.6 kiloparsecs (5,200 ly),[8] a 2002 study estimates this star is farther, at about 2.8 kiloparsecs (9,100 ly) and unrelated to the other two objects.[11]
Physical characteristics edit
Assuming a distance of 2.2 kiloparsecs, the star would be 220,000 times brighter than the Sun, having a surface temperature of 12,000 K.[10] At that distance it can be calculated to be losing mass through a fierce stellar wind at roughly 1.46×10−6 solar masses per year[13] however this is to be muted somewhat as work realized in 2012 from the VLT reveal a binary star system – [14] a companion exists around 4.5 magnitudes fainter than the primary.[15]
Nebula edit
The most notable characteristic of HD 168625 is the presence of a nebula surrounding it that was discovered in 1994[16] and that has been studied with the help of several instruments and observatories and telescopes that include among others the Hubble Space Telescope[11] and the VLT.[13]
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,[11] 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.[17] 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.[17]
East-north-east of the star and nebula is HD 168701 (HIP 90001), an eclipsing binary of beta Lyrae type.[18] It is at about six times the angular separation of HD 168607 viewed from the solar system and is the third very bright point to the south-east of the nebula. Its parallax of 0.7106 ± 0.0451 mas implies it is about 1,700 parsecs (5,500 ly) away.[18]
References edit
- ^ a b c d Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
- ^ Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
- ^ Chentsov, E. L.; Ermakov, S. V.; Klochkova, V. G.; Panchuk, V. E.; Bjorkman, K. S.; Miroshnichenko, A. S. (2003). "An atlas of spectra of B6-A2 hypergiants and supergiants from 4800 to 6700Å". Astronomy and Astrophysics. 397 (3): 1035–1042. Bibcode:2003A&A...397.1035C. doi:10.1051/0004-6361:20021430.
- ^ a b c Mahy, L.; Hutsemékers, D.; Royer, P.; Waelkens, C. (2016). "Tracing back the evolution of the candidate LBV HD168625". Astronomy & Astrophysics. 594: A94. arXiv:1608.01087. Bibcode:2016A&A...594A..94M. doi:10.1051/0004-6361/201628584. S2CID 119243390.
- ^ a b Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.
- ^ Sterken, C.; Arentoft, T.; Duerbeck, H. W.; Brogt, E. (1999). "Light variations of the blue hypergiants HD 168607 and HD 168625 (1973-1999)". Astronomy and Astrophysics. 349: 532. Bibcode:1999A&A...349..532S.
- ^ Kharchenko, N.V.; Scholz, R.-D.; Piskunov, A.E.; Röser, S.; Schilbach, E. (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ~55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889–896. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776. S2CID 119323941.
- ^ a b Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
- ^ Chentsov, E.L.; Gorda, E.S. (2004). "Spatial Closeness of the White Hypergiants HD 168607 and HD 168625". Astronomy Letters. 30 (7): 145–180. Bibcode:2004AstL...30..461C. doi:10.1134/1.1774398. S2CID 122348932.
- ^ a b Nazé, Y.; Rauw, G.; Hutsemékers, D. (2012). "The first X-ray survey of Galactic luminous blue variables". Astronomy & Astrophysics. 538: A47. arXiv:1111.6375. Bibcode:2012A&A...538A..47N. doi:10.1051/0004-6361/201118040. S2CID 43688343. A47.
- ^ a b c 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. S2CID 118968760.
- ^ "ASAS All Star Catalogue". The All Sky Automated Survey. Retrieved 8 December 2021.
- ^ a b 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.
- ^ Martayan, C.; Lobel, A.; Baade, D.; Blomme, R.; Frémat, Y.; Lebouquin, J.-B.; Selman, F.; Girard, J.; Mérand, A.; Montagnier, G.; Patru, F.; Mawet, D.; Martins, F.; Rivinius, Th.; Štefl, S.; Zorec, J.; Semaan, T.; Mehner, A.; Kervella, P.; Sana, H.; Schödel, R. (2012). "On the Binarity of LBV Stars". ASP Conference Proceedings. 464: 293. Bibcode:2012ASPC..464..293M.
- ^ Martayan, C.; Lobel, A.; Baade, D.; Mehner, A.; Rivinius, T.; Boffin, Henry M. J.; Ronny, B.; Girard, J.; Mérand, A.; Montagnier, G.; Patru, F.; Mawet, D.; Martins, F.; Rivinius, Th.; Štefl, S.; Zorec, J.; Semaan, T.; Mehner, A.; Kervella, P.; Sana, H.; Schödel, R. (2016). "Luminous blue variables: An imaging perspective on their binarity and near environment" (PDF). Astronomy & Astrophysics. 587: A115. arXiv:1601.03542. Bibcode:2016A&A...587A.115M. doi:10.1051/0004-6361/201526578. S2CID 1755296. A115.
- ^ 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.
- ^ a b 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. S2CID 17598600.
- ^ a b "HD 168701". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-01-05.