Astronomy:HD 168625

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Short description: Star in the constellation Sagittarius
HD 168625
The star formation region Messier 17.jpg
HD 168625 is the left star of the pair below the Omega Nebula. The other is the hypergiant HD 168607.
Observation data
Equinox J2000.0]] (ICRS)
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[8] mas
Distanceapprox. 5,300 ly
(approx. 1,600 pc)
Absolute magnitude (MV)−8.39[4]
Details[4]
Radius105 R☉
Luminosity380,000 L☉
Surface gravity (log g)1.74 cgs
Temperature14,000 K
Rotational velocity (v sin i)60 km/s
Other designations
V4030 Sgr, HD 168625, BD −16°4830, SAO 161375, HIP 89963, AAVSO 1815-168
Database references
SIMBADdata

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.

Distance

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

A visual band light curve for V4030 Sagittarii, plotted from ASAS data[12]

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

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

  1. ↑ 1.0 1.1 1.2 1.3 Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V. 
  2. ↑ Samus, N. N. 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. 
  3. ↑ 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. doi:10.1051/0004-6361:20021430. Bibcode: 2003A&A...397.1035C. 
  4. ↑ 4.0 4.1 4.2 Mahy, L.; Hutsemékers, D.; Royer, P.; Waelkens, C. (2016). "Tracing back the evolution of the candidate LBV HD168625". Astronomy & Astrophysics 594: A94. doi:10.1051/0004-6361/201628584. Bibcode: 2016A&A...594A..94M. 
  5. ↑ 5.0 5.1 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. 
  6. ↑ 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. 
  7. ↑ 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. doi:10.1002/asna.200710776. Bibcode: 2007AN....328..889K. 
  8. ↑ 8.0 8.1 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G.  Gaia DR2 record for this source at VizieR.
  9. ↑ Chentsov, E.L.; Gorda, E.S. (2004). "Spatial Closeness of the White Hypergiants HD 168607 and HD 168625". Astronomy Letters 30 (7): 145–180. doi:10.1134/1.1774398. Bibcode: 2004AstL...30..461C. 
  10. ↑ 10.0 10.1 Nazé, Y.; Rauw, G.; Hutsemékers, D. (2012). "The first X-ray survey of Galactic luminous blue variables". Astronomy & Astrophysics 538: A47. doi:10.1051/0004-6361/201118040. A47. Bibcode: 2012A&A...538A..47N. 
  11. ↑ 11.0 11.1 11.2 "Multiwavelength Study of the Nebula Associated with the Galactic LBV Candidate HD 168625". The Astronomical Journal 124 (3): 1625–1635. 2002. doi:10.1086/341820. Bibcode: 2002AJ....124.1625P. 
  12. ↑ "ASAS All Star Catalogue". The All Sky Automated Survey. http://www.astrouw.edu.pl/asas/?page=aasc. 
  13. ↑ 13.0 13.1 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. doi:10.1088/0004-637X/718/2/1036. Bibcode: 2010ApJ...718.1036U. 
  14. ↑ Martayan, C.; Lobel, A.; Baade, D.; Blomme, R.; Frémat, Y.; Lebouquin, J.-B.; Selman, F.; Girard, J. et al. (2012). "On the Binarity of LBV Stars". ASP Conference Proceedings 464: 293. Bibcode: 2012ASPC..464..293M. 
  15. ↑ Martayan, C.; Lobel, A.; Baade, D.; Mehner, A.; Rivinius, T.; Boffin, Henry M. J.; Ronny, B.; Girard, J. et al. (2016). "Luminous blue variables: An imaging perspective on their binarity and near environment". Astronomy & Astrophysics 587: A115. doi:10.1051/0004-6361/201526578. A115. Bibcode: 2016A&A...587A.115M. https://hal.archives-ouvertes.fr/hal-01255772/file/article12LBVn5.pdf. 
  16. ↑ 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. 
  17. ↑ 17.0 17.1 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. doi:10.1086/510838. Bibcode: 2007AJ....133.1034S. 
  18. ↑ 18.0 18.1 "HD 168701". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+168701. 



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