WR 128

WR 128

A visual band light curve for QT Sagittae, adapted from Antokhin and Cherepashchuk (1985)
Observation data
Epoch J2000      Equinox ICRS
Constellation Sagitta
Right ascension 19h 48m 32.19674s
Declination +18° 12′ 03.6956″
Apparent magnitude (V) 10.51
Characteristics
Evolutionary stage Wolf–Rayet
Spectral type WN4(h)-w
U−B color index −0.89
B−V color index −0.02
Astrometry
Radial velocity (Rv)100.00 km/s
Proper motion (μ) RA: −0.233 mas/yr
Dec.: −5.455 mas/yr
Parallax (π)0.2836±0.0202 mas
Distance2,900+540
−390 pc
Absolute magnitude (MV)−3.27
Details
Mass11 M☉
Radius2.69 R☉
Luminosity166,000 L☉
Temperature70,800 K
Other designations
QT Sagittae, HD 187282, WR 128, HIP 97456, 2MASS J19483219+1812036
Database references
SIMBADdata

WR 128 is a Wolf–Rayet star located about 9,500 light years away in the constellation of Sagitta. A member of the WN class, WR 128's spectrum resembles that of a WN4 star, but hydrogen is clearly present in the star (hence the h in its spectrum), making it the only known hydrogen-rich WN4 star in the galaxy. However, similar H-rich very early WN stars can be found in the LMC and especially in the SMC, but the only other galactic examples of this are WR 3 and WR 152.

In 1981, Igor Antokhin et al. discovered that the star, then known as HD 187282, is a variable star. It was given its variable star designation, QT Sagittae, in 1985.

Properties

Analysis of WR 128's spectrum with PoWR shows that it has a temperature of around 70,800 K and is losing mass at a very slow pace (in Wolf–Rayet terms), at 10−5.4 M☉/yr, or in other words, 1 solar mass every 250,000 years. All this mass is being carried by a very strong stellar wind with a terminal velocity of 2,050 kilometres per second. Taking its distance into account, WR 128 has a luminosity of 166,000 L☉, or 105.22 L☉, making it one of the dimmest galactic WN stars. Using the Stefan-Boltzmann Law, a radius of 2.69 R☉ is obtained. A "transformed" radius at an optical depth of 2/3, more comparable to other types of stars, is at about 13 R☉.

References

  1. ↑ Antokhin, I. I.; Cherepashchuk, A. M. (January 1985). "Wolf-Rayet stars with possible relativistic companions - Light curves and orbital periods for the WN stars HD 187282, HD 192163". Soviet Astronomy Letters. 11: 355–358. Bibcode:1985SvAL...11..355A.
  2. ↑ Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific. 99 (617): 695. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Constellation record for this object at VizieR.
  3. 1 2 3 4 5 Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  4. 1 2 3 4 5 6 7 8 9 10 Hamann, W.-R.; Gräfener, G.; Liermann, A.; Hainich, R.; Sander, A. A. C.; Shenar, T.; Ramachandran, V.; Todt, H.; Oskinova, L. M. (2019-05-01). "The Galactic WN stars revisited. Impact of Gaia distances on fundamental stellar parameters". Astronomy and Astrophysics. 625: A57. arXiv:1904.04687. Bibcode:2019A&A...625A..57H. doi:10.1051/0004-6361/201834850. ISSN 0004-6361. S2CID 104292503.
  5. 1 2 Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". VizieR Online Data Catalog. 2237. Bibcode:2002yCat.2237....0D.
  6. ↑ Kharchenko, N. V.; Scholz, R.-D.; Piskunov, A. E.; Röser, S.; Schilbach, E. (2007-11-01). "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. ISSN 0004-6337. S2CID 119323941.
  7. ↑ Crowther, Paul A.; Rate, Gemma (2020). "Unlocking Galactic Wolf–Rayet stars with Gaia DR2 – I. Distances and absolute magnitudes". Monthly Notices of the Royal Astronomical Society. 493 (1): 1512–1529. arXiv:1912.10125. Bibcode:2020MNRAS.493.1512R. doi:10.1093/mnras/stz3614. S2CID 209444955.
  8. ↑ Marchenko, S. V.; Moffat, A. F. J.; Crowther, P. A.; Chené, A.-N.; De Serres, M.; Eenens, P. R. J.; Hill, G. M.; Moran, J.; Morel, T. (2004-09-01). "Hydrogen in the atmosphere of the evolved WN3 Wolf-Rayet star WR 3: defying an evolutionary paradigm?". Monthly Notices of the Royal Astronomical Society. 353 (1): 153–161. Bibcode:2004MNRAS.353..153M. doi:10.1111/j.1365-2966.2004.08058.x. ISSN 0035-8711. S2CID 122329869.
  9. ↑ Antokhin, I. I.; Aslanov, A. A.; Cherepashchuk, A. M. (December 1982). "HD 187282 - A possible Wolf-Rayet binary with a low-mass companion". Soviet Astronomy Letters. 8: 395–398. Bibcode:1982SvAL....8..395A.
  10. ↑ Kholopov, P. N.; Samus, N. N.; Kazarovets, E. V.; Perova, N. B. (March 1985). "The 67th Name-List of Variable Stars" (PDF). Information Bulletin on Variable Stars. 2681: 1–32. Bibcode:1985IBVS.2681....1K. Retrieved 26 October 2025.