HD 183143

HD 183143 (HT Sagittae) is a blue hypergiant star located in the constellation of Sagitta.

HD 183143

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Sagitta
Right ascension	19^h 27^m 26.5636^s[1]
Declination	+18° 17′ 45.192″[1]
Apparent magnitude (V)	6.71 - 6.95[2]
Characteristics
Spectral type	B6-8 Ia-0[3]
Apparent magnitude (B)	8.08
Apparent magnitude (J)	4.13
Apparent magnitude (K)	3.46
Variable type	α Cyg?[2]
Astrometry
Proper motion (μ)	RA: 0.19 ± 0.37 mas/yr Dec.: -5.15 ± 0.39 mas/yr
Parallax (π)	0.66 ± 0.28[1] mas
Distance	6,500 ly (2,000 pc)
Absolute magnitude (MV)	−8.7[3]
Details
Surface gravity (log g)	1.40[4] cgs
Temperature	11,500[4] K
Rotational velocity (v sin i)	37[4] km/s
Other designations
HT Sge, BD+18° 4085, HD 183143, HIP 95657, SAO 104860
Database references
SIMBAD	data

This star has an apparent magnitude of 6.86, meaning that can be seen with the naked eye under very dark skies and that is an easy target for binoculars or a small telescope.

Observations

HD 183143 was included in the first catalogue of Be stars, with distinct H_α emission lines.[5] When emission lines in hot supergiant stars were investigated as indicators of expanding atmospheres and mass loss, HD 183143 was found to have H_α lines with P Cygni profiles, but indications of only modest mass loss.[6] Modern high-resolution spectra show emission in lines from H_α, H_β, H_γ, and H_δ, formed by the strong stellar wind.[4]

The introduction of spectral standards for supergiants gave HD 183143 as the standard star for the class B7Ia.[7] The spectral type is sometimes given as B7Iae to indicate the presence of the emission lines.[8]

HD 183143 was listed as being variable in 1976, with a very small amplitude.[9] During the Hipparcos mission, its brightness was observed to vary between magnitude 6.71 and 6.95. ASAS-3 photometry shows a period of 40.44 days.[2] HD 183143 was formally announced as a variable star, probably of the α Cygni type, in 1979 and given the variable star designation HT Sagittae.[10]

HD 183143 has been extensively studied because of the diffuse interstellar bands visible in its spectrum. The strongest lines are caused by interstellar atomic iron, potassium, lithium, sodium, and calcium, as well as ionised calcium, and CH and CN molecules.[11] Infrared bands of ionised buckminsterfullerene have also been found in its spectrum.[12] HD 183143 has been proposed as a reference standard for interstellar polarisation. It shows 6% polarisation.[13]

A 2004 study reclassified the spectral type of HD 183143 as B6.8 Ia-0, a hypergiant. The parallax from the original Hipparcos catalogue was 2.70 mas, indicating a distance around 370 pc, but the revised Hipparcos parallax and the Gaia data release 1 parallax both indicate distances around 2,000 pc. Comparison of the space velocity and interstellar spectral lines produce a similar distance, with the star lying between the Orion-Cygnus Arm and the Carina–Sagittarius Arm.[3]

References

1. Gaia Collaboration (2016). "VizieR Online Data Catalog: Gaia DR1 (Gaia Collaboration, 2016)". VizieR On-line Data Catalog: I/337. Originally Published in: Astron. Astrophys. 1337. Bibcode:2016yCat.1337....0G.
2. Watson, C. L. (2006). "The International Variable Star Index (VSX)". The Society for Astronomical Sciences 25th Annual Symposium on Telescope Science. Held May 23–25. 25: 47. Bibcode:2006SASS...25...47W.
3. Chentsov, E. L. (2004). "HD 183143: A Hypergiant". Astronomy Letters. 30 (5): 325–331. Bibcode:2004AstL...30..325C. doi:10.1134/1.1738155.
4. Galazutdinov, G. A.; Shimansky, V. V.; Bondar, A.; Valyavin, G.; Krełowski, J. (2017). "C60+ - looking for the bucky-ball in interstellar space". Monthly Notices of the Royal Astronomical Society. 465 (4): 3956. arXiv:1612.08898. Bibcode:2017MNRAS.465.3956G. doi:10.1093/mnras/stw2948.
5. Merrill, P. W.; Humason, M. L.; Burwell, C. G. (1925). "Discovery and Observations of Stars of Class Be". Astrophysical Journal. 61: 389. Bibcode:1925ApJ....61..389M. doi:10.1086/142899.
6. Hutchings, J. B. (1970). "Expanding atmospheres in OB supergiants - IV". Monthly Notices of the Royal Astronomical Society. 147 (2): 161. Bibcode:1970MNRAS.147..161H. doi:10.1093/mnras/147.2.161.
7. Morgan, W. W.; Roman, Nancy G. (1950). "Revised Standards for Supergiants on the System of the Yerkes Spectral Atlas". Astrophysical Journal. 112: 362. Bibcode:1950ApJ...112..362M. doi:10.1086/145351.
8. Kohoutek, L.; Wehmeyer, R. (1997). "Catalogue of stars in the Northern Milky Way having H-alpha in emission". Abhandlungen aus der Hamburger Sternwarte. 11. Bibcode:1997AAHam..11.....K.
9. Hill, G.; Hilditch, R. W.; Pfannenschmidt, E. L. (1976). "Photoelectric measures of variable stars observed at Mt. Kobau (1970 - 73)". Publications of the Dominion Astrophysical Observatory Victoria. 15: 1. Bibcode:1976PDAO...15....1H.
10. Kholopov, P. N.; Kukarkina, N. P.; Perova, N. B. (1979). "64th Name-List of Variable Stars". Information Bulletin on Variable Stars. 1581: 1. Bibcode:1979IBVS.1581....1K.
11. Hobbs, L. M.; York, D. G.; Thorburn, J. A.; Snow, T. P.; Bishof, M.; Friedman, S. D.; McCall, B. J.; Oka, T.; Rachford, B.; Sonnentrucker, P.; Welty, D. E. (2009). "Studies of the Diffuse Interstellar Bands. III. HD 183143". The Astrophysical Journal. 705: 32. arXiv:0910.2983. Bibcode:2009ApJ...705...32H. doi:10.1088/0004-637X/705/1/32.
12. Walker, G. A. H.; Bohlender, D. A.; Maier, J. P.; Campbell, E. K. (2015). "Identification of More Interstellar C60+ Bands". The Astrophysical Journal Letters. 812: L8. arXiv:1509.06818. Bibcode:2015ApJ...812L...8W. doi:10.1088/2041-8205/812/1/L8.
13. Wisniewski, John P.; Babler, Brian L.; Bjorkman, Karen S.; Kurchakov, Anatoly V.; Meade, Marilyn R.; Miroshnichenko, Anatoly S. (2006). "The Asymmetrical Wind of the Candidate Luminous Blue Variable MWC 314". The Publications of the Astronomical Society of the Pacific. 118 (844): 820. arXiv:astro-ph/0605602. Bibcode:2006PASP..118..820W. doi:10.1086/506182.