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HD 171978 is a binary star system in the Serpens Cauda segment of the equatorial constellation of Serpens. It may be referred to by its Bright Star Catalogue identifier of HR 6993. This system is dimly visible to the naked eye with a combined apparent visual magnitude of 5.76, although is a suspected variable star of unknown type with a magnitude that has been reported to vary between 5.74 and 5.86. HD 171978 is located at a distance of approximately 537 light-years from the Sun based on parallax, and is drifting further away with a barycentric radial velocity of +11.4 km/s. It is a member of the Ursa Major Moving Group.

The binary nature of this system was reported by Canadian astronomer R. M. Petrie in 1948. It is a double-lined spectroscopic binary with an orbital period of 14.7 days and an eccentricity (ovalness) of 0.25. The orbital inclination is estimated to be ~30°. The two stars have a magnitude difference of 0.4±0.1 mag, which gives respective magnitudes of 6.33 and 6.73. They each show a sharp-lined spectra, indicating their rotation rates are not high. Both are similar A-type main-sequence stars with a combined stellar classification of A0V. In 1970, Geary and Abt noted that the secondary appeared to be an Am star.

References

1. ^ 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.
2. ^ Fekel, Francis C.; Tomkin, Jocelyn; Williamson, Michael H. (2013). "New Precision Orbits of Bright Double-lined Spectroscopic Binaries. VIII. HR 1528, HR 6993, 2 Sagittae, and 18 Vulpeculae". The Astronomical Journal. 146 (5). 129. Bibcode:2013AJ....146..129F. doi:10.1088/0004-6256/146/5/129. hdl:2152/34407. S2CID 121155872.
3. ^ "NSV 11122, database entry". New Catalogue of Suspected Variable Stars, the improved version. Moscow, Russia: Sternberg Astronomical Institute. Retrieved October 3, 2008.
4. ^ Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars". Michigan Spectral Survey. 5. Bibcode:1999MSS...C05....0H.
5. ^ Hoffleit, D.; Warren, Jr., W. H. HR 6993, database entry (5th Revised ed.). Centre de Données astronomiques de Strasbourg. Retrieved October 3, 2008. {{cite book}}: |work= ignored (help) V/50.
6. ^ Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
7. "e Ser". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2015-12-07.
8. ^ Geary, J. C.; Abt, H. A. (August 1970). "Rotational velocities in the Ursa Major group". Astronomical Journal. 75: 718–720. Bibcode:1970AJ.....75..718G. doi:10.1086/111013.
9. Petrie, R. M. (July 1948). "The spectrographic orbits and dimensions of H. D. 171978". Publications of the Dominion Astrophysical Observatory Victoria. 7: 415–418. Bibcode:1948PDAO....7..415P.

v t e Constellation of Serpens
List of stars in Serpens Serpens in Chinese astronomy
Stars	Bayer α (Unukalhai) β (Chow) γ (Ainalhai) δ ε ζ η θ (Alya) ι κ (Gudja) λ μ ν ξ ο π ρ σ τ τ τ τ τ τ τ τ υ φ χ ψ ω Flamsteed 3 4 5 6 7 8 10 11 (A) 14 16 25 (A) 29 36 (b) 39 40 43 45 46 47 59 (d) 60 (c) 61 64 3 Her Variable R W X RT UZ VV VY WX AA AN AO AP AR AU BQ CT CV CW EG FH FI FK FL FQ FR LV LW LX MR MS MT MV MY NN NO NQ NW OO OU PS QV QX QY V382 V411 HR 5665 5690 5692 5706 5711 5740 5745 5783 5796 5831 5850 5859 5861 5874 5909 5913 5931 5992 6005 6011 6014 6016 6449 6496 6544 6562 6568 6600 6620 6666 6681 6755 6756 6757 6785 6830 6840 6843 6858 6890 6898 6928 6993 (e) 6999 7008 7048 7076 7144 HD 135061 135615 136027 136118 138085 142245 143436 145936 146740 157969 168112 168443 168746 (Alasia) 175541 (Kaveh) Other ADS 9544 AS 296 9 11 22 23 27 Gliese 701 Gliese 710 GJ 1224 GX 17+2 IRAS 18418-0440 MWC 297 MWC 922 PG 1510+234 PG 1605+072 PSR B1534+11 PSR J1719−1438 Ross 508 Serpens FIRS 1 Serpens SVS 20 Serpens X-1 W40 IRS 1A South
Exoplanets CoRoT-9b CoRoT-11b CoRoT-22b CoRoT-23b CoRoT-27b HD 168746 b (Onasilos) HD 175541 b (Kavian) ω Serpentis b
Star clusters	NGC NGC 6535 NGC 6539 NGC 6604 NGC 6605 Other IC 4756 Messier 5 Messier 16 Serpens OB2 Serpens South Palomar 5
Nebulae	Other Abell 41 Eagle Nebula L134 L183 L483 Serpens cloud Sh2-54 Westerhout 40 Red Square Nebula S68
Galaxies	NGC 5887 5910 5911 5913 5919 5920 5921 5926 5928 5931 5936 5937 5940 5942 5941 5944 5951 5953 5954 5952 5956 5955 5957 5960 5962 5964 5970 5972 5975 5977 5980 5983 5984 5988 5991 5990 5994 5996 5997 6003 6004 6008 6006 6007 6009 6012 6010 6014 6020 6017 6018 6021 6022 6023 6027 6027a 6027b 6027c 6027d 6027e 6029 6033 6037 6036 6051 6063 6065 6066 6070 6080 6100 6118 6172 Other 317 318 321 323.1 324 326 Arp 72 Arp 220 4C 11.50 CGCG 049-033 Hoag's Object IC 4537 IC 4588 IRAS 15107+0724 NRAO 530 PDS 456 PG 1553+113 PGC 54493 PKS 1546+027
Galaxy clusters Abell 2040 Abell 2052 Abell 2063 Abell 2107 AWM 4 MKW 3s Seyfert's Sextet
Astronomical events GRB 970111 GRB 050813 GRB 060418 GRB 060526 SN 2004dk
Category

• A-type main-sequence stars
• Am stars
• Spectroscopic binaries
• Suspected variables
• Serpens
• Bayer objects
• Durchmusterung objects
• Henry Draper Catalogue objects
• Hipparcos objects
• Bright Star Catalogue objects