17 Comae Berenices

17 Comae Berenices (17 Com) is a multiple star system in the northern constellation of Coma Berenices. The brighter component, 17 Com A, is a naked eye star with an apparent visual magnitude of 5.2.[2] It has a faint companion of magnitude 6.6,[6] 17 Com B, positioned at an angular separation of 146.4″ along a position angle of 251°, as of 2018.[17] They are located at a distance of approximately 240 light years from the Sun based on parallax measurements.[1]

17 Comae Berenices
Location of 17 Com (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Coma Berenices
17 Com A
Right ascension 12h 28m 54.703s[1]
Declination +25° 54′ 46.27″[1]
Apparent magnitude (V) 5.242±0.004[2]
17 Com BC
Right ascension 12h 28m 44.565s[3]
Declination +25° 53′ 57.56″[3]
Apparent magnitude (V) 6.635[4]
Characteristics
17 Com A
Spectral type A0p[5]
A0 SrCrEu[2]
B−V color index −0.056±0.009[6]
Variable type α2 CVn + δ Sct(?)[7]
17 Com BC
Spectral type kA2hA9VmF0[8]
U−B color index 0.084[4]
B−V color index 0.216[4]
Astrometry
17 Com A
Radial velocity (Rv)−1.4±0.5[9] km/s
Proper motion (μ) RA: −23.539 mas/yr[1]
Dec.: −15.620 mas/yr[1]
Parallax (π)13.5382 ± 0.2245 mas[1]
Distance241 ± 4 ly
(74 ± 1 pc)
Absolute magnitude (MV)0.98[6]
17 Com BC
Radial velocity (Rv)−1.8±0.1[10] km/s
Proper motion (μ) RA: −22.296 mas/yr[3]
Dec.: −17.071 mas/yr[3]
Parallax (π)13.6383 ± 0.0913 mas[3]
Distance239 ± 2 ly
(73.3 ± 0.5 pc)
Absolute magnitude (MV)2.46[6]
Orbit[11]
Primary17 Com B
Companion17 Com C
Period (P)68.290±0.012 d
Eccentricity (e)0.296±0.008
Periastron epoch (T)2,448,313.4±0.4 JD
Argument of periastron (ω)
(secondary)		260.7±2.2°
Semi-amplitude (K1)
(primary)		14.0±0.2 km/s
Details
17 Com A
Mass2.38 M☉[2]
2.61 M☉[12]
2.75±0.3[13] M☉
Radius2.09[5] R☉
Luminosity42.7[5] L☉
Surface gravity (log g)4.27 cgs[12]
3.70±0.20[13] cgs
Temperature10,212 K[5]
9,309±250[13] K
Rotational velocity (v sin i)20.4±0.4[5] km/s
Age101[12] Myr
17 Com BC
Mass1.74±0.6[14] M☉
Surface gravity (log g)4.29±0.20[14] cgs
Temperature8,068±200[14] K
Rotational velocity (v sin i)22[4] km/s
Other designations
BU 1080, 17 Com, ADS 8568, WDS J12289+2555[15][16]
17 Com A: AI Com, BD+26°2354, GC 17012, HD 108662, HIP 60904, HR 4752, SAO 82330[15]
17 Com B: BD+26°2353, GC 17007, HD 108651, HIP 60891, HR 4751, SAO 82328[16]
Database references
17 Com A
SIMBADdata
17 Com B
SIMBADdata

The double nature of this system was documented by F. G. W. Struve in 1836.[17] The pair share a common proper motion through space[13] and thus may be associated. Component B is itself a binary star system, although only the brighter component is visible in the spectrum.[11] The Washington Double Star Catalogue lists the companion as component C, with a magnitude of 13.7 and a separation of 1.4″.[17] 17 Com has been recognized as members of the Coma Star Cluster,[18] but this is disputed.[19]

The star 17 Com A was classified as chemically peculiar by A. J. Cannon prior to 1918.[20] W. W. Morgan in 1932 found the star's spectral lines varied in strength and appearance,[21] and detected lines of the element europium.[22] H. W. Babcock and T. G. Cowling measured the Zeeman effect in this star, demonstrating in 1953 that it has a magnetic field.[23] In 1967, E. P. J. van den Heuvel noted the blue excess of this star, suggesting it is a blue straggler.[24] G. W. Preston and associates in 1969 found that the luminosity and magnetic field of this star varied in strength with a time scale of around five days.[25]

A light curve for AI Comae Berenices, plotted from TESS data[26]

17 Com A is a magnetic chemically peculiar Ap star with a stellar classification of A0p[5] or A0 SrCrEu,[2] with the latter indicating the spectrum shows abundance anomalies of the elements strontium, chromium, and europium. The level of silicon in the atmosphere is also enhanced[27] and it shows a significant helium deficiency.[5] It has the variable star designation of AI Com, and is classified as an Alpha2 Canum Venaticorum variable and a suspected Delta Scuti variable.[7] It has been identified as a suspected blue straggler.[13]

The primary has an estimated age of 101[12] million years and is spinning with a projected rotational velocity of 20 km/s.[5] It has more than double the mass and twice the radius of the Sun.[2][5] The magnetic field strength is 3,300±150 G.[5] It is radiating 43[5] times the luminosity of the Sun from its photosphere at an effective temperature of around 10,000 K.[5][13]

The co-moving companion, component B, is a single-lined spectroscopic binary with an orbital period of 68.3 days and an eccentricity (ovalness) of 0.3.[11] The visible member of this binary pair is a strong Am star[4] with a class of kA2hA9VmF0,[8] indicating it has the Calcium K-lines of an A0 star, the hydrogen lines of an A9 star, and the metallic lines of an F0 star.[28]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  2. Paunzen, E.; et al. (July 2021), "Magnetic chemically peculiar stars investigated by the Solar Mass Ejection Imager", Monthly Notices of the Royal Astronomical Society, 504 (3): 3758–3772, arXiv:2105.02206, Bibcode:2021MNRAS.504.3758P, doi:10.1093/mnras/stab1100.
  3. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  4. Iliev, I. Kh.; et al. (August 2006), "Abundance analysis of Am binaries and search for tidally driven abundance anomalies - II. HD861, HD18778, HD20320, HD29479, HD96528 and HD108651", Monthly Notices of the Royal Astronomical Society, 370 (2): 819–827, Bibcode:2006MNRAS.370..819I, doi:10.1111/j.1365-2966.2006.10513.x, S2CID 56133360.
  5. Romanovskaya, A. M.; et al. (September 2020), "Fundamental parameters of Ap-star HD 108662", INASAN Science Reports, 5 (4): 219–223, arXiv:2006.15950, Bibcode:2020INASR...5..219R, doi:10.26087/INASAN.2020.5.4.010, S2CID 220250089.
  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. Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
  8. Abt, H. A.; Cardona, O. (1984), "The nature of the visual companions of AP and AM stars", The Astrophysical Journal, 276: 266, Bibcode:1984ApJ...276..266A, doi:10.1086/161610.
  9. Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065, S2CID 119231169.
  10. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
  11. Abt, Helmut A.; Willmarth, Daryl W. (August 1999), "Binaries in the Praesepe and Coma Star Clusters and Their Implications for Binary Evolution", The Astrophysical Journal, 521 (2): 682–690, Bibcode:1999ApJ...521..682A, doi:10.1086/307569, S2CID 119772785.
  12. David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
  13. Monier, Richard; Deal, Morgan (July 2020), "The Evolutionary Status of 17 Com, The Hottest Member of Coma Berenices", Research Notes of the AAS, 4 (7): 104, Bibcode:2020RNAAS...4..104M, doi:10.3847/2515-5172/aba35a, S2CID 225795832, 104.
  14. Deal, Morgan; Monier, Richard (August 2020), "The Surface Abundances of 17 Com B: A Test for Self-consistent Evolutionary Models", Research Notes of the AAS, 4 (8): 144, Bibcode:2020RNAAS...4..144D, doi:10.3847/2515-5172/abb01f, S2CID 225379385, 144.
  15. "HD 108662". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2022-01-14.
  16. "HD 108651". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2022-01-14.
  17. Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122 (6): 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.
  18. Casewell, S. L.; et al. (January 2006), "New stellar members of the Coma Berenices open star cluster", Monthly Notices of the Royal Astronomical Society, 365 (2): 447–453, arXiv:astro-ph/0510133, Bibcode:2006MNRAS.365..447C, doi:10.1111/j.1365-2966.2005.09689.x, S2CID 17595520.
  19. Silaj, J.; Landstreet, J. D. (June 2014), "Accurate age determinations of several nearby open clusters containing magnetic Ap stars", Astronomy & Astrophysics, 566: 18, arXiv:1407.4531, Bibcode:2014A&A...566A.132S, doi:10.1051/0004-6361/201321468, S2CID 53370832, A132.
  20. Perrine, C. D. (June 1918), "On the cause underlying the spectral differences of the stars", Astrophysical Journal, 47: 289–323, Bibcode:1918ApJ....47..289P, doi:10.1086/142406.
  21. Morgan, W. W. (September 1932), "A Study of the Composite Spectrum of the A-Type Star 14 Comae", Astrophysical Journal, 76: 144, Bibcode:1932ApJ....76..144M, doi:10.1086/143410.
  22. Morgan, W. W. (January 1932), "Studies in Peculiar Stellar Spectra. III. on the Occurrence of Europium in A-Type Stars", Astrophysical Journal, 75: 46, Bibcode:1932ApJ....75...46M, doi:10.1086/143354.
  23. Babcock, H. W.; Cowling, T. G. (1953), "General magnetic fields in the Sun and stars (Report on progress of astronomy)", Monthly Notices of the Royal Astronomical Society, 113: 357–381, Bibcode:1953MNRAS.113..357B, doi:10.1093/mnras/113.3.357.
  24. van den Heuvel, E. P. J. (April 1967), "The origin of blue stragglers and peculiar and metallic-line stars", The Observatory, 87: 68–72, Bibcode:1967Obs....87...68V.
  25. Preston, G. W.; et al. (May 1969), "The magnetic field and light variations of 17 COM and kap Cnc", Astrophysical Journal, 156: 653, Bibcode:1969ApJ...156..653P, doi:10.1086/149995.
  26. "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
  27. Savanov, I. S.; et al. (November 1996), "A study of the atmospheres of the SrCrEu stars 17 Com A and 21 Com in the Coma Cluster", Astronomy Letters, 22 (6): 815–821, Bibcode:1996AstL...22..815S.
  28. Gray, Richard O.; Corbally, J. (2009), Stellar Spectral Classification, Princeton University Press, pp. 176–183, ISBN 978-0691125114
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