17 Comae Berenices
Multiple star system in the constellation Coma Berenices
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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 companion of magnitude 6.6, 17 Com B, positioned at an angular separation of 146.4Ⳡalong a position angle of 251°, as of 2018, and a 14th-magnitude companion 1.4Ⳡfrom 17 Com B. They are located at a distance of approximately 240 light years from the Sun based on parallax measurements.[1]
| A | |||||||||||||||
| 145" | |||||||||||||||
| Ba | |||||||||||||||
| 68.3 days | |||||||||||||||
| Bb | |||||||||||||||
| 1.4" | |||||||||||||||
| C | |||||||||||||||
Hierarchy of orbits in the 14 Ceti system[6]
A0 SrCrEu[2]
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Coma Berenices |
| 17 Com A | |
| Right ascension | 12h 28m 54.702s[1] |
| Declination | +25° 54â² 46.27â³[1] |
| Apparent magnitude (V) | 5.242±0.004[2] |
| 17 Com B | |
| Right ascension | 12h 28m 44.565s[3] |
| Declination | +25° 53â² 57.56â³[3] |
| Apparent magnitude (V) | 6.635[4] |
| 17 Com C | |
| Right ascension | 12h 28m 44.579s[5] |
| Declination | +25° 53â² 56.00â³[5] |
| Apparent magnitude (V) | 13.7[6] |
| Characteristics | |
| 17 Com A | |
| Spectral type | A0p[7] A0 SrCrEu[2] |
| BâV color index | â0.056±0.009[8] |
| Variable type | α2 CVn + δ Sct(?)[9] |
| 17 Com B | |
| Evolutionary stage | main sequence[3] |
| Spectral type | kA2hA9VmF0[10] |
| UâB color index | 0.084[4] |
| BâV color index | 0.216[4] |
| Astrometry | |
| 17 Com A | |
| Radial velocity (Rv) | â1.4±0.5[11] km/s |
| Proper motion (μ) | RA: â23.071 mas/yr[1] Dec.: â15.110 mas/yr[1] |
| Parallax (Ï) | 12.9991±0.3721 mas[1] |
| Distance | 251 ± 7 ly (77 ± 2 pc) |
| Absolute magnitude (MV) | 0.98[8] |
| 17 Com B | |
| Radial velocity (Rv) | â1.8±0.1[12] km/s |
| Proper motion (μ) | RA: â22.231 mas/yr[3] Dec.: â17.055 mas/yr[3] |
| Parallax (Ï) | 13.9752±0.0872 mas[3] |
| Distance | 233 ± 1 ly (71.6 ± 0.4 pc) |
| Absolute magnitude (MV) | 2.46[8] |
| Orbit[13] | |
| Primary | 17 Com B |
| Name | 17 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 (Ï) (secondary) | 260.7±2.2° |
| Semi-amplitude (K1) (primary) | 14.0±0.2 km/s |
| Details | |
| 17 Com A | |
| Mass | 2.38 Mâ[2] 2.61 Mâ[14] 2.75±0.3[15] Mâ |
| Radius | 2.09[7] Râ |
| Luminosity | 42.7[7] Lâ |
| Surface gravity (log g) | 4.27 cgs[14] 3.70±0.20[15] cgs |
| Temperature | 10,212 K[7] 9,309±250[15] K |
| Rotational velocity (v sin i) | 20.4±0.4[7] km/s |
| Age | 101[14] Myr |
| 17 Com B | |
| Mass | 1.74±0.6[16] Mâ |
| Radius | 1.7[17] Râ |
| Luminosity | 8.9[17] Lâ |
| Surface gravity (log g) | 4.29±0.20[16] cgs |
| Temperature | 8,068±200[16] K |
| Rotational velocity (v sin i) | 22[4] km/s |
| 17 Com C | |
| Mass | 0.61[17] Mâ |
| Radius | 0.62[17] Râ |
| Luminosity | 0.101[17] Lâ |
| Temperature | 4,107[17] K |
| Other designations | |
| BU 1080, 17 Com, ADS 8568, WDS J12289+2555[18][19] | |
| 17 Com A: AI Com, BD+26°2354, GC 17012, HD 108662, HIP 60904, HR 4752, SAO 82330[18] | |
| 17 Com B: BD+26°2353, GC 17007, HD 108651, HIP 60891, HR 4751, SAO 82328[19] | |
| Database references | |
| SIMBAD | 17 Com A |
| 17 Com B | |
| 17 Com C | |
The double nature of this system was documented by F. G. W. Struve in 1836.[20] The pair share a common proper motion through space[15] and thus may be associated. Component B is itself a binary star system, although only the brighter component is visible in the spectrum.[13] The Washington Double Star Catalogue lists the companion as component C, with a magnitude of 13.7 and a separation of 1.4â³.[20] The 17 Com stars have been recognized as members of the Coma Star Cluster,[21] but this is disputed.[22]
The star 17 Com A was classified as chemically peculiar by A. J. Cannon prior to 1918.[23] W. W. Morgan in 1932 found the star's spectral lines varied in strength and appearance,[24] and detected lines of the element europium.[25] H. W. Babcock and T. G. Cowling measured the Zeeman effect in this star, demonstrating in 1953 that it has a magnetic field.[26] In 1967, E. P. J. van den Heuvel noted the blue excess of this star, suggesting it is a blue straggler.[27] 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.[28]
17 Com A is a magnetic chemically peculiar Ap star with a stellar classification of A0p[7] 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[30] and it shows a significant helium deficiency.[7] It has the variable star designation of AI Com, and is classified as an Alpha2 Canum Venaticorum variable and a suspected Delta Scuti variable.[9] It has been identified as a suspected blue straggler.[15]
The primary has an estimated age of 101 million years[14] and is spinning with a projected rotational velocity of 20 km/s.[7] It has more than double the mass and twice the radius of the Sun.[2][7] The magnetic field strength is 3,300±150 G.[7] It is radiating 43 times the luminosity of the Sun from its photosphere at an effective temperature of around 10,000 K.[7][15]
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.[13] The visible member of this binary pair is a strong Am star[4] with a class of kA2hA9VmF0,[10] 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.[31]