KQ Velorum
KQ Velorum is a variable star system in the southern constellation of Vela. It has the identifier HD 94660 in the Henry Draper Catalogue; KQ Vel is the variable star designation. This appears as a sixth magnitude star with an apparent visual magnitude of 6.112,[3] and thus is dimly visible to the naked eye under suitable viewing conditions. The system is located at a distance of approximately 373 light years from the Sun based on parallax measurements,[2] and is drifting further away with a radial velocity of around 23 km/s.[7]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Vela |
| Right ascension | 10h 55m 01.002s[2] |
| Declination | –21° 43′ 34.52″[2] |
| Apparent magnitude (V) | 6.112[3] |
| Characteristics | |
| Spectral type | Ap(SiCr)[4] A0p EuCrSi[3] |
| B−V color index | −0.061±0.004[5] |
| Variable type | α2 CVn[6] |
| Astrometry | |
| Radial velocity (Rv) | +23.4±4.0[7] km/s |
| Proper motion (μ) | RA: −36.021 mas/yr[2] Dec.: 5.157 mas/yr[2] |
| Parallax (π) | 8.7507 ± 0.1578 mas[2] |
| Distance | 373 ± 7 ly (114 ± 2 pc) |
| Absolute magnitude (MV) | 0.24[5] |
| Orbit[3] | |
| Period (P) | 848.96±0.13 d |
| Semi-major axis (a) | ≥ 187.3±1.2 Gm |
| Eccentricity (e) | 0.4476±0.0049 |
| Periastron epoch (T) | 2,445,628.6±1.7 HJD |
| Argument of periastron (ω) (secondary) | 264.5±0.8° |
| Semi-amplitude (K1) (primary) | 17.94±0.11 km/s |
| Details[8] | |
| KQ Vel A | |
| Mass | 3.0±0.2 M☉ |
| Radius | 2.53±0.37 R☉ |
| Luminosity | 105 L☉ |
| Surface gravity (log g) | 4.18±0.20 cgs |
| Temperature | 11,300±400 K |
| Rotation | 2,800±200 d |
| Other designations | |
| Database references | |
| SIMBAD | data |
This was first identified as a chemically peculiar star by Carlos and Mercedes Jaschek in 1959, who found spectral peculiarities in the silicon absorption bands.[11] The long-term photometric variability of this star was reported by H. Hensberge in 1993, who noted a possibly complicated light curve with an estimated period on the order of 2,700 days.[12] In 1975, E. F. Borra and J. D. Landstreet detected a strong magnetic field in excess of 1 kG on the star.[13] Radial velocity measurements by G. Mathys and associates (1997) demonstrated this is a spectroscopic binary system.[14]
This single-lined spectroscopic binary has a physical separation of at least 1.25 ± 0.01 AU, an orbital period of 2.32 years, and a high eccentricity (ovalness) of 0.45.[3] The visible component is an Ap star with a stellar classification of Ap(SiCr),[4] although the effective temperature of 11,300 K is a closer match to a spectral type of B8.5p.[1] P. Renson and associates (1991) gave a spectral type of A0p EuCrSi,[9] indicating the spectrum shows peculiarities in the europium, chromium, and silicon bands. It is classified as an Alpha2 Canum Venaticorum variable with a brightness that varies from 6.10 down to 6.12 in magnitude.[6]
KQ Vel is a frequently-studied object that is often used as a magnetic standard star. The magnetic field of this star has a dipole strength of 7.5 kG, while displaying additional quadropole and octopole moments. It is inclined to the rotation axis by 16°. The mean longitudinal field is almost constant, showing a strength of −2 kG.[8] The star is less than halfway through its main sequence lifespan, but is rotating very slowly with a period of around 2,800 days. It has three times the mass and 2.5 times the radius of the Sun, while radiating 105 times the Sun's luminosity.[8]
The mass function of the system indicates that the secondary must have more than two times the mass of the Sun, yet there is no sign of it in otherwise high-quality spectra.[1] A main sequence stellar companion of this mass would have a spectral type earlier than A5V.[1] This led to the suggestion that this companion must be a compact object, either a black hole, a neutron star, or a pair of white dwarfs.[8] In 2018 the companion was detected in the near infrared using the Pioneer instrument at the VLIT observatory, showing an H-band magnitude difference of 1.8±0.03 at an angular separation of 18.72±0.02 mas. This corresponds to a projected linear separation of a little over 2 AU.[1]
X-ray observations with the Chandra X-ray Observatory in 2016 strongly suggested that the companion is a neutron star, which would make KQ Velorum the first known pair of strongly magnetic Ap star and neutron star that have been discovered.[15] Radio emission has also been detected from the secondary object, raising the possibility that the secondary is actually itself a binary containing a magnetically active star.[16]
If KQ Velorum B is a neutron star, the system would be the product of a supernova explosion, possibly of the electron capture type that would not significantly disrupt the orbit. The strongly magnetic Ap star would likely be the result of a merger, perhaps from an W UMa close binary. The current neutron star may have been the tertiary member of the system, and it gained mass during a Roche lobe overflow of the binary components.[15]
References edit
- ^ a b c d e Schöller, M.; et al. (October 2020), "The near-infrared companion to HD 94660 (=KQ Vel)", Astronomy & Astrophysics, 642: 6, arXiv:2009.07060, Bibcode:2020A&A...642A.188S, doi:10.1051/0004-6361/202038950, S2CID 221703222, A188.
- ^ a b c d e 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.
- ^ a b c d e Mathys, G. (May 2017), "Ap stars with resolved magnetically split lines: Magnetic field determinations from Stokes I and V spectra", Astronomy & Astrophysics, 601: 90, arXiv:1612.03632, Bibcode:2017A&A...601A..14M, doi:10.1051/0004-6361/201628429, S2CID 119474886, A14.
- ^ a b Houk, N. (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 2, Dept. of Astronomy, University of Michigan, Bibcode:1978mcts.book.....H.
- ^ a b 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.
- ^ a b 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.
- ^ a b 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.
- ^ a b c d Bailey, J. D.; et al. (March 2015), "A comprehensive analysis of the magnetic standard star HD 94660: Host of a massive compact companion?", Astronomy & Astrophysics, 575: 12, arXiv:1501.07494, Bibcode:2015A&A...575A.115B, doi:10.1051/0004-6361/201425316, S2CID 55189944, A115.
- ^ a b Renson, P.; et al. (September 1991), "General catalogue of AP and AM stars", Astronomy and Astrophysics Supplement Series, 89: 429, Bibcode:1991A&AS...89..429R.
- ^ "KQ Vel". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-10-17.
{{cite web}}: CS1 maint: postscript (link) - ^ Jaschek, Mercedes; Jaschek, Carlos (February 1959), "Southern Peculiar A Stars", Publications of the Astronomical Society of the Pacific, 71 (418): 48, Bibcode:1959PASP...71...48J, doi:10.1086/127332, S2CID 121714862.
- ^ Hensberge, H. (January 1993), Dworetsky, M. M.; Castelli, F.; Faraggiana, R. (eds.), "Longterm Variability in Cp-Stars", Peculiar versus Normal Phenomena in A-type and Related Stars. International Astronomical Union, Colloquium No. 138, held in Trieste, Italy, July 1992, vol. 44, no. 138, San Francisco, CA: Astronomical Society of the Pacific, p. 547, Bibcode:1993ASPC...44..547H, ISBN 0937707635.
- ^ Borra, E. F.; Landstreet, J. D. (December 1975), "Discovery of magnetic fields in four southern Ap stars", Publications of the Astronomical Society of the Pacific, 87: 961–963, Bibcode:1975PASP...87..961B, doi:10.1086/129880, S2CID 121297510.
- ^ Mathys, G.; et al. (June 1997), "The mean magnetic field modulus of AP stars", Astronomy and Astrophysics Supplement Series, 123 (2): 353–402, Bibcode:1997A&AS..123..353M, doi:10.1051/aas:1997103.
- ^ a b Oskinova, Lidia M.; et al. (September 2020), "Chandra X-ray study confirms that the magnetic standard Ap star KQ Vel hosts a neutron star companion", Astronomy & Astrophysics, 641: 8, arXiv:2007.11591, Bibcode:2020A&A...641L...8O, doi:10.1051/0004-6361/202038214, S2CID 220713253, L8.
- ^ Leto, P.; et al. (2022), "Discovery and origin of the radio emission from the multiple stellar system KQ Vel", Monthly Notices of the Royal Astronomical Society, 515 (4): 5523–5538, arXiv:2207.14075, Bibcode:2022MNRAS.515.5523L, doi:10.1093/mnras/stac2163.