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HD 256
Observation data; Epoch J2000 Equinox J2000
Constellation	Cetus
Right ascension	00h 07m 18.26172s
Declination	−17° 23′ 13.2424″
Apparent magnitude (V)	6.20
Characteristics
Spectral type	A3Vn sh
Apparent magnitude (B)	6.33
Apparent magnitude (J)	5.858
Apparent magnitude (H)	5.83
Apparent magnitude (K)	5.747
B−V color index	0.133±0.005
Astrometry
Radial velocity (Rv)	−10.2±0.9 km/s
Proper motion (μ)	RA: −7.217 mas/yr ; Dec.: 21.155 mas/yr
Parallax (π)	6.8882 ± 0.1184 mas
Distance	474 ± 8 ly ; (145 ± 2 pc)
Absolute magnitude (MV)	0.01
Orbit
Period (P)	747.6 days
Semi-major axis (a)	3.08 AU
Eccentricity (e)	0.23
Inclination (i)	93.34°
Details
A
Mass	1.94±0.15 M☉
Luminosity	57.3±2.0 L☉
Surface gravity (log g)	3.8±0.1 cgs
Temperature	9,000±100 K
Rotational velocity (v sin i)	294±9 km/s
Age	530±50 Myr
B
Mass	1.62±0.13 M☉
Luminosity	13.7±0.5 L☉
Surface gravity (log g)	4.2±0.1 cgs
Temperature	8,250±100 K
Rotational velocity (v sin i)	200±20 km/s
Other designations
	BD−18°6428, Gaia DR2 2414558084699665920, GC 103, HD 256, HIP 602, HR 10, SAO 147090, PPM 208364, 2MASS J00071825-1723132
Database references
SIMBAD	data

HD 256 is a binary star^[7] system in the equatorial constellation of Cetus. It has a white hue and is dimly visible to the naked eye with an apparent visual magnitude of 6.20.^[2] Based upon parallax measurements, the system is located at a distance of approximately 474 light years from the Sun.^[1] It is drifting closer with a radial velocity of −10 km/s.^[6]

Originally considered a single star, it was reported to be a shell star in 1982. Circumstellar absorption lines were then found to be variable, showing a similarity to the edge-on debris disk surrounding Beta Pictoris.^[8] The stellar classification of A2 IV/V matched an A-type star near the end of its main sequence lifetime, showing traits of an emerging subgiant star phase.^[9]

A 2019 study using PIONIER (VLTI) and 32 years of radial velocity measurements concluded that HD 256 is instead a binary star. The variable component of the spectral lines do not come from exocomets according to this study, but rather from the binarity. Each individual star holds its own circumstellar shell. The pair have an orbital period of 2.05 years, an eccentricity of around 0.23, and a semimajor axis of 3.08 AU.^[7] The adjusted classification is of a rapidly rotating main sequence shell star of type A3Vn sh.^[3]

References

^ ^a ^b ^c ^d ^e ^f 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 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 Abt, Helmut A.; Morrell, Nidia I. (1995). "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars". Astrophysical Journal Supplement. 95: 135. Bibcode:1995ApJS...99..135A. doi:10.1086/192182.
^ ^a ^b "HR 10". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2015-03-01.
^ ^a ^b ^c Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E.; Fowler, John W.; Gizis, John E.; Howard, Elizabeth V.; Huchra, John P.; Jarrett, Thomas H.; Kopan, Eugene L.; Kirkpatrick, J. Davy; Light, Robert M.; Marsh, Kenneth A.; McCallon, Howard L.; Schneider, Stephen E.; Stiening, Rae; Sykes, Matthew J.; Weinberg, Martin D.; Wheaton, William A.; Wheelock, Sherry L.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues. 2246: II/246. Bibcode:2003yCat.2246....0C.
^ ^a ^b Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 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 Montesinos, B.; et al. (September 2019). "HR 10: A main-sequence binary with circumstellar envelopes around both components. Discovery and analysis". Astronomy & Astrophysics. 629: A19. arXiv:1907.12441. Bibcode:2019A&A...629A..19M. doi:10.1051/0004-6361/201936180. hdl:10150/634605. ISSN 0004-6361. S2CID 198967613.
^ Lagrange-Henri, A. M.; et al. (January 1990). "HR 10 : a new beta Pictoris-like star ?". Astronomy & Astrophysics. 227: L13 – L16. Bibcode:1990A&A...227L..13L. ISSN 0004-6361.
^ Houk, N.; Smith-Moore, M. (1988). Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Vol. 4. Bibcode:1988mcts.book.....H.