88 Tauri

88 Tauri, also known as d Tauri, is a multiple star system in the constellation Taurus. It has an apparent magnitude of about 4.25, meaning that it is visible to the naked eye. Based upon parallax measurements made by the Hipparcos spacecraft, the star system is some 156 light-years (48 parsecs) from the Sun.[1]

This article is about d Tauri. It is not to be confused with δ Tauri.

88 Tauri

Observation data Epoch J2000      Equinox J2000
Constellation	Taurus
88 Tau A
Right ascension	04^h 35^m 39.25910^s[1]
Declination	+10° 09′ 38.8396″[1]
Apparent magnitude (V)	4.250[2]
88 Tau B
Right ascension	04^h 35^m 35.1775^s[3]
Declination	+10° 10′ 13.572″[3]
Apparent magnitude (V)	7.84[4]
Characteristics
88 Tau A
Spectral type	A6m / F5 / G2-3: / G2-3:[5]
U−B color index	+0.08[4]
B−V color index	+0.19[4]
88 Tau B
Spectral type	F8V / M?[6]
U−B color index	+0.04[7]
B−V color index	+0.54[7]
Astrometry
88 Tau A
Radial velocity (Rv)	23.97[8] km/s
Proper motion (μ)	RA: 43.13[1] mas/yr Dec.: -52.71[1] mas/yr
Parallax (π)	20.88 ± 0.94[1] mas
Distance	156 ± 7 ly (48 ± 2 pc)
88 Tau B
Radial velocity (Rv)	23.97[9] km/s
Proper motion (μ)	RA: 51.8[2] mas/yr Dec.: -49.4[2] mas/yr
Orbit[5]
Primary	88 Tau Aa
Companion	88 Tau Ab
Period (P)	6585 ± 12 d
Semi-major axis (a)	240.1 ± 5.3 mas 12.17 ± 0.17 AU
Eccentricity (e)	0.0715 ± 0.0026
Inclination (i)	69.923 ± 0.048°
Longitude of the node (Ω)	146.734 ± 0.067°
Periastron epoch (T)	2455261 ± 22
Argument of periastron (ω) (secondary)	205.7 ± 1.2°
Orbit[5]
Primary	88 Tau Aa1
Companion	88 Tau Aa2
Period (P)	3.571096 ± 0.000003 d
Semi-major axis (a)	1.359 ± 0.034 mas 0.0689 ± 0.0012 AU
Eccentricity (e)	0
Inclination (i)	110.6 ± 2.7°
Longitude of the node (Ω)	287.5 ± 1.8°
Periastron epoch (T)	2453389.3824 ± 0.0030
Argument of periastron (ω) (secondary)	0°
Orbit[5]
Primary	88 Tau Ab1
Companion	88 Tau Ab2
Period (P)	7.886969 ± 0.000066 d
Semi-major axis (a)	1.967 ± 0.054 mas 0.0997 ± 0.0021 AU
Eccentricity (e)	0
Inclination (i)	27.23 ± 0.72°
Longitude of the node (Ω)	34.0 ± 8.2°
Periastron epoch (T)	2452507.31 ± 0.02
Argument of periastron (ω) (secondary)	0°
Orbit[6]
Primary	88 Tau Ba
Companion	88 Tau Bb
Period (P)	1350 ± 35 d
Semi-major axis (a)	0.057″
Eccentricity (e)	0.663 ± 0.075
Periastron epoch (T)	2450498 ± 34
Argument of periastron (ω) (secondary)	223 ± 9°
Semi-amplitude (K1) (primary)	3.24 ± 0.44 km/s
Details
88 Tau Aa1
Mass	2.06 ± 0.11[5] M☉
Rotational velocity (v sin i)	37 ± 2[5] km/s
88 Tau Aa2
Mass	1.361 ± 0.073[5] M☉
Rotational velocity (v sin i)	17 ± 2[5] km/s
88 Tau Ab1
Mass	1.069 ± 0.069[5] M☉
Rotational velocity (v sin i)	5 ± 3[5] km/s
88 Tau Ab2
Mass	1.057 ± 0.068[5] M☉
Rotational velocity (v sin i)	5 ± 3[5] km/s
88 Tau Ba
Mass	1.2[6] M☉
88 Tau Bb
Mass	>0.15[6] M☉
Other designations
ADS 3317, CCDM J04356+1010, WDS J04357+1010AB
88 Tau A: d Tau, 88 Tau, BD+09° 607, HD 29140, HIP 21402, SAO 94026, HR 1458, GC 5599[10]
88 Tau B: BD+09° 606, HD 286909, SAO 94024, GC 5596, TYC 673-1487-1[11]
Database references
SIMBAD	88 Tau
	88 Tau A
	88 Tau B

88 Tauri is a sextuple star system, meaning that it contains six stars in a hierarchical orbit. The brighter component, 88 Tauri A, is a quadruple system consisting of two spectroscopic binaries orbiting each other with an orbital period of 18 years. The fainter component, 88 Tauri B, is also a spectroscopic binary, and is about 69 arcseconds away, bringing up the total to six stars.[5]

Orbit

Aa1

Period = 3.571d a = 1.36 mas

Aa2

Period = 6585d a = 0.24″

Ab1

Period = 7.887d a = 1.97 mas

Ab2

69.6″ separation

Ba

Period = 1350d a = 0.057 mas

Bb

Hierarchy of orbits in the 88 Tauri system

88 Tauri A is a fourth-magnitude star[10] with two components, 88 Tauri Aa and 88 Tauri Ab. 88 Tauri Aa and Ab orbit each other once every 18 years and are separated by about 0.28 arcseconds. Those two components themselves are spectroscopic binaries: binary stars that are too close to be resolved but can be detected by periodic Doppler shifts in their spectrum. In this case, variability in the radial velocity has been recognized as early as 1907.[12] The Aa pair has an orbital period of 3.57 days, the Ab pair has an orbital period of 7.89 days, and both have circular orbits with low orbital eccentricities.[5]

88 Tauri B, 69.56 arcseconds away,[11] is a seventh-magnitude star that is also a binary star system. It is another spectroscopic binary whose components (88 Tauri Ba and Bb) orbit each other every 3.69 years.[5] The orbit of 88 Tauri B around 88 Tauri A likely takes about 70,000 years.[6]

Properties

88 Tauri Aa has a spectral type of A6m,[5] indicating that it is an A-type star. The "m" in its spectral type means that it is an Am star,[5] also known as a metallic-line star. These types of stars have spectra indicating varying amounts of metals, like iron.[13] The rest of the stars in 88 Tauri A have spectral types ranging from F5 to G2-3, meaning that they are regular F-type or G-type main-sequence stars. The spectral types for 88 Tauri Ab1 and Ab2 are less certain, because their spectral lines are weaker, hence the colon after G2. Aa1 does not appears to be rotating synchronously with its companion (nor does it have a convective atmosphere), unlike Aa2. (It is not known if the two stars of 88 Tauri Ab are in synchronous rotation with each other, because of the relatively high errors in their measurements.)[5]

88 Tauri B consists of a F-type main sequence star, with another low-mass star.[6] The mass of the smaller component is at least 0.15 solar masses, so it is most likely a red dwarf.[6]

References

1. van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
2. Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H.
3. Hog, E. (1998). "The Tycho Reference Catalogue". Astronomy and Astrophysics. 335: L65. Bibcode:1998A&A...335L..65H.
4. Feinstein, A. (1974). "Photoelectric UBVRI observations of Am stars". Astronomical Journal. 79: 1290. Bibcode:1974AJ.....79.1290F. doi:10.1086/111675. (Accessed using SIMBAD)
5. Lane, Benjamin F.; Muterspaugh, Matthew W.; Fekel, Francis C.; Williamson, Michael; Browne, Stanley; Konacki, Maciej; Burke, Bernard F.; Colavita, M. M.; Kulkarni, S. R.; Shao, M. (2007). "The Orbits of the Quadruple Star System 88 Tauri A from PHASES Differential Astrometry and Radial Velocity". The Astrophysical Journal. 669 (2): 1209–1219. arXiv:0710.2127. Bibcode:2007ApJ...669.1209L. doi:10.1086/520877.
6. Tokovinin, A. A.; Gorynya, N. A. (2001). "New spectroscopic components in multiple systems. IV". Astronomy and Astrophysics. 374: 227–234. Bibcode:2001A&A...374..227T. doi:10.1051/0004-6361:20010714.
7. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
8. Pourbaix, D.; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; Levato, H.; Morrell, N. I.; Torres, G.; Udry, S. (2004). "S_B⁹: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics. 424 (2): 727–732. arXiv:astro-ph/0406573. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213.
9. Tokovinin, A. A.; Smekhov, M. G. (2002). "Statistics of spectroscopic sub-systems in visual multiple stars". Astronomy and Astrophysics. 382: 118–123. Bibcode:2002A&A...382..118T. doi:10.1051/0004-6361:20011586.
10. "88 Tau". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 16 February 2017.
11. "88 Tau B". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 18 February 2017.
12. Daniel, Zaccheus (1916). "The orbit of 88 D Tauri". Publications of the Allegheny Observatory of the University of Pittsburgh. 3 (12): 93. Bibcode:1916PAllO...3...93D.
13. Am star, The Internet Encyclopedia of Science, David Darling. Accessed on line August 14, 2008.