Mu Crucis

Mu Crucis, Latinized from μ Crucis, is the seventh-brightest star in the constellation Crux commonly known as the Southern Cross. μ Crucis is a wide double star of spectral class B stars, magnitude 4.0 and 5.2 respectively. They lie about 370 light-years away, and both stars are likely physically attached. The brighter component is known as μ¹ Crucis or μ Crucis A, while the fainter is μ² Crucis or μ Crucis B.

Mu Crucis

Observation data Epoch J2000      Equinox
Constellation	Crux
μ^1 Crucis
Right ascension	12^h 54^m 35.6249^s[1]
Declination	−57° 10′ 40.527″[1]
Apparent magnitude (V)	4.03[2]
μ^2 Crucis
Right ascension	12^h 54^m 36.8865^s[1]
Declination	−57° 10′ 07.214″[1]
Apparent magnitude (V)	5.19[2]
Characteristics
μ^1 Cru
Spectral type	B2IV-V[3]
U−B color index	−0.75[2]
B−V color index	−0.17[2]
μ^2 Cru
Spectral type	B5Vne[4]
U−B color index	−0.50[2]
B−V color index	−0.11[2]
Astrometry
μ^1 Cru
Radial velocity (Rv)	+13.9[5] km/s
Proper motion (μ)	RA: −30.45[1] mas/yr Dec.: −13.55[1] mas/yr
Parallax (π)	9.6267 ± 0.3611[6] mas
Distance	340 ± 10 ly (104 ± 4 pc)
Absolute magnitude (MV)	−1.49[7]
μ^2 Cru
Radial velocity (Rv)	+13[5] km/s
Proper motion (μ)	RA: −32.35[1] mas/yr Dec.: −10.93[1] mas/yr
Parallax (π)	8.9486 ± 0.2264[8] mas
Distance	364 ± 9 ly (112 ± 3 pc)
Absolute magnitude (MV)	−0.40[7]
Details
μ^1 Cru
Mass	7.7[9] M☉
Luminosity	1,123[7] L☉
Surface gravity (log g)	3.93[10] cgs
Temperature	21,100[10] K
Metallicity [Fe/H]	−0.21[7] dex
Age	9.2[9] Myr
μ^2 Cru
Mass	5.0[9] M☉
Radius	3.9[11] R☉
Luminosity	205[7] L☉
Surface gravity (log g)	3.40[12] cgs
Temperature	20,400[11] K
Rotational velocity (v sin i)	210[12] km/s
Age	15.9[9] Myr
Other designations
μ Cru, WD 12546-5711, CCDM 12546-5711[13][14]
μ^1 Cru: HR 4898, CD-56°4688, HD 112092, SAO 240366, HIP 63003
μ^2 Cru: HR 4899, CD-56°4689, HD 112091, SAO 240367, HIP 63005
Database references
SIMBAD	μ Cru
	μ^1 Cru
	μ^2 Cru

μ¹ Crucis is the brighter of the two stars with an apparent magnitude of 4.0. It is a hot massive main sequence or subgiant star, over a thousand times as luminous as the sun.

μ² Crucis is the fainter of the pair. Its apparent magnitude is 5.2 and it is a Be star, a star spinning so quickly that it has ejected a disc of material that creates emission lines in its spectrum. The disc is inclined at 36° to our line of sight.[11]

References

1. Perryman, M. A. C.; et al. (April 1997). "The HIPPARCOS Catalogue". Astronomy & Astrophysics. 323: L49–L52. Bibcode:1997A&A...323L..49P.
2. Johnson, H. L.; Iriarte, B.; Mitchell, R. I.; Wisniewskj, W. Z. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99). Bibcode:1966CoLPL...4...99J.
3. Hiltner, W. A.; Garrison, R. F.; Schild, R. E. (1969). "MK Spectral Types for Bright Southern OB Stars". The Astrophysical Journal. 157: 313. Bibcode:1969ApJ...157..313H. doi:10.1086/150069.
4. Levenhagen, R. S.; Leister, N. V. (2006). "Spectroscopic analysis of southern B and be stars". Monthly Notices of the Royal Astronomical Society. 371 (1): 252–262. arXiv:astro-ph/0606149. Bibcode:2006MNRAS.371..252L. doi:10.1111/j.1365-2966.2006.10655.x.
5. Evans, D. S. (June 20–24, 1966). "The Revision of the General Catalogue of Radial Velocities". In Batten, Alan Henry; Heard, John Frederick (eds.). Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30. University of Toronto: International Astronomical Union. Bibcode:1967IAUS...30...57E.
6. 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.
7. 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.
8. 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.
9. Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (2011). "A catalogue of young runaway Hipparcos stars within 3 KPC from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1): 190. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x.
10. Kilian, J. (1994). "Chemical abundances in early B-type stars. V. Metal abundances and LTE/NLTE comparison". Astronomy and Astrophysics. 282: 867. Bibcode:1994A&A...282..867K.
11. Zorec, J.; Arias, M. L.; Cidale, L.; Ringuelet, A. E. (2007). "Be star disc characteristics near the central object". Astronomy & Astrophysics. 470 (1): 239–247. Bibcode:2007A&A...470..239Z. doi:10.1051/0004-6361:20066615.
12. Chauville, J.; Zorec, J.; Ballereau, D.; Morrell, N.; Cidale, L.; Garcia, A. (2001). "High and intermediate-resolution spectroscopy of be stars 4481 lines" (PDF). Astronomy and Astrophysics. 378: 861. Bibcode:2001A&A...378..861C. doi:10.1051/0004-6361:20011202.
13. "HR 4898". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2010-06-08.
14. "HIP 63005". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2010-06-08.