Beta Monocerotis

Beta Monocerotis (Beta Mon, β Monocerotis, β Mon) is a triple star system in the constellation of Monoceros.^[14] To the naked eye, it appears as a single star with an apparent visual magnitude of approximately 3.74, making it the brightest visible star in the constellation.^[7] A telescope shows a curved line of three pale blue stars (or pale yellow stars, depending on the scope's focus). William Herschel who discovered it in 1781 commented that it is "one of the most beautiful sights in the heavens".^[20] The star system consists of three Be stars, β Monocerotis A, β Monocerotis B, and β Monocerotis C. There is also an additional visual companion star that is probably not physically close to the other three stars.^[14]

β Monocerotis

Location of β Monocerotis (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Monoceros
A
Right ascension	06^h 28^m 49.0700^s^[1]
Declination	−07° 01′ 59.025″^[1]
Apparent magnitude (V)	4.60^[2]
B
Right ascension	06^h 28^m 49.4238^s^[3]
Declination	−07° 02′ 03.876″^[4]
Apparent magnitude (V)	5.00^[2]
C
Right ascension	06^h 28^m 49.6128^s^[5]
Declination	−07° 02′ 04.763″^[5]
Apparent magnitude (V)	5.32^[2]
Characteristics
A
Spectral type	B4Veshell^[6]
U−B color index	−0.63^[7]
B−V color index	−0.10^[7]
R−I color index	−0.16^[7]
B
Spectral type	B2Vn(e)^[8]
U−B color index	−0.52^[4]
B−V color index	−0.07^[4]
C
Spectral type	B3V:nne^[8]
B−V color index	−0.1^[9]
Astrometry
Radial velocity (Rv)	17.20^[10] km/s
Proper motion (μ)	RA: −6.86^[11] mas/yr Dec.: −2.76^[11] mas/yr
Parallax (π)	4.82 ± 1.12 mas^[11]
Distance	approx. 700 ly (approx. 210 pc)
Absolute magnitude (MV)	−1.55^[12]
Details
A
Mass	8.7^[13] M☉
Luminosity	3,200^[14] L☉
Surface gravity (log g)	4.06^[15] cgs
Temperature	18,070^[15]^[16] K
Rotational velocity (v sin i)	346^[7] km/s
Age	27.5^[13] Myr
B
Mass	6.2^[14] M☉
Luminosity	1,600^[14] L☉
Rotational velocity (v sin i)	123^[4] km/s
C
Mass	6^[14] M☉
Luminosity	1,300^[14] L☉
Rotational velocity (v sin i)	331^[17] km/s
Other designations
β Mon, Beta Monocerotis, Beta Mon, 11 Monocerotis, 11 Mon, STF 919, ADS 5107, CCDM J06288-0702, HIP 30867,^[note 1] WDS 06288-0702A.^[18]^[19]
A: β^1 Monocerotis, β^1 Mon, Beta^1 Monocerotis, Beta^1 Mon, BD−06°1574, GC 8412, HD 45725, HR 2356
B: BD−06°1575B, HD 45726, HR 2357
C: BD−06°1575C, HD 45727, HR 2358
Database references
SIMBAD	data
	A
	B
	C

System

The three stars of β Monocerotis lie approximately in a straight line. Component B is 7" from component A, and component C a further 3" away.^[19] The stars have a common proper motion across the sky and very similar radial velocities. They share a single Hipparcos satellite identifier and are assumed to be at the same distance, around 700 light years based on their parallax.^[11]

β Monocerotis is classified as a variable star, although it is unclear which of the three components causes the brightness changes.^[21] The magnitude range is given as 3.77 to 3.84 in the Hipparcos photometric band.^[22]

Beta Monocerotis A

Beta Monocerotis A (Beta Mon A, β Monocerotis A, β Mon A) is a Be shell star with a mass of approximately 7 solar masses and a luminosity of 3,200 times the Sun's.^[14][23]

Beta Monocerotis B

Beta Monocerotis B (Beta Mon B / β Monocerotis B / β Mon B) is a Be star with a mass of approximately 6.2 solar masses and a luminosity of 1,600 times the Sun's.^[14]

Beta Monocerotis C

Beta Monocerotis C (Beta Mon C / β Monocerotis C / β Mon C) is a Be star with a mass of approximately 6 solar masses and a luminosity of 1,300 times the Sun's.^[14] This star was observed to be double in speckle interferometric observations in 1988, but this has not been confirmed by later infrared observations.^[24][25]

Visual companion

CCDM J06288-0702D

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Monoceros
Right ascension	06^h 28^m 50.3^s^[26]
Declination	−07° 01′ 41″^[26]
Apparent magnitude (V)	12.2^[26]
Position (relative to A)
Epoch of observation	1999
Angular distance	25.4″ ^[19]
Position angle	47° ^[19]
Other designations
ADS 5107 D, BD−06°1574D, WDS 06288-0702D.^[26]^[19]
Database references
SIMBAD	data

The triple star system has a visual companion, CCDM J06288-0702D, which has an apparent visual magnitude of approximately 12 and is visible approximately 25 arcseconds away from β Monocerotis A.^[19] It is probably not physically close to the other three stars, merely appearing next to them in the sky.^[14]

Notes

1. The Hipparcos Catalogue entry for HIP 30867 includes all three of β Monocerotis A, B, and C. See component 1, component 2, and component 3, entries for HIP 30867, The Hipparcos and Tycho Catalogues, 1997, CDS ID I/239, accessed on line November 21, 2008.

References

1. Entry, component 1, HIP 30867, The Hipparcos and Tycho Catalogues, 1997, CDS ID I/239, accessed on line November 21, 2008.
2. Ducati, J. R (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
3. Entry, component 2, HIP 30867, The Hipparcos and Tycho Catalogues, 1997, CDS ID I/239, accessed on line November 21, 2008.
4. HR 2357, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line November 21, 2008.
5. Entry, component 3, HIP 30867, The Hipparcos and Tycho Catalogues, 1997, CDS ID I/239, accessed on line November 21, 2008.
6. Slettebak, A (1982). "Spectral types and rotational velocities of the brighter Be stars and A-F type shell stars". Astrophysical Journal Supplement Series. 50: 55. Bibcode:1982ApJS...50...55S. doi:10.1086/190820.
7. HR 2356, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line November 21, 2008.
8. Cowley, A; Gugula, E (1973). "Cyclic variations of the Be star beta 1 Monocerotis". Astronomy and Astrophysics. 22: 203. Bibcode:1973A&A....22..203C.
9. "* bet Mon C". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved November 21, 2008.
10. 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.
11. 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. S2CID 18759600.
12. Fabregat, J; Reglero, V (1990). "Determination of Be-Star Parameters from Uvby-Beta Photometry and Hα Equivalent Widths". Monthly Notices of the Royal Astronomical Society. 247: 407. Bibcode:1990MNRAS.247..407F.
13. 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): 190–200. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x. S2CID 118629873.
14. Jim Kaler. "Beta Mon". Stars. Retrieved 2018-01-29.
15. Zorec, J; Frémat, Y; Cidale, L (2005). "On the evolutionary status of Be stars. I. Field Be stars near the Sun". Astronomy and Astrophysics. 441 (1): 235–248. arXiv:astro-ph/0509119. Bibcode:2005A&A...441..235Z. doi:10.1051/0004-6361:20053051. S2CID 17592657.
16. Frémat, Y; Zorec, J; Hubert, A.-M; Floquet, M (2005). "Effects of gravitational darkening on the determination of fundamental parameters in fast-rotating B-type stars". Astronomy and Astrophysics. 440 (1): 305. arXiv:astro-ph/0503381. Bibcode:2005A&A...440..305F. doi:10.1051/0004-6361:20042229. S2CID 19016751.
17. HR 2358, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line November 21, 2008.
18. "* bet01 Mon". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved November 21, 2008.
19. Entry 06288-0702, The Washington Double Star Catalog 2009-01-31 at the Wayback Machine, United States Naval Observatory. Accessed on line November 21, 2008.
20. Proctor, Richard Anthony (1879). Half-hours with the Telescope: A Popular Guide to the Use of the Telescope as a Means of Amusement and Instruction. G. P. Putnam's sons.
21. Kazarovets, E. V; Samus, N. N; Durlevich, O. V (2000). "The 75th Name-List of Variable Stars". Information Bulletin on Variable Stars. 4870: 1. Bibcode:2000IBVS.4870....1K.
22. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
23. Rivinius, Th.; Štefl, S.; Baade, D. (2006). "Bright Be-shell stars". Astronomy and Astrophysics. 459 (1): 137–145. Bibcode:2006A&A...459..137R. doi:10.1051/0004-6361:20053008.
24. Table 1, McAlister Harold A (1993). "ICCD speckle observations of binary stars. X - A further survey for duplicity among the bright stars". The Astronomical Journal. 106: 1639. Bibcode:1993AJ....106.1639M. doi:10.1086/116753..
25. Tokovinin A. A., Chalabaev A., Shatsky N. I., Beuzit J. L. (1999). "§4.1, A near IR adaptive optics search for faint companions to early-type multiple stars". Astronomy and Astrophysics. 346: 481–486. Bibcode:1999A&A...346..481T.{{cite journal}}: CS1 maint: multiple names: authors list (link)
26. "UCAC3 166-34162". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved November 21, 2008.