Regulus

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Regulus
Template:Location mark
Location of Regulus (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Leo
Pronunciation Template:IPAc-en Template:IPAc-en[1]
Regulus A
Right ascension Template:RA[2]
Declination Template:DEC[2]
Apparent magnitude (V) 1.40[3]
Regulus BC
Right ascension Template:RA[4]
Declination Template:DEC[4]
Apparent magnitude (V) 8.13[5]/13.50[5]
Characteristics
Regulus A
Evolutionary stage Subgiant
Spectral type B8 IVn[3]
U−B Template:Engvar –0.36[6]
B−V Template:Engvar –0.11[6]
Variable type Suspected[7]
Regulus BC
Evolutionary stage Main sequence
Spectral type K2 V[8] + M4 V[8]
U−B Template:Engvar +0.51[6]
B−V Template:Engvar +0.86[6]
Astrometry
A
Radial velocity (Rv)Template:Val[9] km/s
Proper motion (μ) RA: Template:Val[2] mas/yr
Dec.: Template:Val[2] mas/yr
Parallax (π)41.13±0.35 mas[2]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)–0.57[10]
BC
Radial velocity (Rv)+6.72[11] km/s
Proper motion (μ) RA: Template:Val[11] mas/yr
Dec.: Template:Val[11] mas/yr
Parallax (π)41.2745±0.0270 mas[11]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)6.20/11.56[12]
Orbit[9]
Primaryα Leo Aa (HD 87901 A)
Companionα Leo Ab (HD 87901 B)
Period (P)Template:Val
Semi-major axis (a)Template:Val
Eccentricity (e)0 (assumed)
Semi-amplitude (K1)
(primary)		Template:Val km/s
Details
A
MassTemplate:Val[13] Template:Solar mass
RadiusTemplate:Val (equatorial), Template:Val (polar)[13] Template:Solar radius
LuminosityTemplate:Val[13] Template:Solar luminosity
Surface gravity (log g)Template:Val[14] cgs
Temperature11,010 (equatorial), 14,520 (polar)[13] K
Metallicity [Fe/H]+0.21[15] dex
Rotation15.9 hours[16]
Rotational velocity (v sin i)Template:Val[17] km/s
Age≳1[18] Gyr
Ab
MassTemplate:Val[9] Template:Solar mass
RadiusTemplate:Val[9] Template:Solar radius
TemperatureTemplate:Val[9] K
Metallicity [Fe/H]{{{metal_fe2}}} dex
B
Mass0.8[19] Template:Solar mass
Radius0.83[12] Template:Solar radius
Luminosity0.50[19] Template:Solar luminosity
Surface gravity (log g)4.4[19] cgs
Temperature4,885[19] K
Metallicity [Fe/H]−0.21[20] dex
C
Mass0.3[5] Template:Solar mass
Radius0.37[12] Template:Solar radius
Temperature3,242[12] K
Metallicity [Fe/H]{{{metal_fe2}}} dex
Other designations
Template:Odlist
α Leo A: Template:Odlist
α Leo B/C: Template:Odlist
Database references
SIMBADRegulus
BC

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Regulus is the brightest object in the constellation Leo and one of the brightest stars in the night sky. It has the Bayer designation designated α Leonis, which is Latinized to Alpha Leonis, and abbreviated Alpha Leo or α Leo. Regulus appears single, but is actually a quadruple star system composed of four stars that are organized into two pairs. The system lies approximately 79 light years from the Solar System.

The spectroscopic binary Regulus A consists of a blue-white main-sequence star and its companion, a pre-white dwarf. Regulus BC, also known as HD 87884, is separated from Regulus A by Template:Val and is itself a close pair.

Regulus and five slightly dimmer stars (Zeta Leonis, Mu Leonis, Gamma Leonis, Epsilon Leonis, and Eta Leonis) have collectively been called 'the Sickle', which is an asterism that marks the head of Leo.

Nomenclature

α Leonis (Latinized to Alpha Leonis) is the star system's Bayer designation. The traditional name Rēgulus is Latin for 'prince' or 'little king'. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[21] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[22] included a table of the first two batches of names approved by the WGSN; which included Regulus for this star. It is now so entered in the IAU Catalog of Star Names.[23]

Observation

File:Regulus 1.JPG
Regulus through Celestron CGEM DX 1100 @ F6.3, Canon T3i, Televue 4X Powermate, ISO 800, 30 sec exposure

The Regulus system as a whole is the twenty-first brightest star in the night sky with an apparent magnitude of +1.35. The light output is dominated by Regulus A. Regulus B, if seen in isolation, would be a binocular object of magnitude +8.1, and its companion, Regulus C, the faintest of the three stars that has been directly observed, would require a substantial telescope to be seen, at magnitude +13.5. Regulus A is itself a spectroscopic binary; the secondary star has not yet been directly observed as it is much fainter than the primary. The BC pair lies at an angular distance of 177 arc-seconds from Regulus A, making them visible in amateur telescopes.[24]

File:MVI 3269-Regulus-1.png
Regulus as viewed through a 110mm refractor in full daylight.

Regulus is 0.465 degrees from the ecliptic,[25] the closest of the bright stars, and is often occulted by the Moon. This occurs in spates every 9.3 years, due to lunar precession. The last spate was around 2017, with occultations every month from December 2016 till July 2017, each one limited to certain areas on Earth.[26] Occultations by Mercury and Venus are possible but rare, as are occultations by asteroids. Seven other stars which have a Bayer designation are less than 0.9° from the ecliptic (perfected, mean plane of Earth's orbit and mean apparent path of the Sun) the next brightest of which is δ (Delta) Geminorum, of magnitude +3.53.

The last occultation of Regulus by a planet was on July 7, 1959, by Venus.[27] The next will occur on October 1, 2044, also by Venus. Other planets will not occult Regulus over the next few millennia because of their node positions. An occultation of Regulus by the asteroid 166 Rhodope was filmed in Italy on October 19, 2005. Differential bending of light was measured to be consistent with general relativity.[28] Regulus was occulted by the asteroid 163 Erigone in the early morning of March 20, 2014.[29] The center of the shadow path passed through New York and eastern Ontario, but no one is known to have seen it, due to cloud cover. The International Occultation Timing Association recorded no observations at all.[30]

Although best seen in the evening in the northern hemisphere's late winter and spring, Regulus appears at some time of night throughout the year except for about a month (depending on ability to compensate for the sun's glare, ideally done so in twilight) on either side of August 22–24, when the Sun is too close.[31] The star can be viewed the whole night, crossing the sky, in late February. Regulus passes through SOHO's LASCO C3 every August.[32]

For Earth observers, the heliacal rising (pre-sunrise appearance) of Regulus occurs late in the first week of September, or in the second week. Every 8 years, Venus passes very near the star system around or a few days before the heliacal rising, as on 5 September 2022 (the superior conjunction of Venus happens about two days earlier with each turn of its 8-year cycle, so as this cycle continues Venus will more definitely pass Regulus before the star's heliacal rising).Script error: No such module "Unsubst".

Stellar system

File:LeoCC.jpg
Regulus is the brightest star in the constellation of Leo (right tip, below is bright Jupiter in 2004).

Regulus is a multiple star system consisting of at least four stars and a substellar object. Regulus A is the dominant star, with a binary companion 177" distant that is thought to be physically related. Regulus D is a 12th magnitude companion at 212",[33] but is an unrelated background object.[34]

Regulus A is a binary star consisting of a blue-white subgiant star of spectral type B8, which is orbited by a star of at least 0.3 solar masses, which is probably a white dwarf. The two stars take approximately 40 days to complete an orbit around their common centre of mass. Given the extremely distorted shape of the primary, the relative orbital motion may be notably altered with respect to the two-body purely Keplerian scenario because of non-negligible long-term orbital perturbations affecting, for example, its orbital period. In other words, Kepler's third law, which holds exactly only for two point-like masses, would no longer be valid for the Regulus system. Regulus A was long thought to be fairly young, only 50–100 million years old, calculated by comparing its temperature, luminosity, and mass. The existence of a white dwarf companion would mean that the system is at least 1 billion years old, just to account for the formation of the white dwarf. The discrepancy can be accounted for by a history of mass transfer onto a once-smaller Regulus A.[18]

The primary of Regulus A has about 4.15 times the Sun's mass.[13] It is spinning extremely rapidly, with a rotation period of only 15.9 hours (for comparison, the rotation period of the Sun is 25 days[35]), which causes it to have a highly oblate shape.[16] This results in so-called gravity darkening: the photosphere at Regulus' poles is considerably hotter, and five times brighter per unit surface area, than its equatorial region.[18] The star's surface at the equator rotates at about 320 kilometres per second (199 miles per second), or 96.5% of its critical angular velocity for break-up. It is emitting polarized light because of this.[17]

Regulus BC is 5,000 AU[36] from Regulus A. A and BC share a common proper motion and are thought to orbit each other[5] taking several million years. Designated Regulus B and Regulus C, the pair has Henry Draper Catalogue number HD 87884. The first is a K2V star, while the second is about M4V.[16] The companion pair has an orbital period of about 600 years[5] with a separation of 2.5" in 1942.[16]

A far more distant brown dwarf named SDSS J1007+1930 (full name: SDSS J100711.74+193056.2) may be bound to the Regulus system, since it shares a similar proper motion and radial velocity and has a similar metal abundance to Regulus B, which hints for a physical connection between both systems. The estimated distance from Regulus is Template:Val (Template:Val), and the orbital period assuming an circular orbit would be around 200 million years, comparable to the Sun's orbital period around the Milky Way (galactic year). It is estimated to have a mass of roughly Template:Jupiter mass (Template:Solar mass),Template:Efn an effective temperature of Template:Val and a spectral type L9 or T0, making it a L dwarf or T dwarf. In the future it will either be stripped away by stellar encounters because it is so weakly bound to the system, or it was once closer and got ejected by dynamical interactions. The extreme distance makes it uncertain to conclude whether it is gravitationally bound to Regulus.[37]

File:Regulus in true color.jpg
Approximate true-color reconstruction of Regulus based on interferometric imaging.[13]
Regulus system
Separation
(arcsec) 		Projected
separation
(AU) 		Orbital
period 		Spectral
type 		Mass
(M☉) 		App. mag.
(V)
Regulus ABC Regulus A[orbit note 1] Regulus Aa 0.015 0.356 40.1 days align=center style="background: Template:Star-color; | B8 IVn 3.44 1.4
(combined)
Regulus Ab align=center style="background: Template:Star-color; | pre-WD 0.31
Regulus BC[orbit note 1] Regulus B 2.1 60 600 years align=center style="background: Template:Star-color; | K2V 0.78 8.1
Regulus C align=center style="background: Template:Star-color; | M4V 0.32 13.5
SDSS J1007+1930 27,200 800,000 200 million
years		 align=center style="background: Template:Star-color; | L9 0.06 26

Template:Reflist

Etymology and cultural associations

Rēgulus is Latin for 'prince' or 'little king';[38] its Greek equivalent is Basiliskos or, in Latinised form, Basiliscus.[39][40][41] The name Regulus first appeared in the early 16th century.[41] It is also known as Qalb al-Asad, from the Arabic قلب الأسد, meaning 'the heart of the lion', a name already attested in the Greek Kardia Leontos[39][42] whose Latin equivalent is Cor Leōnis. The Arabic phrase is sometimes approximated as Kabelaced.[43] In Chinese it is known as 軒轅十四, the Fourteenth Star of Xuanyuan, the Yellow Emperor. In Indian astronomy, Regulus corresponds to the Nakshatra Magha ("the bountiful").

Babylonians called it Sharru ("the King"), and it marked the 15th ecliptic constellation. In India it was known as Maghā ("the Mighty"), in Sogdiana Magh ("the Great"), in Persia Miyan ("the Centre") and also as one of the four 'royal stars' of the Persian monarchy.[44] It was one of the fifteen Behenian stars known to medieval astrologers, associated with granite, mugwort, and the kabbalistic symbol File:Agrippa1531 corLeonis.png.

In the Babylonian MUL.APIN, Regulus is listed as Lugal, meaning king, with co-descriptor, "star of the Lion's breast".[45]

See also

Notes

Template:Notelist

References

Template:Reflist

External links

Template:Sister project

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Template:Stars of Leo Template:Notable stars and star systems coplanar with the solar system Template:Portal bar Template:Sky

  1. ↑ Template:OED
  2. ↑ a b c d e Cite error: Invalid <ref> tag; no text was provided for refs named van Leeuwen2007
  3. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named van Belle2009
  4. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named tycho2
  5. ↑ a b c d e Cite error: Invalid <ref> tag; no text was provided for refs named tokovinin
  6. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named ducati
  7. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named gcvs
  8. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named gies
  9. ↑ a b c d e Cite error: Invalid <ref> tag; no text was provided for refs named Gies2020
  10. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Anderson2012
  11. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named edr3
  12. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named johnson1983
  13. ↑ a b c d e f Cite error: Invalid <ref> tag; no text was provided for refs named che
  14. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named aj129_3_1642
  15. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named baines
  16. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named apj628
  17. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named Cotton2017
  18. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named rappaport2009
  19. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named martin
  20. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named casagrande2011
  21. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named WGSN
  22. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named WGSN1
  23. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named IAU-CSN
  24. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named pugh
  25. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named pratt
  26. ↑ See 2016 Bright Star Occultations and 2017 Bright Star Occultations.
  27. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named planets
  28. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named rhodope
  29. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named sigismondi
  30. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named iota
  31. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named skymap
  32. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named SOHO
  33. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named wds
  34. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named dr2
  35. ↑ Script error: No such module "citation/CS1".
  36. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named lindroos
  37. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Mamajek+Burgasser2024
  38. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named lands
  39. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named Geminus
  40. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named lsj
  41. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named ridpath
  42. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named lsj2
  43. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named pultar
  44. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named allen
  45. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named rogers


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