Delta Equulei

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Double star
δ Equulei
Observation
dates equinox :  J2000.0 , epoch : J2000.0
AladinLite
Constellation To fill
Right ascension 21 h 14 m 28.81 s
declination + 10 ° 00 ′ 25.1 ″
Apparent brightness  4.49 likes
Astrometry
Radial velocity −15.85 ± 0.074 km / s
parallax 54.41 ± 0.14 mas
distance  59.94 ± 0.16 Lj
(18.379 ± 0.048 pc )
Absolute visual brightness M vis 3.16 ± 0.06 mag
Absolute bolometric magnitude M bol 3.01 ± 0.06 mag
Proper movement :
Rec. Share: 42.39 ± 0.68 mas / a
Dec. portion: −304.19 ± 0.42 mas / a
orbit 
period 2,084.03 ± 0.10 d
Major semi-axis 0.231 965 ± 0.000 008 ″
(approx. 4.26 AU )
eccentricity 0.436 851 ± 0.000 025
Periastron approx. 2.40 AU
Apastron approx. 6.13 AU
Orbit inclination 99.408 3 ± 0.009 8 °
Argument of the node 23.362 ± 0.012 °
Epoch of the periastron modif. heliocentr. JD
53 112.071 ± 0.052
(approx. 2004.29)
Argument of the periapsis 7.735 ± 0.013 °
Individual data
Names A; B.
Observation data:
Apparent brightness A. 5.20 ± 0.03 mag
B. 5.29 ± 0.05 mag
Typing:
Spectral class A. F7 V
B. F7 V
B − V color index A. 0.45 ± 0.04
B. 0.55 ± 0.07
Physical Properties:
Absolute vis.
Brightness M vis 		A. 3.87 ± 0.05 mag
B. 3.96 ± 0.06 mag
Absolute bol.
Brightness M bol 		A. 3.72 ± 0.05 mag
B. 3.81 ± 0.06 mag
Dimensions A. 1.192 ± 0.012 M ☉
B. 1.187 ± 0.012 M ☉
radius A. 1.30 ± 0.08 R ☉
B. 1.25 ± 0.08 R ☉
Luminosity A. 2.25 ± 0.13 L ☉
B. 2.07 ± 0.12 L ☉
Effective temperature A. 6 200 ± 150 K
B. 6 200 ± 150 K
Age 2.2 ± 0.6 billion a
Other names
and catalog entries
Bayer name δ Equulei
Flamsteed name 7 Equulei
Bonn survey BD + 9 ° 4746
Bright Star Catalog HR 8123 [1]
Henry Draper Catalog HD 202275 [2]
SAO catalog SAO 126643 [3]
Tycho catalog TYC 1109-2583-1 [4]
Hipparcos catalog HIP 104858 [5]
WDS catalog WDS 21145 + 1000
Further designations: STT 535

δ Equulei ( Delta Equulei , δ Equ for short ) is a double star in the constellation Filling . It is 4.49 m bright and is 60 light-years away from the sun . The single stars orbit each other with an orbital period of 5.7 years.

Physical Properties

The double star consists of the stars δ Equulei A and δ Equulei B , which have apparent magnitudes of 5.2 m (δ Equ A) and 5.3 m (δ Equ B) (this adds up to 4.49 m ). The stars are very similar in their physical properties: They both belong to the spectral and luminosity class F7 V, they have roughly the same surface temperature with about 6,200 K and they are almost equally heavy with just under 1.2 solar masses each . The metallicity [Fe / H] of the star system is −0.07, which in other words corresponds to 85 percent of the solar metallicity. Based on the models for star evolution , the age of the system was calculated to be 2.2 ± 0.6 billion years.

The star system

With an orbital period of 5.7 years, δ Equulei had one of the shortest known orbital periods among the visual binary stars until the 20th century , whereby visual means that he can be examined with a telescope or telescope (before the advent of modern techniques such as interferometry , speckle interferometry , adaptive optics etc.) could still be resolved into two separate light sources. The stars reach the greatest possible angular distance when passing through the apastron with 0.33 ″. At the same time, δ Equulei is a spectroscopic double star , as it shows periodic shifts in the spectral lines in the line spectrum , which are caused by the orbiting of the stars and consequently the change in their radial velocity ( Doppler effect ). The system belongs to the SB2 double stars ( double-lined spectroscopic binary ). The lines of both components are visible in the line spectrum . δ Equulei is one of the few systems that belong to both the visual and the spectroscopic binary stars. This allows all orbital elements to be clearly determined and the position of the system in space to be reproduced in three dimensions (this is not possible with purely visual or purely spectroscopic binary stars).

The binary star nature of δ Equulei was discovered in 1852 by Otto Wilhelm von Struve . William Hussey determined the orbital period correctly to 5.7 years for the first time at the Lick Observatory around 1900 ; its other specified orbit elements differed significantly from the modern values. δ Equulei replaced the previous “record holder” κ Pegasi as a visual double star with the shortest known period of rotation (11.6 years). The complete correct orbit elements were later calculated by Willem Jacob Luyten and published in 1934. In the course of time, further visual and spectroscopic observations made these results more precise. The physical properties and orbit are now so well known that δ Equulei serves as the standard star for various astronomical studies. The modern values ​​for the orbital period are 5.713 years (Söderhjelm, 1999), 5.703 ± 0.007 years (Pourbaix, 2000), 5.705 8 ± 0.000 3 years (Muterspaugh et al. , 2005) and 5.705 89 ± 0.000 27 years (Muterspaugh et al . , 2008).

In a binary star system, both components always revolve around the common barycentre . If the main star now occupies a point of rest in a coordinate system and the orbit of δ Equulei B appears relative to A, this relative orbit has an eccentricity of 0.437 and a major semi-axis of 0.23 ″ (approx. 4.26 AU ). From the earth, however, the orbit appears to be strongly distorted in perspective due to the orbit inclination of 99 ° (apparent orbit).

Calculations show that a stable planetary orbit exists around δ Equulei A as well as B ( exoplanet of type S), provided that the semi-major axis of the (hypothetical) planet does not exceed approx. 2/3 of an AU (approx. 100 million km). The orbital period of a celestial body with this largest possible major semi-axis would be around 0.42 years. Larger orbits would be disturbed by the respective neighboring star and would therefore not be stable. For a stable orbit around both stars ( exoplanet of type P ) the minimum size of the semi-major axis would be 16 AU and the associated period 37 years. A 2005 study could not find a massive planet.

A third star, δ Equulei C , is at a distance of 76.5 ″ at a position angle of 6 ° to δ Equulei A and B (measurement from 2016). This 10.2 m bright star is not a physical member, but only an "optical companion", i. H. this is just a background star. Δ Equulei C was discovered by Wilhelm Herschel . In 1781 he measured a distance and a position angle of 19.5 ″ and 78 °.

Ephemeris

The following ephemeris can be calculated from the orbit elements in the info box on the right (in each case mid-year):

year distance Position angle
2018 0.33 ″ 202.4 °
2019 0.25 ″ 196.8 °
2020 0.05 ″ 163.3 °
2021 0.12 ″ 19.3 °
2022 0.15 ″ 215.6 °
2023 0.31 ″ 205.7 °

Web links

Individual evidence

  1. ↑ Gaia Collaboration : VizieR Online Data Catalog: Gaia DR2 (Gaia Collaboration, 2018) . In: VizieR On-line Data Catalog: I / 345. Originally published in: 2018A & A ... 616A ... 1G . 2018. bibcode : 2018yCat.1345 .... 0G . Catalog entry on VizieR.
  2. ↑ a b Jorge R. Ducati: VizieR Online Data Catalog: Catalog of Stellar Photometry in Johnson's 11-color system . In: CDS / ADC Collection of Electronic Catalogs, 2237, 0 (2002) . 2002. bibcode : 2002yCat.2237 .... 0D . Catalog entry on VizieR .
  3. ↑ a b c Dimitri Pourbaix: Resolved double-lined spectroscopic binaries: A neglected source of hypothesis-free parallaxes and stellar masses . In: Astronomy and Astrophysics Supplement Series . Vol. 145, 2000, p. 219. bibcode : 2000A & AS..145..215P . doi: 10.1051 / aas: 2000237 .
  4. ↑ a b c d e f g h i Matthew W. Muterspaugh et al. : Masses, Luminosities, and Orbital Coplanarities of the μ Orionis Quadruple-Star System from Phases Differential Astrometry . In: The Astronomical Journal . Bd. 135, Ausg. 3, 2008, p. 773. bibcode : 2008AJ .... 135..766M , doi: 10.1088 / 0004-6256 / 135/3/766 , arxiv : 0710.2126 .
  5. ↑ a b c d True semi-major axis calculated from the distance to the sun d in AU (18.379 pc = 3 790 941 AU) and semi-major axis a in degrees (0.231 965 ″ = 0.000 064 434 7 °) according to 2d tan (a / 2 ) = 4.26 AU. Smallest distance = 4.26 AU (1 - eccentricity) = 2.40 AU. Largest distance = 4.26 AU (1 + eccentricity) = 6.13 AU.
  6. ↑ a b c d e Theo A. ten Brummelaar et al. : Binary Star Differential Photometry Using the Adaptive Optics System at Mount Wilson Observatory . In: The Astronomical Journal . Vol. 119, Ausg. 5, 2000, pp. 2.408-2.410, 2.412, bibcode : 2000AJ .... 119.2403T . doi: 10.1086 / 301338 .
  7. ↑ a b c d e f Guillermo Torres, Johannes Andersen, Álvaro Giménez: Accurate masses and radii of normal stars: Modern results and applications . In: The Astronomy and Astrophysics Review . Vol. 18, Ed. 1–2, 2010. bibcode : 2010A & ARv..18 ... 67T , doi: 10.1007 / s00159-009-0025-1 , arxiv : 0908.2624 .
  8. ↑ a b c d e f g h Matthew W. Muterspaugh et al. : PHASES high-precision differential astrometry of δ Equulei . In: The Astronomical Journal . Vol. 130, Ed. 6, 2005, pp. 2.866-2.875. bibcode : 2005AJ .... 130.2866M , doi: 10.1086 / 497035 , arxiv : astro-ph / 0507585 .
  9. ↑ In the textbook of astronomy (Elis Strömgren, Bengt Strömgren , 1933) δ Equulei is even referred to as the visual double star with the shortest known orbital period (p. 422). In Gerard Kuiper's publication The Visual Binary of Shortest Known Period, B. D. −8 ° 4352 from 1936 (In: Publications of the Astronomical Society of the Pacific , Vol. 48, Ed. 281, p. 19, bibcode : 1936PASP ... 48 ... 19K ) it takes third place behind BD −8 ° 4352 (= HD 152751, P = 1.7 years) and δ 31 (= HD 9770, P = 4.6 years).
  10. ↑ a b Calculated with the Binary Star Calculator (Vers. 3) from Brian Workman according to the orbit elements from Muterspaugh et al. , 2008.
  11. ^ Otto Wilhelm von Struve : On some lately discovered double stars . In: Monthly Notices of the Royal Astronomical Society , Vol. 20, 1859, pp. 10-11. bibcode : 1859MNRAS..20 .... 8S .
  12. ^ A b William Joseph Hussey: Trial Elements of the Orbit of δ Equulei, OΣ 535 . In: Publications of the Astronomical Society of the Pacific . Vol. 12, Ed. 76, 1900, pp. 215-218. bibcode : 1900PASP ... 12..215H , doi: 10.1086 / 121393 . There are older but incorrect period determinations (Wroublewsky, 1887: 11.48 years; See, 1895–1896: 11.45 years).
  13. ^ Willem Jacob Luyten : New Orbits for Four Binary Stars . In: Publications of the Astronomical Society of the Pacific . Vol. 46, Ausg. 272, 1934, p. 199. bibcode : 1934PASP ... 46..199L . doi: 10.1086 / 124454 .
  14. ↑ Staffan Söderhjelm: Visual binary orbits and masses post Hipparcos . In: Astronomy and Astrophysics . Vol. 341, 1999, p. 124. bibcode : 1999A & A ... 341..121S . Catalog entry on VizieR.
  15. ^ A b c Matthew J. Holman, Paul A. Wiegert: Long-Term Stability of Planets in Binary Systems . In: The Astronomical Journal . Vol. 117, Ausg. 1, 1999, p. 625. bibcode : 1999AJ .... 117..621H , arxiv : astro-ph / 9809315 .
  16. ↑ Brian D. Mason et al. : VizieR Online Data Catalog: The Washington Visual Double Star Catalog (Mason + 2001-2014) , Version 2018-09-24. In: VizieR On-line Data Catalog: B / wds. Originally published in: 2001AJ .... 122.3466M . 2018. bibcode : 2018yCat .... 102026M . Catalog entry on VizieR.