DI Herculis

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DI Herculis
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension 18h 53m 26.23977s[1]
Declination +24° 16′ 40.7904″[1]
Apparent magnitude (V) 8.47
Spectral type B5 / B4[2]
Variable type Algol
Radial velocity (Rv) -2.1[1] km/s
Proper motion (μ) RA: -1.48[1] mas/yr
Dec.: -4.27[1] mas/yr
Parallax (π) 1.18 ± 1.06 mas
Distance approx. 3,000 ly
(approx. 800 pc)
Primary DI Herculis A
Period (P) 10.550164 days
Eccentricity (e) 0.489
Inclination (i) 89.3°
Argument of periastron (ω)
Semi-amplitude (K1)
110.7 km/s
Semi-amplitude (K2)
126.6 km/s
DI Herculis A
Mass 5.15 M
Radius 2.68 R
Temperature 17300 K
DI Herculis B
Mass 4.52 M
Radius 2.48 R
Temperature 15400 K
Other designations
DI Her, BD+24° 3568, HD 175227, HIP 92708, SAO 86544, TYC 2109-775-1, 2MASS J18532623+2416408
Database references

DI Herculis is an Algol-type binary star in the constellation of Hercules. The system has an apparent magnitude of about +8.5 and consists of two young blue stars of spectral type B5 and B4.[2] It is about two thousand light years from Earth.

The orbit of the stars around their mutual centre of gravity is very elliptical, with an eccentricity of 0.49 and a semi-major axis of 0.496 astronomical units; stellar masses of 5.15 and 4.52 solar masses lead to a theoretical precession of 4.27 degrees per century (1.93 degrees from classical effects and 2.34 degrees from general relativistic effects); but the observed precession original measure is 1.04 degrees per century and the most recent is 1.39 degrees per century.

This observation has led to extensive studies of the bright binary system in the last thirty years; solutions discussed included

  • new theories of gravitation such as MOND
  • tidal forces (perhaps due to unusual internal structure in the stars) leading to a circularisation of the elliptical orbit
  • a third body in the system[5][6]
  • presence of a circumstellar cloud between the two components
  • unusual rotation axes of the stars

After observations of the Rossiter–McLaughlin effect in 2009, it emerged that the rotation axes of the two stars lay roughly in the orbital plane of the system. When this is taken account in calculating the rate of precession, the difference between expected and observed precession disappears; so DI Hercules is no longer a test case for a possible falsification of general relativity. However, a more recent research article[7] shows that the 2009 study leaves many questions unanswered regarding the solution for the axes. For example, orbital effects caused by the tilting of the axes have not been observed; also, the stars' rotation axes themselves may also be precessing.

External links[edit]

Journal references[edit]


  1. ^ a b c d e "V* DI Her". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 1 December 2016. 
  2. ^ a b UBVR photometry of DI Herculis
  3. ^ S. Albrecht; S. Reffert; I. Snellen (2009). "Misaligned spin and orbital axes cause the anomalous precession of DI Herculis". 461. Nature: 373–376. arXiv:0909.2861v1Freely accessible. Bibcode:2009Natur.461..373A. doi:10.1038/nature08408. 
  4. ^ Philippov, A. A. (2013). "Analysis of Spin-Orbit Misalignment in Eclipsing Binary DI Herculis". The Astrophysical Journal. 768. arXiv:1303.6980Freely accessible. doi:10.1088/0004-637X/768/2/112. 
  5. ^ Hsuan, Keith; Mardling, Rosemary A (2006). "A Three Body Solution for the DI Her System". Astrophysics and Space Science. 304: 243–246. Bibcode:2006Ap&SS.304..243H. doi:10.1007/s10509-006-9121-0. 
  6. ^ Khodykon, S A. "Evidence for a Third Body in the Eclipsing Binary DI Herculis". Information Bulletin on Variable Stars (5788). 
  7. ^ Zimmerman N. "The Eclipsing Binary Di Herculis: One Mystery Solved, But Another Takes Its Place". American Astronomical Society. Bibcode:2010AAS...21541934Z.