DI Herculis

DI Herculis

A visual band light curve for DI Herculis, adapted from Marshall et al. (1995)[1]
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension 18h 53m 26.23992s[2]
Declination +24° 16′ 40.7926″[2]
Apparent magnitude (V) 8.47[3]
Characteristics
Spectral type B5 / B4[4]
Variable type Algol
Astrometry
Radial velocity (Rv)−2.1 ± 2[5] km/s
Proper motion (μ) RA: −1.350(17)[2] mas/yr
Dec.: −3.995(22)[2] mas/yr
Parallax (π)1.5813 ± 0.0221 mas[2]
Distance2,060 ± 30 ly
(632 ± 9 pc)
Orbit[6]
PrimaryDI Her A
CompanionDI Her B
Period (P)10.550164 days
Eccentricity (e)0.489
Inclination (i)89.3°
Argument of periastron (ω)
(secondary)		330.2°
Semi-amplitude (K1)
(primary)		110.7 km/s
Semi-amplitude (K2)
(secondary)		126.6 km/s
Details[7]
DI Her A
Mass5.15 M☉
Radius2.68 R☉
Temperature17300 K
DI Her B
Mass4.52 M☉
Radius2.48 R☉
Temperature15400 K
Other designations
DI Her, BD+24 3568, HD 175227, HIP 92708, SAO 86544, WDS J19079+4652AB, TYC 2109-775-1, 2MASS J18532623+2416408[3]
Database references
SIMBADdata

DI Herculis is an Algol-type eclipsing 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.[4] It is about two thousand light years from Earth.[2]

The orbit of the stars around their mutual centre of gravity is very elliptical, with an eccentricity of 0.489 and a semi-major axis of 0.201 astronomical units, resulting in an extremely close approach of the two stars at periastron.

Stellar masses of 5.15 and 4.52 solar masses lead to a theoretical precession of 4.27 degrees per century, at odds with the observed precession. However, detailed observations reveal an unexpectedly extreme obliquity of the spin axes of the two stars.[6] One of the two stars is tipped over by at least 70 degrees from the vertical, and the other is tipped the opposite way by more than 80 degrees. Incorporating the effect of oblateness of the stars due to the unusually tilted axes, the predicted precession is consistent with general relativity.[8]

  1. ^ Cite error: The named reference Marshall was invoked but never defined (see the help page).
  2. ^ a b c d e f Cite error: The named reference Gaia EDR3 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference Simbad was invoked but never defined (see the help page).
  4. ^ a b UBVR photometry of DI Herculis
  5. ^ Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Carnegie Institute Washington D.C. Publication. Bibcode:1953GCRV..C......0W.
  6. ^ a b S. Albrecht; S. Reffert; I. Snellen (2009). "Misaligned spin and orbital axes cause the anomalous precession of DI Herculis". Nature. 461 (7262): 373–376. arXiv:0909.2861v1. Bibcode:2009Natur.461..373A. doi:10.1038/nature08408. PMID 19759615. S2CID 4401340.
  7. ^ Philippov, A. A. (2013). "Analysis of Spin-Orbit Misalignment in Eclipsing Binary DI Herculis". The Astrophysical Journal. 768 (2): 112. arXiv:1303.6980. Bibcode:2013ApJ...768..112P. doi:10.1088/0004-637X/768/2/112. S2CID 119179139.
  8. ^ Naeye, Robert, "Stellar Mystery Solved, Einstein Safe", Sky and Telescope, September 16, 2009. See also MIT Press Release, September 17, 2009. Accessed 8 June 2017.