W Ursae Majoris

W Ursae Majoris
W Ursae Majoris is located in 100x100
W Ursae Majoris

The red dot shows the location of W Ursae Majoris in Ursa Major.
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Right ascension 09h 43m 45.4705s[1]
Declination +55h 57m 09.0667s[1]
Apparent magnitude (V) 7.90[2] (7.75–8.48)
Characteristics
Spectral type F8Vp + F8Vp[3]
U−B color index +0.08[2]
B−V color index +0.66[2]
Variable type W UMa
Astrometry
Radial velocity (Rv)−46[4] km/s
Proper motion (μ) RA: 17.150±0.049[1] mas/yr
Dec.: −29.226±0.050[1] mas/yr
Parallax (π)19.2775 ± 0.0334 mas[1]
Distance169.2 ± 0.3 ly
(51.87 ± 0.09 pc)
Orbit[5]
Period (P)0.3336352(2) d
Semi-major axis (a)2.443 R☉[6]
Inclination (i)88.4 ± 0.8°
Details[5]
W UMa A
Mass1.139 ± 0.019 M☉
Radius1.092 ± 0.016 R☉
Luminosity1.557 ± 0.166 L☉
Temperature6450 ± 100 K
Rotational velocity (v sin i)144.40 ± 6.52[7] km/s
W UMa B
Mass0.551 ± 0.006 M☉
Radius0.792 ± 0.015 R☉
Luminosity0.978 ± 0.071 L☉
Temperature6170 ± 21 K
Other designations
BD+56 1400, HD 83950, SAO 27364, ADS 7494, CCDM 09438+5557, HIP 47727.[3]
Database references
SIMBADThe ADS 7494 pair
W UMa
ADS 7494B

W Ursae Majoris (W UMa) is the variable star designation for a binary star system in the northern constellation of Ursa Major. It has an apparent visual magnitude of about 7.9,[2] which is too faint to be seen with the naked eye. However, it can be viewed with a small telescope.[8] Parallax measurements place it at a distance of roughly 169 light years (52 parsecs) from Earth.[1]

A light curve for W Ursae Majoris, plotted from TESS data[9]

In 1903, the luminosity of this system was found to vary by the German astronomers Gustav Müller and Paul Kempf. It has since become the prototype and eponym for a class of variable stars called W Ursae Majoris variables.[10] This system consists of a pair of stars in a tight, circular orbit with a period of 0.3336 days, or eight hours and 26 seconds.[5] During every orbital cycle, each star eclipses the other, resulting in a decrease in magnitude. The maximum magnitude of the pair is 7.75 mag. During the eclipse of the primary, the net magnitude drops by 0.73 mag, while the eclipse of the secondary causes a magnitude decrease of 0.68 mag.[11]

The two stars in W Ursae Majoris are so close together that their outer envelopes are in direct contact, making them a contact binary system. As a result, they have the same stellar classification of F8Vp, which matches the spectrum of a main-sequence star that is generating energy through the nuclear fusion of hydrogen. However, the primary component has a larger mass and radius than the secondary, with 1.14 times the Sun's mass and 1.09 times the Sun's radius. The secondary has 0.55 solar masses and 0.79 solar radii.[5]

The orbital period of the system has changed since 1903, which may be the result of mass transfer or the braking effects of magnetic fields. Star spots have been observed on the surface of the stars and strong X-ray emissions have been detected, indicating a high level of magnetic activity that is common to W UMa variables. This magnetic activity may play a role in regulating the timing and magnitude of mass transfer occurs.[10]

W Ursae Majoris has a 12th magnitude companion star with the designation ADS 7494B, not to be confused with W UMa B, the secondary of the close eclipsing pair. They may be moving together through space.[12]

  1. ^ a b c d e f Cite error: The named reference Gaia DR2 was invoked but never defined (see the help page).
  2. ^ a b c d Cite error: The named reference aj68_483 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. ^ Cite error: The named reference gcsrv was invoked but never defined (see the help page).
  5. ^ a b c d Gazeas, K.; et al. (February 2021). "Physical parameters of close binary systems: VIII". Monthly Notices of the Royal Astronomical Society. 501 (2): 2897–2919. arXiv:2101.10680. Bibcode:2021MNRAS.501.2897G. doi:10.1093/mnras/staa3753.
  6. ^ Cite error: The named reference mnras390_4_1577 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference aj133_6_2524 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference sherrod_koed2003 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference MAST was invoked but never defined (see the help page).
  10. ^ a b Cite error: The named reference ibvs4517_1 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference aaa446_2_785 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference aj106_3_1174 was invoked but never defined (see the help page).