Star in the constellation Ophiuchus
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! style="text-align: center; background-color: #FFFFC0;" colspan="2" | Observation dataEpoch J2000      Equinox J2000
! style="text-align:left" | Constellation
! style="text-align:left" | Right ascension
! style="text-align:left" | Declination
! style="text-align:left" | Apparent magnitude (V)
! style="background-color: #FFFFC0; text-align: center;" colspan="2"| Characteristics
! style="text-align:left" | Evolutionary stage
! style="text-align:left" | Spectral type
! style="text-align:left" | U−B 
! style="text-align:left" | B−V 
! style="text-align:left" | Variable type
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66 Ophiuchi is a binary variable star in the equatorial constellation of Ophiuchus. It has the variable star designation V2048 Ophiuchi, while "66 Ophiuchi" is the Flamsteed designation. This object is visible to the naked eye as a faint, blue-white hued point of light with a baseline apparent visual magnitude of 4.60. It is located approximately 650 light years away from the Sun based on parallax, but is drifting closer with a radial velocity of −13 km/s. The star has a peculiar velocity of relative to its neighbors.
The primary star, known as 66 Ophiuchi A, is a main sequence Be star with a stellar classification of B2Ve. Be stars are rapidly rotating stars that eject gas from their equators due to their rotation, forming disks that produce emission lines. 66 Ophiuchi A's disk extends out to 115 R☉. Like many other Be stars, it is a γ Cas variable; a shell star with a circumstellar disc of gas and is exhibiting irregular changes in brightness, ranging from 4.85 up to 4.55 magnitude. The star is 14 million years old with 9.6 times the Sun's mass and is spinning rapidly with a projected rotational velocity of 250 km/s. It is radiating 1,525 times the Sun's luminosity from its photosphere at an effective temperature of 22,000 K. Because of its rotation, it has a polar equatorial radius 4.50 that of the Sun, but an equatorial radius 5.11 that of the Sun.
A magnitude 6.5 visual companion at an angular separation of has been reported, and is known as 66 Ophiuchi B. It is 2.61 magnitudes fainter than the primary. This corresponds to a mass of about 3.8 times that of the Sun, and a spectral class of about B8.
References.
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