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25 Serpentis is a star system in the constellation of 
25 Serpentis is a spectroscopic binary, meaning that the individual components are too close to be resolved, but periodic Doppler shifts in their spectra indicate orbital motion. The system consists of a hot
Serpens Caput
Serpens ( grc, , , the Serpent) is a constellation in the northern celestial hemisphere. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it remains one of the 88 modern constellations designated by the International ...
. With an apparent magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...
of 5.37, it is just barely visible to the naked eye. The system is estimated to be some 450 light-years (138 parsec
The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...
s) based on its parallax.
25 Serpentis is a spectroscopic binary, meaning that the individual components are too close to be resolved, but periodic Doppler shifts in their spectra indicate orbital motion. The system consists of a hot B-type giant
In astronomy, a blue giant is a hot star with a luminosity class of III (giant) or II ( bright giant). In the standard Hertzsprung–Russell diagram, these stars lie above and to the right of the main sequence.
The term applies to a variety of ...
and an A-type main-sequence star
An A-type main-sequence star (A V) or A dwarf star is a main-sequence (hydrogen-burning) star of spectral type A and luminosity class V (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between ...
. The two stars orbit each other every 38.9 days, and have a very eccentric orbit, with an orbital eccentricity of 0.731. The primary is a slowly pulsating B-type star, which causes the system to vary by 0.03 magnitudes; for that reason it has been given the variable star designation
In astronomy, a variable star designation is a unique identifier given to variable stars. It uses a variation on the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the conste ...
PT Serpentis.
References
{{DEFAULTSORT:25 Serpentis Serpens (constellation) Slowly pulsating B stars Serpentis, 25 B-type giants A-type main-sequence stars Serpentis, A2 140873 5863 Durchmusterung objects 077227 Serpentis, PT Spectroscopic binaries