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25 Serpentis
	Location of 25 Serpentis (circled)
Observation data; Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation	Serpens
Right ascension	15h 46m 05.63636s
Declination	−01° 48′ 15.0830″
Apparent magnitude (V)	5.37 - 5.40
Characteristics
Spectral type	B8IV/V
U−B color index	−0.40
B−V color index	−0.05
Variable type	SPB
Astrometry
Radial velocity (Rv)	9.50±0.3 km/s
Proper motion (μ)	RA: −23.15 mas/yr ; Dec.: −30.50 mas/yr
Parallax (π)	7.25 ± 0.31 mas
Distance	450 ± 20 ly ; (138 ± 6 pc)
Orbit
Period (P)	38.927±0.004
Eccentricity (e)	0.731±0.006
Periastron epoch (T)	2450132.80±0.06
Argument of periastron (ω); (secondary)	201.8±0.8°
Semi-amplitude (K1); (primary)	43.1±0.7 km/s
Semi-amplitude (K2); (secondary)	86±1 km/s
Details
Mass	4.1 M☉
Luminosity	383 L☉
Temperature	13,932 K
Rotational velocity (v sin i)	80 km/s
Other designations
	A2 Ser, 25 Ser, PT Ser, HD 140873, HIP 77227, HR 5863, SAO 140740, BD−01°3092
Database references
SIMBAD	data

25 Serpentis is a star system in the constellation of Serpens Caput. With an apparent magnitude of 5.37, it is just barely visible to the naked eye. The system is estimated to be some 450 light-years (138 parsecs) based on its parallax.^[1]

A light curve for PT Serpentis, plotted from *Hipparcos* data^[10]

25 Serpentis is a spectroscopic binary,^[11] 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 and an A-type main-sequence star. The two stars orbit each other every 38.9 days, and have a very eccentric orbit, with an orbital eccentricity of 0.731.^[7] The primary is a slowly pulsating B-type star, which causes the system to vary by 0.03 magnitudes;^[2] for that reason it has been given the variable star designation PT Serpentis.

References

^ ^a ^b ^c ^d ^e ^f van Leeuwen, F.; et al. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
^ ^a ^b VSX; Otero, S. A (10 February 2012). "PT Serpentis". AAVSO Website. American Association of Variable Star Observers. Retrieved 28 May 2014.
^ Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars, Vol. 5". Michigan Spectral Survey. 5. Bibcode:1999MSS...C05....0H.
^ ^a ^b Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
^ Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
^ Pourbaix, D.; et al. (2004). "S_B⁹: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics. 424 (2): 727–732. arXiv:astro-ph/0406573. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213. S2CID 119387088.
^ ^a ^b De Cat, P.; et al. (2000). "A study of bright southern slowly pulsating B stars. I. Determination of the orbital parameters and of the main frequency of the spectroscopic binaries". Astronomy and Astrophysics. 355: 1015–1030. Bibcode:2000A&A...355.1015D.
^ Szewczuk, W.; Daszyńska-Daszkiewicz, J. (2015). "Identification of pulsational modes in rotating slowly pulsating B-type stars". Monthly Notices of the Royal Astronomical Society. 450 (2): 1585. arXiv:1504.04490. Bibcode:2015MNRAS.450.1585S. doi:10.1093/mnras/stv715.
^ Hoffleit, D. (July 1979), "Discordances in Star Designations", Bulletin d'Information du Centre de Données Stellaires, 17 (17): 38, Bibcode:1979BICDS..17...38H
^ "Light Curve". Hipparcos ESA. ESA. Retrieved 17 February 2022.
^ Petrie, R. M.; Phibbs, E. (1950). "Redetermination of the spectrographic orbits of iot Peg and 25 Ser". Publications of the Dominion Astrophysical Observatory Victoria. 8: 225. Bibcode:1950PDAO....8..225P.