U Vulpeculae is a variable and spectroscopic binary star located in the northern constellation Vulpecula. It is classified as a classical δ Cephei (Cepheid) variable, whose apparent visual magnitude varies between 6.73 and 7.54 over a regular pulsation cycle of 7.99 days. Because its brightness never exceeds magnitude 6, the star is not visible to the unaided eye but can be observed with binoculars or a small telescope.
Observational data
- Right ascension (J2000): 19 h 36 m 37.7281 s
- Declination (J2000): +20° 19′ 58.5692″
- Spectral type: F6 Iab – G2 (varying with the pulsation phase)
- Parallax: 1.0530 ± 0.0390 mas, corresponding to a distance of approximately 3 100 light‑years (≈ 950 pc)
- Proper motion: RA 0.906 ± 0.050 mas yr⁻¹, Dec −0.960 ± 0.062 mas yr⁻¹
Physical characteristics
- Mass: ≈ 6.5 M☉
- Radius: ≈ 60 R☉ (varies with pulsation)
- Effective temperature: 5 655 – 5 965 K
- Surface gravity (log g): 1.75 – 1.85 (cgs)
- Metallicity: [Fe/H] ≈ +0.09 dex
- Age: ≈ 82 Myr
- Absolute visual magnitude (M_V): −3.69
Variability and pulsation
U Vulpeculae’s light curve follows the typical pattern of a classical Cepheid, with a well‑defined period of 7.99 days. The star’s brightness changes are driven by radial pulsations of its outer layers, which also cause cyclic variations in temperature and radius.
Binary nature
Radial‑velocity measurements made in 1991 revealed that U Vulpeculae is a single‑lined spectroscopic binary. The orbital period of the system is 2 510 days (≈ 6.9 years) with an eccentricity of 0.675. The secondary component is not directly observable; its presence is inferred from the primary star’s orbital motion. The semi‑amplitude of the primary’s radial‑velocity curve is about 3.64 km s⁻¹.
Discovery and research history
The variability of U Vulpeculae was first reported in 1898 by astronomers Gustav Müller and Paul Kempf at the Potsdam Observatory. Subsequent studies, particularly a 1996 orbital analysis, established its binary status and refined its orbital parameters.
Catalog designations
- BD +20 4200 (Bonner Durchmusterung)
- HD 185059 (Henry Draper Catalogue)
- HIP 96458 (Hipparcos Catalogue)
- HR 7458 (Harvard Revised Catalogue)
- SAO 87447 (Smithsonian Astrophysical Observatory Catalogue)
- SIMBAD identifier: U Vulpeculae
References
Information compiled from astronomical catalogues and peer‑reviewed literature, including the General Catalogue of Variable Stars (GCVS), Hipparcos and Gaia astrometric data, and spectroscopic studies of Cepheid binaries.
