15 Vulpeculae
A white-hued, evolved Am star that varies in brightness every 14 days.
15 Vulpeculae, also known by its variable star designation NT Vulpeculae, is a faint white star in the northern constellation Vulpecula. Based on parallax measurements, it lies roughly 243 light-years from Earth, and it is moving closer to our planet. With an apparent visual magnitude of about 4.66, it is just visible to the naked eye. The star is classified as a marginal Am star, typically given a stellar type of A4 IIIm, indicating an evolved A-type giant. However, a 1989 study suggested a more complex classification of kA5hA7mA7 (IV–V), blending subgiant and main-sequence traits, with the K-line matching an A5 star and the hydrogen and metal lines matching an A7 star. While on the main sequence, 15 Vulpeculae was a typical Am star, but as it evolved into a subgiant, it lost most of those peculiar properties, retaining only some elemental abundance anomalies. It has about 2.4 times the Sun's mass and has expanded to four times the Sun's diameter, radiating 62 times the Sun's luminosity from its photosphere. In 1974, L. P. Metik announced it as a variable star, specifically an Alpha² Canum Venaticorum-type variable, with its magnitude fluctuating between 4.62 and 4.67 over a 14-day period. Astrometric data from Gaia DR3 show high margins of error, and the star has an unusually slow projected rotational velocity—both pieces of evidence suggesting it may have a companion star, though the slow rotation could also be explained if the star is viewed pole-on.
- Distance
- approximately 243 light years
- Apparent visual magnitude
- 4.66 typical, ranging from 4.62 to 4.67
- Spectral classification
- A4 IIIm (marginal Am star); also classified as kA5hA7mA7 (IV–V)
- Mass
- 2.4 times the Sun's mass
- Radius
- four times the Sun's diameter
- Luminosity
- 62 times the Sun's luminosity
- Variable type
- Alpha2 Canum Venaticorum-type variable, period 14 days
Lore & Background
15 Vulpeculae is considered a marginal Am star with a stellar classification of A4 IIIm, matching an evolved A-type giant star. However, Gray & Garrison (1989) found a class of kA5hA7mA7 (IV–V), which matches a blend of subgiant and main sequence luminosity classes with the K-line (kA5) of an A5 star and the hydrogen (hA7) and metal (mA7) absorption lines of an A7 star. The star was a typical Am star when on the main sequence; as it evolved into a subgiant, it lost most of the peculiar properties of an Am star but still maintains some element abundance peculiarities.
In 1974 L. P. Metik announced that 15 Vulpeculae is a variable star. It is an Alpha2 Canum Venaticorum-type variable with magnitude ranging from 4.62 down to 4.67 over a period of 14 days. There is evidence that 15 Vulpeculae may have a companion star, given the high margins of error in the astrometric measurements taken by Gaia DR3, as well as its unusually slow projected rotational velocity, which could also be explained if the star is being viewed pole-on.
Reader's Guide
15 Vulpeculae holds significance as a variable star of the Alpha2 Canum Venaticorum type, a class of chemically peculiar stars that exhibit variations in brightness due to rotation and surface inhomogeneities. Its variability was announced in 1974 by L. P. Metik, adding it to the catalog of stars that change in brightness over a 14-day cycle. The star's classification history reflects a transition from a typical Am star on the main sequence to a marginal Am star as it evolved into a subgiant, retaining some element abundance peculiarities. This evolutionary stage provides insight into how chemical peculiarities diminish as stars age. The possibility of a companion star, suggested by astrometric measurement errors and an unusually slow projected rotational velocity, adds to its interest, though the slow rotation could alternatively be due to a pole-on viewing angle. Its legacy lies in illustrating the complexities of stellar classification and the behavior of magnetic chemically peculiar stars in the northern sky.
Did You Know?
- 15 Vulpeculae has the variable star designation NT Vulpeculae.
- It is an Alpha2 Canum Venaticorum-type variable with a period of 14 days.
- The star is 2.4 times more massive than the Sun and has expanded to four times the Sun's diameter.
- There is evidence it may have a companion star, based on Gaia DR3 astrometric errors and its slow rotational velocity.
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