V1401 Aquilae
A pulsating star of uncertain evolutionary status in Aquila.
V1401 Aquilae is a solitary star in the equatorial constellation Aquila that pulsates in a semi-regular fashion. Its brightness, around magnitude 6.3, makes it faintly visible without a telescope, and parallax data place it roughly 2,380 light-years away. The star’s evolutionary stage remains ambiguous; it has been described as a post-AGB object, a UU Herculis variable, or a W Virginis variable (a subtype of type II Cepheids). It sits 21.5° from the galactic plane.
Its variability was first reported in 1965 by W. Strohmeier and colleagues. In 1985, C. Waelkens and M. Burnet detected irregular photometric changes with a period near a month and proposed it as a candidate UU Herculis variable. J. D. Fernie confirmed the star’s variability in 1986, tentatively identifying periods of 28.4 and 11.8 days, and noted very low gravity with shell-like features, hinting at mass loss. A 1990 chemical analysis by R. E. Luck and coauthors found mild enhancements of s-process elements and lithium, suggesting the star may have evolved from a lithium-rich giant.
The stellar classification is F2II, an F-type bright giant. Strong evidence points to it being a population II Cepheid, possibly a W Virginis variable. On the Hertzsprung–Russell diagram, it lies on the hot (blue) side of the population II Cepheid instability strip. Membership in the UU Herculis class appears less likely, as the star has a relatively normal radial velocity and no detected infrared excess. The pulsation period of 28.6 days has been confirmed, but the star’s pulsational behavior is complex and cannot be successfully modeled with a simple harmonic radial pulsation.
The star is strongly metal-deficient—by a factor of 40 compared to the Sun—though it shows a mild enhancement of s-process elements, which is not considered intrinsic. Some researchers have suspected it is in a post-asymptotic giant branch stage, but this is not confirmed by its chemical abundances.
- Designations
- HD 190390, formerly 64 Sagittarii
- Apparent visual magnitude
- ~6.3
- Distance
- ~2,380 light years
- Stellar classification
- F2II
- Pulsation period
- 28.6 days
- Galactic latitude
- 21.5° from the galactic plane
- Metal deficiency
- Factor of 40 relative to the Sun
Lore & Background
The variability of V1401 Aquilae was announced by W. Strohmeier and associates in 1965. In 1985, C. Waelkens and M. Burnet found an irregular photometric variation with a period of around a month and suggested it is a candidate UU Herculis variable. J. D. Fernie confirmed the variability in 1986 and tentatively identified periods of 28.4 and 11.8 days, noting a very low gravity with shell-like features that suggested potential mass loss. An analysis of the chemical composition by R. E. Luck and associates in 1990 found a mild enhancement of s-process elements as well as lithium, indicating it may have evolved from a lithium-rich giant.
The stellar classification of V1401 Aql is F2II, matching an F-type bright giant. There is strong evidence that this star belongs to the population II cepheids, and it may be a W Virginis variable. On the Hertzsprung–Russell diagram it lies on the blue (hot) side of the Cepheid instability strip for population II stars. Membership in the UU Herculis variable class seems less likely since it has a relatively normal radial velocity and no infrared excess has been detected. The pulsation period of 28.6 days has been confirmed, but the pulsational behavior is complex and not successfully modeled using a simple harmonic radial pulsation.
The star is strongly metal deficient by a factor of 40, meaning the abundances of higher mass elements are much lower than in the Sun. There is a mild enhancement of s-process elements, although this is not considered to be intrinsic. Some investigators have suspected the star to be in an evolutionary stage following the asymptotic giant branch, but this is not confirmed based on chemical abundances.
Reader's Guide
V1401 Aquilae holds significance as a pulsating variable star whose evolutionary status remains unresolved, making it a subject of continued interest in stellar astrophysics. Its classification has shifted among post-AGB object, UU Herculis variable, and W Virginis variable, reflecting the complexity of its observed properties. The star's strong metal deficiency—by a factor of 40 relative to the Sun—and mild enhancement of s-process elements and lithium provide clues about its past, though the enhancement is not considered intrinsic. The confirmed pulsation period of 28.6 days, combined with complex pulsational behavior that defies simple harmonic modeling, challenges current theoretical understanding of such stars. Its location 21.5° from the galactic plane and its placement on the blue side of the Cepheid instability strip for population II stars further distinguish it. The lack of infrared excess and relatively normal radial velocity argue against UU Herculis membership, while the chemical abundances do not confirm a post-AGB stage. As a result, V1401 Aquilae serves as a test case for models of late stellar evolution, particularly for stars transitioning between the asymptotic giant branch and the white dwarf cooling track.
Did You Know?
- V1401 Aquilae was formerly designated 64 Sagittarii.
- The star lies 21.5° from the galactic plane.
Frequently Asked Questions
What is V1401 Aquilae?
V1401 Aquilae is a semi-regularly pulsating F2II star located in the constellation Aquila, roughly 2,380 light-years from Earth. It completes one pulsation cycle every 28.6 days and hovers around apparent visual magnitude 6.3, making it barely visible to the unaided eye under dark skies.
Who first identified V1401 Aquilae as a variable star?
The star's variability was first reported in 1965 by W. Strohmeier and his colleagues. Later, in 1985, C. Waelkens and M. Burnet noted additional irregular behavior in its light curve.
What type of variable star is V1401 Aquilae?
Its evolutionary classification remains genuinely uncertain among astronomers. It has been variously described as a post-AGB object, a UU Herculis-type variable, or a W Virginis star (a subtype of type II Cepheids), and no single label has been universally adopted.
What other designations does V1401 Aquilae carry?
Beyond its V-number, the star is catalogued as HD 190390 and was formerly known as 64 Sagittarii before being reassigned to Aquila.
Where does V1401 Aquilae sit relative to the Milky Way?
The star lies 21.5 degrees above the galactic plane, placing it well clear of the dense star fields along the Milky Way's center. This moderate galactic latitude makes it a relatively isolated target for observers studying its pulsation without heavy background confusion.
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