EW Aquarii
A low-amplitude Delta Scuti variable in Aquarius.
EW Aquarii, also designated HR 8102, is a variable star located in the equatorial constellation of Aquarius. Its apparent visual magnitude hovers near 6.4, placing it at the threshold of naked-eye visibility under dark skies. Based on parallax measurements, the star lies roughly 439 light-years from the Sun, though it is moving closer at a radial velocity of −39 km/s. Because it lies near the ecliptic, it is occasionally occulted by the Moon. EW Aquarii may belong to the Hyades Group.
Originally flagged in 1969 as a suspected metal-lined Delta Delphini star, it was catalogued as such. In 1974, during a search for ultra-short period Cepheid variables, astronomers detected brightness variations and classified it as a low-amplitude Delta Scuti variable. It received the variable star designation EW Aqr in the 62nd name-list of variable stars in 1977. Its brightness ranges from magnitude 6.41 to 6.48, with a primary period of 2.16 hours. Three distinct variation periods have been identified: 0.09664, 0.1087, and 0.2121 days, with respective amplitudes of 0.013, 0.010, and 0.007 magnitudes. The pattern of these variations indicates non-radial pulsation.
The star’s stellar classification is Fm δ Del, meaning it is an F-type Am star of the Delta Delphini type. It has about 2.2 times the Sun’s mass and four times its radius. EW Aquarii rotates rapidly, with a projected rotational velocity of 134 km/s. Its photosphere radiates roughly 37 times the Sun’s luminosity at an effective temperature of 7,640 K.
- Constellation
- Aquarius
- Apparent magnitude range
- 6.41 to 6.48
- Distance
- approximately 439 light years
- Radial velocity
- −39 km/s
- Spectral type
- Fm δ Del
- Mass
- 2.2 times the Sun
- Radius
- 4 times the Sun
- Luminosity
- 37 times the Sun
- Effective temperature
- 7,640 K
- Projected rotational velocity
- 134 km/s
Lore & Background
EW Aquarii was first flagged in 1969 as a suspected metal-lined Delta Delphini star. During a 1974 search for ultra-short period Cepheid variables, it was found to vary in brightness and was determined to be a low-amplitude Delta Scuti variable. In 1977, it was catalogued in the 62nd name-list of variable stars with the designation EW Aqr. The star varies between magnitudes 6.41 and 6.48 with a primary period of 2.16 hours, and three known variation periods of 0.09664, 0.1087, and 0.2121 days with amplitudes of 0.013, 0.010, and 0.007 magnitudes, respectively. The pattern of variations indicates it is a non-radial pulsator. Its stellar classification is Fm δ Del, indicating an F-type Am star of the Delta Delphini type. The star has 2.2 times the mass of the Sun and four times the Sun's radius, with a high projected rotational velocity of 134 km/s. It radiates 37 times the luminosity of the Sun at an effective temperature of 7,640 K. The star is located near the ecliptic and is subject to lunar occultations, and it may be a member of the Hyades Group.
Reader's Guide
EW Aquarii is significant as a low-amplitude Delta Scuti variable, a class of pulsating stars important for asteroseismology. Its multiple pulsation periods—0.09664, 0.1087, and 0.2121 days—and non-radial pulsation pattern provide insight into stellar interior structure. The star's classification as Fm δ Del (an F-type Am star of the Delta Delphini type) links it to chemically peculiar stars with enhanced metal lines. Its high rotational velocity of 134 km/s and location near the ecliptic, making it subject to lunar occultations, add to its observational interest. The possibility that it belongs to the Hyades Group suggests a common origin with that moving cluster. Its discovery history—first flagged in 1969, identified as variable in 1974, and catalogued in 1977—illustrates the progression from suspected variable to confirmed pulsator. With an apparent magnitude near 6.4, it is at the limit of naked-eye visibility, making it accessible to amateur astronomers with small telescopes.
Did You Know?
- It has three known variation periods: 0.09664, 0.1087, and 0.2121 days.
- The star is a non-radial pulsator and is classified as Fm δ Del.
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