| |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 21h11m 41.33844s[2] |
| Declination | −14° 28′ 20.5590″[2] |
| Apparent magnitude (V) | 6.47[3] (6.41 - 6.48)[4] |
| Characteristics | |
| Spectral type | A8 III[4]orFm δ Del[5] |
| U−B color index | 0.15[6] |
| B−V color index | 0.316±0.007[3] |
| Variable type | δ Sct[4] |
| Astrometry | |
| Radial velocity (Rv) | −39.2±2.9[3] km/s |
| Proper motion (μ) | RA: +39.263[2] mas/yr Dec.: +0.614[2] mas/yr |
| Parallax (π) | 7.4366 ± 0.0435 mas[2] |
| Distance | 439 ± 3 ly (134.5 ± 0.8 pc) |
| Absolute magnitude (MV) | 0.825[7] |
| Details | |
| Mass | 2.203[7] M☉ |
| Radius | 3.99±0.20[2] R☉ |
| Luminosity | 37.026±0.314[2] L☉ |
| Surface gravity (log g) | 3.91[8] cgs |
| Temperature | 7,640[8] K |
| Rotational velocity (v sin i) | 134[6] km/s |
| Other designations | |
BD−15°5908, FK5 5868, HD 201707, HIP 104634, HR 8102, SAO 164204[9] | |
| Database references | |
| SIMBAD | data |
EW Aquarii, or HR 8102, is a variable star in the equatorial constellationofAquarius. With an apparent visual magnitude that fluctuates around 6.47,[3] it is a dim star near the lower limit of visibility to the naked eye. The star is located at a distance of approximately 439 light years from the Sun based on parallax, but is drifting closer with a radial velocity of −39 km/s.[3] The star is positioned near the ecliptic and thus is subject to lunar occultations.[10] It may be a member of the Hyades Group.[11]
In 1969, HR 8102 was flagged as a suspected metal-lined Delta Delphini star[12] and was catalogued as such.[13] During a search for ultra-short period Cepheid variables in 1974, this star was found to vary in brightness[11] and was determined to be a low amplitude Delta Scuti variable.[14][8] In 1977, it was catalogued in the 62nd name-list of variable stars with the designation EW Aqr.[15] The star varies between magnitudes 6.41 and 6.48 with a primary period of 2.16 hours.[4] There are 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 indicate it is a non-radial pulsator.[13]
The stellar classification of EW Aqr is Fm δ Del, indicating an F-type Am star of the Delta Delphini type.[5] It has 2.2[7] times the mass of the Sun and four[2] times the Sun's radius. The star has a high rate of spin, showing a projected rotational velocity of 134 km/s.[6] On average, it is radiating 37[2] times the luminosity of the Sun from its photosphere at an effective temperature of 7,640 K.[8]
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