EW Aquarii

EW Aquarii, or HR 8102, is a variable star in the equatorial constellation of Aquarius. With an apparent visual magnitude that fluctuates around 6.47,[2] 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.[2] The star is positioned near the ecliptic and thus is subject to lunar occultations.[9] It may be a member of the Hyades Group.[10]

EW Aquarii
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 21h 11m 41.33844s[1]
Declination −14° 28′ 20.5590″[1]
Apparent magnitude (V) 6.47[2] (6.41 - 6.48)[3]
Characteristics
Spectral type A8 III[3] or Fm δ Del[4]
U−B color index 0.15[5]
B−V color index 0.316±0.007[2]
Variable type δ Sct[3]
Astrometry
Radial velocity (Rv)−39.2±2.9[2] km/s
Proper motion (μ) RA: +39.263[1] mas/yr
Dec.: +0.614[1] mas/yr
Parallax (π)7.4366 ± 0.0435[1] mas
Distance439 ± 3 ly
(134.5 ± 0.8 pc)
Absolute magnitude (MV)0.825[6]
Details
Mass2.203[6] M☉
Radius3.99±0.20[1] R☉
Luminosity37.026±0.314[1] L☉
Surface gravity (log g)3.91[7] cgs
Temperature7,640[7] K
Rotational velocity (v sin i)134[5] km/s
Other designations
BD−15°5908, FK5 5868, HD 201707, HIP 104634, HR 8102, SAO 164204[8]
Database references
SIMBADdata

In 1969, HR 8102 was flagged as a suspected metal-lined Delta Delphini star[11] and was catalogued as such.[12] During a search for ultra-short period Cepheid variables in 1974, this star was found to vary in brightness[10] and was determined to be a low amplitude Delta Scuti variable.[13][7] In 1977, it was catalogued in the 62nd name-list of variable stars with the designation EW Aqr.[14] The star varies between magnitudes 6.41 and 6.48 with a primary period of 2.16 hours.[3] 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.[12]

The stellar classification of EW Aqr is Fm δ Del, indicating an F-type Am star of the Delta Delphini type.[4] It has 2.2[6] times the mass of the Sun and four[1] times the Sun's radius. The star has a high rate of spin, showing a projected rotational velocity of 134 km/s.[5] On average, it is radiating 37[1] times the luminosity of the Sun from its photosphere at an effective temperature of 7,640 K.[7]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  3. Watson, Christopher (4 January 2010). "EW Aquarii". The International Variable Star Index. American Association of Variable Star Observers. Retrieved 4 June 2015.
  4. Houk, Nancy; Smith-Moore, M. (1978). Michigan catalogue of two-dimensional spectral types for the HD stars. 4. Ann Arbor: Dept. of Astronomy, University of Michigan. Bibcode:1988mcts.book.....H.
  5. Rodríguez, E.; et al. (June 2000). "A revised catalogue of δ Sct stars". Astronomy and Astrophysics Supplement. 144 (3): 469–474. Bibcode:2000A&AS..144..469R. doi:10.1051/aas:2000221.
  6. Balona, L. A.; Evers, E. A. (January 1999). "Mode identification and asteroseismology of delta Scuti stars". Monthly Notices of the Royal Astronomical Society. 302 (2): 349–361. Bibcode:1999MNRAS.302..349B. doi:10.1046/j.1365-8711.1999.02125.x.
  7. Kilambi, G. C.; et al. (April 1978). "uvby analysis of HR 8102". Publications of the Astronomical Society of the Pacific. 90: 194–200. Bibcode:1978PASP...90..194K. doi:10.1086/130307.
  8. "HD 199603". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 August 2018.
  9. Edwards, D. A.; et al. (April 1980). "Photoelectric observations of lunar occultations. XI". Astronomical Journal. 85: 478–489. Bibcode:1980AJ.....85..478E. doi:10.1086/112700. See run #5217, for example.
  10. Eggen, O. J. (October 1974). "Photometry of Possible Ultrashort Period Cepheids in the Disk Populations". Information Bulletin on Variable Stars. 935: 1. Bibcode:1974IBVS..935....1E.
  11. Cowley, A. P.; et al. (December 1968). "Further Bright Peculiar A Stars". Publications of the Astronomical Society of the Pacific. 80 (477): 746. Bibcode:1968PASP...80..746C. doi:10.1086/128719.
  12. Hobart, M. A.; et al. (December 1989). "EW Aqr, a non radial Delta Scuti pulsator". Revista Mexicana de Astronomía y Astrofísica. 17: 103–108. Bibcode:1989RMxAA..17..103H.
  13. Kilambi, G. C. (July 1975). "H beta-photometry of HR 8024 and HR 8102". Information Bulletin on Variable Stars. 1024: 1. Bibcode:1975IBVS.1024....1K.
  14. Kukarkin, B. V.; et al. (March 1977). "62nd Name-List of Variable Stars". Information Bulletin on Variable Stars. 1248: 1. Bibcode:1977IBVS.1248....1K.
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