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EW Lacertae

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EW Lacertae, also known as HD 217050 and HR 8731, is a star about 940 light years from the Earth, in the constellation Lacerta.[1] It is a 5th magnitude star, so it will be faintly visible to the naked eye of an observer located far from city lights. It is a Gamma Cassiopeiae variable, varying in brightness from magnitude 5.22 to 5.48, over a period of about 8.7 hours.[2] The star's variable spectrum, which shows changes on timescales ranging from hours to decades, has been monitored for more than a century.[9][10]

EW Lacertae
Location of EW Lacertae (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Lacerta
Right ascension 22h 57m 04.50206s[1]
Declination +48° 41′ 2.6456″[1]
Apparent magnitude (V) +5.22 – +5.48[2]
Characteristics
Spectral type B4IIIpe[3]
Variable type γ Cas[2]
Astrometry
Proper motion (μ) RA: 9.298±0.062[1] mas/yr
Dec.: −5.409±0.064[1] mas/yr
Parallax (π)3.4800 ± 0.0706 mas[1]
Distance940 ± 20 ly
(287 ± 6 pc)
Absolute magnitude (MV)−1.65[4]
Details
Mass5.9[1] M☉
Radius7.0[1] R☉
Luminosity2,084[1] L☉
Surface gravity (log g)3.54[1] cgs
Temperature15,230[1] K
Metallicity [Fe/H]+0.51[1] dex
Rotational velocity (v sin i)340[5] km/s
Age40[6] Myr
Other designations
HD 217050, BD+47 3985, HIP 113327, HR 8731, SAO 52526,[7] Boss 5918[8]
Database references
SIMBADdata

The spectral class of EW Lacertae has been given as B4IIIpe,[3] a hot giant star showing emission lines. Other publications have given types between B1 and B5, a luminosity class of III (giant) or IV (subgiant), and noted various spectral peculiarities related to being a shell star.[11] Models published in Gaia Data Release 3 place the star towards the end of its main sequence life.[1]

A light curve for EW Lacertae, plotted from TESS data.[12] The 8.681 hour period is marked in red.

Although spectrograms of EW Lacertae, then known as Boss 5918 or BD+47°3985, had been acquired as early as 1887,[9] the existence of an envelope surrounding EW Lacertae was first noticed in a spectrogram taken in 1913.[10] Edwin Frost noted that the star's spectrum was variable, in 1919.[8] In 1943, Ralph Baldwin reported that EW Lacertae had a shell spectrum.[13] The shell spectrum had disappeared in the years 1918 - 1921, but reappeared in 1922.[14] Spectra taken in 1925, 1926 and 1928 again showed no features associated with a shell, but the shell features in the spectrum were very clear by the end of 1940.[9]

Observations in the early 1950s at the Lick Observatory by Merle Walker revealed that EW Lacertae was a variable star,[15] and it was given its variable star designation in the General Catalogue of Variable Stars.[16]

The complex variations seen in the spectrum of EW Lacertae may be caused by a disk of gas surrounding the star, seen nearly edge-on by an observer on the Earth, which occasionally has temporary density enhancements which persist for years.[17]

References

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  1. ^ a b c d e f g h i j k l m Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. ^ a b c Samus', N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  3. ^ a b Antoniou, A.; Stathopoulos, D.; Danezis, E.; Lyratzi, E. (2011). "Studying the UV mg II Resonance Lines in 20 Be Stars". Baltic Astronomy. 20 (4): 572–575. Bibcode:2011BaltA..20..572A. doi:10.1515/astro-2017-0338. S2CID 99940009.
  4. ^ Anderson, E.; Francis, Ch. (May 2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331–346. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. eISSN 1562-6873. ISSN 1063-7737. S2CID 119257644.
  5. ^ Ahmed, A.; Sigut, T. A. A. (2017). "Rotational mixing in be stars: Nitrogen abundances for a sample of be stars from the MiMeS survey". Monthly Notices of the Royal Astronomical Society. 471 (3): 3398. arXiv:1707.03009. Bibcode:2017MNRAS.471.3398A. doi:10.1093/mnras/stx1737.
  6. ^ Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (October 12, 2010). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1). Oxford University Press (OUP): 190–200. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x. ISSN 0035-8711.
  7. ^ "HD 217050 -- Be Star". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2023-01-16.
  8. ^ a b Frost, E. B. (January 1919). "A star with disappearing bright lines". Astrophysical Journal. 49: 61–62. Bibcode:1919ApJ....49...61F. doi:10.1086/142444.
  9. ^ a b c Hubert, A. M.; Floquet, M.; Chauville, J.; Chambon, M. T. (September 1987). "Spectral features of the B2e star EW Lac before and during the variable shell phase". Astronomy and Astrophysics Supplement Series. 70: 443–464. Bibcode:1987A&AS...70..443H.
  10. ^ a b Voikhanskaya, N. F. (April 1976). "Spectrum of EW Lacertae in 1974". Astrophysics. 12 (2): 135–144. Bibcode:1976Ap.....12..135V. doi:10.1007/BF01002028. S2CID 121399502.
  11. ^ Skiff, B. A. (2014). "VizieR Online Data Catalog: Catalogue of Stellar Spectral Classifications (Skiff, 2009- )". VizieR On-line Data Catalog. Bibcode:2014yCat....1.2023S.
  12. ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 18 January 2023.
  13. ^ Baldwin, Ralph B. (May 1943). "The Shell Spectrum of HR 8731 IN 1940, with an Intercomparison of the Spectra of Several Shells". Astrophysical Journal. 97: 388–393. Bibcode:1943ApJ....97..388B. doi:10.1086/144528.
  14. ^ Kogure, T. (1975). "Shell spectrum of the Be star HD 217050, 1966 - 1972". Publications of the Astronomical Society of Japan. 27: 165–179. Bibcode:1975PASJ...27..165K.
  15. ^ Walker, Merle F. (November 1953). "The Light-Variations of HD 217050". Astrophysical Journal. 118: 481–488. Bibcode:1953ApJ...118..481W. doi:10.1086/145776.
  16. ^ Walker, M. F. (1958). "HD 217050 : A cooperative program of photoelectric observations". The Astronomical Journal. 63: 237. Bibcode:1958AJ.....63..237W. doi:10.1086/107735.
  17. ^ Mon, Masahiro; Suzuki, Masakazu; Moritani, Yuki; Kogure, Tomokazu (August 2013). "Spectroscopic Variations of the Be-Shell Star EW Lacertae in the V/R Variation Periods". Publications of the Astronomical Society of Japan. 65 (4): 77. arXiv:1306.2511. Bibcode:2013PASJ...65...77M. doi:10.1093/pasj/65.4.77.
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