EW Lacertae

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EW Lacertae
Lacerta constellation map.svg
Red circle.svg
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]
Distance 940 ± 20  ly
(287 ± 6  pc)
Absolute magnitude  (MV)−1.65 [4]
Details
Mass 5.9 [1]   M☉
Radius 7.0 [1]   R☉
Luminosity 2,084 [1]   L☉
Surface gravity (log g)3.54 [1]   cgs
Temperature 15,230 [1]   K
Metallicity [Fe/H]+0.51 [1]   dex
Rotational velocity (v sin i)340 [5]  km/s
Age 40 [6]   Myr
Other designations
HD  217050, BD+47 3985, HIP  113327, HR  8731, SAO  52526, [7] Boss 5918 [8]
Database references
SIMBAD data

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]

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

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References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 Vallenari, A.; et al. (Gaia Collaboration) (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics . arXiv: 2208.00211 . doi: 10.1051/0004-6361/202243940 . Gaia DR3 record for this source at VizieR.
  2. 1 2 3 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. 1 2 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. Oxford University Press (OUP). 410 (1): 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. 1 2 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. 1 2 3 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. 1 2 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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