Astronomy:EW Lacertae

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Short description: Variable star in the constellation Lacerta
EW Lacertae
Lacerta constellation map.svg
Red circle.svg
Location of EW Lacertae (circled)
Observation data
Equinox J2000.0]] (ICRS)
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[1] mas
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

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.[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

  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 2.2 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. doi:10.1134/S1063772917010085. Bibcode: 2017ARep...61...80S. 
  3. ↑ 3.0 3.1 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. doi:10.1515/astro-2017-0338. Bibcode: 2011BaltA..20..572A. 
  4. ↑ Anderson, E.; Francis, Ch. (May 2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331–346. doi:10.1134/S1063773712050015. ISSN 1063-7737. Bibcode: 2012AstL...38..331A. 
  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. doi:10.1093/mnras/stx1737. Bibcode: 2017MNRAS.471.3398A. 
  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. doi:10.1111/j.1365-2966.2010.17434.x. ISSN 0035-8711. Bibcode: 2011MNRAS.410..190T. 
  7. ↑ "HD 217050 -- Be Star". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+217050+--+Be+Star. 
  8. ↑ 8.0 8.1 Frost, E. B. (January 1919). "A star with disappearing bright lines". Astrophysical Journal 49: 61–62. doi:10.1086/142444. Bibcode: 1919ApJ....49...61F. 
  9. ↑ 9.0 9.1 9.2 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. ↑ 10.0 10.1 Voikhanskaya, N. F. (April 1976). "Spectrum of EW Lacertae in 1974". Astrophysics 12 (2): 135–144. doi:10.1007/BF01002028. Bibcode: 1976Ap.....12..135V. 
  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. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html. 
  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. doi:10.1086/144528. Bibcode: 1943ApJ....97..388B. 
  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. doi:10.1086/145776. Bibcode: 1953ApJ...118..481W. 
  16. ↑ Walker, M. F. (1958). "HD 217050 : A cooperative program of photoelectric observations". The Astronomical Journal 63: 237. doi:10.1086/107735. Bibcode: 1958AJ.....63..237W. 
  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. doi:10.1093/pasj/65.4.77. Bibcode: 2013PASJ...65...77M. 



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