EW Lacertae

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

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]

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  8. ^ a b Cite error: The named reference Frost1919 was invoked but never defined (see the help page).
  9. ^ a b c Cite error: The named reference Hubert1987 was invoked but never defined (see the help page).
  10. ^ a b Cite error: The named reference Voikhanskaya1976 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference skiff2014 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference MAST was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Baldwin1943 was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference Kogure1975 was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference Walker1953 was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference walker1958 was invoked but never defined (see the help page).
  17. ^ Cite error: The named reference Mon2013 was invoked but never defined (see the help page).