000005162 001__ 5162
000005162 005__ 20210123121532.0
000005162 0247_ $$2DOI$$a10.1051/0004-6361/201936444
000005162 037__ $$aSCART-2021-0030
000005162 100__ $$aCochetti, Y. R. 
000005162 245__ $$aBe and Bn stars: Balmer discontinuity and stellar-class relationship
000005162 260__ $$c2020
000005162 520__ $$aContext. A significant number of Be stars show a second Balmer discontinuity (sBD) attributed to an extended circumstellar envelope (CE). The fast rotational velocity of Be stars undoubtedly plays a significant role in the formation of the CE. However, Bn stars, which are also B-type rapidly rotating stars, do not all present clear evidence of being surrounded by circumstellar material. Aims. We aim to characterize the populations of Be and Bn stars, and discuss the appearance of the sBD as a function of the stellar parameters. We expect to find new indices characterizing the properties of CEs in Be stars and properties relating Be and Bn stars. Methods. We obtained low- and high-resolution spectra of a sample of Be and Bn stars, derived stellar parameters, characterized the sBD, and measured the emission in the Hα line. Results. Correlations of the aspect and intensity of the sBD and the emission in the Hα line with the stellar parameters and the V sin i are presented. Some Bn stars exhibit the sBD in absorption, which may indicate the presence of rather dense CEs. Six Bn stars show emission in the Hα line, so they are reclassified as Be stars. The sBD in emission appears in Be stars with V sin i ≲ 250 km s−1, and in absorption in both Be and Bn stars with V sin i ≳ 50 km s−1. Low-mass Be and Bn stars share the same region in the Hertzsprung-Russell diagram. The distributions of rotational to critical velocity ratios of Be and Bn stars corresponding to the current stellar evolutionary stage are similar, while distributions inferred for the zero-age main sequence have different skewness. Conclusions. We found emission in the Hα line and signs of a CE in some Bn stars, which motivated us to think that Bn and Be stars probably belong to the same population. It should be noted that some of the most massive Bn stars could display the Be phenomenon at any time. The similarities found among Be and Bn stars deserve to be more deeply pursued.
000005162 594__ $$aNO
000005162 6531_ $$acircumstellar matter 
000005162 6531_ $$astars: emission-line 
000005162 6531_ $$aBe 
000005162 6531_ $$astars: fundamental parameters 
000005162 6531_ $$aAstrophysics - Solar and Stellar Astrophysics
000005162 700__ $$aZorec, J. 
000005162 700__ $$aCidale, L. S. 
000005162 700__ $$aArias, M. L. 
000005162 700__ $$aAidelman, Y. 
000005162 700__ $$aTorres, A. F. 
000005162 700__ $$aFrémat, Y.
000005162 700__ $$aGranada, A.
000005162 773__ $$cA18$$pAstronomy & Astrophysics$$v634$$y2020
000005162 8560_ $$fyves.fremat@observatoire.be
000005162 85642 $$ahttps://www.aanda.org/articles/aa/abs/2020/02/aa36444-19/aa36444-19.html
000005162 905__ $$apublished in
000005162 980__ $$aREFERD