000004916 001__ 4916
000004916 005__ 20200612211943.0
000004916 0247_ $$2DOI$$a10.1051/0004-6361/201834358
000004916 037__ $$aSCART-2020-0118
000004916 100__ $$avan Genderen, A. M. 
000004916 245__ $$aPulsations, eruptions, and evolution of four yellow hypergiants
000004916 260__ $$c2019
000004916 500__ $$aFull Tables M.1 and M.2 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr ( or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/631/A48
000004916 520__ $$aAims. We aim to explore the variable photometric and stellar properties of four yellow hypergiants (YHGs), HR 8752, HR 5171A, ρ Cas, and HD 179821, and their pulsations of hundreds of days, and long-term variations (LTVs) of years. We also aim to explore light and colour curves for characteristics betraying evolutionary loops and eruptive episodes and to investigate trends of quasi-periods and the possible need for distance revisions. Methods. We tackled multi-colour and visual photometric data sets, looked for photometric indications betraying eruptions or enhanced mass-loss episodes, calculated stellar properties mainly using a previously published temperature calibration, and investigated the nature of LTVs and their influence on quasi-periods and stellar properties. Results. Based on driven one-zone stellar oscillation models, the pulsations can be characterised as “weakly chaotic”. The BV photometry revealed a high-opacity layer in the atmospheres. When the temperature rises the mass loss increases as well, consequently, as the density of the high-opacity layer. As a result, the absorption in B and V grow. The absorption in B, presumably of the order of one to a few 0.m 1, is always higher than in V. This difference renders redder and variable (B − V) colour indexes, but the absorption law is unknown. This property of YHGs is unpredictable and explains why spectroscopic temperatures (reddening independent) are always higher than photometric ones, but the difference decreases with the temperature. A new (weak) eruption of ρ Cas has been identified. We propose shorter distances for ρ Cas and HR 5171A than the accepted ones. Therefore, a correction to decrease the blue luminescence of HR 5171A by polycyclic aromatic hydrocarbon (PAH) molecules is necessary, and HR 5171A would no longer be a member of the cluster Gum48d. HR 5171A is only subject to one source of light variation, not by two as the literature suggests. Eruptive episodes (lasting one to two years), of YHGs prefer relatively cool circumstances when a red evolutionary loop (RL) has shifted the star to the red on the HR diagram. After the eruption, a blue loop evolution (BL) is triggered lasting one to a few decades. We claim that in addition to HR 8752, also the other three YHGs have shown similar cycles over the last 70 years. This supports the suspicion that HD 179821 might be a YHG (with a possible eruptive episode between 1925 and 1960). The range in temperature of these cyclic Teff variations is 3000 K–4000 K. LTVs mainly consist of such BL and RL evolutions, which are responsible for a decrease and increase, respectively, of the quasi-periods. The reddening episode of HR 5171A between 1960 and 1974 was most likely due to a red loop evolution, and the reddening after the 1975 eruption was likely due to a shell ejection, taking place simultaneously with a blue loop evolution.
000004916 536__ $$aH2020/$$c823734/$$fMCPOEMS
000004916 594__ $$aNO
000004916 6531_ $$astars: massive 
000004916 6531_ $$asupergiants
000004916 6531_ $$astars: oscillations 
000004916 6531_ $$atechniques: photometric
000004916 700__ $$aLobel, A. 
000004916 700__ $$aNieuwenhuijzen, H. 
000004916 700__ $$aHenry, G. W. 
000004916 700__ $$ade Jager, C. 
000004916 700__ $$aBlown, E. 
000004916 700__ $$aDi Scala, G.
000004916 700__ $$avan Ballegoij, E. J.
000004916 773__ $$cA48, 1-26$$nNovember 2019$$pAstronomy and Astrophysics$$v631$$y2019
000004916 8560_ $$falex.lobel@observatoire.be
000004916 85642 $$ahttps://doi.org/10.1051/0004-6361/201834358
000004916 905__ $$apublished in
000004916 980__ $$aREFERD