Are Am stars and hot-Jupiter planets related?

SAFFE, C.; ALACORIA, J.; MIQUELARENA, P.; PETRUCCI, R.; JAQUE ARANCIBIA, M.; ANGELONI, R.; MARTIOLI, E.; FLORES, M.; JOFRE, E.; COLLADO, A.; GUNELLA, F.

ASTRONOMY & ASTROPHYSICS. SUPPLEMENT SERIES (PRINT)

EDP SCIENCES SA

Lugar: Paris; Año: 2022

0365-0138

Context.Metallic-lined Am stars are often components of short-period binary systems, where tidal interactions would result inlowrotational velocities and help to develop the chemical peculiarities observed. However, the origin of single Am stars and Am stars thatbelong to wide binary systems is unclear.Aims.There is very recent evidence of an Am star hosting a hot-brown dwarf likely synchronized and other possible Am starshosting hot-Jupiter planets. Following literature suggestions, we wonder if these hot-low mass companions could playa role in thedevelopment of an Am star, that is to say, if they could help tomitigate the "single Am" problem.Methods.We carried out a detailed abundance determination via spectral synthesis of 19 early-type stars hosting hot-brown dwarfs andhot-Jupiter planets, in order to determine the possible presence of Am stars in this sample. The abundances were determined iterativelyfor 25 different species by fitting synthetic spectra using the SYNTHE program together with local thermodynamic equilibrium (LTE)ATLAS12 model atmospheres. The abundances of Ci, Oiand Mgiwere corrected by non-LTE effects. The complete chemicalpatterns of the stars were then compared to those of Am stars and other chemically peculiar stars.Results.We studied a sample of 19 early-type stars, 7 of them hosting hot-brown dwarfs and 12 of them hosting hot-Jupiter planets.We detected 4 Am stars in our sample (KELT-19A, KELT-17, HATS-70 and TOI-503) and 2 possible Am stars (TOI-681 and HAT-P-69). In particular, we detected the new Am star HATS-70 which hosts a hot-brown dwarf, and rule out this class for the hot-Jupiterhost WASP-189, both showing different composition than previously reported. For the first time, we estimated the incidence of Amstars within stars hosting hot-brown dwarfs (50-75%) and within stars hosting hot-Jupiters (20-42%). In particular, the incidence ofAm stars hosting hot-brown dwarfs resulted higher than the frequency of Am stars in general. This would imply that the presence ofhot-brown dwarfs could play a role in the development of Am stars and possibly help to mitigate the "single Am" problem, differentto the case of hot-Jupiter planets. Notably, these results would also indicate that the search for hot-brown dwarfs may be benefitedby targeting single Am stars or Am stars in wide binary systems. We encourage the analysis offadditional early-type stars hostinghot-companions in order to improve the significance of the initial trends found here.