Discovery of new mercury–manganese stars, including a fast rotator

Abstract

The origin of mercury–manganese (HgMn) stars is still poorly understood and the statistical analysis of an extensive sample of well characterized objects would be very valuable. Nevertheless, the compilation of a clean and reliable list of all known HgMn stars, and complete characterization of those objects, is still a pending issue. We report the identification of 13 new HgMn stars from our own spectroscopic observations and from publicly available spectral libraries. In addition, we perform a thorough literature search to give a list of 46 confirmed HgMn stars (plus a further nine suspected HgMn stars) discovered over the last years or neglected by other compilations. When required, we performed specific observations to confirm doubtful cases. For the 13 newly identified HgMn stars we derived photospheric chemical abundances by spectral synthesis. Besides Hg and Mn, which are overabundant in the whole sample, P, Ga, and Xe are overabundant in the hottest stars of the sample, and Sr, Zr, and Pt among the coolest; Y is present in most stars of the sample. Three of these new HgMn stars are members of open clusters: HD 93549 in IC 2602, HD 96473 in NGC 3532, and HD 322659 in NGC 6281. Furthermore, our sample includes HD 145842, an object remarkable for its high rotation. In fact, its projected rotational velocity of ve sin i = 124 km s−1 is the highest measured in any HgMn star and is more than 30 per cent above the theoretical limit predicted by the diffusion theory, which makes HD 145842 a challenging test case for the current models.

TESS survey of rotational and pulsational variability of mercury-manganese stars

“…Our results challenge the hypothesis of a sharp rotational cutoff of the HgMn phenomenon, but should be verified by confirmation of the HgMn nature of each of these rapid rotators based on high-resolution spectroscopic observations and detailed abundance analysis. This confirmation has already been obtained for HD 169027 by Woolf & Lambert (1999) and for HD 93549 and HD 145842 by González et al (2021).…”

“…The 3 stars with 2-5 mmag g-mode oscillations (HD 29589, HD 93549, HD 171301) are particularly interesting for follow up studies and detailed asteroseismic analyses. All three objects have been studied with high-resolution spectra (Hubrig et al 2011;González et al 2021;Adelman, Gulliver & Gucella 2017) and their HgMn classification is indisputable. Two other well-studied HgMn stars, HD 172728 (Adelman, Gulliver & Rayle 2001) and HD 173524 , have the longest TESS data sets (12 and 10 TESS sectors respectively).…”

“…High-precision photometric observations from space opened another avenue for finding variable HgMn stars. Detection of variability with periods of a few days was reported for individual HgMn stars using CoRoT (Morel et al 2014;Strassmeier et al 2017), Kepler (Balona et al 2011(Balona et al , 2015, K2 (White et al 2017;Krtička et al 2020), the BRITE nanosat constellation (Strassmeier et al 2020), and TESS González et al 2021). In some of these cases, interpretation of photometric variability in terms of rotational modulation was supported by the detection of line profile variations in follow-up time-resolved spectroscopy.…”

“…A compilation of HgMn abundance analyses (Ghazaryan & Alecian 2016;Ghazaryan et al 2018) as well as a number of recent studies reporting discovery of individual HgMn stars (e.g. Catanzaro et al 2010Catanzaro et al , 2020Monier, Gebran & Royer 2015;Monier et al 2019;Sikora, Wade & Rowe 2020;González et al 2021) were also taken into account. These selection steps resulted in a catalogue containing 544 definite and probable HgMn stars brighter than 𝑉 = 12 mag.…”

“…TIC 51612589 (HD 145842, 𝜃 Nor). For this newly identified HgMn star González et al (2021) reported the 1.087 d period based on the same observational data as analysed here. Our measurement yields a close period value of 1.086 d.…”