New mercury-manganese stars and candidates from LAMOST DR4

Abstract

Aims. The present work presents our efforts at identifying new mercury-manganese (HgMn/CP3) stars using spectra obtained with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Methods. Suitable candidates were searched for among pre-selected early-type spectra from LAMOST DR4 using a modified version of the MKCLASS code that probes several Hg ii and Mn ii features. The spectra of the resulting 332 candidates were visually inspected. Using parallax data and photometry from Gaia DR2, we investigated magnitudes, distances from the Sun, and the evolutionary status of our sample stars. We also searched for variable stars using diverse photometric survey sources. Results. We present 99 bona fide CP3 stars, 19 good CP3 star candidates, and seven candidates. Our sample consists of mostly new discoveries and contains, on average, the faintest CP3 stars known (peak distribution 9.5 ≤ G ≤ 13.5 mag). All stars are contained within the narrow spectral temperature-type range from B6 to B9.5, in excellent agreement with the expectations and the derived mass estimates (2.4 ≤ M ⊙ ≤ 4 for most objects). Our sample stars are between 100 Myr and 500 Myr old and cover the whole age range from zero-age to terminal-age main sequence. They are almost homogeneously distributed at fractional ages on the main sequence ≤ 80 %, with an apparent accumulation of objects between fractional ages of 50 % to 80 %. We find a significant impact of binarity on the mass and age estimates. Eight photometric variables were discovered, most of which show monoperiodic variability in agreement with rotational modulation. Conclusions. Together with the recently published catalogue of APOGEE CP3 stars, our work significantly increases the sample size of known Galactic CP3 stars, paving the way for future in-depth statistical studies.

Stellar labels for hot stars from low-resolution spectra - I. the HotPayne method and results for 330,000 stars from LAMOST DR6

“…Particularly, it has long been known that "chemically peculiar" stars are common among hot stars (e.g. Renson & Manfroid 2009;Gray et al 2016;Qin et al 2019;Chojnowski et al 2020;Xiang et al 2020;Paunzen et al 2021), which provide good constraints on these stellar element transport processes (e.g. Talon et al 2006;Vick et al 2010;Michaud et al 2015).…”

A case study of ACV variables discovered in the Zwicky Transient Facility survey

“…Such variables were already excluded in the selection process (Section 2). Both groups show also indications of rotational variability, but with amplitudes of a few mmags only (Balona et al 2015;Paunzen et al 2021;Kochukhov et al 2021). The amplitudes of our variable star sample are much larger (Fig.…”

A case study of ACV variables discovered in the Zwicky Transient Facility survey

“…These variables were already excluded in the selection process (Section 2). Both groups also show indications of rotational variability, but with amplitudes of only a few mmags (Balona et al 2015;Paunzen et al 2021;Kochukhov et al 2021). The amplitudes of our variable star sample are much larger (Fig.…”

“…In addition, there are also the CP1 stars (the metallic-line or Am/Fm stars; Qin et al 2019) and the CP3 stars (the mercurymanganese or HgMn stars; Paunzen et al 2021). These groups are believed to possess only very weak, if any, magnetic fields (Bychkov et al 2003).…”