We present the detailed spectroscopic study of V565 Mon pre-main-sequence star, which is the illuminating star of Parsamian 17 cometary nebula. Observations were performed with 2.6 m telescope in Byurakan Astrophysical Observatory in 15 February 2018. Radial velocities and equivalent widths of the most prominent lines of V565 Mon are presented. We built the spectral energy distribution and estimated the main parameters of the star, for example obtained bolometric luminosity of V565 Mon is $L_{V565}\approx 130L_{\odot} $ . Considering all features of V565 Mon we came to conclusion that this young intermediate-mass star can belongs to some intermediate class between T Tau and HAeBe stars. Very unusual for a young star is the presence of strong absorption Ba II lines in the spectrum. Possible explanations on this issue are discussed. Hence, we think that V565 Mon is a unique example, which can help to understand some open questions in nucleosynthesis problem in young stars.
We analyse Échelle spectra of $θ^1$ Ori F obtained by us on six nights unevenly distributed along six years; we identify several hundred spectral lines and measure, for the first time, the star's heliocentric radial velocity. We also collect and discuss previously published photometry of $θ^1$ OriF . We find that $θ^1$ Ori F is a Chemically Peculiar (CP) star with overabundant silicon and phosphorus, and possibly other elements as well. From the singly ionised Fe, Cr and Ti lines we estimate its spectral type to be between B7 and B8. The radial velocity of $θ^1$ Ori F is possibly marginally va…
We summarise the results of a spectropolarimetric survey of 56 chemically peculiar (CP) stars in the association of Orion OB1. We uniformly collected the observational material with the 6-m telescope BTA of the Special Astrophysical Observatory in 2013-2021. We identify 14 new magnetic CP stars with a longitudinal magnetic field exceeding approximately 500 G. The studied sample contains 31 magnetic stars or 55% of the whole CP population in Orion OB1. We show that the percentage of the magnetic CP stars and the field strength drops sharply with age. The mean longitudinal magnetic field in the …
Magnetic chemically peculiar stars of the main sequence can present rotational periods as long as many decades. Here we report the results of an observational campaign started in 2001 aimed at establishing these very long periods from the variability of the integrated magnetic field modulus, the so-called surface magnetic field $B_s$, as measured from the Zeeman splitting of the Fe{\sc ii}\,6149.258\,Å spectral line. Thirty-six stars have been monitored with various high-resolution spectrographs at different telescopes, totalling 412 newly collected spectra. To improve the phase coverage, we h…
A majority part of magnetic chemically peculiar (mCP) stars of the upper main sequence exhibits strictly periodic light, magnetic, radio, and spectral variations that can be fully explained by the model of a rigidly rotating main-sequence star with persistent surface structures and stable global magnetic field frozen into the body of the star. Nevertheless, there is an inhomogeneous group consisting of a few mCP stars whose rotation periods vary on timescales of decades, while the shapes of their phase curves remain nearly unchanged. Alternations in the rotational period variations, proven in …
The upper main sequence stars CU Virginis is the most enigmatic object among magnetic chemically peculiar (mCP) stars. It is an unusually fast rotator showing strictly periodic light variations in all regions of the electromagnetic spectrum, as well as spectroscopic and spectropolarimetric changes. At same time, it is also the first radio main-sequence pulsar. Exploiting information hidden in phase variations, we monitored the secular oscillation of the rotational period during the last 53 years. Applying own phenomenological approach, we analyzed 37\,975 individual photometric and spectroscop…
We present a comprehensive overview of the properties of a sample of 41 magnetic chemically peculiar stars that have been recently identified in the Kepler field by our team (Hümmerich et al. 2018). The stars populate the whole age range from zero-age to terminal-age main sequence in the mass interval from 1.5 to 4 Ms. Several of the studied objects exhibit a hitherto unobserved wealth of detail in their light curves indicative of persisting complex surface structures. Monoperiodic variability and light curve stability were identified as cardinal criteria for selecting mCP star candidates amon…
From sector 1--44 {\em TESS} observations, 19 new roAp stars, 103 ostensibly non-peculiar stars with roAp-like frequencies and 617 $δ$~Scuti stars with independent frequencies typical of roAp stars were found. Examination of all chemically peculiar stars observed by {\em TESS} resulted in the discovery of 199 Ap stars which pulsate as $δ$~Sct or $γ$~Dor variables. The fraction of pulsating Ap stars is the same as the fraction of pulsating chemically normal stars. There is no distinct separation in frequency or radial order between chemically peculiar $δ$~Sct stars and roAp stars. In fact, all …
The stellar disk of the Milky Way shows complex spatial and abundance structure that is central to understanding the key physical mechanisms responsible for shaping our Galaxy. In this study, we use six very high resolution cosmological zoom simulations of Milky Way-sized haloes to study the prevalence and formation of chemically distinct disc components. We find that our simulations develop a clearly bimodal distribution in the $[\rm α/Fe]$ -- $[\rm Fe/H]$ plane. We find two main pathways to creating this dichotomy which operate in different regions of the galaxies: a) an early ($z>1$) and in…
Using the stellar evolution code---Modules for Experiments in Stellar Astrophysics (MESA), we investigate the evolution of massive stars with different rotational velocities and metallicities towards Wolf-Rayet stars. In our simulations, the initial rotating velocities are taken as 0, 250, 500 and 650 km s$^{-1}$, and the metallicities equal to 0.02, 0.014, 0.008, 0.006, 0.004 and 0.002. We show our rapid rotation models in the HR diagram compared with the observations. We find that the rotational mixing is less efficient at high metallicity, and these stars become Wolf-Rayet (WR) stars when t…
We present detailed chemical compositions of four stars on the first-ascent red giant branch that are classified as chemically peculiar, but lack comprehensive analyses at high spectral resolution. For BD+03°2688, HE 0457-1805, HE 1255-2324, and HE 2207-1746, we derived metallicities [Fe/H] $=-1.21$, $-0.19$, $-0.31$, and $-0.55$, respectively, indicating a range in Galactic population membership. In addition to atmospheric parameters, we extracted elemental abundances for 28 elements, including the evolutionary-sensitive CNO group and $^{12}$C/$^{13}$C ratios. Novel results are also presented…
We present an investigation of three chemically peculiar (CP) stars and one CP star candidate which exhibit photometric periods below 12 hours. New spectroscopic observations have been acquired which confirm the peculiar nature of all objects. HD 77013 and HD 81076 are classical CP1 (Am) stars; HD 67983 is a marginal CP1 (Am: ) star, and HD 98000 is a CP2 (Ap) star. We have procured observations from the ASAS-3 and SuperWASP archives and obtained additional photometry in order to verify the results from the sky survey data. We have derived astrophysical parameters and investigated the position…
Strong magnetic fields in chemically peculiar A-type (Ap) stars typically suppress low-overtone pressure modes (p modes) but allow high-overtone p modes to be driven. KIC 11296437 is the first star to show both. We obtained and analysed a Subaru spectrum, from which we show that KIC 11296437 has abundances similar to other magnetic Ap stars, and we estimate a mean magnetic field modulus of $2.8\pm0.5$ kG. The same spectrum rules out a double-lined spectroscopic binary, and we use other techniques to rule out binarity over a wide parameter space, so the two pulsation types originate in one $δ$ …
Magnetic chemically peculiar (mCP) stars exhibit complex atmospheres that allow the investigation of such diverse phenomena as atomic diffusion, magnetic fields, and stellar rotation. The advent of space-based photometry provides the opportunity for the first precise characterizations of the photometric variability properties of these stars. We carried out a search for new mCP stars in the Kepler field with the ultimate aim of investigating their photometric variability properties using Kepler data. As an aside, we describe criteria for selecting mCP star candidates based on light curve proper…
We present a study based on the high-resolution spectroscopy and K2 space photometry of five chemically peculiar stars in the region of the open cluster M44. The analysis of the high-precision photometric K2 data reveals that the light variations in HD 73045 and HD 76310 are rotational in nature and caused by spots or cloud-like co-rotating structures, which are non-stationary and short-lived. The time-resolved radial velocity measurements, in combination with the K2 photometry, confirm that HD 73045 does not show any periodic variability on timescales shorter than 1.3 d, contrary to previous …
The spectrum of the evolved B8 III giant HR 62 exhibits weak He-lines and strong Mn and P lines. HR 62 therefore resembles both a HgMn star (CP3) and a He-weak PGa star (CP4). This study is a companion project to a high resolution survey of slowly rotationg late-B type stars aiming at finding new chemically peculiar stars. We have analysed the spectra of HR 62 (B8 III) and the dwarf comparison star HR 677 (B8 V) to derive their chemical abundances. Both stars have similar effective temperatures (12500 K) and projected rotational velocities ($\sim$25 km s$^{-1}$). The medium resolution ($R$ $\s…
The $R$-Process Alliance: On J0010$-$1735, an Accreted, Chemically Unusual, Metal-poor Star with $R$-process Enhancement
The University of Texas at Austin（德克萨斯大学奥斯汀分校）；University of Florida（佛罗里达大学）；North Carolina State University（北卡罗来纳州立大学）；Stockholm University（斯德哥尔摩大学）；University of Notre Dame（圣母大学）
Using a sample of nearly 140,000 primary red clump stars selected from the LAMOST and $Gaia$ surveys, we have identified a large sample of "young" [$α$/Fe]-enhanced stars with stellar ages younger than 6.0 Gyr and [$α$/Fe] ratios greater than 0.15 dex. The stellar ages and [$α$/Fe] ratios are measured from LAMOST spectra, using a machine learning method trained with common stars in the LAMOST-APOGEE fields (for [$α$/Fe]) and in the LAMOST-$Kepler$ fields (for stellar age). The existence of these "young" [$α$/Fe]-enhanced stars is not expected from the classical Galactic chemical evolution mode…
To understand the origin of the abundance peculiarities of non-magnetic A-type stars, we present the first detailed chemical abundance analysis of a metallic line star HD 23193 (A2m) and an A-type subgiant HD 170920 (A5) which could have been a HgMn star on the main sequence. Our analysis is based on medium (R$\sim$14000) and high (R$\sim$40000) resolution spectroscopic data of the stars. The abundance of 18 elements are derived: C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn, Sr, Y, and Ba. The masses of HD 23193 and HD 170920 are estimated from evolutionary tracks, as $2.3\pm0.1$ $M…
A detailed spectroscopic survey of chemically peculiar (CP) stars in the Orion OB1 association is the most comprehensive observational program in the field of stellar magnetism that has been carried out at SAO so far. As at the end of 2018, we have completed surveying CP stars in the oldest subgroup $\textit{a}$ of the association. In this paper, we give a short overview of CP members of the subgroup showing both direct and indirect signatures of multiplicity. Among the overall 11 stars which had been classified as peculiar, we found several good candidates for further detailed study.
Planet engulfment in the chemically anomalous HD 129171/HD 129209 pair
Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦阿基米德天体物理研究所）；Universidade de São Paulo, Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG/USP)（圣保罗大学天文、地球物理与大气科学研究所）；INAF – Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）；Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Physics and Astronomy, Monash University（蒙纳士大学物理与天文学院）；INAF - Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切尔菲西天文台）
