A plethora of new, magnetic chemically peculiar stars from LAMOST DR4

Context. Magnetic chemically peculiar (mCP) stars are important to astrophysics because their complex atmospheres lend themselves perfectly to the investigation of the interplay between such diverse phenomena as atomic diffusion, magnetic fields, and stellar rotation. The most up-to-date catalogue of these objects was published a decade ago. Since then, no large scale spectroscopic surveys targeting this group of objects have been carried out. An increased sample size of mCP stars, however, is important for statistical studies. Aims. The present work is aimed at identifying new mCP stars using spectra collected by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Methods. Suitable candidates were selected by searching LAMOST DR4 spectra for the presence of the characteristic 5200 Å flux depression. Spectral classification was carried out with a modified version of the MKCLASS code and the accuracy of the classifications was estimated by comparison with results from manual classification and the literature. Using parallax data and photometry from Gaia DR2, we investigated the space distribution of our sample stars and their properties in the colour-magnitude diagram. Results. Our final sample consists of 1002 mCP stars, most of which are new discoveries (only 59 common entries with the Catalogue of Ap, HgMn and Am stars). Traditional mCP star peculiarities have been identified in all but 36 stars, highlighting the efficiency of the code’s peculiarity identification capabilities. The derived temperature and peculiarity types are in agreement with manually derived classifications and the literature. Our sample stars are between 100 Myr and 1 Gyr old, with the majority having masses between 2 M⊙ and 3 M⊙. Our results could be considered as strong evidence for an inhomogeneous age distribution among low-mass (M < 3 M⊙) mCP stars; however, we caution that our sample has not been selected on the basis of an unbiased, direct detection of a magnetic field. We identified several astrophysically interesting objects: the mCP stars LAMOST J122746.05+113635.3 and LAMOST J150331.87+093125.4 have distances and kinematical properties in agreement with halo stars; LAMOST J034306.74+495240.7 is an eclipsing binary system (Porb = 5.1435 ± 0.0012 d) hosting an mCP star component; and LAMOST J050146.85+383500.8 was found to be an SB2 system likely comprising of an mCP star and a supergiant component. Conclusions. With our work, we significantly increase the sample size of known Galactic mCP stars, paving the way for future in-depth statistical studies.

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The Kepler view of magnetic chemically peculiar stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832938 ◽

2018 ◽

Vol 619 ◽

pp. A98 ◽

Cited By ~ 6

Author(s):

S. Hümmerich ◽

Z. Mikulášek ◽

E. Paunzen ◽

K. Bernhard ◽

J. Janík ◽

...

Keyword(s):

Light Curve ◽

Main Sequence ◽

Complex Surface ◽

Atomic Diffusion ◽

Stellar Rotation ◽

Photometric Variability ◽

Chemically Peculiar ◽

Final Sample ◽

Peculiar Stars ◽

Chemically Peculiar Stars

Context. 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, which might advance our understanding of the processes involved and the atmospheric structures of mCP stars. Aims. 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 properties, and assess the accuracy of the spectral classifications provided by the MKCLASS code. Methods. As only very few known mCP stars are situated in the Kepler field, we had to depend largely on alternative (non-spectroscopic) means of identifying suitable candidates that rely mostly on light curve properties; in particular we relied on monoperiodic variability and light curve stability. Newly acquired and archival spectra were used to confirm most of our mCP star candidates. Linear ephemeris parameters and effective amplitudes were derived from detrended Kepler data. Results. Our final sample consists of 41 spectroscopically confirmed mCP stars of which 39 are new discoveries, 5 candidate mCP stars, and 7 stars in which no chemical peculiarities could be established. Our targets populate the whole age range from zero-age main sequence to terminal-age main sequence and are distributed in the mass interval from 1.5 M⊙ to 4 M⊙. About 25% of the mCP stars show a hitherto unobserved wealth of detail in their light curves indicative of complex surface structures. We identified light curve stability as a primary criterion for identifying mCP star candidates among early-type stars in large photometric surveys, and prove the reliability of the spectral classifications provided by the MKCLASS code.

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K2 space photometry reveals rotational modulation and stellar pulsations in chemically peculiar A and B stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833037 ◽

2018 ◽

Vol 616 ◽

pp. A77 ◽

Cited By ~ 17

Author(s):

D. M. Bowman ◽

B. Buysschaert ◽

C. Neiner ◽

P. I. Pápics ◽

M. E. Oksala ◽

...

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Intrinsic Variability ◽

B Stars ◽

Pulsating Stars ◽

Chemically Peculiar ◽

Large Scale Magnetic Field ◽

Peculiar Stars ◽

Show Evidence ◽

Chemically Peculiar Stars

Context. The physics of magnetic hot stars and how a large-scale magnetic field affects their interior properties is largely unknown. Few studies have combined high-quality observations and modelling of magnetic pulsating stars, known as magneto-asteroseismology, primarily because of the dearth of detected pulsations in stars with a confirmed and well-characterised large-scale magnetic field. Aims. We aim to characterise observational signatures of rotation and pulsation in chemically peculiar candidate magnetic stars using photometry from the K2 space mission. Thus, we identify the best candidate targets for ground-based, optical spectropolarimetric follow-up observations to confirm the presence of a large-scale magnetic field. Methods. We employed customised reduction and detrending tools to process the K2 photometry into optimised light curves for a variability analysis. We searched for the periodic photometric signatures of rotational modulation caused by surface abundance inhomogeneities in 56 chemically peculiar A and B stars. Furthermore, we searched for intrinsic variability caused by pulsations (coherent or otherwise) in the amplitude spectra of these stars. Results. The rotation periods of 38 chemically peculiar stars are determined, 16 of which are the first determination of the rotation period in the literature. We confirm the discovery of high-overtone roAp pulsation modes in HD 177765 and find an additional 3 Ap and Bp stars that show evidence of high-overtone pressure modes found in roAp stars in the form of possible Nyquist alias frequencies in their amplitude spectra. Furthermore, we find 6 chemically peculiar stars that show evidence of intrinsic variability caused by gravity or pressure pulsation modes. Conclusions. The discovery of pulsations in a non-negligible fraction of chemically peculiar stars make these stars high-priority targets for spectropolarimetric campaigns to confirm the presence of their expected large-scale magnetic field. The ultimate goal is to perform magneto-asteroseismology and probe the interior physics of magnetic pulsating stars.

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Statistical Properties of Magnetic CP Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900133376 ◽

2003 ◽

Vol 210 ◽

pp. 209-220

Author(s):

S. Bagnulo

Keyword(s):

Magnetic Fields ◽

Large Scale ◽

Main Sequence ◽

Statistical Properties ◽

Chemically Peculiar ◽

Evolutionary State ◽

Statistical Studies ◽

Magnetic Strength

Magnetic fields of chemically peculiar (CP) stars of the upper main sequence are characterised by a geometry organised at a large scale, permeating the entire photosphere, and with a typical strength of the order of 0.1–30 kG. Here I review the results obtained from statistical studies of the structures of the magnetic fields of CP stars, which are aimed at finding how magnetic strength and morphology are correlated with other stellar characteristics and with the star's evolutionary state.

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First detection of bromine and antimony in hot stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832723 ◽

2018 ◽

Vol 614 ◽

pp. A96 ◽

Cited By ~ 5

Author(s):

K. Werner ◽

T. Rauch ◽

M. Knörzer ◽

J. W. Kruk

Keyword(s):

Model Atmosphere ◽

Atomic Diffusion ◽

Laboratory Measurements ◽

Solar Abundance ◽

Hot Stars ◽

Chemically Peculiar ◽

Peculiar Stars ◽

Resonance Doublet ◽

Chemically Peculiar Stars ◽

Far Ultraviolet

Bromine (Z = 35) and antimony (Z = 51) are extremely difficult to detect in stars. In very few instances, weak and mostly uncertain identifications of Br I, Br II, and Sb II in relatively cool, chemically peculiar stars were successful. Adopted solar abundance values rely on meteoritic determinations. Here, we announce the first identification of these species in far-ultraviolet spectra of hot stars (with effective temperatures of 49 500–70 000 K), namely in helium-rich (spectral type DO) white dwarfs. We identify the Br VI resonance line at 945.96 Å. A previous claim of Br detection based on this line is incorrect because its wavelength position is inaccurate by about 7 Å in atomic databases. Taking advantage of precise laboratory measurements, we identify this line as well as two other, subordinate Br VI lines. Antimony is detected by the Sb V resonance doublet at 1104.23/1225.98 Å as well as two subordinate Sb VI lines. A model-atmosphere analysis reveals strongly oversolar Br and Sb abundances that are caused by radiative-levitation dominated atomic diffusion.

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The nature of the light variations of chemically peculiar stars CU Vir and HD 64740

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311011252 ◽

2010 ◽

Vol 6 (S272) ◽

pp. 517-518

Author(s):

Jiri Krtička ◽

Hana Marková ◽

Zdenek Mikulášek ◽

Theresa Lüftinger ◽

David Bohlender ◽

...

Keyword(s):

Chemical Elements ◽

Variable Stars ◽

Stellar Rotation ◽

Peculiar Star ◽

Silicon Iron ◽

Chemically Peculiar ◽

Peculiar Stars ◽

Chemically Peculiar Stars ◽

Light Variability ◽

Flux Redistribution

AbstractThe nature of the light variations of chemically peculiar stars was studied in detail only in a very few cases. To better understand the mechanisms of light variability of these stars, we study the light variations of the well-known magnetic chemically peculiar star CU Vir and one of the least amplitude variable stars HD 64740. We show that the light variability of these stars is induced by flux redistribution in spots of enhanced abundance of chemical elements (e.g., helium, silicon, iron or chromium), and by the stellar rotation. We conclude that this is a promising model for the explanation of the light variability of most chemically peculiar stars.

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Distribution of Elements Inside Stars

Communications of the Byurakan Astrophysical Observatory ◽

10.52526/25792776-2019.66.1-52 ◽

2019 ◽

pp. 52-59

Author(s):

G. Alecian

Keyword(s):

Chemical Composition ◽

Stellar Evolution ◽

Main Sequence ◽

Stellar Atmospheres ◽

Atomic Diffusion ◽

The Core ◽

Chemically Peculiar ◽

Peculiar Stars ◽

Distribution Of Elements ◽

Chemically Peculiar Stars

The chemical composition measured in stellar atmospheres is not necessarily the same as in deeper layers (outside the core). Indeed, for a significant fraction of main-sequence G to B types stars the discrepancies between superficial and internal abundances go from a few percent (for the coldest of these stars) to huge factors (for hot chemically peculiar stars). This is due to atomic diffusion process, which may produces elements segregation at some stages of the stellar evolution.

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Confirming known planetary trends using a photometrically selected Kepler sample

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3921 ◽

2020 ◽

Author(s):

Jonah T Hansen ◽

Luca Casagrande ◽

Michael J Ireland ◽

Jane Lin

Keyword(s):

Sample Size ◽

Robust Statistics ◽

Narrow Band ◽

Small Sample Size ◽

Small Sample ◽

Fitting Algorithm ◽

Statistical Studies ◽

The Rich ◽

Host Stars ◽

High Metallicity

Abstract Statistical studies of exoplanets and the properties of their host stars have been critical to informing models of planet formation. Numerous trends have arisen in particular from the rich Kepler dataset, including that exoplanets are more likely to be found around stars with a high metallicity and the presence of a “gap” in the distribution of planetary radii at 1.9 R⊕. Here we present a new analysis on the Kepler field, using the APOGEE spectroscopic survey to build a metallicity calibration based on Gaia, 2MASS and Strömgren photometry. This calibration, along with masses and radii derived from a Bayesian isochrone fitting algorithm, is used to test a number of these trends with unbiased, photometrically derived parameters, albeit with a smaller sample size in comparison to recent studies. We recover that planets are more frequently found around higher metallicity stars; over the entire sample, planetary frequencies are 0.88 ± 0.12 percent for [Fe/H] < 0 and 1.37 ± 0.16 percent for [Fe/H] ≥ 0 but at two sigma we find that the size of exoplanets influences the strength of this trend. We also recover the planet radius gap, along with a slight positive correlation with stellar mass. We conclude that this method shows promise to derive robust statistics of exoplanets. We also remark that spectrophotometry from Gaia DR3 will have an effective resolution similar to narrow band filters and allow to overcome the small sample size inherent in this study.

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Imaging and Cognitive Genetics: The Norwegian Cognitive NeuroGenetics Sample

Twin Research and Human Genetics ◽

10.1017/thg.2012.8 ◽

2012 ◽

Vol 15 (3) ◽

pp. 442-452 ◽

Cited By ~ 28

Author(s):

Thomas Espeseth ◽

Andrea Christoforou ◽

Astri J. Lundervold ◽

Vidar M. Steen ◽

Stephanie Le Hellard ◽

...

Keyword(s):

Sample Size ◽

Cognitive Aging ◽

Brain Function ◽

Large Scale ◽

Adult Life ◽

Aging Brain ◽

Adult Life Span ◽

Cross Sectional ◽

A Genome ◽

Effects Of Aging

Data collection for the Norwegian Cognitive NeuroGenetics sample (NCNG) was initiated in 2003 with a research grant (to Ivar Reinvang) to study cognitive aging, brain function, and genetic risk factors. The original focus was on the effects of aging (from middle age and up) and candidate genes (e.g., APOE, CHRNA4) in cross-sectional and longitudinal designs, with the cognitive and MRI-based data primarily being used for this purpose. However, as the main topic of the project broadened from cognitive aging to imaging and cognitive genetics more generally, the sample size, age range of the participants, and scope of available phenotypes and genotypes, have developed beyond the initial project. In 2009, a genome-wide association (GWA) study was undertaken, and the NCNG proper was established to study the genetics of cognitive and brain function more comprehensively. The NCNG is now controlled by the NCNG Study Group, which consists of the present authors. Prominent features of the NCNG are the adult life-span coverage of healthy participants with high-dimensional imaging, and cognitive data from a genetically homogenous sample. Another unique property is the large-scale (sample size 300–700) use of experimental cognitive tasks focusing on attention and working memory. The NCNG data is now used in numerous ongoing GWA-based studies and has contributed to several international consortia on imaging and cognitive genetics. The objective of the following presentation is to give other researchers the information necessary to evaluate possible contributions from the NCNG to various multi-sample data analyses.

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W.S. Gosset and Some Neglected Concepts in Experimental Statistics: Guinnessometrics II

Journal of Wine Economics ◽

10.1017/s1931436100001632 ◽

2011 ◽

Vol 6 (2) ◽

pp. 252-277 ◽

Cited By ~ 3

Author(s):

Stephen T. Ziliak

Keyword(s):

Experimental Design ◽

Sample Size ◽

Large Scale ◽

Statistical Significance ◽

Small Sample ◽

Small Samples ◽

Significant Advance ◽

Economic Approach ◽

Barley Malt ◽

Level Of Significance

AbstractStudent's exacting theory of errors, both random and real, marked a significant advance over ambiguous reports of plant life and fermentation asserted by chemists from Priestley and Lavoisier down to Pasteur and Johannsen, working at the Carlsberg Laboratory. One reason seems to be that William Sealy Gosset (1876–1937) aka “Student” – he of Student'st-table and test of statistical significance – rejected artificial rules about sample size, experimental design, and the level of significance, and took instead an economic approach to the logic of decisions made under uncertainty. In his job as Apprentice Brewer, Head Experimental Brewer, and finally Head Brewer of Guinness, Student produced small samples of experimental barley, malt, and hops, seeking guidance for industrial quality control and maximum expected profit at the large scale brewery. In the process Student invented or inspired half of modern statistics. This article draws on original archival evidence, shedding light on several core yet neglected aspects of Student's methods, that is, Guinnessometrics, not discussed by Ronald A. Fisher (1890–1962). The focus is on Student's small sample, economic approach to real error minimization, particularly in field and laboratory experiments he conducted on barley and malt, 1904 to 1937. Balanced designs of experiments, he found, are more efficient than random and have higher power to detect large and real treatment differences in a series of repeated and independent experiments. Student's world-class achievement poses a challenge to every science. Should statistical methods – such as the choice of sample size, experimental design, and level of significance – follow the purpose of the experiment, rather than the other way around? (JEL classification codes: C10, C90, C93, L66)

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