TESS observations of KIC 7739728 - a new FK Com type star candidate

Ранее по данным наблюдений с космическим телескопом “Kepler” нами было показано, что по своим параметрам KIC 7739728 близка к звездам типа FK Com и может рассматриваться, как потенциальный кандидат для включения в число объектов этого типа. В настоящей работе мы провели анализ всех имеющихся для KIC 7739728 данных в архиве миссии TESS (14 и 26 сектора наблюдений). Показано, что кривая блеска этой звезды ярко проявляет свойства регулярной вращательной модуляции и что в период времени между 14 и 26 секторами произошло явление переключения положений долгот активных областей на поверхности звезды (флип-флоп). Рассматриваются аргументы в пользу возможной принадлежности KIC 7739728 к объектам типа FK Com. Using the observations with the Kepler space telescope we found that parameters of KIC 7739728 are close to that ones of the FK Com type stars and that the object can be considered as a potential candidate for inclusion in the number of objects of this type. In this paper we analysed all available data for KIC 7739728 in the TESS mission archive (14 and 26 sectors). It is shown that the light curve of this star clearly exhibits the properties of regular rotational modulation and that in the time interval between 14 and 26 sectors the phenomenon of switching the positions of the longitudes of the active regions on the surface of the star (flip-flop) occurred. The arguments in favour of the possible relation of KIC 7739728 to objects of the FK Com type are considered.

Design and Fabrication of CLYC-Based Rotational Modulation Collimator (RMC) System for Gamma-Ray/Neutron Dual-Particle Imager

Background: This work aims to develop a new imaging system based on a pulse shape discrimination-capable Cs2LiYCl6:Ce (CLYC) scintillation detector combined with the rotational modulation collimator (RMC) technique for dual-particle imaging.Materials and Methods: In this study, a CLYC-based RMC system was designed based on Monte Carlo simulations, and a prototype was fabricated. Therein, a rotation control system was developed to rotate the RMC unit precisely, and a graphical user interface-based software was also developed to operate the data acquisition with RMC rotation. The RMC system was developed to allow combining various types of collimator masks and detectors interchangeably, making the imaging system more versatile for various applications and conditions.Results and Discussion: Operational performance of the fabricated system was studied by checking the accuracy and precision of the collimator rotation and obtaining modulation patterns from a gamma-ray source repeatedly.Conclusion: The prototype RMC system showed reliability in its mechanical properties and reproducibility in the acquisition of modulation patterns, and it will be further investigated for its dual-particle imaging capability with various complex radioactive source conditions.

Spots and Flares in Hot Main Sequence Stars Observed by Kepler, K2, and TESS

About 22,000 Kepler stars, 7,000 K2 stars, and nearly 60,000 TESS stars from sectors 1–24 have been classified according to variability type. A large proportion of stars of all spectral types appear to have periods in their light curves consistent with the expected rotation periods. A previous analysis of A- and late B-type stars suggests that these stars are indeed rotational variables. In this paper we have accumulated data to show that rotational modulation is present in about 30–40% of A- and B-type stars. A search for flares in TESS A- and B-type stars resulted in the detection of 102 flares in 57 stars. Analysis of flare energies show that the source of the flares cannot be a cool dwarf companion nor a F/G giant. The realization that a considerable fraction of A- and B-type stars are active indicates that a revision of current concepts regarding hot star envelopes is required.

New mercury-manganese stars and candidates from LAMOST DR4

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.

The complex fossil magnetic field of the δ Scuti star HD 41641

ABSTRACT Only three magnetic δ Scuti stars are known as of today. HD 41641 is a δ Scuti star showing chemical peculiarities and rotational modulation of its light curve, making it a good magnetic candidate. We acquired spectropolarimetric observations of this star with NARVAL at Télescope Bernard Lyot (TBL) to search for the presence of a magnetic field and characterize it. We indeed clearly detect a magnetic field in HD 41641, making it the fourth known magnetic δ Scuti star. Our analysis shows that the field is of fossil origin, like magnetic OBA stars, but with a complex field structure rather than the much more usual dipolar structure.

Similar but different: the varied landscape of Onfp/Oef stars variability

ABSTRACT The Oef category gathers rapidly rotating and evolved O-stars displaying a centrally reversed He ii λ 4686 emission line. The origin of the variability of their photospheric and wind spectral lines is debated, with rotational modulation or pulsations as the main contenders. To shed new light on this question, we analysed high-quality and high-cadence Transiting Exoplanet Survey Satellite photometric time series for five Oef stars. We also collected a new time series of spectra for one target (λ Cep) which had been the subject of specific debates in the last years. These observations reveal the variety of Oef behaviours. While space-based photometric data reveal substantial red noise components in all targets, only ζ Pup seems to display a long-lived periodicity. In our sample, stars exhibit a dominant signal at low frequencies but it appears relatively short-lived. This is reminiscent of rotational modulations by transient photospheric spots, though this scenario is challenged by the case of HD 14 442, whose 1.230 d−1 signal significantly exceeds the critical rotational frequency. In parallel, no evidence of persistent p mode non-radial pulsations is found in either photometry or spectroscopy of the stars, only temporary excitation of g mode pulsations could offer an alternative explanation for the dominant signals. Finally, the revised luminosities of the stars using GAIA-DR2 show that they are not all supergiants as ζ Pup. The question then arises whether the Oef peculiarity denotes a homogeneous class of objects after all.