Radial Velocity Variations in Pulsating Ap Stars III. The Discovery of 16.21 min Oscillations in Beta CrB

We present the analysis of 3 hrs of a rapid time series of precise stellar radial velocity (RV) measurements (sigma = 4.5 m/s) of the cool Ap star Beta CrB. The integrated RV measurements spanning the wavelength interval 5000-6000 Ang. show significant variations (false alarm probability = 10^-5) with a period of 16.21 min (nu = 1028.17 micro Hz) and an amplitude of 3.54 +/- 0.56 m/s. The RV measured over a much narrower wavelength interval reveals one spectral feature at 6272 Ang. pulsating with the same 16.21 min period and an amplitude of 138 +/- 23 m/s. These observations establish Beta CrB to be a low-amplitude rapidly oscillating Ap star.Comment: 5 Pages, 5 figure

Detection of an exoplanet around the evolved K giant HD 66141

Aims. We have been carrying out a precise radial velocity (RV) survey for K giants to search for and study the origin of the lowamplitude and long-periodic RV variations. Methods. We present high-resolution RV measurements of the K2 giant HD 66141 from December 2003 to January 2011 using the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) at Bohyunsan Optical Astronomy Observatory (BOAO). Results. We find that the RV measurements for HD 66141 exhibit a periodic variation of 480.5 +/- 0.5 days with a semi-amplitude of 146.2 +/- 2.7 m/s. The Hipparcos photometry and bisector velocity span (BVS) do not show any obvious correlations with RV variations. We find indeed 706.4 +/- 35.0 day variations in equivalent width (EW) measurements of H_alpha line and 703.0 +/- 39.4 day variations in a space-born measurements 1.25{\mu} flux of HD 66141 measured during COBE/DIRBE experiment. We reveal that a mean value of long-period variations is about 705 +/- 53 days and the origin is a rotation period of the star and variability that is caused by surface inhomogeneities. For the 480 day periods of RV variations an orbital motion is the most likely explanation. Assuming a stellar mass of 1.1 +/- 0.1 M_Sun? for HD 66141, we obtain a minimum mass for the planetary companion of 6.0 +/- 0.3 M_Jup with an orbital semi-major axis of 1.2 +/- 0.1 AU and an eccentricity of 0.07 +/- 0.03.Comment: 7 pages, 10 figures, 3 tables, accepted for publisation in Astronomy & Astrophysic

Accretion and outflow activity on the late phases of pre-main-sequence evolution. The case of RZ Piscium

RZ Psc is an isolated high-latitude post-T Tauri star that demonstrates a UX Ori-type photometric activity. The star shows very weak spectroscopic signatures of accretion, but at the same time possesses the unusual footprints of the wind in Na I D lines. In the present work we investigate new spectroscopic observations of RZ Psc obtained in 2014 during two observation runs. We found variable blueshifted absorption components (BACs) in lines of the other alcali metals, K I 7699 \AA\ and Ca II IR triplet. We also confirmed the presence of a weak emission component in the H$\alpha$ line, which allowed us to estimate the mass accretion rate on the star as $\dot{M}\leq$ $7 \cdot 10^{-12}$Msun yr$^{-1}$. We could not reveal any clear periodicity in the appearance of BACs in sodium lines. Nevertheless, the exact coincidence of the structure and velocities of the Na I D absorptions observed with the interval of about one year suggests that such a periodicity should exist

Detection of a delta Scuti-type pulsating component in the detached eclipsing binary system TU CMa

We report the detection of 30.5 min low-amplitude (A=0.003 mag) delta Scuti-type pulsations in an A5V-A7V type component of the detached eclipsing binary system TU CMa

Evaluation of the professional teaching competence: chinese experience

The article describes the rules and procedures for hiring and evaluating the professional competence of teachers on the example ofChina, where there is a system for evaluating the professional competence of teachers

Spectroscopic Devices for Asteroseismology With Small Telescopes in NARIT

The National Astronomical Research Institute of Thailand (NARIT) has a manifold network of small telescopes installed worldwide. These telescopes serve educational and research purposes and are equipped mainly with CCD detectors for direct imaging and photometry. To extend the possible field of applications, several telescopes were fitted with commercially available medium-resolution spectrographs eShel from Shelyak. With these devices, researchers in NARIT obtained a versatile tool for stellar spectroscopy. Here we describe the current status of available equipment, possible ways of upgrading, and briefly introduce the achieved results of the asteroseismologic study of fast-rotating stars.Comment: This paper was submitted as a contribution to the proceedings of the third Belgo-Indian Network for Astronomy and Astrophysics (BINA) workshop, which was held in Bhimtal, Uttarakhand (India) on 22-24 March 2023. The final, peer-reviewed version will be published in Bulletin de la Soci\'et\'e Royale des Sciences de Li\`ege. The manuscript contains 5 pages, 3 figures, and 4 reference

Radial Velocity Variations in Pulsating Ap Stars. II. 33 Librae

We present precise relative radial velocity (RV) measurements for the rapidly oscillating Ap (roAp) star 33 Librae measured from high resolution data spanning the wavelength interval 5000--6200 A. We find that pulsational radial velocity amplitude determined over a broad wavelength range (~100 A) depends on the spectral region that is examined and can be as high as 60 m/s at 5600 A and as low as 7 m/s in the 5900 A region. RV measurements of individual spectral lines can show even higher RV amplitudes. The acoustic cross-sections of the atmosphere, i.e. the phase and amplitude of the pulsations, as a function of optical depth is found for spectral lines of Ca, Cr, Fe, La, Ce, Gd, Er and Nd. This analysis shows that pulsation phase is variable through the atmosphere and that Nd III lines pulsate almost 180 degrees out-of-phase with those of Nd II features and are formed significantly higher in the stellar atmosphere. This conclusively establishes the presence of at least one radial node to the pulsations in the upper stellar atmosphere. The histogram of pulsational phases for all individual spectral feature shows a bi-modal Gaussian distribution with 17% of the lines having a pulsational phase approximatels 165 degrees out-of-phase with most other spectral lines. This is also consistent with the presence of a radial node in the stellar atmosphere. The accumulation of phase due to a running wave component can explain the 165 degree phase difference as well as the broader width (by a factor of two) of one of the Gaussian components of the phase distribution.Comment: 18 pages, 12 Figures, accepted by MNRA

Pulsations in the atmosphere of the roAp star HD 24712 II. Theoretical models

We discuss pulsations of the rapidly oscillating Ap (roAp) star HD 24712 (HR 1217) based on nonadiabatic analyses taking into account the effect of dipole magnetic fields. We have found that all the pulsation modes appropriate for HD 24712 are damped; i.e., the kappa-mechanism excitation in the hydrogen ionization layers is not strong enough to excite high-order p-modes with periods consistent with observed ones, all of which are found to be above the acoustic cut-off frequencies of our models. The main (2.721 mHz) and the highest (2.806 mHz) frequencies are matched with modified $l=2$ and $l=3$ modes, respectively. The large frequency separation ($\approx 68 \mu$Hz) is reproduced by models which lay within the error box of HD 24712 on the HR diagram. The nearly equally spaced frequencies of HD 24712 indicate the small frequency separation to be as small as $\approx 0.5\mu$Hz. However, the small separation derived from theoretical $l=1$ and 2 modes are found to be larger than $\sim 3\mu$Hz. The problem of equal spacings could be resolved by assuming that the spacings correspond to pairs of $l=2$ and $l=0$ modes. The amplitude distribution on the stellar surface is strongly affected by the magnetic field resulting in the predominant concentration at the polar regions. Amplitudes and phases of radial-velocity variations for various spectral lines are converted to relations of amplitude/phase versus optical depth in the atmosphere. Oscillation phase delays gradually outward in the outermost layers indicating the presence of waves propagating outward. The phase changes steeply around $\log\tau\sim-3.5$, which supports a $T-\tau$ relation having a small temperature inversion there.Comment: 11 pages, 13 figures, accepted for publication in MNRA