David Mkrtichian

National Astronomical Research Institute of Thailand

We present the results of a systematic search of the Transiting Exoplanet Survey Satellite (TESS) 2-min cadence data for new rapidly oscillating Ap (roAp) stars observed during the Cycle 2 phase of its mission. We find seven new roAp stars previously unreported as such and present the analysis of a further 25 roAp stars that are already known. Thre...

In this article, we present the new product and its description developed by the CoLiTec (Collection Light Technology) project (Khlamov & Savanevych 2020), called CoLiTecVS (CoLiTec Variable Stars) software as a set of tools for the automated light curve creation of variable stars using the sensor data received from the different sensors. CoLiTecVS...

We present a new study of the Algol-type eclipsing binary system AS Eri based on the combination of the MOST and TESS light curves and a collection of very precise radial velocities obtained with the spectrographs HERMES operating at the Mercator telescope, La Palma, and TCES operating at the Alfred Jensch telescope, Tautenburg. The primary compone...

We present a new study of the Algol-type eclipsing binary system AS Eri based on the combination of the MOST and TESS light curves and a collection of very precise radial velocities obtained with the spectrographs HERMES operating at the Mercator telescope, La Palma, and TCES operating at the Alfred Jensch telescope, Tautenburg. The primary compone...

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 structu...

We present the results of our photometric (V RI) and spectroscopic observations of the young variable star V730 Cep (MisV1147) classified by Uemura et al. (2004) as a Herbig Be star. Our photometry confirms the conclusion of the above authors that this star has a complex pattern of variability including periodic or quasi-periodic brightness variati...

We present the results of an analysis of photometric time-series observations for NGC 2126 acquired during the years 2004, 2013 and 2015. NGC 2126 is an intermediate-age open cluster which has a population of stars inside the δ Scuti instability strip. The main purpose is to search for new variable stars, to study their light curves and pulsation s...

We present precise stellar radial velocity measurements of Gamma Dra taken from 2003 to 2017. The data from 2003 to 2011 show coherent, long-lived variations with a period of 702 d. These variations are consistent with the presence of a planetary companion having m sin i = 10.7 M_Jup whose orbital properties are typical for giant planets found arou...

We analysed photometric time series of the active, semidetached Algol-type system RZ Cas obtained in 1999–2009, in order to search for seasonal and short-term variations in the oscillation spectrum of RZ Cas A. The orbital period shows ±1 s cyclic variations on time-scales of 6–9 years. We detected six low-degree p-mode oscillations with periods be...

Discrete variable absorption components in the RZ Psc spectrum are studied. Two hypothesis of their formation are considered. The effective star radiation scattering computation method is presented. The resonance scattering in both cases is modeled. The model spectra are reviewed and analyzed. The conclusion about the possible reasons of the observ...

Aims. The purpose of this paper is to detect and investigate the nature of long-term radial velocity (RV) variations of K-type giants and to confirm planetary companions around the stars. Methods. We have conducted two planet search programs by precise RV measurement using the 1.8 m telescope at Bohyunsan Optical Astronomy Observatory (BOAO) and th...

The paper deals with a computational method for detection of the solar system minor bodies (SSOs), whose inter-frame shifts in series of CCD-frames during the observation are commensurate with the errors in measuring their positions. These objects have velocities of apparent motion between CCD-frames not exceeding three RMS errors ($3\sigma$) of me...

The "Thai Sky Survey for oEA Stars" (THASSOS) project is focused on searching for and studies of new mass-accreting pulsating components of a semi-detached Algoltype systems, so called class of oEA stars suggested by Mkrtichian et al. (2002, 2004). oEA components of binaries have been evolved into the instability strip after the first high- mass tr...

Aurora phenomenon is an effect of collision between precipitating particles with gyromotion along Earth's magnetic field and Earth's ionospheric atoms or molecules. The particles' precipitation occurs normally around polar regions. However, some auroral particles can reach lower latitude regions when they are highly energetic. A clear emission from...

We present the results of a combined analysis of photometric time series and spectroscopic observations for the semi-detached eclipsing binary AO Ser aimed to study physical parameters of the system. New CCD photometric light curves in the B and V bands and radial velocities of AO Ser are presented. The Wilson-Devinney technique was used to simulta...

We present the detection of long-period RV variations in HD 36384, HD 52030, and HD 208742 by using the high-resolution, fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) for the precise radial velocity (RV) survey of about 200 northern circumpolar stars. Analyses of RV data, chromospheric activity indicators, and bisector variations span...

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 du...

Анотація The run away supergiant star HIP13962 (spectral type G0Ia) was recently pointed as a possible former binary companion of young pulsar PSRJ0826+2637. The spectraof HIP13962 wereo btained in Haute-Provence observatory (France), in Bohuynsan observatory (Korea), and also in NARIT (Thailand) with1.9, 1.8, and 2.4 meter telescopes respectively...

The young Herbig Ae star MWC 480 (HD 31648) is one of the comprehensively spectroscopically studied stars in the ultraviolet, optical, and infrared spectral ranges. Using non-LTE modeling of its hydrogen spectrum, we have calculated the contribution to the hydrogen emission from such important regions of the circumstellar environment as the disk wi...

The hot γ Doradus stars have multiple low frequencies characteristic of γ Dor or SPB variables, but are located between the red edge of the SPB and the blue edge of the γ Dor instability strips where all low-frequency modes are stable in current models of these stars. Though δ Sct stars also have low frequencies, there is no sign of high frequencie...

The hot $\gamma$~Doradus stars have multiple low frequencies characteristic of $\gamma$~Dor or SPB variables, but are located between the red edge of the SPB and the blue edge of the $\gamma$~Dor instability strips where all low-frequency modes are stable in current models of these stars. Though $\delta$~Sct stars also have low frequencies, there i...

We present the main results of a photometric and spectroscopic study of the Λ Boo star 29 Cyg carried out from 1995 – 1998.

We report that the spectroscopic binary μ Ursae Majoris (μ UMa) has secondary RV variations of 471.2 days in addition to those of 230.0 days already known. Keplerian orbit analysis yields stellar mass companions of 1.6 M⊙ for the 230 day period and 0.14 M⊙ for the 471 day period. However, the HIPPARCOS photometries show a period similar to the stel...

With every new discovery of an extra-solar planet, the absence of planets in globular clusters (GCs) becomes more and more conspicuous. Null detection of transiting hot Jupiters in globular clusters 47 Tuc, omega Cen and NGC6397 presents an important puzzle, raising questions about the role played by cluster metallicity and environment on formation...

Motivated by the previously reported high orbital decay rate of the planet WASP-43b, eight newly transit light curves are obtained and presented. Together with other data in literature, we perform a self-consistent timing analysis with data covering a timescale of 1849 epochs. The results give an orbital decay rate dP/dt = -0.02890795\pm 0.00772547...

The goal of the present study is the development and testing of a method for spectral detection of the light of host stars reflected from their exoplanets. The presented method is based on the analysis of dynamical spectra, which make it possible to obtain high signal-to-noise residual spectra after host star spectrum deduction. These residual spec...

R Canis Majoris is a bright, short-period (1^d.1359) Algol-type eclipsing binary. For a long time, it was considered to be a low-mass binary star with $M_1

We present results of a new high-resolution spectroscopic study of the RS CVn-type binary system EI Eridani (HD26337). We used high S/N ratio LSD profiles to measure a new RV orbit of the primary component and new orbital parameters. We found evidence of strong spectral line profile variations at time intervals indicating the existence of short-liv...

The study of variable stars has played a central role in astronomy for over 400 years, and more so in the present than at any time in history. Stars, especially variable stars, are astrophysical laboratories for understanding physical processes in the universe. Stars represent the fundamental components of stellar systems, galaxies and the universe...

We analysed an extended time series of high-resolution spectra of the δ Sct star WASP-33 with the aim to determine the effect of its planet WASP-33b. We found ten frequencies in the measured radial velocities. Three of them we can attribute to previously observed photometric oscillations due to non-radial pulsations. One frequency exactly agrees wi...

We investigate the nature of the long-period radial velocity variations in Alpha Tau first reported over 20 years ago. We analyzed precise stellar radial velocity measurements for Alpha Tau spanning over 30 years. An examination of the Halpha and Ca II 8662 spectral lines, and Hipparcos photometry was also done to help discern the nature of the lon...

Auns. The aim of our paper is to investigate the low-amplitude and long-period variations in evolved stars with a precise radial velocity (RV) survey. Methods. The high-resolution, the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) was used from 2003 to 2013 for a radial velocity survey of giant stars as part of the exoplanet search pr...

We report the detection of an exoplanet candidate in orbit around sigma Persei from a radial velocity (RV) survey. The system exhibits periodic RV variations of 579.8 +/- 2.4 days. The purpose of the survey is to search for low-amplitude and long-period RV variations in giants and examine the origin of the variations using the fiber-fed Bohyunsan O...

Auns. The aim of our paper is to investigate the low-amplitude and long-period variations in evolved stars with a precise radial velocity (RV) survey. Methods. The high-resolution, the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) was used from 2003 to 2013 for a radial velocity survey of giant stars as part of the exoplanet search pr...

We report the detection of an exoplanet candidate in orbit around σ Persei from a radial velocity (RV) survey. The system exhibits periodic RV variations of 579.8 ± 2.4 days. The purpose of the survey is to search for low-amplitude and long-period RV variations in giants and examine the origin of the variations using the fiber-fed Bohyunsan Observa...

We report the discovery of new P=0.303-day variable star TYC 5965-2398-1 of W UMa or Delta Scuti type of variability at the about 4' distance from of Algol-type eclipsing binary stars R CMa.

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 (BOE...

Aims. Our aim is to search for and study the origin of the low-amplitude and long-periodic radial velocity (RV) variations in K giants. Methods. We present high-resolution RV measurements of K2 giant epsilon CrB from February 2005 to January 2012 using the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) at the Bohyunsan Optical Astronom...

RV measurements obtained from February 2005 until January 2012. (1 data file).

We used extensive ground-based multisite and archival spectroscopy to derive observational constraints for a seismic modelling of the magnetic β Cep star V2052 Ophiuchi. The line-profile variability is dominated by a radial mode (f1 = 7.148 46 d−1) and by rotational modulation (Prot = 3.638 833 d). Two non-radial low-amplitude modes (f2 = 7.756 03...

Aims. In order to search for and study the nature of the low-amplitude and long-periodic radial velocity (RV) variations of massive stars, we have been carrying out a precise RV survey for supergiants that lie near or inside the Cepheid instability strip. Methods. We have obtained high-resolution spectra of {\alpha} Per (F5 Ib) from November 2005 t...

High-resolution echelle spectra have been obtained of the semi-detached Algol-type eclipsing binary system, TX UMa with the high-resolution echelle spectrographs of the 1.8m telescope at Bohyunsan Optical Astronomy Observatory in Korea and of the 2.0m telescope of Peak Terskol Observatory in Russia. New accurate radial velocities of its components...

Pollux is yellow giant with known regular surface magnetic field about 1 Gauss. An analysis of the periodic behavior of the magnetic field of Pollux was performed. For this purpose, we used literature data together with spectropolarimetric observations, which were carried out during 10 nights in 2010 at the Crimean Astrophysical Observatory, and sp...

As research on variable stars continues at an ever growing pace, this report can only give a selection of research highlights from the past three years, with a rigorously abbreviated bibliography. The past triennium has been dominated by results of the CoRoT (Astronomy & Astrophysics 2009) and Kepler (Gilliland et al. 2010) space missions, stemming...

This is the triennial report of IAU Commission 27, mostly presenting a review of recent advances in the field.

Tables of differential magnitudes in the sense (CT Her - C1), used to define the B and V light curves, are given in both filters. The radial velocities were measured with the cross-correlation technique using synthetic spectra obtained with the programme SPECTRUM, and a grid of LTE-atmosphere models of solar-type chemical composition. Also tabulate...

High-resolution echelle spectra have been obtained of the semi-detached Algol-type eclipsing binary system, TX UMa with the high-resolution echelle spectrographs of the 1.8 m telescope at Bohyunsan Optical Astronomy Observatory in Korea and of the 2.0 m telescope of Peak Terskol Observatory in Russia. New accurate radial velocities of its component...

We present the results of a multi-site photometric campaign carried out in 2004-2008 for the Algol-type eclipsing binary system CT Her, the primary component of which shows Delta Scuti-type oscillations. Our data consist of differential light curves collected in the filters B and V which have been analysed using the method of Wilson-Devinney (PHOEB...

Aims. To search for extrasolar planets around intermediate-mass stars, we are conducting a precise RV survey around K-giants. Methods. We present high-accuracy RV measurements of {\alpha} Ari made from November 2003 to February 2010. This star belongs to our sample of 55 K-giants studied for extrasolar planet and pulsation searches using the fiber-...

The RV measurements obtained from November 2003 until February 2010. (1 data file).

Based on high-resolution spectra, we investigate the abundance distribution of chromium and silicon on the surface of α Cir using Doppler Imag ing technique. Results of our analysis show the pres ence of chromium and silicon spots on the surface of α Cir as well as large gradients of the abundances of these elements.

We analyze time-series of highresolution spectra of RZCas, one of the brightest Algoltype stars where the primary shows δ Sct-like oscillations. Our inverstigation uses a variety of methods like the KOREL program to derive the orbital solution and to decompose the spectra of the binary components, the SynthV program to derive the elemental abundanc...

We investigate the Algol-type system TW Dra by means of the new computer program Shellspec07_inverse which is specially designed for the fine-tuning of stellar and system parameters of eclipsing binaries. We derive precise atmospheric and system parameters of TW Dra with an accuracy comparable to that expected from photometric data, and give a shor...

I review the present status of the pulsation studies of close binary systems, focusing on pulsating gainers of semi-detached Algol type eclipsing binaries. I discuss the advantages of pulsation studies of eclipsing binaries, influence of the activity cycles of a mass-losing star on mass transfer and accretion rate and on how it can drive the amplit...

We present the results of a three-continent multisite photometric campaign carried out on the Algol-type eclipsing binary system Y Cam, in which the primary component is a multiperiodic δ Sct-type pulsator. The observations consist of 86 nights and more than 450 h of useful data collected mainly during the Northern winter 2002–2003. This means that...

TW Dra is a well-known short-period Algol-type system. It belongs to the class of oEA stars (Algol-type systems with a δ Scuti-like oscillating primary component). We investigate the TW Dra system based on high-resolution spectra taken in 2007 and in 2008 to derive precise stellar and system parameters and to check for phases of active mass transfe...

The RV measurements obtained from May 2003 until May 2009 are listed in Table 3. (1 data file).

Aims: Our primary goal is to search for planets around intermediate mass stars. We are also interested in studying the nature of radial velocity (RV) variations of K giant stars. Methods: We selected about 55 early K giant (K0-K4) stars brighter than fifth magnitude that were observed using BOES, a high resolution spectrograph attached to the 1.8 m...

Aims: Our primary goal is to search for planets around intermediate mass stars. We are also interested in studying the nature of radial velocity (RV) variations of K giant stars. Methods: We selected about 55 early K giant (K0 - K4) stars brighter than fifth magnitude that were observed using BOES, a high resolution spectrograph attached to the 1.8...

Aims: Based on time series of high-resolution spectra, we investigate the oEA star (i.e., Algol-type eclipsing binary with an oscillating primary component) RZ Cas to derive precise system and atmospheric parameters and search for phases of rapid mass-transfer and its effects on various system parameters at different epochs of observations. Method...

As part of a observational project aiming to investigate the effects of rotation on main-sequence g-mode non-radial pulsation we have obtained at least one (generally more) high-resolution spectroscopic observation of more than 50 confirmed or candidate gamma Doradus and slowly pulsating B stars and have completed a spectroscopic multi-site campaig...

We introduce the spectroscopic multi-site campaigns that are organised for a sample of slowly pulsating B and gamma Doradus stars to make a big step forward in the asteroseismic studies of these main-sequence g-mode pulsators.

We present the results of a spectroscopic multisite campaign for the β Cephei star 12 (DD) Lacertae. Our study is based on more than thousand high–resolution high S/N spectra gathered with eight different telescopes in a time span of 11 months. In addition, we make use of numerous archival spectroscopic measurements. We confirm 10 independent frequ...

TW Dra is an Algol type system where the primary shows δ Sct oscillations. Time series of high-resolution spectra taken at the Thüringer Landessternwarte Tautenburg (TLS) show a complex pattern of moving bumps across the line profiles, indicating a rich spectrum of high-degree non-radial pulsation modes. After the reductions to remove the signature...

We report on first results obtained in the framework of a larger study of oEA stars, i.e. Algol-type systems with oscillating components. We investigate an extended time series of high-resolution spectra of the oEA star RZ Cas taken in 2006. By comparing our model calculations with the observations, we try to determine the system and atmospheric pa...

The results of spectropolarimetic study of one of the coolest Ap-stars Β CrB are presented. It was shown that effective magnetic fields measured in different spectral lines and folded in phase with the rotational period of the star significantly differ from each other in amplitudes and mean values of the magnetic field curves.

We present the latest results of a multisite photometric campaign carried out in 2004-2007 on the Algol-type eclipsing binary system CT Her, the primary component of which is a δ Scuti- type pulsator with a main pulsation period of only 27 min. CT Her belongs to the new class of oscillating Algol-type binary systems. We collected enough data in two...

Reinvestigations of the short-period oEA star RZ Cas by using the “SHELLSPEC” code con- firm most of the system parameters obtained by Lehmann & Mkrtichian (2008). Results from spectra obtained in 2001 point to a transient phase of rapid mass transfer and to the existence of dense circumprimary matter of disk-like structure, while results from spec...

We investigate a spectroscopic time series of the oscillating Algol-type star TW Dra to derive basic system and stellar parameters and to prepare for mode identification. From the orbital solution we derive precise masses and get disentangled spectra of the components by using KOREL. For the primary we derive about solar abundance. Computed LSD pro...

We report on the analysis of 436.1 hrs of nearly continuous high-speed photometry on the pulsating DB white dwarf GD358 acquired with the Whole Earth Telescope (WET) during the 2006 international observing run, designated XCOV25. The Fourier transform (FT) of the light curve contains power between 1000 to 4000 microHz, with the dominant peak at 123...

Aims. We investigate the oscillation spectrum of the most chemically-peculiar star in the sky, the rapidly-oscillating magnetic (roAp) star HD 101065.Methods. High-precision radial velocity (RV) measurements, spanning four consecutive nights on 3–6 March, 2004, were obtained with the HARPS echelle-spectrometer at the ESO 3.6-m telescope, and photom...

We present results of a first application of a new computer program for modeling spectroscopic line profiles of eclipsing binaries including eclipse mapping. We apply the program to observed spectra of the oEA star RZ Cas. Basic stellar parameters of RZ Cas are derived from an optimization of the model parameters and compared to those derived from...

We present the detection of a rich l = 0-2 p-mode oscillation spectrum in the most chemically-peculiar roAp star HD 101065 (Przybylski's star). Constructed echelle-diagrams exhibit both large (Δν = 64.07 μHz) and small (5-7 μHz) frequency spacings. We have calculated the nonadiabatic frequencies of axisymmetric high-order p-modes using main sequenc...

By using high dispersion spectra obtained by the 1.8 m telescope of Bohyunsan Optical Astronomy Observatory (South Korea), multiline least-square deconvolution of line profiles, and Fourier analysis techniques, we obtained the rotational velocities of the components of 23 binary systems. The rotational velocities for nine primary, eight secondary,...

To detect exoplanets and study pulsation of K giant stars, we have observed precise RV (radial velocity) of about 55 early K giant (K0 - K4) stars brighter than V = 5 magnitude since 2003 by using BOES, a high resolution Echelle spectrograph attached to the 1.8 m telescope at BOAO (Bohyunsan Optical Astronomy Observatory). We detected periodic RV v...

We present a first results from a long-term program of a radial velocity study of Cepheid Polaris (F7 Ib) aimed to find amplitude and period of pulsations and nature of secondary periodicities. 264 new precise radial velocity measurements were obtained during 2004-2007 with the fiber-fed echelle spectrograph Bohyunsan Observatory Echelle Spectrogra...

We present the first results of a multi-site photometric campaign carried out in 2004-2006 on the Algol-type eclipsing binary system CT Her, the primary component of which is a δ Scuti-type pulsator. Our observations include (almost complete) binary light curves in the filters B and V which have been analysed following the principles of the Wilson-...

Aims:We test the hypothesis that the oEA star RZ Cas has undergone a transient phase of rapid mass-transfer in 2000/2001. Methods: We analyze a time series of high-resolution spectra of RZ Cas obtained in 2001 and in 2006 for radial velocity (RV) and line profile variations. Improved orbital solutions are determined using the method of differential...

An improvement of the radial-velocity measurement accuracy is crucial for the detection of tiny stellar oscillations and exoplanets. Through the analysis of week-long extensive observations of solar-type stars (Procyon in 2000, 2002, and 2006/2007 and $\tau$ Cet in 2002 and 2006/2007), we have carefully examined, revised, and finely tuned the widel...

Aims.We test the hypothesis that the oEA star RZ Cas has undergone a transient phase of rapid mass-transfer in 2000/2001.Methods.We analyze a time series of high-resolution spectra of RZ Cas obtained in 2001 and in 2006 for radial velocity (RV) and line profile variations. Improved orbital solutions are determined using the method of differential c...

Nowadays, the accuracy of individual radial velocity measurements of the best spectroscopic instruments is of about 0.5-1 m/s (see these proceedings). The corresponding pulsational photometric amplitude variation is expected to be of the order of 10-2 mmag — a level that seems impossible to achieve from the ground, but only with specialized photome...

In this paper we present the results of multisite photometric and spectroscopic campaigns, carried out during the years 1995 and 1996, to study the pulsations of a typical lambda Bootis star, 29 Cyg. During the 1995 campaign we found well-defined multiperiodicity in 29 Cyg, which was studied in detail during a multilongitude campaign covering a 65...

Aims:We investigate the abundance distributions of silicon and iron on the surface of HR 7224 and check for the presence of magnetic fields. We try further to find an explanation for the observed Balmer line variations, alternative to that by surface temperature gradients given in a previous article. Methods: Based on time series of more than 570...

The mode identification is the most difficult problem in asteroseismology. Most of the identification techniques operate with the light integrated over the whole disk, while the spatial filtration method in eclipsing binaries with pulsating components (Gamarova et al., 2003, Rodriguez et al., 2004) gives a possibility to resolve the stellar disk. T...

The method of high-precision RV-measurements is based on usage of absorbing iodine cell placed just before the entrance slit to the spectrograph. It acts like the standard wavelength calibrator, which is affected by the same instrumental configuration as the observed data. It was previously developed and used for search for exoplanets (Butler et al...

The surface magnetic field configuration of the Ap star 78 Vir is reconstructed in the framework of the magnetic charge description (MCD) method from the analysis of Stokes IQUV spectra. Magnetically-sensitive Cr I and Cr II lines are analysed by assuming a stellar atmosphere model with Teff=9250K, log(g)=4.5 and by postulating a non-uniform surfac...

We present first results of a spectroscopic multisite campaign for 12 (DD) Lacertae (hereinafter 12 Lac). This star is one of the best observed β Cephei stars. It has a large number of known oscillation frequencies but a lack of identified m-values for its detected modes. In our data set we find seven independent frequencies together with combinati...

We present a status report on the search for pulsations in primary componants of Algols systems (oEA stars). Analysis of 21 systems with A0-F2 spectral type primaries revealed pulsations in two systems suggesting that of the order of ten persent of Algols primaries in this range are actually pulsators.

We present the revised list of presently known oscillating mass-accreting components of semi-detached Algol-type eclipsing binaries (oEA stars) and discuss the pulsation mode visibility and strategies of mode identification. On the example of the best studied oEA star RZ Cas we discuss the reasons for the observed orbital modulation of the pulsatio...

We investigated the radial velocities of the mass-accreting Algol-type star RZ Cas measured from new observations obtained in 2006. After subtracting an improved orbital solution and all low-frequency variations we searched for the signature of short-term non-radial pulsations. We found three pulsation modes where one was never observed before. Als...

The abundance anomalies in chemically peculiar B-F stars are usually explained by diffusion of chemical elements in the stable atmospheres of these stars. But it is well known that Cp stars with similar temperatures and gravities show very different chemical compositions. We show that the abundance patterns of several stars can be influenced by acc...

Aims.We investigate the abundance distributions of silicon and iron on the surface of HR 7224 and check for the presence of magnetic fields. We try further to find an explanation for the observed Balmer line variations, alternative to that by surface temperature gradients given in a previous article.Methods.Based on time series of more than 570 hig...