Search

Around half of the heavy elements in the universe are formed through the slow neutron capture (s-) process, which takes place in thermally pulsing asymptotic giant branch (AGB) stars with masses $1-6\;M_{\odot}$. The nucleosynthetic imprint of the s-process can be studied by observing the material on the surface of binary barium, carbon, CH, and CEMP stars. We study the s-process by observing the luminous components of binary systems polluted by a previous AGB companion. Our radial velocity (RV) monitoring program establishes a collection of binary stars exhibiting enrichment in s-process material for the study of elemental abundances, production of s-process material, and binary mass transfer. From high resolution optical spectra, we measure RVs for 350 stars and derive stellar parameters for 150 stars using ATHOS. For a sub-sample of 24 stars we refine our atmospheric parameters using the Xiru program. We use the MOOG code to compute 1D-LTE abundances of C, Mg, s-process elements Sr, Y, Zr, Mo, Ba, La, Ce, Nd, Pb, and Eu to investigate neutron capture events and stellar chemical composition. We estimate dynamical masses by optimising orbits with MCMC techniques in the ELC program, and we compare our results with low-mass AGB models in the FRUITY database. We find enhancements in s-process material in spectroscopic binaries, a signature of AGB mass transfer. We add Mo to the abundance patterns, and for 12 stars we add Pb detections or upper limits. Computed abundances are in general agreement with the literature. Comparing our abundances to the FRUITY yields, we find correlations in s-process enrichment and AGB mass, and agreements in theoretical and dynamically modelled masses. From our high-resolution observations we expand heavy element abundance patterns and highlight binarity in our chemically interesting systems. We investigate evolutionary stages for a small sub-set of our stars., Comment: 30 pages, 14 figures, 7 tables

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. Three of the new stars show multiperiodic pulsations, while all new members are rotationally variable stars, leading to almost 70 per cent (22) of the roAp stars presented being $\alpha^2$ CVn-type variable stars. We show that targeted observations of known chemically peculiar stars are likely to overlook many new roAp stars, and demonstrate that multi-epoch observations are necessary to see pulsational behaviour changes. We find a lack of roAp stars close to the blue edge of the theoretical roAp instability strip, and reaffirm that mode instability is observed more frequently with precise, space-based observations. In addition to the Cycle 2 observations, we analyse TESS data for all known roAp stars. This amounts to 18 further roAp stars observed by TESS. Finally, we list six known roAp stars that TESS is yet to observe. We deduce that the incidence of roAp stars amongst the Ap star population is just 5.5 per cent, raising fundamental questions about the conditions required to excite pulsations in Ap stars. This work, coupled with our previous work on roAp stars in Cycle 1 observations, presents the most comprehensive, homogeneous study of the roAp stars in the TESS nominal mission, with a collection of 112 confirmed roAp stars in total., Comment: Accepted for publication in MNRAS. 32 Pages, 2 Tables, 77 Figures

We present the results of a systematic search for new rapidly oscillating Ap (roAp) stars using the 2-min cadence data collected by the Transiting Exoplanet Survey Satellite (TESS) during its Cycle 1 observations. We identify 12 new roAp stars. Amongst these stars we discover the roAp star with the longest pulsation period, another with the shortest rotation period, and six with multiperiodic variability. In addition to these new roAp stars, we present an analysis of 44 known roAp stars observed by TESS during Cycle 1, providing the first high-precision and homogeneous sample of a significant fraction of the known roAp stars. The TESS observations have shown that almost 60 per cent (33) of our sample of stars are multiperiodic, providing excellent cases to test models of roAp pulsations, and from which the most rewarding asteroseismic results can be gleaned. We report four cases of the occurrence of rotationally split frequency multiplets that imply different mode geometries for the same degree modes in the same star. This provides a conundrum in applying the oblique pulsator model to the roAp stars. Finally, we report the discovery of non-linear mode interactions in $\alpha$ Cir (TIC 402546736, HD 128898) around the harmonic of the principal mode -- this is only the second case of such a phenomenon., Comment: Accepted for publication in MNRAS. 38 Pages, 50 Figures, 1 Table, 2 Appendices

We present new photometric and spectroscopic observations and analyses for the eclipsing binary systems V1241 Tau and GQ Dra. Our photometric light and radial velocity curves analyses combining with the TESS light curves show that both are conventional semi-detached binary systems. Their absolute parameters are also derived. We present the $O-C$ analyses of the systems and we propose the most possible orbital period modulating mechanisms. Furthermore, Fourier analyses are applied to the photometric residual data of the systems to check for the pulsational behavior of the components. We conclude that the primary component of the system GQ Dra is a $\delta$ Sct type pulsator with a dominant pulsation frequency of 18.58 d$^{-1}$ based on our $B$ filter residual light curve although it can not be justified by 30-minute cadence TESS data. No satisfactory evidence of pulsational behaviour for V1241 Tau was verified. Finally, the evolutionary tracks of the components of both systems are calculated, while their locations within evolutionary diagrams are compared with other Algol-type systems., Comment: Accepted for publication in Acta Astronomica. 24 pages, 10 figures

We present the first asteroseismic results for $\delta$ Scuti and $\gamma$ Doradus stars observed in Sectors 1 and 2 of the TESS mission. We utilise the 2-min cadence TESS data for a sample of 117 stars to classify their behaviour regarding variability and place them in the Hertzsprung-Russell diagram using Gaia DR2 data. Included within our sample are the eponymous members of two pulsator classes, $\gamma$ Doradus and SX Phoenicis. Our sample of pulsating intermediate-mass stars observed by TESS also allows us to confront theoretical models of pulsation driving in the classical instability strip for the first time and show that mixing processes in the outer envelope play an important role. We derive an empirical estimate of 74% for the relative amplitude suppression factor as a result of the redder TESS passband compared to the Kepler mission using a pulsating eclipsing binary system. Furthermore, our sample contains many high-frequency pulsators, allowing us to probe the frequency variability of hot young $\delta$ Scuti stars, which were lacking in the Kepler mission data set, and identify promising targets for future asteroseismic modelling. The TESS data also allow us to refine the stellar parameters of SX Phoenicis, which is believed to be a blue straggler., Comment: 33 pages (incl. appendix), accepted for publications in MNRAS

We present spectroscopic observations of the Be/X-ray binary X Per obtained during the period December 2017 - January 2020 (MJD~58095 - MJD~58865). In December 2017 the $H\alpha$, $H\beta$, and HeI 6678 emission lines were symmetric with violet-to-red peak ratio $V/R \approx 1$. During the first part of the period (December 2017 - August 2018) the V/R-ratio decreased to 0.5 and the asymmetry developed simultaneously in all three lines. In September 2018, a third component with velocity $\approx 250$~km~s$^{-1}$ appeared on the red side of the HeI line profile. Later this component emerged in $H\beta$, accompanied by the appearance of a red shoulder in $H\alpha$. Assuming that it is due to an eccentric wave in the circumstellar disc, we find that the eccentric wave appeared first in the innermost part of the disc, it spreads out with outflowing velocity $v_{wave} \approx 1.1 \pm 0.2 $~km~s$^{-1}$, and the eccentricity of the eccentric wave is $e_{wave} \approx 0.29 \pm 0.07$. A detailed understanding of the origin of such eccentricities would have applications to a wide range of systems from planetary rings to AGNs., Comment: MNRAS (accepted)

Here we analyze high-resolution spectra of the Nova V392 Per obtained during the 2018 outburst. The H$\alpha$ and H$\beta$ emission lines show a triple-peak structure with radial velocities of about -2000 km/s, -250 km/s and 1900 km/s respectively. The near infrared spectrum is dominated by the narrow and single-peaked Paschen lines of hydrogen and the OI $\lambda$8446 and OI $\lambda$7773 emission lines. Using DIBs and the KI line, we estimate the interstellar excess towards V392 Per. Based on AAVSO and ASAS-SN photometry data, we calculate that the t$_2$ and t$_3$ decline times are $\sim$ 3 d and $\sim$ 11 d respectively, which classifies V392 Per as a very fast nova. We also briefly discuss the similarity between V392 Per and other very fast novae and the possible future evolution of the system in terms of the hibernation model., Comment: Accepted for publication in Bulgarian Astronomical Journal, 7 pages, 2 figures

We present the first results from the Transiting Exoplanet Survey Satellite (TESS) on the rotational and pulsational variability of magnetic chemically peculiar A-type stars. We analyse TESS 2-min cadence data from sectors 1 and 2 on a sample of 83 stars. Five new rapidly oscillating Ap (roAp) stars are announced. One of these pulsates with periods around 4.7 min, making it the shortest period roAp star known to date. Four out of the five new roAp stars are multiperiodic. Three of these, and the singly-periodic one show the presence of rotational mode splitting. Individual frequencies are provided in all cases. In addition, seven previously known roAp stars are analysed. Additional modes of oscillation are found in some stars, while in others we are able to distinguish the true pulsations from possible aliases present in the ground-based data. We find that the pulsation amplitude in the TESS filter is typically a factor 6 smaller than that in the $B$ filter which is usually used for ground-based observations. For four roAp stars we set constraints on the inclination angle and magnetic obliquity, through the application of the oblique pulsator model. We also confirm the absence of roAp-type pulsations down to amplitude limits of 6 and 13 micromag, respectively, in two of the best characterised non-oscillating Ap (noAp) stars. We announce 27 new rotational variables along with their rotation periods, and provide different rotation periods for seven other stars. Finally, we discuss how these results challenge state-of-the-art pulsation models for roAp stars., Comment: 29 pages, accepted for publication in the MNRAS

We present results of a study of the variability of the marginal Am star HD\,176843 observed in the {\it Kepler} field. {\it Kepler} photometry and ground-based spectroscopy are used to investigate the light variations of the star. HD\,176843 is classified as a marginal Am star that shows $\delta$\ Sct type pulsations. From an analysis of the {\it Kepler} time series, we find that the light curve of HD\,176843 is dominated by three modes with frequencies $f_{1}$=0.1145, $f_{2}$=0.0162 and $f_{3}$=0.1078 d$^{-1}$. The amplitude of the radial velocity variations of about 10 km/s is much more than the radial velocity errors and allows us to conclude clear radial velocity variations. Using the radial velocity data and the adopted spectra, the orbital solution of HD\,176843 is also obtained with an orbital period of 34.14 days. However, the available photometric data show no significant evidence for any possible motion in the binary system., Comment: Accepted for publication in New Astronomy, 16 pages, 6 figures, 3 tables

A new investigation of the variability of the SPB-type star 53 Per is presented. The analysis of the BRITE photometry allowed us to determine eight independent frequencies and the combination one. Five of these frequencies and the combination one were not known before. In addition, we gathered more than 1800 new moderate and high-resolution spectra of 53 Per spread over approximately six months. Their frequency analysis revealed four independent frequencies and the combination one, all consistent with the BRITE results., Comment: 2 pages, accepted for publication in the Proceedings of the PAS (Proc. of the 2nd BRITE Science conference, Innsbruck)

The high precision data obtained by the {\it Kepler} satellite allows us to detect hybrid type pulsator candidates more accurately than the data obtained by ground-based observations. In this study, we present preliminary results on the new analysis of the {\it Kepler} light curve and high resolution spectroscopic observations of pulsating Am star KIC\,9204718. Our tentative analysis therefore show that the star has hybrid pulsational characteristics., Comment: 'Proceedings of Wide Field variability surveys : a 21 st Century 22nd Los Alamos Stellar Pulsation Conference San Pedro De Atacama ,Chile Nov 28-Dec 2, 2016' to be published by the EPJ Web of Conferences

Results from UBVRI photometric observations of the pre-main sequence star GM Cep obtained in the period April 2011 - August 2014 are reported in the paper. Presented data are a continuation of our photometric monitoring of the star started in 2008. GM Cep is located in the field of the young open cluster Trumpler 37 and over the past years it has been an object of intense photometric and spectral studies. The star shows a strong photometric variability interpreted as a possible outburst from EXor type in previous studies. Our photometric data for a period of over six years show a large amplitude variability (Delta V ~ 2.3 mag.) and several deep minimums in brightness are observed. The analysis of the collected multicolor photometric data shows the typical of UX Ori variables a color reversal during the minimums in brightness. The observed decreases in brightness have a different shape, and evidences of periodicity are not detected. At the same time, high amplitude rapid variations in brightness typical for the classical T Tauri stars also present on the light curve of GM Cep. The spectrum of GM Cep shows the typical of classical T Tauri stars wide H/alpha emission line and absorption lines of some metals. We calculate the outer radius of the H/alpha emitting region as 10.4 +/-0.5 Rsun and the accretion rate as 1.8 x 10 E-7 Msun/yr., Comment: 9 pages, 4 figures, accepted for publication in PASA. arXiv admin note: text overlap with arXiv:1111.2166

We present results of an asteroseismic study on the $\gamma$ Dor type {\it Kepler} target KIC\,6462033. {\it Kepler} photometry is used to derive the frequency content and principal modes. High-dispersion ground-based spectroscopy is also carried out in order to determine the atmospheric parameters and projected rotational velocity. From an analysis of the {\it Kepler} long cadence time series, we find that the light curve of KIC\,6462033 is dominated by three modes with frequencies $f_{1}$=0.92527, $f_{2}$=2.03656 and $f_{3}$=1.42972 d$^{-1}$ as well as we detect more than a few hundreds of combination terms. However, two other independent frequencies appear to have lower amplitudes in addition to these three dominant terms. No significant peaks are detected in the region $>$ 5 d$^{-1}$. We therefore confirm that KIC\,6462033 pulsates in the frequency range of $\gamma$ Dor type variables, and a future study will allow us to investigate modal behaviour in this star., Comment: 14 pages, 3 figures, 1 Table. Accepted for publication in New Astronomy

We present the first preliminary results on the analysis of ground-based time series of the {\gamma} Dor star KIC 6462033 (TYC 3144-646-1, V = 10.83, P = 0.69686 d) as well as Kepler photometry in order to study pulsational behaviour in this star.{\gamma} Dor variables, which exhibit g-mode pulsations, are promising asteroseismic targets to understand their rich complexity of pulsational characteristics in detail. In order to achieve this goal, intensive and numerous multicolour and high resolution spectroscopic observations are also required, to complete space-based data aimed at the determination of their physical parameters., Comment: 2 pages, 2 figures. To be published in proceedings of IAU Symposium 301, Precision Asteroseismology, August 2013, Wroc{\l}aw, Poland

We present results of a multi-site photometric campaign on the high-amplitude $\delta$\,Scuti star KIC\,6382916 in the {\it Kepler} field. The star was observed over a 85-d interval at five different sites in North America and Europe during 2011. {\it Kepler} photometry and ground-based multicolour light curves of KIC\,6382916 are used to investigate the pulsational content and to identify the principal modes. High-dispersion spectroscopy was also obtained in order to derive the stellar parameters and projected rotational velocity. From an analysis of the {\it Kepler} time series, three independent frequencies and a few hundred combination frequencies are found. The light curve is dominated by two modes with frequencies $f_{1}$= 4.9107 and $f_{2}$= 6.4314\,d$^{-1}$. The third mode with $f_{3}$= 8.0350\,d$^{-1}$ has a much lower amplitude. We attempt mode identification by examining the amplitude ratios and phase differences in different wavebands from multicolour photometry and comparing them to calculations for different spherical harmonic degree, $l$. We find that the theoretical models for $f_1$ and $f_2$ are in a best agreement with the observations and lead to value of l = 1 modes, but the mode identification of $f_3$ is uncertain due to its low amplitude. Non-adiabatic pulsation models show that frequencies below 6\,d$^{-1}$ are stable, which means that the low frequency of $f_1$ cannot be reproduced. This is further confirmation that current models predict a narrower pulsation frequency range than actually observed., Comment: 8 pages, 6 figures, 5 tables. Accepted for publication in MNRAS

We report on a multi-site photometric campaign on the high-amplitude $\delta$ Scuti star V2367 Cyg in order to determine the pulsation modes. We also used high-dispersion spectroscopy to estimate the stellar parameters and projected rotational velocity. Time series multicolour photometry was obtained during a 98-d interval from five different sites. These data were used together with model atmospheres and non-adiabatic pulsation models to identify the spherical harmonic degree of the three independent frequencies of highest amplitude as well as the first two harmonics of the dominant mode. This was accomplished by matching the observed relative light amplitudes and phases in different wavebands with those computed by the models. In general, our results support the assumed mode identifications in a previous analysis of Kepler data., Comment: 9 pages, 5 figures, 4 tables. Accepted for publication in MNRAS

Two observational campaigns were carried out during the eclipses of EE Cep in 2003 and 2008/9 to verify whether the eclipsing body in the system is indeed a dark disk and to understand the observed changes in the depth and durations of the eclipses. Multicolour photometric data and spectroscopic observations at both low and high resolution were collected. We numerically modelled the variations in brightness and colour during the eclipses. We tested models with different disk structure. We considered the possibility of disk precession. The complete set of observational data collected during the last three eclipses are made available to the astronomical community. Two blue maxima in the colour indices were detected during these two eclipses, one before and one after the photometric minimum. The first (stronger) blue maximum is simultaneous with a "bump" that is very clear in all the UBVRI light curves. Variations in the spectral line profiles seem to be recurrent during each cycle. NaI lines always show at least three absorption components during the eclipse minimum and strong absorption is superimposed on the H_alpha emission. These observations confirm that the eclipsing object in EE Cep system is indeed a dark, dusty disk around a low luminosity object. The primary appears to be a rapidly rotating Be star that is strongly darkened at the equator and brightened at the poles. Some of the conclusions of this work require verification in future studies: (i) a complex, possibly multi-ring structure of the disk in EE Cep; (ii) our explanation of the "bump" observed during the last two eclipses in terms of the different times of obscuration of the hot polar regions of the Be star by the disk; and (iii) our suggested period of the disk precession (~11-12 P_orb) and predicted depth of about 2 mag the forthcoming eclipse in 2014., Comment: 43 pages, 17 figures, accepted for publication in A&A

We continue here the systematic abundance analysis of a sample of Am binaries in order to search for possible abundance anomalies driven by tidal interaction in these binary systems. New CCD observations in two spectral regions (6400-6500, 6660-6760 AA) of HD116657, HD138213, HD155375, HD159560, HD196544 and HD204188 were obtained. Synthetic spectrum analysis was carried out and basic stellar properties, effective temperatures, gravities, projected rotational velocities, masses, ages and abundances of several elements were determined. We conclude that all six stars are Am stars. These stars were put into the context of other Am binaries with 10 < Porb < 200 days and their abundance anomalies discussed in the context of possible tidal effects. There is clear anti-correlation of the Am peculiarities with v sin i. However, there seems to be also a correlation with the eccentricity and may be with the orbital period. The dependence on the temperature, age, mass, and microturbulence was studied as well. The projected rotational velocities obtained by us were compared to those of Royer et al. (2002) and Abt & Morrell (1995)., Comment: 11 pages, 3 tables, 12 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society

We study the fast rotating M5 giant EK Boo by means of spectropolarimetry to obtain direct and simultaneous measurements of both the magnetic field and activity indicators, in order to infer the origin of the activity in this fairly evolved giant. We used the new spectropolarimeter NARVAL at the Bernard Lyot Telescope (Observatoire du Pic du Midi, France) to obtain a series of Stokes I and Stokes V profiles for EK Boo. Using the Least Square Deconvolution technique we were able to detect the Zeeman signature of the magnetic field. We measured its longitudinal component by means of the averaged Stokes V and Stokes I profiles. The spectra also permitted us to monitor the CaII K&H chromospheric emission lines, which are well known as indicators of stellar magnetic activity. From ten observations obtained between April 2008 and March 2009, we deduce that EK Boo has a magnetic field, which varied in the range of -0.1 to -8 G. We also determined the initial mass and evolutionary stage of EK Boo, based on up-to-date stellar evolution tracks. The initial mass is in the range of 2.0-3.6 M_sun, and EK Boo is either on the asymptotic giant branch (AGB), at the onset of the thermal pulse phase, or at the tip of the first (or red) giant branch (RGB). The fast rotation and activity of EK Boo might be explained by angular momentum dredge-up from the interior, or by the merging of a binary. In addition, we observed eight other M giants, which are known as X-ray emitters, or to be rotating fast for their class. For one of these, beta And, presumably also an AGB star, we have a marginal detection of magnetic field, and a longitudinal component Bl of about 1G was measured. More observations like this will answer the question whether EK Boo is a special case, or whether magnetic activity is, rather, more common among M giants than expected., Comment: Accepted for publication in Astronomy & Astrophysics, 10 pages, 8 figures

We present projected rotational velocity measurements of the red giant in the symbiotic star MWC 560 (V694 Mon), using the high-resolution spectroscopic observations with the FEROS spectrograph. We find that the projected rotational velocity of the red giant is vsini = 8.2 +/- 1.5 km/s, and estimate its rotational period to be P_rot = 144-306 days. Using the theoretical predictions of tidal interaction and pseudosynchronization, we estimate the orbital eccentricity e=0.68-0.82. We briefly discuss the connection of our results with the photometric variability of the object., Comment: AN, accepted

The photometric and spectroscopic observational campaign organized for the 2008/9 eclipse of EE Cep revealed features, which indicate that the eclipsing disk in the EE Cep system has a multi-ring structure. We suggest that the gaps in the disk can be related to the possible planet formation., Comment: 6 pages, 6 figures, contribution to the conference proceedings: Binaries - Key to Comprehension of the Universe, Brno, Czech Republic, 8-12 Jul. 2009

We have measured the projected rotational velocities (vsini) in a number of symbiotic stars and M giants using high resolution spectroscopic observations. On the basis of our measurements and data from the literature, we compare the rotation of mass-donors in symbiotics with vsini of field giants and find that: (1) the K giants in S-type symbiotics rotate at vsini>4.5 km/s, which is 2-4 times faster than the field K giants; (2) the M giants in S-type symbiotics rotate on average 1.5 times faster than the field M giants. Statistical tests show that these differences are highly significant: p-value < 0.001 in the spectral type bins K2III-K5III, M0III-M6III, and M2III-M5III; (3) our new observations of D'-type symbiotics also confirm that they are fast rotators. As a result of the rapid rotation, the cool giants in symbiotics should have 3-30 times larger mass loss rates. Our results suggest also that bipolar ejections in symbiotics seem to happen in objects where the mass donors rotate faster than the orbital period. All spectra used in our series of papers can be obtained upon request from the authors., Comment: MNRAS (accepted), 7 pages, 5 figures

We have measured the projected rotational velocities (v sin i) of the mass donors for 29 S-type symbiotic stars using high resolution spectroscopic observations and the cross-correlation function (CCF) method. The results of the CCF have been controlled with synthetic spectra. The typical rotational velocity of the K and M giants in S-type symbiotics appeared to be 4.5 < vsini < 11.7 km/s. In a sub-sample of 16 S--type symbiotic stars (with known orbital periods and well measured vsini) 15 have deviations from synchronization less then the 3-sigma level. This means that we did not find evidence for a statistically significant deviation from the synchronization for any of these 15 objects. The deviation from synchronization is statistically significant (at confidence level >99%) only for the recurrent nova RS Oph. For 22 S-type symbiotics we give clues as to what their orbital periods could be., Comment: accepted for publication in MNRAS

We carried out a detailed analysis of the helium lines at 4921, 5876 and 6678 A in the spectra of the HgMn stars HD 58661, HD 172044, HD 185330 and HD 186122. For the first of these lines, the isotopic shift reaches +0.33 A for pure 3He, while for the last one, the maximum shift is +0.50 A. The 5876 line does not show any significant isotopic shift and is chosen for comparison. No trace of 3He was found in the atmosphere of HD 172044, while its presence was confirmed in HD 185330. This isotope is clearly present in the atmosphere of HD 58661. The results obtained for HD 186122 were ambiguous, 3He being apparently present in the 4921 line but not in the 6678 line, possibly because the latter is very weak., Comment: 3 pages, 2 figure2, to appear in: Proc. of the 26th workshop of the European Working Group on CP stars, eds. P. North, A. Schnell and J. Ziznovsky, Contrib. Astr. Obs. Skalnate Pleso Vol. 27, No 3