Time Series Of High-resolution Spectra Research Articles

Spectroscopic time-series analysis of R Canis Majoris

R Canis Majoris is the prototype of a small group of Algol-type stars showing short orbital periods and low mass ratios. A previous detection of short-term oscillations in its light curve has not yet been confirmed. We investigate a new time series of high-resolution spectra with the aim to derive improved stellar and system parameters, to search for the possible impact of a third component in the observed spectra, to look for indications of activity in the Algol system, and to search for short-term variations in radial velocities. We disentangled the composite spectra into the spectra of the binary components. Then we analysed the resulting high signal-to-noise spectra of both stars. Using a newly developed program code based on an improved method of least-squares deconvolution, we were able to determine the radial velocities of both components also during primary eclipse. This allowed us to develop a better model of the system including the Rossiter–McLaughlin effect and to derive improved orbital parameters. Combining the results with those from spectrum analysis, we obtain accurate stellar and system parameters. We further deduce at least one oscillation frequency of 21.38 c d−1. It could be detected during primary eclipses only and confirms a previous photometric finding. Results point to an amplitude amplification of non-radial pulsation modes due to the eclipse mapping effect. The presence of a He I line in the spectra indicates mass transfer in the R CMa system. Calculations of its Roche geometry give evidence that the cool secondary component may fill its Roche lobe. No evidence of a third body in the system could be found in the observed spectra.

Star-spot distributions and chromospheric activity on the RS CVn type eclipsing binary SV Cam

Using a time series of high-resolution spectra and high-quality multi-colour photometry, we reconstruct surface maps of the primary component of the RS CVn type rapidly rotating eclipsing binary, SV Cam (F9V + K4V). We measure a mass ratio, q, of 0.641(2) using our highest quality spectra and obtain surface brightness maps of the primary component, which exhibit predominantly high-latitude spots located between 60-70-degree latitudes with a mean filling factor of about 35%. This is also indicated by the R-band light curve inversion, subjected to rigourous numerical tests. The spectral subtraction of the H-alpha line reveals strong activity of the secondary component. The excess H-alpha absorption detected near the secondary minimum hints to the presence of cool material partially obscuring the primary star. The flux ratios of Ca II IRT excess emission indicate that the contribution of chromospheric plage regions associated with star-spots is dominant, even during the passage of the filament-like absorption feature.

Probing gas and dust in the tidal tail of NGC 5221 with the type Ia supernova iPTF16abc

Context. Type Ia supernovae (SNe Ia) can be used to address numerous questions in astrophysics and cosmology. Due to their well known spectral and photometric properties, SNe Ia are well suited to study gas and dust along the lines-of-sight to the explosions. For example, narrow Na I D and Ca II H&K absorption lines can be studied easily, because of the well-defined spectral continuum of SNe Ia around these features. Aims. We study the gas and dust along the line-of-sight to iPTF16abc, which occurred in an unusual location, in a tidal arm, 80 kpc from centre of the galaxy NGC 5221. Methods. Using a time-series of high-resolution spectra, we examine narrow Na I D and Ca II H&K absorption features for variations in time, which would be indicative for circumstellar (CS) matter. Furthermore, we take advantage of the well known photometric properties of SNe Ia to determine reddening due to dust along the line-of-sight. Results. From the lack of variations in Na I D and Ca II H&K, we determine that none of the detected absorption features originate from the CS medium of iPTF16abc. While the Na I D and Ca II H&K absorption is found to be optically thick, a negligible amount of reddening points to a small column of interstellar dust. Conclusions. We find that the gas along the line-of-sight to iPTF16abc is typical of what might be found in the interstellar medium (ISM) within a galaxy. It suggests that we are observing gas that has been tidally stripped during an interaction of NGC 5221 with one of its neighbouring galaxies in the past $\sim10^9$ years. In the future, the gas clouds could become the locations of star formation. On a longer time scale, the clouds might diffuse, enriching the circum-galactic medium (CGM) with metals. The gas profile along the line-of-sight should be useful for future studies of the dynamics of the galaxy group containing NGC 5221.

SPECTROSCOPIC VARIABILITY OF IRAS 22272+5435

ABSTRACT A time series of high-resolution spectra was observed in the optical wavelength region for the bright proto-planetary nebula IRAS 22272+5435 (HD 235858), along with a simultaneous monitoring of its radial velocity and BV R C magnitudes. The object is known to vary in light, color, and velocity owing to pulsation with a period of 132 days. The light and color variations are accompanied by significant changes in spectral features, most of which are identified as lines of carbon-bearing molecules. According to the observations, the C2 Swan system and CN Red system lines are stronger near the light minimum. A photospheric spectrum of the central star was calculated using new self-consistent atmospheric models. The observed intensity variations in the C2 Swan system and CN Red system lines were found to be much larger than expected if due solely to the temperature variation in the atmosphere of the pulsating star. In addition, the molecular lines are blueshifted relative to the photospheric velocity. The site of formation of the strong molecular features appears to be a cool outflow triggered by the pulsation. The variability in atomic lines seems to be mostly due variations of the effective temperature during the pulsation cycle. The profiles of strong atomic lines are split, and some of them are variable in a timescale of a week or so, probably because of shock waves in the outer atmosphere.

Time series of high-resolution spectra of SN 2014J observed with the TIGRE telescope

We present a time series of high resolution spectra of the Type Ia supernova 2014J, which exploded in the nearby galaxy M82. The spectra were obtained with the HEROS echelle spectrograph installed at the 1.2 m TIGRE telescope. We present a series of 33 spectra with a resolution of R = 20, 000, which covers the important bright phases in the evolution of SN 2014J during the period from January 24 to April 1 of 2014. The spectral evolution of SN 2014J is derived empirically. The expansion velocities of the Si II P-Cygni features were measured and show the expected decreasing behaviour, beginning with a high velocity of 14,000 km/s on January 24. The Ca II infrared triplet feature shows a high velocity component with expansion velocities of > 20, 000 km/s during the early evolution apart from the normal component showing similar velocities as Si II. Further broad P-Cygni profiles are exhibited by the principal lines of Ca II, Mg II and Fe II. The TIGRE SN 2014J spectra also resolve several very sharp Na I D doublet absorption components. Our analysis suggests interesting substructures in the interstellar medium of the host galaxy M82, as well as in our Milky Way, confirming other work on this SN. We were able to identify the interstellar absorption of M82 in the lines of Ca II H & K at 3933 and 3968 A as well as K I at 7664 and 7698 A. Furthermore, we confirm several Diffuse Interstellar Bands, at wavelengths of 6196, 6283, 6376, 6379 and 6613 A and give their measured equivalent widths.

IRAS 19135+3937: an SRd variable as interacting binary surrounded by a circumbinary disc

Semi-regular (SR) variables are not a homogeneous class and their variability is often explained due to pulsations and/or binarity. This study focuses on IRAS 19135+3937, an SRd variable with an infra-red excess indicative of a dusty disc. A time-series of high-resolution spectra, UBV photometry as well as a very accurate light curve obtained by the Kepler satellite, allowed us to study the object in unprecedented detail. We discovered it to be a binary with a period of 127 days. The primary has a low surface gravity and an atmosphere depleted in refractory elements. This combination of properties unambiguously places IRAS 19135+3937 in the subclass of post-Asymptotic Giant Branch stars with dusty discs. We show that the light variations in this object can not be due to pulsations, but are likely caused by the obscuration of the primary by the circumbinary disc during orbital motion. Furthermore, we argue that the double-peaked Fe emission lines provide evidence for the existence of a gaseous circumbinary Keplerian disc inside the dusty disc. A secondary set of absorption lines has been detected near light minimum, which we attribute to the reflected spectrum of the primary on the disc wall, which segregates due to the different Doppler shift. This corroborates the recent finding that reflection in the optical by this type of discs is very efficient. The system also shows a variable Halpha profile indicating a collimated outflow originating around the companion. IRAS 19135+3937 thus encompasses all the major emergent trends about evolved disc systems, that will eventually help to place these objects in the evolutionary context.

Mass of WASP-33b

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 with the orbital period of the planet. The semi-amplitude of the corresponding variation is 304 ± 20 m s-1 . This finding allows us to give a new estimate of the mass of WASP-33b of 2.1 ± 0.2 Jupiter masses. Its mean density probably is at least 0.6 g cm-3 , a value that can be expected for a planet of its mass that orbits an A-type star in 1.22 d.

Chemical surface inhomogeneities in late B-type stars with Hg and Mn peculiarity

Aims: Time series of high-resolution spectra of the late B-type star HD 11753 exhibiting HgMn chemical peculiarity are used to study the surface distribution of different chemical elements and their temporal evolution. Methods: High-resolution and high signal-to-noise ratio spectra were obtained using the CORALIE spectrograph at La Silla in 2000, 2009, and 2010. Surface maps of YII, SrII, TiII, and CrII were calculated using the Doppler imaging technique. The results were also compared to equivalent width measurements. The evolution of chemical spots both on short and long time scales were investigated. Results: We determine the binary orbit of HD 11753 and fine-tune the rotation period of the primary. The earlier discovered fast evolution of the chemical spots is confirmed by an analysis using both the chemical spot maps and equivalent width measurements. In addition, a long-term decrease in the overall YII and SrII abundances is discovered. A detailed analysis of the chemical spot configurations reveals some possible evidence that a very weak differential rotation is operating in HD 11753.

Mass Transfer in Two Post-AGB Binaries with Dusty Disks

Abstract We present a time series of high-resolution spectra for two poorly studied candidate post-AGB stars surrounded by dusty disks, BD+46 442 and IRAS 19135+3937. We find that both stars show radial velocity variations with periods of 130-140 days. IRAS 19135+3937 has been previously classified as a semi-regular variable based on the light variations with a similar period, but our spectra reveal an evolved star which is too warm to be on the AGB. the variability of BD+46 442 has not been studied till now. the stars reveal a number of spectroscopic peculiarities that resemble features in the interactive binaries including the S-type Symbiotics. Namely, H profile alternates between a double-peak emission and a P Cyg profile, which correlates with the radial velocity phase. A weak asymmetry is tentatively detected in the cross-correlation function that moves in anti-phase with the main component. In addition, strong photospheric lines reveal a narrow central absorption. We conclude that these peculiarities are consistent with a picture where the observed post-AGB stars orbit a much fainter companion at a sub-AU separation and transfer mass on it. the companion is surrounded by an accretion disk, possibly with some kind of an outflow. the SED shows that whole system is surrounded by stable dusty disk as well. It remains to be seen with more observations how much of the line asymmetry could be due to the contribution of low-amplitude pulsations.

Signatures of pulsations and mass loss in the spectra of post-AGB stars

AbstractThe results of high-resolution spectroscopy and radial velocity monitoringa are presented for selected post-AGB candidate stars. Time series of high-resolution spectra for HD235858 shows spliting of low-excitation atomic lines and significant changes in the intensity of C2 and CN lines originated in the extended atmosphere significantly affected by pulsations and outflow. Mass ejection was confirmed for cool R CrB candidate stars DY Per, V1983 Cyg, and V2074 Cyg.

A DYNAMICAL STUDY OF SUSPECTED RUNAWAY STARS AS TRACES OF PAST SUPERNOVA EXPLOSIONS IN THE REGION OF THE SCORPIUS-CENTAURUS OB ASSOCIATION

We address the question of identifying possible past supernovae events taking place in the region of the Scorpius-Centaurus (Sco-Cen) OB association based on stars proposed by Hoogerwerf et al. With this purpose, we obtained a time series of high-resolution spectra of six stars (HIP 42038, HIP 46950, HIP 48943, HIP 69491, HIP 76013, and HIP 82868) which, according to Hoogerwerf et al., may have been runaway stars with origins in the region of the Sco-Cen association. This also includes the nearby young open clusters IC 2391 and IC 2602. If confirmed, such supernovae events could, in principle, have played a role in triggering the formation of some small stellar groups thought to be associated with the Sco-Cen association. Our analysis shows that, except for HIP 48943, the remaining stars are spectroscopic binary systems. For HIP 46950 and HIP 69491, this was already noted by other authors. Our high-resolution spectra allowed us to obtain the radial velocities for all the stars which, combined with their proper motions and parallaxes from Hipparcos, provide a means to investigate, by retracing their orbits, if the Sco-Cen region was, in fact, the origin of these stars. We find that none of these systems originated in the Sco-Cen region. Exploring the possibility that the birthplace of the studied stars occurred in the clusters IC 2391 and IC 2602, we noticed that at the epoch of 2-3 Myr ago these clusters were at a distance comparable with their tidal radii.

Spectroscopic modeling of oscillating Algol-type stars

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. Methods. We combine a variety of methods including the KOREL program to decompose the components of the spectra and determine the orbital solution, the SynthV program to analyze the disentangled spectra by computing synthetic spectra based on atmosphere models, and the newly developed program Shellspec07_inverse to compute optimized stellar parameters from composite line profiles at all orbital phases. Results. Based on spectra taken in 2006, the RZ Cas system can be modeled accurately by assuming that only two stars are present. For spectra acquired in 2001, we obtained an improved solution by adding a light attenuating accretion annulus surrounding the primary, but were unable to model remaining structures in the O–C value distribution. The primary of RZ Cas is a normal A-type star that shows no λ Boo signatures, both components have close to solar abundance. The derived mass of the primary and the separation of the components are slightly smaller than previously assumed. The effective temperature of the primary of 8900 K, is 300 K higher than derived before. The Roche-lobe-filling secondary is assumed to have a large cool spot on its surface pointing towards the primary. We confirm the increase in the orbital period by 2 s between years 2001 and 2006, but not the previously assumed decrease in the orbital radial velocity amplitudes. Conclusions. With the new Shellspec07_inverse program, we obtained precise stellar parameters of RZ Cas. Results clearly point to the occurrence of a transient phase of rapid mass transfer of RZ Cas in 2001, while in 2006 the system was in a quiet state.

TW Dra: NRP mode identification with FAMIAS

Die Serie Communications in Asteroseismology (CoAst) stellt eine international gefragte Plattform für wissenschaftliche Publikationen der neuesten Forschungsergebnisse auf dem Gebiet der Asteroseismologie dar. Forschungsgegenstand der Asteroseismologie sind veränderliche und pulsierende Sterne. Neben den halbjährlich erscheinenden regulären Ausgaben mit Beiträgen aus der laufenden Forschung werden auch Sonderausgaben für Konferenzberichte bzw. Programmhandbücher herausgegeben. JENAM (Joint European and National Astronomy Meeting) ist die größte jährliche Zusammenkunft der europäischen Berufsastronomen, die diesmal im September 2008 in Wien stattfand. Die Konferenz beherbergte neun Minisymposien, wobei eines der Asteroseismologie gewidmet war. Die neuesten Entwicklungen auf diesem Gebiet sind im vorliegenden Band im Rahmen von Übersichts- und Detailartikeln zusammengefasst.

The eclipsing binary star RZ Cassiopeiae

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 corrections. In the RV residuals, after subtracting the orbital solution and low-frequency variations, we search for non-radial pulsations in the high-frequency domain and for an amplitude modulation of the pulsation modes.We model the observed line profiles using a new computer program based on the method of spectroscopic eclipse mapping and investigate the line intensity residuals and the Rossiter-McLaughlin effect. Results. Between 2001 and 2006, the derived orbital solutions show an increase of the orbital period of the order of 2 seconds that is compatible to the photometrically obtained results. RZ Cas changed its pulsation pattern again. We find at least three pulsation frequencies where one is observed for the first time. All three frequencies show amplitude modulations that are correlated with the position of the star in its orbit. The amplitude amplification around primary minimum is much stronger than in 2001. The modeling of line profiles gives hints to a much more complex and inhomogeneous circumbinary gas density distribution in 2001 compared to 2006. The Rossiter-McLaughlin effect is strongly asymmetric in 2001 and almost normal in 2006. Conclusions. The findings support the assumption that a rapid mass-transfer episode occurred in RZ Cas in 2000/2001.

Interpretation of the variability of the β Cephei star λ Scorpii$^{\ \!\!\!}$

We present the results of our analysis of a time series of high-resolution spectra of the multiple β Cephei star λ Scorpii. The data set has a total time-span of more than 5000 days and includes an intensive monitoring campaign during 8 consecutive nights. We confirm the presence of a dominant frequency c d-1 in the data. We show that the amplitude is variable in time according to the light-time effect in the multiple system. The dominant frequency is identified as a prograde dipole pulsation mode. From modelling of the amplitudes and phases across the profiles we derive pulsational parameters, the inclination angle and km s-1. From a comparison between theoretically calculated forcing eigenfrequencies induced by the close companion and the eigenfrequencies of the observed oscillation mode we find no tidal enhancement or excitation of the pulsation mode of λ Scorpii. We find indications for the presence of additional frequencies with low amplitudes.

Stellar surface imaging: mapping brightness and magnetic fields

AbstractRapidly rotating late‐type stars typically display signs of magnetic activity that exceed those seen on the Sun by over two orders of magnitude. The techniques of Doppler imaging and Zeeman Doppler imaging have been instrumental in unveiling magnetic activity patterns at the photospheres of these active stars. Essentially, these techniques work by inverting time‐series of high resolution spectra to produce temperature, brightness and/or magnetic field maps at the surfaces of stars. I will describe how these techniques work and review what they have taught us about the nature of magnetic activity in rapid rotators over the last 20 years. Finally, I will conclude by outlining the capabilities of these techniques in light of new instrumentation that is now becoming available. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Identification of non-radial pulsation modes in the close-binary β Cephei star ν Centauri

We present time series of high-resolution spectra of the Cephei star Cen, showing multi-periodic variations in the Siiii 4552 and 4567 line profiles. After correction for the binary motion, we analyse the time series of spectra by Fourier transforms for each position in the line profile. For selected frequencies we perform a direct fit of multiple sinusoids. Four frequencies are needed to describe the pattern of moving bumps in the line profiles. We present the distributions of variational amplitude and phase across the line profile and use these diagnostics to show that most of the variability can be explained by multiple non-radial pulsations. From the phase distributions across the line profiles we derive estimates for the degree ' of the individual pulsation modes in Cen. We find' values ranging from 6 to 10. We find no trace of a previously reported low-degree ' < 2 pulsation with a period of 0.17 day. We briefly discuss these observations, and those of the other close-binary Cephei stars Vir and 2 Ori, in terms of tidal eects on pulsation-mode stability.

Optical and ultraviolet observations of the star LkHα 264

We present new ultraviolet and optical data for the classical T Tauri star LkHa 264. The most important features in the ultraviolet spectrum are identified and their fluxes are measured. These fluxes are then compared to the corresponding values in the Sun and in other T Tauri stars. Our time series of high-resolution spectra for the regions of the Hα, He I λ5876 and Na I D lines includes data from seven consecutive nights. This allows the study of variability and provides hints on the location and characteristics of the regions producing the He I and Hα lines.