Scuti Type Research Articles

The OmegaWhite survey for short-period variable stars – III: follow-up photometric and spectroscopic observations

We present photometric and spectroscopic follow-up observations of short-period variables discovered in the OmegaWhite survey: a wide-field high-cadence g-band synoptic survey targeting the Galactic Plane. We have used fast photometry on the SAAO 1.0-m and 1.9-m telescopes to obtain light curves of 27 variables, and use these results to validate the period and amplitude estimates from the OmegaWhite processing pipeline. Furthermore, 57 sources (44 unique, 13 also with new light curves) were selected for spectroscopic follow-up using either the SAAO 1.9-m telescope or the Southern African Large Telescope. We find many of these variables have spectra which are consistent with being delta Scuti type pulsating stars. At higher amplitudes, we detect four possible pulsating white dwarf/subdwarf sources and an eclipsing cataclysmic variable. Due to their rarity, these targets are ideal candidates for detailed follow-up studies. From spectroscopy, we confirm the symbiotic binary star nature of two variables identified as such in the SIMBAD database. We also report what could possibly be the first detection of the `Bump Cepheid' phenomena in a delta Scuti star, with OW J175848.21-271653.7 showing a pronounced 22% amplitude dip lasting 3 minutes during each pulsational cycle peak. However, the precise nature of this target is still uncertain as it exhibits the spectral features of a B-type star.

Oscillating classical Algol-type binary XZ Aql

New CCD photometric observations of the neglected classical Algol-type binary XZ Aql were obtained over 53 nights during the observing season of 2011. Photometric elements were determined from analysis of multi-colour light curves. This first comprehensive investigation of the system revealed that the system is in semi-detached configuration with a mass ratio of 0.204 ± 0.02 and a filling ratio of the primary of 50%. Absolute parameters of components and distance of the system were estimated. Based on all eclipse timings, the (O–C) variation indicating orbital period behaviour can be represented by a periodic term superimposed on an upward parabola. Secular increase with a rate of dP/dt = 7.82 × 10−7 day yr−1 is due to mass transfer from the less massive to more massive component. A possible third body around the eclipsing pair and also magnetic activity of the late-type component were used to interpret cyclic variation in the orbital period. Short-period light variations out-of-eclipse imply that XZ Aql is an oscillating eclipsing binary with a pulsating, mass gainer component. From Fourier analysis, two frequencies were detected as 30.6325 c/d and 34.5009 c/d. Pulsational properties and estimated absolute parameters indicate that the primary component may be classified as a δ Scuti type variable.

Pulsation in pre-main sequence stars

AbstractAsteroseismology has been proven to be a successful tool to unravel details of the internal structure for different types of stars in various stages of evolution well after birth. We can now show that it has similar power for pre-main sequence (pre-MS) objects. Pre-MS stars with masses between ~1 and 6 solar masses that have recently been formed and gain their energy mainly from gravitational contraction can become vibrationally unstable during their evolution to the main sequence. Within the past ~15 years, several dozens of pulsating pre-MS stars were discovered using data obtained from ground and from space. Depending on their masses, pre-MS stars can show three different types of pulsations: (i) δ Scuti type p-mode pulsations, (ii) γ Doradus like g-mode oscillations and (iii) g-mode Slowly Pulsating B star pulsations.Our asteroseismic investigations yielded new insights into the connection between the pulsations and early stellar evolution: We revealed a relation between the stars' oscillatory behavior and their relative evolutionary stages that might lead us to a model-independent determination of the stars' fundamental parameters. With this we will be able to put constraints on theoretical models and help to answer some of the yet open questions in early stellar evolution.

CoRoT 105906206: a short-period and totally eclipsing binary with aδScuti type pulsator

Eclipsing binary systems with pulsating components allow the determination of several physical parameters of the stars, such as mass and radius, that, when combined with the pulsation properties, can be used to constrain the modeling of stellar interiors and evolution. Hereby, we present the results of the study of CoRoT 105906206, an eclipsing binary system with a pulsating component located in the CoRoT LRc02 field. The analysis of the CoRoT light curve was complemented by high-resolution spectra from the Sandiford at McDonald Observatory and FEROS at ESO spectrographs, which revealed a double-lined spectroscopic binary. We used an iterative procedure to separate the pulsation-induced photometric variations from the eclipse signals. First, a Fourier analysis was used to identify the significant frequencies and amplitudes due to pulsations. Second, after removing the contribution of the pulsations from the light curve we applied the PIKAIA genetic-algorithm approach to derive the best parameters that describe the orbital properties of the system. The light curve cleaned for pulsations contains the partial eclipse of the primary and the total eclipse of the secondary. The system has an orbital period of about 3.694 days and is formed by a primary star with mass M1 = 2.25 +/- 0.04 solar masses, radius R1 = 4.24 +/- 0.02 solar radii, and effective temperature Teff1 = 6750 +/- 150 K, and a secondary with M2 = 1.29 +/- 0.03 solar masses, R2 = 1.34 +/- 0.01 solar radii, and Teff2 = 6152 +/- 162 K. The best solution for the parameters was obtained by taking into account the asymmetric modulation observed in the light curve, known as the O'Connell effect, presumably caused by Doppler beaming. The analysis of the Fourier spectrum revealed that the primary component has p-mode pulsations in the range 5-13 c/d, which are typical of Delta Scuti type stars.

PHOTOMETRIC PROPERTIES FOR SELECTED ALGOL-TYPE BINARIES. VI. THE NEWLY DISCOVERED oEA STAR FR ORIONIS

New photometry of the neglected eclipsing binary FR Orionis was obtained in 2012 November and December. Using the updated Wilson–Devinney program, the photometric elements were deduced from two-color light curves. The results indicate that this system is a semi-detached binary, with a mass ratio of 0.325(±0.002) and a fill-out factor of the primary of fp = 73.5(±0.2)%. The oscillating light curves imply that FR Ori may be an oscillating EA (oEA)-type star with a rapidly pulsating, mass-accreting primary component. After we removed the theoretical light curves from the observations, Fourier analysis revealed that the more massive component possibly shows a δ Scuti type pulsation with four detected frequencies. The dominant frequency is f1 = 38.6c day −1 (i.e., Ppuls = 37.3 minutes), and the pulsation constant is Q = 0.014 days. Based on all available eclipsing times, the orbital period is undergoing a secular period increase with a rate of dP/dt = +8.85(±0.66) × 10 −8 day yr −1 , which may be interpreted by mass transfer from the secondary to the primary. We expect that the more massive component will fill its Roche lobe due to mass transfer of the secondary. Therefore, the oEA star FR Ori may evolve into a contact configuration.

Observations, light curves analysis and pulsation behavior of the Algol-type eclipsing binary system XX Cep

We present the long term photometric variations of the classical Algol type binary XX Cep with a δ Scuti type pulsating component. Modeling of the system shows that the secondary component fills its Roche lobe. The derived physical and geometrical parameters of the system are M1=1.92M⊙,M2=0.36M⊙,R1=2.08R⊙,R2=2.39R⊙,L1=19.8L⊙,L2=2.1L⊙,a=9.8R⊙ and the distance of the system as 312(18) pc. We obtained five new times of minima. Analysis of the mid-eclipse times indicate a period decrease of dP/dt=-1.9(2)×10-8days/yr that can be interpreted in terms of a mass transfer rate (dM/dt=-1.2(3)×10-9M⊙/yr) from the secondary to primary component. The O−C diagram formed from all available timings, and thus the orbital period of the system, can be partly represented as a beat effect between two cyclical variations with different periods (P1=48(1)yr, P2=81(4)yr). We used PHOEBE program for light curves analysis and after modeling, the eclipse and proximity effects were removed from the light curves to analyze intrinsic variations caused by components of the system. Frequency analysis was done by Period04 and the residuals represent the pulsation of a more massive component of the system XX Cep with a period of 0.031days, confirming the results of Lee et al. (2007).

The position of confirmed pre-main sequence pulsators in the H-R diagram and an overview of their properties

AbstractPre-main sequence (PMS) stars can become vibrationally unstable during their evolution to the zero-age main sequence (ZAMS). As they gain their energy from gravitational contraction and have not started nuclear fusion in their cores yet, their inner structures are significantly different to those of (post-) main sequence stars and can be probed by asteroseismology.Using photometric time series from ground and from space (MOST, CoRoT & Spitzer) the number of confirmed pulsating pre-main sequence stars has increased significantly within the last years and allowed to find members of new classes of PMS pulsators. Apart from the well-established group of δ Scuti type PMS stars, members of the groups of PMS γ Doradus, PMS δ Scuti – γ Doradus hybrid and PMS slowly pulsating B (SPB) stars have been discovered. For five PMS δ Scuti candidates, space photometry has revealed that they only show irregular variability, but no pulsations.The unique high-precision space data were combined with dedicated high-resolution spectra to probe the parameter space in the H-R diagram and study the properties of PMS pulsators in comparison to their evolutionary stage.

Abundance analysis of the γ Doradus–δ Scuti hybrid metallic line (Am) star HD 8801

AbstractLow frequency oscillation, typical for γ Doradus g‐mode type stellar core sensitive pulsation, as well as higher frequency δ Scuti type pulsation typical for p ‐modes, sensitive to the envelope, make HD 8801 a remarkable hybrid pulsator with the potential to probe a stellar structure over a wide range of radius. In addition HD 8801 is a rare pulsating metallic line (Am) star. We determined the astro‐physical fundamental parameters to locate HD 8801 in the H‐R diagram. We analyzed the element abundances, paying close attention to the errors involved, and confirm the nature of HD 8801 as a metallic line (Am) star. We also determined an upper limit on the magnetic field strength. Our abundance analysis is based on classical techniques, but uses for the final step a model atmosphere calculated with the abundances determined by us. We also discuss spectropolarimetric observations obtained for HD 8801. This object is remarkable in several respects. It is a nonmagnetic metallic line (Am) star, pulsating simultaneously in p‐ and g‐modes, but also shows oscillations with periods in between these two domains, whose excitation requires explanation. Overall, the pulsational incidence in unevolved classical Am stars is believed to be quite low; HD 8801 does not conform to this picture. Finally, about 75 % of Am stars are located in short‐period binaries, but there is no evidence that HD 8801 has a companion. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nature of the oscillating semi-detached eclipsing binary system IO Ursae Majoris

This paper presents results from analysing spectroscopic and multicolour photometric observations of the neglected semi-detached eclipsing binary system IO Ursae Majoris (IO UMa). For the first time, the orbital parameters of the system and fundamental physical properties of its components were determined from simultaneous analysis of BVR light curves and radial velocities of the components. The masses and radii of the primary and secondary components were found to be M1 = 2.11 ± 0.07 M⊙, M2 = 0.29 ± 0.02 M⊙ and R1 = 3.00 ± 0.04 R⊙ and R2 = 3.92 ± 0.05 R⊙, respectively. Derived absolute parameters yield the photometric distance of IO UMa as 263 ± 13 pc. The projected rotational velocity of the mass-accreting hotter component was measured as 34.5 ± 2 km s−1, just 1.28 times faster than the synchronous value. The hotter component of the system, located in the region of the instability strip, indicates pulsational variation with short period and small amplitude. Frequency analysis after subtracting the theoretical light curve from photometric data revealed that the more massive component shows δ Scuti type pulsation with four detected frequencies. The total amplitude of the variation in the V filter was found to be 0.03 mag. Mode identification using amplitude ratios and phase differences in different filters suggests that the main pulsation frequency of 22.0148 d−1 is probably a radial mode.

Regular frequency patterns in the youngδScuti star HD 261711 observed by the CoRoT and MOST satellites

We concentrate on an asteroseismological study of HD 261711, a rather hot delta Scuti type pulsating member of the young open cluster NGC 2264 located at the blue border of the instability region. HD 261711 was discovered to be a pre-main sequence delta Scuti star using the time series photometry obtained by the MOST satellite in 2006. High-precision, time-series photometry of HD 261711 was obtained by the MOST and CoRoT satellites in 4 separate new observing runs that are put into context with the star's fundamental atmospheric parameters obtained from spectroscopy. With the new MOST data set from 2011/12 and the two CoRoT light curves from 2008 and 2011/12, the delta Scuti variability was confirmed and regular groups of frequencies were discovered. The two pulsation frequencies identified in the data from the first MOST observing run in 2006 are confirmed and 23 new delta Scuti-type frequencies were discovered using the CoRoT data. Weighted average frequencies for each group are related to l=0 and l=1 p-modes. Evidence for amplitude modulation of the frequencies in two groups is seen. The effective temperature was derived to be 8600$\pm$200 K, log g is 4.1$\pm$0.2, and the projected rotational velocity is 53$\pm$1km/s. Using our Teff value and the radius of 1.8$\pm$0.5 Rsun derived from SED fitting, we get a log L/Lsun of 1.20$\pm$0.14 which agrees well to the seismologically determined values of 1.65 Rsun and, hence, a log L/Lsun of 1.13. The radial velocity of 14$\pm$2 km/s we derived for HD 261711, confirms the star's membership to NGC 2264. Our asteroseismic models suggest that HD 261711 is a delta Scuti-type star close to the zero-age main sequence (ZAMS) with a mass of 1.8 to 1.9Msun. HD 261711 is either a young ZAMS star or a late PMS star just before the onset of hydrogen-core burning.

산개성단 NGC 6871을 중심으로 한 Cyg OB3 성협 영역의 변광성 I: δ Scuti 형 변광성

As a part of the short-period variability survey (SPVS) at Bohyunsan Optical Astronomy Observatory, we obtained time-series BV CCD images in the region of Cyg OB3 association centered on the open cluster NGC 6871. The observations were performed for 18 nights from September 5, 2008 to September 1, 2009. We found 15 short-period variable stars in the region. They are Scuti type stars belonging to the local spiral arm, Orion spur. Among them, only two stars were previously known, and the rest are newly discovered ones. In this paper, we have performed a multiple-frequency analysis to determine frequencies of the 15 Scuti type stars, using the discrete Fourier transform and linear least-square fitting methods. One of the newly discovered variable stars is a double-mode Scuti type star with the fundamental and the first overtone modes, and two are high amplitude Scuti stars.

Spectroscopic monitoring of the Herbig Ae star HD 104237

Context. Herbig Ae/Be stars are intermediate-mass pre-main sequence (PMS) stars showing signs of intense activity and strong stellar winds, whose origin is not yet understood in the frame of current theoretical models of stellar evolution for young stars. In addition, the evolutionary tracks of the earlier Herbig Ae stars cross the theoretical PMS instability strip located roughly in the same area of the HR diagram as the δ Scuti variables. Many of these stars exhibit pulsations of δ Scuti type.

Strong interactions betweeng- andp-modes in the hybridγ Doradus-δ Scuti CoRoT star ID 105733033

CoRoT ID 105733033 is an excellent example of hybrid pulsators as it shows g- and p-modes with almost similar amplitudes in two clearly distinct frequency domains. Classical Fourier analysis allows the dectection of frequencies with an amplitude as small as 0.1 mmag up to 50c/d. The frequency spectrum of CoRoT ID 105733033 clearly consists of two distinct ranges, which are typical of gamma Doradus and delta Scuti pulsation. Focus was placed on the identification of linear combinations and frequencies due to the coupling between gamma Doradus and delta Scuti modes. We detect 198 gamma Doradus type frequencies in the range [0.25;4]c/d, of which 180 are not combination frequencies, and 24 of them are separated by a constant period-interval Delta P=0.03074d. According to the asymptotic theory, these 24 frequencies correspond to a series of g-modes of the same ell-degree and different radial orders n. We also detect 246 delta Scuti type frequencies in the range [10.1;63.4]c/d. The dominant frequency F=12.6759c/d was identified as the fundamental radial mode. Our most noteworthy result is that all the main gamma Doradus frequencies f_i are also detected in the delta Scuti domain as F +- f_i with four times smaller amplitudes. Once these frequencies were removed, only 59 can be considered as individual delta Scuti frequencies. A coupling between g- and p-modes is proposed to be a tool for detecting g-modes in the Sun, but this coupling has never yet been observed. Our present study may be valuable input to theoretical studies, addressing the mutual influence of g- and p-mode cavities and the deviation from classical theory. Furthermore, we identify a sequence of g-modes belonging to the same ell but with consecutive orders n.

HD 210111: a new λ Bootis-type spectroscopic binary system

The small group of lambda Bootis stars comprises late B to early F-type stars, with moderate to extreme (up to a factor 100) surface underabundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O, and S). The main mechanisms responsible for this phenomenon are atmospheric diffusion, meridional mixing and accretion of material from their surroundings. Especially spectroscopic binary (SB) systems with lambda Bootis type components are very important to investigate the evolutionary status and accretion process in more details. For HD 210111, also delta Scuti type pulsation was found which gives the opportunity to use the tools of asteroseismology for further investigations. The latter could result in strict constraints for the amount of diffusion for this star. Together with models for the accretion and its source this provides a unique opportunity to shed more light on these important processes. We present classification and high resolution spectra for HD 210111. A detailed investigation of the most likely combinations of single star components was performed. For this, composite spectra with different stellar astrophysical parameters were calculated and compared to the observations to find the best fitting combination. HD 210111 comprises two equal (within the estimated errors) stars with T(eff)=7400K, logg=3.8dex, [M/H]=-1.0dex and vsini=30km/s. This result is in line with other strict observational facts published so far for this object. It is only the third detailed investigated lambda Bootis type SB system, but the first one with a known IR-excess.

δ Scuti light variations as a test for choosing the mechanism of cyclic orbital period changes in Algols

The temporal behaviour of the orbital period and pulsation period of the δ Scuti type primary component is studied in the eclipsing binary AB Cas, where the secondary fills its Roche lobe. Orbital period changes observed over 80 years are a superposition of secular variations due to mass exchange between the components and cyclic variations with a quasi-period of about 46 years. At the same time, the period of δ Scuti light variations is found to remain constant to a high accuracy. This result rules out the explanation of cyclic orbital period changes in AB Cas by the presence of a third body and forces us to seek other interpretations. In view of our results, the only mechanism that currently seems to be acceptable for the observed cyclic orbital period changes in AB Cas and, possibly, many other Algols is the mechanism proposed by Applegate in 1992, which explains these modulations by the variations in the quadrupole moment of the component with a convective shell caused by its cyclic magnetic activity.

Spectroscopic Binaries Among λ Bootis-type Stars

AbstractThe small group of λ Bootis stars comprises late B to early F-type stars, with moderate to extreme (up to a factor 100) surface under-abundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O, and S). The main mechanisms responsible for this phenomenon are atmospheric diffusion, meridional mixing, and accretion of material from their surroundings. Especially spectroscopic binary (SB) systems with λ Bootis-type components are very important to investigate the evolutionary status and accretion process in more details. Because also δ Scuti type pulsation was found for several members, it gives the opportunity to use the tools of astroseismology for further investigations. We present the results of our long term efforts of detailed abundance analysis, orbital parameter estimation and photometric time series analysis for five well investigated SB systems.

Pre-main-sequence stars in the star-forming complex Sh 2-284

Located at the galactic anticenter, Sh 2-284 is a HII region which harbors several young open clusters; Dolidze 25, a rare metal poor (Z~0.004) young cluster, is one of these. Given its association with Sh 2-284, it is reasonable to assume the low metallicity for the whole HII region. Sh~2-284 is expected to host a significant population of Pre-Main Sequence (PMS) stars of both low and intermediate mass stars (Herbig Ae stars). We aim at characterizing these stars by means of a spectroscopic and photometric survey conducted with VIMOS@VLT and complemented with additional optical and infrared observations. In this survey we selected and characterized 23 PMS objects. We derived the effective temperature, the spectral energy distribution and luminosity of these objects; using theoretical PMS evolutionary tracks, with the appropriate metallicity, we estimated the mass and the age of the studied objects. We also estimated a distance of 4 Kpc for Sh 2-284 by using spectroscopic parallax of 3 OB stars. From the age determination we concluded that triggered star formation is in act in this region. Our results show that a significant fraction of the young stellar objects (YSOs) may have preserved their disk/envelopes, in contrast with what is found in other recent studies of low-metallicity star forming regions in the Galaxy. Finally, among the 23 bona fide PMS stars, we identified 8 stars which are good candidates to pulsators of the delta Scuti type.

Close binary and other variable stars in the solar-age Galactic open cluster M 67

We present multi-colour time-series CCD photometry of the solar-age galactic open cluster M67 (NGC 2682). About 3600 frames spread over 28 nights were obtained with the 1.5 m Russian-Turkish and 1.2 m Mercator telescopes. High-precision observations of the close binary stars AH Cnc, EV Cnc, ES Cnc, the $\delta$ Scuti type systems EX Cnc and EW Cnc, and some long-period variables belonging to M67 are presented. Three full multi-colour light curves of the overcontact binary AH Cnc were obtained during three observing seasons. Likewise we gathered three light curves of EV Cnc, an EB-type binary, and two light curves of ES Cnc, a blue straggler binary. Parts of the light change of long-term variables S1024, S1040, S1045, S1063, S1242, and S1264 are obtained. Period variation analysis of AH Cnc, EV Cnc, and ES Cnc were done using all times of mid-eclipse available in the literature and those obtained in this study. In addition, we analyzed multi-colour light curves of the close binaries and also determined new frequencies for the $\delta$ Scuti systems. The physical parameters of the close binary stars were determined with simultaneous solutions of multi-colour light and radial velocity curves. Finally we determined the distance of M67 as 857(33) pc via binary star parameters, which is consistent with an independent method from earlier studies.

2005 Photometric observations and multiple frequencies of the δ Scuti variable V350 Peg

We present the V light curves of δ Scuti type variable V350 Peg, obtained between August and October 2005 at the Ankara University Observatory (AUG) and the TUBITAK National Observatory (TUG). By application of multiple-frequency analyses using Period04 to 7878 photometric V measurements (which are consist of our 747 V data and 7131 V data obtained at Monegrillo Observatory) of V350 Peg, a five-frequency solution was found to be fitted well to the data. In accordance with the computed Q values for V350 Peg, it was found that this star has probably radial mode with l=0 and g-mode oscillations.

Pulsating pre-MS stars in the young open cluster NGC 2264: V588 Monocerotis and V589 Monocerotis

We report on the first high-accuracy, photometric multisite campaign to study the two, first-detected pulsating, pre-main sequence stars V588 Mon and V589 Mon in the direction of the young open cluster NGC 2264. We carried out the campaign from November 2002 to February 2003 with a photometric coverage of about 216 h at four observatories. A detailed frequency analysis results in wellpopulated eigenspectra, typical for δ Scuti type pulsation, with 16 and 20 significant frequencies in the V588 Mon and V589 Mon data, respectively. Using Strogrem uvbyβ photometry and spectroscopic observations as well as published Geneva and infrared photometry feasible fundamental parameters we deduced, placing both stars in the δ Scuti instability strip and giving strong evidence that both stars are members of NGC 2264 and are indeed in their pre-main sequence phase of evolution.