Classical Algol Research Articles

Semi-detached Algol type binaries with increasing orbital periods: Case studies of BD Vir, BO Gem, DG Lac, RW Cet, and RX Hya

This paper presents results from photometric investigations of five semi-detached binaries. Using the TESS and KEPLER (K2) databases, light curves of classical Algol systems BD Vir, BO Gem, DG Lac, RW Cet, and RX Hya were performed in detail. As a result of light curve analysis, the basic astrophysical parameters of the systems were estimated. The masses and radii of the primary components were estimated as 1.95(20) M⊙, 2.22(22) M⊙, 1.95(20) M⊙, 1.95(20) M⊙, 1.75(18) M⊙ and 2.29(3) R⊙, 2.21(2) R⊙, 2.09(1) R⊙, 1.86(2) R⊙, 1.79(3) R⊙ for BD Vir, BO Gem, DG Lac, RW Cet, and RX Hya, respectively. Likewise, the masses and radii of the secondary components were estimated as 0.45(4) M⊙, 0.47(4) M⊙, 0.26(2) M⊙, 0.50(5) M⊙, 0.47(2) M⊙ and 2.94(3) R⊙, 3.90(2) R⊙, 2.17(1) R⊙, 1.35(2) R⊙, 2.57(4) R⊙ for BD Vir, BO Gem, DG Lac, RW Cet, and RX Hya, respectively. It was determined that the orbital periods of the BD Vir, BO Gem, DG Lac, RW Cet, and RX Hya increased with rates of 8.4(3), 24.2(8), 8.1(3), 1.3(1) and 12.5(6) s century−1, respectively. In addition, sinusoidal changes were determined in the orbital period analysis and it was discussed that these sinusoidal changes could be caused by possible component(s) or magnetic activity around the binary. The positions of the components of BD Vir, BO Gem, DG Lac, RW Cet, and RX Hya in logTeff−logL and logM−logR diagrams are discussed.

V404 Andromedae – Observations and Analysis

The first radial velocity curves for V404 And have been obtained. Combined with new light curve data, simultaneous Roche-based light curve analyses have been carried out using the 2003 version of the Wilson-Devinney code. New values for the masses, radii, and luminosities have been obtained: M1 = 0.870 (11) M ʘ, M 2 = 0.706 (9) M ʘ, R1 = 1.10 (13) Rʘ, R2 = 1.37 (13) Rʘ, L1 = 0.75 (7) L ʘ, and L 2 = 0.87 (8) L ʘ. Reference to the sample of close binary stars from Yakut and Eggleton (2005) and the ZAMS indicates that both stars are evolved. Further, the system may have been a classical Algol in the past but with the secondary then contracting, yielding the near semi-contact binary that we have today.

Observation, Modern Light-curve Analysis, and 89 yr Period Study of the Short-period Algol, AE Cassiopeia

Abstract AE Cas was observed some 40 yr ago by Srivastava & Kandpal and was analyzed by Kopal’s Fourier frequency -domain technique. No further precision observations have taken place until the present study, which represents the first modern synthetic analysis of light curves using the 2016 version of the Wilson–Devinney (W–D) Program. It was observed in 2015 October 2, 3 and 23, inclusive, at Dark Sky Observatory in North Carolina with the 0.81 m reflector of Appalachian State University and the 0.9 m reflector at Kitt Peak National Observatory remotely through the Southeastern Association for Research in Astronomy (SARA) consortia. V, R c, I c observations were taken. Five times of minimum light were determined from our present observations, which include three primary eclipses and two secondary eclipses. In addition, eight observations at minima were introduced as low weighted times of minimum light from archived All-Sky Automated Survey for Supernovae Variable Star Catalog (ASAS) data and 74 times of minimum light from the literature, some of which were from visual observations. This period study covers an interval of some 89 yr. The period was found to be decaying at a constant rate with a high level of confidence. A VR c I c simultaneous W–D Program solution indicates that the system has a mass ratio somewhat less than unity (q = 0.856 ± 0.001), and a component temperature difference of ∼2060 K. A q-search was performed and the mass ratio minimized at the above value. The large temperature difference in the components verifies that the binary is not yet in contact. No spots were needed for the solution. The fill-out of our model is 83.2% for the primary component (smaller radius) and 99.1% for the secondary component. So, it is near a classical Algol configuration.

Evidence for conservative mass transfer in the classical Algol system δ Librae from its surface carbon-to-nitrogen abundance ratio

Algol-type binary systems are the product of rapid mass transfer between the initially more massive component to its companion. It is still unknown whether the process is conservative, or whether substantial mass is lost from the system. The history of a system prior to mass exchange is imprinted in the photospheric chemical composition, in particular in the carbon-to-nitrogen (C/N) ratio. We use this to trace the efficiency of mass-transfer processes in the components of a classical Algol-type system, $\delta$ Librae. The present analysis is based on new spectroscopic data (ground-based high-resolution \'echelle spectra) and extracted archival photometric observations (space-based measurements from the STEREO satellites). In the orbital solution, non-Keplerian effects on the radial-velocity variations were taken into account. This reduces the primary's mass by 1.1 \Msun\ ($\sim$23\%) significantly in comparison to previous studies, and removes a long-standing discrepancy between the radius and effective temperature. A spectral disentangling technique is applied to the \'echelle observations and the spectra of the individual components are separated. Atmospheric and abundance analyses are performed for the mass-gaining component and we found C/N $= 1.55 \pm 0.40$ for this star. An extensive set of evolutionary models ($3.5\times10^6$) for both components are calculated from which the best-fitting model is derived. It is found that $\beta$, the parameter which quantifies the efficiency of mass-loss from a binary system, is close to zero. This means that the mass-transfer in $\delta$ Lib is mostly conservative with little mass loss from the system.

Radial Velocities of 41 Kepler Eclipsing Binaries

Abstract Eclipsing binaries are vital for directly determining stellar parameters without reliance on models or scaling relations. Spectroscopically derived parameters of detached and semi-detached binaries allow us to determine component masses that can inform theories of stellar and binary evolution. Here we present moderate resolution ground-based spectra of stars in close binary systems with and without (detected) tertiary companions observed by NASA’s Kepler mission and analyzed for eclipse timing variations. We obtain radial velocities and spectroscopic orbits for five single-lined and 35 double-lined systems, and confirm one false positive eclipsing binary. For the double-lined spectroscopic binaries, we also determine individual component masses and examine the mass ratio distribution, which is dominated by binaries with like-mass pairs and semi-detached classical Algol systems that have undergone mass transfer. Finally, we constrain the mass of the tertiary component for five double-lined binaries with previously detected companions.

BVRI Photometric Analysis and Spectra of the Dwarf Solar Type Algol Binary, V500 Pegasi

Observations and analyses of V500 Pegasi taken at the Dark Sky Observatory (DSO), the SARA North Observatory and the Dominion Astrophysical Observatory are presented. V500 Peg is an eclipsing binary with a period of 0.57983 d. The light curves have the appearance of a detached or semi-detached binary. Spectroscopy reveals that it is of F5V-type. A continuous 14-year period study may show an orbital period increase is occurring. This may be due to weak matter transfer with the primary component as the gainer. The light curve has a large difference in primary and secondary amplitudes that is typical of this class of binary. The final solution shows a total secondary eclipse. The solution is that of a classical Algol system (semi-detached with the secondary component filling its Roche lobe), but it is of solar type, with a magnetic spot. This may mean that magnetic braking is interfering in the nuclear evolution. The secondary component has a temperature of ∼4700 K (K3), which means it is somewhat overluminous for its mass.

Orbit and physical characteristics of the components of the massive Algol V622 Per, a member of the open star cluster χ Per

Analysis of the radial velocities based on spectra of high (near the Hα line) and moderate (4420–4960 A) resolutions supplemented by the published radial velocities has revealed the binarity of a bright member of the young open star cluster χ Per, the star V622 Per. The derived orbital elements of the binary show that the lines of both components are seen in its spectrum, the orbital period is 5.2 days, and the binary is in the phase of active mass exchange. The photometric variability of the star is caused by the ellipsoidal shape of its components. Analysis of the spectroscopic and photometric variabilities has allowed the absolute parameters of the binary’s orbit and its components to be found. V622 Per is shown to be a classical Algol with moderate mass exchange in the binary. Mass transfer occurs from the less massive (\({M_1} = 9.1 \pm 2.7{M_ \odot }\)) but brighter (\(\log {L_1} = 4.52 \pm 0.10{L_ \odot }\)) component onto the more massive (\({M_2} = 13.0 \pm 3.5{M_ \odot }\)) and less bright (\(\log {L_2} = 3.96 \pm 0.10{L_ \odot }\)) component. Analysis of the spectra has confirmed an appreciable overabundance of CNO-cycle products in the atmosphere of the primary component. Comparison of the positions of the binary’s components on the Teff–log g diagram with the age of the cluster χ Per points to a possible delay in the evolution of the primary component due to mass loss by no more than 1–2Myr.

KIC 4739791: A NEW R CMa-TYPE ECLIPSING BINARY WITH A PULSATING COMPONENT

ABSTRACT The Kepler light curve of KIC 4739791 exhibits partial eclipses, the inverse O’Connell effect, and multiperiodic pulsations. Including a starspot on either of the binary components, the light-curve synthesis indicates that KIC 4739791 is in detached or semi-detached configuration with both a short orbital period and a low mass ratio. Multiple frequency analyses were performed in the light residuals after subtracting the binarity effects from the original Kepler data. We detected 14 frequencies: 6 in the low-frequency region (0.1−2.3 days−1) and 8 in the high-frequency region (18.2−22.0 days−1). Among these, six high frequencies with amplitudes of 0.62−1.97 mmag were almost constant over time for 200 days. Their pulsation periods and pulsation constants are in the ranges of 0.048−0.054 days and 0.025−0.031 days, respectively. In contrast, the other frequencies may arise from the alias effects caused by the orbital frequency or combination frequencies. We propose that KIC 4739791 is a short-period R CMa binary with the lowest mass ratio in the known classical Algols and that its primary component is a δ Sct pulsating star. Only four R CMa stars have been identified, three of which exhibit δ Sct-type oscillations. These findings make KIC 4739791 an attractive target for studies of stellar interior structure and evolution.

The VLT-FLAMES Tarantula Survey

We investigate the characteristics of two newly discovered short-period, double-lined, massive binary systems, VFTS 450 (O9.7$\;$II--Ib$\,$+$\,$O7::) and VFTS 652 (B1$\;$Ib$\,+\,$O9:$\;$III:). We perform model-atmosphere analyses to characterise the photospheric properties of both members of each binary (denoting the `primary' as the spectroscopically more conspicuous component). Radial velocities and optical photometry are used to estimate the binary-system parameters. We estimate $T_{\rm eff}=27$ kK, $\log{(g)}=2.9$ (cgs) for the VFTS 450 primary spectrum (34kK, 3.6: for the secondary spectrum); and $T_{\rm eff} = 22$kK, $\log{(g)}=2.8$ for the VFTS 652 primary spectrum (35kK, 3.7: for the secondary spectrum). Both primaries show surface nitrogen enrichments (of more than 1 dex for VFTS 652), and probable moderate oxygen depletions relative to reference LMC abundances. We determine orbital periods of 6.89d and 8.59d for VFTS 450 and VFTS 652, respectively, and argue that the primaries must be close to filling their Roche lobes. Supposing this to be the case, we estimate component masses in the range $\sim$20--50M$_\odot$. The secondary spectra are associated with the more massive components, suggesting that both systems are high-mass analogues of classical Algol systems, undergoing case-A mass transfer. Difficulties in reconciling the spectroscopic analyses with the light-curves and with evolutionary considerations suggest that the secondary spectra are contaminated by (or arise in) accretion disks.

Analysis of selected Kepler Mission planetary light curves

We have modified the graphical user interfaced close binary system analysis program CurveFit to the form WinKepler and applied it to 16 representative planetary candidate light curves found in the NASA Exoplanet Archive (NEA) at the Caltech website http://exoplanetarchive.ipac.caltech.edu, with an aim to compare different analytical approaches. WinKepler has parameter options for a realistic physical model, including gravity-brightening and structural parameters derived from the relevant Radau equation. We tested our best-fitting parameter-sets for formal determinacy and adequacy. A primary aim is to compare our parameters with those listed in the NEA. Although there are trends of agreement, small differences in the main parameter values are found in some cases, and there may be some relative bias towards a 90 degrees value for the NEA inclinations. These are assessed against realistic error estimates. Photometric variability from causes other than planetary transits affects at least 6 of the data-sets studied; with small pulsational behaviour found in 3 of those. For the false positive KOI 4.01, we found that the eclipses could be modelled by a faint background classical Algol as effectively as by a transiting exoplanet. Our empirical checks of limb-darkening, in the cases of KOI 1.01 and 12.01, revealed that the assigned stellar temperatures are probably incorrect. For KOI 13.01, our empirical mass-ratio differs by about 7% from that of Mislis and Hodgkin (2012), who neglected structural effects and higher order terms in the tidal distortion. Such detailed parameter evaluation, additional to the usual main geometric ones, provides an additional objective for this work.

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).

A new photometric and spectroscopic study of the eclipsing binaries CC Her and CM Lac: physical parameters and evolutionary status

New complete light and radial velocities curves were obtained for the eclipsing binaries CC Her and CM Lac. The data are analysed with modern techniques in order to derive the physical parameters of the systems and study their present evolutionary status. We found that CC Her is a classical Algol type binary, while CM Lac is a detached system with two Main Sequence stars in asynchronous orbit.

A photometric study of the neglected eclipsing binaries: V405 Cep, V948 Her, KR Mon and UZ Sge

CCD multi-band light curves of the neglected eclipsing binaries V405 Cep, V948 Her, KR Mon and UZ Sge were obtained and analysed using the Wilson–Devinney code. New geometric and absolute parameters were derived and used to determine their current evolutionary state. V405 Cep, V948 Her and KR Mon are detached systems with their components in almost the same evolutionary stage. UZ Sge is a classical Algol system with a tertiary companion around it. Moreover, since the systems V405 Cep, V948 Her and UZ Sge contain an early type component, their light curves were examined for possible pulsation behaviour.

A fresh insight into the evolutionary status and third body hypothesis of the eclipsing binaries AD Andromedae, AL Camelopardalis, and V338 Herculis

Aims: We aim to derive the absolute parameters of the components of AD And, AL Cam, and V338 Her, interpret their orbital period changes and discuss their evolutionary status. Methods: New and complete multi-filter light curves of the eclipsing binaries AD And, AL Cam, and V338 Her were obtained and analysed with modern methods. Using all reliably observed times of minimum light, we examined orbital period irregularities using the least squares method. In addition, we acquired new spectroscopic observations during the secondary eclipses for AL Cam and V338 Her. Results: For AL Cam and V338 Her, we derive reliable spectral types for their primary stars. Statistical checks of orbital period analysis for all systems are very reassuring in the cases of V338 Her and AD And, although less so for AL Cam. The LIght-Time Effect (LITE) results are checked by inclusion of a third light option in the photometric analyses. Light curve solutions provide the means to calculate the absolute parameters of the components of the systems and reliably estimate their present evolutionary status. Conclusions: AL Cam and V338 Her are confirmed as classical Algols of relatively low mass in similar configurations. Unlike AL Cam, however, V338 Her is still transferring matter between its components, raising interest in the determinability of the evolutionary histories of Algols. AD And is found to be a detached system in which both close stars are of age ~109 yr and is probably a "non-classical" young triple, at an interesting stage of its dynamical evolution.

Carbon deficiencies in the primaries of some classical Algols★

The equivalent widths of C II $\lambda$ 4267 \AA line were measured for the mass-gaining primary stars of the 18 Algol-type binary systems. The comparison of the EWs of the gainers with those of the single standard stars having the same effective temperature and luminosity class clearly indicates that they are systematically smaller than those of the standard stars. The primary components of the classical Algols, located in the main-sequence band of the HR diagram, appear to be C poor stars. We estimate $ [N_{C} /N_{tot}] $ relative to the Sun as -1.91 for GT Cep, -1.88 for AU Mon and -1.41 for TU Mon, indicating poorer C abundance. An average differential carbon abundance has been estimated to be -0.82 dex relative to the Sun and -0.54 dex relative to the main-sequence standard stars. This result is taken to be an indication of the transferring material from the evolved less-massive secondary components to the gainers such that the CNO cycle processed material changed the original abundance of the gainers. There appear to be relationships between the EWs of C II $\lambda$ 4267 \AA line and the rates orbital period increase and mass transfer in some Algols. As the mass transfer rate increases the EW of the C II line decreases, which indicates that accreted material has not been completely mixed yet in the surface layers of the gainers. This result supports the idea of mixing as an efficient process to remove the abundance anomaly built up by accretion. Chemical evolution of the classical Algol-type systems may lead to constrains on the initial masses of the less massive, evolved, mass-losing stars.

Period studies of classical Algol-type binaries II: UX Leo, RW Mon, EQ Ori, XZ UMa and AX Vul

This study presents an investigation of the orbital period variations of five Algol type binaries, UX Leo, RW Mon, EQ Ori, XZ UMa and AX Vul based on all available minima times. The O– C diagrams of all systems exhibit a periodic variation superimposed on a downward parabolic segment. The mass loss due to magnetic braking effect in the cooler components is assumed to account for the parabolic variation with a downward shape, while it is suggested that the light-time effect (LITE) due to an unseen component around the eclipsing binaries explains the tilted sinusoidal changes in their O– C diagrams. The orbital period decrease rates for the systems are estimated as approximately between about 0.7 and 2.5 s per century. It is clearly seen that mass loss effect is more dominant than the expected mass transfer for classical Algols in this study. The minimum mass of the probable third bodies around the eclipsing pairs was calculated to be ⩽0.5 M ⊙ except for UX Leo, in which it was estimated to be approximately 0.9 M ⊙. In order to search for third lights in the light curves of five systems, the V-light curves of the systems were analyzed and their physical and photometric parameters were determined. For UX Leo, a significant third light contribution was determined. We found a very small third light that can be tested using multi-color light curves, for RW Mon, EQ Ori and XZ UMa, while a third light for AX Vul could not be exposed.

A comprehensive photometric study of the Algol-type eclipsing binary: BG Pegasi

This study presents new photometric observations of classical Algol type binary BG Peg with a δ Scuti component. The light curve modeling was provided with the physical parameters of the component stars in the BG Peg system for the first time. After modeling light curves in B and V filters, the eclipse and proximity effects were removed from the light curve to analyze intrinsic variations caused by the hotter component of the system. Frequency analysis of the residuals light represents the multi-mode pulsation of the more massive component of the BG Peg system at periods of 0.039 and 0.047 days. Two frequencies could be associated with non-radial ( l = 2) modes. The total amplitude of the pulsational variability in the V light curve was found to be about 0.045 mag. The long-term orbital period variation of the system was also investigated for the first time. The O– C analysis indicates periodic variation superimposed on a downward parabola. The secular period variation means that the orbital period of the system is decreasing at a rate of −5.5 seconds per century, probably due to the magnetic activity of the cooler component. The tilted sinusoidal O– C variation may be caused by the gravitational effect of an unseen component around the system.

Spin angular momentum evolution of the long-period Algols

We consider the spin angular momentum evolution of the accreting components of Algol-type binary stars. In wider Algols the accretion is through a disc so that the accreted material can transfer enough angular momentum to the gainer that material at its equator should be spinning at breakup. We demonstrate that even a small amount of mass transfer, much less than required to produce today's mass ratios, transfers enough angular momentum to spin the gainer up to this critical rotation velocity. However the accretors in these systems have spins typically between 10 and 40 per cent of the critical rate. So some mechanism for angular momentum loss from the gainers is required. Unlike solar-type chromospherically active stars, with enhanced magnetic activity which leads to angular momentum and mass loss, the gainers in classical Algols have radiative envelopes. We further find that normal radiative tides are far too weak to account for the necessary angular momentum loss. Thus enhanced mass loss in a stellar wind seems to be required to spin-down the gainers in classical Algol systems. We consider generation of magnetic fields in the radiative atmospheres in a differentially rotating star and the possibility of angular momentum loss driven by strong stellar winds in the intermediate-mass stars, such as the primaries of the Algols. Differential rotation, induced by the accretion itself, may produce such winds which carry away enough angular momentum to reduce their rotational velocities to the today's observed values. We apply this model to two systems with initial periods of 5 d, one with initial masses 5 and and the other with 3.2 and ⁠. Our calculations show that, if the mass outflow rate in the stellar wind is about 10 per cent of the accretion rate and the dipole magnetic field is stronger than about 1 kG, the spin rate of the gainer is reduced to below breakup velocity even in the fast phase of mass transfer. Larger mass loss is needed for smaller magnetic fields. The slow rotation of the gainers in the classical Algol systems is explained by a balance between the spin-up by mass accretion and spin-down by a stellar wind linked to a magnetic field.

The O-C curve analysis and simultaneous light curve solutions of classical Algol system U Cephei

New Photometric data in R and V passband filters of the classical Algol system U Cep were analyzed. The orbital and physical parameters of the system were obtained via light curve solutions, using Wilson-Devinney code. The absolute dimensions are also estimated. The O-C curve (only photometric data) is analyzed through Kalimeris method. Fourier analysis of P(E) function gave at least two modulation periods, i.e., P1=16.38 yr and P2=9.77 yr, the first was attributed to magnetic cycle effects and the second to mean time interval of occasional mass out bursts.

Possible third body effects in the period changes of four Algol binaries: RY Aqr, SZ Her, RV Lyr and V913 Oph

AbstractAn investigation of the orbital period changes of the neglected eclipsing binaries, RY Aqr, SZ Her, RV Lyr and V913 Oph, is presented based on all published minima times. Although the explanation of magnetic activity on the surface of the secondaries of the studied Algols is still open, the preferred light‐time effect due to the unseen components around the systems seems more plausible in explaining the tilted sinusoidal variations with relatively high‐amplitudes. The minimal mass values of possible tertiary components have been estimated to be about 1.06, 0.25, 0.78 and 2.85 M⊙ for RY Aqr, SZ Her, RV Lyr and V913 Oph, respectively and the results indicate that their contributions to the total light of the eclipsing pairs are measurable with high accuracy photometric and spectroscopic data, if they exist. Applegate's (1992) model has been discussed as an alternative mechanism assuming that the cooler components have magnetic cycles. It is found that the model parameters of RY Aqr and V913 Oph are consistent with the required values in Applegate's model. In addition to the first detailed orbital study on these systems, a statistical survey on the character of the O – C variations of classical Algols has revealed that about 50 percent of the systems show cyclic behavior. This means that the presence of possible third bodies around classical Algols should be tested with careful analysis using new data. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)