Double-lined Binaries Research Articles

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.

Spectroscopic binaries in the Solar Twin Planet Search program: from substellar–mass to M dwarf companions

Previous studies on the rotation of Sun-like stars revealed that the rotational rates of young stars converge towards a well-defined evolution that follows a power-law decay. It seems, however, that some binary stars do not obey this relation, often by displaying enhanced rotational rates and activity. In the Solar Twin Planet Search program we observed several solar twin binaries, and found a multiplicity fraction of $42\% \pm 6\%$ in the whole sample; moreover, at least three of these binaries (HIP 19911, HIP 67620 and HIP 103983) clearly exhibit the aforementioned anomalies. We investigated the configuration of the binaries in the program, and discovered new companions for HIP 6407, HIP 54582, HIP 62039 and HIP 30037, of which the latter is orbited by a $0.06$ M$_\odot$ brown dwarf in a 1-month long orbit. We report the orbital parameters of the systems with well-sampled orbits and, in addition, the lower limits of parameters for the companions that only display a curvature in their radial velocities. For the linear trend binaries, we report an estimate of the masses of their companions when their observed separation is available, and a minimum mass otherwise. We conclude that solar twin binaries with low-mass stellar companions at moderate orbital periods do not display signs of a distinct rotational evolution when compared to single stars. We confirm that the three peculiar stars are double-lined binaries, and that their companions are polluting their spectra, which explains the observed anomalies.

Models for 60 double-lined binaries containing giants

The observed masses, radii and temperatures of 60 medium- to long-period binaries, most of which contain a cool, evolved star and a hotter less-evolved one, are compared with theoretical models which include (a) core convective overshooting, (b)mass loss, possibly driven by dynamo action as in RS CVn binaries, and (c) tidal friction, including its effect on orbital period through magnetic braking. A reasonable fit is found in about 42 cases, but in 11 other cases the primaries appear to have lost either more mass or less mass than the models predict, and in 4 others the orbit is predicted to be either more or less circular than observed. Of the remaining 3 systems, two ($\gamma$ Per and HR 8242) have a markedly `over-evolved' secondary, our explanation being that the primary component is the merged remnant of a former short-period sub-binary in a former triple system. The last system (V695 Cyg) defies any agreement at present. Mention is also made of three other systems (V643 Ori, OW Gem and V453 Cep), which are relevant to our discussion.

BEER analysis ofKeplerand CoRoT light curves

(abridged for arXiv) The BEER algorithm searches stellar light curves for the BEaming, Ellipsoidal, and Reflection photometric modulations that are caused by a short-period companion. Applying the search to the first five long-run center CoRoT fields, we identified $481$ non-eclipsing candidates with periodic flux amplitudes of $0.5-87$ mmag. Optimizing the Anglo-Australian-Telescope pointing coordinates and the AAOmega fiber-allocations with dedicated softwares, we acquired six spectra for $231$ candidates and seven spectra for another $50$ candidates in a seven-night campaign. Analysis of the red-arm AAOmega spectra, which covered the range of $8342-8842\AA{}$, yielded a radial-velocity precision of $\sim1$ km/s. Spectra containing lines of more than one star were analyzed with the two-dimensional correlation algorithm TODCOR. The measured radial velocities confirmed the binarity of seventy of the BEER candidates$-45$ single-line binaries, $18$ double-line binaries, and $7$ diluted binaries. We show that red giants introduce a major source of false candidates and demonstrate a way to improve BEER's performance in extracting higher fidelity samples from future searches of CoRoT light curves. The periods of the confirmed binaries span a range of $0.3-10$ days and show a rise in the number of binaries per $\Delta$log$P$ toward longer periods. The estimated mass ratios of the double-line binaries and the mass ratios assigned to the single-line binaries, assuming an isotropic inclination distribution, span a range of $0.03-1$. On the low-mass end, we have detected two brown-dwarf candidates on a $\sim1$ day period orbit. This is the first time non-eclipsing beaming binaries are detected in CoRoT data, and we estimate that $\sim300$ such binaries can be detected in the CoRoT long-run light curves.

GRAVITY-MODE PERIOD SPACINGS AS A SEISMIC DIAGNOSTIC FOR A SAMPLE OF γ DORADUS STARS FROM KEPLER SPACE PHOTOMETRY AND HIGH-RESOLUTION GROUND-BASED SPECTROSCOPY

Gamma Doradus stars (hereafter ? Dor stars) are gravity-mode pulsators of spectral type A or F. Such modes probe the deep stellar interior, offering a detailed fingerprint of their structure. Four-year high-precision space-based Kepler photometry of ? Dor stars has become available, allowing us to study these stars with unprecedented detail. We selected, analyzed, and characterized a sample of 67 ? Dor stars for which we have Kepler observations available. For all the targets in the sample we assembled high-resolution spectroscopy to confirm their F-type nature. We found fourteen binaries, among which are four single-lined binaries, five double-lined binaries, two triple systems, and three binaries with no detected radial velocity variations. We estimated the orbital parameters whenever possible. For the single stars and the single-lined binaries, fundamental parameter values were determined from spectroscopy. We searched for period spacing patterns in the photometric data and identified this diagnostic for 50 of the stars in the sample, 46 of which are single stars or single-lined binaries. We found a strong correlation between the spectroscopic and the period spacing values, confirming the influence of rotation on ? Dor-type pulsations as predicted by theory. We also found relations between the dominant g-mode frequency, the longest pulsation period detected in series of prograde modes, , and .

The rvfit Code: A Detailed Adaptive Simulated Annealing Code for Fitting Binaries and Exoplanets Radial Velocities

The fitting of radial velocity curves is a frequent procedure in binary star and exoplanet research. In the majority of cases, the fitting routines need to be fed with a set of initial parameter values and priors from which to begin the computations and their results can be affected by local minima. We present a new code, the rvfit code, for fitting radial velocities of stellar binaries and exoplanets using an adaptive simulated annealing (ASA) global minimization method, which quickly converges to a global solution minimum without the need to provide preliminary parameter values. We show the performance of the code using both synthetic and real datasets: double-lined binaries, single-lined binaries, and exoplanet systems. In all examples, the Keplerian orbital parameters fitted by the rvfit code and their computed uncertainties are compared with literature solutions. Finally, we provide the source code, with a working example and a detailed description of how to use it.

RADIAL VELOCITIES OF SOUTHERN VISUAL MULTIPLE STARS*

ABSTRACT High-resolution spectra of visual multiple stars were taken in 2008–2009 to detect or confirm spectroscopic subsystems and to determine their orbits. Radial velocities of 93 late-type stars belonging to visual multiple systems were measured by numerical cross-correlation. We provide the individual velocities, the width, and the amplitude of the Gaussians that approximate the correlations. The new information on the multiple systems resulting from these data is discussed. We discovered double-lined binaries in HD 41742B, HD 56593C, and HD 122613AB, confirmed several other known subsystems, and constrained the existence of subsystems in some visual binaries where both components turned out to have similar velocities. The orbits of double-lined subsystems with periods of 148 and 13 days are computed for HD 104471 Aa,Ab and HD 210349 Aa,Ab, respectively. We estimate individual magnitudes and masses of the components in these triple systems and update the outer orbit of HD 104471 AB.

Spectroscopic study of early-type multiple stellar systems

Context. This work is part of a long-term spectroscopic study of a sample of 30 multiple stars with early-type components. In this second paper we present the results of six multiple systems in which new stellar components have been detected. Aims. The main aim is to increase the knowledge of stellar properties and dynamical structure of early-type multiple stellar systems. Methods. Using spectroscopic observations taken over a time baseline of more than 5 years we measured RVs by cross-correlations and applied a spectral disentangling method to double-lined systems. Besides the discovery of objects with double-lined spectra, the existence of new spectroscopic subsystems have been inferred from the radial velocity variations of single-lined components and through the variation of the barycentric velocity of double-lined subsystems. Orbital elements have been calculated when possible. Results. Seven new stellar components and two members that we expect to confirm with new observations have been discovered in the six studied multiples. We present orbital parameters for two double-lined binaries and preliminary orbits for three single-lined spectroscopic binaries. Five of the six analysed systems are quadruples, while the remaining has five components distributed in four hierarchical levels. These multiplicity orders are in fact lower limits, since these systems lack high-resolution visual observations and additional hierarchical level might exist in that separation range. Conclusions. The six analysed systems have greater multiplicity degree and a more complex hierarchical structure than previously known, which suggests that high-order multiple systems are significantly more frequent that it is currently estimated. The long term spectroscopic monitoring of multiple systems has shown to be useful for the detection of companions in intermediate hierarchical levels.

Spectroscopic orbits of 10 nearby solar-type dwarfs

Several nearby solar-type dwarfs with variable radial velocity were monitored to find their spectroscopic orbits. Orbital elements of HIP 179, 1989, 2981, 5276, 6439, 11218, 21443, 96434 are determined, as well as tentative orbits for HIP 28678 and 41214. We discuss each of those objects. Three of the four double-lined binaries are twins with nearly equal components. All four orbits with periods shorter than 10 days are circular, the remaining orbits are eccentric.

EXPECTED LARGE SYNOPTIC SURVEY TELESCOPE (LSST) YIELD OF ECLIPSING BINARY STARS

In this paper we estimate the Large Synoptic Survey Telescope (LSST) yield of eclipsing binary stars, which will survey ~20,000 square degrees of the southern sky during the period of 10 years in 6 photometric passbands to r ~ 24.5. We generate a set of 10,000 eclipsing binary light curves sampled to the LSST time cadence across the whole sky, with added noise as a function of apparent magnitude. This set is passed to the Analysis of Variance (AoV) period finder to assess the recoverability rate for the periods, and the successfully phased light curves are passed to the artificial intelligence-based pipeline EBAI to assess the recoverability rate in terms of the eclipsing binaries' physical and geometric parameters. We find that, out of ~24 million eclipsing binaries observed by LSST with S/N>10 in mission life-time, ~28% or 6.7 million can be fully characterized by the pipeline. Of those, ~25% or 1.7 million will be double-lined binaries, a true treasure trove for stellar astrophysics.

STELLAR ASTROPHYSICS WITH A DISPERSED FOURIER TRANSFORM SPECTROGRAPH. II. ORBITS OF DOUBLE-LINED SPECTROSCOPIC BINARIES

We present orbital parameters for six double-lined spectroscopic binaries (iota Pegasi, omega Draconis, 12 Bootis, V1143 Cygni, beta Aurigae, and Mizar A) and two double-lined triple star systems (kappa Pegasi and eta Virginis). The orbital fits are based upon high-precision radial velocity observations made with a dispersed Fourier Transform Spectrograph, or dFTS, a new instrument which combines interferometric and dispersive elements. For some of the double-lined binaries with known inclination angles, the quality of our RV data permits us to determine the masses M_1 and M_2 of the stellar components with relative errors as small as 0.2%.

NEW PRECISION ORBITS OF BRIGHT DOUBLE-LINED SPECTROSCOPIC BINARIES. VI. HD 24623 AND V923 SCORPII

Using new radial velocities obtained at KPNO and Fairborn Observatory, we have determined improved spectroscopic orbits for two double-lined F-type binaries, HD 24623 and V923 Sco. The orbital periods are 19.66304 and 34.8386 days, respectively, so it is not surprising that their orbits have relatively high eccentricities of nearly 0.5. The orbital dimensions (a1 sin i and a2 sin i) and minimum masses (m1 sin 3 i and m2 sin 3 i )h ave accuracies of 0.2% or better. Extensive photometry of HD 24623 with the T4 0.75 m automatic photometric telescope at Fairborn Observatory shows no evidence of eclipses. Instead, a very weak reflection effect is seen, making the system a new variable star. Our spectroscopic ephemeris for V923 Sco indicates that the eclipse detected by Bolton and Herbst is a partial eclipse of the primary but detection of the secondary eclipse is uncertain. For HD 24623, we have determined spectral types of F2 dwarf and F4 dwarf for the primary and secondary, respectively. Our spectral types are F4 dwarf for the two components of V923 Sco. Both components of HD 24623 are rotating more slowly than their pseudosynchronous velocities, as is the primary of V923 Sco. However, the secondary of V923 Sco is likely rotating pseudosynchronously.

The chemically peculiar double-lined spectroscopic binary HD 90264

Context. HD 90264 is a chemically peculiar (CP) double-lined spectroscopic binary system of the type He-weak. Double-lined binaries are unique sources of data for stellar masses, physical properties, and evolutionary aspects of stars. Therefore, the determination of orbital elements is of great importance to study how the physical characteristics of CP stars are affected by a companion. Aims. We carried out a detailed spectral and polarimetric study of the spectroscopic binary system HD 90264 to characterize its orbit, determine the stellar masses, and investigate the spectral variability and possible polarization of the binary components. Methods. We employed medium-resolution echelle spectra and polarimetric data obtained at the 2.15-m telescope at CASLEO Observatory, Argentina. We measured radial velocities and line equivalent widths with IRAF packages. The radial velocity curves of both binary components were obtained combining radial velocity data derived from the single line of Hg ii λ3984 A and the double lines of Mg ii λ4481 A. Polarimetric data were studied by means of the statistical method of Clarke & Stewart and the Welch test. Results. We found that both components of the binary system are chemically peculiar stars, deficient in helium, where the primary is a He variable and the secondary is a Hg-Mn star. We derived for the first time the orbital parameters of the binary system. We found that the system has a quasi-circular orbit (e ∼ 0.04) with an orbital period of 15.727 days. Taking into account the circular orbit solution, we derived a mass ratio of q = MHe−w/MHg−Mn = 1.22. We also found a rotational period of around 15−16 days, suggesting a spin-orbit synchronization. Possible signs of intrinsic polarization have also been detected. Conclusions. HD 90264 is the first known binary system comprised of a He variable star as the primary component and a Hg-Mn star as the secondary one.

THE XO PLANETARY SURVEY PROJECT: ASTROPHYSICAL FALSE POSITIVES

Searches for planetary transits find many astrophysical false positives as a by-product. There are four main types analyzed in the literature: a grazing-incidence eclipsing binary star, an eclipsing binary star with a small radius companion star, a blend of one or more stars with an unrelated eclipsing binary star, and a physical triple star system. We present a list of 69 astrophysical false positives that had been identified as candidates of transiting planets of the on-going XO survey. This list may be useful in order to avoid redundant observation and characterization of these particular candidates independently identified by other wide-field searches for transiting planets. The list may be useful for those modeling the yield of the XO survey and surveys similar to it. Subsequent observations of some of the listed stars may improve mass-radius relations, especially for low-mass stars. From the candidates exhibiting eclipses, we report three new spectroscopic double-line binaries and give mass function estimations for 15 single lined spectroscopic binaries.

NEW PRECISION ORBITS OF BRIGHT DOUBLE-LINED SPECTROSCOPIC BINARIES. IV. 66 ANDROMEDAE, HR 6979, AND HR 9059

We have determined improved spectroscopic orbits for three double-lined binaries, 66 And (F4 V), HR 6979 (Am), and HR 9059 (F5 IV) using radial velocities from the 2.1 m telescope at McDonald Observatory, the coudé feed telescope at Kitt Peak National Observatory, and 2 m telescope at Fairborn Observatory. The orbital periods range from 11.0 to 14.3 days, and all three systems have eccentric orbits. The new orbital dimensions (a1 sin i and a2 sin i) and minimum masses (m1 sin3 i and m2 sin3 i) have accuracies of 0.2% or better. All six components of the three binary systems are rotating more slowly than their predicted pseudosynchronous rotational velocities. Hipparcos photometry of HR 9059 shows that this system has partial eclipses. Its components are nearly identical in mass and are at the very end of their main-sequence lifetimes or perhaps have just begun to traverse the Hertsprung gap.

NEW PRECISION ORBITS OF BRIGHT DOUBLE-LINED SPECTROSCOPIC BINARIES. III. HD 82191, ω DRACONIS, AND 108 HERCULIS

We have determined improved spectroscopic orbits for three double-lined binaries, HD 82191 (Am), ω Dra (F5 V), and 108 Her (Am), using radial velocities from the 2.1 m telescope at McDonald Observatory, the coude feed telescope at Kitt Peak National Observatory, and 2 m telescope at Fairborn Observatory. The orbital periods range from 5.28 to 9.01 days, and all three systems have circular orbits. The new orbital dimensions (a 1 sin i and a 2 sin i) and minimum masses (m 1 sin3 i and m 2 sin3 i) have accuracies of 0.2% or better. Our improved results confirm the large minimum masses of HD 82191 and also agree with the values previously found for ω Dra. However, for the components of 108 Her our minimum masses are about 20% larger than the previous best values. We conclude that both components of HD 82191 as well as the primary of 108 Her are Am stars. However, the A9 secondary of 108 Her has normal abundances. We estimate spectral types of F4 dwarf and G0 dwarf for the components of ω Dra. The primaries of the three binaries are synchronously rotating as is the secondary of 108 Her. The secondaries of HD 82191 and ω Dra are possibly synchronously rotating.

RADIAL VELOCITY STUDIES OF CLOSE BINARY STARS. XIV

Radial-velocity measurements and sine-curve fits to the orbital radial velocity variations are presented for ten close binary systems: TZ Boo, VW Boo, EL Boo, VZ CVn, GK Cep, RW Com, V2610 Oph, V1387 Ori, AU Ser, and FT UMa. Our spectroscopy revealed two quadruple systems, TZ Boo and V2610 Oph, while three stars showing small photometric amplitudes, EL Boo, V1387 Ori, and FT UMa, were found to be triple systems. GK Cep is close binary with a faint third component. While most of the studied eclipsing systems are contact binaries, VZ CVn and GK Cep are detached or semi-detached double-lined binaries, and EL Boo, V1387 Ori and FT UMa are close binaries of uncertain binary type. The large fraction of triple and quadruple systems found in this sample supports the hypothesis of formation of close binaries in multiple stellar systems; it also demonstrates that low photometric amplitude binaries are a fertile ground for further discoveries of multiple systems.

The eclipsing double-lined binaries V883 Cen and Mus

We derive the orbital period and monitor in detail the eclipses of two deep-southern double-lined eclipsing binaries of considerable interest. We present new uvby photometry over more than 100 nights for V883 Cen, scan for the first time the eclipses of η Mus and analyse the data for these two systems together with earlier published photometry. We also add information from high-dispersion spectra. V883 Cen consists of two sharp-lined, mid-B-type stars in an orbit of 35.44733 d. The slower rotating component, Prot= 55.215 d, is a chemically peculiar star of the type He-weak SrTi that is partially eclipsed by its slightly more massive companion. Owing to the high eccentricity of the orbit and its orientation, only one eclipse occurs. The orbital period of η Mus is 57.5 h, rather than the 20 d quoted up to the present in the literature. That close binary, consisting of two late-B-type stars, shows identical partial eclipses. Interest in the close binary is triggered by the pre-main-sequence companion at 2.7 arcsec. HD 118978, one of the comparison stars used for V883 Cen, is identified as a new variable. This fast-rotating B9 (sub)giant belongs presumably to the class of slowly pulsating B-type stars.

Photometry and Spectroscopy of 11 γ Doradus Stars

We have used precise photometric and high-dispersion spectroscopic observations to study 11 γ Doradus stars, 10 of them newly confirmed. Only five of these 11 γ Doradus stars appear to be single; two are primaries of double-lined spectroscopic binaries, one is the secondary of a double-lined binary, two are primaries of visual binaries and, in the case of the double-lined binary (HD 86371), either or both components could be a pulsating γ Doradus star. We have determined a preliminary orbital period of 5.32 days for the double-lined binary HD 41547. Several of the stars show spectroscopic line-profile and low-amplitude radial velocity variability indicative of pulsation. All 11 stars are photometrically variable with amplitudes between 4 and 94 mmag in Johnson B and periods between 0.38 and 1.86 days. The 11 stars have between two and five independent periods. The variability at all periods approximates a sinusoid. We provide a new tabulation of all 66 γ Doradus stars confirmed to date and list some of their properties. All are dwarfs or subgiants and lie within a well-defined region of the H-R diagram that overlaps the cool edge of the δ Scuti instability strip. Four of the new γ Doradus variables from this paper also lie within the δ Scuti instability strip but do not exhibit the additional higher frequency variability typical of δ Scuti stars. Among the 66 confirmed γ Doradus variables, we find no correlation between the period of the strongest pulsation mode and the (B - V) color index, absolute magnitude, or luminosity.

Radial Velocity Studies of Southern Close Binary Stars. II. Spring/Summer Systems

Radial velocity measurements and sine-curve fits to the orbital velocity variations are presented for 14 close binary stars, S Ant, TT Cet, TW Cet, AA Cet, RW Dor, UX Eri, YY Eri, BV Eri, CT Eri, SZ Hor, AD Phe, TY Pup, HI Pup, and TZ Pyx. All are double-lined binaries, and all except the last one are contact binaries. The orbital data must be considered preliminary because of the relatively small number of observations (6-12), a circumstance that is partly compensated by the good definition of the broadening functions used for the radial velocity determinations.