Our preliminary orbital parameters for DF Tau, T Tau Sa-Sb, ZZ Tau and the Pleaides binary are presented in the paper Orbital Motion in Pre-Main Sequence Binaries by G.H. Schaefer, L. Prato, M. Simon, & J. Patience (2013, in prep. for AJ). In the few pages available here I present an overview of our motivation for this work and of our results. The slides and complete references for my talk at the Leuven conference are available at www.astro.sunysb.edu/msimon/public.

The VLT-FLAMES Tarantula Survey (VFTS) has acquired multi-epoch spectroscopy of over 800 O, B and Wolf-Rayet stars in the 30 Doradus region with the aim to investigate a number of important questions related to the evolution of massive stars and of cluster dynamics. In this paper, I first provide an overview of the scientific results obtained by the VFTS consortium so far. I then review the constraints obtained on the multiplicity properties of massive stars in 30 Dor and compare them to our recent results from a Milky Way sample.

We investigate the multiplicity as a function of stellar mass. For this purpose we have created three complete samples of O, B, and FGK stars and performed multi-epoch, high-resolution (R ∼ 50 000) optical spectroscopy. The current results for the O-type stars suggest a multiplicity fraction of more than 80%. Many O-type systems contain components of similar mass. The multiplicity fraction for B stars seems to decrease from 70% to 20%. We argue that this general decrease is most likely due to observational biases; however, similar-mass systems – like common for O-type stars – seem to vanish toward later B-types. Within the sample of F stars we observe an increasing multiplicity fraction with primary mass (∼50% – 80%); simultaneously there is a decrease of single stars toward the A-type regime. Closer inspection of spectroscopic binaries – either by spectral disentangling or by common proper motion studies – reveals higher-level systems in each mass range.

Binarity is often invoked to explain peculiarities that can not be explained by the standard theory of stellar evolution. Detecting orbital motion via the Doppler effect is the best method to test binarity when direct imaging is not possible. However, when the orbital period exceeds length of a typical observing run, monitoring often becomes problematic. Placing a high-throughput spectrograph on a small semi-robotic telescope allowed us to carry out a radial velocity survey of various types of peculiar evolved stars. In this review we highlight some findings after the first four years of observations. Thus, we detect eccentric binaries among hot subdwarfs, barium, S stars, and post-AGB stars with disks, which are not predicted by the standard binary interaction theory. In disk objects, in addition, we find signs of the on-going mass transfer to the companion, and an intriguing line splitting, which we attribute to the scattered light of the primary.

Observations of spectroscopic double stars with long baseline optical interferometry have resolved many pairs, allowing their orbits to be measured and stellar masses and distances to be derived. A number of these measurements have accuracies worthy of comparison with high quality results from eclipsing binaries, thus able challenge stellar evolution models. I will review the contributions, and also show recent results, among them observations of massive O-stars and multiple systems.

This paper provides a summary of binary star research conducted at the CHARA Array. The high angular resolution provided by the longest baselines of the interferometer can resolve binaries down to sub-milli-arcsecond separations. Combining the visual orbit of a binary with spectroscopic radial velocity variations of the components provides a measurement of the stellar masses and distance to the system. This paper provides an overview of interferometric methods used to resolve binaries and a table of orbits that have been resolved spatially using the CHARA Array. In addition to mapping the orbits of binary stars, the six telescopes in the array provide excellent coverage on the sky for studying the circumstellar environments within binary systems and investigating tidal effects within interacting binaries.

The bright southern star δ Vel is a multiple system comprising at least three stars, with two of these stars in an eclipsing binary system. We searched for infrared excess and determined fundamental stellar parameters for the three components from a combination of photometry, spectroscopy, adaptive optics imaging (VLT/NACO), thermal infrared imaging (VLT/VISIR) and near-infrared interfero- metry (VLTI/AMBER). The main eclipsing component is a pair of A-type stars in rapid rotation. We modeled the photometric and radial velocity measurements of the eclipsing pair Aa-Ab using a self consistent method based on physical parameters (mass, radius, luminosity, rotational velocity). From this modeling, we derive the fundamental parameters of the eclipsing stars with a typical accuracy of 1%. We find that they have similar masses, respectively 2.43 ± 0.02 and 2.27 ± 0.02 M⊙. As we spatially resolve the eclisping binary orbit, we also derive the parallax of the system, 39.8 ± 0.4 mas, in satisfactory agreement (− 1.2σ) with the Hipparcos value (40.5 ± 0.4 mas). Finally, we measured the differential astrometric displacement of the center of light of the eclipsing binary relatively to δ Vel B with an uncertainty of ≈100 microarcseconds per epoch, from adaptive optics imaging, thus demonstrating the capabilities of this technique for high-precision astrometry. This accuracy appears to be limited by astrophysical noise (activity of the Aa or Ab stars).

Classical Cepheid stars have been considered since more than a century as reliable tools to estimate distances in the universe thanks to their Period-Luminosity (P-L) relationship. Moreover, they are also powerful astrophysical laboratories, providing fundamental clues for studying the pulsation and evolution of intermediate-mass stars. When in binary systems, we can investigate the age and evolution of the Cepheid, estimate the mass and distance, and constrain theoretical models. However, most of the companions are located too close to the Cepheid (∼1–40 mas) to be spatially resolved with a 10-meter class telescope. The only way to spatially resolve such systems is to use long-baseline interferometry. Recently, we have started a unique and long-term interferometric program that aims at detecting and characterizing physical parameters of the Cepheid companions, with as main objectives the determination of accurate masses and geometric distances.

When observed with optical long-baseline interferometers (OLBI), components of a binary star which are sufficiently separated such that their interferometric fringe packets do not overlap are referred to as Separated Fringe Packet (SFP) binaries. These SFP binaries extend out into the regime of systems resolvable by speckle interferometry at single, large-aperture telescopes and can provide additional measurements for preliminary orbits lacking good phase coverage, help constrain elements of already established orbits, and locate new binaries in the undersampled regime between the bounds of spectroscopic surveys and speckle interferometry. In this process, a visibility calibration star is not needed, and the separated fringe packets can provide an accurate vector separation. Presented here we describe the method, usage, and modified orbits for several systems used to validate the procedure.

The advantage of analysis of observed data using their fit with theoretical model of the directly observed quantities is shown as well as the need for simultaneous solution of all available data. Some particular problems of disentangling of stellar spectra and model atmospheres of component stars of multiple systems are discussed.

The investigation of eclipsing spectroscopic binaries provides basic parameters of stars in a direct way. Whereas the measurable absolute masses can be used to calibrate stellar evolutionary scenarios, the effective temperatures derived from spectroscopic analysis are an important input to light curve and asteroseismic modelling. We compare different methods for investigating eclipsing SB2 stars focusing on radial velocity determination and spectrum decomposition and analysis. Used methods are the two-dimensional cross-correlation technique todcor, spectral disentangling with the Fourier transform-based korel program, and a grid search-based method of spectrum analysis using spectrum synthesis. The study is based on the investigation of two eclipsing SB2 stars observed by the Kepler satellite mission.

Spectral modelling and especially for massive stars is not a straightforward problem and over the past decades many advances have been made in this field. We now have sophisticated model atmosphere codes that allow to derive the stellar parameters. However, these codes are based on the assumption that the star is single and spherical which is no longer valid for the components of a binary system. On the other hand, observational studies indicate that binarity has an impact on the spectra. This is why we have developed a model called CoMBiSpeC (code of massive binary spectral computation) that specifically accounts for the impact of binarity on the spectra.

In recent years, astronomical photometry has been revolutionised by space missions such as MOST, CoRoT and Kepler. However, despite this progress, high-quality spectroscopy is still required as well. Unfortunately, high-resolution spectra can only be obtained using ground-based telescopes, and since many interesting targets are rather faint, the spectra often have a relatively low S/N. Consequently, we have developed an algorithm based on the least-squares deconvolution profile, which allows to reconstruct an observed spectrum, but with a higher S/N. We have successfully tested the method using both synthetic and observed data, and in combination with several common spectroscopic applications, such as e.g. the determination of atmospheric parameter values, and frequency analysis and mode identification of stellar pulsations.

We present absolute physical and orbital parameters for double-lined detached eclipsing binary systems from the All Sky Automated Survey (ASAS) catalogue with subgiant and giant components. The radial velocities were calculated from high quality optical spectra we obtained with the 8.2 m Subaru/hds, ESO 3.6 m/harps, 1.9 m Radcliffe/giraffe, CTIO 1.5 m/chiron, and 1.2 m Euler/coralie using the two-dimensional cross-correlation technique (todcor) and synthetic template spectra chosen for every system separately as references. We checked the evolutionary status of the systems with several sets of evolutionary tracks and determined distances for each system. The derived uncertainties for individual masses and radii of components are better than 3% for several systems. Additionally, we performed atmospheric parameters determination and chemical abundances analysis for the system which spectra we disentangled.

As part of a Kepler Guest Observer program to search for tertiary companions to close eclipsing binaries via eclipse timing, we are determining fundamental properties of the central binaries through radial velocity and light curve analysis. We have obtained moderate resolution blue spectra of 41 systems to produce double-lined radial velocity curves and spectroscopic orbital solutions. In addition, we reconstruct the spectra of the individual binary components and compare them to libraries of synthetic spectra to determine effective temperatures, surface gravities, and rotational velocities. Using these data and constraints we then model the Kepler light curves to determine the fundamental properties of each system. Here we present parameters for KIC 5738698, two F-type stars orbiting with a 4.8-day period.

We present our first results in the analysis of the secondary star in the Low-Mass X-Ray binary (LMXB) Cygnus X-2, using a high resolution spectrum obtained with UES@WHT in ORM (La Palma, Tenerife). We have used a χ2 minimization procedure to create a grid of 1 500 000 LTE synthetic spectra that allow us to obtain a plausible range of values of the stellar parameters, taking into account any possible veiling from the accretion disk produced by the presence of a neutron star as the primary. We will study the chemical abundances of several elements and study their anomalies regarding Galactic trends.

Modeling tools for eclipsing binary stars are lagging behind the modern observations that are unprecedented both in quality and in quantity. We assembled a team of modeling and interpretation experts and propose to enhance the modeling code to tackle this new-age data. In this paper we outline some of the most important advancements planned and being implemented into the new version of the phoebe code. These advancements will greatly reduce systematics and allow us to focus on prime astrophysics to be gleaned in studying eclipsing binaries and exoplanet transits. For the first time the errors on the masses and radii will be pushed well below 1%.

Recent ultra-high precision observations of eclipsing binaries, especially data acquired by the Kepler satellite, have made accurate light curve modelling increasingly challenging but also more rewarding. In this contribution, we discuss low-amplitude signals in light curves that can now be used to derive physical information about eclipsing binaries but that were unaccessible before the Kepler era. A notable example is the detection of Doppler beaming, which leads to an increase in flux when a star moves towards the satellite and a decrease in flux when it moves away. Similarly, Rømer delays, or light travel time effects, also have to taken into account when modelling the supreme quality data that is now available. The detection of offsets between primary and secondary eclipse phases in binaries with extreme mass ratios, and the observation of Rømer delays in the signals of pulsators in binary stars, have allowed us to determine the orbits of several binaries without the need for spectroscopy. A third example of a small-scale effect that has to be taken into account when modelling specific binary systems, are lensing effects. A new binary light curve modelling code, PHOEBE 2.0, that takes all these effect into account is currently being developed.

phoebe 2.0 is an open source framework bridging the gap between stellar observations and models. It allows to create and fit models simultaneously and consistently to a wide range of observational data such as photometry, spectroscopy, spectrapolarimetry, interferometry and astrometry. To reach the level of precision required by the newest generation of instruments such as Kepler, GAIA and the arrays of large telescopes, the code is set up to handle a wide range of phenomena such as multiplicity, rotation, pulsations and magnetic fields, and to model the involved physics to a new level.

Heartbeat stars are a relatively new class of eccentric ellipsoidal variable first discovered by Kepler. An overview of the current field is given with details of some of the interesting objects identified in our current Kepler sample of 135 heartbeats stars. Three objects that have recently been or are undergoing detailed study are described along with suggestions for further avenues of research. We conclude by discussing why heartbeat stars are an interesting new tool to study tidally induced pulsations and orbital dynamics.