In this brief communication we provide the rationale for, and the outcome of the International Astronomical Union (IAU) resolution vote at the XXIX th General Assembly in Honolulu, Hawaii, in 2015, on recommended nominal conversion constants for selected solar and planetary properties. The problem addressed by the resolution is a lack of established conversion constants between solar and planetary values and SI units: a missing standard has caused a proliferation of solar values (e.g., solar radius, solar irradiance, solar luminosity, solar effective temperature and solar mass parameter) in the literature, with cited solar values typically based on best estimates at the time of paper writing. As precision of observations increases, a set of consistent values becomes increasingly important. To address this, an IAU Working Group on Nominal Units for Stellar and Planetary Astronomy formed in 2011, uniting experts from the solar, stellar, planetary, exoplanetary and fundamental astronomy, as well as from general standards fields to converge on optimal values for nominal conversion constants. The effort resulted in the IAU 2015 Resolution B3, passed at the IAU General Assembly by a large majority. The resolution recommends the use of nominal solar and planetary values, which are by definition exact and are expressed in SI units. These nominal values should be understood as conversion factors only, not as the true solar/planetary properties or current best estimates. Authors and journal editors are urged to join in using the standard values set forth by this resolution in future work and publications to help minimize further confusion.

We have investigated a group of 18 Algol-type binaries to determine the general morphologies and physical properties of the accretion regions in these systems. The systems studied were V505 Sgr, RZ Cas, AI Dra, TV Cas, TW Cas, d Lib, RW Tau, TW Dra, b Per, TX UMa, U Sge, S Equ, U CrB, RS Vul, SW Cyg, CX Dra, TT Hya, and AU Mon, in order of increasing orbital period P \ 1.18È11.11 days. In addition, the RS CVn-type binary HR 1099 (V711 Tau) was observed to illustrate the appearance of chromospheric Ha emission. Nearly 2200 time-resolved Ha spectra were collected from 1992 March to 1994 December with the McMath-Pierce Solar Telescope at NSO and mostly with the Coude Feed Telescope at KPNO. The spectra were obtained at phases around the entire orbit of each binary and were closely spaced to permit the detection of transitions in the proÐles. Moreover, the spectra were obtained typically within three orbital cycles to reduce the inÑuence of secular variations. Di †erence proÐles were calculated by subtracting a composite theoretical photospheric spectrum from the observed spectrum.The analysis of the Ha di †erence proÐles demonstrates that the accretion structures in Algol binaries have four basic morphological types : (1) double-peaked emission systems in which the accretion structure is a transient or classical accretion disk ; (2) single-peaked emission systems in which the accreted gas was found along the trajectory of the gas stream and also between the two stars in an accretion annulus ; (3) alternating single-and double-peaked emission systems, which can change between a single-peaked and a double-peaked type within an orbital cycle ; and (4) weak spectrum systems in which there was little evidence of any accretion structure since the di †erence spectra are weak at all phases. The Ðrst two types are the dominant morphologies. The Ðrst type can be interpreted physically as a disklike distribution, while the second is a gas streamÈlike distribution.The most common type in short-period Algols with 2.7 days \ P \ 4.5 days is a predominantly singlepeaked emission feature in the Ha di †erence proÐles (Type 2). This feature is redshifted during the phase interval / D 0.15È0.45 and blueshifted from / D 0.55È0.85. This single-peaked emission is often composed of two closely spaced emission peaks where one peak is at the Ha rest wavelength. The other peak is blueshifted at / D 0.65, where the line of sight is along the length of the approaching gas stream. Systems which display this morphology include RZ Cas, RW Tau, TW Dra, b Per, TX UMa, S Equ, and RS Vul. The orbital variation of the Ha observed proÐles of HR 1099 was similar to that seen in the di †erence spectra of this group and suggests that chromospheric emission may play a signiÐcant role in these binaries. A less common morphological type in the group of short-period Algols was a widely separated double-peaked disk-like distribution (Type 1) where the gas is in a transient or classical accretion disk. All of the long-period systems (P [ 6 days) were f...

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Abstract. Periodicities of radio flaring activity from the Algol systems (3 Per and 6 Lib and the RS CVn systems V711 Tau and UX Ari were determined from a continuous 5-year survey. The radio continuum fluxes at 2.3 GHz and 8.3 GHz were monitored with the NRAO-Green Bank

Two-dimensional hydrodynamic simulations of mass transfer in short-period Algol-type binaries were performed using the numerical code Virginia Hydrodynamics 1. This code uses the piecewise parabolic method with a Lagrangian remap. Our version of the code also accounts for radiative cooling and collisional ionization and excitation processes. The purpose of performing the simulations was to study the Ha emission from circumstellar gas in the Algols. Using observational evidence from the literature to constrain the gas stream properties, hydrodynamic maps of the Ha emissivity in the two systems b Per (P \ 2.87 days) and TT Hya (P \ 6.95 days) were made in both Cartesian and velocity coordinates from the simulation data. The velocity maps were then compared to Doppler tomograms constructed from observed Ha line emission in these systems. Since the tomograms cannot be directly transformed to maps of emission in spatial coordinates, the simulated Cartesian maps enabled us to interpret the dynamical processes that produce the features observed in the Doppler tomograms. We Ðnd that the simulations produce asymmetric accretion structures with many features similar to those found in the Doppler tomograms of Algol systems.

We have developed a systematic procedure to study the disks in Algol-type binaries using spectroscopic analysis, synthetic spectra, and tomography. We analyzed 119 Hα spectra of TT Hya, an Algol-type eclipsing interacting binary, collected from 1985-2001. The new radial velocities enabled us to derive reliable orbital elements, including a small non-zero eccentricity, and to improve the accuracy of the absolute dimensions of the system. High resolution IUE spectra were also analyzed to study the formation of the ultraviolet lines and continuum.Synthetic spectra of the iron curtain using our new shellspec program enabled us to derive a characteristic disk temperature of 7000K. We have demonstrated that the UV emission lines seen during total primary eclipse cannot originate from the accretion disk, but most likely arise from a hotter disk-stream interaction region.The synthetic spectra of the stars, disk, and stream allowed us to derive a mass transfer rate ≥ 2 × 10 −10 M ⊙ yr −1 . Doppler tomography of the observed Hα profiles revealed a distinct accretion disk. The difference spectra produced by subtracting the synthetic spectra of the stars resulted in an image of the disk, which virtually disappeared once the composite synthetic spectra of the stars and disk were used to calculate the difference spectra. An intensity enhancement of the resulting tomogram revealed images of the gas stream and an emission arc. We successfully modeled the gas stream using shellspec and associated the emission arc with an asymmetry in the accretion disk.

Interacting binaries typically have separations in the milli-arcsecond regime and hence it has been challenging to resolve them at any wavelength. However, recent advances in optical interferometry have improved our ability to discern the components in these systems and have now enabled the direct determination of physical parameters. We used the Navy Prototype Optical Interferometer to produce for the first time images resolving all three components in the well-known 1 Algol triple system. Specifically, we have separated the tertiary component from the binary and simultaneously resolved the eclipsing binary pair, which represents the nearest and brightest eclipsing binary in the sky. We present revised orbital elements for the triple system, and we have rectified the 180-degree ambiguity in the position angle of Algol C. Our directly determined magnitude differences and masses for this triple star system are consistent with earlier light curve modeling results.

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