E. F. Milone

The High Road to Astronomical Photometric Precision: Differential Photometry

Differential photometry offers the most precise method for measuring the brightness of astronomical objects. We attempt to demonstrate why this should be the case, and then describe how well it has been done through a review of the application of differential techniques from the earliest visual methods to photoelectric and CCD photometry. We pay special attention to the work of Theodore Walraven and his legacy.

A Lack of Planets in 47 Tucanae from a Hubble Space Telescope Search

We report results from a large Hubble Space Telescope project to observe a significant (~34,000) ensemble of main-sequence stars in the globular cluster 47 Tucanae with a goal of defining the frequency of inner orbit, gas giant planets. Simulations based on the characteristics of the 8.3 days of time series data in the F555W and F814W Wide Field Planetary Camera 2 (WFPC2) filters show that ~17 planets should be detected by photometric transit signals if the frequency of hot Jupiters found in the solar neighborhood is assumed to hold for 47 Tuc. The experiment provided high-quality data sufficient to detect planets. A full analysis of these WFPC2 data reveals ~75 variables, but no light curves resulted for which a convincing interpretation as a planet could be made. The planet frequency in 47 Tuc is at least an order of magnitude below that for the solar neighborhood. The cause of the absence of close-in planets in 47 Tuc is not yet known; presumably the low metallicity and/or crowding of 47 Tuc interfered with planet formation, with orbital evolution to close-in positions, or with planet survival.

Eclipsing binary stars : modeling and analysis

Introduction.- The Data Base and Methods of Acquisition.- A General Approach to Modeling Eclipsing Binaries.- Determination of Eclpsing Binary Parameters.- Light Curve Models and Software.- The Wilson-Devinney Program and WD95.- The Structure of Light Curve Programs and the Outlook for the Future.- Appendix A: A Brief Review of Mathematical Optimization.- Appendix B: Estimation of Fitted Parameter Errors: the Details.- Appendix C: Geometry and Coordinate Systems.- Appendix E: Subroutines of the Wilson-Devinney Program.- Appendix F: Graphics Utilities and Visualization.- Appendix G: Glossary of Symbols.- Bibliography.- Subject Index.

Light Curve Modeling of Eclipsing Binary Stars

In the two decades since the development of the first eclipsing-binary modelling code, new analytic techniques and the availability of powerful, sometimes dedicated computing facilities have made possible vastly improved determinations of fundamental and even transient stellar parameters. The scale of these developments, of course, raises questions about modelling tools, techniques and philosophies, such as: Who will maintain and upgrade the codes? Will the codes be open to improvement by outsiders, and if so, how? And, indeed, what should be the goals of a modelling program? Such questions had not been aired for a long time and, for this reason alone, deserved to be discussed in as general a forum as the community provides. This volume contains material presented by Comission 42 (Close Binary Stars) duiring the International Astronomical Unions XXI General Assembly in Argentina, July 1991, and during IAU Colloquium 151, Cordoba, Argentina, August 1991. The techniques discussed include simulations of stellar bright and dark spots, streams, partial and complete stellar disks, prominences, and other features characterizing active stars; modelling of polarization parameters; models that use radial velocity field variation across stellar disks; the weighted effects of brightness asymmetries; and models for translucent eclipsing agents such as stellar winds.

RECENT IMPROVEMENTS TO A VERSION OF THE WILSON-DEVINNEY PROGRAM

We summarize recent improvements to a version of the Wilson-Devinney program that is widely used for the analysis of eclipsing binary data, and we describe the new WD95 program. WD95 contains the University of Calgary version of the Wilson-Devinney code, which supports the use of the Kurucz atmo- sphere models; it provides options to use multiple epoch data and multiwavelength synoptic passbands. The WD95 program contains an improved input/output interface, simplex algorithms for initial searches and tests, and versions of Wilson-Devinney DC and LC programs and options to switch to automatic di†erential corrections or a damped least-squares solver using normal equations that are modi-ed as per the Levenberg-Marquardt scheme. This paper describes some tests of the damped least-squares solver with simulated data. Subject headings: binaries: eclipsing E methods: numerical

NOMINAL VALUES FOR SELECTED SOLAR AND PLANETARY QUANTITIES: IAU 2015 RESOLUTION B3

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.

Short-Period Binary Stars: Observations, Analyses, and Results

Compact Relativistic Binary Systems.- Black Hole Binaries: The Journey from Astrophysics to Physics.- Searches for Gravitational Waves from Binary Neutron Stars: A Review.- Observations of the Double Pulsar PSR J0737-3039A/B.- Gravitational Lensing in Compact Binary Systems.- Accreting Neutron Star Binaries.- Accreting Neutron Stars in Low-Mass X-Ray Binary Systems.- Observations and Modeling of Accretion Flows in X-ray Binaries.- Cataclysmic Variable Systems.- Modeling the Hot Components in Cataclysmic Variables: Info on the White Dwarf and Hot Disk from GALEX, FUSE, HST and SDSS.- The Cool Components in Cataclysmic Variables: Recent Advances and New Puzzles.- Models for Dynamically Stable Cataclysmic Variable Systems.- Modeling Short-Period Eclipsing Binaries.- Distance Estimation for Eclipsing X-ray Pulsars.- The Tools of the Trade and the Products they Produce: Modeling of Eclipsing Binary Observables.- The Closest of the Close: Observational and Modeling Progress.- Aspects of Short-Period Binary Evolution.- Common Envelope Evolution Redux.

Asiago eclipsing binaries program - I. V432 Aurigae

The orbit and physical parameters of the previously unsolved eclipsing binary V432 Aur, discovered by Hipparcos, have been derived with errors better than 1% from extensive Echelle spectroscopy and B, V photometry. Synthetic spectral analysis of both components has been performed, yielding Teff and log g in close agreement with the orbital solution, a metal- licity (Z/Z� ) = −0.6 and rotational synchronization for both components. Direct comparison on the theoretical L,Teff plane with the Padova evolutionary tracks and isochrones for the masses of the two components (1.22 and 1.08 M� ) provides a perfect match and a 3.75 Gyr age. The more massive and cooler component is approaching the base of the giant branch and displays a probable pulsation activity with an amplitude of ∆V = 0.075 mag and ∆rad.vel. = 1.5 km s −1 . With a Teff = 6080 K it falls to the red of the nearby instability strip populated by δ Sct and γ Dor types of pulsating variables. Orbital modeling reveals a large and bright surface spot on it. The pulsations activity and the large spot(s) suggest the presence of macro-turbulent motions in its atmosphere. They reflect in a line broadening that at cursory inspection could be taken as indication of a rotation faster than synchronization, something obviously odd for an old, expanding star.The orbit and physical parameters of the previously unsolved eclipsing binary V432 Aur, discovered by Hipparcos, have been derived with errors better than 1% from extensive Echelle spectroscopy and B, V photometry. Synthetic spectral analysis of both components has been performed, yielding T_eff and log g in close agreement with the orbital solution, a metallicity [Z/Z_sun]=-0.60 and rotational synchronization for both components. Direct comparison on the theoretical L, T_eff plane with the Padova evolutionary tracks and isochrones for the masses of the two components (1.22 and 1.08 M_sun) provides a perfect match and a 3.75 Gyr age. The more massive and cooler component is approaching the base of the giant branch and displays a probable pulsation activity with an amplitude of Delta V = 0.075 mag and Delta rad.vel. = 1.5 km/sec. With a T_eff = 6080 K it falls to the red of the nearby instability strip populated by delta Sct and gamma Dor types of pulsating variables. Orbital modeling reveals a large and bright surface spot on it. The pulsations activity and the large spot(s) suggest the presence of macro-turbulent motions in its atmosphere. They reflect in a line broadening that at cursory inspection could be taken as indication of a rotation faster than synchronization, something obviously odd for an old, expanding star.

Analysis and solution of the light and radial velocity curves of the contact binary TY Bootis

Observations and analyses of the binary TY Bootis are presented. Radial velocity data are used for the first time to establish the mass ratio without ambiguity, and an advanced version of the Wilson-Devinney synthetic light curve program is used to analyze and solve the system. A reasonably robust set of parameters is obtained. TY Boo is found to be a W-type W UMa system with a mass ratio near two and a contact parameter of 0.12 + or - 0.903, indicating only shallow contact. 69 refs.

Modeling of the eclipsing binaries in the globular cluster NGC 5466

The discovery of three eclipsing binaries in the globular cluster NGC 5466 (Mateo M. et al., 1990, AJ, 100) is a boon to studies of both this ancient (18 Gy) cluster and close binaries. Two of the systems discovered by Mateo et al. appear to be contact systems and one appears to be a short-period Algol system. Basic parameters, especially the masses, of the stars in these systems are urgently required for the evaluation of the binary merger hypothesis for the origin of blue stragglers, and as a test of cluster evolution models. Here we present the results of a study of viable models of these interesting systems, based on a simplex-enhanced, Kurucz-atmospheres version of the Wilson-Devinney Program