Main-sequence Pairs Research Articles

Finding binaries from phase modulation of pulsating stars with Kepler: V. Orbital parameters, with eccentricity and mass-ratio distributions of 341 new binaries

The orbital parameters of binaries at intermediate periods ($10^2$--$10^3$ d) are difficult to measure with conventional methods and are very incomplete. We have undertaken a new survey, applying our pulsation timing method to {\it Kepler} light curves of 2224 main-sequence A/F stars and found 341 non-eclipsing binaries. We calculate the orbital parameters for 317 PB1 systems (single-pulsator binaries) and 24 PB2s (double-pulsators). The method reaches down to small mass ratios $q=0.02$ and yields a highly homogeneous sample. We parametrize the mass-ratio distribution using both inversion and MCMC forward-modelling techniques, and find it to be skewed towards low-mass companions, peaking at $q=0.2$. While solar-type primaries show a brown dwarf desert across intermediate periods, we find a small but significant (2.6$\sigma$) population of extreme-mass-ratio companions ($q<0.1$) to our intermediate-mass primaries. Across periods of 100--1500 d and at $q>0.1$, we measure the binary fraction of current A/F primaries to be 15.4%$\pm$1.4%, though we find that a large fraction of the companions (21%$\pm$6%) are white dwarfs in post-mass-transfer systems with primaries that are now blue stragglers, some of which are the progenitors of Type Ia supernovae, barium stars, symbiotics, and related phenomena. Excluding these white dwarfs, we find the binary fraction of original A/F primaries to be 13.9%$\pm$2.1% over the same parameter space. Combining literature measurements with ours, we find the binary fraction across these periods is a constant 5% for primaries $M_1<0.8$ M$_{\odot}$, but then increases linearly with $\log M_1$, demonstrating that natal discs around more massive protostars $M_1>1$ M$_{\odot}$ become increasingly more prone to fragmentation. Finally, we find the eccentricity distribution of the main-sequence pairs to be much less eccentric than the thermal distribution.

Application of USNO-B1.0 towards selecting objects with displaced blue and red components

We have conducted a feasibility study to determine the effectiveness of using USNO-B1.0 data to preferentially detect objects with displaced red and blue components. A procedure was developed to search catalogue entries for such objects, which include M dwarfs paired with white dwarfs or with earlier main-sequence stars, and galaxies with asymmetric colour distributions. Residual differences between red and blue and infrared and blue scanned emulsion images define vectors, which, when appropriately aligned and of sufficient length, signal potential candidates. Test sample sets were analysed to evaluate the effective discrimination of the technique. Over 91,000 USNO-B1.0 catalogue entries at points throughout the celestial sphere were then filtered for acceptable combinations of entry observations and magnitudes and the resulting total of about 17,000 entries was winnowed down to a little more than 200 objects of interest. These were screened by visual examination of photo images to a final total of 146 candidates. About one quarter of these candidates coincide with SDSS data. Those constituents fall into two groups, single and paired objects. SDSS identified several galaxies in the first group. Regarding the second group, at least half of its members were tentatively identified as main-sequence pairs, the greater portion being of widely separated spectral types. Two white dwarf--main-sequence pairs were also identified. Most importantly, the vectors formed from USNO-B1.0 residuals were in alignment with corresponding SDSS pair position angles, thereby supporting this work`s central thesis.

INTERESTING FEATURES IN THE COMBINEDGALEXAND SLOAN COLOR DIAGRAMS OF SOLAR-LIKE GALACTIC POPULATIONS

We report on intriguing photometric properties of Galactic stars observed in the GALEX satellite's far-UV and near-UV bandbasses as well as from the SDSS survey and the Kepler Input Catalog. First, the FUV-NUV color distribution of stars in the Kepler field consists of 2 distinct peaks. Second, curiously, for stars with spectral types G or later the mean FUV-NUV color becomes much bluer, contrary to expectation. we have found in two samples of mid-F through K type stars that ~14-18% of them exhibit FUV-excesses relative to their NUV fluxes and spectral types. Nearly the same fractions are also discovered among members of the Kepler Eclipsing Binary Catalog and in the published list of Kepler Objects of Interest. These UV-excess ("UVe") colors are confirmed by the UV continuum slopes in GALEX spectra. The SDSS spectra of some UVe stars exhibit metallic line weakening especially in the blue. This suggests an enhanced contribution of UV flux relative to photospheric flux of a solar-type single star. We consider the possibility that the UV excesses originate from various types of hot stars, including binaries, and strong chromosphere stars that. Our model atmosphere-derived simulations of colors for binaries with main sequence pairs with a hot secondary demonstrate that the color loci conflict with the observed sequence. We are left with the active chromospheres explanation, whether in active binaries or young stars, as a still tentative explanation for the UVe stars. We also address the presence of an island of "UV red" stars in the NUV-g, g-i color diagram. The subpopulation comprising this island are mainly horizontal branch stars. These objects do not exhibit UV excesses and therefore have UV colors typical for their spectral types. This subpopulation appears "red" in the UV because their colors are not pulled to the blue by the UVe stars.

NEW β LYRAE AND ALGOL CANDIDATES FROM THE NORTHERN SKY VARIABILITY SURVEY

We have classified 409 objects in the Northern Sky Variability Survey (NSVS) as new β Lyrae or Algol-type eclipsing binaries. These candidates have outside of eclipse magnitudes of ~10-13. Through automated Fourier analysis routines and some manual inspection, we list the period, eclipse depths, coordinates, an estimate of the time of primary eclipse, and the 2MASS colors for these candidates. This list of new β Lyrae type candidates greatly increases the number of known systems of this type. We have also identified 37 candidate low-mass, main-sequence pairs (M 1,2 < 1 M ☉, T < 5500 K) in the NSVS database. If confirmed, these systems will greatly increase the number of such low-mass systems known as well as help constrain atmospheric models for these types of stars.

Where Are the Magnetic White Dwarfs with Detached, Nondegenerate Companions?

The Sloan Digital Sky Survey has already more than doubled the sample of white dwarfs with spectral classifications, the subset with detached M dwarf companions, and the subset of magnetic white dwarfs. In the course of assessing these new discoveries, we have noticed a curious, unexpected property of the total lists of magnetic white dwarfs and of white dwarf plus main-sequence binaries: there appears to be virtually zero overlap between the two samples! No confirmed magnetic white dwarf has yet been found in such a pairing with a main-sequence star. The same statement can be made for the samples of white dwarf–M dwarf pairs in wide, common proper motion systems. This contrasts with the situation for interacting binaries, in which an estimated 25% of the accreting systems have a magnetic white dwarf primary. Alternative explanations are discussed for the observed absence of magnetic white dwarf–main-sequence pairs, but the recent discoveries of very low accretion rate magnetic binaries pose difficulties for each. A plausible explanation may be that the presence of the companion and the likely large mass and small radius of the magnetic white dwarf (relative to nonmagnetic degenerate dwarfs) may provide a selection effect against the discovery of the latter in such binary systems. More careful analysis of the existing samples may yet uncover members of this class of binary, and the sample sizes will continue to grow. The question of whether the mass and field distributions of the magnetic primaries in interacting binaries are similar to those of the isolated magnetic white dwarfs (including those in wider binaries) must also be answered.

Disk and Halo Wide Binaries from the Revised Luyten Catalog: Probes of Star Formation and MACHO Dark Matter

We present a catalog of 1147 candidate common proper motion binaries selected from the revised New Luyten Two-Tenths Catalog (NLTT). Among these, we identify 999 genuine physical pairs using the measured proper-motion difference and the relative positions of each binary's components on a reduced proper motion (RPM) diagram. The RPM positions also serve to classify them as either disk main-sequence pairs (801), halo subdwarf (116) pairs, or pairs containing at least one white dwarf (82). The disk and halo samples are complete to separations of Δθ = 500'' and Δθ = 900'', which correspond to ~0.1 and ~1 pc, respectively. At wide separations, both distributions are well described by single power laws dN/dΔθ (Δθ)-α, with α = 1.67 ± 0.07 for the disk and α = 1.55 ± 0.10 for the halo. The fact that these distributions have similar slopes (and similar normalizations as well) argues for similarity of the star formation conditions of these two populations. The fact that the halo binaries obey a single power law out to ~1 pc permits strong constraints on halo dark matter candidates. At somewhat closer separations (10'' Δθ 25''), the disk distribution shows a pronounced flattening, which is detected at very high statistical significance and is not due to any obvious systematic effect. We also present a list of 11 previously unknown halo stars with parallaxes that are recognized here as companions of Hipparcos stars.

CLC][ITAL]uvby[/ITAL][/CLC]β Photometry of Selected Eclipsing Binary Stars

New uvbyβ observations of 51 eclipsing binary stars are presented, and outside-eclipse averages for 45 of them are given. Many of these binaries are detached main-sequence pairs that have been discovered to be double-lined spectroscopic binaries and appear suitable for determinations of accurate absolute dimensions and masses. Photometric properties are recomputed for 14 of the binaries, for which absolute properties have been published previously. Intercomparisons are made with previous photometry, when available, and notes are given for some individual systems.

The frequencies of supernovae in binaries

The formation frequencies of about two dozen different kinds of supernovae have been obtained with a numerical program which calculates such frequencies according to algorithms based on several observed properties of binary stars (distribution of initial main-sequence pairs with regard to primary mass, mass ratio q, and orbital separation A) and on rough estimates of the consequences of Roche lobe overflow (a transformation between initial mass and remnant mass

Radio emission from EA eclipsing binaries - Evidence for kilogauss surface fields on both early-type and late-type stars

Radio observations of a sample of EA eclipsing binaries, including early-type main-sequence pairs as well as classical Algol-type eclipsing binaries, indicate the presence of a moderately strong coronal magnetic field, B of about 100 G, between the component stars. This translates to a surface magnetic field of about 1000-10,000 G on one or both stars. This is the first compelling evidence for magnetic fields on early-type stars, apart from the Ap and Bp magnetic stars first detected in 1947. 47 refs.

Radio Emission from EA Eclipsing Binaries: Evidence for Kilogauss Early- and Late-Type Stars

A recent survey of EA eclipsing binaries by the Parkes 64-m telescope operating at 8.4 GHz detected 15 out of 47 systems on at least one out of the 10 nights surveyed. The detected systems were HD 6882 (ξ Phe), HD 36486 (δ Ori A), HD 39780 (TZ Men), HD 57167 (R CMa), HD 58713 (RY Gem), HD 74307 (S Cnc), HD 132742 (δ Lib), HD 147683 (V769 Sco), HD 161741 (V393 Sco), HD 163708 (V1647 Sgr), HD 16871Q(XZ Sgr), HD 183794 (V822 Aql), HD 187949 (V505 Sgr), HD 199005 (KZ Pav), and HD 207098 (δ Cap).A full account of the observations and interpretation has been submitted to The Astrophysical Journal.About one-half of the 15 detections refer to main-sequence pairs of spectral types earlier than F and the remainder are classical Algols.

THE VISUAL BINARY 55 TAURI AND THE HYADES DISTANCE

ABSTRACT Observations through the recent periastron passage give a revised orbit (P = 89.06 yr, a = 0arcsec.559). From the masses of this and five other main-sequence pairs, a cluster distance modulus of 3.35±0.07 is computed.

Stellar evolution: Are population II binary systems inherited or acquired?

Stellar evolution: Are population II binary systems inherited or acquired?