Time filter

Source Type

Mamajek E.E.,Cerro Tololo Inter American Observatory | Mamajek E.E.,University of Rochester
Astrophysical Journal Letters | Year: 2012

The nearby (d = 7.7pc) A3V star Fomalhaut is orbited by a resolved dusty debris disk and a controversial candidate extrasolar planet. The commonly cited age for the system (200 ± 100Myr) from Barrado y Navascues et al. relied on a combination of isochronal age plus youth indicators for the K4V common proper-motion system TW PsA. TW PsA is 196 away from Fomalhaut and was first proposed as a companion by Luyten, but the physicality of the binarity is worth testing with modern data. I demonstrate that TW PsA is unequivocally a physical stellar companion to Fomalhaut, with true separation 0.280+0.019 - 0.012pc (57.4+3.9 - 2.5kAU) and sharing velocities within 0.1±0.5kms-1 - consistent with being a bound system. Hence, TW PsA should be considered "FomalhautB." Combining modern H-R diagram constraints with four sets of evolutionary tracks, and assuming the star was born with protosolar composition, I estimate a new isochronal age for Fomalhaut of 450 ± 40Myr and mass of 1.92±0.02 M .Various stellar youth diagnostics are re-examined for TW PsA. The star's rotation, X-ray emission, and Li abundances are consistent with approximate ages of 410, 380, and 360Myr, respectively, yielding a weighted mean age of 400 ± 70Myr. Combining the independent ages, I estimate a mean age for the Fomalhaut-TW PsA binary of 440 ± 40Myr. The older age implies that substellar companions of a given mass are approximately 1mag fainter at IR wavelengths than previously assumed. © 2012. The American Astronomical Society. All rights reserved..


Tokovinin A.,Cerro Tololo Inter American Observatory | Mason B.D.,Us Naval Observatory | Hartkopf W.I.,Us Naval Observatory
Astronomical Journal | Year: 2014

We report the results of speckle runs at the 4.1 m Southern Astronomical Research telescope in 2012 and 2013. A total of 586 objects were observed. We give 699 measurements of 487 resolved binaries and upper detection limits for 112 unresolved stars. Eleven pairs (including one triple) were resolved for the first time. Orbital elements have been determined for the first time for 13 pairs; orbits of another 45 binaries are revised or updated. © 2014. The American Astronomical Society. All rights reserved.


Tokovinin A.,Cerro Tololo Inter American Observatory
Astronomical Journal | Year: 2014

Statistics of hierarchical multiplicity among solar-type dwarfs are studied using the distance-limited sample of 4847 targets presented in the accompanying Paper I. Known facts about binaries (multiplicity fraction 0.46, lognormal period distribution with median period 100 yr and logarithmic dispersion 2.4, and nearly uniform mass-ratio distribution independent of the period) are confirmed with a high statistical significance. The fraction of hierarchies with three or more components is 0.13 ± 0.01, and the fractions of targets with n = 1, 2, 3, ... components are 54:33:8:4:1. Subsystems in the secondary components are almost as frequent as in the primary components, but in half of such cases both inner pairs are present. The high frequency of those 2+2 hierarchies (4%) suggests that both inner pairs were formed by a common process. The statistics of hierarchies can be reproduced by simulations, assuming that the field is a mixture coming from binary-rich and binary-poor environments. Periods of the outer and inner binaries are selected recursively from the same lognormal distribution, subject to the stability constraint and accounting for the correlation between inner subsystems. The simulator can be used to evaluate the frequency of multiple systems with specified parameters. However, it does not reproduce the observed excess of inner periods shorter than 10 days, caused by tidal evolution. © 2014. The American Astronomical Society. All rights reserved..


Tokovinin A.,Cerro Tololo Inter American Observatory
Astronomical Journal | Year: 2014

Data on the multiplicity of F- and G-type dwarf stars within 67 pc of the Sun are presented. This distance-limited sample based on the Hipparcos catalog contains 4847 primary stars (targets) with 0.5 < V-IC < 0.8 and is >90% complete. There are 2196 known stellar pairs; some of them belong to 361 hierarchical systems from triples to quintuples. Models of companion detection by radial velocity, astrometric acceleration, direct resolution, and common proper motion are developed. They serve to compute completeness for each target, using the information on its coverage collected here. About 80% of companions to the primary stars are detected, but the census of subsystems in the secondary components is only about 30%. Masses of binary components are estimated from their absolute magnitudes or by other methods; the periods of wide pairs are evaluated from their projected separations. A third of binaries with periods shorter than 100 yr are spectroscopic and/or astrometric pairs with yet unknown periods and mass ratios. These data are used in the accompanying Paper II to derive unbiased statistics of hierarchical multiple systems. © 2014. The American Astronomical Society. All rights reserved..


Tokovinin A.,Cerro Tololo Inter American Observatory
Astronomical Journal | Year: 2014

To improve the statistics of hierarchical multiplicity, secondary components of wide nearby binaries with solar-type primaries were surveyed at the SOAR telescope for evaluating the frequency of subsystems. Images of 17 faint secondaries were obtained with the SOAR Adaptive Module that improved the seeing; one new 0″.2 binary was detected. For all targets, photometry in the g′, i′, z′ bands is given. Another 46 secondaries were observed by speckle interferometry, resolving 7 close subsystems. Adding literature data, the binarity of 95 secondary components is evaluated. We found that the detection-corrected frequency of secondary subsystems with periods in the well-surveyed range from 103 to 105 days is 0.21 ± 0.06 - same as the normal frequency of such binaries among solar-type stars, 0.18. This indicates that wide binaries are unlikely to be produced by dynamical evolution of N-body systems, but are rather formed by fragmentation. © 2014. The American Astronomical Society. All rights reserved.


Tokovinin A.,Cerro Tololo Inter American Observatory
Astronomical Journal | Year: 2012

Results of speckle observations at the 4.1m SOAR telescope in 2012 (158 measures of 121 systems, 27 non-resolutions) are reported. The aim is to follow fast orbital motion of recently discovered or neglected close binaries and sub-systems. Here, eight previously known orbits are defined better, two more are completely revised, and five orbits are computed for the first time. Using differential photometry from Hipparcos or speckle and the standard relation between mass and absolute magnitude, the component's masses and dynamical parallaxes are estimated for all 15 systems with new or updated orbits. Two astrometric binaries HIP 54214 and 56245 are resolved here for the first time, another eight are measured. We highlight several unresolved pairs that may actually be single despite multiple historic measures, such as 104 Tau and f Pup AB. Continued monitoring is needed to understand those enigmatic cases. © © 2012. The American Astronomical Society. All rights reserved.


Walker A.R.,Cerro Tololo Inter American Observatory
Astrophysics and Space Science | Year: 2012

The Magellanic Clouds, especially the Large Magellanic Cloud, are places where multiple distance indicators can be compared with each other in a straight-forward manner at considerable precision. We here review the distances derived from Cepheids, Red Variables, RR Lyraes, Red Clump Stars and Eclipsing Binaries, and show that the results from these distance indicators generally agree to within their errors, and the distance modulus to the Large Magellanic Cloud appears to be defined to ±3% with a mean value (m-M) 0=18. 48 mag, corresponding to 49. 7 kpc. The utility of the Magellanic Clouds in constructing and testing the distance scale will remain as we move into the era of Gaia. © 2011 Springer Science+Business Media B.V.


Tokovinin A.,Cerro Tololo Inter American Observatory
Astronomical Journal | Year: 2013

Bright and nearby (22 pc) solar-type dwarf κ For (HIP 11072) is a triple system. The close pair of M-type dwarfs Ba,Bb with a tentative period of 3.7 days moves around the main component A on a 26 yr orbit. The mass of the "dark companion" Ba+Bb is comparable to the mass of A, causing large motion of the photo-center. The combined spectro-interferometric orbit of AB is derived, and the relative photometry of the components A and B is given. A weak signature of Ba and Bb is detected in the high-resolution spectra by cross-correlation and by variable emission in the Balmer hydrogen lines. The activity of the M dwarfs, manifested by a previously detected radio flare, is likely maintained by synchronization with their tight orbit. We discuss the frequency of similar hidden triple systems, methods of their detection, and the implications for multiple-star statistics. © 2013. The American Astronomical Society. All rights reserved.


James D.J.,Cerro Tololo Inter American Observatory
Publications of the Astronomical Society of the Pacific | Year: 2013

We have created a digital spectral library, using low resolution optical spectra, of photometric and spectral standard stars. The data were acquired using the Cassegrain spectrograph installed on the 1.9 m Radcliffe telescope at the South African Astronomical Observatory. The library consists of optical wavelength (≃3500-7500 Å) spectra for main sequence and giant stars encompassing those most commonly observed in the Galaxy, namely the late-B, A, F, G, K, and early- to mid-M stars. We intend that our standard star spectra will be especially useful for spectral classification of stars in the field and Galactic clusters alike and will have high pedagogic value when included into representative "Introductory Astronomy" or "Stellar Astronomy" curricula for undergraduate astronomy major and minor programs. We exploit the spectral library in order to derive spectral types for 76 optically and X-ray selected members of the young open cluster NGC 6475. Comparison of spectral type, optical and infrared photometric data to theoretical colors derived from spectral type show that the reddening of the cluster is EBV = 0.068 ± 0.012 (1σ = 0.058), a vector consistent with earlier surveys. Our analysis also highlights the utility of such spectra in rejecting cluster nonmembers, thereby allowing the creation of a clean sample of bona fide cluster members for follow-up science observations. © 2013. The Astronomical Society of the Pacific. All rights reserved.


Tokovinin A.,Cerro Tololo Inter American Observatory
Astronomical Journal | Year: 2011

A complete census of wide visual companions to nearby G-dwarf stars can be achieved by selecting candidates from the Two Micron All Sky Survey (2MASS) Point-Source Catalog and checking their status by second-epoch imaging. Such data are obtained for 124 candidates with separations up to 20′, 47 of which are shown to be new physical low-mass stellar companions. A list of visual binaries with G-dwarf primaries is produced by combining newly found companions with historical data. Maximum likelihood analysis leads to a companion frequency of 0.13 ± 0.015 per decade of separation. The mass ratio is distributed almost uniformly, with a power-law index between -0.4 and 0. The remaining uncertainty in the index is related to modeling of the companion detection threshold in 2MASS. These findings are confirmed by an alternative analysis of wider companions in 2MASS, removing the contamination by background stars statistically. Extension of this work will lead to a complete detection of visual companions-a necessary step toward reaching unbiased multiplicity statistics over the full range of orbital periods and, eventually, understanding the origin of multiple systems. © 2011. The American Astronomical Society.

Loading Cerro Tololo Inter American Observatory collaborators
Loading Cerro Tololo Inter American Observatory collaborators