We present the results of a comprehensive assessment of companions to solar-type stars. A sample of 454 stars, including the Sun, was selected from the Hipparcos catalog with {pi}>40 mas, {sigma}{sub {pi}/{pi}} < 0.05, 0.5 {<=} B - V {<=} 1.0 ({approx}F6-K3), and constrained by absolute magnitude and color to exclude evolved stars. These criteria are equivalent to selecting all dwarf and subdwarf stars within 25 pc with V-band flux between 0.1 and 10 times that of the Sun, giving us a physical basis for the term 'solar-type'. New observational aspects of this work include surveys for (1) very close companions with long-baseline interferometry at the Center for High Angular Resolution Astronomy Array, (2) close companions with speckle interferometry, and (3) wide proper-motion companions identified by blinking multi-epoch archival images. In addition, we include the results from extensive radial-velocity monitoring programs and evaluate companion information from various catalogs covering many different techniques. The results presented here include four new common proper-motion companions discovered by blinking archival images. Additionally, the spectroscopic data searched reveal five new stellar companions. Our synthesis of results from many methods and sources results in a thorough evaluation of stellar and brown dwarf companions to nearby Sun-likemore » stars. The overall observed fractions of single, double, triple, and higher-order systems are 56% {+-} 2%, 33% {+-} 2%, 8% {+-} 1%, and 3% {+-} 1%, respectively, counting all confirmed stellar and brown dwarf companions. If all candidate, i.e., unconfirmed, companions identified are found to be real, the percentages would change to 54% {+-} 2%, 34% {+-} 2%, 9% {+-} 2%, and 3% {+-} 1%, respectively. Our completeness analysis indicates that only a few undiscovered companions remain in this well-studied sample, implying that the majority (54% {+-} 2%) of solar-type stars are single, in contrast to the results of prior multiplicity studies. Our sample is large enough to enable a check of the multiplicity dependence on various physical parameters by analyzing appropriate subsamples. Bluer, more massive stars are seen as more likely to have companions than redder, less massive ones, consistent with the trend seen over the entire spectral range. Systems with larger interaction cross sections, i.e., those with more than two components or long orbital periods, are preferentially younger, suggesting that companions may be stripped over time by dynamical interactions. We confirm the planet-metallicity correlation (i.e., higher metallicity stars are more likely to host planets), but are unable to check it for brown dwarfs due to the paucity of such companions, implying that the brown dwarf desert extends over all separation regimes. We find no correlation between stellar companions and metallicity for B - V < 0.625, but among the redder subset, metal-poor stars ([Fe/H] <-0.3) are more likely to have companions with a 2.4{sigma} significance. The orbital-period distribution of companions is unimodal and roughly log normal with a peak and median of about 300 years. The period-eccentricity relation shows the expected circularization for periods below 12 days, caused by tidal forces over the age of the Galaxy, followed by a roughly flat distribution. The mass-ratio distribution shows a preference for like-mass pairs, which occur more frequently in relatively close pairs. The fraction of planet hosts among single, binary, and multiple systems are statistically indistinguishable, suggesting that planets are as likely to form around single stars as they are around components of binary or multiple systems with sufficiently wide separations. This, along with the preference of long orbital periods among stellar systems, increases the space around stars conducive for planet formation, and perhaps life.« less

/pdf/a-survey-of-stellar-families-multiplicity-of-solar-type-4mf1i754rb.pdf

A survey of stellar families: multiplicity of solar-type stars

A stellar spectral flux library of wide spectral coverage and an example of its application are presented. The new library consists of 131 flux-calibrated spectra, encompassing all normal spectral types and luminosity classes at solar abundance, and metal-weak and metal-rich F-K dwarf and G-K giant components. Each library spectrum was formed by combining data from several sources overlapping in wavelength coverage. The SIMBAD database, measured colors, and line strengths were used to check that each input component has closely similar stellar type. The library has complete spectral coverage from 1150 to 10620 Afor all components and to 25000 Afor about half of them, mainly later types of solar abundance. Missing spectral coverage in the infrared currently consists of a smooth energy distribution formed from standard colors for the relevant types. The library is designed to permit inclusion of additional digital spectra, particularly of non-solar abundance stars in the infrared, as they become available. The library spectra are each given as Fl versus l, from 1150 to 25000 Ain steps of 5 A ˚. A program to combine the library spectra in the ratios appropriate to a selected isochrone is described and an example of a spectral component signature of a composite population of solar age and metallicity is illustrated. The library spectra and associated tables are available as text files by remote electronic access.

VizieR Online Data Catalog: A Stellar Spectral Flux Library: 1150 - 25000 A (Pickles 1998)

Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the Gemini Planet Imager, we discovered a planet orbiting the ~20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10(-6) and an effective temperature of 600 to 750 kelvin. For this age and luminosity, "hot-start" formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the "cold-start" core-accretion process that may have formed Jupiter.

https://science.sciencemag.org/content/sci/350/6256/64.full.pdf

Discovery and spectroscopy of the young Jovian planet 51 Eri b with the Gemini Planet Imager

We present an analysis of the ages and star formation history of the F-type stars in the Upper Scorpius (US), Upper Centaurus-Lupus (UCL), and Lower Centaurus-Crux (LCC) subgroups of Scorpius-Centaurus (Sco-Cen), the nearest OB association. Our parent sample is the kinematically selected Hipparcos sample of de Zeeuw et al., restricted to the 138 F-type members. We have obtained classification-resolution optical spectra and have also determined the spectroscopic accretion disk fraction. With Hipparcos and 2MASS photometry, we estimate the reddening and extinction for each star and place the candidate members on a theoretical H-R diagram. For each subgroup we construct empirical isochrones and compare to published evolutionary tracks. We find that (1) our empirical isochrones are consistent with the previously published age-rank of the Sco-Cen subgroups; (2) subgroups LCC and UCL appear to reach the main-sequence turn-on at spectral types ~F4 and ~F2, respectively. An analysis of the A-type stars shows US reaching the main sequence at about spectral type ~A3. (3) The median ages for the pre-main-sequence members of UCL and LCC are 16 Myr and 17 Myr, respectively, in agreement with previous studies, however we find that (4) Upper Sco is much older than previously thought. The luminosities of the F-type stars in US are typically a factor of ~2.5 less luminous than predicted for a 5 Myr old population for four sets of evolutionary tracks. We re-examine the evolutionary state and isochronal ages for the B-, A-, and G-type Upper Sco members, as well as the evolved M supergiant Antares, and estimate a revised mean age for Upper Sco of 11 ± 1 ± 2 Myr (statistical, systematic). Using radial velocities and Hipparcos parallaxes we calculate a lower limit on the kinematic expansion age for Upper Sco of >10.5 Myr (99% confidence). However, the data are statistically consistent with no expansion. We reevaluate the inferred masses for the known substellar companions in Upper Sco using the revised age and find that the inferred masses are typically ~20%-70% higher than the original estimates which had assumed a much younger age; specifically, we estimate the mass of 1RXS J1609-2105b to be 14+2 –3 M Jup, suggesting that it is a brown dwarf rather than a planet. Finally, we find the fraction of F-type stars exhibiting Hα emission and/or a K-band excess consistent with accretion to be 0/17 (<19%; 95% CL) in US at ~11 Myr, while UCL has 1/41 (2+5 –1%; 68% CL) accretors and LCC has 1/50 (2+4 –1%; 68% CL) accretors at ~16 Myr and ~17 Myr, respectively.

https://iopscience.iop.org/article/10.1088/0004-637X/746/2/154/pdf

A revised age for upper scorpius and the star formation history among the f-type members of the scorpius-centaurus ob association

We present a self-consistent, absolute isochronal age scale for young (< 200 Myr), nearby (< 100 pc) moving groups in the solar neighbourhood based on homogeneous fitting of semi-empirical pre-main-sequence model isochrones using the tau^2 maximum-likelihood fitting statistic of Naylor & Jeffries in the M_V, V-J colour-magnitude diagram. The final adopted ages for the groups are: 149+51-19 Myr for the AB Dor moving group, 24+/-3 Myr for the {\beta} Pic moving group (BPMG), 45+11-7 Myr for the Carina association, 42+6-4 Myr for the Columba association, 11+/-3 Myr for the {\eta} Cha cluster, 45+/-4 Myr for the Tucana-Horologium moving group (Tuc-Hor), 10+/-3 Myr for the TW Hya association, and 22+4-3 Myr for the 32 Ori group. At this stage we are uncomfortable assigning a final, unambiguous age to the Argus association as our membership list for the association appears to suffer from a high level of contamination, and therefore it remains unclear whether these stars represent a single population of coeval stars. 
Our isochronal ages for both the BPMG and Tuc-Hor are consistent with recent lithium depletion boundary (LDB) ages, which unlike isochronal ages, are relatively insensitive to the choice of low-mass evolutionary models. This consistency between the isochronal and LDB ages instills confidence that our self-consistent, absolute age scale for young, nearby moving groups is robust, and hence we suggest that these ages be adopted for future studies of these groups. 
Software implementing the methods described in this study is available from http: //www.astro.ex.ac.uk/people/timn/tau-squared/.

A self-consistent, absolute isochronal age scale for young moving groups in the solar neighbourhood

The Pulkovo Compilation of Radial Velocities (PCRV) has been made to study the stellar kinematics in the local spiral arm. The PCRV contains weighted mean absolute radial velocities for 35 495 Hipparcos stars of various spectral types and luminosity classes over the entire celestial sphere mainly within 500 pc of the Sun. The median accuracy of the radial velocities obtained is 0.7 km s −1 .R esults from 203 publications were used in the catalogue. Four of them were used to improve the radial velocities of standard stars from the IAU list. The radial velocities of 155 standard stars turned out to be constant within 0.3 km s −1 . These stars were used to analyze 47 768 mean radial velocities for 37 200 stars from 12 major publications (∼80% of all the data used). Zero-point discrepancies and systematic dependences on radial velocity, B-V color index, right ascension, and declination were found in radial velocity differences of the form "publication minus IAU list of standards." These discrepancies and dependences were approximated and taken into account when calculating the weighted mean radial velocities. 1128 stars whose independent radial-velocity determinations were available at least in three of these publications and agreed within 3k m s −1 were chosen as the work list of secondary standards. Radial-velocity differences of the form "publication minus list of secondary standards" were used by analogy to correct the zero points and systematic dependences in the radial velocities from 33 more publications (∼13% of the data used). In addition, the radial velocities from 154 minor publications (∼7% of the data used) pertaining to well-known instruments were used without any corrections.

/pdf/pulkovo-compilation-of-radial-velocities-for-35-495-3z96jjk4z9.pdf

Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system

The Pulkovo Compilation of Radial Velocities (PCRV) has been made to study the stellar kinematics in the local spiral arm. The PCRV contains weighted mean absolute radial velocities for 35 495 Hipparcos stars of various spectral types and luminosity classes over the entire celestial sphere mainly within 500 pc of the Sun. The median accuracy of the radial velocities obtained is 0.7 km s$^{-1}$. Results from 203 publications were used in the catalogue. Four of them were used to improve the radial velocities of standard stars from the IAU list. The radial velocities of 155 standard stars turned out to be constant within 0.3 km s$^{-1}$. These stars were used to analyze 47 768 mean radial velocities for 37 200 stars from 12 major publications ($\sim80\%$ of all the data used). Zero-point discrepancies and systematic dependences on radial velocity, $(B-V)$ color index, right ascension, and declination were found in radial velocity differences of the form "publication minus IAU list of standards". These discrepancies and dependences were approximated and taken into account when calculating the weighted mean radial velocities. 1128 stars whose independent radial-velocity determinations were available at least in three of these publications and agreed within 3 km s$^{-1}$ were chosen as the work list of secondary standards. Radial-velocity differences of the form "publication minus list of secondary standards" were used by analogy to correct the zero points and systematic dependences in the radial velocities from 33 more publications (~13\% of the data used). In addition, the radial velocities from 154 minor publications ($\sim7\%$ of the data used) pertaining to well-known instruments were used without any corrections.

Pulkovo Compilation of Radial Velocities for 35495 Hipparcos Stars in a Common System

The product of the previously constructed 3D maps of stellar reddening (Gontcharov 2010) and Rv variations (Gontcharov 2012) has allowed us to produce a 3D interstellar extinction map within the nearest kiloparsec from the Sun with a spatial resolution of 50 pc and an accuracy of {ie87-1}. Thismap is compared with the 2D reddening map by Schlegel et al. (1998), the 3D extinction map at high latitudes by Jones et al. (2011), and the analytical extinctionmodels by Arenou et al. (1992) and Gontcharov (2009). In all cases, we have found good agreement and show that there are no systematic errors in the new map everywhere except the direction toward the Galactic center. We have found that the map by Schlegel et al. (1998) reaches saturation near the Galactic equator at E(B - V) > 0.8, has a zero-point error and systematic errors gradually increasing with reddening, and among the analytical models those that take into account the extinction in the Gould Belt are more accurate. Our extinction map shows that it is determined by reddening variations at low latitudes and Rv variations at high ones. This naturally explains the contradictory data on the correlation or anticorrelation between reddening and Rv available in the literature. There is a correlation in a thin layer near the Galactic equator, because both reddening and Rv here increase toward the Galactic center. There is an anticorrelation outside this layer, because higher values of Rv correspond to lower reddening at high and middle latitudes. Systematic differences in sizes and other properties of the dust grains in different parts of the Galaxy manifest themselves in this way. The largest structures within the nearest kiloparsec, including the Local Bubble, the Gould Belt, the Great Tunnel, the Scorpius, Perseus, Orion, and other complexes, have manifested themselves in the constructed map.

3D interstellar extinction map within the nearest kiloparsec

The Pulkovo Compilation of Radial Velocities (PCRV) catalogue has been produced to study stellar kinematics in the local spiral arm. The PCRV contains the mean weighted absolute radial velocities of 35 495 Hipparcos stars of various spectral types and luminosity classes over the whole celestial sphere mainly within the radius of 500 pc from the Sun. The median precision of the obtained radial velocities is 0.7 km s−1. The results from 203 publications have been used in the catalogue. They are linked to the system of IAU standard stars or a list of secondary standards by means of the analysis of zero-point deviations and systematic dependences of the radial velocity differences ‘new observations minus standards’ on the radial velocity, colour index B−V, right ascension and declination.

Radial velocities of 35 495 Hipparcos stars in a common system

An improved version of the 3D stellar reddening map in a space with a radius of 1200 pc around the Sun and within 600 pc of the Galactic midplane is presented. As in the previous 2010 and 2012 versions of the map, photometry with an accuracy better than 0.05
 m
 in the J and Ks bands for more than 70 million stars from the 2MASS catalogue is used in the new version. However, the data reduction technique is considerably more complicated. As before, an analysis of the distribution of stars near the main-sequence turnoff on the (J − Ks)−Ks diagram, where they form a distribution maximum, provides a basis for the method. The shift of this maximum, i.e., the mode (J − Ks), along (J − Ks) and Ks, given the spatial variations of the mean dereddened color (J − Ks)0 of these stars, is interpreted as a growth of the reddening with increasing distance. The main distinction of the new method is that instead of the fixed mean absolute magnitude, dereddened color, distance, and reddening for each cell, the individual values of these quantities are calculated for each star by iterations when solving the system of equations relating them. This has allowed one to increase the random accuracy of the map to 0.01
 m
 and its spatial resolution to 20 pc in coordinates and distance and to 1° in longitude and latitude. Comparison with other reddening estimates for the same spatial cells and Gaia DR1 TGAS stars shows that the constructed map is one of the best maps for the space under consideration. Its systematic errors have been estimated to be σ(E(J − Ks)) = 0.025
 m
 , or σ(E(B − V)) = 0.04
 m
 . The main purpose of the map is to analyze the characteristics of Galactic structures, clouds, and cloud complexes. For this purpose, the reddening map within each spatial cell has also been computed by analyzing the reddening along each line of sight.

George Gontcharov

Papers

Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system

Pulkovo Compilation of Radial Velocities for 35495 Hipparcos Stars in a Common System

3D interstellar extinction map within the nearest kiloparsec

Radial velocities of 35 495 Hipparcos stars in a common system

3D stellar reddening map from 2MASS photometry: An improved version