Valeri V. Makarov

The Third US Naval Observatory CCD Astrograph Catalog (UCAC3)

The second US Naval Observatory (USNO) CCD Astrograph Catalog, UCAC2 was released in 2003 July. Positions and proper motions for 48,330,571 sources (mostly stars) are available on 3 CDs, supplemented with Two Micron All Sky Survey photometry for 99.5% of the sources. The catalog covers the sky area from -90° to +40° declination, going up to +52° in some areas; this completely supersedes the UCAC1 released in 2001. Current epoch positions are obtained from observations with the USNO 8 inch (0.2 m) Twin Astrograph equipped with a 4K CCD camera. The precision of the positions are 15–70 mas, depending on magnitude, with estimated systematic errors of 10 mas or below. Proper motions are derived by using over 140 ground- and space-based catalogs, including Hipparcos/Tycho and the AC2000.2, as well as yet unpublished remeasures of the AGK2 plates and scans from the NPM and SPM plates. Proper-motion errors are about 1–3 mas yr-1 for stars to 12th magnitude, and about 4–7 mas yr-1 for fainter stars to 16th magnitude. The observational data, astrometric reductions, results, and important information for the users of this catalog are presented.

The Tycho double star catalogue

We report the discovery of 13 251 visual double stars, mostly with separations between 0.3 and 1 arcsec, from a dedicated re-reduction of the Tycho data from the star mapper of the ESA Hipparcos satellite. The new doublesare combined with 18 160 WDS systems identified in the Tycho-2 Catalogue, and 1220 new Tycho-2 doubles, to form the Tycho Double Star Catalogue, TDSC, a catalogue of absolute astrometry and B T , V T photometry for 66219 components of 32631 double and multiple star systems. We also include results for 32 263 single components for systems unresolved in TDSC, and a supplement gives Hipparcos and Tycho-1 data for 4777 additional components. The TDSC thus contains a total of 103 259 entries. Cross identifications are given to WDS, HD, Hipparcos and Tycho-2.

No Pseudosynchronous Rotation for Terrestrial Planets and Moons

We reexamine the popular belief that a telluric planet or satellite on an eccentric orbit can, outside a spin-orbit resonance, be captured in a quasi-static tidal equilibrium called pseudosynchronous rotation. The existence of such configurations was deduced from oversimplified tidal models assuming either a constant tidal torque or a torque linear in the tidal frequency. A more accurate treatment requires that the torque be decomposed into the Darwin-Kaula series over the tidal modes, and that this decomposition be combined with a realistic choice of rheological properties of the mantle. This development demonstrates that there exist no stable equilibrium states for solid planets and moons, other than spin-orbit resonances.

Internal kinematics of the TW Hya association of young stars

Thirty one probable kinematic members of the nearby TW Hya association of young stars are selected from the RASSBSC/Tycho-2 sample of stars luminous in X-rays, detected by ROSAT. Eight of them have been listed already as members of the association, and 23 are new candidates. The association occupies a volume of some 10 6 pc 3 , the nearest member being at a distance of only 17.5 pc from the Sun. The lower bound internal velocity dispersion is estimated at 0.8 km s -1 , which is considerably larger than is expected in a gravitationally bound open cluster. The total mass of the group is estimated at 31 solar masses. The centre of mass lies at 73 pc from us in the direction close to the position of the prototype star TW Hya. A realistic kinematical model fitting both the observed trigonometric parallaxes and radial velocities involves a linear expansion of the group with the rate 0.12 km s -1 pc -1 , which defines a dynamical age of 8.3 Myr, in good agreement with previous age estimations for T Tauri members. Likewise the nearby Carina-Vela moving group of X-ray stars, the TW Hya association appears to be an outpost of the Gould Belt structure rather than an isolated open cluster.

IDENTIFICATION OF 1.4 MILLION ACTIVE GALACTIC NUCLEI IN THE MID-INFRARED USING WISE DATA

Abstract : We present an all-sky sample of approx. equal 1.4 million active galactic nuclei (AGNs) meeting a two-color infrared photometric selection criteria for AGNs as applied to sources from the Wide-field Infrared Survey Explorer final catalog release (AllWISE). We assess the spatial distribution and optical properties of our sample and find that the results are consistent with expectations for AGNs. These sources have a mean density of approx. equal 38 AGNs per square degree on the sky, and their apparent magnitude distribution peaks at g approx. equal 20, extending to objects as faint as g approx. equal 26. We test the AGN selection criteria against a large sample of optically identified stars and determine the leakage (that is, the probability that a star detected in an optical survey will be misidentified as a quasi-stellar object (QSO) in our sample) rate to be less than or = 4.0 x 10(exp -5). We conclude that our sample contains almost no optically identified stars (less than or = 0.041%), making this sample highly promising for future celestial reference frame work as it significantly increases the number of all-sky, compact extragalactic objects. We further compare our sample to catalogs of known AGNs/QSOs and find a completeness value of greater than or approx. 84% (that is, the probability of correctly identifying a known AGN/QSO is at least 84%) for AGNs brighter than a limiting magnitude of R less than or approx. 19. Our sample includes approximately 1.1 million previously uncataloged AGNs.

Revealing Companions to Nearby Stars with Astrometric Acceleration

A subset of 51 Hipparcos astrometric binaries among FG dwarfs within 67 pc has been surveyed with the Near-Infrared Coronagraphic Imager adaptive optics system at Gemini-S, directly resolving for the first time 17 subarcsecond companions and 7 wider ones. Using these data together with published speckle interferometry of 57 stars, we compare the statistics of resolved astrometric companions with those of a simulated binary population. Thefractionofresolvedcompanionsisslightlylowerthanexpectedfrombinarystatistics.About10%ofastrometric companions could be “dark” (white dwarfs and close pairs of late M-dwarfs). To our surprise, several binaries are found with companions too wide to explain the acceleration. Re-analysis of selected intermediate astrometric data shows that some acceleration solutions in the original Hipparcos catalog are spurious. Key word: binaries: general

Tidal dissipation in a homogeneous spherical body. I. Methods

A formula for the tidal dissipation rate in a spherical body is derived from first principles to correct some mathematical inaccuracies found in the literature. The development is combined with the Darwin-Kaula formalism for tides. Our intermediate results are compared with those by Zschau and Platzman. When restricted to the special case of an incompressible spherical planet spinning synchronously without libration, our final formula can be compared with the commonly used expression from Peale & Cassen. However, the two turn out to differ, as in our expression the contributions from all Fourier modes are positive-definite, which is not the case with the formula from Peale & Cassen. Examples of the application of our expression for the tidal damping rate are provided in the work by Makarov & Efroimsky (Paper II) published back to back with the current paper.

Henry Draper catalogue identifications for Tycho-2 stars

We present identications in the Tycho-2 Catalogue, for 99.8 per cent of the stars in the Henry Draper Catalogue and for 96 per cent of the Henry Draper Extensions.

Equilibrium Rotation of Semiliquid Exoplanets and Satellites

A wide range of exoplanet and exomoon models are characterized by a finite average rigidity and a viscosity much lower than the typical values for terrestrials. Such semiliquid bodies may or may not have rigid crusts with permanent figures. Unlike planets with solid mantles and Earth-like rheology, semiliquid bodies can be captured into stable pseudosynchronous spin resonance, where the average rate of rotation is higher than the synchronous 1:1 resonance. Two basic conditions are derived for capture of planets with a triaxial figure into pseudosynchronous rotation, one related to the characteristic tidal wave number (the product of the tidal frequency by the Maxwell time), and the other to the orbital eccentricity. If a semiliquid object does not satisfy either of the two conditions, it is captured into the synchronous resonance. For nearly axially symmetric bodies, only the first condition is in place, and the other is much relaxed, so they should predominantly be pseudosynchronous. It is also pointed out that the equilibrium pseudosychronous rotation rate can not reach the widely used asymptotic value from the constant time lag model but is in reality closer to the synchronous spin.

TIDAL DISSIPATION IN A HOMOGENEOUS SPHERICAL BODY. II. THREE EXAMPLES: MERCURY, IO, AND Kepler-10 b

Abstract : In Efroimsky & Makarov (Paper I), we derived from the first principles a formula for the tidal heating rate in a homogeneous sphere, compared it with the previously used formulae, and noted the differences. Now we present case studies: Mercury, Kepler-10 b, and a triaxial Io. A sharp frequency dependence of k (sub2) /Q near spin orbit resonances yields a sharp dependence of k (sub2) /Q (and, therefore, of tidal heating) upon the spin rate. Thereby physical libration plays a major role in tidal heating of synchronously rotating planets. The magnitude of libration in the spin rate being defined by the planet s triaxiality, the latter becomes a factor determining the dissipation rate. Other parameters equal, a strongly triaxial synchronized body generates more heat than a similar body of a more symmetrical shape. After an initially triaxial object melts and loses its triaxiality, dissipation becomes less intensive; the body can solidify, with the tidal bulge becoming a new figure with triaxiality lower than the original. We derive approximate expressions for the dissipation rate in a Maxwell planet with the Maxwell time longer than the inverse tidal frequency. The expressions derived pertain to the 1:1 and 3:2 resonances and a nonresonant case; so they are applicable to most close-in super-Earths detected. In these planets, the heating outside synchronism is weakly dependent on the eccentricity and obliquity, provided both these parameters s values are moderate. According to our calculation, Kepler-10 b could hardly survive the intensive tidal heating without being synchronized, circularized, and reshaped through a complete or partial melt-down.