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An extremely wide and very low-mass pair with common proper motion. Is it representative of a nearby halo stream?
Aims. We describe the discovery of an extremely wide pair of low-massstars with a common large proper motion and discuss their possiblemembership in a Galactic halo stream crossing the Solar neighbourhood. Methods: In a high proper motion survey of the southern sky we usedmulti-epoch positions and photometry from the SuperCOSMOS Sky Surveys.New nearby ultracool dwarf and subdwarf candidates were selected amongthe faint and red high proper motion objects, and subsequently confirmedby low-resolution classification spectroscopy. The resultingspectroscopic distance estimates, approximate radial velocitymeasurements and improved proper motions involving additional epochsfrom the Two Micron All Sky Survey and from the DEep Near-InfraredSurvey were used to compute Galactic space velocities. Results: Thelate-type (M 7) dwarf SSSPM J2003-4433 and the ultracool subdwarf SSSPMJ1930-4311 (sdM 7) sharing the same very large proper motion of about860 mas/yr were found in the same sky region with an angular separationof about 6°. From the comparison with other high proper motioncatalogues we have estimated the probability of a chance alignment ofthe two new large proper motions to be less than 0.3%. From theindividually estimated spectroscopic distances of about38+10-7 pc and 72+21-16 pc,respectively for the M 7 dwarf and the sdM 7 subdwarf, and in view ofthe accurate agreement in their large proper motions we assume a commondistance of about 50 pc and a projected physical separation of about 5pc. The mean heliocentric space velocity of the pair (U,V,W)=(-232,-170, +74) km s-1, based on the correctness of thepreliminary radial velocity measurement for only one of the componentsand on the assumption of a common distance and velocity vector, istypical of the Galactic halo population. Conclusions: The largeseparation and the different metallicities of dwarfs and subdwarfs makea common formation scenario as a wide binary (later disrupted)improbable, although there remains some uncertainty in the spectroscopicclassification scheme of ultracool dwarfs/subdwarfs so that a dissolvedbinary origin cannot be fully ruled out yet. It seems more likely thatthis wide pair is part of an old halo stream. Higher-resolutionspectroscopic observations are needed to measure accurate radialvelocities of both components. Further, we suggest to check the M 7dwarf for an unresolved binary status, which would explain its shorterspectroscopic distance estimate, and to place both objects on atrigonometric parallax program.Based onobservations with the ESO 3.6 m/EFOSC2 at the European SouthernObservatory, La Silla (ESO program 70.C-0568).
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| The Pul-3 catalogue of 58483 stars in the Tycho-2 system
A catalogue of positions and proper motions of 58483 stars (Pul-3) hasbeen constructed at the Pulkovo observatory. The Pul-3 is based on theresults of measurements of photographic plates with galaxies (Deutsch'splan). All plates were taken using the Pulkovo Normal Astrograph (thefirst epoch is in the 1950s and the second epoch is in the 1970s).The Pul-3 catalogue contains stars of mainly 12 to 16.5 mag in 146fields with galaxies in the declination zone from -5o to+85o. The Tycho-2 has been used as a reference catalogue.The mean epoch of the Pul-3 is 1963.25. The internal positional accuracyof the Pul-3 catalogue at the mean epoch of observations is ±80mas. The accuracy of the proper motions is mostly within ±3mas/yr to ±12 mas/yr. Comparisons of the Pul-3 with Tycho-2 andARIHIP have been done at the mean epoch of the Pul-3. The Pul-3 externalpositional accuracy relative to Tycho-2 is ±150 mas.The catalogue is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/357
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| The general catalogue of trigonometric [stellar] paralaxes
Not Available
| A photometric search for halo binaries. I - New observatinal data. II - Results
Carney (1982) has reported JHK photometry for 76 Hyades dwarfs. Inconnection with the present investigation, results of similarobservations of field halo stars are provided along with some uvbyphotometry. In addition, older spectrophotometric and photometric dataused previously for temperature determinations have been collected. Theinfrared and uvby data were obtained primarily with the objective ofidentifying binaries with dissimilar components among a sample of fieldhalo dwarfs by comparing metallicity insensitive blue and infraredcolors. Attention is given to 111 spectrophotometric scans of 89 stars,67 uvby measures of 41 stars, 127 UBV measures of 87 stars, 147 (RI)Jmeasures of 127 stars, 8 JHK measures of eight stars in the 'HCO'system, and 212 JHK measures of 137 stars in the 'CIT' system. Themajority of these stars are dwarfs, and most of them are metal poor. Theresults of a search for binaries in 71 halo dwarf stars are alsopresented, taking into account a few other dwarfs of special interest.
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Observation and Astrometry data
| Constellation: | Ursa Minor |
| Right ascension: | 16h39m07.50s |
| Declination: | +77°52'10.0" |
| Apparent magnitude: | 8.056 |
| Distance: | 413.223 parsecs |
| Proper motion RA: | -86.3 |
| Proper motion Dec: | 91.3 |
| B-T magnitude: | 9.41 |
| V-T magnitude: | 8.168 |
Catalogs and designations:
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INHABITED SKY
