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Cool Subdwarf Investigations. II. Multiplicity
Cool subdwarfs of types K and M are the fainter counterparts of coolmain-sequence dwarfs that dominate the Galactic population. In thispaper, we present the results of an optical speckle survey of 62confirmed cool subdwarf systems within 60 pc. We have resolved twonew companions and confirmed two previously known companions withseparations 0farcs13-3farcs29. After including previously known widecompanions and all known spectroscopic binaries, we determine themultiplicity rate of cool subdwarfs to be 26% ± 6%, which issomewhat lower than comparable main-sequence stars that have amultiplicity rate of 37% ± 5%. We find that only 3% of the coolsubdwarfs surveyed have companions within 10 AU, 3% have companionsbetween 10 and 100 AU, and 14% have companions beyond 100 AU.The other 6% of cool subdwarfs are spectroscopic binaries. This is verydifferent from K/M dwarfs that have most companions (13%) at separationscloser than 10 AU. However, because a search for close binariesamong a large sample of nearby cool subdwarfs remains elusive, it is notyet settled whether or not the multiplicity rates are significantlydifferent. Nonetheless, several different observational results andtheories pointing to a possible dearth of subdwarf multiples arediscussed.
| The outskirts of Cygnus OB2
Context: Cygnus OB2 is one of the richest OB associations in the localGalaxy, and is located in a vast complex containing several otherassociations, clusters, molecular clouds, and HII regions. However, thestellar content of Cygnus OB2 and its surroundings remains rather poorlyknown largely due to the considerable reddening in its direction atvisible wavelength. Aims: We investigate the possible existence of anextended halo of early-type stars around Cygnus OB2, which is hinted atby near-infrared color-color diagrams, and its relationship to CygnusOB2 itself, as well as to the nearby association Cygnus OB9 and to thestar forming regions in the Cygnus X North complex. Methods: Candidateselection is made with photometry in the 2MASS all-sky point sourcecatalog. The early-type nature of the selected candidates is confirmedor discarded through our infrared spectroscopy at low resolution. Inaddition, spectral classifications in the visible are presented for manylightly-reddened stars. Results: A total of 96 early-type stars areidentified in the targeted region, which amounts to nearly half of theobserved sample. Most of them have featureless near-infrared spectra asexpected from OB stars at the available resolution. Another 18 starsthat display Brackett emission lines can be divided between evolvedmassive stars (most likely Be stars) and Herbig Ae/Be stars based ontheir infrared excesses. A component associated with Cygnus OB9/NGC 6910is clearly identified, as well as an enhancement in the surface densityof early-type stars at Cygnus X North. We also find a field population,consisting largely of early B giants and supergiants, which is probablythe same as identified in recent studies of the inner 1° circlearound Cygnus OB2. The age and large extension of this populationdiscards a direct relationship with Cygnus OB2 or any other particularassociation. Conclusions: Earlier claims of the possible large extentof Cygnus OB2 beyond its central, very massive aggregate seem to bedismissed by our findings. The existence of a nearly ubiquitouspopulation of evolved stars with massive precursors suggests a massivestar formation history in Cygnus having started long before theformation of the currently observed OB associations in the region.Based on observations collected at the Centro AstronómicoHispano-Alemán (CAHA) at Calar Alto, operated jointly by theMax-Planck Institut für Astronomie and the Instituto deAstrofísica de Andalucía (CSIC).Tables 1-9 are only available in electronic form at http://www.aanda.org
| A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)
The LSPM catalog is a comprehensive list of 61,977 stars north of theJ2000 celestial equator that have proper motions larger than 0.15"yr-1 (local-background-stars frame). The catalog has beengenerated primarily as a result of our systematic search for high propermotion stars in the Digitized Sky Surveys using our SUPERBLINK software.At brighter magnitudes, the catalog incorporates stars and data from theTycho-2 Catalogue and also, to a lesser extent, from the All-SkyCompiled Catalogue of 2.5 million stars. The LSPM catalog considerablyexpands over the old Luyten (Luyten Half-Second [LHS] and New LuytenTwo-Tenths [NLTT]) catalogs, superseding them for northern declinations.Positions are given with an accuracy of <~100 mas at the 2000.0epoch, and absolute proper motions are given with an accuracy of ~8 masyr-1. Corrections to the local-background-stars propermotions have been calculated, and absolute proper motions in theextragalactic frame are given. Whenever available, we also give opticalBT and VT magnitudes (from Tycho-2, ASCC-2.5),photographic BJ, RF, and IN magnitudes(from USNO-B1 catalog), and infrared J, H, and Ks magnitudes(from 2MASS). We also provide an estimated V magnitude and V-J color fornearly all catalog entries, useful for initial classification of thestars. The catalog is estimated to be over 99% complete at high Galacticlatitudes (|b|>15deg) and over 90% complete at lowGalactic latitudes (|b|>15deg), down to a magnitudeV=19.0, and has a limiting magnitude V=21.0. All the northern starslisted in the LHS and NLTT catalogs have been reidentified, and theirpositions, proper motions, and magnitudes reevaluated. The catalog alsolists a large number of completely new objects, which promise to expandvery significantly the census of red dwarfs, subdwarfs, and white dwarfsin the vicinity of the Sun.Based on data mining of the Digitized Sky Surveys (DSSs), developed andoperated by the Catalogs and Surveys Branch of the Space TelescopeScience Institute (STScI), Baltimore.Developed with support from the National Science Foundation (NSF), aspart of the NASA/NSF NStars program.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| A search for previously unrecognized metal-poor subdwarfs in the Hipparcos astrometric catalogue
We have identified 317 stars included in the Hipparcos astrometriccatalogue that have parallaxes measured to a precision of better than 15per cent, and the location of which in the(MV,(B-V)T) diagram implies a metallicitycomparable to or less than that of the intermediate-abundance globularcluster M5. We have undertaken an extensive literature search to locateStrömgren, Johnson/Cousins and Walraven photometry for over 120stars. In addition, we present new UBV(RI)C photometry of 201of these candidate halo stars, together with similar data for a further14 known metal-poor subdwarfs. These observations provide the firstextensive data set of RCIC photometry ofmetal-poor, main-sequence stars with well-determined trigonometricparallaxes. Finally, we have obtained intermediate-resolution opticalspectroscopy of 175 stars. 47 stars still lack sufficient supplementaryobservations for population classification; however, we are able toestimate abundances for 270 stars, or over 80 per cent of the sample.The overwhelming majority have near-solar abundance, with theirinclusion in the present sample stemming from errors in the colourslisted in the Hipparcos catalogue. Only 44 stars show consistentevidence of abundances below [Fe/H]=-1.0. Nine are additions to thesmall sample of metal-poor subdwarfs with accurate photometry. Weconsider briefly the implication of these results for clustermain-sequence fitting.
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Observation and Astrometry data
| Constellation: | Cygnus |
| Right ascension: | 20h40m07.92s |
| Declination: | +41°15'11.0" |
| Apparent magnitude: | 10.556 |
| Proper motion RA: | 167.4 |
| Proper motion Dec: | 116.4 |
| B-T magnitude: | 11.58 |
| V-T magnitude: | 10.641 |
Catalogs and designations:
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