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Fourier Analysis of Hubble Space Telescope Fine Guidance Sensor Data of Binary Stars and Application to the Multiple System HD 157948
A Fourier-based method is presented for the analysis of binary andmultiple star data taken with the Hubble Space Telescope Fine GuidanceSensors (FGSs). Relative astrometry and magnitude differences areobtained as with standard FGS analysis techniques, and although the FGSsystem is essentially unfiltered, this method also permits thecharacterization of color differences between components of binary ormultiple star systems based on the wavelength dependence of theinterference fringes produced by the instrument. Using the multiplesystem HD 157948, we show that the method produces astrometric andphotometric measurements that are consistent with previous FGS analysisfor the three components that lie within the field of view of FGS andgives color differences relative to the primary for two of the threeknown companions. Speckle observations of the system with the WIYN 3.5 mtelescope at Kitt Peak National Observatory are also presented, which,in combination with the FGS results and other data available in theliterature, permit B-V colors and absolute V magnitudes to be obtainedof all four components in the system. Their colors and magnitudes areplotted on the H-R diagram, and a comparison with theoretical isochronesindicates that the results are consistent with theory for a relativelyyoung, somewhat metal-poor system.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS5-26555.
| The Solar Neighborhood. IX. Hubble Space Telescope Detections of Companions to Five M and L Dwarfs within 10 Parsecs of the Sun
We report the detections of low-mass companions to five M and L dwarfswithin 10 pc of the Sun using the Hubble Space Telescope (HST)Near-Infrared Camera and Multi-Object Spectrometer (NICMOS). Follow-upobservations using the HST Advanced Camera for Surveys (ACS) and FineGuidance Sensor 1r (FGS1r) confirm our NICMOS discoveries of companionsto the L4.5 dwarf GJ 1001B (LHS 102B) and the M5 dwarf LHS 224,respectively. Images obtained with the Astrophysical Research Consortium3.5 m telescope at Apache Point Observatory verify our discovery of acompanion to the M3 dwarf G239-25. Our NICMOS images confirm thepreviously suspected duplicity of the M3 dwarfs GJ 54 and GJ 84. Thecomponents of GJ 1001BC and LHS 224AB have nearly equal luminosities inall the ACS and/or NICMOS bandpasses in which they were observed. Themagnitudes of GJ 54A and B in one FGS1r bandpass and four NICMOSbandpasses differ by <~1. GJ 84B and G239-25B are ~4 mag fainter thantheir M3 companions in the NICMOS bandpasses. We estimate from ourNICMOS photometry that GJ 84B and G239-25B have spectral types M7 andM8, respectively, and masses near the lower limit for sustained hydrogenburning. The apparent separations of GJ 1001BC, GJ 54AB, and LHS 224ABsuggest orbital periods less than 5 yr. These binary dwarfs are idealcandidates for continued astrometric monitoring that will quickly yieldaccurate dynamic masses needed to constrain the mass-luminosity relationfor low-mass stars and brown dwarfs.
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997
| The stellar distribution in the galactic anticenter.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967AJ.....72.1199M&db_key=AST
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