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HD 154948



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Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).

Research Note Hipparcos photometry: The least variable stars
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/367/297

Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases
We have investigated the variation of coronal X-ray emission duringearly post-main-sequence phases for a sample of 120 late-type starswithin 100 pc, and with estimated masses in the range 1-3Msun, based on Hipparcos parallaxes and recent evolutionarymodels. These stars were observed with the ROSAT/PSPC, and the dataprocessed with the Palermo-CfA pipeline, including detection andevaluation of X-ray fluxes (or upper limits) by means of a wavelettransform algorithm. We have studied the evolutionary history of X-rayluminosity and surface flux for stars in selected mass ranges, includingstars with inactive A-type progenitors on the main sequence and lowermass solar-type stars. Our stellar sample suggests a trend of increasingX-ray emission level with age for stars with masses M > 1.5Msun, and a decline for lower-mass stars. A similar behaviorholds for the average coronal temperature, which follows a power-lawcorrelation with the X-ray luminosity, independently of their mass andevolutionary state. We have also studied the relationship between X-rayluminosity and surface rotation rate for stars in the same mass ranges,and how this relationships departs from the Lx ~vrot2 law followed by main-sequence stars. Ourresults are interpreted in terms of a magnetic dynamo whose efficiencydepends on the stellar evolutionary state through the mass-dependentchanges of the stellar internal structure, including the properties ofenvelope convection and the internal rotation profile.

A Broadband X-Ray Study of the Young Neutron Star PSR B1706-44
The young "Vela"-like neutron star PSR B1706-44 was imaged by both theHRI aboard ROSAT and the solid-state imaging spectrometers and gasimaging spectrometers aboard ASCA during a 6 month period in late 1994and early 1995. The broadband data set, extending over two decades inenergy, allowed a detailed spatial, spectral, and temporal study to beconducted. PSR B1706-44 is found embedded in a compact synchrotronnebula of physical size ~0.32 pc and displays the morphologycharacteristic of the other young neutron stars in the 104-105 yr agerange. No pulsations at the radio period were detected in either theROSAT or the ASCA data. The spectrum is well described by a power-lawdistribution, and the data are consistent with there being no spectralbreak from the radio through the soft X-ray band. The unpulsed TeVemission that has been observed from PSR B1706-44 can be reconciled withthese observations if the TeV emission results from the up-scattering ofbackground IR photons by the population of high-energy particles thatproduce the soft X-ray photons.

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.

ROSAT observations of the radio and gamma-ray pulsar PSR 1706-44.
We report on the detection of PSR 1706-44 in two ROSAT-PSPCobservations. The recorded source counts are unpulsed with a 2σpulsed fraction upper limit of 18%. Spectral analysis did notdistinguish between black-body and power law models; however, we arguethat the lack of pulsations and the similarity in the pulsar's spinparameters to those of the Vela pulsar favour a power law modeldN/dE{prop.to}E^-2.4+/-0.6^ and indicate synchrotron emission from apulsar-powered nebula as the origin of the detected X-radiation. TheX-ray flux derived for the power law model isf_x_=3.2^+6.5^_-1.8_x10^-12^erg/s/cm^2^ within the 0.1-2.4keV energyrange. An upper limit for the neutron star's surface temperature is putat LogT_s_infinity^~6.03K for a neutron star with a mediumstiff equation of state (FP-model with M=1.4Msun_,R=10.85km). Slightly different values for T_s_infinity^ arecomputed for the various neutron star models available in theliterature, reflecting the difference in the equation of state. No softX-ray emission is detected from the supernova remnant G 343.1-2.3,proposed to be associated with PSR 1706-44.

Evolved GK stars near the Sun. 2: The young disk population
From a sample of nearly 2000 GK giants a group of young disk stars withwell determined space motions has been selected. The zero point of theluminosity calibrations, both from the ultraviolet flux (modifiedStroemgren system) and that in the region of 4200 to 4900 A (DDOsystem), show a discontinuity of about a half magnitude at the border ofthe young disk and old disk domains. The population separation is basedon the space velocity components, which are also an age discriminant,with the population interface near 2 x 109 yr, based onmodels with convective overshoot at the core. This age corresponds togiant masses near 1.7 solar mass, near the critical mass separating theyoung stars that do not burn helium in degenerate cores from older starsthat do. Ten percent of both populations show CN anomalies in that thederived value of P(Fe/H) from CN (Cm) and fromFe(M1) differ by more than 0.1 dex and the weak and strong CNstars occur equally in the old disk but the weak CN stars predominate inthe young disk. Peculiar stars, where flux distortions affect theluminosity calibrations, are of the CH+(Ba II) and CH-(weak G band)variety and represent less than 1% of the stars in both populations. Theyoung disk giants are restricted to ages greater than about109 yr, because younger stars are bright giants orsupergiants (luminosity class 2 or 1), and younger than about 2 x109 yr, because the old disk-young disk boundary occurs near1.7 solar mass. The distribution of heavy element abundances, P(Fe/H),for young disk giants is both more limited in range (+/- 0.4 dex) and isskewed toward higher abundances, compared with the nearly normaldistribution for old disk giants. The distribution of (U,V) velocityvectors gives (U,V,W) and their dispersions = (+17.6 +/- 18.4, -14.8 +/-8.4, -6.9 +/- 13.0) and (+3.6 +/- 38.4, -20.7 +/- 27.5, -6.7 +/-17.3)km/s for young and old disk giants, respectively.

Nova Scorpii 1992
IAUC 5536 available at Central Bureau for Astronomical Telegrams.IAUC 5536 available at Central Bureau for Astronomical Telegrams.

Secondary UVBY standards in the Harvard E-regions
Photoelectric uvby photometry for 201 stars which are already UBV (RI)cstandards is presented. The photoelectric data are closely tied to theCousins uvby standards and the stars should be suitable for use asfainter (7-11 mag) secondary standards.

Secondary standards for H-beta photometry in the Southern Hemisphere (second series).
Not Available

Southern JHKL standards
The basis for the current SAAO standard photometric system at JHKL isgiven. This depends on an extensive investigation involving 230 starsdistributed around the sky. The accuracy is estimated at + or - 0.02 magfor J, H and K and + or - 0.05 mag for L.

Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.

UBV (RI)c standard stars in the E- and F-regions and in the Magellanic Clouds - a revised catalogue.
Not Available

Secondary standards for the Stromgren UVBY system
Observations of 158 E region stars have been made in the Stromgrensystem, using the 46-cm reflector at Cape Town. They are mostly brighterthan eighth magnitude and are intended for use as secondary standardsfor the four-color system. The E region relative zero points are definedwith a precision of + or - 0.001 mag, and the internal standard errorsof the colors life between + or - 0.001 and + or - 0.002 mag.

On the (B-V) colors of the bright stars
The possible causes of the dispersion of (B-V) colors of nearby stars inthe Bright Star Catalog are investigated. The distribution of (B-V)colors is presented for the entire range of spectral classes.Explanations for the dispersion in terms of a nonuniform distribution ofinterstellar absorbing material and a variability of metallicity areaddressed. A new statistical model for reddening by interstellar dustclouds is developed. It is concluded that extinction by nonuniforminterstellar matter is an important contribution to the reddening ofnearby stars, and that a part of the dispersion of (B-V) colors of Kand, possibly, M giants may be due to some unidentified variableproperty of those stars.

Infrared spectra of WN stars. II - WN7 and WN8 stars
Moderate resolution (lambda/delta lambda less than 400) infrared spectrain the range 1-2.5 microns are presented for HD 86161(WN8), HD96548(WN8), and HD 151932(WN7). These data, in conjunction with existingoptical and UV data, will provide new insights into the structure ofWolf-Rayet stellar atmospheres, and are suitable for model input.

DDO Observations of Southern Stars
Not Available

Photometric standard stars for the UBV and (RI)KC systems.
Not Available

VRI standards in the E regions
Not Available

Luminosity and velocity distributions of high-luminosity red stars. IV. The G-type giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974PASP...86..129E&db_key=AST

Standard Stars for VRI Photometry with S25 Response Photocathodes [Errata: 1974MNSSA..33....1C]
Not Available

Standard magnitudes in the E regions.
Not Available

Magnitudes of bright stars in the E regions observed by the Fabry method
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1950MNRAS.110..531C&db_key=AST

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Observation and Astrometry data

Right ascension:17h10m42.30s
Apparent magnitude:5.08
Distance:91.996 parsecs
Proper motion RA:-34.6
Proper motion Dec:-64.5
B-T magnitude:6.147
V-T magnitude:5.157

Catalogs and designations:
Proper Names   (Edit)
HD 1989HD 154948
TYCHO-2 2000TYC 7882-570-1
USNO-A2.0USNO-A2 0450-26651857
BSC 1991HR 6371
HIPHIP 84033

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