내용
사진
사진 업로드
DSS Images Other Images
관련 글
An Observational Pursuit for Population III Stars in a Lyα Emitter at z = 6.33 through He II Emission
We present a very deep near-infrared spectroscopic observation of astrong Lyα emitter at z=6.33, SDF J132440.6+273607, which we usedto search for He II λ1640. This emission line is expected if thetarget hosts a significant number of Population III stars. Even after 42ks of integration with the Subaru/OHS spectrograph, no emission-linefeatures are detected in the J and H bands, which confirms that SDFJ132440.6+273607 is neither an active galactic nucleus nor a low-zemission-line object. We obtained a 2 σ upper limit of9.06×10-18 ergs s-1 cm-2 on theHe II λ1640 emission-line flux, which corresponds to a luminosityof 4.11×1042 ergs s-1. This upper limit onthe He II λ1640 luminosity implies that the upper limit on thePopulation III star formation rate is in the range 4.9-41.2Msolar yr-1 if Population III stars suffer no massloss and in the range 1.8-13.2 Msolar yr-1 ifstrong mass loss is present. The nondetection of He II in SDFJ132440.6+273607 at z=6.33 may thus disfavor weak feedback models forPopulation III stars.Based on data collected at the Subaru Telescope, which is operated bythe National Astronomical Observatory of Japan.
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| UvbyHbeta_ photometry of main sequence A type stars.
We present Stroemgren uvby and Hbeta_ photometry for a set of575 northern main sequence A type stars, most of them belonging to theHipparcos Input Catalogue, with V from 5mag to 10mag and with knownradial velocities. These observations enlarge the catalogue we began tocompile some years ago to more than 1500 stars. Our catalogue includeskinematic and astrophysical data for each star. Our future goal is toperform an accurate analysis of the kinematical behaviour of these starsin the solar neighbourhood.
| Fifth fundamental catalogue. Part 2: The FK5 extension - new fundamental stars
The mean positions and proper motions for 3117 new fundamental starsessentially in the magnitude range about 4.5 to 9.5 are given in thisFK5 extension. Mean apparent visual magnitude is 7.2 and is on average2.5 magnitudes fainter then the basic FK5 which has a mean magnitude of4.7. (The basic FK5 gives the mean positions and proper motions for theclassical 1535 fundamental stars). The following are discussed: theobservational material, reduction of observations, star selection, andthe system for the FK5 extension. An explanation and description of thecatalog are given. The catalog of 3117 fundamental stars for the equinoxand epoch J2000.0 and B1950.0 is presented. The parallaxes and radialvelocities for 22 extension stars with large forecasting effects aregiven. Catalogs used in the compilation of the FK5 fundamental catalogare listed.
| Electronographic polarimetry - The Durham polarimeter
The present investigation is concerned with an instrument for mappingthe linear polarization of extended astronomical objects at opticalwavelengths. The first important studies of this type were based uponthe use of photographic techniques and photoelectric observations.Later, improvements in detector technology have made it possible toobserve fainter objects at higher spatial resolution. A description ispresented of the principles of operation of the Durham Universitypolarimeter which has been extensively used in the observations. Thepolarimeter uses a 40-mm McMullan electronographic camera to providesimultaneous detection at all the image points. The selected approachprovides advantages of increased speed, linearity, resolution, dynamicrange, and storage capacity in comparison to photographic detection.
| New map of the optical polarisation of galaxy M82
Observations of the linear optical polarization of the galaxy M82 wereobtained during the period Feb. 27-Mar. 15, 1975 using a polarimetrictechique derived from that of Ohman (1939). A rotating achromatichalf-wave plate and a Wollaston prism were used to separate orthogonallypolarized beams. The optical polarization map shows a centrallysymmetric pattern which permits the derivation of the position of thecentral source of radiation. A singular nucleus could not be identified;there is no detailed correspondence between the various central featuresin M82. The most intense radio component has no special position in theinfrared source, which is not coincident with the center of symmetry.The optically brightest spot is close to the center of the infraredsource but not to the other features. It is suggested that galaxies ofthe type of M82 might represent a connecting link between Seyferts andnormal galaxies.
| Photoelectric UBV observations made on the Palomar 20-inch telescope
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973MNRAS.164..133P&db_key=AST
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
