내용
사진
사진 업로드
DSS Images Other Images
관련 글
Broad-band optical polarimetric study of IC 1805
We present the BVR broad-band polarimetric observations of 51 starsbelonging to the young open cluster IC 1805. Along with the photometricdata from the literature, we have modelled and subtracted the foregrounddust contribution from the maximum polarization (Pmax) andcolour excess [E (B - V)]. The mean value of the Pmax forintracluster medium and the foreground are found to be 5.008 +/- 0.005and 4.865 +/- 0.022 per cent, respectively. Moreover, the mean value ofthe wavelength of maximum polarization (λmax) forintracluster medium is 0.541 +/- 0.003μ m, which is quite similar asthe general interstellar medium (ISM). The resulting intracluster dustcomponent is found to have negligible polarization efficiency ascompared to interstellar dust. Some of the observed stars in IC 1805have shown the indication of intrinsic polarization in theirmeasurements.
| Mass-luminosity relation for massive stars
A catalog of massive (⩾10 M ȯ) stars in binary andmultiple systems with well-known masses and luminosities has beencompiled. The catalog is analyzed using a theoretical mass-luminosityrelation. This relation allows both normal main-sequence stars and starswith peculiarities: with clear manifestations of mass transfer, massaccretion, and axial rotation, to be identified. Least-squares fittingof the observational data in the range of stellar masses 10Mȯ ⩽ M ≲ 50 M ȯ yields therelation L ˜ M 2.76.
| Precise Times of Minimum Light of Neglected Eclipsing Binaries
Not Available
| Young Stars in the Camelopardalis Dust and Molecular Clouds. I. The Cam OB1 Association
The distribution of dust and molecular clouds in the direction ofGalactic longitudes 132--158° and latitudes ± 12\degr\ isinvestigated. The maps of dust distribution in the area were plottedfrom the following surveys: the star counts in the DSS I database byDobashi et al. (2005), the survey of the average infrared color excessesby Froebrich et al. (2007) and the thermal dust emission survey at 100μ m by Schlegel et al. (1998). The distribution of molecular cloudswas taken from the whole sky CO survey by Dame et al. (2001). All thesesurveys show very similar cloud patterns in the area. Using the radialvelocities of CO, the distances to separate clouds are estimated. Arevised list of the Cam OB1 association members contains 43 stars andthe open cluster NGC 1502. 18 young irregular variable and Hαemission stars are identified in the area. All this proves that the starforming process in the Camelopardalis clouds is still in progress.
| Spectropolarimetry of the Peculiar Type Ia Supernova 2005hk
We present Keck spectropolarimetry of the unusual Type Ia supernova (SNIa) 2005hk several days before maximum light. An analysis of the highsignal-to-noise ratio total-flux spectrum shows the object's extremesimilarity to the peculiar SN 2002cx. SN 2005hk has an optical spectrumdominated by Fe III lines and only weak lines of intermediate-masselements, unlike a normal SN Ia at this epoch. The photospheric velocitymeasured from the minima of strong absorption lines is very low for anSN Ia (~6000 km s-1), solidifying the connection to SN2002cx. The spectrum-synthesis code SYNOW was used to identify thepresence of iron-peak elements, intermediate-mass elements, and possiblyunburned carbon at similar velocities in the outer ejecta of SN 2005hk.Many weak spectral features remain unidentified. The spectropolarimetryshows a low level of continuum polarization (~0.4%) after correction forthe interstellar component, and only a weak Fe III line feature isdetected. The level of continuum polarization is normal for an SN Ia,implying that the unusual features of SN 2005hk cannot be readilyexplained by large asymmetries.
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| Evidence for Spectropolarimetric Diversity in Type Ia Supernovae
We present single-epoch, postmaximum spectropolarimetry of four Type Iasupernovae (SNe Ia) that span a range of spectral and photometricproperties: SN 2002bf and SN 2004dt exhibit unusually high-velocity (HV)absorption lines. SN 1997dt is probably somewhat subluminous, and SN2003du is slightly overluminous. We detect polarization modulationsacross strong lines in all four objects, demonstrating that all areintrinsically polarized. However, the nature and degree of thepolarization varies considerably. Including all SNe Ia studied thus far,the following order emerges in terms of increasing strength ofline-polarization features: ordinary/overluminous
| To see or not to see a bow shock. Identifying bow shocks with Hα allsky surveys
OB-stars have the highest luminosities and strongest stellar winds ofall stars, which enables them to interact strongly with theirsurrounding ISM, thus creating bow shocks. These offer us an idealopportunity to learn more about the ISM. They were first detected andanalysed around runaway OB-stars using the IRAS allsky survey by vanBuren et al. (1995, AJ, 110, 2614). Using the geometry of such bowshocks information concerning the ISM density and its fluctuations canbe gained from such infrared observations. As to help to improve the bowshock models, additional observations at other wavelengths, e.g.Hα, are most welcome. However due to their low velocity these bowshocks have a size of 1°, and could only be observed as awhole with great difficulties. In the light of the new Hα allskysurveys (SHASSA/VTSS) this is no problem any more. We developeddifferent methods to detect bow shocks, e.g. the improved determinationof their symmetry axis with radial distance profiles. Using twoHα-allsky surveys (SHASSA/VTSS), we searched for bow shocks andcompared the different methods. From our sample we conclude, that thecorrelation between the direction of both proper motion and the symmetryaxis determined with radial distance profile is the most promisingdetection method. We found eight bow shocks around HD17505, HD 24430, HD48099, HD 57061, HD92206, HD 135240, HD149757, and HD 158186 from 37 candidatestaken from van Buren et al. (1995, AJ, 110, 2614). Additionally to thetraditional determination of ISM parameters using the standoff distanceof the bow shock, another approach was chosen, using the thickness ofthe bow-shock layer. Both methods lead to the same results, yieldingdensities ( 1 cm-3) and the maximal temperatures (104 K), that fit well to the up-to-date picture of the WarmIonised Medium.
| Times of Minimum Light of Neglected Eclipsing Binaries
Not Available
| On the Hipparcos parallaxes of O stars
We compare the absolute visual magnitude of the majority of bright Ostars in the sky as predicted from their spectral type with the absolutemagnitude calculated from their apparent magnitude and the Hipparcosparallax. We find that many stars appear to be much fainter thanexpected, up to five magnitudes. We find no evidence for a correlationbetween magnitude differences and the stellar rotational velocity assuggested for OB stars by Lamers et al. (1997, A&A, 325, L25), whosesmall sample of stars is partly included in ours. Instead, by means of asimulation we show how these differences arise naturally from the largedistances at which O stars are located, and the level of precision ofthe parallax measurements achieved by Hipparcos. Straightforwardlyderiving a distance from the Hipparcos parallax yields reliable resultsfor one or two O stars only. We discuss several types of bias reportedin the literature in connection with parallax samples (Lutz-Kelker,Malmquist) and investigate how they affect the O star sample. Inaddition, we test three absolute magnitude calibrations from theliterature (Schmidt-Kaler et al. 1982, Landolt-Börnstein; Howarth& Prinja 1989, ApJS, 69, 527; Vacca et al. 1996, ApJ, 460, 914) andfind that they are consistent with the Hipparcos measurements. AlthoughO stars conform nicely to the simulation, we notice that some B stars inthe sample of \citeauthor{La97} have a magnitude difference larger thanexpected.
| Close binary stars in ob-association regions i. preliminary investigation
We performed a sample of O- and B-eclipsing binary stars inOB-association regions and obtained the preliminary list of 147 binariesin 45 OB-association regions. We tried to elucidate the question whether(or not) the close binaries belong to corresponding OB-associations,from the commonness of their proper motions, radial velocities anddistances. Based on the completeness of the data,the binaries aredevided into three groups and the scheme for calculation of degree ofbelonging of stars to OB-associations is developed. Necessary data arenot available for nine systems and they are given in a specific table.For 12 cases, the binaries project onto the regions of two associations.We show that 33 (22.3%) close binary stars are members, 65 (43.9%) areprobable members and 39 (26.4%) are less probable members of theOB-associations. We find that 11 binaries belong to the Galaxybackground. The comparison of the distributions of orbital periods forthe binaries in OB-associations and for O-, B-binaries of the Galaxybackground shows their considerable differences in the vicinity of thetwo-day period.
| A Galactic O Star Catalog
We have produced a catalog of 378 Galactic O stars with accuratespectral classifications that is complete for V<8 but includes manyfainter stars. The catalog provides cross-identifications with othersources; coordinates (obtained in most cases from Tycho-2 data);astrometric distances for 24 of the nearest stars; optical (Tycho-2,Johnson, and Strömgren) and NIR photometry; group membership,runaway character, and multiplicity information; and a Web-based versionwith links to on-line services.
| Apsidal Motion in Binaries: Rotation of the Components
A sample of 51 separated binary systems with measured apsidal periodsand rotational velocities of the components is examined. The ranges ofthe angles of inclination of the equatorial planes of the components tothe orbital plane are estimated for these systems. The observed apsidalvelocities can be explained by assuming that the axes of rotation of thestars are nonorthogonal to the orbital plane in roughly 47% of thesystems (24 of the 51) and the rotation of the components is notsynchronized with the orbital motion in roughly 59% of the systems (30of 51). Nonorthogonality and nonsynchrony are defined as deviations from90° and a synchronized angular velocity, respectively, at levels of1 or more.
| Optical Spectropolarimetry of the GRB 020813 Afterglow
The optical afterglow of gamma-ray burst GRB 020813 was observed for 3hr with the LRIS spectropolarimeter at the Keck I telescope, beginning4.7 hr after the burst was detected by the HETE-2. The spectrum revealsnumerous metal absorption lines that we identify with two systems atz=1.223 and z=1.255. We also detect an [O II] λ3727 emission lineat z=1.255, and we identify this galaxy as the likely host of the GRB.After a correction for Galactic interstellar polarization, the opticalafterglow has a linear polarization of 1.8%-2.4% during 4.7-7.9 hr afterthe burst. A measurement of p=0.80%+/-0.16% on the following night byCovino et al. demonstrates significant polarization variability over thenext 14 hr. The lack of strong variability in the position angle oflinear polarization indicates that the magnetic field in the jet islikely to be globally ordered rather than composed of a number ofrandomly oriented cells. Within the framework of afterglow models withcollimated flows, the relatively low observed polarization suggests thatthe magnetic field components perpendicular and parallel to the shockfront are only different by about 20%.
| Masses and other parameters of massive binaries
Binary stars provide us with the means to measure stellar mass. Here Ipresent several lists of known O-type stars with reliable mass estimatesthat are members of eclipsing, double-lined spectroscopic binaries. Themasses of young, unevolved stars in binaries are suitable for testingthe predictions of evolutionary codes, and there is good agreementbetween the observed and predicted masses (based upon temperature andluminosity) if the lower temperature scale from line-blanketed modelatmospheres is adopted. A final table lists masses for systems in awide variety of advanced evolutionary stages.
| The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| Einige interessante Bedeckungsveraenderliche.
Not Available
| The Stars in Camelopardalis OB1: Their Distance and Evolutionary History
An investigation is undertaken of the optically identified Population Iobjects in the Cam OB1 region. From the analysis of these objects it isdetermined that the distance to the Cam OB1 stars is 975+/-90 pc. Atheoretical H-R diagram for the Cam OB1 stars reveals that starformation has been going on in the region for1×106-1×108 yr. At present, the mostactive site of star formation is Cam R1, which shows an asymmetry in thedistribution of optically identified Population I objects. The majorityof the pre-main-sequence stars lie in the northern half of theassociation, while the main-sequence stars and evolved stars lie in thesouthern half.
| The comparative accuracy of photographic observations of radio stars observed at the Engelhardt Astronomical Observatory
At the Engelhardt Astronomical Observatory (EAO), we observedphotographic positions of 113 Galactic Radio Sources (GRS) in the systemPPM catalogue (Rizvanov & Dautov 1998). Analysis of their accuracyis made by comparison with the Hipparcos catalogue (Perryman et al.1997) and astrometric catalogue of radio stars in the radio window fromthe article of Walter et al. (1991). Table 2 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/375/670
| Is It Round? Spectropolarimetry of the Type II-p Supernova 1999EM
We present the first multiepoch spectropolarimetry of a Type II plateausupernova (SN II-P), with optical observations of SN 1999em on days 7,40, 49, 159, and 163 after discovery. These data are used to probe thegeometry of the electron scattering atmosphere before, during, and afterthe plateau phase, which ended roughly 90 days after discovery. Weakcontinuum polarization with an unchanging polarization angle(θ~160deg) is detected at all epochs, with p~0.2% onday 7, p~0.3% on days 40 and 49, and p~0.5% in the final observations.Distinct polarization modulations across strong line features arepresent on days 40, 49, 159, and 163. Uncorrected for interstellarpolarization (which is believed to be quite small), polarization peaksare associated with strong P Cygni absorption troughs, and nearlycomplete depolarization is seen across the Hα emission profile.The temporal evolution of the continuum polarization and sharp changesacross lines indicate polarization intrinsic to SN 1999em. When modeledin terms of the oblate, electron scattering atmospheres of Höflich,the observed polarization suggests an asphericity of at least 7% duringthe period studied. The temporal polarization increase may indicategreater asphericity deeper into the ejecta. We discuss the implicationsof asphericity on the use of Type II-P supernovae as primaryextragalactic distance indicators through the expanding photospheremethod (EPM). If asphericity produces directionally dependent flux andpeculiar galaxy motions are characterized byσvrec=300 km s-1, it is shownthat the agreement between previous EPM measurements of SNe II anddistances to the host galaxies predicted by a linear Hubble lawrestricts mean SN II asphericity to values less than 30% (3 σ)during the photospheric phase.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable 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/qcar?J/A+A/367/521
| On the Variability of O4-B5 Luminosity Class III-V Stars
We investigate the Hipparcos Satellite photometry of O4-B5 luminosityclass III-V stars. Some for which further study is desirable areidentified. These stars in general are more variable than cooler stars
| A New Spectropolarimeter at the Dodaira Observatory
We report a newly developed spectropolarimeter with a low-dispersionresolution (R=40-200) and a wide coverage in wavelength (400-900 nm). Itis mainly used along with the 0.91 m telescope at the DodairaObservatory of the National Astronomical Observatory, Japan. Thisinstrument and the related reduction software are described briefly. Thepresent polarimetric accuracy (rms) is estimated to be[(P/50)^2+(0.05)^2]^1/2%, where P is the linear polarization degree inpercent. The spectropolarimeter has the advantage of being most usefulin the polarimetric studies of both the continuum and the strongemission and/or absorption lines. It is mainly used for the short- orlong-term monitoring of variable circumstellar polarization and ofpolarization in comets, and for studies on interstellar polarization.
| Absolute declinations with the photoelectric astrolabe at Calern Observatory (OCA)
A regular observational programme with a photoelectric astrolabe havebeen performed at ``Observatoire du Calern" (Observatoire de laCôte d'Azur, OCA, phi = +43() o44′55.011″; lambda =-0() h27() m42.44() s, Calern, Caussols, France) for the last twentyyears. It has been almost fully automatized between 1984 and 1987. Since1988 the photoelectric astrolabe was used without any modification. Inaddition to determining the daily orientation of the local vertical, theyearly analysis of the residuals permits to derive corrections to theused star catalogue \cite[(Vigouroux et al. 1992)]{vig92}. A globalreduction method was applied for the ASPHO observations. The new form ofthe equations \cite[(Martin & Leister 1997)]{mar97} give us thepossibility of using the entire set of the observing program using datataken at two zenith distances (30() o and 45() o). The program containsabout 41648 stars' transits of 269 different stars taken at``Observatoire du Calern" (OCA). The reduction was based on theHIPPARCOS system. We discuss the possibility of computing absolutedeclinations through stars belonging simultaneously to the 30() o and45() o zenith distances programmes. The absolute declination correctionswere determined for 185 stars with precision of 0.027arcsec and thevalue of the determined equator correction is -0.018arcsec +/-0.005arcsec . The instrumental effects were also determined. The meanepoch is 1995.29. Catalogue only available at CDS in electronic from viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Apsidal Motion in Double Stars. I. Catalog
A catalog of 128 double stars with measured periods of apsidal motion iscompiled. Besides the apsidal periods, the orbital elements of binariesand physical parameters of components (masses, radii, effectivetemperatures, surface gravities) are given. The agreement of the apsidalperiods found by various authors is discussed.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| ICCD speckle observations of binary stars. XIX - an astrometric/spectroscopic survey of O stars
We present the results of a speckle interferometric survey made with theCHARA speckle camera and 4 m class telescopes of Galactic O-type starswith V less than 8. We can detect with the speckle camera binaries inthe angular separation range 0.035-1.5 arcsec with delta M less than 3,and we have discovered 15 binaries among 227 O-type systems. We combinedour results on visual binaries with measurements of wider pairs from theWashington Double Star Catalog and fainter pairs from the HipparcosCatalog, and we made a literature survey of the spectroscopic binariesamong the sample. We then investigated the overall binary frequency ofthe sample and the orbital characteristics of the known binaries.Binaries are common among O stars in clusters and associations but lessso among field and especially runaway stars. There are many triplesystems among the speckle binaries, and we discuss their possible rolein the ejection of stars from clusters. The period distribution of thebinaries is bimodal in log P, but we suggest that binaries with periodsof years and decades may eventually be found to fill the gap. The massratio distribution of the visual binaries increases toward lower massratios, but low mass ratio companions are rare among close,spectroscopic binaries. We present distributions of the eccentricity andlongitude of periastron for spectroscopic binaries with ellipticalorbits, and we find strong evidence of a bias in the longitude ofperiastron distribution.
| Neglected binaries of special interest
Not Available
| UV Spectral Classification of O and B Stars in the Small Magellanic =
We present an ultraviolet classification system for 0 and B stars of theSmall Magellanic Cloud (SMC). This system is defined by a set ofstandard, low resolution, International Ultraviolet Explorer (JUE)spectra. This UV classification system results from the development ofspectral sequences demonstrating systematic patterus of UV spectralfeatures. These spectral sequences yield Uv classifications for 133 0and B stars of the SMC, which we also present here. Although independentof the MK System, our UV classifications show general agreement withthose deduced from visual data. This UV classification system isdesigned to be applicable to 0 and B stars in other nearby galaxies ofmetallicity comparable to the SMC. The classification technique itselfis applicable to any UV dataset of sufficient size and quality, and canbe used to extend our UV classification system to other galactic metalabundances. These UV classification systems will be essential foranalysis of datasets from new spaceborne instrumentation such as theSpace Telescope Imaging Spectrograph (STIS), which will be capable ofobserving stars in external galaxies for which no opticalclassifications exist. 0 1997 American Astronomical Society.[S0004-6256(97)0231 1-X]
| Accurate Positions for Radio Stars as Determined from CCD Observations in the Extragalactic Reference Frame.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1679S&db_key=AST
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
INHABITED SKY
