내용
사진
사진 업로드
DSS Images Other Images
관련 글
First Simultaneous Photometric and Spectroscopic Analysis of the Active star IT Com
In this paper we report the variations of luminosity, effectivetemperature and H emission of the RS CVn binary IT Com, which are due tophotospheric and chromospheric
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
| Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution
The kinematics of 237 chromospherically active binaries (CABs) werestudied. The sample is heterogeneous with different orbits andphysically different components from F to M spectral-type main-sequencestars to G and K giants and supergiants. The computed U, V, W spacevelocities indicate that the sample is also heterogeneous in velocityspace. That is, both kinematically younger and older systems exist amongthe non-evolved main sequence and the evolved binaries containing giantsand subgiants. The kinematically young (0.95 Gyr) subsample (N= 95),which is formed according to the kinematical criteria of moving groups,was compared with the rest (N= 142) of the sample (3.86 Gyr) toinvestigate any observational clues of binary evolution. Comparing theorbital period histograms between the younger and older subsamples,evidence was found supporting the finding of Demircan that the CABs losemass (and angular momentum) and evolve towards shorter orbital periods.The evidence of mass loss is noticeable on the histograms of the totalmass (Mh+Mc), which is compared between theyounger (only N= 53 systems available) and older subsamples (only N= 66systems available). The orbital period decrease during binary evolutionis found to be clearly indicated by the kinematical ages of 6.69, 5.19and 3.02 Gyr which were found in the subsamples according to the periodranges of logP<= 0.8, 0.8 < logP<= 1.7 and 1.7 < logP<=3, respectively, among the binaries in the older subsample.
| The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| The HRX-BL Lac sample - Evolution of BL Lac objects
The unification of X-ray and radio selected BL Lacs has been anoutstanding problem in the blazar research in the past years. Recentinvestigations have shown that the gap between the two classes can befilled with intermediate objects and that apparently all differences canbe explained by mutual shifts of the peak frequencies of the synchrotronand inverse Compton component of the emission. We study the consequencesof this scheme using a new sample of X-ray selected BL Lac objectscomprising 104 objects with z<0.9 and a mean redshift bar {z} = 0.34.77 BL Lacs, of which the redshift could be determined for 64 (83%)objects, form a complete sample. The new data could not confirm ourearlier result, drawn from a subsample, that the negative evolutionvanishes below a synchrotron peak frequency log nupeak =16.5. The complete sample shows negative evolution at the 2sigma level(< Ve/Va > = 0.42 +/- 0.04). We concludethat the observed properties of the HRX BL Lac sample show typicalbehaviour for X-ray selected BL Lacs. They support an evolutionarymodel, in which flat-spectrum radio quasars (FSRQ) with high energeticjets evolve towards low frequency peaked (mostly radio-selected) BL Lacobjects and later on to high frequency peaked (mostly X-ray selected) BLLacs.Appendix (Tables 8 and 9, Fig. 8) is only available in electronic format http://www.edpsciences.org
| Reprocessing the Hipparcos Intermediate Astrometric Data of spectroscopic binaries. II. Systems with a giant component
By reanalyzing the Hipparcos Intermediate Astrometric Data of a largesample of spectroscopic binaries containing a giant, we obtain a sampleof 29 systems fulfilling a carefully derived set of constraints andhence for which we can derive an accurate orbital solution. Of these,one is a double-lined spectroscopic binary and six were not listed inthe DMSA/O section of the catalogue. Using our solutions, we derive themasses of the components in these systems and statistically analyzethem. We also briefly discuss each system individually.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997) and on data collected with theSimbad database.
| Vertical distribution of Galactic disk stars. I. Kinematics and metallicity
Nearly 400 Tycho-2 stars have been observed in a 720 square degree fieldin the direction of the North Galactic Pole with the high resolutionechelle spectrograph ELODIE. Absolute magnitudes, effectivetemperatures, gravities and metallicities have been estimated, as wellas distances and 3D velocities. Most of these stars are clump giants andspan typical distances from 200 pc to 800 pc to the galactic mid-plane.This new sample, free of any kinematical and metallicity bias, is usedto investigate the vertical distribution of disk stars. The old thindisk and thick disk populations are deconvolved from thevelocity-metallicity distribution of the sample and their parameters aredetermined. The thick disk is found to have a moderate rotational lag of-51 +/- 5 km s-1 with respect to the Sun with velocityellipsoid (sigmaU , sigmaV , sigmaW )=(63+/- 6, 39+/- 4, 39+/- 4) km s-1, mean metallicity of[Fe/H] = -0.48 +/- 0.05 and a high local normalization of 15 +/- 7%.Combining this NGP sample with a local sample of giant stars from theHipparcos catalogue, the orientation of the velocity ellipsoid isinvestigated as a function of distance to the plane and metallicity. Wefind no vertex deviation for old stars, consistent with an axisymmetricGalaxy. Paper II is devoted to the dynamical analysis of the sample,puting new constraints on the vertical force perpendicular to thegalactic plane and on the total mass density in the galactic plane.Based on observations made at the Observatoire de Haute Provence(France). Data are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/141
| The Vienna-KPNO search for Doppler-imaging candidate stars. I. A catalog of stellar-activity indicators for 1058 late-type Hipparcos stars
We present the results from a spectroscopic Ca ii H&K survey of 1058late-type stars selected from a color-limited subsample of the Hipparcoscatalog. Out of these 1058 stars, 371 stars were found to showsignificant H&K emission, most of them previously unknown; 23% withstrong emission, 36% with moderate emission, and 41% with weak emission.These spectra are used to determine absolute H&K emission-linefluxes, radial velocities, and equivalent widths of theluminosity-sensitive Sr ii line at 4077 Ä. Red-wavelengthspectroscopic and Strömgren y photometric follow-up observations ofthe 371 stars with H&K emission are used to additionally determinethe absolute Hα -core flux, the lithium abundance from the Li i6708 Å equivalent width, the rotational velocity vsin i, theradial velocity, and the light variations and its periodicity. Thelatter is interpreted as the stellar rotation period due to aninhomogeneous surface brightness distribution. 156 stars were found withphotometric periods between 0.29 and 64 days, 11 additional systemsshowed quasi-periodic variations possibly in excess of ~50 days. Further54 stars had variations but no unique period was found, and four starswere essentially constant. Altogether, 170 new variable stars werediscovered. Additionally, we found 17 new SB1 (plus 16 new candidates)and 19 new SB2 systems, as well as one definite and two possible new SB3systems. Finally, we present a list of 21 stars that we think are mostsuitable candidates for a detailed study with the Doppler-imagingtechnique. Tables A1--A3 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The ROSAT Bright Survey: II. Catalogue of all high-galactic latitude RASS sources with PSPC countrate CR > 0.2 s-1
We present a summary of an identification program of the more than 2000X-ray sources detected during the ROSAT All-Sky Survey (Voges et al.1999) at high galactic latitude, |b| > 30degr , with countrate above0.2 s-1. This program, termed the ROSAT Bright Survey RBS, isto more than 99.5% complete. A sub-sample of 931 sources with countrateabove 0.2 s-1 in the hard spectral band between 0.5 and 2.0keV is to 100% identified. The total survey area comprises 20391deg2 at a flux limit of 2.4 x 10-12 ergcm-2 s-1 in the 0.5 - 2.0 keV band. About 1500sources of the complete sample could be identified by correlating theRBS with SIMBAD and the NED. The remaining ~ 500 sources were identifiedby low-resolution optical spectroscopy and CCD imaging utilizingtelescopes at La Silla, Calar Alto, Zelenchukskaya and Mauna Kea. Apartfrom completely untouched sources, catalogued clusters and galaxieswithout published redshift as well as catalogued galaxies with unusualhigh X-ray luminosity were included in the spectroscopic identificationprogram. Details of the observations with an on-line presentation of thefinding charts and the optical spectra will be published separately.Here we summarize our identifications in a table which contains opticaland X-ray information for each source. As a result we present the mostmassive complete sample of X-ray selected AGNs with a total of 669members and a well populated X-ray selected sample of 302 clusters ofgalaxies with redshifts up to 0.70. Three fields studied by us remainwithout optical counterpart (RBS0378, RBS1223, RBS1556). While the firstis a possible X-ray transient, the two latter are isolated neutron starcandidates (Motch et al. 1999, Schwope et al. 1999).
| Alignment of rotational axes in asynchronous late type binaries
41 RS CVn and BY Dra type binaries with reliable orbital and physicalparameters have been found to rotate asynchronously with the orbitalrevolution. For this sample inclinations of the rotational axes, i_r, ofthe primaries and the orbital inclinations, i_o, are independentlydetermined to test the alignment between the equatorial and the orbitalplanes. The observed difference Delta i=| {i_o} - {i_r}| measures adeviation from coplanarity of these planes. It turns out that mostasynchronous systems prove to be misaligned, especially when theinfluence of the position angle is taken into account. Thus, thegenerally accepted assumption that rotational axes are perpendicular toorbital planes is not valid for asynchronous RS CVn and BY Dra typebinaries. The influence of the position angle of the observer on thederived values of Delta i can be studied only by statistical methods.The distribution of the observed Delta i is compared wih the expectedvalues of Delta i() e for two cases: a) the rotational axes are randomlyinclined to the orbital planes, and b) the rotational axes areperpendicular to the orbital planes. The best fit to our observed sampleof asynchronous binaries is obtained for the case a), while for thesynchronous RS CVn and BY Dra type binaries the rotational axes areperpendicular to their orbital planes. The appendix is available onlyelectronically with the on-line publication athttp://link.springer.de/link/service/journals/00230
| Rotational Velocities of Late-Type Stars
A calibration based on the results of Gray has been used to determineprojected rotational velocities for 133 bright stars with spectral typesof F, G, or K, most of which appear in {\it The Bright Star Catalogue}.The vast majority have {\it v} sin {\it i} $\leq$ 10 km s$^{-1}$ and,thus, are slow rotators. With the new calibration, projected rotationalvelocities have been determined for a sample of 111 late-type stars,most of which are chromospherically active. Some of the stars have hadtheir rotational velocities measured for the first time. (SECTION:Stars)
| The 73rd Name-List of Variable Stars
Not Available
| An Automated Search for Variability in Chromospherically Active Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2926H&db_key=AST
| Chromospheric activity in G and K giants: the spectroscopic data base
I present high-resolution CCD spectra of CaII H and K emission lines of59 evolved stars of spectral type G and K and luminosity Class III,III-IV, and IV. This includes active stars like RS CVn binaries but alsoactive and inactive single stars. Most of the objects were observed forthe first time and several were discovered to be chromosphericallyactive. Spectra for ten stars of luminosity Class V are also given.
| Chromospheric activity in G and K giants and their rotation-activity relation
We obtained high-resolution CCD spectra of Ca II H and K emission linesof 59 evolved stars of spectral type G and K and luminosity class III,III-IV, and IV. Our sample includes active stars like RS CVn binariesbut also active and inactive single stars. Whenever possible wedetermine absolute emission line surface fluxes and use them,supplemented by previously published fluxes from high-resolutionspectra, to quantify the rotation-activity relation for evolved stars.We find that the Ca II surface fluxes from evolved stars scale linearlywith stellar rotational velocity and that the flux from the cooler starsdepends stronger upon rotation than the flux from the hotter stars, inagreement with previous findings for main-sequence stars. However, largescatter indicates that rotational velocity might not be the onlyrelevant parameter. We also present some evidence for the existence of a'basal' flux for evolved stars that scales approximately with the eightpower of the effective surface temperature.
| Statistical Analysis of a Sample of Spectroscopic Binaries Containing Late Type Giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...271..125B&db_key=AST
| The 71st Name-List of Variable Stars
Not Available
| Spectroscopic binaries near the north galactic pole. XXII - HR 4793
Results are presented on photoelectric radial-velocity observations of aK1 III star HR 4793, made by several observatories. The data indicatethat the HR 4793 is a spectroscopic binary. It has a circular orbit witha period of 111 days and an amplitude of 7 km/sec.
| Spectroscopic binaries near the North Galactic Pole. XIV - HD 118234
Photoelectric radial-velocity measurements for HD 118234 are presentedfor the 1971-1987 period. The results suggest that HD 118234 is aspectroscopic binary in a very eccentric 59-day orbit. Although the59-day period is quite short for a giant star, the widths of the dips onthe radial-velocity traces do not imply that HD 118234 has an unusuallyrapid rotation.
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
