Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
Speckle Observations of Binary Stars with a 0.5 m Telescope
We present 36 observations of 17 visual binaries of moderate separation(ranging from 0.15" to 0.790") made with the 50 cm Cassegrain telescopeof the Jagiellonian University in Kraków. The speckleinterferometry technique was combined with modest optical hardware and astandard photometric CCD camera. We used broadband VRI filters without aRisley prism to reduce differential color refraction. Thus, we performeda model analysis to investigate the influence of this effect on theresults of the measurements. For binary components of spectral type O-F,the difference of three spectral classes between them should bias theirrelative positions by no more than a couple of tens of milliarcseconds(mas) for moderate zenith distances. The statistical analysis of ourresults confirmed this conclusion. A cross-spectrum approach was appliedto resolve the quadrant ambiguity. Our separations have rms deviationsof 0.012", and our position angles have rms deviations of 1.8d. Relativephotometry in V, R, and I filters appeared to be the less accuratelydetermined parameter. We discuss our errors in detail and compare themto other speckle data. This comparison clearly shows the quite goodaccuracy of our measurements. We also present an example of theenhancement of image resolution for an extended object with an angularsize that is greater than the atmospheric coherence patch, using speckleinterferometry techniques.
| Optical Turbulence Profiles at Mauna Kea Measured by MASS and SCIDAR
The vertical distribution of turbulence over Mauna Kea has been measuredon four nights in 2002 October, simultaneously using two differentinstruments based on stellar scintillation-the generalized SCIDAR(scintillation detection and ranging) and MASS (multiaperturescintillation sensor). The turbulence integrals match within 20%, andthe low-resolution profiles delivered by MASS correctly reveal thelocalization of the strongest high-altitude turbulent layers. As deducedfrom DIMM (differential image motion monitor), MASS, and SCIDARmeasurements, optical turbulence in the first 0.7 km above the summitcontributed typically half of the total integral, the lattercorresponding to a seeing of 0.5". The ground layer and free atmosphereare not correlated.
| Visual Star Colours from Instrumental Photometry
In order to display graphically the visual colours of stars and otherastronomical objects, photometric broadband R, V, B colours are used toproxy for the r, g, b colours of the three visual sensors of the eye.From photometric Johnson B-V and V-R colour indices, R, V, and Bmagnitudes (V = 0) are calculated, and from these the respectivebrightnesses (r, v = 1 = g, and b) are calculated. After suitablenormalization these are then placed in a ternary diagram having r, g,and b as the vertices. All B-V and V-R are adjusted so that the Sunfalls in the same place as a blackbody at 5800 K. The resulting ternaryplot shows all of its objects (stars, planets) in their visual coloursat their relative positions in the ternary diagram. The star coloursdisplayed on a computer monitor screen or as a print with a colourprinter are more vivid than the usual visual impressions of isolatedstars, undoubtedly because of properties of the dark-adapted eye, butdouble-star pairs with contrasting colours correspond nicely totelescopic visual impressions.
| Caroline Herschel as observer
Not Available
| A Spitzer Study of Dusty Disks around Nearby, Young Stars
We have obtained Spitzer Space Telescope MIPS (Multiband ImagingPhotometer for Spitzer) observations of 39 A- through M-type dwarfs,with estimated ages between 12 and 600 Myr; IRAC observations for asubset of 11 stars; and follow-up CSO SHARC II 350 μm observationsfor a subset of two stars. None of the objects observed with IRACpossess infrared excesses at 3.6-8.0 μm however, seven objectsobserved with MIPS possess 24 and/or 70 μm excesses. Four objects(κ Phe, HD 92945, HD 119124, and AU Mic), with estimated ages12-200 Myr, possess strong 70 μm excesses, >=100% larger thantheir predicted photospheres, and no 24 μm excesses, suggesting thatthe dust grains in these systems are cold. One object (HD 112429)possesses moderate 24 and 70 μm excesses with a color temperature,Tgr=100 K. Two objects (α1 Lib and HD177724) possess such strong 24 μm excesses that their 12, 24, and 70μm fluxes cannot be self-consistently modeled using a modifiedblackbody despite a 70 μm excess >2 times greater than thephotosphere around α1 Lib. The strong 24 μm excessesmay be the result of emission in spectral features, as observed towardthe Hale-Bopp star HD 69830.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| A survey of 10-μm silicate emission from dust around young sun-like stars
We obtained low resolution (R=100) mid-infrared (8-13 μm wavelengths)spectra of 8 nearby young main sequence stars with the Keck 1 telescopeand Long-Wavelength Spectrometer (LWS) to search for 10 μm silicate(Si-O stretch) emission from circumstellar dust. No stars exhibitedreadily apparent emission: Spectra were then analyzed by least-squaresfitting of a template based on a spectrum of Comet Hale-Bopp. Using thistechnique, we were able to constrain the level of silicate emission to athreshold 10 times below what was previously possible from space. Wefound one star, HD 17925, with a spectrum statistically differentfrom its calibrator and consistent with a silicate emission peak of 7%of the photosphere at a wavelength of 10 μm. Excess emission at 60μm from this star has already been reported.
| Nearby stars of the Galactic disk and halo. III.
High-resolution spectroscopic observations of about 150 nearby stars orstar systems are presented and discussed. The study of these and another100 objects of the previous papers of this series implies that theGalaxy became reality 13 or 14 Gyr ago with the implementation of amassive, rotationally-supported population of thick-disk stars. The veryhigh star formation rate in that phase gave rise to a rapid metalenrichment and an expulsion of gas in supernovae-driven Galactic winds,but was followed by a star formation gap for no less than three billionyears at the Sun's galactocentric distance. In a second phase, then, thethin disk - our ``familiar Milky Way'' - came on stage. Nowadays ittraces the bright side of the Galaxy, but it is also embedded in a hugecoffin of dead thick-disk stars that account for a large amount ofbaryonic dark matter. As opposed to this, cold-dark-matter-dominatedcosmologies that suggest a more gradual hierarchical buildup throughmergers of minor structures, though popular, are a poor description forthe Milky Way Galaxy - and by inference many other spirals as well - if,as the sample implies, the fossil records of its long-lived stars do notstick to this paradigm. Apart from this general picture that emergeswith reference to the entire sample stars, a good deal of the presentwork is however also concerned with detailed discussions of manyindividual objects. Among the most interesting we mention the bluestraggler or merger candidates HD 165401 and HD 137763/HD 137778, thelikely accretion of a giant planet or brown dwarf on 59 Vir in itsrecent history, and HD 63433 that proves to be a young solar analog at\tau200 Myr. Likewise, the secondary to HR 4867, formerly suspectednon-single from the Hipparcos astrometry, is directly detectable in thehigh-resolution spectroscopic tracings, whereas the visual binary \chiCet is instead at least triple, and presumably even quadruple. Withrespect to the nearby young stars a complete account of the Ursa MajorAssociation is presented, and we provide as well plain evidence foranother, the ``Hercules-Lyra Association'', the likely existence ofwhich was only realized in recent years. On account of its rotation,chemistry, and age we do confirm that the Sun is very typical among itsG-type neighbors; as to its kinematics, it appears however not unlikelythat the Sun's known low peculiar space velocity could indeed be thecause for the weak paleontological record of mass extinctions and majorimpact events on our parent planet during the most recent Galactic planepassage of the solar system. Although the significance of thiscorrelation certainly remains a matter of debate for years to come, wepoint in this context to the principal importance of the thick disk fora complete census with respect to the local surface and volumedensities. Other important effects that can be ascribed to this darkstellar population comprise (i) the observed plateau in the shape of theluminosity function of the local FGK stars, (ii) a small thoughsystematic effect on the basic solar motion, (iii) a reassessment of theterm ``asymmetrical drift velocity'' for the remainder (i.e. the thindisk) of the stellar objects, (iv) its ability to account for the bulkof the recently discovered high-velocity blue white dwarfs, (v) itsmajor contribution to the Sun's 220 km s-1 rotationalvelocity around the Galactic center, and (vi) the significant flatteningthat it imposes on the Milky Way's rotation curve. Finally we note ahigh multiplicity fraction in the small but volume-complete local sampleof stars of this ancient population. This in turn is highly suggestivefor a star formation scenario wherein the few existing single stellarobjects might only arise from either late mergers or the dynamicalejection of former triple or higher level star systems.
| X-ray astronomy of stellar coronae
X-ray emission from stars in the cool half of the Hertzsprung-Russelldiagram is generally attributed to the presence of a magnetic coronathat contains plasma at temperatures exceeding 1 million K. Coronae areubiquitous among these stars, yet many fundamental mechanisms operatingin their magnetic fields still elude an interpretation through adetailed physical description. Stellar X-ray astronomy is thereforecontributing toward a deeper understanding of the generation of magneticfields in magnetohydrodynamic dynamos, the release of energy in tenuousastrophysical plasmas through various plasma-physical processes, and theinteractions of high-energy radiation with the stellar environment.Stellar X-ray emission also provides important diagnostics to study thestructure and evolution of stellar magnetic fields from the first daysof a protostellar life to the latest stages of stellar evolution amonggiants and supergiants. The discipline of stellar coronal X-rayastronomy has now reached a level of sophistication that makes tests ofadvanced theories in stellar physics possible. This development is basedon the rapidly advancing instrumental possibilities that today allow usto obtain images with sub-arcsecond resolution and spectra withresolving powers exceeding 1000. High-resolution X-ray spectroscopy has,in fact, opened new windows into astrophysical sources, and has played afundamental role in coronal research.
| Stellar Coronal Astronomy
Coronal astronomy is by now a fairly mature discipline, with a quartercentury having gone by since the detection of the first stellar X-raycoronal source (Capella), and having benefitted from a series of majororbiting observing facilities. Serveral observational characteristics ofcoronal X-ray and EUV emission have been solidly established throughextensive observations, and are by now common, almost text-book,knowledge. At the same time the implications of coronal astronomy forbroader astrophysical questions (e.g.Galactic structure, stellarformation, stellar structure, etc.) have become appreciated. Theinterpretation of stellar coronal properties is however still often opento debate, and will need qualitatively new observational data to bookfurther progress. In the present review we try to recapitulate our viewon the status of the field at the beginning of a new era, in which thehigh sensitivity and the high spectral resolution provided by Chandraand SMM-Newton will address new questions which were not accessiblebefore.
| 400 years of Uranometria.
Not Available
| Optical-Turbulence and Wind Profiles at San Pedro Mártir
Results of monitoring optical-turbulence profiles and velocity of theturbulence layers at San Pedro Mártir, Mexico, are presented. Thedata were collected during 11 nights in April-May 1997 and 16 nights inMay 2000 using the Generalized Scidar of Nice University installed onthe 1.5-m and 2.1-m telescopes. The statistical analysis of the 6414turbulence profiles obtained shows that the seeing produced by theturbulence in the first 1.2 km, not including dome seeing, at the 1.5-mand the 2.1-m telescopes have median values of 0 to z 0. hss'' 63 and0 to z 0. hss'' 44, respectively. The dome seeing at those telescopeshave median values of 0 to z 0. hss'' 64 and 0 to z 0. hss'' 31. Theturbulence above 1.2 km and in the whole atmosphere produces seeing withmedian values of 0 to z 0. hss'' 38 and 0 to z 0. hss'' 71. Thetemporal correlation of the turbulence strength drops to 50% in timelags of 2 and 0.5 hours, approximately, for altitudes below and above 16km above sea level, respectively. The turbulence above 9 kmremained notably calm during 9 consecutive nights, which is encouragingfor adaptive optics observations at the site. The 3016 profiles of theturbulent-layer velocity that are analyzed show that the fastest layersare found between 10 and 17 km, where the tropopause and the jet streamare located, with median speed of 24.4 m s-1. In the first 2.2 km andabove 17 km, the turbulent layers move relatively slowly, with medianspeeds of 2.3 and 9.2 m s-1. The median of the wavefront coherence-timeis 6.5 ms, in the visible. The results obtained here places San PedroMártir among the best suited sites for installing next generationoptical telescopes.
| The ɛ Chamaeleontis Young Stellar Group and the Characterization of Sparse Stellar Clusters
We present the outcomes of a Chandra X-Ray Observatory snapshot studyof five nearby Herbig Ae/Be (HAeBe) stars that are kinematically linkedwith the Oph-Sco-Cen association (OSCA). Optical photometric andspectroscopic follow-up was conducted for the HD 104237 field. Theprincipal result is the discovery of a compact group ofpre-main-sequence (PMS) stars associated with HD 104237 and itscodistant, comoving B9 neighbor ɛ Chamaeleontis AB. We name thegroup after the most massive member. The group has five confirmedstellar systems ranging from spectral type B9 to M5, including aremarkably high degree of multiplicity for HD 104237 itself. The HD104237 system is at least a quintet, with four low-mass PMS companionsin nonhierarchical orbits within a projected separation of 1500 AU ofthe HAeBe primary. Two of the low-mass members of the group are activelyaccreting classical T Tauri stars. The Chandra observations alsoincrease the census of companions for two of the other four HAeBe stars,HD 141569 and HD 150193, and identify several additional new members ofthe OSCA. We discuss this work in light of several theoretical issues:the origin of X-rays from HAeBe stars; the uneventful dynamical historyof the high-multiplicity HD 104237 system; and the origin of the ɛCha group and other OSCA outlying groups in the context of turbulentgiant molecular clouds. Together with the similar η Cha cluster, wepaint a portrait of sparse stellar clusters dominated byintermediate-mass stars 5-10 Myr after their formation.
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.
We have embarked on a project, under the aegis of the Nearby Stars(NStars)/Space Interferometry Mission Preparatory Science Program, toobtain spectra, spectral types, and, where feasible, basic physicalparameters for the 3600 dwarf and giant stars earlier than M0 within 40pc of the Sun. In this paper, we report on the results of this projectfor the first 664 stars in the northern hemisphere. These resultsinclude precise, homogeneous spectral types, basic physical parameters(including the effective temperature, surface gravity, and overallmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. Observed and derived data presented in this paper arealso available on the project's Web site.
| Empirically Constrained Color-Temperature Relations. I. BV(RI)C
This investigation presents a set of transformations to Johnson B-V,Cousins V-R, and Cousins V-I, as well as bolometric corrections to V,for [Fe/H]=-3, -2, -1, -0.5, 0.0, and +0.3 and, in each case, values oflogg from -0.5 to 5.0 for 3000 K<=Teff<=5500 K and from2.0 to 5.0 for 6000 K<=Teff<=40,000 K. Thesetransformations employ the predictions from Kurucz model atmospheres athigh temperatures (Teff>=8000 K) and from MARCS modelatmospheres at intermediate temperatures (from 7000 K down to atemperature in the range 4000 K<=Teff<=5500 K,depending on [Fe/H], where adjustments to satisfy observationalconstraints become necessary). Thus, theoretical color-Teffrelations are used exclusively down to a minimum temperature that iscooler than the temperatures of turnoff stars in open and globular starclusters. To better represent the color transformations obeyed by coolstars (down to 3000 K), corrections to the synthetic transformationshave been determined from a careful consideration of observations for afew globular clusters (M92, M68, and 47 Tucanae), the color-magnitudediagrams (CMDs) of several open clusters (M67, the Pleiades, the Hyades,and NGC 6791), the CMDs and mass-luminosity diagram for solarneighborhood stars having good distance measurements from Hipparcos,empirical (B-V)-Teff and (V-K)-Teff relations, andcolor-color diagrams for field giants. The semiempirical colortransformations that have been produced as a result of our analysis arealso compared with several others that have been published in recentyears: some of the deficiencies of the latter are revealed.
| Symplectic integration of hierarchical stellar systems
Symplectic integration has been used successfully for many years now forthe study of dynamics in planetary systems. This technique takesadvantage of the fact that in a planetary system, the mass of thecentral body is much larger than all the other ones; it fails if allmassive bodies have comparable masses, such as in multiple stellarsystems. A new symplectic integrator is presented that permits the studyof the dynamics of hierarchical stellar systems of any size and shape,provided that the hierarchical structure of the system is preservedalong the integration. Various application tests of this new integratorare given, such as the gap formation in circumbinary disks, the Kozairesonance in triple systems, the truncated circumbinary disk in thequadruple system GG Tauw, and the dynamics of the sextuple systemCastor.
| Absolute Dimensions of the M-Type Eclipsing Binary YY Geminorum (Castor C): A Challenge to Evolutionary Models in the Lower Main Sequence
We present new spectroscopic observations of the detached late-typedouble-lined eclipsing binary YY Geminorum (P=0.814 day), a member ofthe Castor sextuple system and one of the benchmarks for the comparisonbetween observations and stellar evolution theory in the lower mainsequence. In addition, we have reanalyzed existing light curves inseveral passbands using modern techniques that account for theconspicuous presence of spots. This, combined with the spectroscopy, hasyielded a very precise determination of the absolute dimensions of thecomponents, which are virtually identical to each other. We obtain forthe mean mass, radius, and effective temperature the valuesM=0.5992+/-0.0047 Msolar, R=0.6191+/-0.0057Rsolar, and Teff=3820+/-100 K, respectively. Boththe mass and the radius determinations are good to better than 1%, whichin the case of the radius represents a fourfold improvement overprevious results and significantly enhances the value of this quantityfor testing the models. We discuss the importance of systematic effectsin these measurements by comparison with another high-precisiondetermination of the mass by Ségransan and coworkers. Areanalysis of the Hipparcos transit data for Castor AB that accounts forthe relative motion of the pair in its 467 yr period orbit has yieldedan improved parallax for the system of 66.90+/-0.63 mas. With this, wehave estimated the age (~370 Myr) and metal abundance ([Fe/H]~0.0) of YYGem from isochrone fits to Castor A and B under the assumption of acommon origin. This, along with the other physical properties, allow foran unusually stringent test of the models for low-mass stars. We havecompared the observations of YY Gem with a large number of recenttheoretical calculations, and we show that all models underestimate theradius by up to 20% and that most overestimate the effective temperatureby 150 K or more. Both of these trends are confirmed by observations ofanother similar system in the Hyades (V818 Tau). Consequently,theoretical ages for relatively low mass objects such as T Tauri starsderived by placing them on the H-R diagram may be considerably biased.If the radius is used directly as a measure of evolution, ages could beunderestimated by as much as a factor of 10 in this mass regime. In viewof these discrepancies, absolute ages from essentially all currentmodels for the lower main sequence must be viewed with at least somemeasure of skepticism. Finally, we derive a new and very accurateephemeris based on all available times of eclipse, and we lay to restprevious claims of sudden changes in the orbital period of the binary,which we show to be spurious. Some of the observations reported herewere obtained with the Multiple Mirror Telescope, a joint facility ofthe Smithsonian Institution and the University of Arizona.
| Speckle Interferometry at the US Naval Observatory. VIII.
The results of 2044 speckle interferometric observations of doublestars, made with the 26 inch (66 cm) refractor of the US NavalObservatory, are presented. Each speckle interferometric observation ofa system represents a combination of over a thousand short-exposureimages. These observations are averaged into 1399 mean positions andrange in separation from 0.16" to 14.97", with a mean separation of2.51". This is the eighth in a series of papers presenting measuresobtained with this system and covers the period 2001 March 18 through2001 December 30.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} 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/393/897
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is available in electronic form atthe 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/386/492, and from theauthors on CD-Rom.
| The Southwest Texas Honors Astronomy Class, Identifying the "Star" in a Long-Lost van Gogh
Not Available
| A Short History and Other Stories of Binary Stars
A short history of binary stars from the first discoveries is presented.Examples of currently known binary systems with components of highesttemperature and mass are discussed.
| Visionary memories : William Huggins and the origins of astrophysics.
Not Available
| Optical Interferometry
The field of optical and infrared (IR) interferometry has seen rapidtechnical and scientific progress over the past few years. A number ofinstruments capable of precise visibility measurements have been built,and closure-phase imaging with multitelescope arrays has beendemonstrated. Astronomical results from these instruments includemeasurements of stellar diameters and their wavelength dependence, limbdarkening, stellar surface structure, and distances of Cepheids and ofNova Cygni 1992. Precise stellar masses have been obtained frominterferometric observations of spectroscopic binaries, andcircumstellar disks and shells have been resolved. Searches forsubstellar companions and extrasolar planets with interferometricastrometry will begin soon. Nulling interferometry will enable studiesof exozodiacal disks from the ground and the detection andcharacterization of terrestrial extrasolar planets from space. Thesedevelopments are reviewed, as well as progress in some key technologicalareas.
| Vertical Chromium Distribution in the Atmosphere of a Chemically Peculiar Star. I. Diagnostics
On the basis of CCD spectrograms obtained with high resolution at theCoudé focus of the 2.6-m telescope of the Crimean AstrophysicalObservatory, Cr II lines lying in the wings of the H hydrogen line areinvestigated. Vertical chromium stratification in the atmospheres of twonormal and eight chemically peculiar stars is diagnosed using the methodof spectral synthesis. An increase in Cr abundance with depth is foundfor the cool Ap stars CrB, HR 7575, Equ, and 10 Aql. Some increase in Crabundance in the upper layers of the atmosphere is presumed for all Amstars and for both HgMn components of 46 Dra. The verticalchromium distribution in the atmospheres of the hot, spotted Ap stars 17Com and 2 CVn is evidently uniform.
| The XMM-Newton view of stellar coronae: Coronal structure in the Castor X-ray triplet
We present results of a comprehensive X-ray investigation of themultiple stellar system Castor AB + YYGem. The observations were obtained with the XMM-Newtonobservatory. We report the first spatially separated detection andidentification of both Castor A and B as frequentlyflaring X-ray sources. Spectral modeling of the YYGem and Castor coronal sources indicates abroad plasma distribution between 2-15 MK. Elemental abundances arefound to be below solar photospheric values, with the abundance of Nebeing highest ( ~ 0.7 times solar photospheric). The abundances increaseduring a large flare, most notably for Fe. The O Vii He-like linetriplet indicates average coronal densities of the cooler plasma of afew times 1010 cm-3 for YY Gemand Castor. The YY Gem light curveshows three deep eclipses, indicating that the coronae of both binarycomponents are similarly active and are relatively compact. A 3-D lightcurve inversion shows that coronal active regions follow density scaleheights compatible with spectroscopically measured temperatures. Thedominant densities also agree with spectroscopic values. Most activeregions are located between +/- 50 degrees latitude, in agreement withfindings from previous Doppler imaging. We also report the tentativedetection of line broadening due to orbital motion. Based onobservations obtained with {\it XMM-Newton}, an ESA science mission withinstruments and contributions directly funded by ESA Member States andthe USA (NASA).
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| Speckle Interferometry at the US Naval Observatory. VI.
The results of 1068 speckle interferometric observations of doublestars, made with the 26 inch (0.66 m) refractor of the US NavalObservatory, are presented. These observations are averaged into 841means of 815 binary stars. The systems range in separation from 0.22" to6.01" with a mean separation of 2.21" and have a limiting secondarymagnitude of V=12.5. This is the sixth in a series of papers presentingmeasures obtained with this system, and it covers the period 1999January 1 through 2000 January 9.
| Speckle Interferometry at the US Naval Observatory. V.
The results of 1544 speckle interferometric observations of 637 binarystars, ranging in separation from 0.25" to 5.25", are tabulated. Theseobservations were obtained using the 66 cm refractor at the US NavalObservatory in Washington, DC, with an intensified CCD detector. This isthe fifth in a series of papers presenting measures obtained with thissystem and covers the period 1998 January 1 through December 31. Randomerrors for all measures are estimated to be 17.6 mas in separation and0.55d/ρ in position angle, where ρ is the separation inarcseconds.
| Fundamental Parameters of Low-Mass Stars from Broadband Photometry. I. Method and First Results
Spectral energy distributions from recent model atmospheres covering abroad range of temperature and metallicity are used to synthesize colorsfor low-mass stars. Color-color diagrams can therefore be prepared inwhich each point corresponds to a particular combination ofTeff and M/H. Comparison of observed with synthetic colorsyields estimates of those parameters generally, but not necessarilyunder the assumption that log gcgs=5. Results are presentedfor twelve stars of astrophysical interest.
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
Каталог и designations:
|
INHABITED SKY
