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Integrated optics for astronomical interferometry. VI. Coupling the light of the VLTI in K band
Aims. Our objective is to prove that integrated optics (IO) is not onlya good concept for astronomical interferometry but also a workingtechnique with high performance. Methods: . We used thecommissioning data obtained with the dedicated K-band integrated opticstwo-telescope beam combiner that now replaces the fiber coupler MONA inthe VLTI/VINCI instrument. We characterize the behavior of this IOdevice and compare its properties to other single mode beam combinerlike the previously used MONA fiber coupler. Results: . The IOcombiner provides a high optical throughput, a contrast of 89% with anight-to-night stability of a few percent. Even if a dispersive phase ispresent, we show that it does not bias the measured Fourier visibilityestimate. An upper limit of 5×10-3 for the cross-talkbetween linear polarization states has been measured. We take advantageof the intrinsic contrast stability to test a new astronomical procedurefor calibrating diameters of simple stars by simultaneously fitting theinstrumental contrast and the apparent stellar diameters. This methodreaches an accuracy with diameter errors on the order of previous onesbut without the need of an already known calibrator. Conclusions:. These results are an important step for IO, since they prove itsmaturity in an astronomical band where the technology has been speciallydeveloped for astronomical convenience. It paves the way to incomingimaging interferometer projects.
| Atlas and Catalog of Dark Clouds Based on Digitized Sky Survey I
We present a quantitative atlas and catalog of dark clouds derived byusing the optical database ``Digitized Sky Survey I''. Applying atraditional star-count technique to 1043 plates contained in thedatabase, we produced an AV map covering the entire region inthe galactic latitude range |b| ≤ 40°. The map was drawn at twodifferent angular resolutions of 6' and 18', and is shown in detail in aseries of figures in this paper. Based on the AV map, weidentified 2448 dark clouds and 2841 clumps located inside them. Somephysical parameters, such as the position, extent, and opticalextinction, were measured for each of the clouds and clumps. We alsosearched for counterparts among already known dark clouds in theliterature. The catalog of dark clouds presented in this paper lists thecloud parameters as well as the counterparts.
| Dust scattering in the Miras R Car and RR Sco resolved by optical interferometric polarimetry
We present optical interferometric polarimetry measurements of theMira-like variables R Car and RR Sco, using the Sydney UniversityStellar Interferometer. By making visibility measurements in twoperpendicular polarizations, the relatively low-surface brightness lightscattered by atmospheric dust could be spatially separated from thebright Mira photospheric flux. This is the first reported successful useof long-baseline optical interferometric polarimetry. Observations wereable to place constraints on the distribution of circumstellar materialin R Car and RR Sco. The inner radius of dust formation for both starswas found to be less than 3 stellar radii: much closer than the expectedinnermost stable location for commonly assumed astrophysical `dirtysilicate' dust in these systems (silicate dust with a significant ironcontent). A model with the dust distributed over a shell which isgeometrically thin compared to the stellar radius was preferred over anoutflow. We propose dust components whose chemistry and opacityproperties enable survival at these extreme inner radii.
| Can Life Develop in the Expanded Habitable Zones around Red Giant Stars?
We present some new ideas about the possibility of life developingaround subgiant and red giant stars. Our study concerns the temporalevolution of the habitable zone. The distance between the star and thehabitable zone, as well as its width, increases with time as aconsequence of stellar evolution. The habitable zone moves outward afterthe star leaves the main sequence, sweeping a wider range of distancesfrom the star until the star reaches the tip of the asymptotic giantbranch. Currently there is no clear evidence as to when life actuallyformed on the Earth, but recent isotopic data suggest life existed atleast as early as 7×108 yr after the Earth was formed.Thus, if life could form and evolve over time intervals from5×108 to 109 yr, then there could behabitable planets with life around red giant stars. For a 1Msolar star at the first stages of its post-main-sequenceevolution, the temporal transit of the habitable zone is estimated to beseveral times 109 yr at 2 AU and around 108 yr at9 AU. Under these circumstances life could develop at distances in therange 2-9 AU in the environment of subgiant or giant stars, and in thefar distant future in the environment of our own solar system. After astar completes its first ascent along the red giant branch and the Heflash takes place, there is an additional stable period of quiescent Hecore burning during which there is another opportunity for life todevelop. For a 1 Msolar star there is an additional109 yr with a stable habitable zone in the region from 7 to22 AU. Space astronomy missions, such as proposed for the TerrestrialPlanet Finder (TPF) and Darwin, that focus on searches for signatures oflife on extrasolar planets, should also consider the environments ofsubgiants and red giant stars as potentially interesting sites forunderstanding the development of life. We performed a preliminaryevaluation of the difficulty of interferometric observations of planetsaround red giant stars compared to a main-sequence star environment. Weshow that pathfinder missions for TPF and Darwin, such as Eclipse andFKSI, have sufficient angular resolution and sensitivity to search forhabitable planets around some of the closest evolved stars of thesubgiant and red giant class.
| The sub-arcsecond dusty environment of Eta Carinae
The core of the nebula surrounding Eta Carinae has been observed withthe VLT Adaptive Optics system NACO and with the interferometerVLTI/MIDI to constrain spatially and spectrally the warm dustyenvironment and the central object. In particular, narrow-band images at3.74 μm and 4.05 μm reveal the butterfly shaped dusty environmentclose to the central star with unprecedented spatial resolution. A voidwhose radius corresponds to the expected sublimation radius has beendiscovered around the central source. Fringes have been obtained in theMid-IR which reveal a correlated flux of about 100 Jy situated 0.3arcsec south-east of the photocenter of the nebula at 8.7 μm, whichcorresponds with the location of the star as seen in other wavelengths.This correlated flux is partly attributed to the central object, andthese observations provide an upper limit for the SED of the centralsource from 2.2 μm to 13.5 μm. Moreover, we have been able tospectrally disperse the signal from the nebula itself at PA = 318degree, i.e. in the direction of the bipolar nebula (~310°) withinthe MIDI field of view of 3 arcsec. A large amount of corundum (Al2O3)is discovered, peaking at 0.6 arcsec-1.2 arcsec south-east from thestar, whereas the dust content of the Weigelt blobs is dominated bysilicates. We discuss the mechanisms of dust formation which are closelyrelated to the geometry of this Butterfly nebulae.
| First results from the ESO VLTI calibrators program
The ESO Very Large Telescope Interferometer (VLTI) is one of the leadinginterferometric facilities. It is equipped with several 8.2 and 1.8 mtelescopes, a large number of baselines up to 200 m, and with severalsubsystems designed to enable high quality measurements and to improvesignificantly the limits of sensitivities currently available tolong-baseline interferometry. The full scientific potential of the VLTIcan be exploited only if a consistent set of good quality calibrators isavailable. For this, a large number of observations of potentialcalibrators have been obtained during the commissioning phase of theVLTI. These data are publicly available. We briefly describe theinterferometer, the VINCI instrument used for the observations, the dataflow from acquisition to processed results, and we present and commenton the volume of observations gathered and scrutinized. The result is alist of 191 calibrator candidates, for which a total of 12 066observations can be deemed of satisfactory quality. We present a generalstatistical analysis of this sample, using as a starting point theangular diameters previously available in the literature. We derive thegeneral characteristics of the VLTI transfer function, and its trendwith time in the period 2001 through mid-2004. A second paper will bedevoted to a detailed investigation of a selected sample, aimed atestablishing a VLTI-based homogeneous system of calibrators.
| 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
| Mid-infrared interferometry of the Mira variable RR Sco with the VLTI MIDI instrument
We present the results of the first mid-infrared interferometricobservations of the Mira variable RR Sco with the MID-infraredInterferometer (MIDI) coupled to the European Southern Observatory's(ESO) Very Large Telescope Interferometer (VLTI), together with K-bandobservations using VLTI VINCI. The observations were carried out in June2003, when the variability phase of the object was 0.6, using two unittelescopes (UT1 and UT3), as part of the Science Demonstration Time(SDT) program of the instrument. Projected baseline lengths ranged from73 to 102 m, and a spectral resolution of 30 was employed in theobservations, which enabled us to obtain the wavelength dependence ofthe visibility in the region between 8 and 13 μm. The uniform-diskdiameter was found to be 18 mas between 8 and 10 μm, while itgradually increases at wavelengths longer than 10 μm to reach 24 masat 13 μm. The uniform-disk diameter between 8 and 13 μm issignificantly larger than the K-band uniform-disk diameter of 10.2± 0.5 mas measured using VLTI VINCI with projected baselinelengths of 15-16 m, three weeks after the MIDI observations. Our modelcalculations show that optically thick emission from a warm molecularenvelope consisting of H2O and SiO can cause the apparent mid-infrared diameter to be much larger than the continuum diameter. Wefind that the warm molecular envelope model extending to 2.3R\star with a temperature of 1400 K and column densitiesof H2O and SiO of 3 × 1021 cm-2and 1 × 1020 cm-2, respectively, canreproduce the observed uniform-disk diameters between 8 and 10 μm.The observed increase of the uniform-disk diameter longward of 10 μmcan be explained by an optically thin dust shell consisting of silicateand corundum grains. The inner radius of the optically thin dust shellis derived to be 7-8 R\star with a temperature of 700 K,and the optical depth at 10 μm is found to be 0.025.Based on observations made with the Very Large Telescope Interferometerof the European Southern Observatory.
| Onset of Mass Loss in Red Giants: Association with an Evolutionary Event
Stencel & Mullan used asymmetries in the Mg II k emission lineprofile to determine the location of a ``velocity dividing line'' (VDL)in the H-R diagram. Stars to the right of (and above) the VDL wereobserved to have asymmetries that are consistent with the presence ofcool massive winds. Stars to the left of (and below) the VDL showed noevidence for winds. We show that the VDL lies close to a certain eventof stellar evolution on the red giant branch (RGB). The event occurswhen the hydrogen-burning shell evolves outward through a discontinuityin molecular weight. In some low-mass stars, this event causes a kink inthe evolutionary track of an individual low-mass star. In a cluster, thecombined effects of such kinks create a ``bump'' in the luminosityfunction. Our result suggests that evolution through the kink (or bump)on the RGB is associated with the onset of a cool massive wind.Theoretical possibilities to explain this association will be exploredin a subsequent paper.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Dating the Almagest star catalogue using proper motions : a reconsideration.
Not Available
| Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalog
We present refined coordinates and proper-motion data for the highproper-motion (HPM) stars in the Luyten Half-Second (LHS) catalog. Thepositional uncertainty in the original Luyten catalog is typicallygreater than 10" and is often greater than 30". We have used the digitalscans of the POSS I and POSS II plates to derive more accurate positionsand proper motions of the objects. Out of the 4470 candidates in the LHScatalog, 4323 objects were manually reidentified in the POSS I and POSSII scans. A small fraction of the stars were not found because of thelack of finder charts and digitized POSS II scans. The uncertainties inthe revised positions are typically ~2" but can be as high as ~8" in afew cases, which is a large improvement over the original data.Cross-correlation with the Tycho-2 and Hipparcos catalogs yielded 819candidates (with mR<~12). For these brighter sources, theposition and proper-motion data were replaced with the more accurateTycho-2/Hipparcos data. In total, we have revised proper-motionmeasurements and coordinates for 4040 stars and revised coordinates for4330 stars. The electronic version of the paper5 contains the updated information on all 4470stars in the LHS catalog.
| Metal Abundance of Red Clump Stars in Baade's Window
Thirteen red clump stars from Baade's window were observed with highresolution in the red part of the optical spectrum with the UVES echellespectrograph at the Mount Paranal ESO Observatory. The model atmosphereabundance analysis placed their [Fe/H] values in a range from 0.0 to-1.52 dex. Present results, based on direct measurements of ironabundance, confirm former suggestions that the I-band brightness of thered clump giants only weakly depends on [Fe/H]. The determined values of[Fe/H] may contain a slight systematic error connected with still nowunexplained difference in colors between stars in the Galactic bulge andin the solar vicinity.
| A catalogue of calibrator stars for long baseline stellar interferometry
Long baseline stellar interferometry shares with other techniques theneed for calibrator stars in order to correct for instrumental andatmospheric effects. We present a catalogue of 374 stars carefullyselected to be used for that purpose in the near infrared. Owing toseveral convergent criteria with the work of Cohen et al.(\cite{cohen99}), this catalogue is in essence a subset of theirself-consistent all-sky network of spectro-photometric calibrator stars.For every star, we provide the angular limb-darkened diameter, uniformdisc angular diameters in the J, H and K bands, the Johnson photometryand other useful parameters. Most stars are type III giants withspectral types K or M0, magnitudes V=3-7 and K=0-3. Their angularlimb-darkened diameters range from 1 to 3 mas with a median uncertaintyas low as 1.2%. The median distance from a given point on the sky to theclosest reference is 5.2degr , whereas this distance never exceeds16.4degr for any celestial location. The catalogue 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/393/183
| 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.
| On the Photometric Variability of Red Clump Giants
Hipparcos photometry of the 308 red clump giants identified by Paczynskiet al. (1999) is investigated. These stars are found to be quite stableduring the three years of observation, but questions remain about longerterm stability.
| On the Wilson-Bappu relationship in the Mg II k line
An investigation is carried out on the Wilson-Bappu effect in the Mg Iik line at 2796.34 Å. The work is based on a selection of 230 starsobserved by both the IUE and HIPPARCOS satellites, covering a wide rangeof spectral types (F to M) and absolute visual magnitudes (-5.4<=MV <=9.0). A semi-automatic procedure is used to measurethe line widths, which applies also in the presence of strong centralabsorption reversal. The Wilson-Bappu relationship here provided isconsidered to represent an improvement over previous recent results forthe considerably larger data sample used, as well as for a properconsideration of the measurement errors. No evidence has been found fora possible dependence of the WB effect on stellar metallicity andeffective temperature.
| 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
| 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
| Dating Ptolemy's star catalogue through proper motions : the Hipparchan epoch.
Not Available
| K-Band Calibration of the Red Clump Luminosity
The average near-infrared (K-band) luminosity of 238 Hipparcos red clumpgiants is derived and then used to measure the distance to the Galacticcenter. These Hipparcos red clump giants have been previously employedas I-band standard candles. The advantage of the K-band is a decreasedsensitivity to reddening and perhaps a reduced systematic dependence onmetallicity. In order to investigate the latter, and also to refer ourcalibration to a known metallicity zero point, we restrict our sample ofred clump calibrators to those with abundances derived fromhigh-resolution spectroscopic data. The mean metallicity of the sampleis [Fe/H]=-0.18 dex (σ=0.17 dex). The data are consistent with nocorrelation between MK and [Fe/H] and only weakly constrainthe slope of this relation. The luminosity function of the sample peaksat MK=-1.61+/-0.03 mag. Next, we assemble published opticaland near-infrared photometry for ~20 red clump giants in a Baade'swindow field with a mean metallicity of [Fe/H]=-0.17+/-0.09 dex, whichis nearly identical to that of the Hipparcos red clump. Assuming thatthe average (V-I)0 and (V-K)0 colors of these twored clumps are the same, the extinctions in the Baade's window field arefound to be AV=1.56, AI=0.87, andAK=0.15, in agreement with previous estimates. We derive thedistance to the Galactic center: (m-M)0=14.58+/-0.11 mag, orR=8.24+/-0.42 kpc. The uncertainty in this distance measurement isdominated by the small number of Baade's window red clump giantsexamined here.
| Ca II activity and rotation in F-K evolved stars
Ca II H and K high resolution observations for 60 evolved stars in thefield and in 5 open clusters are presented. From these spectrachromospheric fluxes are derived, and a homogeneous sample of more than100 giants is built adding data from the literature. In addition, formost stars, rotational velocities were derived from CORAVELobservations. By comparing chromospheric emission in the cluster starswe confirm the results of Pasquini & Brocato (1992): chromosphericactivity depends on the stellar effective temperature, and mass, whenintermediate mass stars (M ~ 4 Msun) are considered. TheHyades and the Praesepe clump giants show the same level of activity, asexpected from stars with similar masses and effective temperatures. Adifference of up to 0.4 dex in the chromospheric fluxes among the Hyadesgiants is recorded and this sets a clear limit to the intrinsic spreadof stellar activity in evolved giants. These differences in otherwisevery similar stars are likely due to stellar cycles and/or differencesin the stellar initial angular momentum. Among the field stars none ofthe giants with (V-R)o < 0.4 and Ia supergiants observedshows a signature of Ca II activity; this can be due either to the realabsence of a chromosphere, but also to other causes which preclude theappearance of Ca II reversal. By analyzing the whole sample we find thatchromospheric activity scales linearly with stellar rotational velocityand a high power of stellar effective temperature: F'k ~Teff7.7 (Vsini)0.9. This result can beinterpreted as the effect of two chromospheric components of differentnature: one mechanical and one magnetic. Alternatively, by using theHipparcos parallaxes and evolutionary tracks, we divide the sampleaccording to the stellar masses, and we follow the objects along anevolutionary track. For each range of masses activity can simply beexpressed as a function of only one parameter: either theTeff or the angular rotation Omega , with laws F'k~ Omega alpha , because angular velocity decreases witheffective temperature along an evolutionary track. By using theevolutionary tracks and the observed Vsini we investigate the evolutionof the angular momentum for evolved stars in the range 1-5Msun. For the 1.6-3 solar mass stars the data are consistentwith the IOmega =const law while lower and higher masses follow a lawsimilar to IOmega 2=const, where I is the computed stellarmomentum of inertia. We find it intriguing that Vsini remains almostconstant for 1Msun stars along their evolution; if a similarbehavior is shared by Pop II stars, this could explain the relativelyhigh degree of activity observed in Pop II giants. Finally, through theuse of models, we have verified the consistency of the F'k ~Omega alpha and the IOmega beta = Const lawsderived, finding an excellent agreement. This representation, albeitcrude (the models do not consider, for instance, mass losses) representsthe evolution of Ca II activity and of the angular momentum in asatisfactory way in most of the portion of HR diagram analyzed.Different predictions could be tested with observations in selectedclusters. Based on observations collected at ESO, La Silla. Tables 1-3are only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over more than twocenturies and summarized in the FK5. Part I of the FK6 (abbreviatedFK6(I)) contains 878 basic fundamental stars with direct solutions. Suchdirect solutions are appropriate for single stars or for objects whichcan be treated like single stars. From the 878 stars in Part I, we haveselected 340 objects as "astrometrically excellent stars", since theirinstantaneous proper motions and 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,199 of the stars in Part I 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(I) proper motion in the single-star mode is 0.35 mas/year. This isabout a factor of two better than the typical HIPPARCOS errors for thesestars of 0.67 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(I) proper motions have atypical mean error of 0.50 mas/year, which is by a factor of more than 4better than the corresponding error for the HIPPARCOS values of 2.21mas/year (cosmic errors included).
| Digging Deeper in the Coronal Graveyard: Postscript
An X-ray upper limit-from the ROSAT High Resolution Imager-is presentedfor ɛ Corvi (HD 105707), a K2 giant that lies in the``noncoronal'' zone of the Hertzsprung-Russell diagram, but whichpreviously was detected by the Hubble Space Telescope Goddard HighResolution Spectrograph in far-ultraviolet coronal proxies. The newmeasurement strengthens the anticorrelation between coronal X-rays andλ1380 carbon monoxide emission among the red giants.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| Spectral Irradiance Calibration in the Infrared. X. A Self-Consistent Radiometric All-Sky Network of Absolutely Calibrated Stellar Spectra
We start from our six absolutely calibrated continuous stellar spectrafrom 1.2 to 35 μm for K0, K1.5, K3, K5, and M0 giants. These wereconstructed as far as possible from actual observed spectral fragmentstaken from the ground, the Kuiper Airborne Observatory, and the IRAS LowResolution Spectrometer, and all have a common calibration pedigree.From these we spawn 422 calibrated ``spectral templates'' for stars withspectral types in the ranges G9.5-K3.5 III and K4.5-M0.5 III. Wenormalize each template by photometry for the individual stars usingpublished and/or newly secured near- and mid-infrared photometryobtained through fully characterized, absolutely calibrated,combinations of filter passband, detector radiance response, and meanterrestrial atmospheric transmission. These templates continue ourongoing effort to provide an all-sky network of absolutely calibrated,spectrally continuous, stellar standards for general infrared usage, allwith a common, traceable calibration heritage. The wavelength coverageis ideal for calibration of many existing and proposed ground-based,airborne, and satellite sensors, particularly low- tomoderate-resolution spectrometers. We analyze the statistics of probableuncertainties, in the normalization of these templates to actualphotometry, that quantify the confidence with which we can assert thatthese templates truly represent the individual stars. Each calibratedtemplate provides an angular diameter for that star. These radiometricangular diameters compare very favorably with those directly observedacross the range from 1.6 to 21 mas.
| Catalogs of temperatures and [Fe/H] averages for evolved G and K stars
A catalog of mean values of [Fe/H] for evolved G and K stars isdescribed. The zero point for the catalog entries has been establishedby using differential analyses. Literature sources for those entries areincluded in the catalog. The mean values are given with rms errors andnumbers of degrees of freedom, and a simple example of the use of thesestatistical data is given. For a number of the stars with entries in thecatalog, temperatures have been determined. A separate catalogcontaining those data is briefly described. Catalog only available atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Evolution of X-ray activity and rotation on G-K giants
The recent availability of stellar parallaxes provided by the Hipparcosstar catalogue (ESA 1997) enables an accurate determination of thepositions of single field giants in a theoretical H-R diagram and areliable estimate of their masses. The present study combines these newastrometric data with previously published X-ray fluxes and rotationalvelocities. The results confirm the existence of a sharp decrease ofX-ray emission at spectral type K1 for 2.5 M_sun < M < 5 M_sungiants. The study shows that the rotational velocity of these starsreaches a minimum at the same location in the H-R diagram. However, notight relationship between X-ray luminosities and projected equatorialvelocities was found among the sample stars. I suggest that theseresults could reflect the importance of differential rotation indetermining the level of coronal emission among >= 2.5Msun G and K giants. The restoration of rigid rotation at thebottom of the red giant branch could prevent the maintenance of largescale magnetic fields, thus explaining the sharp decrease of coronalX-ray emission at spectral type K1.
| The Wilson-Bappu effect of the MgII K line - dependence on stellar temperature, activity and metallicity
The Wilson-Bappu effect is investigated using accurate absolutemagnitudes of 65 stars obtained through early release of data from theHipparcos satellite together with MgII k line widths determined fromhigh resolution spectra observed with the International UltravioletExplorer (IUE) observatory. Stars of spectral classes F, G, K and M andluminosity classes I-V are represented in the sample. Wilson-Bappurelations for the Mg II k line for stars of different temperatures i.e.spectral classes are determined. The relation varies with spectral classand there is a significant scatter of the line widths around theregression lines. The sample contains slowly rotating stars of differentactivity levels and is suitable for investigations of a possiblerelation between line width and stellar activity. A difference inbehavior between dwarfs and giants (and supergiants) of spectral class Kseems to be present. Magnetic activity affects the width of the Mg II kline in dwarfs. Metallicity is found to influence the Mg II k line widthin giants and supergiants. Possible interpretations of the new resultsare briefly discussed.
| Recalibration of the Wilson-Bappu Effect Using the Singly Ionized Magnesium K Line
A new calibration of the Wilson-Bappu effect is presented using datafrom a survey of the singly ionized magnesium (Mg ii) h and k lines(near 280 nm) taken from the archives of the International UltravioletExplorer satellite. Our sample consisted of 94 stars with absolutemagnitudes derived from parallaxes reported from Hipparcos. We describethe dependencies of the base widths, peak widths, and full widths athalf-maximum (FWHM) on the fundamental stellar parameters T_eff,metallicity, log g, and activity.
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Besorolás csoportokba:
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Pozíciós és asztrometriai adatok
| Csillagkép: | Skorpió |
| Rektaszcenzió: | 16h50m09.80s |
| Deklináció: | -34°17'36.0" |
| Vizuális fényesség: | 2.29 |
| Távolság: | 20.06 parszek |
| RA sajátmozgás: | -613.1 |
| Dec sajátmozgás: | -255.2 |
| B-T magnitude: | 3.781 |
| V-T magnitude: | 2.393 |
Katalógusok és elnevezések:
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