Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
The Period Changes of Polaris
The evolutionary changes in pulsation period for the Cepheid Polaris arereinvestigated using archival observational material (radial velocities,photometry, and eye observations) over the interval 1844 to the present,including new photometry for the star obtained in 2003-2004. The star'spulsation period increased at a rate of 4.5 s yr-1 duringthat interval, with the exception of a brief hiatus between 1963 and1966, when it suddenly decreased, possibly as a result of a briefreduction in average stellar radius amounting to -0.055%. At roughly thesame time, the pulsation amplitude of Polaris underwent a marked change.Prior to 1963 the V amplitude was in excess of about 0.1 mag, possiblydecreasing at a rate of 0.019 mag century-1. Following thehiatus of 1963-1966, the pulsation amplitude underwent a sharp declineand now appears to be erratic on a cycle-to-cycle basis, always smallerthan 0.05 mag. The rapid rate of period increase for Polaris isconsistent with a first crossing of the Cepheid instability strip, whilethe hiatus of 1963-1966 and sudden decrease in pulsation amplitudethereafter suggest that the star may have left the instability strip forfirst crossers at that time, leaving it near the center of theinstability strip for Cepheids in higher crossing modes.
| Broad-band photometric colors and effective temperature calibrations for late-type giants. I. Z = 0.02
We present new synthetic broad-band photometric colors for late-typegiants based on synthetic spectra calculated with the PHOENIX modelatmosphere code. The grid covers effective temperatures T_eff=3000dots5000 K, gravities log g=-0.5dots{+3.5}, and metallicities[M/H]=+0.5dots{-4.0}. We show that individual broad-band photometriccolors are strongly affected by model parameters such as molecularopacities, gravity, microturbulent velocity, and stellar mass. Ourexploratory 3D modeling of a prototypical late-type giant shows thatconvection has a noticeable effect on the photometric colors too, as italters significantly both the vertical and horizontal thermal structuresin the outer atmosphere. The differences between colors calculated withfull 3D hydrodynamical and 1D model atmospheres are significant (e.g.,Δ(V-K)0.2 mag), translating into offsets in effectivetemperature of up to 70 K. For a sample of 74 late-type giants in theSolar neighborhood, with interferometric effective temperatures andbroad-band photometry available in the literature, we compare observedcolors with a new PHOENIX grid of synthetic photometric colors, as wellas with photometric colors calculated with the MARCS and ATLAS modelatmosphere codes. We find good agreement of the new synthetic colorswith observations and published T_eff-color and color-color relations,especially in the T_eff-(V-K), T_eff-(J-K) and (J-K)-(V-K) planes.Deviations from the observed trends in the T_eff-color planes aregenerally within ±100 K for T_eff=3500 to 4800 K. Syntheticcolors calculated with different stellar atmosphere models agree to±100 K, within a large range of effective temperatures andgravities. The comparison of the observed and synthetic spectra oflate-type giants shows that discrepancies result from the differencesboth in the strengths of various spectral lines/bands (especially thoseof molecular bands, such as TiO, H2O, CO) and the continuum level.Finally, we derive several new T_eff-log g-color relations for late-typegiants at solar-metallicity (valid for T_eff=3500 to 4800 K), based bothon the observed effective temperatures and colors of the nearby giants,and synthetic colors produced with PHOENIX, MARCS and ATLAS modelatmospheres.
| 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
| 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}
| Infrared Irradiance Calibration
Infrared astronomical measurements are calibrated against referencesources, usually primary standard stars that are, in turn, calibratedeither by direct or indirect means. A direct calibration compares thestar with a certified source, typically a blackbody. Indirect methodsextrapolate a direct measurement of the flux at one wavelength to theflux at another. Historically, α Lyr (Vega) has been used as theprimary standard as it is bright, easily accessible from the northernhemisphere, and is well calibrated in the visual. Until recently, thedirect absolute infrared calibrations of α Lyr and those derivedfrom the absolute solar flux scaled to the observed spectral energydistributions of solar type stars increasingly diverged with wavelengthfrom those obtained using a model atmosphere to extrapolate the absolutevisual flux of Vega into the infrared. The exception is the directcalibration by the 1996/97 Midcourse Space Experiment of the absolutefluxes for a number of the commonly used infrared standard stars,including Vega.
| Improved Baade-Wesselink surface brightness relations
Recent, and older accurate, data on (limb-darkened) angular diameters iscompiled for 221 stars, as well as BVRIJK[12][25] magnitudes for thoseobjects, when available. Nine stars (all M-giants or supergiants)showing excess in the [12-25] colour are excluded from the analysis asthis may indicate the presence of dust influencing the optical andnear-infrared colours as well. Based on this large sample,Baade-Wesselink surface brightness (SB) relations are presented fordwarfs, giants, supergiants and dwarfs in the optical and near-infrared.M-giants are found to follow different SB relations from non-M-giants,in particular in V versus V-R. The preferred relation for non-M-giantsis compared to the earlier relation by Fouqué and Gieren (basedon 10 stars) and Nordgren et al. (based on 57 stars). Increasing thesample size does not lead to a lower rms value. It is shown that theresiduals do not correlate with metallicity at a significant level. Thefinally adopted observed angular diameters are compared to thosepredicted by Cohen et al. for 45 stars in common, and there isreasonable overall, and good agreement when θ < 6 mas.Finally, I comment on the common practice in the literature to average,and then fix, the zero-point of the V versus V-K, V versus V-R and Kversus J-K relations, and then rederive the slopes. Such a commonzero-point at zero colour is not expected from model atmospheres for theV-R colour and depends on gravity. Relations derived in this way may bebiased.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Synthetic Lick Indices and Detection of α-enhanced Stars. II. F, G, and K Stars in the -1.0 < [Fe/H] < +0.50 Range
We present an analysis of 402 F, G, and K solar neighborhood stars, withaccurate estimates of [Fe/H] in the range -1.0 to +0.5 dex, aimed at thedetection of α-enhanced stars and at the investigation of theirkinematical properties. The analysis is based on the comparison of 571sets of spectral indices in the Lick/IDS system, coming from fourdifferent observational data sets, with synthetic indices computed withsolar-scaled abundances and with α-element enhancement. We useselected combinations of indices to single out α-enhanced starswithout requiring previous knowledge of their main atmosphericparameters. By applying this approach to the total data set, we obtain alist of 60 bona fide α-enhanced stars and of 146 stars withsolar-scaled abundances. The properties of the detected α-enhancedand solar-scaled abundance stars with respect to their [Fe/H] values andkinematics are presented. A clear kinematic distinction betweensolar-scaled and α-enhanced stars was found, although a one-to-onecorrespondence to ``thin disk'' and ``thick disk'' components cannot besupported with the present data.
| On the analysis of band 3 of the ISO-SWS calibration sources
We analyse ISO-SWS 01 (R 1500) 12-27.5 μm (band 3) spectra ofthe 10 standard calibration stars with the highest flux using syntheticspectra generated from (MARCS) atmosphere models. The comparison betweenthe observed and synthetic spectra reveals the quality of (1) theatmospheric model construction and subsequent synthetic spectracomputation and of (2) the (OLP 10.1) calibration and data reduction ofthe spectrometer at these wavelengths.The models represent the general features of the observations, but thesynthetic spectrum computation is hampered by the lack of comprehensivemolecular and atomic line lists. We also suspect some problems with thetemperature distribution in the outer layers of the model andinaccuracies in the extrapolation of the collision-induced absorptioncoefficients of H2 pairs. We detect baseline ripples andfringes in the observed spectra, that survive the calibration anddetailed reduction process. Photometric calibration uncertainties areestimated by means of the scaling factors between the synthetic andobserved spectra.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 173: HD 111306, HD 113023, HD 117901, and HD 142474.
Not Available
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 171: HD 152028 and HDE 284195 (GK Dra and V1094 Tau)
The two stars that form the subject of this paper are both short-perioddouble- lined eclipsing binaries having non-circular orbits despitetheir short periods. Although the HD type of HD 152028 is G0, theintegrated spectral type of the system must actually be much earlier:the B-V colour index is only about 0.37 mag and the parallax indicatesan integrated absolute magnitude as bright as +1.4 mag. A publishedphotometric investigation suggests that the primary star exhibits deltaScuti pulsations, with a period of 0.1138 days. That period is notpresent in the radial velocities, but we have identified a comparableperiodicity in the initially excessive residuals (sigma of the order of2 km/s) in the radial velocities of the primary star: there is anasymmetrical pulsational velocity curve with a semi-amplitude of about 3km/s and a period of 0.1178 days. HDE 284195 was not observed byHipparcos, but its HDE type of G0 is in reasonable agreement with itscolour and the nature of its radial-velocity traces. The rotations ofboth stars appear to be pseudo-synchronized to the orbit. The orbitalinclinations are not formally determined but they must be veryhigh,however and there is specific evidence that the inclination of HD152028 is very close to 90 degrees,so it is permissible to assume thatthe masses are scarcely above the minimum values, which in the case ofHD 152028 are 1.78 and 1.42 solar mass and in that of HDE 284195 are1.10 and 1.01 solar mass, with uncertainties below 1%.(ABRIDGED)
| Oxygen isotopic ratios in first dredge-up red giant stars and nuclear reaction rate uncertainties revisited
We describe a general yet simple method to analyse the propagation ofnuclear reaction rate uncertainties in a stellar nucleosynthesis andmixing context. The method combines post-processing nucleosynthesis andmixing calculations with a Monte Carlo scheme. With this approach wereanalyse the dependence of theoretical oxygen isotopic ratiopredictions in first dredge-up red giant branch stars in a systematicway. Such predictions are important to the interpretation of pre-solarAl2O3 grains from meteorites. The reaction rateswith uncertainties were taken from the NACRE compilation of Angulo etal. We include seven reaction rates in our systematic analysis ofstellar models with initial masses from 1 to 3 Msolar. Wefind that the uncertainty of the 18O(p,α)15N reaction rate typically causes an error in thetheoretical 16O/18O ratio of ~= +20/ - 5 per cent.The error of the 16O/17O prediction is 10-40 percent depending on the stellar mass, and is persistently dominated by thecomparatively small uncertainty of the 16O(p,γ)17F reaction. With the new estimates on reaction rateuncertainties by the NACRE compilation, the p-capture reactions17O(p, α)14N and 17O(p,γ)18F have virtually no impact on theoreticalpredictions for stellar mass <=1.5 Msolar. However, theuncertainty in 17O(p, α)14N has an effectcomparable to or greater than that of 16O(p,γ)17F for masses >1.5 Msolar, where coremixing and subsequent envelope mixing interact. In these cases wherecore mixing complicates post-dredge-up surface abundances, uncertaintyin other reactions have a secondary but noticeable effect on surfaceabundances.
| Angular Diameters of Stars from the Mark III Optical Interferometer
Observations of 85 stars were obtained at wavelengths between 451 and800 nm with the Mark III Stellar Interferometer on Mount Wilson, nearPasadena, California. Angular diameters were determined by fitting auniform-disk model to the visibility amplitude versus projected baselinelength. Half the angular diameters determined at 800 nm have formalerrors smaller than 1%. Limb-darkened angular diameters, effectivetemperatures, and surface brightnesses were determined for these stars,and relationships between these parameters are presented. Scatter inthese relationships is larger than would be expected from themeasurement uncertainties. We argue that this scatter is not due to anunderestimate of the angular diameter errors; whether it is due tophotometric errors or is intrinsic to the relationship is unresolved.The agreement with other observations of the same stars at the samewavelengths is good; the width of the difference distribution iscomparable to that estimated from the error bars, but the wings of thedistribution are larger than Gaussian. Comparison with infraredmeasurements is more problematic; in disagreement with models, coolerstars appear systematically smaller in the near-infrared than expected,warmer stars larger.
| Infrared Colors and Variability of Evolved Stars from COBE DIRBE Data
For a complete 12 μm flux-limited sample of 207 IRAS sources(F12>=150 Jy, |b|>=5deg), the majority ofwhich are AGB stars (~87%), we have extracted light curves in seveninfrared bands between 1.25 and 60 μm using the database of theDiffuse Infrared Background Experiment (DIRBE) instrument on the CosmicBackground Explorer (COBE) satellite. Using previous infrared surveys,we filtered these light curves to remove data points affected by nearbycompanions and obtained time-averaged flux densities and infraredcolors, as well as estimates of their variability at each wavelength. Inthe time-averaged DIRBE color-color plots, we find clear segregation ofsemiregulars, Mira variables, carbon stars, OH/IR stars, and red giantswithout circumstellar dust (i.e., V-[12]<5) and with little or novisual variation (ΔV<0.1 mag). The DIRBE 1.25-25 μm colorsbecome progressively redder and the variability in the DIRBE databaseincreases along the oxygen-rich sequence nondusty slightly varying redgiants-->SRb/Lb-->SRa-->Mira-->OH/IR and the carbon-richSRb/Lb-->Mira sequence. This supports previous assertions that theseare evolutionary sequences involving the continued production andejection of dust. The carbon stars are redder than their oxygen-richcounterparts for the same variability type, except in theF12/F25 ratio, where they are bluer. Of the 28sources in the sample not previous noted to be variable, 18 are clearlyvariable in the DIRBE data, with amplitudes of variation of ~0.9 mag at4.9 μm and ~0.6 mag at 12 μm, consistent with them being verydusty Mira-like variables. We also present individual DIRBE light curvesof a few selected stars. The DIRBE light curves of the semiregularvariable L2 Pup are particularly remarkable. The maxima at1.25, 2.2, and 3.5 μm occur 10-20 days before those at 4.9 and 12μm, and, at 4.9 and 12 μm, another maximum is seen between the twonear-infrared maxima.
| Spectral Irradiance Calibration in the Infrared. XIII. ``Supertemplates'' and On-Orbit Calibrators for the SIRTF Infrared Array Camera
We describe the technique that will be used to develop a set of on-orbitcalibrators for the Infrared Array Camera (IRAC) and demonstrate thevalidity of the method for stars with spectral types either K0-M0 III orA0-A5 V. For application to SIRTF, the approach is intended to operatewith all available optical, near-infrared (NIR), and mid-infrared (MIR)photometry and to yield complete absolute spectra from UV to MIR. Oneset of stars is picked from Landolt's extensive network of optical(UBVRI) calibrators, the other from the Carter-Meadows set of faint IRstandards. Traceability to the ``Cohen-Walker-Witteborn'' framework ofabsolute photometry and stellar spectra is assured. The method is basedon the use of either ``supertemplates,'' which represent the intrinsicshapes of the spectra of K0-M0 III stars from far-UV (1150 Å) toMIR (35 μm) wavelengths, or Kurucz synthetic spectra for A0-A5 Vstars. Each supertemplate or Kurucz model is reddened according to theindividual star's extinction and is normalized using availablecharacterized optical photometry. This paper tests our capability topredict NIR (JHK) magnitudes using supertemplates or models constrainedby Hipparcos/Tycho or precision ground-based optical data. We provideabsolutely calibrated 0.275-35.00 μm spectra of 33 Landolt andCarter-Meadows optical standard stars to demonstrate the viability ofthis technique, and to offer a set of IR calibrators 100-1000 timesfainter than those we have previously published. As an indication ofwhat we can expect for actual IRAC calibration stars, we have calculatedthe absolute uncertainties associated with predicting the IRACmagnitudes for the faintest cool giant and hot dwarf in this new set ofcalibration stars.
| ISO-SWS calibration and the accurate modelling of cool-star atmospheres. IV. G9 to M2 stars
A detailed spectroscopic study of 11 giants with spectral type from G9to M2 is presented. The 2.38-4.08 mu m wavelength-range of band 1 ofISO-SWS (Short-Wavelength Spectrometers on board of the Infrared SpaceObservatory) in which many different molecules - with their owndependence on each of the stellar parameters - are absorbing, enables usto estimate the effective temperature, the gravity, the microturbulence,the metallicity, the CNO-abundances, the12C/13C-ratio and the angular diameter from theISO-SWS data. Using the Hipparcos' parallax, the radius, luminosity andgravity-inferred mass are derived. The stellar parameters obtained arein good agreement with other published values, though also somediscrepancies with values deduced by other authors are noted. For a fewstars (delta Dra, xi Dra, alpha Tuc, H Sco and alpha Cet) someparameters - e.g. the CNO-abundances - are derived for the first time.By examining the correspondence between different ISO-SWS observationsof the same object and between the ISO-SWS data and the correspondingsynthetic spectrum, it is shown that the relative accuracy of ISO-SWS inband 1 (2.38-4.08 mu m) is better than 2% for these high-flux sources.The high level of correspondence between observations and theoreticalpredictions, together with a confrontation of the estimatedTeff (ISO) value with Teff values derived fromcolours - which demonstrates the consistency between V-K,BCK, Teff and thetad derived fromoptical or IR data - proves that both the used MARCS models to derivethe stellar quantities and the flux calibration of the ISO-SWS detectorshave reached a high level of reliability.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Appendices A-D are only available in electronic form athttp://www.edpsciences.org
| ISO-SWS calibration and the accurate modelling of cool-star atmospheres. II. General results
The fine calibration of the ISO-SWS detectors (Infrared SpaceObservatory - Short Wavelength Spectrometer) has proven to be a delicateproblem. We therefore present a detailed spectroscopic study in the2.38-12 mu m wavelength range of a sample of 16 A0-M2 stars used for thecalibration of ISO-SWS. By investigating the discrepancies between theISO-SWS data of these sources, the theoretical predictions of theirspectra, the high-resolution FTS-KP (Kitt Peak) spectrum of alpha Booand the solar FTS-ATMOS (Atmospheric Trace Molecule Spectroscopy)spectrum, both calibration problems and problems in computing thetheoretical models and the synthetic spectra are revealed. Theunderlying reasons for these problems are sought for and the impact onthe further calibration of ISO-SWS and on the theoretical modelling isdiscussed extensively.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Appendix is only available in electronic form athttp://www.edpsciences.org
| Astrophysics in 2001
During the year, astronomers provided explanations for solar topicsranging from the multiple personality disorder of neutrinos tocannibalism of CMEs (coronal mass ejections) and extra-solar topicsincluding quivering stars, out-of-phase gaseous media, black holes ofall sizes (too large, too small, and too medium), and the existence ofthe universe. Some of these explanations are probably possibly true,though the authors are not betting large sums on any one. The data oughtto remain true forever, though this requires a careful definition of``data'' (think of the Martian canals).
| The latitude and epoch for the formation of the southern Greek constellations
Not Available
| Infrared spectral classification of normal stars.
Moderate resolution (~400) 2.38-45.2 mu m infrared spectra of starswithout dust features were obtained with the Short WavelengthSpectrometer (SWS) on board the Infrared Space Observatory (ISO). Theobservations are part of a larger program with the objective to extendand refine the current infrared classification schemes. In particular,our data provide the basis for a more detailed classification of the1.N-1.NO sources (ordinary and oxygen rich naked stars) as defined byKraemer et al. (\cite{kraemer}) in a comprehensive classification of theISO-SWS spectra. For our analysis, the continuum was determined byfitting Engelke's function (Engelke \cite{engelke}) to the SWS data. Thestellar angular diameters derived from these estimates of the continuumare in good agreement with values obtained by other methods. Analysis ofthe equivalent widths of the CO fundamental and first overtone molecularbands, the SiO fundamental and first overtone, as well as theH2O bending mode band as a function of MK class, reveals thatthere is sufficient information in the SWS spectra to distinguishbetween hot (B, A, F) and cool stars. Furthermore, it is possible todetermine the spectral type for the G, K and M giants, and subtyperanges in a sequence of K and M giants. The equivalent widths of the COand SiO bands are found to be well correlated in K and M stars, suchthat the equivalent widths of the CO fundamental, the SiO first overtoneand the SiO fundamental can be reasonably well extrapolated from thedepth of the CO first overtone. We have identified two stars,HR 365 and V Nor, whosemid-infrared spectrum does not correspond to their respective opticalclassification. HR 365 may have a late M companion,which dominates the observed infrared spectrum while VNor is a late type giant that was included because itsspectrum was classified as featureless under the IRAS LRS scheme.According to Kraemer et al. (\cite{kraemer}), V Norhas a thin dust shell, which distorts the analysis of its mid-infraredabsorption bands. Based on observations with ISO, an ESA project withinstruments funded by ESA Member States (especially the PI countries:France, Germany, The Netherlands and the UK) and with the participationof ISAS and NASA.
| The ISO-SWS post-helium atlas of near-infrared stellar spectra
We present an atlas of near-infrared spectra (2.36 mu m-4.1 mu m) of ~300 stars at moderate resolution (lambda /delta lambda ~ 1500-2000). Thespectra were recorded using the Short-Wavelength Spectrometer aboard theInfrared Space Observatory (ISO-SWS). The bulk of the observations wereperformed during a dedicated observation campaign after the liquidhelium depletion of the ISO satellite, the so-called post-heliumprogramme. This programme was aimed at extending the MK-classificationto the near-infrared. Therefore the programme covers a large range ofspectral types and luminosity classes. The 2.36 mu m-4.05 mu m region isa valuable spectral probe for both hot and cool stars. H I lines(Bracket, Pfund and Humphreys series), He I and He II lines, atomiclines and molecular lines (CO, H2O, NH, OH, SiO, HCN,C2H2, ...) are sensitive to temperature, gravityand/or the nature of the outer layers of the stellar atmosphere(outflows, hot circumstellar discs, etc.). Another objective of theprogramme was to construct a homogeneous dataset of near-infraredstellar spectra that can be used for population synthesis studies ofgalaxies. At near-infrared wavelengths these objects emit the integratedlight of all stars in the system. In this paper we present the datasetof post-helium spectra completed with observations obtained during thenominal operations of the ISO-SWS. We discuss the calibration of the SWSdata obtained after the liquid helium boil-off and the data reduction.We also give a first qualitative overview of how the spectral featuresin this wavelength range change with spectral type. The dataset isscrutinised in two papers on the quantitative classification ofnear-infrared spectra of early-type stars ({Lenorzer} et al.\cite{lenorzer:2002a}) and late-type stars (Vandenbussche et al., inprep). Based on observations with ISO, an ESA project with instrumentsfunded by ESA Members States (especially the PI countries France,Germany, the Netherlands and the United Kingdom) and with theparticipation of ISAS and NASA. The full atlas is available inelectronic form at www.edpsciences.org Table 1 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?/A+A/390/1033
| 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.
| 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
| 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.
| A catalog of rotational and radial velocities for evolved stars
Rotational and radial velocities have been measured for about 2000evolved stars of luminosity classes IV, III, II and Ib covering thespectral region F, G and K. The survey was carried out with the CORAVELspectrometer. The precision for the radial velocities is better than0.30 km s-1, whereas for the rotational velocity measurementsthe uncertainties are typically 1.0 km s-1 for subgiants andgiants and 2.0 km s-1 for class II giants and Ib supergiants.These data will add constraints to studies of the rotational behaviourof evolved stars as well as solid informations concerning the presenceof external rotational brakes, tidal interactions in evolved binarysystems and on the link between rotation, chemical abundance and stellaractivity. In this paper we present the rotational velocity v sin i andthe mean radial velocity for the stars of luminosity classes IV, III andII. Based on observations collected at the Haute--Provence Observatory,Saint--Michel, France and at the European Southern Observatory, LaSilla, Chile. Table \ref{tab5} also available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| High resolution spectroscopy over lambda lambda 8500-8750 Å for GAIA. I. Mapping the MKK classification system
We present an Echelle+CCD high resolution spectroscopic atlas (0.25Ä/pix dispersion, 0.43 Ä FWHM resolution and 20 000 resolvingpower) mapping the MKK classification system over the interval lambdalambda 8500-8750 Ä. The wavelength interval is remarkably free fromtelluric lines and it is centered on the near-IR triplet of Ca II, thehead of hydrogen Paschen series and several strong metallic lines. Thespectra of 131 stars of types between O4 and M8 and luminosity classes Ithrough V are included in the atlas. Special care was put in maintainingthe highest instrumental homogeneity over the whole set of data. Thecapability to derive accurate MKK spectral types from high resolutionobservations over the interval lambda lambda 8500-8750 Ä isdiscussed. The observations have been performed as part of an evaluationstudy of possible spectroscopic performances for the astrometric missionGAIA planned by ESA. Tables~3 and 4 are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/ Abstract.html}\fnmsep\thanks{ Thespectra of the stars listed in Table~2 are also available in electronicform at the CDS or via the personal HomePagehttp://ulisse.pd.astro.it/Astro/Atlases/}\fnmsep\thanks{ Figures 3--28are only available in electronic form at http://www.edpsciences.com
| 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
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Orsa Minore |
| Ascensione retta: | 14h50m42.30s |
| Declinazione: | +74°09'20.0" |
| Magnitudine apparente: | 2.08 |
| Distanza: | 38.775 parsec |
| Moto proprio RA: | 0 |
| Moto proprio Dec: | 0 |
| B-T magnitude: | 3.998 |
| V-T magnitude: | 2.215 |
Cataloghi e designazioni:
|
INHABITED SKY
