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# α UMa (Dubhe)

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 Discovery of solar-like oscillations in the red giant \varepsilon OphiuchiWe present the discovery of solar-like oscillations in time-series ofthe G9.5 red giant \varepsilon Ophiuchi. The data were obtained with theCORALIE spectrograph at the 1.2 m Swiss telescope in La Silla and theELODIE spectrograph at the 1.93 m telescope at the Observatoire de HauteProvence. Periodic variations can be observed in the radial velocitytime series of individual nights. In the power spectrum of the radialvelocity time series there is a clear power excess around 60 μHz, andseveral individual oscillation frequencies can be distinguished. Ourauto-correlation and comb response analysis reveals a large separationof either 4.8 μHz or (its 11.57 μHz alias) 6.7 μHz. We estimatethe position of \varepsilon Oph in the HR diagram, and verify whetherCESAM shell hydrogen-burning stellar models exist that can reproduce theobserved frequency separation. Shapes of Spectral Line Bisectors for Cool StarsThe shape of the line bisector for the prototype spectral line Fe Iλ6253 was measured for an array of 54 stars on the cool half ofthe HR diagram. These bisectors are given in tables along with theirerrors. The classic C shape is shown by only a rather restricted rangein effective temperature and luminosity. The detailed change in bisectorshape with effective temperature and luminosity is documented moreprecisely than in previous work. The most blueward point on the bisectorchanges its height systematically with luminosity and can be used as aluminosity or gravity discriminant. The wide range of bisector shapescontains significant information about the velocity fields in theatmospheres of these stars, but extracting that information may requireextensive modeling. The light curve of the semiregular variable L2 Puppis - II. Evidence for solar-like excitation of the oscillationsWe analyse visual observations of the pulsations of the red giantvariable L2 Puppis (L2 Pup). The data cover 77 yrbetween 1927 and 2005, thus providing an extensive empirical base forcharacterizing properties of the oscillations. The power spectrum of thelight curve shows a single mode resolved into multiple peaks under anarrow envelope. We argue that this results from stochastic excitation,as seen in solar oscillations, with a mode lifetime of about 5 yr. Therandom fluctuations in phase also support this idea. A comparison with XCam, a true Mira star with the same pulsation period, and W Cyg, a truesemiregular star, illustrates the basic differences in phase behaviours.The Mira shows very stable phase, consistent with excitation by theκ-mechanism, whereas W Cyg shows large phase fluctuations thatimply stochastic excitation. We find L2 Pup to beintermediate, implying that both mechanisms play a role in itspulsation. Finally, we also checked the presence of low-dimensionalchaos and could safely exclude it. Speckle observations with PISCO in Merate - I. Astrometric measurements of visual binaries in 2004We present relative astrometric measurements of visual binaries madewith the Pupil Interferometry Speckle camera and Coronagraph (PISCO) atthe 1-m Zeiss telescope of Brera Astronomical Observatory, in Merate. Weprovide 135 new observations of 103 objects, with angular separations inthe range 0.1-4.0 arcsec and with an accuracy better than ~0.01 arcsec.Our sample is made of orbital couples as well as binaries whose motionis still uncertain. Our purpose is to improve the accuracy of the orbitsand constrain the masses of the components.This work already leads to the revision of the orbits of three systems(ADS 5447, 8035 and 8739). Predicting accurate stellar angular diameters by the near-infrared surface brightness techniqueI report on the capabilities of the near-infrared (near-IR) surfacebrightness technique to predict reliable stellar angular diameters asaccurate as <~2 per cent using standard broad-band Johnson photometryin the colour range -0.1 <= (V-K)O<= 3.7 includingstars of A, F, G, K spectral type. This empirical approach is fast toapply and leads to estimated photometric diameters in very goodagreement with recent high-precision interferometric diametermeasurements available for non-variable dwarfs and giants, as well asfor Cepheid variables. Then I compare semi-empirical diameters predictedby model-dependent photometric and spectrophotometric (SP) methods withnear-IR surface brightness diameters adopted as empirical referencecalibrators. The overall agreement between all these methods is withinapproximately +/-5 per cent, confirming previous works. However, on thesame scale of accuracy, there is also evidence for systematic shiftspresumably as a result of an incorrect representation of the stellareffective temperature in the model-dependent results. I also comparemeasurements of spectroscopic radii with near-IR surface brightnessradii of Cepheids with known distances. Spectroscopic radii are found tobe affected by a scatter as significant as >~9 per cent, which is atleast three times greater than the formal error currently claimed by thespectroscopic technique. In contrast, pulsation radii predicted by theperiod-radius (PR) relation according to the Cepheid period result aresignificantly less dispersed, indicating a quite small scatter as aresult of the finite width of the Cepheid instability strip, as expectedfrom pulsation theory. The resulting low level of noise stronglyconfirms our previous claims that the pulsation parallaxes are the mostaccurate empirical distances presently available for Galactic andextragalactic Cepheids. Variability of Stars in the Pulkovo Spectrophotometric CatalogWe present the results of a statistical study of brightness variabilityfor 693 stars of the Pulkovo spectrophotometric database in fivespectral bands in the range λλ 320 1080 nm. Significantbrightness variations were detected in at least one spectral bandagainst the background of the random noise for one-third of the starsnot earlier believed to be variable. A comparison of the distributionsof these variations in amplitude and spectral band for the normal andvariable stars shows that variability is inherent to most stars to someextent and is often wavelength dependent. Survey for Transiting Extrasolar Planets in Stellar Systems. II. Spectrophotometry and Metallicities of Open ClustersWe present metallicity estimates for seven open clusters based onspectrophotometric indices from moderate-resolution spectroscopy.Observations of field giants of known metallicity provide a correlationbetween the spectroscopic indices and the metallicity of open clustergiants. We use χ2 analysis to fit the relation ofspectrophotometric indices to metallicity in field giants. The resultingfunction allows an estimate of the target-cluster giants' metallicitieswith an error in the method of +/-0.08 dex. We derive the followingmetallicities for the seven open clusters: NGC 1245, [M/H]=-0.14+/-0.04NGC 2099, [M/H]=+0.05+/-0.05 NGC 2324, [M/H]=-0.06+/-0.04 NGC 2539,[M/H]=-0.04+/-0.03 NGC 2682 (M67), [M/H]=-0.05+/-0.02 NGC 6705,[M/H]=+0.14+/-0.08 NGC 6819, [M/H]=-0.07+/-0.12. These metallicityestimates will be useful in planning future extrasolar planet transitsearches, since planets may form more readily in metal-richenvironments. Pulsation of the K 2.5 giant star GSC 09137-03505?In July, 1999, the Hubble Space Telescope (HST) pointed for more than 8days continuously at the globular cluster 47 Tucanae. Two guide starswere used during this campaign by the Fine Guidance Sensors (FGS). Usingmore than 19 million photometric FGS data for the guide star GSC09137-03505 we found brightness variability corresponding to threeapproximately equidistant frequencies. The detected frequencies rangefrom 21 to 71 μHz with amplitudes between 341 and 291 ppm. MulticolorCCD photometry was obtained at the Cerro Tololo Inter-AmericanObservatory to derive color information for the guide stars. Inaddition, flux calibrated spectra were observed at the South AfricanAstronomical Observatory. Temperature and surface gravity weredetermined from a comparison of observed and synthetic spectral fluxesusing the nemo (Vienna New Model Grid of Stellar Atmospheres) modelatmosphere grid developed by Heiter et al. (2002, A&A, 392, 619) andNendwich et al. (2004, CoAst, 144, 43). We also performed linearnonadiabatic analyses of various stellar models in an attempt tointerprete the frequencies. CHARM2: An updated Catalog of High Angular Resolution MeasurementsWe 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 Improved Baade-Wesselink surface brightness relationsRecent, 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. Determination of fundamental characteristics for stars of the F, G, and K spectral types. The surface gravities and metallicity parameters.Not Available Synthetic Lick Indices and Detection of α-enhanced Stars. II. F, G, and K Stars in the -1.0 < [Fe/H] < +0.50 RangeWe 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. Matching Stellar Models to Oscillation DataWe describe a method to match stellar models to a set of low-l p-modeoscillation frequencies. The method provides a quality of fit measuresimilar to that obtained from a χ2 fit. With asufficiently dense grid of stellar models, the method can determine thebest-fitting model to the oscillation data as constrained solely by theoscillation data. That is to say, the method can be used to constrainthe mass, age, composition, surface temperature, and luminosity of astar from the oscillation data. We evaluate the method on solar data andapply the method to the recently observed oscillation data for αCen and α UMa. Speckle Observations of Binary Stars with the WIYN Telescope. IV. Differential PhotometryFive hundred seventy-six magnitude difference measures are presented for260 binary stars. These measures are derived from CCD-based speckleobservations taken at the WIYN 3.5 m telescope at Kitt Peak NationalObservatory during the period 1997-2000. Separations of the systemsrange from over 1" down to near the diffraction limit of the telescope.A study of multiple measures of the same targets indicates that themeasures have a typical uncertainty of better than 0.13 mag per 2 minuteobservation, and that multiple observations can be averaged to arrive atsmaller uncertainties. Results presented here are also compared, insofaras it is possible, with measures in the Hipparcos Catalogue and toprevious studies using adaptive optics. No major systematic errors wereidentified.The WIYN Observatory is a joint facility of the University ofWisconsin-Madison, Indiana University, Yale University, and the NationalOptical Astronomy Observatory. Empirically Constrained Color-Temperature Relations. II. uvbyA new grid of theoretical color indices for the Strömgren uvbyphotometric system has been derived from MARCS model atmospheres and SSGsynthetic spectra for cool dwarf and giant stars having-3.0<=[Fe/H]<=+0.5 and 3000<=Teff<=8000 K. Atwarmer temperatures (i.e., 8000-2.0. To overcome thisproblem, the theoretical indices at intermediate and high metallicitieshave been corrected using a set of color calibrations based on fieldstars having well-determined distances from Hipparcos, accurateTeff estimates from the infrared flux method, andspectroscopic [Fe/H] values. In contrast with Paper I, star clustersplayed only a minor role in this analysis in that they provided asupplementary constraint on the color corrections for cool dwarf starswith Teff<=5500 K. They were mainly used to test thecolor-Teff relations and, encouragingly, isochrones thatemploy the transformations derived in this study are able to reproducethe observed CMDs (involving u-v, v-b, and b-y colors) for a number ofopen and globular clusters (including M67, the Hyades, and 47 Tuc)rather well. Moreover, our interpretations of such data are verysimilar, if not identical, with those given in Paper I from aconsideration of BV(RI)C observations for the sameclusters-which provides a compelling argument in support of thecolor-Teff relations that are reported in both studies. Inthe present investigation, we have also analyzed the observedStrömgren photometry for the classic Population II subdwarfs,compared our final'' (b-y)-Teff relationship with thosederived empirically in a number of recent studies and examined in somedetail the dependence of the m1 index on [Fe/H].Based, in part, on observations made with the Nordic Optical Telescope,operated jointly on the island of La Palma by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.Based, in part, on observations obtained with the Danish 1.54 mtelescope at the European Southern Observatory, La Silla, Chile. Solar-like OscillationsThe five-minute oscillations in the Sun have provided a wealth ofinformation about the solar interior. After many attempts, positivedetections of similar oscillations in solar-type stars have now beenmade. This review discusses the properties of solar-like oscillations,the methods used to observe them, and the results on individual stars.We conclude that the study of solar-like oscillations from the groundand space has an exciting future. Red variables in the OGLE-II data base - I. Pulsations and period-luminosity relations below the tip of the red giant branch of the Large Magellanic CloudWe present period-luminosity relations for more than 23 000 red giantsin the Large Magellanic Cloud observed by the OGLE-II microlensingproject. The OGLE period values were combined with the 2MASSsingle-epoch JHKS photometric data. For the brighter stars wefind agreement with previous results (four different sequencescorresponding to different modes of pulsation in asymptotic giant branchstars). We also discovered two distinct and well-separated sequencesbelow the tip of the red giant branch. They consist of almost 10 000short-period (15 < P < 50 d), low-amplitude (AI <0.04) mag red variable stars, for which we propose that a significantfraction is likely to be on the red giant branch, showing radialpulsations in the second and third overtone modes. The excitationmechanism could be either Mira-like pulsation or solar-like oscillationsdriven by convection. Oxygen isotopic ratios in first dredge-up red giant stars and nuclear reaction rate uncertainties revisitedWe 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. Oscillations in Arcturus from WIRE PhotometryObservations of the red giant Arcturus (α Boo) obtained with thestar tracker on the Wide Field Infrared Explorer (WIRE) satellite duringa baseline of 19 successive days in 2000 July-August are analyzed. Theamplitude spectrum has a significant excess of power at low frequencies.The highest peak is at ~4.1 μHz (2.8 days), which is in agreementwith previous ground-based radial velocity studies. The variability ofArcturus can be explained by sound waves, but it is not clear whetherthese are coherent p-mode oscillations or a single mode with a shortlifetime. Onset of Mass Loss in Red Giants: Association with an Evolutionary EventStencel & 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. Angular Diameters of Stars from the Mark III Optical InterferometerObservations 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. 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. Line Absorption as a Metallicity Index for Giant StarsThe fraction of light removed from a star's spectrum by the spectrallines, the line absorption, is shown to be a precise empirical indicatorof metallicity. We measured the line absorption in 89 class III giantstars in a 42.5 Å window between 6219.0 and 6261.5 Å andthen calibrated these values against published metallicities. We showthat the line absorption can be measured precisely enough to improve themetallicity precision about fivefold over the original calibrationmetallicities, reaching a precision of 0.01 dex in favorable cases. The latitude and epoch for the formation of the southern Greek constellationsNot Available Astrometric Orbits from a Direct Combination of Ground-Based Catalogs with the Hipparcos CatalogNot Available The Rotation of Binary Systems with Evolved ComponentsIn the present study we analyze the behavior of the rotational velocity,vsini, for a large sample of 134 spectroscopic binary systems with agiant star component of luminosity class III, along the spectral regionfrom middle F to middle K. The distribution of vsini as a function ofcolor index B-V seems to follow the same behavior as their singlecounterparts, with a sudden decline around G0 III. Blueward of thisspectral type, namely, for binary systems with a giant F-type component,one sees a trend for a large spread in the rotational velocities, from afew to at least 40 km s-1. Along the G and K spectral regionsthere are a considerable number of binary systems with moderate tomoderately high rotation rates. This reflects the effects ofsynchronization between rotation and orbital motions. These rotatorshave orbital periods shorter than about 250 days and circular or nearlycircular orbits. Except for these synchronized systems, the largemajority of binary systems with a giant component of spectral type laterthan G0 III are composed of slow rotators. Speckle Observations of Binary Stars with the WIYN Telescope. II. Relative Astrometry Measures during 1998-2000Five hundred twelve relative astrometry measures are presented for 253double stars, including 53 double stars discovered by Hipparcos. In 15cases, relative astrometry is reported for the first time for newlyconfirmed pairs. In addition, 20 high-quality nondetections ofcompanions are reported for stars suspected of being nonsingle byHipparcos. Observations were taken using a fast-readout CCD camerasystem at the WIYN 3.5 m telescope at Kitt Peak, Arizona. In comparingthese measures with ephemeris predictions for binary stars with verywell known orbits, we find that the measurement precision is better than3 mas in separation and 1° in position angle per individualobservation. Measurement precision and detection capabilities are fullydiscussed, and confirmed orbital motion is reported in four cases of theHipparcos double star discoveries. The WIYN Observatory is a jointfacility of the University of Wisconsin-Madison, Indiana University,Yale University, and the National Optical Astronomy Observatory. Detection of Solar-like oscillations in the G7 giant star xi HyaWe report the firm discovery of solar-like oscillations in a giant star.We monitored the star xi Hya (G7III) continuously during one month withthe CORALIE spectrograph attached to the 1.2 m Swiss Euler telescope.The 433 high-precision radial-velocity measurements clearly revealmultiple oscillation frequencies in the range 50-130 muHz, correspondingto periods between 2.0 and 5.5 hours. The amplitudes of the strongestmodes are slightly smaller than 2 ms. Current model calculations arecompatible with the detected modes. Based on observations obtained withthe CORALIE spectrograph on the 1.2-m Swiss Euler telescope at La Silla,Chile. 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. Photocentric orbits from a direct combination of ground-based astrometry with Hipparcos. I. Comparison with known orbitsComplementing the Proper Motions of Fundamental Stars catalogue byGontcharov et al. (CDS, I-266) the photocentric orbits of someFK5/Hipparcos stars are calculated in a direct combination of theHipparcos data with astrometric ground-based observational catalogueshaving epochs later than 1939. Some capabilities and limitations of thismethod are discussed in a comparison of our results with known orbits ofSirius, Procyon, Rasalhague, mu Cas and others. We conclude that thisdirect combination is an acceptable tool to discover and investigatephotocentric orbits with periods from 10 to 55 years and the semi-majoraxis of apparent ellipses >0.08 arcsec. It is particularly suitablefor pairs with large magnitude difference as well as for calculation ofthe preliminary orbits of new astrometric binaries which will beconsidered in forthcoming papers. In this paper new photocentric orbitsand component masses are calculated for 4 pairs: alpha UMa, beta LMi,delta And and xi Aqr.
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