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The Calar Alto lunar occultation program: update and new results
We present an update of the lunar occultation program which is routinelycarried out in the near-IR at the Calar Alto Observatory. A total of 350events were recorded since our last report (Fors et al. 2004, A&A,419, 285). In the course of eight runs we have observed, among others,late-type giants, T-Tauri stars, and infrared sources. Noteworthy was apassage of the Moon close to the galactic center, which produced a largenumber of events during just a few hours in July 2004. Results includethe determinations of the angular diameter of RZ Ari,and the projected separations and brightness ratios for one triple and13 binary stars, almost all of which representing first time detections.Projected separations range from 0farcs09 to 0farcs007. We provide aquantitative analysis of the performance achieved in our observations interms of angular resolution and sensitivity, which reach about 0farcs003and K ≈8.5 mag, respectively. We also present a statisticaldiscussion of our sample, and in particular of the frequency ofdetection of binaries among field stars.
| 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}
| 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.
| High-Resolution Near-Infrared Spectroscopy of FU Orionis Objects
We present an analysis of recent near-infrared, high-resolution spectraof the variable FU Ori objects. During a phase of rapid fading inoptical brightness during 1997, V1057 Cyg exhibited shell absorption infirst-overtone (v''-v'=2-0) CO lines, blueshiftedby about 50 km s-1 from the system velocity. This shellcomponent had not been seen previously, nor was it present in 1999,although some blueshifted absorption asymmetry is seen at the latterepoch. The appearance of this CO absorption shell is connected with theroughly contemporaneous appearance of blueshifted, low-excitationoptical absorption lines with comparable low velocities; we suggest thatthis shell was also responsible for some of the peculiar emissionfeatures seen in red-optical spectra of V1057 Cyg. FU Ori continues toexhibit broad CO lines, with some evidence for the double-peakedprofiles characteristic of an accretion disk; the line profiles areconsistent with previous observations. Both FU Ori and V1057 Cygcontinue to exhibit lower rotational broadening at 2.3 μm than atoptical wavelengths, in agreement with the prediction of differentiallyrotating disk models; we have a marginal detection of the same effect inV1515 Cyg. The relative population of the first-overtone CO rotationallevels in the FU Ori objects suggests low excitation temperatures. Wecompare disk models to the observations and find agreement with overallline strengths and rotational broadening, but the observed line profilesare generally less double-peaked than predicted. We suggest that thediscrepancy in line profiles is due to turbulent motions in FU Oridisks, an effect qualitatively predicted by recent simulations of themagnetorotational instability in vertically stratified accretion disks.Based on observations obtained at the Gemini Observatory, which isoperated by the Association of Universities for Research in Astronomy(AURA), Inc., under a cooperative agreement with the NSF, on behalf ofthe Gemini partnership: the National Science Foundation (United States),the Particle Physics and Astronomy Research Council (United Kingdom),the National Research Council (Canada), CONICYT (Chile), the AustralianResearch Council (Australia), CNPq (Brazil), and CONICRT (Argentina).Based on observations obtained with the Phoenix infrared spectrograph,developed and operated by the National Optical Astronomy Observatory.The National Optical Astronomy Observatory is operated by the AURA, Inc.under cooperative agreement with the National Science Foundation.
| Synthetic Lick Indices and Detection of α-Enhanced Stars
Synthetic Lick indices computed with solar scaled abundances and withα-element enhancement are presented and compared with predictionsfrom both theoretical computations (Tripicco & Bell; Thomas,Maraston, & Bender; Barbuy et al.) and empirical fitting functions(de Freitas Pacheco). We propose selected combinations of indicescapable of singling out α-enhanced stars without requiringprevious knowledge of their main atmospheric parameters. By applyingthis approach to the 460 stars in the Worthey et al. catalog, wedetected a list of 82 candidate α-enhanced stars. The confirmationof α-enhancement was obtained by searching the literature forindividual element abundance determinations from high-resolutionspectroscopy for a subsample of 34 stars. Preliminary discussion of theproperties of the detected α-enhanced stars with respect to their[Fe/H] values and kinematics is presented.
| Further Results of TiO-Band Observations of Starspots
We present measurements of starspot parameters (temperature and fillingfactor) on five highly active stars, using absorption bands of TiO, fromobservations made between 1998 March and 2001 December. We determinedstarspot parameters by fitting TiO bands using spectra of inactive G andK stars as proxies for the unspotted photospheres of the active starsand spectra of M stars as proxies for the spots. For three evolved RSCVn systems, we find spot filling factors between 0.28 and 0.42 for DMUMa, 0.22 and 0.40 for IN Vir, and 0.31 and 0.35 for XX Tri; thesevalues are similar to those found by other investigators usingphotometry and Doppler imaging. Among active dwarfs, we measured a lowerspot temperature (3350 K) for EQ Vir than found in a previous study ofTiO bands, and for EK Dra a lower spot temperature (~3800 K) than foundthrough photometry. For all active stars but XX Tri, we achieved goodphase coverage through a stellar rotational period. We also present ourfinal, extensive grid of spot and nonspot proxy stars.This paper includes data taken at McDonald Observatory of the Universityof Texas at Austin.
| Evolutionary synthesis of galaxies at high spectral resolution with the code PEGASE-HR. Metallicity and age tracers
We present PEGASE-HR, a new stellar population synthesis programgenerating high resolution spectra (R=10 000) over the optical rangeλλ = 400-680 nm. It links the spectro-photometric model ofgalaxy evolution PEGASE.2 (Fioc & Rocca-Volmerange 1997) to anupdated version of the ELODIE library of stellar spectra observed withthe 193 cm telescope at the Observatoire de Haute-Provence\citep{ELODIE}. The ELODIE star set gives a fairly complete coverage ofthe Hertzprung-Russell (HR) diagram and makes it possible to synthesizepopulations in the range [Fe/H]=-2 to +0.4. This code is an exceptionaltool for exploring signatures of metallicity, age, and kinematics. Wefocus on a detailed study of the sensitivity to age and metallicity ofthe high-resolution stellar absorption lines and of the classicalmetallic indices proposed until now to solve the age-metallicitydegeneracy. Validity tests on several stellar lines are performed bycomparing our predictions for Lick indices to the models of othergroups. The comparison with the lower resolution library BaSeL\citep{Lejeune97} confirms the quality of the ELODIE library when usedfor single stellar populations (SSPs) from 107 to2×1010 yr. Predictions for the evolved populations ofglobular clusters and elliptical galaxies are given and compared toobservational data. Two new high-resolution indices are proposed aroundthe Hγ line. They should prove useful in the analysis of spectrafrom the new generation of telescopes and spectrographs.
| Heavenly Harmony: Red Giants Pulsating in Many Modes
We have analyzed the complex variability of five small-amplitudepulsating red giants--RZ Ari, V523 Mon, BC CMi, UX Lyn, FS Com--using a5000-day database of V photometry from a robotic telescope. For each ofthese stars, two or three periods recur in each season, and are presentin separate halves of the dataset. The periods and their ratios areconsistent with low-order radial pulsation modes; the stars arepulsating in multiple overtones, or harmonics. The amplitudes of themodes rise and fall significantly on time scales of 2000 to 3500 days. In UX Lyn and FS Com, there are long secondary periods which add a bassdrone to the wavering chord of the radial modes. Even with all theseperiods accounted for, there are small residuals, which suggest that thecelestial harmony is even more complex than we might think.
| Multiperiodicity in Five Small-Amplitude Pulsating Red Giants
We report multiperiodicity in five small-amplitude pulsating red giants:RZ Ari, V523 Mon, BC CMi, UX Lyn, and FS Com. For each of these stars,two or three periods recur in each season of our 5000 day database of Vobservations. The periods and their ratios are consistent with low-orderradial pulsation modes. The amplitudes of the modes change significantlyon timescales of 1-5 yr; specifically, the amplitudes of the dominantperiods vary on timescales of 2000-3500 days. Most often, the amplitudesof the modes in a given star rise and fall in unison.
| High resolution spectroscopy over lambda lambda 8500-8750 Å for GAIA. IV. Extending the cool MK stars sample
A library of high resolution spectra of MK standard and reference stars,observed in support to the GAIA mission, is presented. The aim of thispaper is to integrate the MK mapping of Paper I of this series as wellas to consider stars over a wider range of metallicities. Radialvelocities are measured for all the target stars.The spectra are available in electronic form (ASCII format) at CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/406/995 and from the webpage http://ulisse.pd.astro.it/MoreMK/, where further bibliographicalinformation for the target stars is given.
| STELIB: A library of stellar spectra at R ~ 2000
We present STELIB, a new spectroscopic stellar library, available athttp://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneouslibrary of 249 stellar spectra in the visible range (3200 to 9500Å), with an intermediate spectral resolution (la 3 Å) andsampling (1 Å). This library includes stars of various spectraltypes and luminosity classes, spanning a relatively wide range inmetallicity. The spectral resolution, wavelength and spectral typecoverage of this library represents a substantial improvement overprevious libraries used in population synthesis models. The overallabsolute photometric uncertainty is 3%.Based on observations collected with the Jacobus Kaptein Telescope,(owned and operated jointly by the Particle Physics and AstronomyResearch Council of the UK, The Nederlandse Organisatie voorWetenschappelijk Onderzoek of The Netherlands and the Instituto deAstrofísica de Canarias of Spain and located in the SpanishObservatorio del Roque de Los Muchachos on La Palma which is operated bythe Instituto de AstrofÃsica de Canarias), the 2.3 mtelescope of the Australian National University at Siding Spring,Australia, and the VLT-UT1 Antu Telescope (ESO).Tables \ref{cat1} to \ref{cat6} and \ref{antab1} to A.7 are onlyavailable in electronic form at http://www.edpsciences.org. The StellarLibrary STELIB library is also available at the CDS, via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/433
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable 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/qcat?J/A+A/397/997
| Do red giant stars pulsate in high overtones?
About 30 photometrically variable red giant stars have periods less than10d, as determined by the compilers of the Hipparcos Catalogue fromHipparcos photometric measurements. These periods, when combined withestimates of the radii and masses of these stars, and with pulsationtheory, imply that these stars are pulsating in very high overtones. Wepresent several pieces of evidence which suggest that the periods may bespurious, as a result of the particular aliasing properties of theHipparcos photometry. We conclude that the evidence for high-overtonepulsation in red giant stars is equivocal.
| 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.
| 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.
| Long-Term VRI Photometry of Small-Amplitude Red Variables. I. Light Curves and Periods
We report up to 5000 days of VRI photometry, from a robotic photometrictelescope, of 34 pulsating red giants, namely, TV Psc, EG And, Z Psc, RZAnd, 4 Ori, RX Lep, UW Lyn, η Gem, μ Gem, ψ1 Aur,V523 Mon, V614 Mon, HD 52690, Y Lyn, BC CMi, X Cnc, UX Lyn, RS Cnc, VYUMa, ST UMa, TU CVn, FS Com, SW Vir, 30 Her, α1 Her,V642 Her, R Lyr, V450 Aql, V1293 Aql, δ Sge, EU Del, V1070 Cyg, WCyg, and μ Cep, as well as a few variable comparison stars. V, R, andI variations are generally in phase. The length and density of the dataenable us to look for variations on timescales ranging from days toyears. We use both power-spectrum (Fourier) analysis and autocorrelationanalysis, as well as light-curve analysis; these three approaches arecomplementary. The variations range from regular to irregular, but inmost of the stars, we find a period in the range of 20-200 days, whichis probably due to low-order radial pulsation. In many of the stars, wealso find a period which is an order of magnitude longer. It may be dueto rotation, or it may be due to a new kind of convectively inducedoscillatory thermal mode, recently proposed by P. Wood.
| Single Channel Photoelectric Photometry of RZ Arietis, 1983-2001
The AAVSO Photoelectric Photometry Archives contain 568 V observationsof the SRb star RZ Ari covering 17 years. During this time, there are 22clearly defined cycles evident in the data, ranging from 26 to 71 daysand giving an average period of 51.32 days. Assuming a V magnitude of5.87 for the comparison star, RZ Ari varied from 5.45 to 6.19, giving anamplitude of 0.74 magnitude. When the complete data set is graphed,there is also clear evidence of a secondary period on the order of 1100to 1500 days. Catalogue data on RZ Ari differ from our findings. The"General Catalogue of Variable Stars", "Bright Star Catalogue", and"Catalogue 2000.0" are all the same: 5.62-6.01 V(amplitude 0.39 mag.)with a period of 30 days. Hipparcos values are 5.297-5.643 (amplitude0.346 mag.) and no evident period. None of the catalogues mention asecondary period.
| Hydroxyl 1.563 Micron Absorption from Starspots on Active Stars
We present results from a study of starspots on active stars using apair of vibrational-rotational absorption lines of the OH molecule near1.563 μm. We detect excess OH absorption due to dark, cool starspotson several active stars of the RS CVn and BY Dra classes. Our resultsfor the single-lined spectroscopic binaries II Pegasi, V1762 Cygni, andλ Andromedae augment those from a previous study that used a lesssensitive detector. In this study, we were able for the first time touse molecular absorption features to measure starspot properties ondouble-lined spectroscopic binaries. Measuring the equivalent widths ofthese OH lines in inactive giant and dwarf stars of spectral types G, K,and M, we find that the total equivalent width of the line pairincreases approximately linearly as effective temperature decreases from5000 to 3000 K. We measure starspot filling factors by fitting thespectra of active stars with linear combinations of comparison starspectra representing the spot and nonspot regions of the star.
| 4 μm spectra of AGB stars I. Observations
We present times series of high resolution spectra of AGB variables at 4mu m. Line profiles from the major contributors to the spectra ofoxygen-rich stars at 4 mu m, OH, H_2O, HCl and SiO, are examined. Thevelocity as well as shape variations of these profiles with time arediscussed. The line profiles investigated frequently have emission andmultiple absorption components. The changes with time of the 4 mu mregion lines do not always follow the cyclic variability seen in NIRspectra and in the photometric light curve. We interpret and discuss theresults qualitatively considering comparing the spectral variabilitywith that of the well behaved 1.6 mu m region and of dynamical modelatmospheres. Miras and semiregular variables are compared. The originsof non-periodic behavior are discussed, including the role of spatialinhomogeneities in the stellar atmosphere.
| Long period variable stars: galactic populations and infrared luminosity calibrations
In this paper HIPPARCOS astrometric and kinematic data are used tocalibrate both infrared luminosities and kinematical parameters of LongPeriod Variable stars (LPVs). Individual absolute K and IRAS 12 and 25luminosities of 800 LPVs are determined and made available in electronicform. The estimated mean kinematics is analyzed in terms of galacticpopulations. LPVs are found to belong to galactic populations rangingfrom the thin disk to the extended disk. An age range and a lower limitof the initial mass is given for stars of each population. A differenceof 1.3 mag in K for the upper limit of the Asymptotic Giant Branch isfound between the disk and old disk galactic populations, confirming itsdependence on the mass in the main sequence. LPVs with a thin envelopeare distinguished using the estimated mean IRAS luminosities. The levelof attraction (in the classification sense) of each group for the usualclassifying parameters of LPVs (variability and spectral types) isexamined. Table only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/374/968 or via ASTRIDdatabase (http://astrid.graal.univ-montp2.fr).
| 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
| Hipparcos parallaxes for Mira-like long-period variables
This paper concerns the calibration of the K period-luminosity relationfor Mira variables using Hipparcos parallaxes. K magnitudes areavailable for 255 Mira-like variables which were observed by Hipparcos.Period-luminosity zero-points are evaluated for various subgroups ofdata. The best solution for oxygen-rich Miras, which uses 180 stars,omitting the short-period red group (which had different kinematics fromthe short-period blue stars) and the low-amplitude variables, provides azero-point of σ2σ2π +(0.4605)2π2PL(K)σ2K + σ2PL(K),0.84+/-0.14mag, which implies a distance modulus for the LargeMagellanic Cloud of σK = 0.3ΔK√N,18.64+/-0.14mag, or perhaps slightly greater if a metallicity correctionis required, in good agreement with the value derived from Cepheids. Thezero-point of the period-luminosity relation for carbon stars is brieflydiscussed. Linear diameters are derived for red variables with measuredangular diameters and parallaxes, and are used to examine thelong-standing question of the pulsation mode(s) of these stars. Evidenceis presented to suggest that most of them are pulsating in the same modeand, if published model atmospheres are correct, this is probably thefirst overtone. Some discussion is given of sequences in theperiod-luminosity and period-colour diagrams and their bearing on thepulsation mode problem.
| Dust features in the 10-mu m infrared spectra of oxygen-rich evolved stars
We have analyzed the 8-13.5 mu m UKIRT CGS3 spectra of 142 M-type starsincluding 80 oxygen-rich AGB stars and 62 red supergiants, with a viewto understanding the differences and similarities between the dustfeatures of these stars. We have classified the spectra into groupsaccording to the observed appearance of the infrared features. In eachcase the normalized continuum-subtracted spectrum has been compared tothose of the other stars to find similarities and form groups. The dustfeatures of the AGB stars are classified into six groups: broad AGB,where the feature extends from 8 mu m to about 12.5 mu m with littlestructure; broad+sil AGB, which consists of a broad feature with anemerging 9.7 mu m silicate bump; and four silicate AGB groups in which a``classic'' 9.7 mu m silicate feature gets progressively narrower.Likewise, the supergiant spectra have also been classified into groups,however these do not all coincide with the AGB star groups. In thesupergiant case we again have six groups: featureless, where there islittle or no emission above the continuum; broad Super, where thefeature extends from about 9 mu m to about 13 mu m; and four silicateSuper groups, which again show a progression towards the narrowest``classic'' 9.7 mu m silicate feature. We compare the mean spectrum foreach group, which yields two main results. Firstly, while the``classic'' silicate feature is essentially identical for both AGB starsand red supergiants, the broad features observed for these two stellartypes are quite different. We suggest that the dust in these twoenvironments follows different evolutionary paths, with the dust aroundMira stars, whose broad feature spectra can be fit by a combination ofalumina (Al2O3) and magnesium silicate,progressing from this composition to dust dominated by magnesiumsilicate only, while the dust around supergiants, whose broad featurecan be fit by a combination of Ca-Al-rich silicate andAl2O3, progresses from this initial composition toone eventually also dominated by magnesium silicate. The reason for thedifference in the respective broad features is not clear as yet, butcould be influenced by lower C/O ratios and chromospheric UV radiationfields in supergiant outflow environments. The second result concernsthe 12.5 - 13.0 mu m feature discovered in IRAS LRS spectra and widelyattributed to Al2O3. This feature is seenpredominantly in the spectra of semiregular variables, sometime in Mirasand only once (so far) in supergiant spectra. We argue that it isunlikely that this feature is due to Al2O3 or, ashas more recently been suggested, spinel(MgAl2O4), but could be associated with silicondioxide or highly polymerized silicates (not pyroxenes or olivines).
| Photometric modelling of starspots - I. A Barnes-Evans-like surface brightness-colour relation using (Ic-K)
In the first part of this work, the empirical correlation of stellarsurface brightness FV with (Ic-K) broad-bandcolour is investigated by using a sample of stars cooler than the Sun. Abilinear correlation is found to represent well the brightness of G, Kand M giant stars. The change in slope occurs at (Ic-K)~2.1or at about the transition from K to M spectral types. The samerelationship is also investigated for dwarf stars and found to bedistinctly different from that of the giants. The dwarf star correlationdiffers by an average of -0.4 in (Ic-K) or by a maximum inFV of ~-0.1, positioning it below that of the giants, withboth trends tending towards convergence for the hotter stars in oursample. The flux distribution derived from theFV-(Ic-K) relationship for the giant stars,together with that derived from an FV-(V-K) relationship andthe blackbody flux distribution, is then utilized to compute syntheticlight V and colour (V-R)c, (V-I)c and (V-K) curvesof cool spotted stars. We investigate the effects on the amplitudes ofthe curves by using these FV-colour relations and by assumingthe effective gravity of the spots to be lower than the gravity of theunspotted photosphere. We find that the amplitudes produced by using theFV-(Ic-K) relationship are larger than thoseproduced by the other two brightness correlations, meaning smallerand/or warmer spots.
| Revision and Calibration of MK Luminosity Classes for Cool Giants by HIPPARCOS Parallaxes
The Hipparcos parallaxes of cool giants are utilized in two ways in thispaper. First, a plot of reduced parallaxes of stars brighter than 6.5,as a function of spectral type, for the first time separates members ofthe clump from stars in the main giant ridge. A slight modification ofthe MK luminosity standards has been made so that luminosity class IIIbdefines members of the clump, and nearly all of the class III stars fallwithin the main giant ridge. Second, a new calibration of MK luminosityclasses III and IIIb in terms of visual absolute magnitudes has beenmade.
| Speckle Interferometry of New and Problem HIPPARCOS Binaries
The ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged ``G,''``O,'' ``V,'' or ``X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as ``suspected nonsingle'' (flag ``S'' in field H61), thusyielding a total of 11,687 ``problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras.
| CCD spectra of MK standards and a preliminary extension of the MK classification to the yellow-red region.
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| Takýmyýldýz: | Koc |
| Sað Açýklýk: | 02h55m48.50s |
| Yükselim: | +18°19'54.0" |
| Görünürdeki Parlaklýk: | 5.91 |
| Uzaklýk: | 123.762 parsek |
| özdevim Sað Açýklýk: | -7.5 |
| özdevim Yükselim: | -15.5 |
| B-T magnitude: | 7.416 |
| V-T magnitude: | 5.951 |
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