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A new analysis of the nucleus of NGC 1068 with MIDI observations
We present a new analysis of the first mid-infrared N-band long-baselineinterferometric observations of an extragalactic source: the nucleus ofthe Seyfert 2 galaxy NGC 1068, obtained with MIDI (Mid-InfrareDInterferometer), the mid-infrared beamcombiner at the European SouthernObservatory (ESO) Very Large Telescope Interferometer (VLTI). Theresolution of λ/B 10 mas allows us to study the compactcentral core of the galaxy between 8 and 13 μm. Both visibilitymeasurements and MIDI spectrum are well reproduced by a simple radiativetransfer model with two concentric spherical components. The derivedangular sizes and temperatures are ~35 and 83 mas, and ~361 K and 226 Kfor these two components respectively. Other evidence strongly supportssuch low temperatures. This modeling also provides the variation ofoptical depth as a function of wavelength for the extended componentacross the N-band suggesting the presence of amorphous silicate grains.This shows that MIDI has carried out the first direct observations ofthe distribution of dust around the central engine.
| First results from the ESO VLTI calibrators program
The ESO Very Large Telescope Interferometer (VLTI) is one of the leadinginterferometric facilities. It is equipped with several 8.2 and 1.8 mtelescopes, a large number of baselines up to 200 m, and with severalsubsystems designed to enable high quality measurements and to improvesignificantly the limits of sensitivities currently available tolong-baseline interferometry. The full scientific potential of the VLTIcan be exploited only if a consistent set of good quality calibrators isavailable. For this, a large number of observations of potentialcalibrators have been obtained during the commissioning phase of theVLTI. These data are publicly available. We briefly describe theinterferometer, the VINCI instrument used for the observations, the dataflow from acquisition to processed results, and we present and commenton the volume of observations gathered and scrutinized. The result is alist of 191 calibrator candidates, for which a total of 12 066observations can be deemed of satisfactory quality. We present a generalstatistical analysis of this sample, using as a starting point theangular diameters previously available in the literature. We derive thegeneral characteristics of the VLTI transfer function, and its trendwith time in the period 2001 through mid-2004. A second paper will bedevoted to a detailed investigation of a selected sample, aimed atestablishing a VLTI-based homogeneous system of calibrators.
| 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.
| 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.
| How many Hipparcos Variability-Induced Movers are genuine binaries?
Hipparcos observations of some variable stars, and especially oflong-period (e.g. Mira) variables, reveal a motion of the photocentercorrelated with the brightness variation (variability-induced mover -VIM), suggesting the presence of a binary companion. A re-analysis ofthe Hipparcos photometric and astrometric data does not confirm the VIMsolution for 62 among the 288 VIM objects (21%) in the Hipparcoscatalogue. Most of these 288 VIMs are long-period (e.g. Mira) variables(LPV). The effect of a revised chromaticity correction, which accountsfor the color variations along the light cycle, was then investigated.It is based on ``instantaneous'' V-I color indices derived fromHipparcos and Tycho-2 epoch photometry. Among the 188 LPVs flagged asVIM in the Hipparcos catalogue, 89 (47%) are not confirmed as VIM afterthis improved chromaticity correction is applied. This dramatic decreasein the number of VIM solutions is not surprising, since the chromaticitycorrection applied by the Hipparcos reduction consortia was based on afixed V-I color. Astrophysical considerations lead us to adopt a morestringent criterion for accepting a VIM solution (first-kind risk of0.27% instead of 10% as in the Hipparcos catalogue). With this moresevere criterion, only 27 LPV stars remain VIM, thus rejecting 161 ofthe 188 (86%) of the LPVs defined as VIMs in the Hipparcos catalogue.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).Table 1 is also available in electronic form at the CDS, via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/1167
| 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
| Photometric and TiO modelling of the starspots on AG Dor and HU Vir
In this work, spot parameters are determined for two stars, namely,AG Dor and HU Vir, from theirphotometric variability and lambda 7055 Å TiO band depth. Applyingthe photometric modelling code SPOTPIC, we have found two modulatingspots together with a non-modulating component on the photosphere of AGDor in December 96/January 97. The spot temperatures are constrained tobe between 4300 K and 4600 K for the modulating component, and cooler,viz., 4000 K, for the non-modulating one. Therefore, the non-modulatingcomponent of the spot distribution on AG Dor at this epoch is held to betotally responsible for the presence of the TiO band in the spectra ofthis K1 dwarf with photospheric temperature of 5000 K. AG Dor's totalcoverage of spots is determined to be between 4% and 7% for themodulating component and 26.5% for the non-modulating one. For HU Vir,the light and colour curves were modelled with two spots withtemperatures of 4450 and 4050 K. In this case we did not include thenon-modulating component in the model.
| 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.
| High mass Class I sources in M 17
The region of M 17 has been imaged at 10.5 and 20.0 mr um with thegroundbased infrared camera MANIAC. In addition to a prominent diffuseemission bar (4\farcm5x0\farcm 3) extending southeast to northwest atthe interface between the H Ii region and the southwestern molecularcloud, the mosaic of 133 single frames at each wavelength revealed 22compact sources. One of these sources is the Kleinmann-Wright-Object andanother was previously identified as the ultra-compact H Ii region M17-UC1. Combining the N-band and Q-band data with near infrared datayielded spectral energy distributions that classifies all sources to beof Class I. The observed luminosities were between 55 and 4775 L_sun,which suggests that these sources represent the youngest generation ofmassive early type stars in M 17 and are surrounded by relics of theirprotostellar clouds. The morphology of the 10.5 and 20.0 mr um emissiontowards some of the sources reveals flattened structures and may be thefirst evidence of the presence of circumstellar disks around massivestars.
| On the Wilson-Bappu relationship in the Mg II k line
An investigation is carried out on the Wilson-Bappu effect in the Mg Iik line at 2796.34 Å. The work is based on a selection of 230 starsobserved by both the IUE and HIPPARCOS satellites, covering a wide rangeof spectral types (F to M) and absolute visual magnitudes (-5.4<=MV <=9.0). A semi-automatic procedure is used to measurethe line widths, which applies also in the presence of strong centralabsorption reversal. The Wilson-Bappu relationship here provided isconsidered to represent an improvement over previous recent results forthe considerably larger data sample used, as well as for a properconsideration of the measurement errors. No evidence has been found fora possible dependence of the WB effect on stellar metallicity andeffective temperature.
| 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).
| 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.
| Complex Structure of η Carinae in the Mid-Infrared
We report high angular resolution observations of complex mid-infrared(4.8-18 μm) structure in the η Carinae Nebula. This massive (~120Msolar), luminous star is surrounded by a large bipolarnebula extending as much as ~22" in the mid-infrared. Our observationsreveal the presence of several condensations within the complex coreknown as the Homunculus, as well as what may be a toroidal structurevisible at 18 μm. This structure may be related to a similar torusseen at near-infrared wavelengths. Our high angular resolutionphotometry reveals for the first time the spatial variation of thesilicate feature in the nucleus of the η Car Nebula. Finally, wepresent the first high-resolution mid-infrared color-temperature andoptical depth maps for the nebula and discuss their significance inrelation to the origin of the emission and evolutionary status of thestar.
| Stellar radii of M giants
We determine the stellar radii of the M giant stars in the Hipparcoscatalogue that have a parallax measured to better than 20% accuracy.This is done with the help of a relation between a visual surfacebrightness parameter and the Cousins (V - I) colour index, which wecalibrate with M giants with published angular diameters.The radii of(non-Mira) M giants increase from a median value of 50 R_Sun at spectraltype M0 III to 170 R_Sun at M7/8 III. Typical intermediate giant radiiare 65 R_Sun for M1/M2, 90 R_Sun for M3, 100 R_Sun for M4, 120 R_Sun forM5 and 150 R_Sun for M6. There is a large intrinsic spread for a givenspectral type. This variance in stellar radius increases with latertypes but in relative terms, it remains constant.We determineluminosities and, from evolutionary tracks, stellar masses for oursample stars. The M giants in the solar neighbourhood have masses in therange 0.8-4 M_Sun. For a given spectral type, there is a close relationbetween stellar radius and stellar mass. We also find a linear relationbetween the mass and radius of non-variable M giants. With increasingamplitude of variability we have larger stellar radii for a given mass.
| The Infrared Spectral Classification of Oxygen-rich Dust Shells
This paper presents infrared spectral classifications for a flux-limitedsample of 635 optically identified oxygen-rich variables includingsupergiants and sources on the asymptotic giant branch (AGB). Severalclasses of spectra from oxygen-rich dust exist, and these can bearranged in a smoothly varying sequence of spectral shapes known as thesilicate dust sequence. Classification based on this sequence revealsseveral dependencies of the dust emission on the properties of thecentral star. Nearly all S stars show broad emission features fromalumina dust, while most of the supergiants exhibit classic featuresfrom amorphous silicate dust. Mira variables with symmetric light curvesgenerally show broad alumina emission, while those with more asymmetriclight curves show classic silicate emission. These differences may arisefrom differences in the photospheric C/O ratio.
| Measurements of Starspot Parameters on Active Stars using Molecular Bands in Echelle Spectra
We present results from a study of starspot areas (f_S) and temperatures(T_S), primarily on active, single-lined spectroscopic binaries,determined using molecular absorption bands. Expanding upon our previousstudies, we have analyzed multiorder echelle spectra of eight systems tosimultaneously measure several different molecular bands andchromospheric emission lines. We determined starspot parameters byfitting the molecular bands of interest, using spectra of inactive G andK stars as proxies for the nonspotted photosphere of the active stars,and using spectra of M stars as proxies for the spots. At least twobands with different T_eff sensitivities are required. We found thatfitting bands other than the TiO 7055 and 8860 Å features does notgreatly extend the temperature range or sensitivity of our technique.The 8860 Å band is particularly important because of its sharplydifferent temperature sensitivity. We did not find any substantialdepartures from f_S or T_S that we have measured previously based onsingle-order spectra. We refined our derived spot parameters usingcontemporaneous photometry where available. We found that using M giantsas spot proxies for subgiant active stars often underestimates f_Sneeded to fit the photometry; this is presumably due to the increase instrength of the TiO bands with decreasing gravity. We also investigatedcorrelations between f_S and chromospheric emission, and we developed asimple method to measure nonspot temperature (T_Q) solely from ourechelle spectra.
| Spectral Irradiance Calibration in the Infrared. IX. Calibrated Stellar Spectra Using DIRBE Radiometry
The absolute calibration of the COBE/DIRBE data in the range 1-25 μmis examined through the in-band fluxes of DIRBE's own set ofpoint-source calibration objects. Using the values of DIRBE fluxesexpected for Sirius and for 10 of our published set of absolutelycalibrated K and M giants that are in common with DIRBE's owncalibration network, I find consistency with the project's formal basis,namely, our published calibrated spectrum of Sirius. This consistencymeans that one can use the DIRBE radiometry to construct absolutelycalibrated ``stellar templates'' (i.e., continuous calibrated spectrafrom 1 to 35 μm) on the assumption that the intrinsic stellarspectrum of a star of given spectral class matches the intrinsicspectrum for the star of the same spectral class among the set of K andM giants, the spectrum of which has been absolutely defined. Thistechnique is validated using a set of early M giants withwell-characterized ground-based photometry and confirmed with IRASlow-resolution spectra.
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| High resolution infrared spectroscopy of CN and NH lines: nitrogen abundance in oxygen-rich giants through K to late M
The analyses of high resolution infrared spectra have been done for CNlines in oxygen-rich cool evolved stars including 2 K giants, 20 Mgiants and 1 S-type star. Since CN lines analyzed in the present workare weak and resolved well, they are appropriate for quantitativeanalyses. CN lines of Delta v=-2 and -1 sequences (red system) which arein the K- and the H-window regions, respectively, give the consistentnitrogen abundance for each star. The analyses of NH lines in theL-window region have been done for 5 late M giants for which CN lineshave been also analyzed. Although the triplet structure of NH linescannot be fully resolved, they are preferable because determination ofnitrogen abundance is almost independent of other elemental abundanceswhile nitrogen abundance based on CN depends on carbon abundance. Thenitrogen abundances derived from NH for late M giants agree well withthose from CN for which we adopt 7.75eV as the dissociation energy inthe analysis. The results show that the nitrogen abundances in late Mgiants are larger than those in early M giants while decrease of thecarbon abundance was found in late M giants by our previous work (Tsuji1991). These variations of abundances can not be explained by the firstdredge-up model but require additional processing by the CN cycle andmixing after the first dredge-up. However, there is no obvious evidenceof other processes such as the 3alpha -process and subsequent hot bottomburning in our program stars. Such variation of the carbon and nitrogenabundances is not well understood by the present evolutionary models oflow-mass and intermediate-mass stars. Table~10 is only available inelectronic form at the CDS (Strasbourg) via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Absolute Measurements of Starspot Area and Temperature: II Pegasi in 1989 October
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...452..879N&db_key=AST
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| On the spectra and photometry of M-giant stars
From a sample of 97 very bright M-giant stars in the Solarneighbourhood, high-quality "intrinsic" spectra in the spectral range380 <~ λ[nm] <~ 900 for all M-spectral subtypes of the Caseand MK classification systems are obtained. The results are fitted tophotospheric synthetic spectra in the range 99 <~ λ [nm]<=12500 in order to infer the corresponding continua. The syntheticspectra are also compared to the intrinsic spectra. The effectivetemperatures are derived and mathematical spectral classificationcriteria are found. The (UB)_j_(VRI)_c_(JHKLM)_ESO_ photometric data ofthe sample are also given. The data are available on the StrasbourgAstronomical Data Centre (CDS).
| 86 GHz SiO, v=1, J=2--> 1 survey of southern IRAS point sources. II. Detection of 74 new maser sources
The detection of 74 new southern stellar SiO, v=1, J=2->1 masersassociated with IRAS point sources is reported. 57 of these were foundin an IRAS based survey of oxygen rich stellar envelopes. The detectionrate in this survey was 45%. 17 further new maser sources were detectedduring a search for strong pointing sources for the Swedish-ESOSubmillimeter Telescope (SEST). The distribution of the IRAS lowresolution spectral (LRS) classes of all the SiO masers (this paper andliterature) peaks sharply at class 15. The distribution of the LRSclasses of the maser sources from 21 to 29 is similar to thedistribution of these classes of all the point sources in the pointsource catalogue except for class 25. Only few maser sources of thisspectral class are known. This is possibly explained by a selectioneffect.
| A catalog of stellar Lyman-alpha fluxes
We present a catalog of stellar Ly-alpha emission fluxes, based on newand archival images obtained with the IUE spacecraft. The catalogincludes 227 stars with detectable Ly-alpha emission fluxes, and upperlimits on the Ly-alpha emission flux for another 48 stars. Multiple fluxmeasurements are given for 52 stars. We present a model for correctingthe observed Ly-alpha flux for attenuation by the local interstellarmedium, and we apply this model to derive intrinsic Ly-alpha fluxes for149 catalog stars which are located in low H I column density directionsof the local interstellar medium. In our catalog, there are 14 late-Aand early-F stars at B-V = 0.29 or less that show detectable emission atLy-alpha. We find a linear correlation between the intrinsic Ly-alphaflux and C II 1335 A flux for stars with B-V greater than 0.60, but theA and F stars deviate from this relation in the sense that theirLy-alpha flux is too low. We also find a good correlation betweenLy-alpha strength and coronal X-ray emission. This correlation holdsover most of the H-R diagram, even for the F stars, where an X-raydeficit has previously been found relative to the transition regionlines of C II and C IV.
| Asymptotic giant branch stars near the sun
Available red and near-infrared photometry and apparent motions of M, S,and C asymptotic giant branch (AGB) stars in the Bright Star Catalogueare tabulated and discussed. It is shown that the red and near infraredindices normally used for late-type stars are interchangeable except forcarbon stars. The M-type giants are variable with visual amplitudegreater than 0.05 mag. The reddening-free parameter m2 from Genevaphotometry is essentially a temperature parameter for M giants, whilethe reddening-free parameter d is a sensitive detector of blue stellarcompanions. The space density of AGB stars near the sun decreases by afactor of 35 in a temperature range 3800 to 3400 K. Two of the S starsnear the sun were found to have nearly equal space motions and may becomembers of the Arcturus group.
| Stellar Lyman-alpha emission and the local interstellar medium
The UV spectra now available in the IUE archives have beensystematically searched for the presence of Lyman-alpha emission inlate-type stars. The results provide the first survey of the behavior ofthe Ly-alpha emission line across most of the cool half of the H-Rdiagram. The normalized Ly-alpha emission flux is strongest in thechromospherically active RS CVn stars and in the dMe stars. The range ofnormalized flux values is much smaller among F-type stars than in starsof later spectral type. A dropoff appears in the flux levels of stars atB-V less than 0.30 mag. The measurements are used to search for evidenceof possible high column density clouds in the local ISM. The cloudpreviously identified toward Alpha Oph may be seen in the reduced fluxobserved toward Beta Oph.
| High resolution spectroscopy of CO in the infrared spectra of cool stars. III - Line intensities, shifts, and asymmetries as probes of stellar turbulence and abundance in oxygen-rich giants
The CO spectrum in cool giant stars is studied in detail. It is foundthat CO lines show large differential shifts and asymmetries, indicatingthe presence of complicated velocity fields in stellar atmospheres. Itis suggested that this finding implies that the notion of stellarturbulence is not necessarily valid.
| M Giant Populations and Galactic Structure
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990MNRAS.247..227F&db_key=AST
| Third list of corrections to the identifications of IRAS sources in Astron. & Astrophys Suppl. 65, 607 and Astron. J. 98, 931
Not Available
| The Perkins catalog of revised MK types for the cooler stars
A catalog is presented listing the spectral types of the G, K, M, and Sstars that have been classified at the Perkins Observatory in therevised MK system. Extensive comparisons have been made to ensureconsistency between the MK spectral types of stars in the Northern andSouthern Hemispheres. Different classification spectrograms have beengradually improved in spite of some inherent limitations. In thecatalog, the full subclasses used are the following: G0, G5, G8, K0, K1,K2, K3, K4, K5, M0, M1, M2, M3, M4, M5, M6, M7, and M8. Theirregularities are the price paid for keeping the general scheme of theoriginal Henry Draper classification.
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| Görünürdeki Parlaklýk: | 3.69 |
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