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The Detection of Infrared SiS Bands in Spectra of S Stars
We present Spitzer spectra of S stars, which are cool evolved stars witha C/O ratio near unity, some of which have enhanced s-processabundances. We present the detection of a strong and unusual band in themid-infrared, at 13 μm, within the N-band window. Usingquantum-chemically calculated line lists, and model spectra, we identifythis band as the fundamental rovibrational band of SiS. Detection of theovertone band at 6.7 μm confirms the identification. Fitting the lineprofile shows that the molecule is located in relatively cool layers, atT ~ 1500 K. We discuss these results in the context of chemicalequilibrium models. The observed strength of these bands in the cool Sstars makes them a promising observational diagnostic tool for studyingthe atmospheres of brown dwarfs and exoplanets.
| The Magellanic Zoo: Mid-Infrared Spitzer Spectroscopy of Evolved Stars and Circumstellar Dust in the Magellanic Clouds
We observed a sample of evolved stars in the Large and Small MagellanicClouds (LMC and SMC) with the Infrared Spectrograph on the Spitzer SpaceTelescope. Comparing samples from the SMC, LMC, and the Galaxy revealsthat the dust production rate depends on metallicity for oxygen-richstars, but carbon stars with similar pulsation properties producesimilar quantities of dust, regardless of their initial metallicity.Other properties of the oxygen-rich stars also depend on metallicity. Asthe metallicity decreases, the fraction of naked (i.e., dust-free) starsincreases, and among the naked stars, the strength of the 8 μmabsorption band from SiO decreases. Our sample includes several massivestars in the LMC with long pulsation periods that produce significantamounts of dust, probably because they are young and relativelymetal-rich. Little alumina dust is seen in circumstellar shells in theSMC and LMC, unlike in Galactic samples. Three oxygen-rich sources alsoshow emission from magnesium-rich crystalline silicates. Many also showan emission feature at 14 μm. The one S star in our sample shows anewly detected emission feature centered at 13.5 μm. At lowermetallicity, carbon stars with similar amounts of amorphous carbon intheir shells have stronger absorption from molecular acetylene(C2H2) and weaker emission from SiC and MgS dust,as discovered in previous studies.
| PAH Emission from Herbig Ae/Be Stars
We present spectra of a sample of Herbig Ae and Be (HAeBe) starsobtained with the Infrared Spectrograph on Spitzer. All but one of theHerbig stars show emission from PAHs, and seven of the spectra show PAHemission, but no silicate emission at 10 μm. The central wavelengthsof the 6.2, 7.7-8.2, and 11.3 μm emission features decrease withstellar temperature, indicating that the PAHs are less photoprocessed incooler radiation fields. The apparent low level of photoprocessing inHAeBe stars, relative to other PAH emission sources, implies that thePAHs are newly exposed to the UV-optical radiation fields from theirhost stars. HAeBe stars show a variety of PAH emission intensities andionization fractions but a narrow range of PAH spectral classificationsbased on positions of major PAH feature centers. This may indicate that,regardless of their locations relative to the stars, the PAH moleculesare altered by the same physical processes in the protoplanetary disksof intermediate-mass stars. Analysis of the mid-IR SEDs indicates thatour sample likely includes both radially flared and moreflattened/settled disk systems, but we do not see the expectedcorrelation of overall PAH emission with disk geometry. We suggest thatthe strength of PAH emission from HAeBe stars may depend not only on thedegree of radial flaring but also on the abundance of PAHs inilluminated regions of the disks and possibly on the vertical structureof the inner disk as well.
| The Mid-Infrared Spectrum of the Transiting Exoplanet HD 209458b
We report the spectroscopic detection of mid-infrared emission from thetransiting exoplanet HD 209458b. Using archive data taken with theSpitzer IRS instrument, we have determined the spectrum of HD 209458bbetween 7.46 and 15.25 μm. We have used two independent methods todetermine the planet spectrum, one differential in wavelength and oneabsolute, and find the results are in good agreement. Over much of thisspectral range, the planet spectrum is consistent with featurelessthermal emission. Between 7.5 and 8.5 μm, we find evidence for anunidentified spectral feature. If this spectral modulation is due toabsorption, it implies that the dayside vertical temperature profile ofthe planetary atmosphere is not entirely isothermal. Using the IRS data,we have determined the broadband eclipse depth to be 0.00315+/-0.000315,implying significant redistribution of heat from the dayside to thenightside. This work required the development of improved methods forSpitzer IRS data calibration that increase the achievable absolutecalibration precision and dynamic range for observations of bright pointsources.
| Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. II. 70 μm Imaging
The absolute calibration and characterization of the Multiband ImagingPhotometer for Spitzer (MIPS) 70 μm coarse- and fine-scale imagingmodes are presented based on over 2.5 yr of observations. Accuratephotometry (especially for faint sources) requires two simple processingsteps beyond the standard data reduction to remove long-term detectortransients. Point-spread function (PSF) fitting photometry is found togive more accurate flux densities than aperture photometry. Based on thePSF fitting photometry, the calibration factor shows no strong trendwith flux density, background, spectral type, exposure time, or timesince anneals. The coarse-scale calibration sample includes observationsof stars with flux densities from 22 mJy to 17 Jy, on backgrounds from 4to 26 MJy sr-1, and with spectral types from B to M. Thecoarse-scale calibration is 702+/-35 MJy sr-1MIPS70-1 (5% uncertainty) and is based on measurements of 66stars. The instrumental units of the MIPS 70 μm coarse- andfine-scale imaging modes are called MIPS70 and MIPS70F, respectively.The photometric repeatability is calculated to be 4.5% from two starsmeasured during every MIPS campaign and includes variations on alltimescales probed. The preliminary fine-scale calibration factor is2894+/-294 MJy sr-1 MIPS70F-1 (10% uncertainty)based on 10 stars. The uncertainties in the coarse- and fine-scalecalibration factors are dominated by the 4.5% photometric repeatabilityand the small sample size, respectively. The 5 σ, 500 ssensitivity of the coarse-scale observations is 6-8 mJy. This work showsthat the MIPS 70 μm array produces accurate, well-calibratedphotometry and validates the MIPS 70 μm operating strategy,especially the use of frequent stimulator flashes to track the changingresponsivities of the Ge:Ga detectors.
| Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. I. The Stellar Calibrator Sample and the 24 μm Calibration
We present the stellar calibrator sample and the conversion frominstrumental to physical units for the 24 μm channel of the MultibandImaging Photometer for Spitzer (MIPS). The primary calibrators are Astars, and the calibration factor based on those stars is4.54×10-2 MJy sr-1 (DNs-1)-1, with a nominal uncertainty of 2%. Wediscuss the data reduction procedures required to attain this accuracy;without these procedures, the calibration factor obtained using theautomated pipeline at the Spitzer Science Center is 1.6%+/-0.6% lower.We extend this work to predict 24 μm flux densities for a sample of238 stars that covers a larger range of flux densities and spectraltypes. We present a total of 348 measurements of 141 stars at 24 μm.This sample covers a factor of ~460 in 24 μm flux density, from 8.6mJy up to 4.0 Jy. We show that the calibration is linear over that rangewith respect to target flux and background level. The calibration isbased on observations made using 3 s exposures; a preliminary analysisshows that the calibration factor may be 1% and 2% lower for 10 and 30 sexposures, respectively. We also demonstrate that the calibration isvery stable: over the course of the mission, repeated measurements ofour routine calibrator, HD 159330, show a rms scatter of only 0.4%.Finally, we show that the point-spread function (PSF) is well measuredand allows us to calibrate extended sources accurately; InfraredAstronomy Satellite (IRAS) and MIPS measurements of a sample of nearbygalaxies are identical within the uncertainties.
| The Unusual Hydrocarbon Emission from the Early Carbon Star HD 100764: The Connection between Aromatics and Aliphatics
We have used the Infrared Spectrograph (IRS) on the Spitzer SpaceTelescope to obtain spectra of HD 100764, an apparently single carbonstar with a circumstellar disk. The spectrum shows emission featuresfrom polycyclic aromatic hydrocarbons (PAHs) that are shifted to longerwavelengths than normally seen, a characteristic of ``class C'' systemsin the classification scheme of Peeters et al. All seven of the knownclass C PAH sources are illuminated by radiation fields that are coolerthan those which typically excite PAH emission features. The observedwavelength shifts are consistent with hydrocarbon mixtures containingboth aromatic and aliphatic bonds. We propose that the class C PAHspectra are distinctive because the carbonaceous material has not beensubjected to a strong ultraviolet radiation field, allowing relativelyfragile aliphatic materials to survive.
| Spitzer spectroscopy of carbon stars in the Small Magellanic Cloud
We present Spitzer Space Telescope spectroscopic observations of 14carbon-rich asymptotic giant branch (AGB) stars in the Small MagellanicCloud (SMC). SiC dust is seen in most of the carbon-rich stars but it isweak compared to Large Magellanic Cloud (LMC) stars. The SiC feature isstrong only for stars with significant dust excess, opposite to what isobserved for Galactic stars. We argue that in the SMC, SiC forms atlower temperature than graphite dust, whereas in the Galaxy SiC andgraphite condensate at more comparable temperatures. Dust input into theinterstellar medium by AGB stars consists mostly of carbonaceous dust,with little SiC or silicate dust. Only the two coolest stars show a30-μm band due to MgS dust. We suggest that this is due to the factthat, in the SMC, mass-losing AGB stars generally have low circumstellar(dust) optical depth and therefore effective heating of dust by thecentral star does not allow temperatures below the 650K necessary forMgS to exist as a solid. Gas phase C2H2 bands arestronger in the SMC than in the LMC or Galaxy. This is attributed to anincreasing C/O ratio at low metallicity. We present a colour-colourdiagram based on Spitzer InfraRed Array Camera (IRAC) and MultibandImaging Photometer for Spitzer (MIPS) colours to discriminate between O-and C-rich stars. We show that AGB stars in the SMC become carbon starsearly in the thermal-pulsing AGB evolution, and remain optically visiblefor ~6 × 105yr. For the LMC, this lifetime is ~3× 105yr. The superwind phase traced with Spitzer lastsfor ~104yr. Spitzer spectra of a K supergiant and a compactHII region are also given.
| Formation and Evolution of Planetary Systems: Upper Limits to the Gas Mass in Disks around Sun-like Stars
We have carried out a sensitive search for gas emission lines at IR andmillimeter wavelengths for a sample of 15 young Sun-like stars selectedfrom our dust disk survey with Spitzer. We have used mid-IR lines totrace the warm (300-100 K) gas in the inner disk and millimetertransitions of 12CO to probe the cold (~20 K) outer disk. Wereport no gas line detections from our sample. Line flux upper limitsare first converted to warm and cold gas mass limits using simpleapproximations allowing a direct comparison with values from theliterature. We also present results from more sophisticated modelsfollowing Gorti & Hollenbach that confirm and extend our simpleanalysis. These models show that the [S I] 25.23 μm line can setconstraining limits on the gas surface density at the disk inner radiusand traces disk regions up to a few AU. We find that none of the 15systems have more than 0.04MJ of gas within a few AU from thedisk inner radius for disk radii from 1 to ~40 AU. These gas mass upperlimits even in the eight systems younger than ~30 Myr suggest that mostof the gas is dispersed early. The gas mass upper limits in the 10-40 AUregion, which is mainly traced by our CO data, are <2M⊕. If these systems are analogs of the solar system,they either have already formed Uranus- and Neptune-like planets or willnot form them beyond 100 Myr. Finally, the gas surface density upperlimits at 1 AU are smaller than 0.01% of the minimum mass solar nebulafor most of the sources. If terrestrial planets form frequently andtheir orbits are circularized by gas, then circularization occurs early.
| A Spitzer mid-infrared spectral survey of mass-losing carbon stars in the Large Magellanic Cloud
We present a Spitzer Space Telescope spectroscopic survey of mass-losingcarbon stars (and one oxygen-rich star) in the Large Magellanic Cloud(LMC). The stars represent the superwind phase on the asymptotic giantbranch (AGB), which forms a major source of dust for the interstellarmedium (ISM) in galaxies. Bolometric magnitudes indicate progenitormasses of 1.5-2.5Msolar. The spectra cover the wavelengthrange 5-38μm. They show varying combinations of dust continuum, dustemission features (SiC, MgS) and molecular absorption bands(C2H2, HCN). A 10-μm absorption feature isattributed to C3. A weak band at 5.8μm is suggestive ofcarbonyl. The circumstellar 7.5-μm C2H2 band isfound to be stronger at lower metallicity, explained by higher C/Oratios at low metallicity. The J - K versus K - A colours, used toselect the sample, are shown to be relatively insensitive in separatingcarbon versus oxygen-rich AGB stars. The predominance of carbon starstherefore indicates that in the range 1.5-2.5Msolar, LMC AGBstars become carbon-rich before onset of the superwind. A set of fournarrow bands, dubbed the Manchester system, is used to define theinfrared continuum for dusty carbon stars. We investigate the strengthand central wavelength of the SiC and MgS dust bands as a function ofcolour and metallicity. The line-to-continuum ratio of these bands showssome indication of being lower at low metallicity. The MgS band is onlyseen at dust temperatures below 600K. Metal-poor carbon stars can formamorphous carbon dust from self-produced carbon. The formationefficiency of oxygen-rich dust depends more strongly on metallicity. Inlower-metallicity environments, the dust input into the ISM by AGB starsmay be strongly biased towards carbonaceous dust.
| Mid-Infrared Spectroscopy of Carbon Stars in the Small Magellanic Cloud
We have observed a sample of 36 objects in the Small Magellanic Cloud(SMC) with the Infrared Spectrometer on the Spitzer Space Telescope.Nineteen of these sources are carbon stars. An examination of the near-and mid-infrared photometry shows that the carbon-rich and oxygen-richdust sources follow two easily separated sequences. A comparison of thespectra of the 19 carbon stars in the SMC to spectra from the InfraredSpace Observatory (ISO) of carbon stars in the Galaxy revealssignificant differences. The absorption bands at 7.5 and 13.7 μm dueto C2H2 are stronger in the SMC sample, and theSiC dust emission feature at 11.3 μm is weaker. Our measurements ofthe MgS dust emission feature at 26-30 μm are less conclusive, butthis feature appears to be weaker in the SMC sample as well. All ofthese results are consistent with the lower metallicity in the SMC. Thelower abundance of SiC grains in the SMC may result in less efficientcarbon-rich dust production, which could explain the excessC2H2 gas seen in the spectra. The sources in theSMC with the strongest SiC dust emission tend to have redder infraredcolors than the other sources in the sample, which implies moreamorphous carbon, and they also tend to show stronger MgS dust emission.The weakest SiC emission features tend to be shifted to the blue; thesespectra may arise from low-density shells with large SiC grains.
| The Detection of Crystalline Silicates in Ultraluminous Infrared Galaxies
Silicates are an important component of interstellar dust, and thestructure of these grains (amorphous or crystalline) is sensitive to thelocal physical conditions. We have studied the infrared spectra of asample of ultraluminous infrared galaxies (ULIRGs). Here we report thediscovery of weak, narrow absorption features at 11, 16, 19, 23, and 28μm, characteristic of crystalline silicates, superimposed on thebroad absorption bands at 10 and 18 μm due to amorphous silicates ina subset of this sample. These features betray the presence offorsterite (Mg2SiO4), the magnesium-rich endmember of the olivines. Previously, crystalline silicates have only beenobserved in circumstellar environments. The derived fraction offorsterite to amorphous silicates is typically 0.1 in these ULIRGs. Thisis much larger than the upper limit for this ratio in the interstellarmedium of the Milky Way, 0.01. These results suggest that the timescalefor injection of crystalline silicates into the ISM is short in amerger-driven starburst environment (e.g., as compared to the total timeto dissipate the gas), pointing toward massive stars as a prominentsource of crystalline silicates. Furthermore, amorphization due tocosmic rays, which is thought to be of prime importance for the localISM, lags in vigorous starburst environments.
| The Unusual Silicate Dust around HV 2310, an Evolved Star in the Large Magellanic Cloud
The spectrum of HV 2310, an evolved star in the Large Magellanic Cloud,taken with the Infrared Spectrograph (IRS) on the Spitzer SpaceTelescope, reveals the presence of an optically thin shell of silicatedust with unusual spectral structure in the 10 μm feature: anemission peak at 9.7 μm, a saddle at 10.4 μm, and an extendedshoulder to 11.2 μm. This structure is similar to spectra fromcrystalline silicate grains, and of the available optical constants,forsterite provides the best fit. The spectrum also shows structure at14 μm that may arise from an unidentified dust feature.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| R CrB Candidates in the Small Magellanic Cloud: Observations of Cold, Featureless Dust with the Spitzer Infrared Spectrograph
We observed 36 evolved stars in the Small Magellanic Cloud (SMC) usingthe low-resolution mode of the Infrared Spectrograph (IRS) on theSpitzer Space Telescope. Two of these stars, MSX SMC 014 and 155, havenearly featureless spectral energy distributions over the IRS wavelengthrange (5.2-35 μm) and Fν peaking at ~8-9 μm. Thedata can be fit by sets of amorphous carbon shells or by single 600-700K blackbodies. The most similar spectra found in extant spectraldatabases are of R CrB, although the spectral structure seen in R CrBand similar stars is much weaker or absent in the SMC sources. Both SMCstars show variability in the near-infrared. Ground-based visual spectraconfirm that MSX SMC 155 is carbon-rich, as expected for R CrB (RCB)stars, and coincides with an object previously identified as an RCBcandidate. The temperature of the underlying star is lower for MSX SMC155 than for typical RCB stars. The strength of the C2 Swanbands and the low temperature suggest that it may be a rare DY Per-typestar, only the fifth such identified. MSX SMC 014 represents a new RCBcandidate in the SMC, bringing the number of RCB candidates in the SMCto six. It is the first RCB candidate discovered with Spitzer and thefirst identified by its infrared spectral characteristics rather thanits visual variability.
| The Detection of Silicate Emission from Quasars at 10 and 18 Microns
We report the spectroscopic detection of silicate emission at 10 and 18μm in five PG quasars, the first detection of these two features ingalaxies outside the Local Group. This finding is consistent with theunification model for active galactic nuclei (AGNs), which predicts thatan AGN torus seen pole-on should show a silicate emission feature in themid-infrared. The strengths of the detected silicate emission featuresrange from 0.12 to 1.25 times the continuum at 10 μm and from 0.20 to0.79 times the continuum at 18 μm. The silicate grain temperaturesinferred from the ratio of 18 μm to 10 μm silicate features underthe assumption of optically thin emission range from 140 to 220 K.
| 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}
| The Serendipitous Discovery of a Debris Disk around the A Dwarf HD 46190
The Infrared Spectrograph on the Spitzer Space Telescope has observedseveral A dwarfs as potential standards and cross-calibrators, and oneof these stars, HD 46190, shows the spectroscopic signature of a debrisdisk. The disk produces a spectral excess that can be fitted with a coolblackbody of ~81 K. If the emitting particles are spherical blackbodies,they would lie at a distance of ~82 AU from the central star. Thespectrum from the disk can also be fitted with a spectrum risingproportionally with wavelength, and this spectral behavior is consistentwith material falling into the inner disk as a result ofPoynting-Robertson drag.
| 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.
| Theoretical colours and isochrones for some Hubble Space Telescope colour systems. II
A grid of synthetic surface brightness magnitudes for 14 bandpasses ofthe Hubble Space Telescope Faint Object Camera is presented, as well asa grid of UBV, uvby, and Faint Object Camera surface brightnessmagnitudes derived from the Gunn-Stryker spectrophotometric atlas. Thesynthetic colors are used to examine the transformations between theground-based Johnson UBV and Stromgren uvby systems and the Faint ObjectCamera UBV and uvby. Two new four-color systems, similar to theStromgren system, are proposed for the determination of abundance,temperature, and surface gravity. The synthetic colors are also used tocalculate color-magnitude isochrones from the list of theoretical tracksprovided by VandenBerg and Bell (1990). It is shown that by using theappropriate filters it is possible to minimize the dependence of thiscolor difference on metallicity. The effects of interstellar reddeningon various Faint Object Camera colors are analyzed as well as theobservational requirements for obtaining data of a given signal-to-noisefor each of the 14 bandpasses.
| A critical appraisal of published values of (Fe/H) for K II-IV stars
'Primary' (Fe/H) averages are presented for 373 evolved K stars ofluminosity classes II-IV and (Fe/H) values beween -0.9 and +0.21 dex.The data define a 'consensus' zero point with a precision of + or -0.018 dex and have rms errors per datum which are typically 0.08-0.16dex. The primary data base makes recalibration possible for the large(Fe/H) catalogs of Hansen and Kjaergaard (1971) and Brown et al. (1989).A set of (Fe/H) standard stars and a new DDO calibration are given whichhave rms of 0.07 dex or less for the standard star data. For normal Kgiants, CN-based values of (Fe/H) turn out to be more precise than manyhigh-dispersion results. Some zero-point errors in the latter are alsofound and new examples of continuum-placement problems appear. Thushigh-dispersion results are not invariably superior to photometricmetallicities. A review of high-dispersion and related work onsupermetallicity in K III-IV star is also given.
| Some notes on the Gunn-Stryker spectrophotometry and synthetic VRI colors
Cousins VRI photometry is presented for 26 stars with continuous scansby Gunn and Stryker. This photometry is combined with literature dataand a few unpublished results to critique synthetic colors from theGunn-Stryker scans. For V - R, it is found that all pertinent resultsare consistent at the several-mmag level. For R - I, however, systematicdifferences are found which are most simply interpreted as a declinationeffect in the Gunn-Stryker scans. In addition, it is found that theGunn-Stryker synthetic colors are unexpectedly noisy, with sigma perdatum of about 0.02 mag. It is suggested that future users of theGunn-Stryker data keep both these effects in mind.
| Stellar spectrophotometric atlas, wavelengths from 3130 to 10800 A
Over the course of the past 10 years, a large body of homogeneousspectrophotometric data on relatively bright stars has been gathered toserve as a library with which to synthesize galaxy spectra in populationstudies. As the data might be generally useful, they are presented inthree tables. One hundred seventy-five (175) stars were selected, mostfrom the Navy photometric catalog. Covered are complete ranges ofspectral type and luminosity class. Normalized spectral energydistributions of these stars in pictorial form are provided along withtables of calculated colors, scan line and continuum indices, and someinformation on the relation of the scan colors to real photometricsystems.
| Further spectrophotometry of the transient X-ray source A0620-00
Observations of the transient X-ray source A0620-00 in November 1976show that the optical object had an apparent visual magnitude of 18.35.The spectrum is cool and shows that one component of the light comesfrom a K5 V to K7 V star. The distance is estimated to be 870 pc if thecool star is normal. Some support for the 7.8-day X-ray period recentlyfound is provided by observations made in 1975 during the outburst. Inaddition to the cool K star, there is a second radiation source whichhas a flat spectrum. This source can be modeled by a 10,000-K blackbodywith a radius (if spherical) of 17,000 km plus a 4000-K blackbody with aradius of 13,400 km and is probably a residual accretion disk. It isvery unlikely that the K star can fill its Roche lobe, so that masstransfer to a neutron-star companion by this mechanism is unlikely. Itis possible that the K star is losing mass by processes such as thosethat occur in T Tauri stars.
| Determination of atmospheric parameters for G and K giants by means of photoelectric indices.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971A&A....15..123H&db_key=AST
| Radial Velocities, Spectral Types, and Luminosity Classes of 820 Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1950ApJ...112...48M&db_key=AST
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Dades d'Observació i Astrometria
| Constel·lació: | Draco |
| Ascensió Recta: | 18h08m38.85s |
| Declinació: | +57°58'46.9" |
| Magnitud Aparent: | 7.348 |
| Distancia: | 255.102 parsecs |
| Moviment propi RA: | -33.6 |
| Moviment propi Dec: | -9.6 |
| B-T magnitude: | 9.198 |
| V-T magnitude: | 7.501 |
Catàlegs i designacions:
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