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Публикации по объекту
The Coronae of γ Draconis
The Chandra X-Ray Observatory has detected coronal (T>~106K) emission from the red giant γ Draconis (HD 164058: K5 III; d=45pc), now fully resolved from a stronger source 21" to the SE that hadconfused earlier measurements by Röntgensatellit (ROSAT). Thesecond source is coincident with the 13th magnitude visual component ADS10923B (γ Dra B), possibly a dM star in a wide orbit around thered giant. The 0.2-2 keV luminosity of γ Dra isLX~1.2+0.4-0.2×1027ergs s-1 (1 σ confidence interval), assuminglog(Tcor)>~6.5 K, while that of the faint opticalcompanion is 3.2+0.7-0.5×1027ergs s-1, assuming the same distance. Both sources have anintermediate spectral hardness within the range displayed by coronalstars. γ Dra has LX/Lbol an order of magnitude brighter than theother red giants previously imaged by Chandra, Arcturus (α Boo:K1.5 III) and Aldebaran (α Tau: K5 III), despite having an only 2× elevated LC IV/Lbol (T~105 K).
| Chemical Evolution of the Galactic Bulge as Derived from High-Resolution Infrared Spectroscopy of K and M Red Giants
We present chemical abundances in K and M red giant members of theGalactic bulge derived from high-resolution infrared spectra obtainedwith the Phoenix spectrograph on Gemini-South. The elements studied arecarbon, nitrogen, oxygen, sodium, titanium, and iron. The evolution of Cand N abundances in the studied red giants shows that their oxygenabundances represent the original values with which the stars were born.Oxygen is a superior element for probing the timescale of bulge chemicalenrichment via [O/Fe] versus [Fe/H]. The [O/Fe]-[Fe/H] relation in thebulge does not follow the disk relation, with [O/Fe] values fallingabove those of the disk. Titanium also behaves similarly to oxygen withrespect to iron. Based on these elevated values of [O/Fe] and [Ti/Fe]extending to large Fe abundances, it is suggested that the bulgeunderwent a more rapid chemical enrichment than the halo. In addition,there are declines in both [O/Fe] and [Ti/Fe] in those bulge targetswith the largest Fe abundances, signifying another source affectingchemical evolution: perhaps supernovae of Type Ia. Sodium abundancesincrease dramatically in the bulge with increasing metallicity, possiblyreflecting the metallicity-dependent yields from supernovae of Type II,although Na contamination from H-burning in intermediate-mass starscannot be ruled out.
| Confirmation of the planet hypothesis for the long-period radial velocity variations of β Geminorum
Aims.Our aim is to confirm the nature of the long period radial velocitymeasurements for β Gem first found by Hatzes & Cochran (1993). Methods: .We present precise stellar radial velocity measurementsfor the K giant star β Gem spanning over 25 years. An examinationof the Ca II K emission, spectral line shapes from high resolution data(R = 210 000), and Hipparcos photometry was also made to discern thetrue nature of the long period radial velocity variations. Results: . The radial velocity data show that the long period, lowamplitude radial velocity variations found by Hatzes & Cochran(1993) are long-lived and coherent. Furthermore, the Ca II K emission,spectral line bisectors, and Hipparcos photometry show no significantvariations of these quantities with the radial velocity period. Anorbital solution assuming a stellar mass of 1.7 M_ȯ yields aperiod, P = 589.6 days, a minimum mass of 2.3 M_Jupiter, and asemi-major axis, a = 1.6 AU. The orbit is nearly circular (e = 0.02). Conclusions: .The data presented here confirm the planetarycompanion hypothesis suggested by Hatzes & Cochran (1993). βGem is one of six intermediate mass stars known to host a sub-stellarcompanion and suggests that planet-formation around stars much moremassive than the sun may common.
| Photoelectric radial velocities, Paper XVI 625 ninth-magnitude K0 stars in the six southern Clube Selected Areas
Paper XIII of this series presented radial velocities for 406 stars incertain of the Clube Selected Areas, a set of areas systematicallyarranged in Galactic coordinates. We now complete the survey byproviding the radial velocities, mostly obtained at the EuropeanSouthern Observatory (ESO), of 625 stars in the six southernmost Areas.Each star has been measured at least twice; the mean velocities havestandard errors typically of 0.2-0.3 km s-1. Additionalobservations made from Haute-Provence of many of the stars that areobservable from there have helped to identify, and in some instances tocharacterize, the ~70 spectroscopic binaries discovered in thisprogramme. The final results of the programme, complementing those givenin table 3 of Paper XIII, are summarized in Table 12, which presents themean velocities and velocity dispersions in the six southern Areas. Itis noted that the difference between Paper XIII and this one as regardsthe provenance of the radial velocities has led to a small difference inzero-points, which is discussed in Section 3 and needs to be taken intoaccount in any analysis of the combined data.
| Precise radial velocities with BOES. Detection of low-amplitude pulsations in the K-giant α Arietis
We present the first results from a high-precision radial velocity studyof the K2 III giant star α Ari. Observationswere acquired over 6 nights in 2004 using the new high-resolutionspectrograph BOES (Bohyunsan Observatory Echelle Spectrograph) of the1.8-m telescope. A high radial-velocity precision was achieved by usingthe high-resolution (R=90 000) mode of BOES and an iodine gas absorptioncell. The radial velocity measurements made during JD = 2 452 948{-}2452 950 show coherent, low-amplitude variations with a period ofP1=0.571 days (or aliases at 0.445 or 0.821 days), and anamplitude of 18.9 m s-1. Observations of τ Cet over thissame interval are constant to within 3 m s-1. Aftersubtracting the contribution of the 0.57-day period, we find evidencefor a second period, P2 = 0.190 days. Observations made on asecond run during JD = 2 452 975{-}2 452 981 show that the radialvelocity variations are indeed present, but on shorter time-scales andwith a lower amplitude. Two probable periods fit the radial velocitymeasurements from the second run reasonably well: 0.185 days or an aliasof 0.256 days. The shorter period coincides with the secondary one foundin the earlier measurements. We conclude that, similar to other K-giantpulsating stars, α Ari shows unstable acousticpulsations or mode switching on time scales of tens of days. Thecalculated pulsation constants for the dominant 0.571-day period isconsistent with third-overtone pulsations, while the secondaryperiodicity found in both data runs corresponds to a high overtone(n≥ 12).
| Automated derivation of stellar atmospheric parameters and chemical abundances: the MATISSE algorithm
We present an automated procedure for the derivation of atmosphericparameters (Teff, log g, [M/H]) and individual chemicalabundances from stellar spectra. The MATrix Inversion for SpectralSynthEsis (MATISSE) algorithm determines a basis,Bθ(λ), allowing the derivation of a particularstellar parameter θ by projection of an observed spectrum. TheBθ(λ) function is determined from an optimallinear combination of theoretical spectra and it relates, in aquantitative way, the variations in the spectrum flux with variations inθ. An application of this method to the Gaia Radial VelocitySpectrograph spectral range is described, together with its performancesfor different types of stars of various metallicities. Blind tests withsynthetic spectra of randomly selected parameters and observed inputspectra are also presented. The method gives rapid, accurate and stableresults and it can be efficiently applied to the study of stellarpopulations through the analysis of large spectral data sets, includingmoderate to low signal-to-noise ratio spectra.
| Infrared Spectra and Visibilities as Probes of the Outer Atmospheres of Red Supergiant Stars
In the light of the recent results of the stellar interferometry, weexamine the nature of the extra molecular layer outside the photosphereof red supergiant stars, so far studied mostly with the use of theinfrared spectra. Although the visibility data are more direct probes ofthe spatial structure of the outer atmosphere, it is essential that theyare analyzed in combination with the spectral data. In the case of theM2 supergiant μ Cephei, several sets of data, both spectra andvisibilities, strongly suggested the presence of an extra molecularlayer (which we referred to as ``MOLsphere'' for simplicity), and thebasic parameters of the MOLsphere are estimated to be excitationtemperature Tex~1600 K, column densities of CO andH2O molecules Ncol~3.0×1020cm-2, and located at about one stellar radius above thephotosphere or Rin~2.0R*. The result showsreasonable agreement with the one based on the infrared spectra alone,and the model inferred from the spectra is now fully supported with therecent visibility data. In the case of the M2 supergiant αOrionis, the infrared spectra and visibilities show a consistent picturein that its MOLsphere is closer to the photosphere(Rin~1.3R*) with higher gas temperature(Tex~2250 K) and lower gas column density(Ncol~1020 cm-2), compared with that ofμ Cep. Some controversy on the interpretation of the mid-infrareddata of α Orionis can be reconciled. Given that the presence ofthe extra molecular layer is reasonably well established, the majorunsolved problem is how to understand the origin of such a rather warmand dense layer in the outer atmosphere.
| Water Vapor on Supergiants: The 12 μm TEXES Spectra of μ Cephei
Several recent papers have argued for warm, semidetached, molecularlayers surrounding red giant and supergiant stars, a concept known as aMOLsphere. Spectroscopic and interferometric analyses have oftencorroborated this general picture. Here we present high-resolutionspectroscopic data of pure rotational lines of water vapor at 12 μmfor the supergiant μ Cep. This star has often been used to test theconcept of molecular layers around supergiants. Given the prediction ofan isothermal, optically thick water vapor layer in local thermodynamicequilibrium around the star (MOLsphere), we expected the 12 μm linesto be in emission or at least in absorption but filled in by emissionfrom the molecular layer around the star. Our data, however, show thecontrary; we find definite absorption. Thus, our data do not easily fitinto the suggested isothermal MOLsphere scenario. The 12 μm lines,therefore, put new, strong constraints on the MOLsphere concept and onthe nature of water seen in signatures across the spectra of early Msupergiants. We also find that the absorption is even stronger than thatcalculated from a standard, spherically symmetric model photospherewithout any surrounding layers. A cool model photosphere, representingcool outer layers, is, however, able to reproduce the lines, but thismodel does not account for water vapor emission at 6 μm. Thus, aunified model for water vapor on μ Cep appears to be lacking. It doesseem necessary to model the underlying photospheres of these supergiantsin their whole complexity. The strong water vapor lines clearly revealinadequacies of classical model atmospheres.
| Dwarfs in the Local Region
We present lithium, carbon, and oxygen abundance data for a sample ofnearby dwarfs-a total of 216 stars-including samples within 15 pc of theSun, as well as a sample of local close giant planet (CGP) hosts (55stars) and comparison stars. The spectroscopic data for this work have aresolution of R~60,000, a signal-to-noise ratio >150, and spectralcoverage from 475 to 685 nm. We have redetermined parameters and derivedadditional abundances (Z>10) for the CGP host and comparison samples.From our abundances for elements with Z>6 we determine the meanabundance of all elements in the CGP hosts to range from 0.1 to 0.2 dexhigher than nonhosts. However, when relative abundances ([x/Fe]) areconsidered we detect no differences in the samples. We find nodifference in the lithium contents of the hosts versus the nonhosts. Theplanet hosts appear to be the metal-rich extension of local regionabundances, and overall trends in the abundances are dominated byGalactic chemical evolution. A consideration of the kinematics of thesample shows that the planet hosts are spread through velocity space;they are not exclusively stars of the thin disk.
| A High-Resolution Spectral Atlas of α Persei from 3810 to 8100 Å
We present a high-resolution (λ/δλ=90,000) spectralatlas of the F5 Ib star α Per covering the 3810-8100 Åregion. The atlas, based on data obtained with the aid of the echellespectrograph BOES fed by the 1.8 m telescope at Bohyunsan Observatory(Korea), is the result of the co-addition of a few well-exposed spectra.The final signal-to-noise ratio is ~800 at ~6000 Å. The atlas iscompared with a synthetic spectrum computed using a code based on Kuruczsoftware and databases. The adopted model atmosphere parameters areTeff=6240+/-20 K, logg=0.58+/-0.04, andvmicro=3.20+/-0.05 km s-1. We also derived an ironabundance of [Fe/H]=-0.28+/-0.06. The spectral lines of α Per havebeen identified by matching the synthetic spectrum with the observedone. The atlas is presented in figures and available in digital form onthe World Wide Web, along with the synthetic spectrum and spectral lineidentification tables.Based on data collected with the 1.8 m telescope at Bohyunsan OpticalAstronomy Observatory, South Korea.
| Elemental Abundance Ratios in Stars of the Outer Galactic Disk. III. Cepheids
We present metallicities, [Fe/H], and elemental abundance ratios,[X/Fe], for a sample of 24 Cepheids in the outer Galactic disk based onhigh-resolution echelle spectra. The sample members have galactocentricdistances covering 12 kpc<=RGC<=17.2 kpc, making themthe most distant Galactic Cepheids upon which detailed abundanceanalyses have been performed. We find subsolar ratios of [Fe/H] andoverabundances of [α/Fe], [La/Fe], and [Eu/Fe] in the programstars. All abundance ratios exhibit a dispersion that exceeds themeasurement uncertainties. As seen in our previous studies of old openclusters and field giants, enhanced ratios of [α/Fe] and [Eu/Fe]reveal that recent star formation has taken place in the outer disk withType II supernovae preferentially contributing ejecta to theinterstellar medium and with Type Ia supernovae playing only a minorrole. The enhancements for La suggest that asymptotic giant branch starshave contributed to the chemical evolution of the outer Galactic disk.Some of the young Cepheids are more metal-poor than the older openclusters and field stars at comparable galactocentric distances. Thisdemonstrates that the outer disk is not the end result of the isolatedevolution of an ensemble of gas and stars. We showed previously that theolder open clusters and field stars reached a basement metallicity atabout 10-11 kpc. The younger Cepheids reach the same metallicity but atlarger galactocentric distances, roughly 14 kpc. This suggests that theGalactic disk has been growing with time, as predicted from numericalsimulations. The outer disk Cepheids appear to exhibit a bimodaldistribution for [Fe/H] and [α/Fe]. Most of the Cepheids continuethe trends with galactocentric distance exhibited by S. M. Andrievsky'slarger Cepheid sample, and we refer to these stars as the ``GalacticCepheids.'' A minority of the Cepheids show considerably lower [Fe/H]and higher [α/Fe], and we refer to these stars as the ``MergerCepheids.'' One signature of a merger event would be compositiondifferences between the Galactic and Merger Cepheids. The Cepheidssatisfy this requirement, and we speculate that the distinctcompositions suggest that the Merger Cepheids may have formed under theinfluence of significant merger or accretion events. The short lifetimesof the Cepheids reveal that the merger event may be ongoing, with theMonoceros Ring and Canis Major galaxy being possible merger candidates.This paper makes use of observations obtained at the National OpticalAstronomy Observatory, which is operated by the Association ofUniversities for Research in Astronomy (AURA), Inc., under contract fromthe National Science Foundation. We also employ data products from theTwo Micron All Sky Survey, which is a joint project of the University ofMassachusetts and the Infrared Processing and Analysis Center,California Institute of Technology, funded by the National Aeronauticsand Space Administration and the National Science Foundation.
| Fine structure in the phase space distribution of nearby subdwarfs
We analysed the fine structure of the phase space distribution functionof nearby subdwarfs using data extracted from various catalogues.Applying a new search strategy based on Dekker's theory of galacticorbits, we found four overdensely populated regions in phase space.Three of them were correlated with previously known star streams: theHyades-Pleiades and Hercules streams in the thin disk of the Milky Wayand the Arcturus stream in the thick disk. In addition we find evidencefor another stream in the thick disk, which resembles closely theArcturus stream and probably has the same extragalactic origin.
| Precise Spectroscopic Radial Velocity Measurements Using Telluric Lines
Telluric absorption inside our coudé spectrograph is used as areference spectrum for precise radial velocity measurement. The opticalpath for this telluric absorption is stable and is not compromised byatmospheric disturbances, such as the jet stream. As an added bonus, thetelluric fiducial spectrum is free; i.e., one does not need toconstruct, regulate, maintain, or suffer throughput losses from acaptive-gas absorption cell. The telluric and stellar spectra span thesame portion of the detector and are observed sequentially, but indifferent diffraction orders. In this way the stellar line profiles arenot contaminated by the telluric spectrum and can therefore be used fornormal astrophysical line profile analyses, as well as radial velocitystudies. However, precise measurements of the temperature and pressureare needed for differential corrections between orders, because theindex of refraction of the air in the spectrograph is wavelengthdependent. Precision in radial velocity of ~25 m s-1 isdemonstrated.
| Subarcsecond Mid-Infrared Observations of NGC 6240: Limitations of Active Galactic Nucleus-Starburst Power Diagnostics
In order to examine the relative importance of powerful starbursts andCompton-thick active galactic nuclei (AGNs) in NGC 6240, we haveobtained mid-infrared images and low-resolution spectra of the galaxywith subarcsecond spatial resolution using the Keck telescopes. Despitethe high spatial resolution (~200 pc) of our data, no signature of thehidden AGNs has been detected in the mid-infrared. The southern nucleus,which we show provides 80%-90% of the total 8-25 μm luminosity of thesystem, has a mid-infrared spectrum and a mid-/far-infrared spectralenergy distribution consistent with starbursts. At the same time,however, it is also possible to attribute up to 60% of the bolometricluminosity to an AGN, consistent with X-ray observations, if the AGN isheavily obscured and emits mostly in the far-infrared. This ambiguityarises because the intrinsic variation of properties among a givengalaxy population (e.g., starbursts) introduces at least a factor of afew uncertainty even into the most robust AGN-starburst diagnostics. Weconclude that with present observations it is not possible to determinethe dominant power source in galaxies when AGN and starburstluminosities are within a factor of a few of each other.The data presented herein were obtained at the W. M. Keck Observatory,which is operated as a scientific partnership among the CaliforniaInstitute of Technology, the University of California, and the NationalAeronautics and Space Administration. The Observatory was made possibleby the generous financial support of the W. M. Keck Foundation.
| Oscillation mode lifetimes in ξ Hydrae: will strong mode damping limit asteroseismology of red giant stars?
We introduce a new method to measure frequency separations and modelifetimes of stochastically excited and damped oscillations, so-calledsolar-like oscillations. Our method shows that velocity data of the redgiant star ξ Hya (Frandsen et al. 2002) support a large frequencyseparation between modes of roughly 7~μHz. We also conclude that thedata are consistent with a mode lifetime of 2 days, which is so shortrelative to its pulsation period that none of the observed frequenciesare unambiguous. Hence, we argue that the maximum asteroseismic outputthat can be obtained from these data is an average large frequencyseparation, the oscillation amplitude and the average mode lifetime.However, the significant discrepancy between the theoreticalcalculations of the mode lifetime (Houdek & Gough 2002) and ourresult based on the observations of ξ Hya, implies that red giantstars can help us better understand the damping and driving mechanismsof solar-like p-modes by convection.
| Pieces of the puzzle: ancient substructure in the Galactic disc
We search for signatures of past accretion events in the Milky Way inthe recently published catalogue by Nordström et al., containingaccurate spatial and kinematic information as well as metallicities for13240 nearby stars. To optimize our strategy, we use numericalsimulations and characterize the properties of the debris from disruptedsatellites. We find that stars with a common progenitor should showdistinct correlations between their orbital parameters; in particular,between the apocentre (A) and pericentre (P), as well as their z-angularmomentum (Lz). In the APL space, such stars are expected tocluster around regions of roughly constant eccentricity.The APL space for the Nordström catalogue exhibits a wealth ofsubstructure, much of which can be linked to dynamical perturbationsinduced by spiral arms and the Galactic bar. However, our analysis alsoreveals a statistically significant excess of stars on orbits of common(moderate) eccentricity, analogous to the pattern expected for mergerdebris. Besides being dynamically peculiar, the 274 stars in thesesubstructures have very distinct metallicity and age distributions,providing further evidence of their extragalactic provenance. It ispossible to identify three coherent groups among these stars, that, inall likelihood, correspond to the remains of disrupted satellites. Themost metal-rich group ([Fe/H] > -0.45dex) has 120 stars distributedinto two stellar populations of ~8Gyr (33 per cent) and ~12Gyr (67 percent) of age. The second group with <[Fe/H]>~-0.6dex has 86 starsand shows evidence of three populations of 8Gyr (15 per cent), 12Gyr (36per cent) and 16Gyr (49 per cent) of age. Finally, the third group has68 stars, with typical metallicity around -0.8dex and a single age of~14Gyr. The identification of substantial amounts of debris in theGalactic disc whose origin can be traced back to more than one satellitegalaxy, provides evidence of the hierarchical formation of the MilkyWay.
| Investigating Disk Evolution: A High Spatial Resolution Mid-Infrared Survey of T Tauri Stars
We present a high spatial resolution, 10-20 μm survey of 65 T Tauribinary stars in Taurus, Ophiuchus, and Corona Australis using the Keck10 m telescopes. Designed to probe the inner ~1 AU region of thecircumstellar disks around the individual stellar components in thesebinary systems, this study increases the number of binaries withspatially resolved measurements at 10 μm by a factor of ~5. Combinedwith resolved near-infrared photometry and spectroscopic accretiondiagnostics, we find that ~10% of stars with a mid-infrared excess donot appear to be accreting. In contrast to an actively accreting disksystem, these passive disks have significantly lower near-infraredcolors that are, in most cases, consistent with photospheric emission,suggesting the presence of an inner disk hole. In addition, thereappears to be a spectral type/mass dependence associated with thepresence of a passive disk, with all passive disks occurring aroundM-type stars. The presence of a passive disk does not appear to berelated to the fact that these objects are in visual binary systems; thepassive disk systems span the entire range of binary separations presentin the sample, and a similar fraction of passive disks is observed in asample of single stars. The possibility that the passive disks arecaused by the presence of an as yet undetected companion at a smallseparation (0.3-3 AU) is possible for any individual system; however, itcannot account for the spectral type dependence of the passive disksample as a whole. We propose that these passive disks represent asubset of T Tauri stars that are undergoing significant disk evolution.The fraction of observed passive disks and the observed spectral typedependence can both be explained by models of disk evolution thatinclude disk photoevaporation from the central star.
| Abundances of Baade's Window Giants from Keck HIRES Spectra. I. Stellar Parameters and [Fe/H] Values
We present the first results of a new abundance survey of the Milky Waybulge based on Keck HIRES spectra of 27 K giants in the Baade's Window(l=1deg, b=-4deg) field. The spectral data used inthis study are of much higher resolution and signal-to-noise ratio thanprevious optical studies of Galactic bulge stars. The [Fe/H] values ofour stars, which range between -1.29 and +0.51, were used to recalibratelarge low-resolution surveys of bulge stars. Our best value for the mean[Fe/H] of the bulge is -0.10+/-0.04. This mean value is similar to themean metallicity of the local disk and indicates that there cannot be astrong metallicity gradient inside the solar circle. The metallicitydistribution of stars confirms that the bulge does not suffer from theso-called G dwarf problem. This paper also details the new abundancetechniques necessary to analyze very metal-rich K giants, including anew Fe line list and regions of low blanketing for continuumidentification.Based on data obtained at the W. M. Keck Observatory, which is operatedas a scientific partnership among the California Institute ofTechnology, the University of California, and NASA and was made possibleby the generous financial support of the W. M. Keck Foundation.
| A Survey of Merger Remnants. II. The Emerging Kinematic and Photometric Correlations
This paper is the second in a series exploring the properties of 51optically selected, single-nuclei merger remnants. Spectroscopic datahave been obtained for a subsample of 38 mergers and combined withpreviously obtained infrared photometry to test whether mergers exhibitthe same correlations as elliptical galaxies among parameters such asstellar luminosity and distribution, central stellar velocity dispersion(σ0), and metallicity. Paramount to the study is totest whether mergers lie on the fundamental plane. Measurements ofσ0 have been made using the Ca triplet absorption lineat 8500 Å for all 38 mergers in the subsample. Additionalmeasurements of σ0 were made for two of the mergers inthe subsample using the CO absorption line at 2.29 μm. The resultsindicate that mergers show a strong correlation among the parameters ofthe fundamental plane but fail to show a strong correlation betweenσ0 and metallicity (Mg2). In contrast toearlier studies, the σ0 values of the mergers areconsistent with objects that lie somewhere between intermediate-mass andluminous giant elliptical galaxies. However, the discrepancies withearlier studies appear to correlate with whether the Ca triplet or COabsorption lines are used to derive σ0, with the latteralmost always producing smaller values. Finally, the photometric andkinematic data are used to demonstrate for the first time that thecentral phase-space densities of mergers are equivalent to those inelliptical galaxies. This resolves a long-standing criticism of themerger hypothesis.Some of the data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation.
| San Pedro Mártir Mid-Infrared Photometric System
With the goal of defining the San Pedro Martir Mid-infrared PhotometricSystem (SPM-MIR), observations of well-defined calibration stars werecarried out on 9 photometric runs from 2000 to 2005. The mid-infrared (2- 28 μm) camera CID-BIB of the Observatorio AstronómicoNacional was used. A set of 9 filters, the ``silicate'' series SiN, SiO,SiP, SiQ, SiR, SiS, the broad-band N (10.8 μm) filter, and thenarrow-band QH2 (17.15 μm) and Q2 (18.7 μm), was used to derivethe extinction coefficients and zero magnitude points. Atmosphericextinction corrections were carried out making use of Padéapproximants and we found a linear dependence on the parameters with thelow air mass extinction coefficient. The atmospheric transmission curvesand extinction coefficients of SPM were compared with those obtained forthe Mauna Kea site. Color terms were derived using a set of IRAS LSRsources observed with the CID-BIB.
| On the Energy Flux Reaching Planets during the Parent Star's Evolutionary Track:The Earth-Sun System
The total flux of energy emitted by a star is a basic source of almostall physical and chemical processes in the atmosphere and on the surfaceof a planet. On the other hand, the upper parts of atmosphere,ionosphere, and magnetosphere are influenced to a great extent by tinyenergy fluxes contained in the stellar XUV radiation and wind that aremostly responsible for ionization and photodissociation of atmosphericconstituents and their escape. The latter problem is essential for theeventual detection of planets around stars. This paper demonstratesquantitatively how the above energy fluxes vary during a star'sevolution. The results are presented for a solar-type star and a planetlocated initially at a distance of 1 AU from the star, providing insightinto the past and future of the Sun and Earth. Among other things, theadopted model predicts that the maximum values of the energy fluxreaching the Earth during giant phases of the Sun are greater than therespective values observed at present (the quiet Sun) by about 5 ordersof magnitude for the solar wind, 3 orders of magnitude for the totalradiation, and 2 orders of magnitude for the XUV radiation. On the otherhand, the latter increases enormously (about 6 orders of magnitude)during a brief period of the post-asymptotic giant stage and decreasesfast when moving to and during the white dwarf phase.
| The Rotation of Arcturus and Active Longitudes on Giant Stars
From two decades of high-resolution spectroscopic measurements ofArcturus (HR 5340, K2 III), we identify a 2 yr modulation in thevelocity span of the bisector of the Fe I λ6252.57 line. It seemslikely that this is the rotation period, and we deduce the equatorialrotation rate to be 1.8 +/- 0.3 km s-1, based on a radius of25.4 Rsolar. From detailed Fourier analysis of the broadeningand shapes of the spectral lines, we derive vsini = 1.5 +/- 0.3 kms-1 and a radial-tangential macroturbulence dispersion of 5.2+/- 0.2 km s-1. The inclination of the rotation axis to theline of sight is then 58° +/- 25°. Considering the periods foundby H.-J. Choi et al. from variations in the Ca II H and K line emission,we suggest that giant stars have two or three active longitudes and,therefore, that periods found from the modulation of magnetic featureswill be one-half or one-third of the rotation period.
| Astrophysics in 2005
We bring you, as usual, the Sun and Moon and stars, plus some galaxiesand a new section on astrobiology. Some highlights are short (the newlyidentified class of gamma-ray bursts, and the Deep Impact on Comet9P/Tempel 1), some long (the age of the universe, which will be found tohave the Earth at its center), and a few metonymic, for instance theterm ``down-sizing'' to describe the evolution of star formation rateswith redshift.
| Reliability Checks on the Indo-US Stellar Spectral Library Using Artificial Neural Networks and Principal Component Analysis
The Indo-US coudé feed stellar spectral library (CFLIB) madeavailable to the astronomical community recently by Valdes et al. (2004,ApJS, 152, 251) contains spectra of 1273 stars in the spectral region3460 to 9464Å at a high resolution of 1Å (FWHM) and a widerange of spectral types. Cross-checking the reliability of this databaseis an important and desirable exercise since a number of stars in thisdatabase have no known spectral types and a considerable fraction ofstars has not so complete coverage in the full wavelength region of3460-9464Å resulting in gaps ranging from a few Å to severaltens of Å. We use an automated classification scheme based onArtificial Neural Networks (ANN) to classify all 1273 stars in thedatabase. In addition, principal component analysis (PCA) is carried outto reduce the dimensionality of the data set before the spectra areclassified by the ANN. Most importantly, we have successfullydemonstrated employment of a variation of the PCA technique to restorethe missing data in a sample of 300 stars out of the CFLIB.
| Multi-periodic oscillations of HD 32887 and HD 81797.
In this paper we present two evolved stars, HD 32887 and HD 81797, whichshow multi-periodic oscillations. We observed the oscillations by meansof the precise radial velocity technique with the simultaneouscalibration method. The high-resolution spectra of each star have beenobtained with FEROS at the 2.2 m-MPG/ESO telescope in La SillaObservatory, Chile. We found variation in the stellar radial velocitiesand spectral line profiles. The periods of the oscillations are fromseveral hours up to few days. The sources of the short-term oscillationsof HD 32887 and HD 81797 are obviously due to stellar pulsations, whichare similar to solar-like oscillations. In particular, in HD 81797 wefound a clear correlation between the variation in the asymmetry of thespectral line profile, measured in the bisector velocity spans, and theradial velocity. Both stars have bisector velocity spans which also showoscillations. The periods of the bisector oscillations are similar tothose of the radial velocity variation. The detection of themulti-periodic oscillations in HD 32887 and HD 81797 makes these star tobe amenable targets for asteroseismology, in particular, of stars in thered giant branch.
| High-precision photometry with the WIRE satellite .
Around 200 bright stars (V<6) have been monitored with the two-inchstar tracker on the WIRE satellite since observations started in 1999.Here we present new results for the solar-like star Procyon A, the twodelta Scuti stars Altair and epsilon Cephei, and the triple systemlambda Scorpii which consist of two B-type stars - one of which we findto be an eclipsing binary.
| Extended Emission by Dust in the Dwarf Galaxy UGC 10445
We present Spitzer Space Telescope images of the isolated dwarf galaxyUGC 10445. The galaxy is detected at all photometric bands (3.6-160μm), as well as in the Multiband Imaging Photometer for Spitzer(MIPS) spectral energy distribution mode (55-95 μm). We derive a starformation rate of 0.25 Msolar yr-1, based onHα and infrared flux densities. There is over 106Msolar of cold dust (T~18 K) in the galaxy, represented by160 μm emission, which extends to a larger radius than theultraviolet (UV), optical, and near-infrared light. Such extendedemission has been seen previously only in dwarf galaxies in clusterenvironments. We suggest that the source of heating for this dust is UVlight, originating in star-forming complexes. To produce the largequantity of dust requires a higher rate of star formation in the pastthan is currently observed.
| Near-Ultraviolet Observations of HD 221170: New Insights into the Nature of r-Process-rich Stars
Employing high-resolution spectra obtained with the near-UV-sensitivedetector on the Keck I HIRES, supplemented by data obtained with theMcDonald Observatory 2d-coudé, we have performed a comprehensivechemical composition analysis of the bright r-process-rich metal-poorred giant star HD 221170. Analysis of 57 individual neutral and ionizedspecies yielded abundances for a total of 46 elements and significantupper limits for an additional five. Model stellar atmosphere parameterswere derived with the aid of ~200 Fe peak transitions. From more than350 transitions of 35 neutron-capture (Z>30) species, abundances for30 neutron-capture elements and upper limits for three others werederived. Utilizing 36 transitions of La, 16 of Eu, and seven of Th, wederive ratios of logε(Th/La)=-0.73 (σ=0.06) andlogε(Th/Eu)=-0.60 (σ=0.05), values in excellent agreementwith those previously derived for other r-process-rich metal-poor starssuch as CS 22892-052, BD +17 3248, and HD 115444. Based on the Th/Euchronometer, the inferred age is 11.7+/-2.8 Gyr. The abundancedistribution of the heavier neutron-capture elements (Z>=56) isfitted well by the predicted scaled solar system r-process abundances,as also seen in other r-process-rich stars. Unlike other r-process-richstars, however, we find that the abundances of the lighterneutron-capture elements (37
| NLTE Strontium and Barium in Metal-poor Red Giant Stars
We present atmospheric models of red giant stars of variousmetallicities, including extremely metal poor (XMP; [Fe/H]<-3.5)models, with many chemical species, including, significantly, the firsttwo ionization stages of strontium (Sr) and barium (Ba), treated innon-local thermodynamic equilibrium (NLTE) with various degrees ofrealism. We conclude that (1) for all lines that are useful Sr and Baabundance diagnostics, the magnitude and sense of the computed NLTEeffect on the predicted line strength is metallicity dependent, (2) theindirect NLTE effect of overlap between Ba and Sr transitions andtransitions of other species that are also treated in NLTE nonnegligiblyenhances NLTE abundance corrections for some lines, (3) the indirectNLTE effect of NLTE opacity of other species on the equilibriumstructure of the atmospheric model is not significant, (4) the computedNLTE line strengths differ negligibly if collisional b-b and b-f ratesare an order of magnitude smaller or larger than those calculated withstandard analytic formulae, and (5) the effect of NLTE on the resonanceline of Ba II at 4554.03 Å is independent of whether that line istreated with hyperfine splitting. As a result, the derivation ofabundances of Ba and Sr for metal-poor red giant stars with LTE modelingthat are in the literature should be treated with caution.
| Early Infrared Spectral Development of V1187 Scorpii (Nova Scorpii 2004 No. 2)
We report on an unprecedented infrared time series of spectra of V1187Sco, a very fast ONeMg nova. The observations covered a 56 day period(2004 August 6-September 30) starting 2 days after the nova's peakbrightness. Time evolution of the spectra revealed changing linestrengths and profiles on timescales of less than a day to weeks as thenova evolved from early postmaximum to early coronal phases. When ourground-based optical and Spitzer Space Telescope data were combined, thewavelength coverage of 0.38-36 μm allowed an accurate spectral energydistribution to be derived when it was about 6 weeks after outburst.Developing double structure in the He I lines showed them changing fromnarrow to broad in only a few days. Using the O I lines in combinationwith the optical spectra, we derived a reddening of E(B-V)=1.56+/-0.08and a distance of 4.9+/-0.5 kpc. Modeling of the ejected materialstrongly suggested that it was geometrically thick withΔR/R=0.8-0.9 (more of a wind than a shell) and a low fillingfactor of order a few percent. The line shapes were consistent with acylindrical jet, bipolar, or spherical Hubble flow expansion with amaximum speed of about -3000 km s-1. The central peakappeared to be more associated with the spherical component, while thetwo peaks (especially in Hβ) suggested a ring with either a lowervelocity component or with its axis inclined to the line of sight.
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