Contents
Images
Upload your image
DSS Images Other Images
Related articles
Calibrating M Dwarf Metallicities Using Molecular Indices
We report progress in the calibration of a method to determine cooldwarf star metallicities using molecular band strength indices. Themolecular band index to metallicity relation can be calibrated usingchemical abundances calculated from atomic-line equivalent widthmeasurements in high-resolution spectra. Building on previous work, wehave measured Fe and Ti abundances in 32 additional M and K dwarf starsto extend the range of temperature and metallicity covered. A test ofour analysis method using warm star-cool star binaries shows we cancalculate reliable abundances for stars warmer than 3500 K. We have usedabundance measurements for warmer binary or cluster companions toestimate abundances in six additional cool dwarfs. Adding stars measuredin our previous work and others from the literature provides 76 starswith Fe abundance and CaH2 and TiO5 index measurements. The CaH2molecular index is directly correlated with temperature. TiO5 depends ontemperature and metallicity. Metallicity can be estimated to within+/-0.3 dex within the bounds of our calibration, which extends fromroughly [Fe/H]=+0.05 to -1.0, with a limited extension to -1.5.
| Anharmonic and standing dynamo waves: theory and observation of stellar magnetic activity
The familiar decadal cycle of solar activity is one expression ofinterannual variability of surface magnetism observed in stars on ornear the lower main sequence. From studies of time-series of CaII H andK emission fluxes that go back more than 35 yr and have been accumulatedfor such stars at the Mount Wilson Observatory by the HK Project, wedefine a quantitative measure, called anharmonicity, of the cycliccomponent of interannual magnetic variability. Anharmonicity provides aconnection between observed variations in magnetic activity and thetwo-dimensional description of a Parker dynamo model. We explore theparameter space of the Parker dynamo model and find an excellentcounterpart in the records of several of the lowest-mass (late K-type toearly M-type) active stars in the HK Project sample to the solutionscontaining highly anharmonic, standing dynamo waves. We interpretanharmonicity apparent in the records as resulting from non-propagatingor standing dynamo waves, which operate in a regime that issubstantially supercriticial. There, for the majority of a cycle, orpulse of decadal-to-interdecadal variability, the large-scale magneticfields are generated and maintained by winding of field by differentialrotation rather than by the joint action of differential rotation andhelical convection. Among the less active stars (the Sun is consideredsuch a star in the HK Project sample) we find a correspondence betweenanharmonicity and Parker dynamo model solutions that include simpleharmonic, migratory and/or intermediate-type dynamo wave patterns over abroad range of dynamo parameters.
| The Classical Algol XZ UMa - Observations and Analysis
Not Available
| Establishing Observational Baselines for Two δ Scuti Variables: V966 Herculis and V1438 Aquilae
We have examined the previously understudied δ Scuti stars V966Herculis and V1438 Aquilae. We find that V966 Her is a stable pulsatorwith a refined period of 0.1330302 days with a full V amplitude of 0.096mag. We also find that V966 Her has an average radial velocity of +7.8km s-1, a full radial velocity amplitude of 7.6 kms-1, and a vsini=63.8 km s-1. For V1438 Aql wereport a revised Hipparcos period of 0.1612751 days with a fullamplitude of 0.056. The average radial velocity is found to be -43 kms-1, with full amplitude of 9.7 km s-1, and avsini=76.7 km s-1. Due to some anomalies seen in V1438 Aql wefeel that a much larger photometric and spectroscopic campaign isrequired to determine the true nature of this star.
| 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.
| New Precision Orbits of Bright Double-Lined Spectroscopic Binaries. I. RR Lyncis, 12 Bootis, and HR 6169
Radial velocities from the 2.1 m telescope at McDonald Observatorysupplemented with radial velocities from the coudé feed telescopeat Kitt Peak National Observatory provide new precise orbits for thedouble-lined spectroscopic binaries RR Lyn (A3/A8/A6), 12 Boo (F8 IV),and HR 6169 (A2 V). We derive orbital dimensions (a1sini anda2sini) and minimum masses (m1sin3i andm2sin3i) with accuracies of 0.06%-0.9%. The three systems,which have V magnitudes of 5.53, 4.82, and 6.42, respectively, are allsufficiently bright that they are easily within the grasp of modernoptical interferometers and so afford the prospect, when ourspectroscopic observations are complemented by interferometricobservations, of fully determined orbits, precise masses, and distances.In the case of RR Lyn, which is also a detached eclipsing binary with awell-determined orbital inclination (i=87.45d+/-0.11d), we are able todetermine the semimajor axis of the relative orbit, a=29.32+/-0.04Rsolar primary and secondary radii of 2.57+/-0.02 and1.59+/-0.03 Rsolar, respectively; and primary and secondarymasses of 1.927+/-0.008 and 1.507+/-0.004 Msolar,respectively. Comparison of our new systemic velocity determination,γ=-12.03+/-0.04 km s-1, with the earlier one of Kondo,γ=-11.61+/-0.30 km s-1, shows no evidence of any changein the systemic velocity in the 40 yr separating the two measurements, anull result that neither confirms nor contradicts the presence of thelow-mass third component proposed by Khaliullin & Khaliullina. Ourspectroscopic orbit of 12 Boo is more precise than that of Boden et al.but confirms their results about this system. Our analysis of HR 6169has produced a major improvement in its orbital elements. The minimummasses of the primary and secondary are 2.20+/-0.01 and 1.64+/-0.02Msolar, respectively. Although all three systems haveeccentric orbits, the six components of the systems are eitherpseudosynchronously rotating or very nearly so.
| Spectroscopy and Photometry of the Double-lined Binary HD 149420
We have used new spectroscopic and photometric observations of HD 149420to obtain an improved orbital element solution and determine some basicproperties of the system. This double-lined binary has an orbital periodof 3.39430 days, a circular orbit, and a mass ratio of 0.52. The primaryis somewhat evolved, with an A9 IV spectral type, while the secondary isestimated to be an F5: dwarf. The secondary may be synchronouslyrotating, but the primary is rotating substantially slower than itssynchronous velocity. Our photometric observations confirm the lightvariability and period found by Hipparcos. We determine a photometricperiod of 1.698 days, essentially half the value of the orbital period,with a peak-to-peak amplitude of 0.028 mag in V. In addition to thisellipsoidal light variation, we also detect more rapid, low-amplitudevariability with a period of 0.076082 days and a peak-to-peak Vamplitude of 0.008 mag, as well as a possible second short 0.059256 dayperiod with a peak-to-peak amplitude of only 0.005 mag. This indicatesthat the A9 IV primary in HD 149420 is a pulsating δ Scutivariable. Our binary model that best fits both the radial velocity andphotometric observations indicates the possibility of extremely shallowgrazing eclipses, a circumstance not unexpected given the large minimummasses from the orbital solution, the evolved nature of the primary, andthe short orbital period.
| Prospects for population synthesis in the H band: NeMo grids of stellar atmospheres compared to observations
Context: .For applications in population synthesis, libraries oftheoretical stellar spectra are often considered an alternative totemplate libraries of observed spectra, because they allow a completesampling of stellar parameters. Most of the attention in publishedtheoretical spectral libraries has been devoted to the visual wavelengthrange.Aims.The goal of the present work is to explore the near-infraredrange where few observed fully calibrated spectra and no theoreticallibraries are available.Methods.We make a detailed comparison oftheoretical spectra in the range 1.57-1.67 μm for spectral types fromA to early M and for giant and dwarf stars, with observed stellarspectra at resolutions around 3000, which would be sufficient todisentangle the different groups of late-type stars. We selected theNeMo grids of stellar atmospheres to perform this comparison.Results.Wefirst demonstrate that observed spectral flux distributions can bematched very well with theoretical ones for almost the entire parameterrange covered by the NeMo grids at moderate resolution in the visualrange. In the infrared range, although the overall shape of the observedflux distributions still matches reasonably well, the individualspectral features are reproduced by the theoretical spectra only forstars earlier than mid F type. For later spectral types the differencesincrease, and theoretical spectra of K type stars have systematicallyweaker line features than those found in observations. Thesediscrepancies are traced back to stem primarily from incomplete data onneutral atomic lines, although some of them are also related tomolecules.Conclusions.Libraries of theoretical spectra for A to early Mtype stars can be successfully used in the visual regions for populationsynthesis, but their application in the infrared is restricted to earlyand intermediate type stars. Improving atomic data in the near infraredis a key element in making the construction of reliable libraries ofstellar spectra feasible in the infrared.
| Lithium Abundances of F-, G-, and K-Type Stars: Profile-Fitting Analysis of the Li I 6708 Doublet
An extensive profile-fitting analysis was performed for the Li(+Fe)6707-6708Å feature of nearby 160 F-K dwarfs/subgiants (including27 planet-host stars) in the Galactic disk ( 7000 K ≳Teff ≳ 5000 K, -1 ≲ [Fe/H] ≲ +0.4), in orderto establish the photospheric lithium abundances of these stars. Thenon-LTE effect (though quantitatively insignificant) was taken intoaccount based on our statistical equilibrium calculations, which werecarried out on an adequate grid of models. Our results confirmed most ofthe interesting observational characteristics revealed by recentlypublished studies, such as the bimodal distribution of the Li abundancesfor stars at Teff ≳ 6000 K, the satisfactory agreementof the upper envelope of the A(Li) vs. [Fe/H] distribution with thetheoretical models, the existence of a positive correlation betweenA(Li) and the stellar mass, and the tendency of lower lithium abundancesof planet-host stars (as compared to stars without planets) at thenarrow ``transition'' region of 5900 K ≳ Teff ≳5800 K. The solar Li abundance derived from this analysis is 0.92 (H =12.00), which is by 0.24dex lower than the widely referenced standardvalue of 1.16.
| Spectroscopic Study on the Atmospheric Parameters of Nearby F--K Dwarfs and Subgiants
Based on a collection of high-dispersion spectra obtained at OkayamaAstrophysical Observatory, the atmospheric parameters (Teff,log g, vt, and [Fe/H]) of 160 mid-F through early-K starswere extensively determined by the spectroscopic method using theequivalent widths of Fe I and Fe II lines along with the numericaltechnique of Takeda et al. (2002, PASJ, 54, 451). The results arecomprehensively discussed and compared with the parameter values derivedby different approaches (e.g., photometric colors, theoreticalevolutionary tracks, Hipparcos parallaxes, etc.) as well as with thepublished values found in various literature. It has been confirmed thatour purely spectroscopic approach yields fairly reliable and consistentresults.
| New clues on outburst mechanisms and improved spectroscopic elements of the black hole binary V4641 Sagittarii*
We present spectroscopic observations of the black hole binary V4641Sagittarii, obtained between 2004 July 4 and 2005 March 28, which coverthe minor outburst of the star in early 2004 July and quiescencevariations on 19 nights scattered over six months. During the outburst,the star peaked approximately 3 mag brighter than usual, and our spectrawere dominated by broad hydrogen, helium and iron emission lines. Thevery first spectra showed P Cygni profiles, which disappeared within afew hours, indicating rapid changes in matter ejection. The Hαline had multiple components, one being a broad blueshifted wingexceeding 5000 km s-1. During a simultaneously observed10-min photometric flare up, the equivalent width of the Hα linetemporarily decreased, implying that it was a flare of the continuum.The overall spectral appearance was similar to that observed in the 1999September active phase, which suggests that similar mass-ejectionprocesses were associated with both eruptions. In quiescence, thespectra were those of the early-type secondary star showing its orbitalmotion around the primary. By measuring cross-correlation radialvelocities, we give an improved set of spectroscopic elements. Whereaswe measure the same velocity amplitude (K2= 211.3 +/- 1.0 kms-1), within errors, as Orosz et al., our centre-of-massvelocity (γ= 72.7 +/- 3.3 km s-1) differs significantlyfrom the previously published value (107.4 +/- 2.9 km s-1).However, we find evidence that the difference is caused by a systematicerror in data reduction in the previous study, rather than bygravitational effects of an invisible third component.
| Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs
We present a uniform catalog of stellar properties for 1040 nearby F, G,and K stars that have been observed by the Keck, Lick, and AAT planetsearch programs. Fitting observed echelle spectra with synthetic spectrayielded effective temperature, surface gravity, metallicity, projectedrotational velocity, and abundances of the elements Na, Si, Ti, Fe, andNi, for every star in the catalog. Combining V-band photometry andHipparcos parallaxes with a bolometric correction based on thespectroscopic results yielded stellar luminosity, radius, and mass.Interpolating Yonsei-Yale isochrones to the luminosity, effectivetemperature, metallicity, and α-element enhancement of each staryielded a theoretical mass, radius, gravity, and age range for moststars in the catalog. Automated tools provide uniform results and makeanalysis of such a large sample practical. Our analysis method differsfrom traditional abundance analyses in that we fit the observed spectrumdirectly, rather than trying to match equivalent widths, and wedetermine effective temperature and surface gravity from the spectrumitself, rather than adopting values based on measured photometry orparallax. As part of our analysis, we determined a new relationshipbetween macroturbulence and effective temperature on the main sequence.Detailed error analysis revealed small systematic offsets with respectto the Sun and spurious abundance trends as a function of effectivetemperature that would be inobvious in smaller samples. We attempted toremove these errors by applying empirical corrections, achieving aprecision per spectrum of 44 K in effective temperature, 0.03 dex inmetallicity, 0.06 dex in the logarithm of gravity, and 0.5 kms-1 in projected rotational velocity. Comparisons withprevious studies show only small discrepancies. Our spectroscopicallydetermined masses have a median fractional precision of 15%, but theyare systematically 10% higher than masses obtained by interpolatingisochrones. Our spectroscopic radii have a median fractional precisionof 3%. Our ages from isochrones have a precision that variesdramatically with location in the Hertzsprung-Russell diagram. We planto extend the catalog by applying our automated analysis technique toother large stellar samples.
| Radial Velocities of Galactic Cepheids
We report 490 radial velocities for 16 Galactic Cepheid variables. Thetypical uncertainty of a single velocity is +/-0.40 km s-1.Comparison with published velocities shows excellent agreement. Two ofthe Cepheids (Z Lac, S Sge) are known binaries and exhibit orbitalvelocity changes in our observing interval.
| A 2 Micron H2 Spectral Survey of Proto-Planetary Nebulae
We measured 2.1-2.3 μm spectra for a mostly complete sample of knownproto-planetary nebulae (PPNe) at declinations north of -30°. Thisspectral range includes the H2 emission lines 1-0 S(1), 1-0S(0), 2-1 S(1), 2-1 S(2), and 3-2 S(3). We detected H2emission from 16 of the 51 objects in our survey. Twelve of these arenew detections, doubling the number of PPNe with detected H2emission. We find that H2 emission commences at a spectralclass of mid-G in PPNe with bipolar morphologies and optically thickequatorial regions; in fact, all bipolar F-G PPNe with an opticallythick equatorial region have collisionally excited H2emission. Radiative excitation becomes important in PPNe when thecentral star reaches an early B spectral type, just beforephotoionization of the nebula and the commencement of the planetarynebula (PN) phase. Almost all of the PPNe with B central stars showH2 emission, with either a purely radiative or a mixedcollisional plus radiative spectrum. Since H2 emission israre in nonbipolar PNe, the destruction of the H2 in thenonbipolars must be roughly coincident with the photoionization of thenebula. As with H2-emitting PNe, the bipolarH2-emitting PPNe are found at low Galactic latitudes.Optically thin H2-emitting nebulae are not similarlyrestricted to low latitudes. Brγ emission is detected in 15 of thesources, including all those of B spectral type.
| UVBLUE: A New High-Resolution Theoretical Library of Ultraviolet Stellar Spectra
We present an extended ultraviolet-blue (850-4700 Å) library oftheoretical stellar spectral energy distributions computed at highresolution, λ/Δλ=50,000. The UVBLUE grid, as wenamed the library, is based on LTE calculations carried out with ATLAS9and SYNTHE codes developed by R. L. Kurucz and consists of nearly 1800entries that cover a large volume of the parameter space. It spans arange in Teff from 3000 to 50,000 K, the surface gravityranges from logg=0.0 to 5.0 with Δlogg=0.5 dex, while sevenchemical compositions are considered:[M/H]=-2.0,-1.5,-1.0,-0.5,+0.0,+0.3, and +0.5 dex. For its coverageacross the Hertzsprung-Russell diagram, this library is the mostcomprehensive one ever computed at high resolution in theshort-wavelength spectral range, and useful application can be foreseenfor both the study of single stars and in population synthesis models ofgalaxies and other stellar systems. We briefly discuss some relevantissues for a safe application of the theoretical output to ultravioletobservations, and a comparison of our LTE models with the non-LTE (NLTE)ones from the TLUSTY code is also carried out. NLTE spectra are found,on average, to be slightly ``redder'' compared to the LTE ones for thesame value of Teff, while a larger difference could bedetected for weak lines, which are nearly wiped out by the enhanced coreemission component in case of NLTE atmospheres. These effects seem to bemagnified at low metallicity (typically [M/H]<~-1). A match with aworking sample of 111 stars from the IUE atlas, with availableatmosphere parameters from the literature, shows that UVBLUE modelsprovide an accurate description of the main mid- and low-resolutionspectral features for stars along the whole sequence from the B to ~G5type. The comparison sensibly degrades for later spectral types, withsupergiant stars that are in general more poorly reproduced than dwarfs.As a possible explanation of this overall trend, we partly invoke theuncertainty in the input atmosphere parameters to compute thetheoretical spectra. In addition, one should also consider the importantcontamination of the IUE stellar sample, where the presence of binaryand variable stars certainly works in the sense of artificiallyworsening the match between theory and observations.
| Single-Visit Photometric and Obscurational Completeness
We report a method that uses ``completeness'' to estimate the number ofextrasolar planets discovered by an observing program with adirect-imaging instrument. We develop a completeness function forEarth-like planets on ``habitable'' orbits for an instrument with acentral field obscuration, uniform sensitivity in an annular detectionzone, and limiting sensitivity that is expressed as a ``deltamagnitude'' with respect to the star, determined by systematic effects(given adequate exposure time). We demonstrate our method of estimationby applying it to our understanding of the coronagraphic version of theTerrestrial Planet Finder (TPF-C) mission as of 2004 October. Weestablish an initial relationship between the size, quality, andstability of the instrument's optics and its ability to meet missionscience requirements. We provide options for increasing the fidelity andversatility of the models on which our method is based, and we discusshow the method could be extended to model the TPF-C mission as a wholeto verify that its design can meet the science requirements.
| The Planet-Metallicity Correlation
We have recently carried out spectral synthesis modeling to determineTeff, logg, vsini, and [Fe/H] for 1040 FGK-type stars on theKeck, Lick, and Anglo-Australian Telescope planet search programs. Thisis the first time that a single, uniform spectroscopic analysis has beenmade for every star on a large Doppler planet search survey. We identifya subset of 850 stars that have Doppler observations sufficient todetect uniformly all planets with radial velocity semiamplitudes K>30m s-1 and orbital periods shorter than 4 yr. From this subsetof stars, we determine that fewer than 3% of stars with-0.5<[Fe/H]<0.0 have Doppler-detected planets. Above solarmetallicity, there is a smooth and rapid rise in the fraction of starswith planets. At [Fe/H]>+0.3 dex, 25% of observed stars have detectedgas giant planets. A power-law fit to these data relates the formationprobability for gas giant planets to the square of the number of metalatoms. High stellar metallicity also appears to be correlated with thepresence of multiple-planet systems and with the total detected planetmass. This data set was examined to better understand the origin of highmetallicity in stars with planets. None of the expected fossilsignatures of accretion are observed in stars with planets relative tothe general sample: (1) metallicity does not appear to increase as themass of the convective envelopes decreases, (2) subgiants with planetsdo not show dilution of metallicity, (3) no abundance variations for Na,Si, Ti, or Ni are found as a function of condensation temperature, and(4) no correlations between metallicity and orbital period oreccentricity could be identified. We conclude that stars with extrasolarplanets do not have an accretion signature that distinguishes them fromother stars; more likely, they are simply born in higher metallicitymolecular clouds.Based on observations obtained at Lick and Keck Observatories, operatedby the University of California, and the Anglo-Australian Observatories.
| Chromospherically Active Stars. XXV. HD 144110=EV Draconis, a Double-lined Dwarf Binary
New spectroscopic and photometric observations of HD 144110 have beenused to obtain an improved orbital element solution and determine somebasic properties of the system. This chromospherically active,double-lined spectroscopic binary has an orbital period of 1.6714012days and a circular orbit. We classify the components as G5 V and K0 Vand suggest that they are slightly metal-rich. The photometricobservations indicate that the rotation of HD 144110 is synchronous withthe orbital period. Despite the short orbital period, no evidence ofeclipses is seen in our photometry.
| HD 8801: A Unique Single Am Star with γ Doradus and δ Scuti Pulsations
We have discovered the first example of a star pulsating intrinsicallywith both γ Doradus and δ Scuti frequencies. The star, HD8801, is an Am metallic-line star that appears to be single. Since thevast majority of Am stars are members of binary systems with periodsless than 1000 days and also do not pulsate, HD 8801 possesses a veryunusual, if not unique, combination of physical properties. Ourphotometry, acquired with an automatic telescope at FairbornObservatory, resolves six independent pulsation periods between 0.048and 0.404 days. The two longest periods lie within the range of γDor variables, while the four shorter periods are within the range ofδ Sct stars. Eleven radial velocities, obtained over an 11 monthperiod, have a mean of 0.8+/-0.3 km s-1, providing noevidence for a spectroscopic companion. The star is on the main sequenceand lies within both the γ Dor and δ Sct instability strips.Pulsation constants computed for the six periods agree with pulsationconstants computed for other γ Dor and δ Sct variables. HD8801 is also the first confirmed case of a metallic-line star pulsatingwith γ Dor frequencies. Its projected rotational velocity of 55 kms-1 is typical for Am stars, which, as a group, rotate moreslowly than normal A stars. HD 8801's slow rotation compared to normal Astars does not appear to arise from either a binary companion orevolutionary expansion and thus remains a puzzle. The coexistence ofmetallicism and pulsation in several main-sequence stars near the rededge of the δ Sct strip contradicts recent models that predictpulsations only in more evolved stars.
| Chromospherically Active Stars. XXIV. The Giant, Single-lined Binaries HD 37824, HD 181809, and HD 217188
We have obtained spectroscopy and photometry of three chromosphericallyactive, single-lined spectroscopic binaries, HD 37824 (V1149 Ori), HD181809 (V4138 Sgr), and HD 217188 (AZ Psc). HD 37824 has a circularorbit with a period of 53.57 days. Its primary is a K0 III star, whilethe secondary is likely a G or K dwarf. HD 181809 has an orbit with aperiod of 13.04667 days and a low eccentricity of 0.040. The primary hasa spectral type of K0 III-IV, and its secondary is probably an M dwarf.The orbit of HD 217188 has a period of 47.1209 days and a moderatelyhigh eccentricity of 0.470. The spectral type of the primary is K0 III,while the secondary is likely an M dwarf. All three systems areestimated to have near solar iron abundances. Photometric observationsspanning 15-16 years for all three stars yield mean photometric periodsof 53.12, 59.85, and 90.89 days for HD 37824, HD 181809, and HD 217188,respectively. Thus, HD 37824 is rotating synchronously with the orbitalperiod, while HD 181809 and HD 217188 are both rotating considerablyslower than synchronously. All three stars show long-term variations inmean brightness and photometric amplitude, but no correlations areobserved between the seasonal mean brightness, photometric amplitude,and seasonal photometric period in any of the stars. No clear evidencefor long-term periodic variations in any of these parameters is present.The circular orbit of HD 37824 and the synchronous rotation of its Kgiant argue that the star is in the core helium-burning phase of itsevolution. The giant components of HD 181809 and HD 217188 areasynchronous rotators, and both systems have eccentric orbits. Thus,those two stars are likely first-ascent giants.
| Metallicity of M dwarfs. I. A photometric calibration and the impact on the mass-luminosity relation at the bottom of the main sequence
We obtained high resolution ELODIE and CORALIE spectra for bothcomponents of 20 wide visual binaries composed of an F-, G- or K-dwarfprimary and an M-dwarf secondary. We analyse the well-understood spectraof the primaries to determine metallicities ([Fe/H]) for these 20systems, and hence for their M dwarf components. We pool thesemetallicities with determinations from the literature to obtain aprecise (±0.2 dex) photometric calibration of M dwarfmetallicities. This calibration represents a breakthrough in a fieldwhere discussions have had to remain largely qualitative, and it helpsus demonstrate that metallicity explains most of the large dispersion inthe empirical V-band mass-luminosity relation. We examine themetallicity of the two known M-dwarf planet-host stars, Gl876 (+0.02 dex) and Gl 436 (-0.03 dex), inthe context of preferential planet formation around metal-rich stars. Wefinally determine the metallicity of the 47 brightest single M dwarfs ina volume-limited sample, and compare the metallicity distributions ofsolar-type and M-dwarf stars in the solar neighbourhood.
| Abundance trends in kinematical groups of the Milky Way's disk
We have compiled a large catalogue of metallicities and abundance ratiosfrom the literature in order to investigate abundance trends of severalalpha and iron peak elements in the thin disk and the thick disk of theGalaxy. The catalogue includes 743 stars with abundances of Fe, O, Mg,Ca, Ti, Si, Na, Ni and Al in the metallicity range -1.30 < [Fe/H]< +0.50. We have checked that systematic differences betweenabundances measured in the different studies were lower than randomerrors before combining them. Accurate distances and proper motions fromHipparcos and radial velocities from several sources have been retreivedfor 639 stars and their velocities (U, V, W) and galactic orbits havebeen computed. Ages of 322 stars have been estimated with a Bayesianmethod of isochrone fitting. Two samples kinematically representative ofthe thin and thick disks have been selected, taking into account theHercules stream which is intermediate in kinematics, but with a probabledynamical origin. Our results show that the two disks are chemicallywell separated, they overlap greatly in metallicity and both showparallel decreasing alpha elements with increasing metallicity, in theinterval -0.80 < [Fe/H] < -0.30. The Mg enhancement with respectto Fe of the thick disk is measured to be 0.14 dex. An even largerenhancement is observed for Al. The thick disk is clearly older than thethin disk with tentative evidence of an AMR over 2-3 Gyr and a hiatus instar formation before the formation of the thin disk. We do not observea vertical gradient in the metallicity of the thick disk. The Herculesstream has properties similar to that of the thin disk, with a widerrange of metallicity. Metal-rich stars assigned to the thick disk andsuper-metal-rich stars assigned to the thin disk appear as outliers inall their properties.
| Time-spectra of chromospheric activity of old solar-type stars: detection of rotational signals from double wavelet analysis
We introduce a novel technique, called the double wavelet analysis(DWA), for the determination of stellar rotation periods from timeserial data. This first paper aims narrowly at the discussion,introduction and application of the DWA technique to records of surfacemagnetism in solar-type (relatively old) lower main sequence stars thatare obtained by the Mount Wilson Observatory (MWO) HK Project. Thetechnique takes a series of careful steps that seek to optimize waveletparameters and normalization schemes, ultimately allowing fine-tuned,arguably more accurate, estimates of rotation-modulated signals (with,e.g., periods of days to months) in records that contain longerperiodicities such as stellar magnetic activity cycles (with, e.g.,period of years). The apparent rotation periods estimated from the DWAtechnique are generally consistent with results from both ``first-pass''(i.e., ordinary) global wavelet spectrum and earlier classicalperiodogram analyses. But there are surprises as well. For example, therotation period of the ancient subdwarf Goombridge 1830 (HD 103095),previously identified as ~31 days, suggests under the DWAtechnique a significantly slower period of 60 days. DWA spectra alsogenerally reveal a shift in the cycle period toward high frequencies(hence shorter periods) compared to the first-pass wavelet spectrum. Forsolar-type stars analyzed here, the character of the DWA spectrum andslope of the first-pass global wavelet spectrum produce a classificationscheme that allows a star's record to be placed into one of threecategories.
| Lithium abundances of the local thin disc stars
Lithium abundances are presented for a sample of 181 nearby F and Gdwarfs with accurate Hipparcos parallaxes. The stars are on circularorbits about the Galactic centre and, hence, are identified as belongingto the thin disc. This sample is combined with two published surveys toprovide a catalogue of lithium abundances, metallicities ([Fe/H]),masses, and ages for 451 F-G dwarfs, almost all belonging to the thindisc. The lithium abundances are compared and contrasted with publishedlithium abundances for F and G stars in local open clusters. The fieldstars span a larger range in [Fe/H] than the clusters for which [Fe/H]~=0.0 +/- 0.2. The initial (i.e. interstellar) lithium abundance of thesolar neighbourhood, as derived from stars for which astration oflithium is believed to be unimportant, is traced from logɛ(Li) =2.2 at [Fe/H]=-1 to logɛ(Li) = 3.2 at +0.1. This form for theevolution is dependent on the assumption that astration of lithium isnegligible for the stars defining the relation. An argument is advancedthat this latter assumption may not be entirely correct, and, theevolution of lithium with [Fe/H] may be flatter than previouslysupposed. A sharp Hyades-like Li dip is not seen among the field starsand appears to be replaced by a large spread among lithium abundances ofstars more massive than the lower mass limit of the dip. Astration oflithium by stars of masses too low to participate in the Li dip isdiscussed. These stars show little to no spread in lithium abundance ata given [Fe/H] and mass.
| The Detached Solar-Type Binary CV Boo
Not Available
| A Spectral Atlas of F and G Stars
We present an atlas of a group of bright stars in the range of spectralclasses F--G and luminosity classes I--V. The spectra were obtainedwith spectral resolution R 15,000 within spectral region4500--6620 Å. Typical spectra of stars with different metallicity[Fe/H] are included. We also show the digital version of the spectraldata in FITS format.
| Stars of Extragalactic Origin in the Solar Neighborhood
For 77 main-sequence F-G stars in the solar neighborhood with publishediron, magnesium, and europium abundances determined from high-dispersionspectra and with the ages estimated from theoretical isochrones, wecalculated the spatial velocities using Hipparcos data and the Galacticorbital elements. A comparison with the orbital elements of the globularclusters that are known to have been accreted by our Galaxy in the pastreveals stars of extragalactic origin. We show that the abundance ratiosof r- and alpha-elements in all the accreted stars differ sharply fromthose in the stars that are genetically associated with the Galaxy.According to current theoretical models, europium is produced mainly inlow-mass type-II supernovae (SNe II), while magnesium is synthesized inlarge quantities in high-mass SN II progenitors. Since all the oldaccreted stars of our sample exhibit a significant Eu overabundancerelative to Mg, we conclude that the maximum masses of the SN IIprogenitors outside the Galaxy were much lower than those inside it. Onthe other hand, only a small number of young accreted stars exhibit lownegative ratios [Eu/Mg] < 0. This can be explained by the delay ofprimordial star formation and the explosions of high-mass SNe II in arelatively small part of extragalactic space. We provide evidence thatthe interstellar medium was weakly mixed at the early evolutionarystages of the Galaxy formed from a single protogalactic cloud, and thatthe maximum mass of the SN II progenitors increased in it with timesimultaneously with the increase in mean metallicity.
| Chromospheric Ca II Emission in Nearby F, G, K, and M Stars
We present chromospheric Ca II H and K activity measurements, rotationperiods, and ages for ~1200 F, G, K, and M type main-sequence stars from~18,000 archival spectra taken at Keck and Lick Observatories as a partof the California and Carnegie Planet Search Project. We have calibratedour chromospheric S-values against the Mount Wilson chromosphericactivity data. From these measurements we have calculated medianactivity levels and derived R'HK, stellar ages,and rotation periods from general parameterizations for 1228 stars,~1000 of which have no previously published S-values. We also presentprecise time series of activity measurements for these stars.Based on observations obtained at Lick Observatory, which is operated bythe University of California, and on observations obtained at the W. M.Keck Observatory, which is operated jointly by the University ofCalifornia and the California Institute of Technology. The KeckObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Synthetic Lick Indices and Detection of α-enhanced Stars. II. F, G, and K Stars in the -1.0 < [Fe/H] < +0.50 Range
We present an analysis of 402 F, G, and K solar neighborhood stars, withaccurate estimates of [Fe/H] in the range -1.0 to +0.5 dex, aimed at thedetection of α-enhanced stars and at the investigation of theirkinematical properties. The analysis is based on the comparison of 571sets of spectral indices in the Lick/IDS system, coming from fourdifferent observational data sets, with synthetic indices computed withsolar-scaled abundances and with α-element enhancement. We useselected combinations of indices to single out α-enhanced starswithout requiring previous knowledge of their main atmosphericparameters. By applying this approach to the total data set, we obtain alist of 60 bona fide α-enhanced stars and of 146 stars withsolar-scaled abundances. The properties of the detected α-enhancedand solar-scaled abundance stars with respect to their [Fe/H] values andkinematics are presented. A clear kinematic distinction betweensolar-scaled and α-enhanced stars was found, although a one-to-onecorrespondence to ``thin disk'' and ``thick disk'' components cannot besupported with the present data.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | わし座 |
| Right ascension: | 19h51m01.60s |
| Declination: | +10°24'56.0" |
| Apparent magnitude: | 5.11 |
| Distance: | 19.391 parsecs |
| Proper motion RA: | 241.1 |
| Proper motion Dec: | -135.9 |
| B-T magnitude: | 5.776 |
| V-T magnitude: | 5.185 |
Catalogs and designations:
|
