Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
A Complicated Pulsation δ Scuti Variable in Praesepe: HD 74028
We report the pulsation characteristics of the δ Scuti star HD74028, a low-amplitude pulsator in the Praesepe cluster. Amplitudespectra of 126 hr of observations spanning 16 nights indicatemultiperiodic pulsation behavior. We identify three frequencies,f1=22.6652, f2=23.8505, and f3=20.5254cycles day-1, and find four additional candidate frequencies,f4=17.3060, f5=12.0643, f6=14.8160, andf7=17.1143 cycles day-1. This complicatedfrequency distribution requires an explanation that includes rotationalsplitting.
| Zero-Age Main Sequence in the HR Diagram of the Vilnius Photometric System
The zero-age main sequence for solar metallicity stars in the absolutemagnitude vs. color diagram of the Vilnius seven-color photometricsystem is determined. The calibration is based on the results ofphotoelectric photometry of stars in the Hyades, Pleiades and Praesepeopen clusters and the Ori OB1 association. A theoretical Victoria-Reginaisochrone, corresponding to an age of 10 million years, coincides wellwith the lower envelope of the unevolved main sequence.
| Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| Is Praesepe really different from the coeval Hyades cluster? The XMM-Newton view
The Praesepe open cluster represents a puzzle since it has about thesame age as the Hyades, and only slightly different metallicity, yetprevious ROSAT observations resulted in a detection rate of clustersources significantly lower than for the Hyades. We present a new 50ksec observation of Praesepe performed with the EPIC instrument on boardXMM-Newton, which resulted in the detection of ~ 200 sources, including48 cluster members. We detected all solar-type (F-G) stars in the fieldof view, ~ 90% of the K stars and ~ 70% of the M stars. We find thatthe distribution of X-ray luminosities of solar-type Praesepe members iscomparable to that of the Hyades, in contrast with the previous ROSATresults; however, the disagreement between the ROSAT and XMM-Newtonresults appears to be mostly due to X-ray faint Praesepe members fallingoutside the XMM-Newton field of view, while it is considerably reducedwhen considering only the subsample of stars in the ROSAT survey incommon with the present observation. The finding supports an earliersuggestion that Praesepe may be formed by two merged clusters ofdifferent age.
| δ Scuti stars and their related objects
δ Scuti stars are a group of stars located on or a little abovethe main sequence of H-R diagram with spectral type from A3 to F5. Theyare low amplitude single or multi period pulsators with period shorterthan 0.3 d. Within the same area there are several groups of variablesor special stars correlated with them, e.g., Dwarf Cepheids, γ Dorvariables, Blue Stragglers, Am stars, Ap stars, ROAp variables, λBoo variables and δ Del variables. In this paper a general reviewin this field, including the number of new variables discovered after1995, is presented. The most reliable period variation rates for all thehigh amplitude variables and several low amplitude variables are listed.Statistic shows the higher the rotation rate v sin i is, the lower thelight variation amplitude is. Thus within young open clusters highamplitude variables cannot be found. The amplitudes-periods distributionhave 3 peaks with the highest of 1.0 mag in V at 0.17 d in period. Forδ Scuti variables in stellar systems the shorter the averageperiod is, the lower the metallicity and the older the age of thestellar system are.
| delta Scuti stars in Praesepe. II. The STACC 1998 campaign - The spectroscopy
We present the results of a large international spectroscopic campaignon the delta Scuti star BN Cnc. Combiningobservations from five observatories taken over more than two weeks, wecalculate line indices of the Hα line. A line index is theintegrated line flux in a software filter divided by the continuum flux.We demonstrate that this can be used in combination with simultaneousphotometry to classify the oscillation modes. We recover all thefrequencies also found from photometry and assign likely modeidentifications, which differ slightly from previously published values,but are found to be consistent with simple models. The difference inidentification is found to have very little effect on the derivedluminosity and temperature.
| delta Scuti stars in Praesepe I. The STACC 1998 campaign - the photometry
We present the results of the multisite differential CCD photometry forthe two delta Scuti stars, BN and BV Cnc, in the open cluster Praesepe.The main objective was to identify the character of the pulsation modesin BN Cnc deriving their accurate periods, amplitudes and phases. Theseparameters are essential for the mode identification which uses combinedphotometric and spectroscopic data and is presented in the secondarticle. For BN Cnc, six pulsation modes with amplitudes above thedetection limit ( ~ 0.5 mmag) were detected. Using the same CCD framesit was possible to verify the presence of the four pulsation modes in BVCnc, the faintest of delta Scuti stars in Praesepe. It is shown that inthis very low-amplitude pulsator, substantial amplitude variations areseen between 1997 and 1998. Based in part on observations obtained atthe European Southern Observatory at La Silla, Chile (Application60D-0148).
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| delta Scuti and related stars: Analysis of the R00 Catalogue
We present a comprehensive analysis of the properties of the pulsatingdelta Scuti and related variables based mainly on the content of therecently published catalogue by Rodríguez et al.(\cite{retal00a}, hereafter R00). In particular, the primaryobservational properties such as visual amplitude, period and visualmagnitude and the contributions from the Hipparcos, OGLE and MACHOlong-term monitoring projects are examined. The membership of thesevariables in open clusters and multiple systems is also analyzed, withspecial attention given to the delta Scuti pulsators situated ineclipsing binary systems. The location of the delta Scuti variables inthe H-R diagram is discussed on the basis of HIPPARCOS parallaxes anduvbybeta photometry. New borders of the classical instability arepresented. In particular, the properties of the delta Scuti pulsatorswith nonsolar surface abundances (SX Phe, lambda Boo, rho Pup, delta Deland classical Am stars subgroups) are examined. The Hipparcos parallaxesshow that the available photometric uvbybeta absolute magnitudecalibrations by Crawford can be applied correctly to delta Scutivariables rotating faster than v sin i ~ 100 km s{-1} withnormal spectra. It is shown that systematic deviations exist for thephotometrically determined absolute magnitudes, which correlate with vsin i and delta m1. The photometric calibrations are found tofit the lambda Boo stars, but should not be used for the group ofevolved metallic-line A stars. The related gamma Dor variables and thepre-main-sequence delta Scuti variables are also discussed. Finally, thevariables catalogued with periods longer than 0fd 25 are examined on astar-by-star basis in order to assign them to the proper delta Scuti, RRLyrae or gamma Dor class. A search for massive, long-period delta Scutistars similar to the triple-mode variable AC And is also carried out.
| ICCD Speckle Observations of Binary Stars. XXIII. Measurements during 1982-1997 from Six Telescopes, with 14 New Orbits
We present 2017 observations of 1286 binary stars, observed by means ofspeckle interferometry using six telescopes over a 15 year period from1982 April to 1997 June. These measurements constitute the 23dinstallment in CHARA's speckle program at 2 to 4 m class telescopes andinclude the second major collection of measurements from the MountWilson 100 inch (2.5 m) Hooker Telescope. Orbital elements are alsopresented for 14 systems, seven of which have had no previouslypublished orbital analyses.
| A revised catalogue of delta Sct stars
An extensive and up-dated list of delta Sct stars is presented here.More than 500 papers, published during the last few years, have beenrevised and 341 new variables have been added to our last list, sixyears ago. This catalogue is intended to be a comprehensive review onthe observational characteristics of all the delta Sct stars known untilnow, including stars contained in earlier catalogues together with othernew discovered variables, covering information published until January2000. In summary, 636 variables, 1149 references and 182 individualnotes are presented in this new list. Tables 1 and 2 will be accessibleonly in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Binaries in the Praesepe and Coma Star Clusters and Their Implications for Binary Evolution
This completes a study of the evolution of binary systems in five openclusters of various ages. Among 21 stars observed in Praesepe, eight arefound or confirmed to be spectroscopic binaries and orbital elements arederived, while one more shows long-term binary motion. Among 18 starsobserved in the Coma Berenices cluster, five are found or confirmed tobe spectroscopic binaries and orbital elements are derived, while asixth has tentative elements. Among five clusters studied we searchedfor three expected evolutionary effects, namely an increase with age inthe mass ratios, a decrease with age of the binary periods, and anincrease in binary frequencies. We find that there is a progression (atthe 3 sigma level) from no binaries out of 10 with mass ratios greaterthan 0.5 in the youngest cluster (combined with the published resultsfor NGC 6193) to 25% such stars in the intermediate-age clusters to 43%such stars in these two oldest clusters. There is no evidence for anincrease in short-period binaries with age. And there is slight evidence(at the 1 sigma level) for an increase with age from 15% to 28% in thefraction of large-amplitude binaries. These results are mostlyconsistent with the idea that most binaries are formed or modified inthree-body interactions, and successive generations of formation anddisruptions tend to form binaries with larger mass ratios. However, partof the initial generation of binaries is probably primordial.
| Photometric parameters for rotating models of A- and F-type stars
We have computed the photometric magnitudes of rotatingatmospheres-based on the simple model of Collins-for a grid suitable formain-sequence and slightly evolved stars of spectral type A0 to F5. Agravity-darkening law valid for radiative and convective envelopes hasbeen considered. The general results are given as magnitude differencesbetween rotating and non-rotating copartners to allow for the use of anyphotometric calibration. A simple interpolation on these results givesthe photometric parameters for interior rotating models but we alsoindicate how they can be used to correct for the effect of rotation whenan investigation with non-rotating models is carried out. We illustratethe procedure with the interesting case of the Praesepe Cluster.
| Open clusters with Hipparcos. I. Mean astrometric parameters
New memberships, mean parallaxes and proper motions of all 9 openclusters closer than 300 pc (except the Hyades) and 9rich clusters between 300 and 500 pc have been computed using Hipparcosdata. Precisions, ranging from 0.2 to 0.5 mas for parallaxes and 0.1 to0.5 mas/yr for proper motions, are of great interest for calibratingphotometric parallaxes as well as for kinematical studies. Carefulinvestigations of possible biases have been performed and no evidence ofsignificant systematic errors on the mean cluster parallaxes has beenfound. The distances and proper motions of 32 more distant clusters,which may be used statistically, are also indicated. Based onobservations made with the ESA Hipparcos astrometry satellite
| Pulsation, binarity and close frequency spacing in $delta Scuti ta$ Scuti stars: BQ and BW Cancri. Results of the STEPHI VI campaign in Praesepe Cluster
New pulsation modes in two delta Scuti stars of Praesepe cluster, BQ andBW Cnc, have been detected during the STEPHI VI campaign in 1995. Inparticular, 3 frequencies for BQ Cnc and 9 frequencies for BW Cnc havebeen found above a 99% confidence level. The possibility of the presenceof a g-mode present in BQ Cnc is discussed, considering its binarity.The effect of mutual interference between very close detectedfrequencies in BW Cnc during the observations, is also considered. Thislast effect reveals the necessity of long-period observing runs, inorder to avoid its influence in the final number of detected modes. Insuch situation, studies of secular amplitude changes can be stronglyaffected.
| Photometry and asteroseismology of delta Scuti stars in Praesepe
We discuss observations and seismic analyses for three multi-periodicdelta Scuti stars in the Praesepe cluster: BU, BN and BV Cnc. For twostars (BU and BN Cnc) we re-analyse published photoelectric photometryand show that using statistical weights results in a dramatic reductionin the noise level. We detect seven frequencies in BU Cnc and eight inBN Cnc, with three of the latter being previously unknown. We alsopresent new time-series CCD observations of BN and BV Cnc thatsuccessfully demonstrate high-precision differential photometry onstrongly defocussed images. The observations show that BV Cnc is amulti-periodic variable, with at least four oscillation frequencies.Finally, we compare the observed oscillation frequencies in the threestars with models and derive luminosities, effective temperatures andmasses.
| The Age Range of Hyades Stars
On the basis of canonical models, the age of Hyades supercluster stars,whether in the Hyades and Praesepe clusters or the noncluster field,ranges from (5-6) x 10^8 to 10^9 yr. The difference between the parallaxderived from the supercluster motion and that obtained from Hipparcosobservations has a dispersion only twice that of the mean dispersion ofthe individual Hipparcos values. The supercluster appears not to containred giants on the first ascent of the red giant branch, but onlyasymptotic giant branch (``clump'') stars. The masses obtained forindividual components of binary stars in the supercluster show adispersion of less than 10% when compared with model predictions.
| Evolution of mass segregation in open clusters: some observational evidences
On the basis of the best available member list and duplicityinformation, we have studied the radial structure of Praesepe and of thevery young open cluster NGC 6231. We have found mass segregation amongthe cluster members and between binaries and single stars, which isexplained by the greater average mass of the multiple systems. However,the degree of mass segregation for stars between 1.5 and 2.3 M_sun isless pronounced in Praesepe than in the Pleiades. Furthermore, masssegregation is already present in the very young open cluster NGC 6231although this cluster is likely still not dynamically relaxed. Wediscuss the implications of these results and propose a qualitativescenario for the evolution of mass segregation in open clusters. InPraesepe the mass function of single stars and primaries appears to besignificantly different, like in the Pleiades. We observe an absence ofellipticity of the outer part of Praesepe. Tables 2 and 3 are availableonly in electronic form from the Strasbourg ftp server at 130.79.128.5
| Photoelectric photometry and period analysis of selected Delta Scuti stars in Praesepe
Photoelectric photometry of seven Delta Scuti stars in Praesepe wassecured. Three of them were observed simultaneously at observatorieslocated at different longitudes. Period analysis has been carried outfor each star with different computing packages and the results comparedto those in the literature. Their physical characteristics have beendetermined from the Stroemgren photometry and theoretical and empiricalcalibrations. The observations are available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.70.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Metal abundances of A-type stars in galactic clusters. II. Pleiades, Coma Berenices, Hyades, and Praesepe
A study of chemical composition for 23 A-type stars in four nearby openclusters (Pleiades, Coma, Hyades and Praesepe) has derived detailedabundances for Mg, Ca, Sc, Cr, Fe, and Ni from high resolutionspectroscopy. These results are discussed using the microscopicdiffusion model, which yields time-dependent element stratifications asin the case of Am stars. For the Pleiades, the youngest cluster, we findseveral atypical abundance patterns, which may be transient phases ofthe Am phenomenon. The members of the older clusters show globally moreclassical patterns. Based on observations collected at the Observatoirede Haute-Provence (France)
| ICCD Speckle Observations of Binary Stars. XVII. Measurements During 1993-1995 From the Mount Wilson 2.5-M Telescope.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1639H&db_key=AST
| ICCD Speckle Observations of Binary Stars. XVI. Measurements During 1982-1989 from the Perkins 1.8-M Telescope.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1623F&db_key=AST
| Spectrophotometry of 237 Stars in 7 Open Clusters
Spectrophotometry is presented for 237 stars in 7 nearby open clusters:Hyades, Pleiades, Alpha Persei, Praesepe, Coma Berenices, IC 4665, andM39. The observations were taken by Lee McDonald and David Bursteinusing the Wampler single-channel scanner on the Crossley 0.9m telescopeat Lick Observatory from July 1973 through December 1974. Sixteenbandpasses spanning the spectral range 3500 Angstroms to 7780 Angstromswere observed for each star, with bandwidths 32Angstroms, 48 Angstromsor 64 Angstroms. Data are standardized to the Hayes-Latham system tomutual accuracy of 0.016 mag per passband. The accuracy of thespectrophotometry is assessed in three ways on a star-by-star basis.First, comparisons are made with previously published spectrophotometryfor 19 stars observed in common. Second, (B-V) colors and uvby colorsare compared for 236 stars and 221 stars, respectively. Finally,comparsions are made for 200 main sequence stars to the spectralsynthesis models of Kurucz, fixing log g = 4.0 and [Fe/H] = 0.0, andonly varying effective temperature. The accuracy of tests using uvbycolors and the Kurucz models are shown to track each other closely,yielding an accuracy estimate (1 sigma ) of 0.01 mag for the 13 colorsformed from bandpasses longward of the Balmer jump, and 0.02 mag for the3 colors formed from the three bandpasses below the Balmer jump. Incontrast, larger scatter is found relative to the previously publishedspectrophotometry of Bohm-Vitense & Johnson (16 stars in common) andGunn & Stryker (3 stars). We also show that the scatter in the fitsof the spectrophotometric colors and the uvby filter colors is areasonable way to identify the observations of which specific stars areaccurate to 1 sigma , 2 sigma , .... As such, the residuals from boththe filter color fits and the Kurucz model fits are tabulated for eachstar where it was possible to make a comparison, so users of these datacan choose stars according to the accuracy of the data that isappropriate to their needs. The very good agreement between the modelsand these data verifies the accuracy of these data, and also verifiesthe usefulness of the Kurucz models to define spectrophotometry forstars in this temperature range (>5000 K). These data define accuratespectrophotometry of bright, open cluster stars that can be used as asecondary flux calibration for CCD-based spectrophotometric surveys.
| 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.
| High-precision study of proper motions and membership of 924 stars in the central region of Praesepe.
High-precision proper motions for 257 and 296 stars in a 90'x90' regioncentered on BD+20 2170 were obtained from seven plates taken with the40cm refractor (f=6895mm) at Zo-Se station of Shanghai Observatory withsix AC plates and the stellar positions in Russell's (1976) catalogue,respectively. Combining with the data given by Klein-Wassink (1927),Jones (1971), Artyukhina (1971), and Jones & Cudworth (1983), theseproper motions give a sample of 924 stars in the region mentioned above.With membership probabilities estimated by an improved maximumlikelihood method, a very good sample of 198 members is obtained withproper motion accuracies ranging from +/-0.2 to +/-5.0mas/yr, of which60 per cent are better than +/-1.0mas/yr, and the completeness nearlydown to B=15.5.
| Pulsating periods of HR 8851.
A total of 18 days of photometric observations on the newly discoveredδ Scuti star, HR 8851, in V band is presented. Frequency analysiswas carried out carefully on these data and a two frequency solution,3.57c/d and 4.28c/d was obtained. From uvbyβ photometry, thephysical parameters were estimated. Based on all the information we havegot, the evolutionary stage and possible pulsation modes of HR 8851 arediscussed.
| A catalogue of variable stars in the lower instability strip.
Identifications, positions, photometry, spectra, some pulsationalfeatures, other astrophysical parameters and literature for 302pulsating variable stars in the lower instability strip, near the ZAMS,are given. About 185 stars have near homogeneous photometric informationin the Stroemgren's uvby-β photometric system. Thiscatalogue/database covers information published until November 1993.
| Is Praesepe KW284 Actually a delta Scuti Star?
Not Available
| δ Scuti stars: a new revised list
An extensive and up to date list of δ Sct stars is presented. Thiscatalogue is intended to be a comprehensive review of observationalcharacteristics of all the δ Sct stars known until now, includingstars contained in earlier catalogues together with other new discoveredvariables, covering information published until November 1993. Globalinformation in the form of histograms and diagrams are also shown.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Yengec |
| Sað Açýklýk: | 08h40m20.14s |
| Yükselim: | +19°20'56.4" |
| Görünürdeki Parlaklýk: | 6.759 |
| Uzaklýk: | 148.148 parsek |
| özdevim Sað Açýklýk: | -34.7 |
| özdevim Yükselim: | -12 |
| B-T magnitude: | 7.077 |
| V-T magnitude: | 6.786 |
Kataloglar ve belirtme:
|
INHABITED SKY
