תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
An Analysis of the Shapes of Ultraviolet Extinction Curves. IV. Extinction without Standards
In this paper we present a new method for deriving UV through IRextinction curves, based on the use of stellar atmosphere models toprovide estimates of the intrinsic (i.e., unreddened) stellar spectralenergy distributions (SEDs), rather than unreddened (or lightlyreddened) standard stars. We show that this ``extinction withoutstandards'' technique greatly increases the accuracy of the derivedextinction curves and allows realistic estimations of the uncertainties.An additional benefit of the technique is that it simultaneouslydetermines the fundamental properties of the reddened stars themselves,making the procedure valuable for both stellar and interstellar studies.Given the physical limitations of the models we currently employ, thetechnique is limited to main-sequence and mildly evolved B stars.However, in principle, it can be adapted to any class of star for whichaccurate model SEDs are available and for which the signatures ofinterstellar reddening can be distinguished from those of the stellarparameters. We demonstrate how the extinction without standards curvesmake it possible to (1) study the uniformity of curves in localizedspatial regions with unprecedented precision, (2) determine therelationships between different aspects of curve morphology, (3) producehigh-quality extinction curves from low color excess sight lines, and(4) derive reliable extinction curves for mid to late B stars, therebyincreasing spatial coverage and allowing the study of extinction in openclusters and associations dominated by such stars. The application ofthis technique to the available database of UV through IR SEDs, and tofuture observations, will provide valuable constraints on the nature ofinterstellar grains and on the processes that modify them, and it willenhance our ability to remove the multiwavelength effects of extinctionfrom astronomical energy distributions.
| A Spectroscopic Search for λ Bootis and Other Peculiar A-Type Stars in Intermediate-Age Open Clusters
As part of our continuing search for peculiar A-type stars, especiallyλ Bootis stars, in open clusters of all ages, we have obtainedclassification spectra of 130 late B, A, and early F-type stars in 12intermediate-age open clusters, including NGC 1039, 2281, 2548, 6633,7039, 7063, 7092, and 7209, IC 4665, IC 4756, Stock 2, and Praesepe. Thespectra were obtained with resolutions of 1.8 and 3.6 Å on the 0.8m telescope of Appalachian State University and were classified on theMK system. Numerous classical Ap and Am stars were found among the 130,including two new Ap stars in NGC 7092. In addition, three emission-linestars and two candidate λ Bootis stars were found. Neither ofthese λ Bootis candidates turned out to be members of theirrespective clusters. Combined with 184 stars previously classified in 10other intermediate-age open clusters, also devoid of λ Bootisstars, a statistically significant null result is obtained. We discussthe implications of this null result for our understanding of theλ Bootis mechanism.
| 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
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| X-Ray Activity in the Open Cluster IC 4665
We present the results of a joint ROSAT High Resolution Imager (HRI) andoptical investigation of the open cluster IC 4665. The ROSAT datacontains detections for 28 stellar sources in the field, including 22cluster members and candidate members spanning the color range -0.18<= (B-V)0 <= 1.63 (~B3-M3). Upper limits are given for theremaining members (or candidate members) in the HRI field. Keck HIRESspectra have been obtained that yield radial and rotational velocitymeasures, respectively, for faint, low-mass candidate members locatedwithin the field of the ROSAT HRI observation. In addition, photometryof possible optical counterparts to previously uncataloged X-ray sourcesin the HRI field is presented. The trends in X-ray properties with B-Vcolor in IC 4665 are found to be quite similar to that for other, morenearby young clusters such as the Pleiades and alpha Persei. Inparticular a maximum in normalized X-ray luminosity of log (LX/Lbol) ~=-3 is observed, beginning in the color range of (B-V)0 = 0.7-0.8. Thisis similar to the corresponding color range among Pleiades members, inagreement with the earlier estimate by Prosser & Giampapa that theage of IC 4665 is similar to the age of the Pleiades. The correlation ofrotation and X-ray emission levels is consistent with that in otheryoung clusters. Among the high-mass stars in IC 4665, five B stars aredetected as X-ray sources. Of these, one is a spectroscopic binary whilethe remaining objects are apparently single stars. The level ofintrinsic X-ray emission observed in the rapidly rotating (v sin i >200 km s-1), single B stars is consistent with an origin due to shockheating of the ambient medium by radiatively driven, rotationallyenhanced winds. On the basis of these observations and the results forother clusters, we argue that observed levels of X-ray emission inhigh-mass stars of log (LX/Lbol) > -6.0 are likely due to intrinsicemission associated with the B star itself rather than emission from alate-type secondary. Finally, our results suggest that the initialangular momentum distributions and the subsequent evolution of rotation,LX, and (LX/Lbol) occur in practically identical fashions in clusterswith ages <~100 Myr.
| 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.
| UBV (RI)c observations of Johnson's standard sequence in IC 4665.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996MNRAS.282..313M&db_key=AST
| New Variable in Ophiuchus
Not Available
| ICCD speckle observations of binary stars. IX - A duplicity survey of the Pleiades, Praesepe, and IC 4665 clusters
Multiplicity of stars within clusters is a well-studied phenomenon.However, recent survey work done on the Hyades by Mason et al. (1993)would seem to indicate that even in the most often studied clusters,there may be binaries yet undiscovered. In order to expand the sample ofcluster binaries with potentially short-period visual orbits, a specklesurvey of 45 Pleiades, 54 Praesepe, and 22 IC 4665 bright stars (V isless than 10) for possible multiplicity was conducted at the KPNO 4 mMayall telescope between 1987 October and 1991 November. Of these, threenew binaries have been discovered: one in the Pleiades where the newcomponent may be spectroscopic, another in Praesepe which has beenconfirmed from examinations of archival observations and also has beenresolved by occultation, and the third in IC 4665. Continued study ofthese new binary stars could further refine the cluster distance modulias well as the cluster mass-luminosity relations.
| The open cluster IC 4665
The results of a combined astrometric, photometric, and spectroscopicprogram to identify members of the open cluster IC 4665 are presented.Numerous new proper motion/photometric candidate members and at least 23M dwarfs with H-alpha emission have been identified. A reanalysis of IC4665 age using different methods yields conflicting results ranging fromabout 3 X 10 exp 7 yr to the age of the Pleiades. This study provides alist of candidate cluster members in the intermediate and low-massregime of this cluster. Future spectroscopic observations of thesecandidates should eventually identify true cluster members.
| Reinvestigation of the binary frequency in the open cluster IC 4665
The radial velocities of 15 bright B3-A2 stars in the cluster IC 4665are measured using a CCD. Only four of the 15 stars are spectroscopicbinaries, giving a binary frequency of 27 percent. Four of the sixsharp-lined stars are binaries, and none of the more rapidly rotatingstars are binaries with K at least 10 km/s. Statistically, nearly all ofthe stars with low projected rotational velocities are slow rotators,and most are binaries; two of the four binaries may rotatesynchronously. In two of the four binaries, the mass ratios are near1.0, as would be expected for binary formation in three-bodyinteractions after many crossing times. The measured cluster velcoitydispersion is only 1.6 km/s, but most of that is still probably due tomeasuring errors.
| Observations that link infrared cirrus and ultraviolet extinction
Results are presented of UV extinction measurements of 17 stars in theopen cluster IC 4665 and of four stars in the open cluster NGC 1647,showing that the UV extinctions of the two clusters stars have differentproperties. Whereas the stars in NGC 1647 cluster are typical of generalinterstellar space, the stars in IC 4665 have a small 'linear' termwhich is typical of stars found near regions of active star formation.Using data from the IRAS satellite to study the emission by the'infrared cirrus' for each of the regions and to measure theI(60-micron)/I(100-micron) ratio for the two regions, it was found that,when the linear term component is present, it dominates the 100-microncirrus emission. When it is absent, the 100-micron emission is from therelatively hot particles that are responsible for the 60-micronemission. It is suggested that the 60-micron emitters are smallcarbonaceous grains that are major contributors to all parts of the UVextinction except the linear term.
| Early type high-velocity stars in the solar neighborhood. IV - Four-color and H-beta photometry
Results are presented from photometric obaservations in the Stromgrenuvby four-color and H-beta systems of early-type high-velocity stars inthe solar neighborhood. Several types of photometrically peculiar starsare selected on the basis of their Stromgren indices and areprovisionally identified as peculiar A stars, field horizontal-branchstars, metal-poor stars near the Population II and old-disk turnoffs,metal-poor blue stragglers, or metallic-line A stars. Numerousphotometrically normal stars were also found.
| V728 Herculis - an active W Ursae Majoris system of F spectral type
Observations made of the short-period eclipsing binary system V728 Herusing a photoelectric telescope on four nights in June 1988 at LowellObservatory are presented. Three times of minimum light were revealed byobservations covering the eclipse portions of the light curves. A periodstudy covering 80 years of observations indicates that a drastic periodincrease may have recently occurred, while indications such as apossible reversal of eclipse depths may suggest that V728 Her ismagnetically active. Standard magnitudes derived for V728 Her and forcomparison and check stars indicate that V728 Her is approximately ofspectral type F3 while the comparison and check stars are K type. Apreliminary light-curve solution indicates that the system consists oftwo nearly equal temperature components in the spectral class F3 to F4in contact with a substantial fillout of near 20 percent and a massratio of about 0.4. This degree of contact is supported by the positionof V728 Her on the period, color plane of Eggen. The period increase mayindicate a mass exchange from the secondary to the primary component ora catastrophic angular-momentum loss due to an episode of massivestellar wind expulsion along lines of a corotating magnetic field.
| Merged log of IUE observations.
Not Available
| B and V light curves of TY Bootis
The short-period eclipsing binary system TY Boo was observed on fiveconsecutive nights with facilities at Lowell Observatory. Theobservations covering the eclipse portions of the light curves yieldedfive epochs of minimum light. The light curves, defined by 348observations with the B filter and 353 with the V filter, are of the WUrsae Majoris type and are symmetric. The system becomes redder duringeach eclipse with a momentary dereddening at phase 0.0.
| Catalogue of Eclipsing and Spectroscopic Binary Stars in the Regions of Open Clusters
Not Available
| Photoelectric search for CP2-stars in open clusters. V - NGC 6281, NGC 6405, IC 4665
130 stars in the medium age clusters NGC 6281, NGC 6405, and IC 4665were observed by photoelectric photometry in the Delta a-system(Maitzen, 1976) in order to detect CP2-peculiarity by the presence ofthe lambda 5200 depression feature. No CP2-star was found in IC 4665,one in NGC 6281, and 3 in NGC 6405. Star No. 77 of NGC 6405 exhibits thestrongest lambda 5200 depression ever measured by this type ofphotometry. The (very small) reddening correction of the a-values isdiscussed and found to agree well with previous papers of this series.
| Discoveries on southern, red-sensitive objective-prism plates. IV Extension to higher latitudes
This fourth in a series of papers (MacConnel, (1978, 1979, 1981) listingnewly-found objects detected on Curtis Schmidt objective-prism platesextends the previous, 4500-sq deg coverage, confined to within 15 deg ofthe southern galactic plane, to higher galactic latitudes and to anadditional 3100 sq deg. The lists presented cover 107 non-banded H-alphaemission stars, 12 M-type H-alpha emission stars, five suspectedplanetary nebulae, 10 carbon stars, 121 S/MS stars, three M dwarfs, anda peculiar and previously unreported star.
| Relative radial velocities from objective prism spectra in the region of nine southern open star clusters and a star field at Eta Carinae
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&AS...41..245G&db_key=AST
| Spectral types in the open cluster IC 4665.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975PASP...87..849A&db_key=AST
| Evidence for a rotational reddening in early B-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975A&A....42..471M&db_key=AST
| IC 4665, a Cluster of Binaries
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972ApJ...171..259A&db_key=AST
| Four-color and H beta photometry for open clusters.8 IC 4665.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972AJ.....77..862C&db_key=AST
| Membership of the open cluster IC 4665.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&A....17..193S&db_key=AST
| A photometric study of the open cluster IC 4665
Not Available
| Rotational Velocities of Stars in IC 4665
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967ApJ...148..459A&db_key=AST
| Catalogue des étoiles mesurées dans le système photométrique de l'Observatoire de Genève
Not Available
| A photoelectric investigation of the galactic clusters IC 4665 and IC 4756
Not Available
| The Galactic Cluster IC 4665.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1964ApJ...139.1139A&db_key=AST
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | נושא הנחש |
| התרוממות ימנית: | 17h46m57.77s |
| סירוב: | +05°25'32.5" |
| גודל גלוי: | 8.846 |
| מרחק: | 1219.512 פארסק |
| תנועה נכונה: | -1.3 |
| תנועה נכונה: | -8.8 |
| B-T magnitude: | 8.979 |
| V-T magnitude: | 8.857 |
קטלוגים וכינוים:
|
