Contents
Images
Upload your image
DSS Images Other Images
Related articles
Dynamical phasing of Type II Cepheids
In this paper we examine the problems of phasing using light curves andoffer an alternate technique using the changes in acceleration toestablish the zero point. We give astrophysical justification as to whythis technique is useful and apply the technique to a selection of TypeII Cepheids. We then examine some limitations of the technique whichqualify its use.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| A W Roberts: the observations (paper 2).
Not Available
| J - K DENIS photometry of a VLTI-selected sample of bright southern stars
We present a photometric survey of bright southern stars carried outusing the DENIS instrument equipped with attenuating filters. Theobservations were carried out not using the survey mode of DENIS, butwith individual target pointings. This project was stimulated by theneed to obtain near-infrared photometry of stars to be used in earlycommissioning observations of the ESO Very Large TelescopeInterferometer, and in particular to establish a network of brightcalibrator sources.We stress that near-infrared photometry is peculiarly lacking for manybright stars. These stars are saturated in 2MASS as well as in regularDENIS observations. The only other observations available for brightinfrared stars are those of the Two Micron Sky Survey dating from overthirty years ago. These were restricted to declinations above≈-30°, and thus cover only about half of the sky accessible fromthe VLTI site.We note that the final 2MASS data release includes photometry of brightstars, obtained by means of point-spread function fitting. However, thismethod only achieves about 30% accuracy, which is not sufficient formost applications.In this work, we present photometry for over 600 stars, each with atleast one and up to eight measurements, in the J and K filters. Typicalaccuracy is at the level of 0\fm05 and 0\fm04 in the J and K_s bands,respectively.Based on observations collected at the European Southern Observatory, LaSilla.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/413/1037
| The Cepheids of Population II and Related Stars
The Type II Cepheids include most intrinsic variables with periodsbetween 1 and about 50 days, except for the classical Cepheids and theshortest semiregular variables of type M. The Type II Cepheids may bedivided in groups by period, such that the stars with periods beween 1and 5 days (BL Her class), 10-20 days (W Vir class), and greater than 20days (RV Tau class) have differing evolutionary histories. The chemicalcomposition of Type II Cepheids reflects the material they were madefrom as modified by their internal nuclear evolution and mixing.Finally, RV Tau stars are affected by mass loss by dust and speciesattached to the dust. The populations to which the various classes ofType II Cepheids are assigned constitute important clues to the originand evolution of the halo of our Galaxy and the dwarf spheroidal systemsfrom which at least part of the halo seems to have been accreted.
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/386/492, and from theauthors on CD-Rom.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Photoelectric Observations of Southern Cepheids in 2001
A total of 2097 photometric observations in the BVIc systemare presented for 117 Cepheids located in the southern hemisphere. Themain purpose of the photometry is to provide new epochs of maximumbrightness for studying Cepheid period changes, as well as to establishcurrent light elements for the Cepheids.
| 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
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| A photometric and spectroscopic study of the brightest northern Cepheids - III. A high-resolution view of Cepheid atmospheres
We present new high-resolution spectroscopic observations(λ/Δλ~40000) of 18 bright northern Cepheids carriedout at the David Dunlap Observatory in 1997. The measurements mainlyextend those presented in Paper I of this series, adding three morestars (AW Per, SV Vul, T Mon). The spectra were obtained in theyellow-red spectral region in the interval of 5900 and 6660Å,including strong lines of sodium D and Hα. New radial velocitiesdetermined with the cross-correlation technique and the bisectortechnique are presented. The new data are compared with those recentlypublished by several groups. We found systematic differences between thespectroscopic and CORAVEL-type measurements as large as1-3kms-1 in certain phases. We performed Baade-Wesselinkanalysis for CK Cam discovered by the Hipparcos satellite. The resultingradius is 31+/-1Rsolar, which is in very good agreement withrecent period-radius relation by Gieren, Moffett & Barnes III. It isshown that the systematic velocity differences do not affect theBaade-Wesselink radius more than 1per cent for CK Cam. Observationalpieces of evidence of possible velocity gradient affecting theindividual line profiles are studied. The full-width at half minimum(FWHM) of the metallic lines, similarly to the velocity differences,shows a very characteristic phase dependence, illustrating the effect ofglobal compression in the atmosphere. The smallest line widths alwaysoccur around the maximal radius, while the largest FWHM is associatedwith velocity reversal before the minimal radius. Three first overtonepulsators do not follow the general trend: the largest FWHM in SU Casand SZ Tau occurs after the smallest radius, during the expansion, whilein V1334 Cyg there are only barely visible FWHM variations. Thepossibility of a bright yellow companion of V1334 Cyg is brieflydiscussed. The observed line-profile asymmetries exceed the valuespredicted with a simple projection effect by a factor of 2-3. This couldbe associated with the velocity gradient, which is also supported by thedifferences between individual line velocities of different excitationpotentials.
| Period Changes in Population II Cepheids: TX Del and W Vir
We have used the Hipparcos database of epoch photometry to study thevariability of two Population II Cepheids: TX Del and W Vir. We haveconstructed (O-c) diagrams for these stars, using the new data and datafrom the literature. The period of TX Del is decreasing, at a ratewhich is consistent with evolutionary predictions. THe periodchange ofW Vir is uncertain because of the many recent gaps in the data of thisstar. We urge AAVSO visual and photoelectric observers to monitorPopulation II Cepheids more systematically, since amny of these starshave unstable periods, and at least one has an unstable amplitude.
| Fourier Analysis of Hipparcos Photometry of Cepheid Variables
Fourier parameters have been computed for 240 field Cepheids observed bythe Hipparcos satellite. We have identified three new PopulationIovertone Cepheids: V411Lac, V898 Cen and V572 Aql. We have comparedFourier progressions of Population I and Population II Cepheids. Thepossibility of using Fourier parameters to distinguish between the twotypes is discussed.
| I- and JHK-band photometry of classical Cepheids in the HIPPARCOS catalog
By correlating the \cite[Fernie et al. (1995)]{F95} electronic databaseon Cepheids with the ``resolved variable catalog'' of the hipparcosmission and the simbad catalog one finds that there are 280 Cepheids inthe hipparcos catalog. By removing W Vir stars (Type ii Cepheids),double-mode Cepheids, Cepheids with an unreliable solution in thehipparcos catalog, and stars without photometry, it turns out that thereare 248 classical Cepheids left, of which 32 are classified asfirst-overtone pulsators. For these stars the literature was searchedfor I-band and near-infrared data. Intensity-mean I-band photometry onthe Cousins system is derived for 189 stars, and intensity-mean JHK dataon the Carter system is presented for 69 stars.
| Spectroscopic survey of field Type II Cepheids
A sample of relatively bright, short- and intermediate-period (P=1-10d)Type II Cepheids in the Galactic field have been observedspectroscopically with an intermediate-resolution(lambda/Deltalambda=11000) spectrograph. The wavelength region was6500-6700A, including the Hα line and some photospheric ironlines. The signal-to-noise ratio (S/N) was usually between 50 and 100,depending on weather conditions and the brightness of target stars.Radial velocities were determined by cross-correlating the Cepheidspectra with those of selected IAU velocity standard stars having F-Gspectral types. The internal error of the velocity determination processwas calculated to be about 1 km s^-1. Hα emission and strong linesplitting were observed in BL Her during the expansion phase, but nosimilar phenomenon was detected in any other stars in this programme,except for AU Peg which has an unusual Hα line showing a PCygni-like profile. The velocity curve agrees well with recent CORAVELmeasurements. The velocity gradients in Cepheid atmospheres are studiedusing the Hα minus metallic velocities. Similar data are collectedfrom the literature. It seems that having large velocity differences(v_Hα-v_metal>40 km s^-1) is a characteristic feature of thevery short-period (P<1.5d) and longer period (P>10d) Cepheids.Between these period regions the Cepheid atmospheres exhibit smallervelocity differences. Most of the Type II Cepheids observed in thepresent study fall into this latter category. There might be a tendencyfor classical Cepheids of intermediate period to have larger maximumvelocity differences.
| Baade-Wesselink Radius Determination of Type II Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113.1833B&db_key=AST
| 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.
| Line Profiles of Cepheid Variables - Projection Factors and Metallic Cline Asymmetries
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.267..548A&db_key=AST
| Metallic-line and H-alpha radial velocities of seven southern Cepheids - A comparative analysis
New metallic-line and H-alpha velocity curves have been produced forseven southern Cepheids. A comprehensive comparison is made betweenthese data and those of previous observers and also with other Cepheidshaving similar periods. Use is made of the line bisector method toderive the velocity information and also to investigate asymmetries inthe H-alpha lines. These bisectors provide a consistent approach to theanalysis of spectroscopic data of Cepheids and will enable morequantitative studies of the structure of Cepheid atmospheres. This willin turn enable more reliable radii and hence distances to be deduced anda better use of Cepheids to establish the distances to nearby galaxies.
| UBV(RI)c observations for 13 bright Cepheids
Photometry in the UBV(RI)c system has been obtained for 13 of thebrightest Cepheids in the southern sky available to the new SydneyUniversity Stellar Interferometer. The stars observed were Eta Aq1, 1Car, U Car, AX Cir, Beta Dor, Zeta Gem, T Mon, Kappa Pav, U Sgr, W Sgr,X Sgr, Y Sgr, and AH Vel. The main purpose of the photometry is toprovide current epoch data for the phases of the variables, although forseveral of the stars these data are also the first in the (RI)c system.
| Fifth fundamental catalogue. Part 2: The FK5 extension - new fundamental stars
The mean positions and proper motions for 3117 new fundamental starsessentially in the magnitude range about 4.5 to 9.5 are given in thisFK5 extension. Mean apparent visual magnitude is 7.2 and is on average2.5 magnitudes fainter then the basic FK5 which has a mean magnitude of4.7. (The basic FK5 gives the mean positions and proper motions for theclassical 1535 fundamental stars). The following are discussed: theobservational material, reduction of observations, star selection, andthe system for the FK5 extension. An explanation and description of thecatalog are given. The catalog of 3117 fundamental stars for the equinoxand epoch J2000.0 and B1950.0 is presented. The parallaxes and radialvelocities for 22 extension stars with large forecasting effects aregiven. Catalogs used in the compilation of the FK5 fundamental catalogare listed.
| The System of Equivalent Widths of FeI-Absorption Lines for Determining Regional Temperatures in Physical Variable Stars
Not Available
| Color Excesses on a Uniform Scale for 328 Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990ApJS...72..153F&db_key=AST
| The structure of the Cepheid instability strip
About 100 classical Cepheids having color excesses on a homogeneoussystem with standard errors of 0.02 or less mag are used with theFeast-Walker period-luminosity-color relation to study the distributionof such stars in the instability strip. It is found that mean (B-V)magis a better indicator of mean effective temperature than is mean B(i) -mean V(i)(i). The blue edge of the color-magnitude distribution isconsistent with the theoretical blue edge for Y = 0.28 and Z = 0.02.Although the highest amplitude stars are found near the center of theperiod-color array, high- and low-amplitude stars can intermingle, andboth kinds are to be found near the edges of the distribution. The sameis true on the C-M array. Finally, it is pointed out that the Cepheidsdo not populate the instability strip uniformly if the red edge is takento be parallel to the theoretical blue edge. Rather, the localinstability region runs as a parallelogram in the C-M array from thetheoretical blue edge upward and to the red.
| The magnetic field of pulsating stars
The physical values determining variations in magnetic field intensityin pulsating stars are analyzed to obtain a constant R describing therelations between the amplitude of magnetic field intensity,semiamplitude of radial velocity variation, and the effectivetemperature of the envelope. Calculations for several types of pulsatingstars are performed to validate the constant. The formula is used toestimate the probable amplitude of the field intensity variation of astar from values for the semiamplitude of radial velocity variation andthe effective temperature of the envelope.
| S-process deficiencies in low-mass supergiant variables
Abundance analyses of four low-mass supergiant variable stars and twoPopulation I Cepheids have been carried out. The Population I Cepheidsshow normal, solar element ratios, and the low-mass variables showmetallicities ranging from solar down to (Fe/H) values typical ofthick-disk and, in a few cases, of halo stars. Most low-mass variablesshow a systematic underabundance of the heavy s- and r-process elements.The heavy-element underabundances correlate with second ionizationpotential in a manner suggesting that they are a non-LTE phenomenonarising from overionization by Lyman-continuum photons. Several low-massvariables, including RU Cen and V553 Cen, show carbon enhancements andsolar s-process abundances. Relative to the majority of the type IIvariables, these stars are s-process enhanced, and it is argued thatthey are related to the Ba II and CH stars.
| The Binary Type II Cepheids IX CAS and TX Del
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989AJ.....98..981H&db_key=AST
| Some Errors Detected in Three Catalogues
Not Available
| s-Process Deficiencies in Post-AGB Stars
Not Available
| On the (B-V) colors of the bright stars
The possible causes of the dispersion of (B-V) colors of nearby stars inthe Bright Star Catalog are investigated. The distribution of (B-V)colors is presented for the entire range of spectral classes.Explanations for the dispersion in terms of a nonuniform distribution ofinterstellar absorbing material and a variability of metallicity areaddressed. A new statistical model for reddening by interstellar dustclouds is developed. It is concluded that extinction by nonuniforminterstellar matter is an important contribution to the reddening ofnearby stars, and that a part of the dispersion of (B-V) colors of Kand, possibly, M giants may be due to some unidentified variableproperty of those stars.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Paon |
| Right ascension: | 18h56m57.00s |
| Declination: | -67°14'01.0" |
| Apparent magnitude: | 4.44 |
| Distance: | 166.667 parsecs |
| Proper motion RA: | -7.3 |
| Proper motion Dec: | 14.1 |
| B-T magnitude: | 5.22 |
| V-T magnitude: | 4.439 |
Catalogs and designations:
|
