Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
The Pul-3 catalogue of 58483 stars in the Tycho-2 system
A catalogue of positions and proper motions of 58483 stars (Pul-3) hasbeen constructed at the Pulkovo observatory. The Pul-3 is based on theresults of measurements of photographic plates with galaxies (Deutsch'splan). All plates were taken using the Pulkovo Normal Astrograph (thefirst epoch is in the 1950s and the second epoch is in the 1970s).The Pul-3 catalogue contains stars of mainly 12 to 16.5 mag in 146fields with galaxies in the declination zone from -5o to+85o. The Tycho-2 has been used as a reference catalogue.The mean epoch of the Pul-3 is 1963.25. The internal positional accuracyof the Pul-3 catalogue at the mean epoch of observations is ±80mas. The accuracy of the proper motions is mostly within ±3mas/yr to ±12 mas/yr. Comparisons of the Pul-3 with Tycho-2 andARIHIP have been done at the mean epoch of the Pul-3. The Pul-3 externalpositional accuracy relative to Tycho-2 is ±150 mas.The catalogue is 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/418/357
| Doppler imaging of stellar surface structure. XX. The rapidly-rotating single K2-giant HD 31993 = V1192 Orionis
We present two Doppler images from two consecutive stellar rotations ofthe single K2-giant HD 31993. Each Doppler image is reconstructed fromspectra obtained within a single stellar rotation. With its 25-dayrotational period and a radius of ~18 solar radii, HD 31993 isconsidered a very rapidly rotating star and thus allows the applicationof the Doppler-imaging technique, despite the unusually long period. Allmaps reveal 7 isolated, predominantly low-latitude spots with atemperature difference, photosphere minus spot, of just ~200 K. No polarspot or high-latitude activity above, say, +60° is seen. A largewarm feature is detected at high latitude and is believed to be real.These spots act as tracers for a cross correlation analysis and yield aclear signature of anti-solar differential surface rotation, i.e. thepolar regions rotating faster than the equator, with alpha =0.125+/-0.05 corresponding to a lap time of ~200 days. A detailed parameterstudy is carried out to verify the reality of the HD 31993 maps.
| Doppler images of starspots
I present a literature survey of the currently available Doppler imagesof cool stars. The 65 individual stars with Doppler images consist of 29single stars and 36 components in close binaries. Out of the total, 31were observed only once but 12 stars are (or were) being monitored foryears. Each image for each star is identified with the time when it wasobserved, whether photometry was used in the imaging, the inclination ofthe stellar rotation axis, the vsin i, the stellar rotation period, andwhether a polar spot and/or a high-latitude or low-latitude spot wasseen. The type of variable star and its M-K spectral classification isalso listed to identify the evolutionary status. The sample consists of3 classical T Tauri stars, 8 weak-lined T Tauri's, 27 main-sequencestars, 9 subgiants, and 18 giants. The total number of Doppler images is245 as of June 2002.
| Measuring starspots on magnetically active stars with the VLTI
We present feasibility studies to directly image stellar surfacefeatures, which are caused by magnetic activity, with the Very LargeTelescope Interferometer (VLTI). We concentrate on late typemagnetically active stars, for which the distribution of starspots onthe surface has been inferred from photometric and spectroscopic imaginganalysis. The study of the surface spot evolution during consecutiverotation cycles will allow first direct measurements (apart from theSun) of differential rotation which is the central ingredient ofmagnetic dynamo processes. The VLTI will provide baselines of up to 200m, and two scientific instruments for interferometric studies at near-and mid-infrared wavelengths. Imaging capabilities will be made possibleby closure-phase techniques. We conclude that a realistically modeledcool surface spot can be detected on stars with angular diametersexceeding ~ 2 mas using the VLTI with the first generation instrumentAMBER. The spot parameters can then be derived with reasonable accuracy.We discuss that the lack of knowledge of magnetically active stars ofthe required angular size, especially in the southern hemisphere, is acurrent limitation for VLTI observations of these surface features.
| Doppler imaging of stellar surface structure. XV. A possible detection of differential rotation and local meridional flows on the rapidly-rotating giant HD 218153 = KU Pegasi
Time-resolved Doppler images of the rapidly rotating, but long-period(25 days), giant KU Pegasi show several cool low-to-medium latitudespots as well as an asymmetric polar feature. The average spottemperature is about 700 K below the photospheric temperature of 4700 K.KU Peg is one of the most massive, and currently the most evolved,late-type star with a Doppler image. We obtained two independent imagesfrom two consecutive stellar rotations covering 50 nights with a totalof 43 spectra. From a cross-correlation analysis of the two maps, wedetect systematic longitudinal and latitudinal shifts that wetentatively interpret as latitude-dependent differential rotation andlocal meridional flows, respectively. The differential-rotation patternis more complex than on the Sun, but on average in the sense that thepoles rotate slower than the stellar equator, i.e. in the same directionand also of the same order than on the Sun. The latitudinal shifts areof the order of 0.4° day-1 towards the stellar pole andoccur at longitudes of around 40° and 330°. The residual{Hα } profiles show a stationary emission component at restwavelength and a blue-shifted absorption. The latter suggests an outwardpointed velocity field with a flow velocity of approximately 35 kms-1.
| Doppler imaging of stellar surface structure. XIII. The flaring RS CVn-binary HD 291095 = V1355 Orionis
We present the first Doppler images of the newly discovered RS CVnbinary HD 291095. The star is a synchronuously rotating subgiant in a4-day spectroscopic binary with an unseen companion and is particularlyinteresting because it is one of the few evolved stars that show largeflares. Three consecutive years of moderate-resolution KPNO spectra andcontinuous VI and by photometry with our APTs reveal a large, cool, andlong-living asymmetric polar spot. Its temperature is approximately 1100K below the average photospheric temperature. Several low latitude andeven equatorial spots were evident at the same time. We interpret thislatitudinal spot bimodality to be due to a combination of polewardmeridional circulation and more frequent magnetic reconnections near thepole than near the equator. During the 1998 Doppler-imagingobservations, a strong flare in Hα was detected which coincidedwith a meridian passage of the most asymmetric part of the polar spot.We estimate a total flare energy of 5x1034 erg typical forflares on very active RS CVn systems. No photospheric heating is evidentin our surface maps from optically thin spectral lines of varioustemperature sensitivities.
| Doppler imaging of stellar surface structure. XII. Rapid spot changes on the RS CVn binary V711 Tauri = HR 1099
We present a time series of Doppler images of the RS CVn binary V711Tauri from spectra taken during 57 consecutive nights in November andDecember 1996. VRI-band APT photometry throughout the entire observingseason is used to support the Doppler imaging. A set of altogether 37overlapping images from the Ca i-6439 line allows us to trace thelatitudinal and longitudinal migration of individual starspots and theirmorphological evolution. We confirm the poleward migration scenariodiscovered by Vogt & Hatzes (\cite{vog:hat}) and obtain an averagelatitudinal migration rate of +0.41+/-0.23 (rms) °/day. Of the fivespots detected, one was migrating clockwise and one counter clockwisewith respect to the orbital period. One feature possibly changed itsdirection of migration. The two dominating polar features remained attheir respective longitudes. Therefore, we are unable to fully attributethe poleward migration to differential rotation and suggest that acombination of differential rotation, meridional circulation, and localcrosstalk between starspots causes the observed migration pattern. Forone low-latitude spot, the latitudinal migration was briefly interruptedand seen to reverse before it resumed its poleward migration. Wepossibly witnessed the merging of two spots after they got too close toeach other. One spot became significantly cooler shortly before itmerged with the bigger and already cooler polar spot, suggesting thatsome flux exchange took place likely due to a partial reconnection oftheir magnetic field lines. The polar spot appeared in our images as anon-axisymmetric feature barely covering the actual stellar rotationpole and was not a cap-like feature as seen in several previous maps.Relative spot temperatures varied between 400 K for the weakest featuresand 1100 K for the main polar spot.
| Rapidly oscillating M giant stars?
The Hipparcos mission discovered a few dozen M giant stars with periodsP shorter than 10d. Similar stars may be found in other large data basesof new variables (e.g., OGLE). The three possible sources of themagnitude variations - pulsation, starspots and ellipsoidal deformation- are discussed in general terms. The parallaxes and V-I colour indicesare used to calculate radii and temperatures for all M giant variableswith P<100d. Masses are estimated from the positions of the stars ina Hertzsprung-Russell (HR) diagram, using evolutionary tracks. Usingthese data, it is shown that starspots can be ruled out as a variabilitymechanism in almost all cases, and ellipsoidal variations in about halfof the stars. Pulsation in very high-overtone modes appears to be theonly viable explanation for the stars with P<10d. Many of the starsmay be multiperiodic. IRAS data are used to deduce information aboutreddening and circumstellar dust. The apparently low level of mass-loss,as well as the kinematics and the spatial distribution of the stars,indicates that they are from a relatively young (i.e., thin disc) giantstar population.
| Starspot photometry with robotic telescopes. UBV(RI)_C and by light curves of 47 active stars in 1996/97
We present continuous multicolor photometry for 47 stars from October1996 through June 1997. Altogether, 7073 V(RI)_c, UBV, and by datapoints, each the average of three individual readings, were acquiredwith three automatic photoelectric telescopes (APTs) at FairbornObservatory in southern Arizona. Most of our targets arechromospherically active single and binary stars of spectral type G to Kbut there are also four pre-main-sequence objects and three pulsatingstars in our sample. The light variability is generally due torotational modulation of an asymmetrically spotted stellar surface andtherefore precise rotational periods and their seasonal variations aredetermined from Fourier analysis. We also report on photometricvariations of gamma CrB (A0V) with a period of 0.44534 days. All dataare available in numerical form. All data are available from CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Doppler imaging of stellar surface structure. X. The FK Comae-type star HD 199178 = V 1794 Cygni
Doppler imaging is used to derive the surface temperature distributionof the FK Comae star HD 199178 for five observing epochs between 1988and 1997. Our maps are mainly based on Ca i 6439-Ä line profilesand simultaneous and contemporary BV and VI photometry. All images of HD199178 are characterized by a large polar spot and several low-latitudespots with an average surface temperature difference, photosphere minusspots, of 710+/-260(rms) K for the equatorial spots, ~1700 K for thepolar spot, and 1300+/-300(rms) K for the polar-spot appendages. Thelifetime of some of the low-latitude spots was found to be as short asone month or even less. The lifetime of the polar spot and most of itsvery cool appendages must exceed the time of our observations, i.e. 9years or approximately 1000 stellar rotations, and could be as long as12 years since its discovery by Vogt in 1985. Two consecutive Dopplermaps in 1989 show no evidence for differential surface rotation, nor isthere substantial evidence for the existence of active longitudes in anyof our five images. Instead, we suspect that most of the timevariability of the surface features on HD 199178 is short term andpossibly chaotic in origin. We conclude that spot lifetimes estimatedfrom the timing of light-curve minima could lead to grosslyoverestimated lifetimes of individual spots. With the aid of our opticalspectra and the Hipparcos parallax, we redetermine the absolute stellarparameters of HD 199178 and confirm it to be a single G5III-IV star andfind 1.65 M_sun and 11 L_sun with T_eff~ 5450 K, log g=2.5, and solarabundances.
| Doppler imaging of stellar surface structure. VIII. The effectively single and rapidly-rotating G8-giant HD 51066 = CM Camelopardalis
We present first Doppler images of HD 51066 from observations in 1994,1995, 1996 and 1997, and find evidence for a vanishing polar spot inaccordance with the system's long-term brightness increase. Severalsmall spots with Delta T~500 K appear also at low latitudes. Ourcross-correlation maps indicate a latitude-dependent phase-shift patternbetween annual maps. New and continuous BVRI photometry from 1996 to1998 is presented and suggest a photometric period of 16.053+/-0.004days, that we interpret to be the stellar rotation period. Additionaloptical spectroscopy and the Hipparcos data are used to obtain absolutestellar parameters for HD 51066. A comparison with evolutionary tracksand the assumption of angular-momentum and magnetic-flux conservationsuggest that the main-sequence progenitor was a very rapidly-rotating Bpstar with a several kiloGauß\ magnetic field. We also examine theHα line profiles in this star and find some evidence that itsequivalent width is modulated with the stellar rotation period in phasewith the photospheric starspots. Our radial velocities indicate that HD51066 is likely a long-period (~10 yrs) spectroscopic binary and apreliminary orbit is presented. We emphasize that HD 51066 is aninteresting target for studies of evolutionary angular-momentum lossbecause it is effectively single, significantly evolved but stillrapidly rotating.
| HIPPARCOS distances of X-ray selected stars: implications on their nature as stellar population.
We present the parallaxes, measured by Hipparcos, for a sample of X-rayselected stars. The stars belong to the stellar sample of the EinsteinExtended Medium Sensitivity Survey. They are all at galactic latitude|b|>20deg, and are generally far away from known star formingregions. Several of these stars show lithium abundance and activitylevel typical of very young stars with ages comparable to that of thePleiades. We show that the majority of our sample stars are on the mainsequence, with only =~20% being giants. We do not find a significantpresence of pre-main sequence stars in our sample, notwithstanding thefact that some of our stars have a considerable lithium abundance,showing that the stars observed are most likely young and activemain-sequence objects.
| Rotational Velocities of Late-Type Stars
A calibration based on the results of Gray has been used to determineprojected rotational velocities for 133 bright stars with spectral typesof F, G, or K, most of which appear in {\it The Bright Star Catalogue}.The vast majority have {\it v} sin {\it i} $\leq$ 10 km s$^{-1}$ and,thus, are slow rotators. With the new calibration, projected rotationalvelocities have been determined for a sample of 111 late-type stars,most of which are chromospherically active. Some of the stars have hadtheir rotational velocities measured for the first time. (SECTION:Stars)
| The 73rd Name-List of Variable Stars
Not Available
| GPM1 - a catalog of absolute proper motions of stars with respect to galaxies
The description of the first version of the General Compiled Catalogueof Absolute Proper Motions (GPM1) for a sample of HIPPARCOS stars,derived with respect to galaxies within the plan called Catalogue ofFaint Stars (KSZ, Deutch 1952), is presented. The principal aim of theGPM1 construction was to provide absolute proper motions of stars todetermine the rotation of the HIPPARCOS system. The GPM1 cataloguecontains 977 HIPPARCOS Input Catalogue stars with V magnitudes $5^m -11^m in 180 fields north of -25 degrees of declination. The accuracy ofthe proper motions is 8 mas/yr (milliarcseconds per year). Comparison ofproper motions of GPM1 with those of the PPM and ACRS was performed andanalyzed with respect to systematic errors caused by spurious rotationof the FK5 system. The standard errors show that the rotation may bedetermined with an accuracy better than 1 mas/yr. Catalog is onlyavailable in electronic form at the CDS via anonymous ftpcdsarc.u-strasbg.fr or ftp 130.79.128.5.
| GPM - compiled catalogue of absolute proper motions of stars in selected areas of sky with galaxies.
Not Available
| An Automated Search for Variability in Chromospherically Active Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2926H&db_key=AST
| The Einstein Extended Medium-Sensitivity Survey Second Epoch: Results for the Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..701F&db_key=AST
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Chromospheric activity in G and K giants: the spectroscopic data base
I present high-resolution CCD spectra of CaII H and K emission lines of59 evolved stars of spectral type G and K and luminosity Class III,III-IV, and IV. This includes active stars like RS CVn binaries but alsoactive and inactive single stars. Most of the objects were observed forthe first time and several were discovered to be chromosphericallyactive. Spectra for ten stars of luminosity Class V are also given.
| Chromospheric activity in G and K giants and their rotation-activity relation
We obtained high-resolution CCD spectra of Ca II H and K emission linesof 59 evolved stars of spectral type G and K and luminosity class III,III-IV, and IV. Our sample includes active stars like RS CVn binariesbut also active and inactive single stars. Whenever possible wedetermine absolute emission line surface fluxes and use them,supplemented by previously published fluxes from high-resolutionspectra, to quantify the rotation-activity relation for evolved stars.We find that the Ca II surface fluxes from evolved stars scale linearlywith stellar rotational velocity and that the flux from the cooler starsdepends stronger upon rotation than the flux from the hotter stars, inagreement with previous findings for main-sequence stars. However, largescatter indicates that rotational velocity might not be the onlyrelevant parameter. We also present some evidence for the existence of a'basal' flux for evolved stars that scales approximately with the eightpower of the effective surface temperature.
| The 71st Name-List of Variable Stars
Not Available
| The Einstein Observatory Extended Medium-Sensitivity Survey. II - The optical identifications
The optical identifications are presented of the Einstein ExtendedMedium-Sensitivity Survey (EMSS), including the methodology used tooptically identify the EMSS sources and the uncertainties involved withthat process. The optical properties of the classes of X-ray, optical,and radio data for each of the identified and, as yet, unidentifiedsources of the survey are described. A new class of X-ray emitters,cooling flow galaxies, is proposed. The criteria used to determinewhether the proposed optical counterpart to the X-ray source is aplausible identification are described. Plausibility is based on theoptical classification of the counterpart, e.g., AGN, cluster, G star,and the X-ray-to-optical flux ratios previously observed for theseclasses of X-ray emitters. Two independent schemes of opticalclassification of the counterparts are used to check the plausibility ofthese identifications; one is based on moderate-resolution opticalspectroscopy, and the other, on inferred X-ray luminosity and theoverall energy distribution.
| The Einstein Observatory Extended Medium-Sensitivity Survey. I - X-ray data and analysis
This paper presents the results of the analysis of the X-ray data andthe optical identification for the Einstein Observatory ExtendedMedium-Sensitivity Survey (EMSS). The survey consists of 835serendipitous sources detected at or above 4 times the rms level in 1435imaging proportional counter fields with centers located away from theGalactic plane. Their limiting sensitivities are about (5-300) x 10 tothe -14th ergs/sq cm sec in the 0.3-3.5-keV energy band. A total area of778 square deg of the high-Galactic-latitude sky has been covered. Thedata have been analyzed using the REV1 processing system, which takesinto account the nonuniformities of the detector. The resulting EMSScatalog of X-ray sources is a flux-limited and homogeneous sample ofastronomical objects that can be used for statistical studies.
| The relation between X-ray emission and rotation in late-type stars from the perspective of X-ray selection
An X-ray-selected sample of 128 late-type (F-M) stars analyzed. Thesestars were identified as optical counterparts to serendipitous X-raydetections made by the Einstein Observatory Extended Medium SensitivitySurvey. Once identified as X-ray sources, the sample was followed up byan extensive program of optical observations, including high-resolutionand low-resolution spectroscopy and photometry. Spectral types,luminosity classes, distances, X-ray luminosities, projected rotationrates (v sin i), radial velocities, and binary status have beendetermined for the sample.
| Photographic magnitudes of stars brighter than 7m.75 between +75° and +80° declination (Errata: 11 270)
Not Available
| Yerkes actinometry. Zone +73deg to +90deg.
Not Available
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Zsiráf |
| Rektaszcenzió: | 07h04m15.05s |
| Deklináció: | +75°24'40.6" |
| Vizuális fényesség: | 7.003 |
| Távolság: | 275.482 parszek |
| RA sajátmozgás: | -8 |
| Dec sajátmozgás: | -7.4 |
| B-T magnitude: | 8.179 |
| V-T magnitude: | 7.101 |
Katalógusok és elnevezések:
|
