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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).
| Preparing the COROT space mission: Incidence and characterisation of pulsation in the lower instability strip
By pursuing the goal to find new variables in the COROT field-of-view wecharacterised a sample of stars located in the lower part of theinstability strip. Our sample is composed of stars belonging to the diskpopulation in the solar neighbourhood. We found that 23% of the starsdisplay multiperiodic light variability up to a few mmag in amplitude,i.e., easily detectable on a single night of photometry. uvbybetaphotometry fixed most of the variables in the middle of the instabilitystrip and high-resolution spectroscopy established that they have vsin i>100 km s-1. An analysis of the Rodríguez &Breger (\cite{Rodr01}) sample (delta Sct stars in the whole Galaxy)shows slightly different features, i.e., most delta Sct stars have a0.05-mag redder (b-y)0 index and lower vsin i values.Additional investigation in the open cluster NGC 6633 confirms the sameincidence of variability, i.e., around 20%. The wide variety ofpulsational behaviours of delta Sct stars (including unusual objectssuch as a variable beyond the blue edge or a rapidly rotatinghigh-amplitude pulsator) makes them very powerful asteroseismic tools tobe used by COROT. Being quite common among bright stars, delta Sctstars are suitable targets for optical observations from space.Based on observations collected at the S. Pedro Martír, SierraNevada, La Silla, Haute-Provence, South African and Roque de LosMuchachos observatories.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| On the Period-Luminosity-Colour-Metallicity relation and the pulsational characteristics of lambda Bootis type stars
Generally, chemical peculiarity found for stars on the upper mainsequence excludes delta Scuti type pulsation (e.g. Ap and Am stars), butfor the group of lambda Bootis stars it is just the opposite. This makesthem very interesting for asteroseismological investigations. The groupof lambda Bootis type stars comprises late B- to early F-type,Population I objects which are basically metal weak, in particular theFe group elements, but with the clear exception of C, N, O and S. Thepresent work is a continuation of the studies by Paunzen et al.(\cite{Pau97}, \cite{Pau98}), who presented first results on thepulsational characteristics of the lambda Bootis stars. Since then, wehave observed 22 additional objects; we found eight new pulsators andconfirmed another one. Furthermore, new spectroscopic data (Paunzen\cite{Pau01}) allowed us to sort out misidentified candidates and to addtrue members to the group. From 67 members of this group, only two arenot photometrically investigated yet which makes our analysis highlyrepresentative. We have compared our results on the pulsationalbehaviour of the lambda Bootis stars with those of a sample of deltaScuti type objects. We find that at least 70% of all lambda Bootis typestars inside the classical instability strip pulsate, and they do sowith high overtone modes (Q < 0.020 d). Only a few stars, if any,pulsate in the fundamental mode. Our photometric results are inexcellent agreement with the spectroscopic work on high-degree nonradialpulsations by Bohlender et al. (\cite{Boh99}). Compared to the deltaScuti stars, the cool and hot borders of the instability strip of thelambda Bootis stars are shifted by about 25 mmag, towards smaller(b-y)_0. Using published abundances and the metallicity sensitiveindices of the Geneva 7-colour and Strömgren uvbybeta systems, wehave derived [Z] values which describe the surface abundance of theheavier elements for the group members. We find that thePeriod-Luminosity-Colour relation for the group of lambda Bootis starsis within the errors identical with that of the normal delta Scutistars. No clear evidence for a statistically significant metallicityterm was detected. Based on observations from the Austrian AutomaticPhotoelectric Telescope (Fairborn Observatory), SAAO and Siding SpringObservatory.
| CO 1st overtone spectra of cool evolved stars: Diagnostics for hydrodynamic atmosphere models
We present spectra covering the wavelength range 2.28 to 2.36 mu m at aresolution of Delta lambda = 0.0007 mu m (or R = 3500) for a sample of24 cool evolved stars. The sample comprises 8 M supergiants, 5 M giants,3 S stars, 6 carbon stars, and 2 RV Tauri variables. The wavelengthscovered include the main parts of the 12C16O v =2-0 and 3-1 overtone bands, as well as the v = 4-2 and 13CO v= 2-0 bandhead regions. CO lines dominate the spectrum for all the starsobserved, and at this resolution most of the observed features can beidentified with individual CO R- or P-branch lines or blends. Theobserved transitions arise from a wide range of energy levels extendingfrom the ground state to E/k > 20 000 K. We looked for correlationsbetween the intensities of various CO absorption line features and otherstellar properties, including IR colors and mass loss rates. Two usefulCO line features are the v = 2-0 R14 line, and the CO v = 2-0 bandhead.The intensity of the 2-0 bandhead shows a trend with K-[12] color suchthat the reddest stars (K-[12] > 3 mag) exhibit a wide range in 2-0bandhead depth, while the least reddened have the deepest 2-0 bandheads,with a small range of variation from star to star. Gas mass loss ratesfor both the AGB stars and the red supergiants in our sample correlatewith the K-[12] color, consistent with other studies. The data implythat stars with dot M_gas < 5x 10-7 Msuny-1 exhibit a much narrower range in the relative strengthsof CO 2-0 band features than stars with higher mass loss rates. Therange in observed spectral properties implies that there are significantdifferences in atmospheric structure among the stars in this sample.Figures 4-9, 11-14, 16, 17, 19-21, 23, 24 are only avalaible inelectronic form at http://www.edpsciences.org
| Rotational velocities of A-type stars. I. Measurement of v sin i in the southern hemisphere
Within the scope of a Key Programme determining fundamental parametersof stars observed by HIPPARCOS, spectra of 525 B8 to F2-type starsbrighter than V=8 have been collected at ESO. Fourier transforms ofseveral line profiles in the range 4200-4500 Å are used to derivev sin i from the frequency of the first zero. Statistical analysis ofthe sample indicates that measurement error is a function of v sin i andthis relative error of the rotational velocity is found to be about 6%on average. The results obtained are compared with data from theliterature. There is a systematic shift from standard values from\citet{Slk_75}, which are 10 to 12% lower than our findings. Comparisonswith other independent v sin i values tend to prove that those fromSlettebak et al. are underestimated. This effect is attributed to thepresence of binaries in the standard sample of Slettebak et al., and tothe model atmosphere they used. Based on observations made at theEuropean Southern Observatory (ESO), La Silla, Chile, in the frameworkof the Key Programme 5-004-43K. Table 4 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/105
| 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
| Speckle Interferometry of New and Problem HIPPARCOS Binaries
The ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged ``G,''``O,'' ``V,'' or ``X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as ``suspected nonsingle'' (flag ``S'' in field H61), thusyielding a total of 11,687 ``problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras.
| Radial velocities of HIPPARCOS southern B8-F2 type stars
Radial velocities have been determined for a sample of B8-F2 type starsobserved by the Hipparcos satellite. Observations were obtained withinthe framework of an ESO key-program. Radial velocities have beenmeasured using a cross-correlation method, the templates being a grid ofsynthetic spectra. The obtained precision depends on effectivetemperature and projected rotational velocity of the star as well as ona possible asymmetry of the correlation peak generally due to secondarycomponents. New spectroscopic binaries have been detected from theseasymmetries and the variability of the measured radial velocity.Simulations of binary and triple systems have been performed. Forbinaries our results have been compared with Hipparcos binary data.Adding the variable radial velocities, the minimum binary fraction hasbeen found 60% for physical systems. Radial velocities have beendetermined for 581 B8-F2 stars, 159 being new. Taking into accountpublished radial velocities, 39% south A-type stars with V magnitudelower than 7.5 have a radial velocity. Based on observations obtained atthe European Southern Observatory (ESO, La Silla, Chile) and on datafrom the ESA Hipparcos astrometry satellite.}\fnmsep \thanks{Tables 7, 8and 9 are only available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| X-ray/optical observations of stars with shallow convection zones (A8-G2 V)
We present Walraven photometry and ROSAT All-Sky Survey data for asample of 173 bright main-sequence stars with spectral types between A8Vand G2V\@. These observations are part of a study of the onset ofmagnetic surface activity along the main sequence. Values for theeffective temperature, surface gravity and interstellar reddening havebeen obtained from a comparison of the observed Walraven colours withtheoretical values. These parameters have been used to derive accurateX-ray\ surface flux densities.
| The Angular Momentum of Main Sequence Stars and Its Relation to Stellar Activity
Rotational velocities are reported for intermediate-mass main sequencestars it the field. The measurements are based on new, high S/N CCDspectra from the Coudé Feed Telescope of the Kitt Peak NationalObservatory. We analyze these rotation rates for a dependence on bothmass and age. We compare the average rotation speeds of the field starswith mean velocities for young stars in Orion, the Alpha Persei cluster,the Pleiades, and the Hyades. The average rotation speeds of stars moremassive than $\sim1.6$ \msun\experience little or no change during theevolutionary lifetimes of these stars on the zero age main sequence orwithin the main sequence band. Less massive stars in the range betwee n1.6\msun\ and 1.3\msun\ also show little decline in mean rotation ratewhile they are on the main sequence, and at most a factor of 2 decreasein velocity as they evolve off the main sequence. The {\it e}-foldingtime for the loss of angular momentum b y the latter group of stars isat least 1--2 billion years. This inferred characteristic time scale forspindown is far longer than the established rotational braking time forsolar-type stars with masses below $\sim1.3$ \msun. We conclude from acomparison of the trends in rotation with trends in chromospheric andcoronal activity that the overall decline in mean rotation speed alongthe main sequence, from $\sim2$ \msun\ down to $\sim1.3$ \msun, isimposed during the pre-main sequence phase of evolution, and that thispattern changes little thereafter while the star resides on the mainsequence. The magnetic activity implicated in the rotational spindown ofthe Sun and of similar stars during their main sequence lifetimes mus ttherefore play only a minor role in determining the rotation rates ofthe intermediate mass stars, either because a solar-like dynamo is weakor absent, or else the geometry of the magnetic field is appreciablyless effective in removing angular momentu m from these stars. (SECTION:Stars)
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| Rapid oscillations of five stars in the spectral range A and F. I
The five stars HD 4849, HD 24712, HD 182475, HD 184552 and HD 215874 area small group of objects enclosed in a larger observational program forsearching of rapid oscillations. They have been observed with the 50 cmESO-telescope at La Silla (Chile). These objects are characterized as asuspected delta Scuti-type star, an Ap star, an A9 V star, an A1m starand an A9 III-IV star, respectively. For the first two stars theperiods, detected by other authors, were confirmed. For HD 182475 aperiod of 112.3 min has been estimated. In the case of HD 184552 anoscillation with a period of 163.3 min has been found. The star HD215874 shows unambiguously a variation with a period of 97.2 min.
| The early F-type stars - Refined classification, confrontation with Stromgren photometry, and the effects of rotation
The classification for early F-type stars in the MK spectralclassification system presented by Gray and Garrison (1987) is refined.The effect of rotation on spectral classification and ubvy-betaphotometry of early F-type stars is examined. It is found that theclassical luminosity criterion, the 4417 A/4481 A ratio givesinconsistent results. It is shown that most of the stars in the DeltaDelphini class of metallic-line stars are either normal or areindistinguishable from proto-Am stars. It is suggested that thedesignation Delta Delphini should be dropped. The classifications arecompared with Stromgren photometry. The effects of rotation on thedelta-c1 index in the early-F field dwarfs is demonstrated.
| Photoelectric H-beta photometry for A and F stars brighter than V = 14 M in four areas in directions towards the South Galactic Pole
Data from photoelectric H-beta observations of 145 mainly A and F starswith V = 14 mag or brighter in four regions totalling 60 sq deg andlocated near galactic latitude b(II) = -60 deg, obtained using atwo-channel H-beta photometer on the 1.5-m Danish reflecting telescopeat ESO on two nights in 1981 and four nights in 1982, are presented intables along with the Stromgren b magnitudes calculated from thewide-channel H-beta counts. These observations are undertaken in theframework of a uvby photometric search for A-F stars of Population IIbrighter than V = 15.5 mag. The mean error per observation is given as +or - 0.020 mag in b and + or - 0.009 mag in H-beta.
| Spectral classification of the bright F stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976PASP...88...95C&db_key=AST
| Study of the F-type 1 MK spectral types.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975AJ.....80..637M&db_key=AST
| Four-colour and H BET photometry of some bright southern stars- II.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972MNRAS.160..155S&db_key=AST
| Rotation of evolving A and F stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&A....18..428D&db_key=AST
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Pozíciós és asztrometriai adatok
| Csillagkép: | Vízöntő |
| Rektaszcenzió: | 19h25m01.60s |
| Deklináció: | -04°53'03.0" |
| Vizuális fényesség: | 6.52 |
| Távolság: | 100.806 parszek |
| RA sajátmozgás: | 33 |
| Dec sajátmozgás: | 1.4 |
| B-T magnitude: | 6.897 |
| V-T magnitude: | 6.54 |
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INHABITED SKY
