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Публикации по объекту
Detection of 75+ pulsation frequencies in the δ Scuti star FG Virginis
Extensive photometric multisite campaigns of the δ Scuti variableFG Vir are presented. For the years 2003 and 2004, 926 h of photometryat the millimag precision level were obtained. The combinations withearlier campaigns lead to excellent frequency resolution and highsignal/noise. A multifrequency analysis yields 79 frequencies. Thisrepresents a new record for this type of star. The modes discoveredearlier were confirmed. Pulsation occurs over a wide frequency band from5.7 to 44.3 c/d with amplitudes of 0.2 mmag or larger. Within this wideband the frequencies are not distributed at random, but tend to clusterin groups. A similar feature is seen in the power spectrum of theresiduals after 79 frequencies are prewhitened. This indicates that manyadditional modes are excited. The interpretation is supported by ahistogram of the photometric amplitudes, which shows an increase ofmodes with small amplitudes. The old question of the "missing modes" maybe answered now: the large number of detected frequencies as well as thelarge number of additional frequencies suggested by the power spectrumof the residuals confirms the theoretical prediction of a large numberof excited modes. FG Vir shows a number of frequency combinations of thedominant mode at 12.7162 c/d (m = 0) with other modes of relatively highphotometric amplitudes. The amplitudes of the frequency sums are higherthan those of the differences. A second mode (20.2878 c/d) also showscombinations. This mode of azimuthal order m = -1 is coupled with twoother modes of m = +1.
| 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
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| 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
| 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.
| Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald Observatory
The Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos ``problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos ``problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission.
| Photometry of the Delta Scuti Star FG VIR during the 1995 Multi-Site Campaign
The results of the 1995 FG Vir multi-site campaign, organized by theDelta Scuti Network, are presented. Between 1995 March 2 and April 20over 430 hours of photoelectric an 120 hours of CCD measurements wereobtained during a time span of 40 days at six observatories. Thepreviously known ten frequencies range from 9.20 to 34.12 cycles/day(106.5 and 394.9 mu Hz). Fourteen additional frequencies were detected.The precision of the FG Vir measurements was better than 3 mmag for thephotoelectric measurements and better than 3.5 mmag per single 1 minuteintegration for the CCD measurements. Further it is shown that thepresent CCD measurements are of similar quality as those obtainedsimultaneously by photometers with photomultiplier detectors using thethree-star observing technique.
| Oscillation mode identifications and models for the delta Scuti star FG Virginis
We present new spectroscopic and photometric time series observations ofthe delta Scuti star FG Vir. We detect the oscillations via changes inthe equivalent widths of hydrogen and metal absorption lines. From theratios between spectroscopic and photometric amplitudes, we assign lvalues to the eight strongest oscillation modes. In particular, weidentify two radial modes (l =0) and find that the main pulsation mode(147 mu Hz) has l =1. One of the radial modes (at 140mu Hz) is thefundamental, implying that two modes with lower frequencies are g-modes.For the radial modes, we compare frequencies with those calculated froma scaled delta Scuti star model and derive a density 0.1645+/- 0.0005rho_ ȯ. We then obtain a distance of 84+/- 3 pc, in excellentagreement with the Hipparcos value. Finally, we suggest that a 3.5-dayvariability in all observables (equivalent widths and intensity) iscaused by stellar rotation.
| The delta Scuti star FG Vir. III. The 1995 multisite campaign and the detection of 24 pulsation frequencies
We carried out the largest photometric multisite campaign for a deltaScuti star to date and acquired 435 hours of Stromgren v and ytime-series photometry at 6 observatories during a time span of 40 days.The new 1995 data set allows us to extract 19 frequencies of the lightvariations. By including the data published by Breger et al. (1995) wecan increase the number of significant frequencies of FG Vir to 24. Thepulsation of FG Vir occurs in a frequency range from 9.2 to 34.1 c/d(106 to 395 mu Hz) with amplitudes as small as 0.4 mmag detected in y.Two peaks may be identified as combinations of other pulsation modes.There is strong evidence for the presence of further pulsation modes inthe same frequency range. Their detection would require a data set withan even larger time base. An examination of all the availabletime-series photometric data to determine amplitude variability was alsoundertaken. Statistical tests show that only a single pulsation mode(f_3 =3D 23.40 c/d) is definitely variable and has changed in amplitudefrom 1.4 mmag in 1992, 2.3 mmag in 1993 to 4.1 mmag in 1995. Argumentsare given that photometrically at least three different degrees, (l),have been detected. An upcoming paper will discuss possible modeidentifications and pulsational model calculations.
| uvby beta Photometry of Stars of "Astrophysical Interest"
Not Available
| Main Sequence Variables
The pulsators along and near the main sequence are well-suited forasteroseismology and provide a probe of the stellar interior and itschanges with evolution. With the exception of rapidly oscillating Apstars (roAp), the pulsation periods range from 0.5 h to days. Thisrequires multisite campaigns lasting several weeks. The delta Scuti,roAp and beta Cephei variables offer the greatest potential, while thelonger-period g-mode pulsators (SPB -- slowly pulsating B stars -- andgamma Doradus variables) are very difficult to study. A summary of themultiperiod structure of delta Scuti stars is given. The twobest-studied stars, FG Vir and CD--24(deg) 7599, both have been WETtargets. A preliminary analysis of the 1995 campaign of FG Vir hasalready detected 19 frequencies. The standard photometric WET techniquehas a high duty cycle since the variable star is observed continuouslywith one channel. The study of main sequence variables requiresphotometric stability at low frequencies. The extension of the WETtechnique to low frequencies and its modification are discussed.
| The δ Scuti star FG Virginis. I. Multiple pulsation frequencies determined with a combined DSN/WET campaign.
A coordinated photometric campaign of FG Vir at nine observatoriescovering 170 hours was undertaken by DSN (Delta Scuti Network) and WET(Whole Earth Telescope). Two different observing techniques were adoptedfor the two telescope networks in order to optimize different frequencyranges. Ten pulsation frequencies between 9.19 and 34.12c/d (112 and395μHz) were detected with amplitudes ranging from 0.8 to 22mmag.Pulsational instability is observed only in specific frequency regions.Additional frequencies of pulsation within these regions probably exist,but do not reach the significance criterion of amplitude signal/noiseadopted by us. Comparisons with previously obtained data show that theamplitudes of the main frequencies are stable over a year or longer. Apreliminary identification of the ten dominant frequencies is proposedin a stellar model with 1.8Msun_ in advanced main-sequencephase of evolution. The frequencies correspond to low order p and gmodes with l<=2 and radial order 1 to 6. According to the linearnonadiabatic calculations, the identified modes are driven by theopacity mechanism along with many other modes. For asteroseismology ofδ Scuti stars, FG Vir is an extremely important candidate,especially because of the probable presence of g modes.
| Photoelectric observations of lunar occultations. X
Photoelectric occulation results for 461 events observed during 15months are reported. They include 77 reappearances, 4 determinations ofangular diameter, 38 analyses of double or multiple stars including twopreviously unknown bright stars, and 8 previously known bright double ormultiple stars.
| MK classifications for F-and G-type stars. 3.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974AJ.....79..682H&db_key=AST
| A catalogue of four-color photometry of late F-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..705P&db_key=AST
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Дева |
| Прямое восхождение: | 12h11m21.80s |
| Склонение: | -03°46'43.9" |
| Видимая звёздная величина: | 6.953 |
| Расстояние: | 50.251 парсек |
| Собственное движение RA: | -100.7 |
| Собственное движение Dec: | -62.8 |
| B-T magnitude: | 7.441 |
| V-T magnitude: | 6.994 |
Каталоги и обозначения:
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