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1.
L. Meillon 《Astrophysics and Space Science》1999,265(1-4):179-180
A large number of high-velocity stars was included in the Hipparcos Input Catalogue for the purpose of determining the galactic
escape velocity in the solar vicinity. However, the `fastest' stars known, listed by Carney et al. (1994, CLLA) were not included because they are too faint. In the intersection between the CLLA list and the Hipparcos Catalogue
(770 common stars), the metal-deficient stars with the most reliable parallaxes (fracσππ)HIP ≤ 0.15) are used for recalibrating CLLA absolute magnitudes and photometric parallaxes, using metallicities and VandenBerg
et al. (1998) isochrones. In this way, about twenty non-Hipparcos stars get improved parallaxes and are added to our primary sample
of Hipparcos high-velocity stars, for a better determination of the escape velocity from the Galaxy.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
I. Neill Reid F. van Wyk F. Marang G. Roberts D. Kilkenny S. Mahoney 《Monthly notices of the Royal Astronomical Society》2001,325(3):931-962
We have identified 317 stars included in the Hipparcos astrometric catalogue that have parallaxes measured to a precision of better than 15 per cent, and the location of which in the ( M V ,( B − V ) T ) diagram implies a metallicity comparable to or less than that of the intermediate-abundance globular cluster M5. We have undertaken an extensive literature search to locate Strömgren, Johnson/Cousins and Walraven photometry for over 120 stars. In addition, we present new UBV ( RI )C photometry of 201 of these candidate halo stars, together with similar data for a further 14 known metal-poor subdwarfs. These observations provide the first extensive data set of R C I C photometry of metal-poor, main-sequence stars with well-determined trigonometric parallaxes. Finally, we have obtained intermediate-resolution optical spectroscopy of 175 stars.
47 stars still lack sufficient supplementary observations for population classification; however, we are able to estimate abundances for 270 stars, or over 80 per cent of the sample. The overwhelming majority have near-solar abundance, with their inclusion in the present sample stemming from errors in the colours listed in the Hipparcos catalogue. Only 44 stars show consistent evidence of abundances below [Fe/H]=−1.0 . Nine are additions to the small sample of metal-poor subdwarfs with accurate photometry. We consider briefly the implication of these results for cluster main-sequence fitting. 相似文献
47 stars still lack sufficient supplementary observations for population classification; however, we are able to estimate abundances for 270 stars, or over 80 per cent of the sample. The overwhelming majority have near-solar abundance, with their inclusion in the present sample stemming from errors in the colours listed in the Hipparcos catalogue. Only 44 stars show consistent evidence of abundances below [Fe/H]=−1.0 . Nine are additions to the small sample of metal-poor subdwarfs with accurate photometry. We consider briefly the implication of these results for cluster main-sequence fitting. 相似文献
3.
Li abundance is determined for 23 halo subdwarfs. About half of the stars show [Fe/H] < −1.4 and a space velocityV > 160 km s−1 Li appears to be present in all our halo stars, with an abundance within about ± 0.2 dex of the value logn (Li) = 2.0 found by Spite & Spite (1982). Thus our results provide confirmation of the main conclusion of Spite & Spite. 相似文献
4.
The Galactic orbits of 27 440 stars of all classes with accurate coordinates and parallaxes of more than 3 mas from the Hipparcos catalogue, proper motions from the Tycho-2 catalogue, and radial velocities from the Pulkovo Compilation of Radial Velocities (PCRV) are analyzed. The sample obtained is much more representative than the Geneva-Copenhagen survey and other studies of Galactic orbits in the solar neighborhood. An estimation of the influence of systematic errors in the velocities on orbital parameters shows that the errors of the proper motions due to the duplicity of stars are tangible only in the statistics of orbital parameters for very small samples, while the errors of the radial velocities are noticeable in the statistics of orbital parameters for halo stars. Therefore, previous studies of halo orbits may be erroneous. The distribution of stars in selection-free regions of the multidimensional space of orbital parameters, dereddened colors, and absolute magnitudes is considered. Owing to the large number of stars and the high accuracy of PCRV radial velocities, nonuniformities of this distribution (apart from the well-known dynamical streams) have been found. Stars with their peri- and apogalacticons in the disk, perigalacticons in the bulge and apogalacticons in the disk, perigalacticons in the bulge and apogalacticons in the halo, and perigalacticons in the disk and apogalacticons in the halo have been identified. Thus, the bulge and the halo are inhomogeneous structures, each consisting of at least two populations. The radius of the bulge has been determined: 2 kpc. 相似文献
5.
We present a catalogue of radial velocities of Galactic stars with high precision astrometric data CRVAD which is the result of the cross‐identification of star lists from the General Catalog of Average Radial Velocities (GCRV) and from the homogeneous All‐sky Compiled Catalogue of 2.5Million Stars (ASCC‐2.5). The CRVAD includes accurate J2000 equatorial coordinates, proper motions and trigonometric parallaxes in the Hipparcos system, Johnson's BV photometric data, spectral types, multiplicity and variability flags from the ASCC‐2.5, and radial velocities, stellar magnitudes and spectral types from the GCRV for 34553 ASCC‐2.5 stars. The CRVAD was used for the construction of a sample of standard stars with accurate astrometric, photometric and radial velocity data for the RAVE project. A second application of the CRVAD , the radial velocity determination for 292 open clusters (including 97 with previously unknown radial velocities), using their newly defined members from proper motions and photometry in the ASCC‐2.5, is briefly described. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
6.
While implementing the first stage of the Pulkovo program of research on stars with large proper motions, we determined the
trigonometric parallaxes of 29 stars (12
m
< V < 16
m
) based on CCD observations with a 26-inch refractor. The mean standard error was 3.7 mas. Comparison of the Pulkovo parallaxes
with those obtained at the Observatory of the Yale University and the US Naval Observatory (USNO) has shown that the parallax
differences (Pulkovo-Yale/USNO) lie within the limits of their measurement errors in an overwhelming majority of cases. On
average, they are −0.6 ± 1.0 mas. No systematic dependences on stellar distance, magnitude, and color in this set of differences
have been found. Our comparisons show that the observing and data reduction techniques used in the Pulkovo program of research
on fast stars allow highly accurate trigonometric parallaxes of these objects to be obtained. All program stars are within
50 pc of the Sun; most of them belong to the immediate solar neighborhood (D < 25 pc). For two stars (J0522+3814 and J1202+3636), the trigonometric parallaxes have been determined for the first time. 相似文献
7.
The methods used to derive effective temperatures, projected rotational velocities and surface gravities of a sample of low
and high-amplitude δ Sct stars are presented here. Effective temperatures were derived using Hα and Hβ line profiles whereas
rotational velocities were calculated following the method described in Solano & Fernley (1997). Surface gravities were obtained
using Hipparcos parallaxes and evolutionary models (Claret 1995). The results of this analysis will be published in a subsequent
paper (Solano & Pintado 1999).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
We investigate the relative motion of three stars, ADS 7446, 9346, and 9701, based on long-term observations with the Pulkovo
26-inch refractor. The relative motion of all three stars shows a perturbation that could be produced by the gravitational
influence of an invisible companion. For ADS 7446, we have determined the orbit of the photocenter with a period of 7.9 yr;
the mass of the companion is more than 0.4M
⊙. For ADS 9346, we have determined the radial velocities of the components: −14.60 km s−1 for A and −13.94 km s−1 for B. For ADS 9346 and 9701, we have determined the dynamical parallaxes, 24 and 20 mas, respectively, which are larger
than those in the Hipparcos catalog by 5 mas, and calculated the orbits by the apparent motion parameter (AMP) method. The
new orbit of ADS 9346 is: a = 5″.2, P = 2035 yr, and e = 0.46 at the system’s mass M = 2.5M
⊙. The new orbits of ADS 9701 are: (a = 2″.9, P = 829 yr, e = 0.54, M = 4.3M
⊙) and (a = 3″.8, P = 1157 yr, e = 0.53, M = 5.0M
⊙). 相似文献
9.
Based on a new version of the Hipparcos catalogue and an updated Geneva-Copenhagen survey of F and G dwarfs, we analyze the
space velocity field of ≈17 000 single stars in the solar neighborhood. The main known clumps, streams, and branches (Pleiades,
Hyades, Sirius, Coma Berenices, Hercules, Wolf 630-α Ceti, and Arcturus) have been identified using various approaches. The evolution of the space velocity field for F and G
dwarfs has been traced as a function of the stellar age. We have managed to confirm the existence of the recently discovered
KFR08 stream. We have found 19 Hipparcos stars, candidates for membership in the KFR08 stream, and obtained an isochrone age
estimate for the stream, 13 Gyr. The mean stellar ages of the Wolf 630-α Ceti and Hercules streams are shown to be comparable, 4–6 Gyr. No significant differences in the metallicities of stars belonging
to these streams have been found. This is an argument for the hypothesis that these streams owe their origin to a common mechanism. 相似文献
10.
Filippina Caputo 《Astronomy and Astrophysics Review》1998,9(1-2):33-61
The current knowledge of the evolution of Population II stars, as observed in galactic halos and globular clusters, is outlined.
The recent theoretical results provided by an improved physical understanding of the stars are reported, with a particular
emphasis upon those stellar evolutionary phases which are the keystones of the interpretation of globular cluster stars. Within
the up–to–date theoretical scenario, the luminosity of the turn–off stars and horizontal branch stars, which are of fundamental
importance for distance and age determinations, turns out to be fainter and brighter, respectively, in comparison with previous
theoretical computations. The predicted absolute magnitude of RR Lyrae stars is consistent with the bright values suggested from the long distance scale (Sandage 1993), but the slope of the relation between and metallicity ([Fe/H]) agrees with that suggested from the short distance scale (see, e.g., Carney et al. 1992, Clementini et al. 1995), at least with [Fe/H]-1.3. As to the globular cluster ages, the new computations provide younger ages ( 10 Gyr–13 Gyr), weakening the conflict with current cosmological estimates. The recent results derived from the fitting of
HIPPARCOS parallaxes of field subdwarfs to the fiducial main sequence of globular clusters are consistent with the up–to–date theoretical
models. However, the direct determinations of , which are based on the HIPPARCOS proper motions and trigonometric parallaxes of field RR Lyrae stars, give fainter absolute magnitudes than those obtained
from the improved evolutionary models. This seems to suggest that the problem of the globular cluster distance and age is
still open.
Received 6 April 1998 相似文献
11.
Michael Feast Patricia Whitelock John Menzies 《Monthly notices of the Royal Astronomical Society》2002,329(1):L7-L12
A globular cluster distance scale based on Hipparcos parallaxes of subdwarfs has been used to derive estimates of M K for cluster Miras, including one in the Small Magellanic Cloud (SMC) globular cluster NGC 121. These lead to a zero-point of the Mira infrared period–luminosity (PL) relation, PL( K ), in good agreement with that derived from Hipparcos parallaxes of nearby field Miras. The mean of these two estimates together with data on LMC Miras yields a Large Magellanic Cloud (LMC) distance modulus of in evident agreement with a metallicity-corrected Cepheid modulus .
The use of luminous asymptotic giant branch (AGB) stars as extragalactic population indicators is also discussed. 相似文献
The use of luminous asymptotic giant branch (AGB) stars as extragalactic population indicators is also discussed. 相似文献
12.
S. K. Balayan 《Astrophysics》1997,40(4):413-415
A brief analysis of a sample of stars from the Second Byurakan Spectroscopic Survey is given. It contains 626 objects in the
range of apparent magnitudes 10.1 ≤ m(pg) ≤ 19.5 and consists mainly of white dwarfs and subdwarfs of early spectral types.
Most of the objects have been classified for the first time. Their distributions with respect to stellar magnitude and spectral
type are given.
Translated from Astrofizika, Vol. 40, No. 4, pp. 627–631, October-December, 1997. 相似文献
13.
A sample containing 1 026 stars of spectral types F, G, and K, mainly dwarfs, from the solar neighbourhood with available space velocities and metallicities is treated. The treatment comprises a statistical analysis of the metallicity and velocity data and calculation of galactocentric orbits. Sample stars identified as members of the galactic halo are detached from the rest of the sample based on the values of their metallicities, velocity components and galactocentric orbits. In identifying halo stars a new, kinematical, criterion is proposed. Except one, these halo stars are the metal‐poorest ones in the sample. Besides, they have very high velocities with respect to LSR. On the other hand, the separation between the thin disc and thick one is done statistically based on LSR space velocities, membership probability (Schwarzschild distribution with assumed parameters) and galactocentric orbits. In the metallicity these two groups are not much different. For each of the three subsamples the mean motion and velocity ellipsoid are calculated. The elements of the velocity ellipsoids agree well with the values found in the literature, especially for the thin disc. The fractions of the subsystems found for the present sample are: thin disc 93%, thick disc 6%, halo 1%. The sample stars established to be members of the thin disc are examined for existence of star streams. Traces of both, known and unknown, star streams are not found (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
14.
Part five of optically identified point sources from the IRAS Point Source Catalog (PSC) contains data on 19 late-type stars.
The identifications were based on the Digitized Sky Survey (DSS), the First Byurakan Survey (FBS), blue and red maps of the
Palomar survey (POSS), and infrared fluxes at 12, 25, 60, and 100 mm in the region of +61° ≤ δ ≤ +65° and 05
h
30
m
≤ α ≤ 18
h
35
m
with an area of 357 sq. deg. Of the 76 objects given in the IRAS PSC as unidentified sources of infrared radiation, 51 are
associated with known stars in existing catalogs, 6 are objects from the FBS of late-type stars, and 19 sources remained unknown
in the optical range. For the identified stars we determined the optical coordinates, their departures from the IR coordinates,
the Vstellar magnitudes, the color indices CI,and the preliminary spectral subtypes. The objects have optical magnitudes in the range of 8
m
−16
m
.Gas-dust shells are assumed to exist around four of the sources. Finder charts from the DSS are given for 19 of the objects.
Translated from Astrofizika, Vol. 42, No. 1, pp. 53–59, January–March, 1999. 相似文献
15.
Data from our compiled catalog of spectroscopically determined magnesium abundances in dwarfs and subgiants with accurate parallaxes are used to select Galactic halo stars according to kinematic criteria and to identify presumably accreted stars among them. Accreted stars are shown to constitute the majority in the Galactic halo. They came into the Galaxy from disrupted dwarf satellite galaxies. We analyze the relations between the relative magnesium abundances, metallicities, and Galactic orbital elements for protodisk and accreted halo stars. We show that the relative magnesium abundances in protodisk halo stars are virtually independent of metallicity and lie within a fairly narrow range, while presumably accreted stars demonstrate a large spread in relative magnesium abundances up to negative [Mg/Fe]. This behavior of protodisk halo stars suggests that the interstellar matter in the early Galaxy mixed well at the halo formation phase. The mean metallicity of magnesium-poor ([Mg/Fe] < 0.2 dex) accreted stars has been found to be displaced toward the negative values when passing from stars with low azimuthal velocities (|Θ| < 50 km s?1) to those with high ones at Δ[Fe/H] ≈ ?0.5 dex. The mean apogalactic radii and inclinations of the orbits also increase with increasing absolute value of |Θ|, while their eccentricities decrease. As a result, negative radial and vertical gradients in relative magnesium abundances are observed in the accreted halo in the absence of correlations between the [Mg/Fe] ratios and other orbital elements, while these correlations are found at a high significance level for genetically related Galactic stars. Based on the above properties of accreted stars and our additional arguments, we surmise that as the masses of dwarf galaxies decrease, the maximum SN II masses and, hence, the yield of α-elements in them also decrease. In this case, the relation between the [Mg/Fe] ratios and the inclinations and sizes of the orbits of accreted stars is in complete agreement with numerical simulations of dynamical processes during the interaction of galaxies. Thus, the behavior of the magnesium abundance in accreted stars suggests that the satellite galaxies are disrupted and lose their stars en masse only after dynamical friction reduces significantly the sizes of their orbits and drags them into the Galactic plane. Less massive satellite galaxies are disrupted even before their orbits change appreciably under tidal forces. 相似文献
16.
P. G. Niarchos 《Astrophysics and Space Science》2006,304(1-4):387-390
The space experiment Gaia, the approved cornerstone 6 ESA mission, will observe up to a billion stars in our Galaxy and obtain their astrometric positions on a micro-arcsec level, multi-band photometry as well as spectroscopic observations. It is expected that about one million Eclipsing Binaries (EBs) (with V ≤ 16 mag) will be discovered and the observing fashion will be quite similar to Hipparcos/Tycho mission operational mode. The combined astrometric, photometric and spectroscopic data will be used to compute the physical parameters of the observed EBs. From a study of a small sample of EBs, it is shown that the agreement between the fundamental stellar parameters, derived from ground-based and Hipparcos (Gaia-like) observations, is more than satisfactory and the Gaia data will be suitable to obtain accurate binary solutions. 相似文献
17.
A 10th list of late-type M and C stars found on plates of the First Byurakan Spectral Sky Survey in the − 11° ≤ δ ≤ − 7° belt
with an area of about 1070 deg2 is given. The list contains data on 169 red stars, 117 of which were found for the first time: 8 are new C stars, 3 are Cstar
candidates, 104 are M stars, 1 is either an M or an S star, and 1 object on the survey plate cannot be classified. Of the
117 objects, 47 are unidentified IRAS sources. A statistical analysis of the objects that are and are not identified with
IRAS sources shows that the identified stars are, with a high probability, brighter and have relatively more massive envelopes.
Two stars were found to have fairly large brightness variability (with an amplitude of at least 6m.O). Gasdust shells are assumed to exist around nine of the IRAS sources. The equatorial coordinates, spectral types, and
stellar magnitudes, determined on Palomar E maps, are given for the selected objects.
Translated from Astrofizika, Vol. 41. No. 4, pp. 545–559, October–December, 1998. 相似文献
18.
A. M. Mickaelian 《Astrophysics》1997,40(1):1-9
The low-dispersion spectra of the First Byurakan Survey and the red and blue images of the Palomar Observatory Sky Survey
have been used to identify optically 100 infrared sources from the IRAS Point Source Catalog. The work was carried out over
the region 3h 50m ≤ α ≤ 7h 40m and +69° ≤ δ −73° with an area of 75 square degrees. The optical coordinates, their deviations from the infrared coordinates,
V magnitudes, color indices, preliminary classes for all the objects, and a number of remarks on interesting objects are presented.
Three objects were found to be quasars, 36 are galaxies (including Seyferts and an interacting pair), 5 are faint planetary
nebulae, 9 are carbon stars, and 47 are stars of late M subclasses.
Translated fromAstrofizika, Vol. 40, No. 1, pp. 5–18, February, 1997. 相似文献
19.
We re‐discuss the evolutionary state of upper main sequence magnetic stars using a sample of Ap and Bp stars with accurate Hipparcos parallaxes and definitely determined longitudinal magnetic fields. We confirm our previous results obtained from the study of Ap and Bp stars with accurate measurements of the mean magnetic field modulus and mean quadratic magnetic fields that magnetic stars of mass M < 3 M⊙ are concentrated towards the centre of the main‐sequence band. In contrast, stars with masses M > 3 M⊙ seem to be concentrated closer to the ZAMS. The study of a few known members of nearby open clusters with accurate Hipparcos parallaxes confirms these conclusions. Stronger magnetic fields tend to be found in hotter, younger and more massive stars, as well as in stars with shorter rotation periods. The longest rotation periods are found only in stars which spent already more than 40% of their main sequence life, in the mass domain between 1.8 and 3 M⊙ and with log g values ranging from 3.80 to 4.13. No evidence is found for any loss of angular momentum during the main‐sequence life. The magnetic flux remains constant over the stellar life time on the main sequence. An excess of stars with large obliquities β is detected in both higher and lower mass stars. It is quite possible that the angle β becomes close to 0. in slower rotating stars of mass M > 3 M⊙ too, analog to the behaviour of angles β in slowly rotating stars of M < 3 M⊙. The obliquity angle distribution as inferred from the distribution of r ‐values appears random at the time magnetic stars become observable on the H‐R diagram. After quite a short time spent on the main sequence, the obliquity angle β tends to reach values close to either 90. or 0. for M < 3 M⊙. The evolution of the obliquity angle β seems to be somewhat different for low and high mass stars. While we find a strong hint for an increase of β with the elapsed time on the main sequence for stars with M > 3 M⊙, no similar trend is found for stars with M < 3 M⊙. However, the predominance of high values of β at advanced ages in these stars is notable. As the physics governing the processes taking place in magnetised atmospheres remains poorly understood, magnetic field properties have to be considered in the framework of dynamo or fossil field theories. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
20.
J. H. J. de Bruijne 《Astrophysics and Space Science》2012,341(1):31-41
Gaia is the next astrometry mission of the European Space Agency (ESA), following up on the success of the Hipparcos mission. With a focal plane containing 106 CCD detectors, Gaia will survey the entire sky and repeatedly observe the brightest 1,000 million objects, down to 20th magnitude, during its 5-year lifetime. Gaia’s science data comprises absolute astrometry, broad-band photometry, and low-resolution spectro-photometry. Spectroscopic data with a resolving power of 11,500 will be obtained for the brightest 150 million sources, down to 17th magnitude. The thermo-mechanical stability of the spacecraft, combined with the selection of the L2 Lissajous point of the Sun-Earth/Moon system for operations, allows stellar parallaxes to be measured with standard errors less than 10 micro-arcsecond (μas) for stars brighter than 12th magnitude, 25 μas for stars at 15th magnitude, and 300 μas at magnitude 20. Photometric standard errors are in the milli-magnitude regime. The spectroscopic data allows the measurement of radial velocities with errors of 15 km s−1 at magnitude 17. Gaia’s primary science goal is to unravel the kinematical, dynamical, and chemical structure and evolution of the Milky Way. In addition, Gaia’s data will touch many other areas of science, e.g., stellar physics, solar-system bodies, fundamental physics, and exo-planets. The Gaia spacecraft is currently in the qualification and production phase. With a launch in 2013, the final catalogue is expected in 2021. The science community in Europe, organised in the Data Processing and Analysis Consortium (DPAC), is responsible for the processing of the data. 相似文献