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1.
A suite of vast stellar surveys mapping the Milky Way, culminating in the Gaia mission, is revolutionizing the empirical information about the distribution and properties of stars in the Galactic stellar disk. We review and lay out what analysis and modeling machinery needs to be in place to test mechanism of disk galaxy evolution and to stringently constrain the Galactic gravitational potential, using such Galactic star-by-star measurements. We stress the crucial role of stellar survey selection functions in any such modeling; and we advocate the utility of viewing the Galactic stellar disk as made up of ‘mono-abundance populations’ (MAPs), both for dynamical modeling and for constraining the Milky Way’s evolutionary processes. We review recent work on the spatial and kinematical distribution of MAPs, and point out how further study of MAPs in the Gaia era should lead to a decisively clearer picture of the Milky Way’s dark-matter distribution and formation history.  相似文献   

2.
Recent numerical simulations have demonstrated that the Sun’s dynamical history within the Milky Way may be much more complex than that suggested by its current low peculiar velocity (Sellwood, J.A., Binney, J.J. [2002]. Mon. Not. R. Astron. Soc. 336, 785-796; Roškar, R., Debattista, V.P., Quinn, T.R., Stinson, G.S., Wadsley, J. [2008]. Astrophys. J. 684, L79-L82). In particular, the Sun may have radially migrated through the galactic disk by up to 5-6 kpc (Roškar, R., Debattista, V.P., Quinn, T.R., Stinson, G.S., Wadsley, J. [2008]. Astrophys. J. 684, L79-L82). This has important ramifications for the structure of the Oort Cloud, as it means that the Solar System may have experienced tidal and stellar perturbations that were significantly different from its current local galactic environment. To characterize the effects of solar migration within the Milky Way, we use direct numerical simulations to model the formation of an Oort Cloud around stars that end up on solar-type orbits in a galactic-scale simulation of a Milky Way-like disk formation. Surprisingly, our simulations indicate that Sedna’s orbit may belong to the classical Oort Cloud. Contrary to previous understanding, we show that field star encounters play a pivotal role in setting the Oort Cloud’s extreme inner edge, and due to their stochastic nature this inner edge sometimes extends to Sedna’s orbit. The Sun’s galactic migration heightens the chance of powerful stellar passages, and Sedna production occurs around ∼20-30% of the solar-like stars we study. Considering the entire Oort Cloud, we find its median distance depends on the minimum galactocentric distance attained during the Sun’s orbital history. The inner edge also shows a similar dependence but with increased scatter due to the effects of powerful stellar encounters. Both of these Oort Cloud parameters can vary by an order of magnitude and are usually overestimated by an Oort Cloud formation model that assumes a fixed galactic environment. In addition, the amount of material trapped in outer Oort Cloud orbits (a > 20,000 AU) can be extremely low and may present difficulties for traditional models of Oort Cloud formation and long-period comet production.  相似文献   

3.
《New Astronomy》2002,7(7):395-433
The stellar initial mass function at high redshift is an important defining property of the first stellar systems to form and may also play a role in various dark matter problems. We here determine the faint stellar luminosity function in an apparently dark-matter-dominated external galaxy in which the stars formed at high redshift. The Ursa Minor dwarf spheroidal galaxy is a system with a particularly simple stellar population—all of the stars being old and metal-poor—similar to that of a classical halo globular cluster. A direct comparison of the faint luminosity functions of the UMi dSph and of similar metallicity, old globular clusters is equivalent to a comparison of the initial mass functions and is presented here, based on deep HST WFPC2 and STIS imaging data. We find that these luminosity functions are indistinguishable, down to a luminosity corresponding to ∼0.3 M⊙. Our results show that the low-mass stellar IMF for stars that formed at very high redshift is apparently invariant across environments as diverse as those of an extremely low-surface-brightness, dark-matter-dominated dwarf galaxy and a dark-matter-free, high-density globular cluster within the Milky Way.  相似文献   

4.
With more and more exoplanets being detected, it is paid closer attention to whether there are lives outside solar system. We try to obtain habitable zones and the probability distribution of terrestrial planets in habitable zones around host stars. Using Eggleton’s code, we calculate the evolution of stars with masses less than 4.00 M ⊙. We also use the fitting formulae of stellar luminosity and radius, the boundary flux of habitable zones, the distribution of semimajor axis and mass of planets and the initial mass function of stars. We obtain the luminosity and radius of stars with masses from 0.08 to 4.00 M ⊙, and calculate the habitable zones of host stars, affected by stellar effective temperature. We achieve the probability distribution of terrestrial planets in habitable zones around host stars. We also calculate that the number of terrestrial planets in habitable zones of host stars is 45.5 billion, and the number of terrestrial planets in habitable zones around K type stars is the most, in the Milky Way.  相似文献   

5.
《New Astronomy》2002,7(4):161-169
In the usual and most widespread textbook picture of the Milky Way Galaxy, disk stars like the Sun are referred to as Population I, the spheroidal or halo component in turn as Population II. The latter is thought of as the pressure-supported, metal-poor relic of the early Galaxy, with renewed interest in recent years in the search for dark matter via microlensing. Modelling the putative massive compact halo objects however, faces the problem that the stellar halo is generally considered to consist of only a few billion solar masses. Here we present observational evidence that even this low budget may be a factor ten too high. If so, this immediately implies that the classical population II of halo stars is fairly irrelevant, not only in the dark matter context, but, in particular, in models of the formation and evolution of the Milky Way Galaxy.  相似文献   

6.
At the dynamic center of the Milky Way high spatial resolution, near-infrared imaging and spectroscopy have made it possible in the last few years to measure stellar velocities down to separations of less than five light days from the compact radio source SgrA* (in the constellation Sagittarius). These measurements make a compelling case for the presence of a compact, central dark mass of 2.6 × 106 solar masses. Simple physical considerations show that this dark mass cannot consist of a stable cluster of stars, stellar remnants, substellar condensations or a degenerate gas of elementary particles. Energy equipartition requires that at least 105 solar masses must be associated with SgrA* itself and is enclosed within less than 8 light minutes (equivalent to 15 Schwarzschild radii of a million solar mass black hole). If one accepts these arguments it is hard to escape the conclusions that there must be a massive black hole at the core of the Milky Way.  相似文献   

7.
We aim to characterize the properties of the stellar clusters in the Milky Way. Utilising an expectation-maximization method, we determined that the cluster FSR 0358, originally discovered by J.D. Kirkpatrick, is the most likely real cluster amongst the cluster candidates from Froebrich et al. Here, we present new deep high resolution near-infrared imaging of this object obtained with the United Kingdom Infrared Telescope (UKIRT). The analysis of the data reveals that FSR 0358 (Kirkpatrick 1) is a  5 ± 2 Gyr  old open cluster in the outer Milky Way. Its age, metallicity of   Z = 0.008  and distance from the Galactic Centre of 11.2 kpc are typical for the known old open galactic clusters. So far six of the FSR cluster candidates have been identified as having an age above 5 Gyr. This shows the significance of this catalogue in enhancing our knowledge of the oldest open clusters in the Galaxy.  相似文献   

8.
The evolution of the Solar neighbourhood is followed using a unique, magnitude complete and kinematically unbiased sample of 14,000 F, G, and K dwarfs. Metallicity, age, space motion and galactic orbits have been determined for all stars. The result is a detailed view of the complex evolution of the local Milky Way, which must be matched by any model for the chemical and dynamical evolution of the Galactic disk. E.g., such models must explain the shape and large scatter in the age-metallity relation as well as the overall metallicity distribution; the evolution of stellar kinematics with age; the distribution of stars in velocity space; and the contributions from the thick and thin disks to all these relations. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

9.
We present a review of elemental abundances in the Milky Way stellar disk, bulge, and halo with a focus on data derived from high-resolution stellar spectra. These data are fundamental in disentangling the formation history and subsequent evolution of the Milky Way. Information from such data is still limited and confined to narrowly defined stellar samples. The astrometric Gaia satellite will soon be launched by the European Space Agency. Its final data set will revolutionize information on the motions of a billion stars in the Milky Way. This will be complemented by several ground-based observational campaigns, in particular spectroscopic follow-up to study elemental abundances in the stars in detail. Our review shows the very rich and intriguing picture built from rather small and local samples. The Gaia data deserve to be complemented by data of the same high quality that have been collected for the solar neighborhood.  相似文献   

10.
We reviewed the recent progress in the field of stellar/galactic archeology, which is a study of the relics from the early galaxy. The oldest and most pristine objects that can be observed in the galaxy are the low mass metal poor stars of the Milky Way. They were formed during the early phases, when the ISM might have been polluted only by the Pop-III supernovae. With the recent large spectroscopic surveys (e.g. HK survey by Beers and collaborators, the Hamburg-ESO survey by Christlieb and collaborators and Sloan Digital Sky Survey) it has been possible to get clues on the nature of the first stars that has contributed to the heavy elements. Most of these metal-poor low mass stars also retain their signature of the early dynamical evolution of the galaxy, which can be studied through their orbits around the galaxy and spatial distribution. Here, we discuss the connection between the chemical and the kinematical properties of metal-poor stars in order to probe the early galaxy formation. We also discuss about the globular clusters, the satellite galaxies around the Milky Way and its possible contribution to the formation of the galaxy halo.  相似文献   

11.
An algorithm of an automatic search for HI shells is presentedand results of identifications in the Leiden-DwingelooHI survey are shown. An identification algorithm searches forlocal minima in channel maps, then creates 3-dimensional objects,HI holes. There is no a priori constraint on the shape of an HI hole, only the dimension criterion: dimensions of the structuremust lie in a preselected interval.When this algorithm is applied to the Leiden-Dwingeloo HI survey,it finds about 1000 structures, which are seen in 4 or more consecutivevelocity channels (Δ v ≥ 4 kms-1. A total energy contained in all structures in the Milky Way is of theorder of 1055 erg, which is less than the energy correspondingto the observed SNR. 80% of the energy contained in holes resides at low galactic z-coordinates, |z|<2 kpc.  相似文献   

12.
The picture of the young stellar groups in the Canis Major–Puppis–Vela (215°< l <275°) section of the Milky Way is studied and updated utilizing uvbyβ photometry of intrinsically luminous OB stars. We use all data from the literature to create a sample with 98 per cent completeness to 9.5 mag.
The very dense low reddened OB association CMa OB1 is confirmed at a distance of 0.99 (±0.05 s.e. ) kpc. Towards Puppis the brightest intrinsically luminous stars do not reveal Pup OB1 and Pup OB2. In the same direction, we separate two small groups, previously related to the association surrounding NGC 2439 at 3.5–4.5 kpc. The first one contains four highly reddened B-type supergiants situated in front of the cluster at 1.03 (±0.14 s.e.) kpc – much closer to the Sun than has been estimated before. The second one lies north-west from the cluster at 3.2 (±0.23 s.e.) kpc according to our estimate. In the direction to Vela, the bright OB stars are apparently embedded in a dust cloud and spread out between 0.3 and 2.5 kpc, forming clumps over this distance range.
In general, the prominent apparent young structures delineated by the brightest intrinsically luminous OB stars in the directions of Canis Major and Vela are some 20–25 per cent closer to the Sun than has previously been thought. This is in agreement with the Hipparcos results for the Galactic OB associations, and is highly likely to be caused by the overestimation of the spectroscopic distances used in the previous studies.  相似文献   

13.
A project of a spectroscopic survey of Galactic structure and evolution with a Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) is presented. The spectroscopic survey consists of two observational modes for various targets in our Galaxy. One is a major survey of the Milky Way aimed at a systematic study of the stellar abundance and Galactic chemical evolution through low resolution (R=1000-2000) spectroscopy. Another is a follow-up observation with medium resolution (R = 10000) spectrographs aimed at detailed studies of the selected stars with different chemical composition, kinematics and dynamics.  相似文献   

14.
We discuss a possible use of the asymptotic giant branch (AGB) stars for tracing star formation histories on the Galactic and extragalactic distance scales with the ESA's astrometric space mission GAIA. Extensive numerical simulations demonstrate that metallicities (Δ [M/H] ≲ 0.3) can be obtained for the AGB stars with GAIA up to the distances of ∼ 200 kpc, if no interstellar extinction is present. Reliable population ages can be also obtained from the AGB stars if their T eff are constrained precisely. We show that precise effective temperatures can be obtained by fitting observed spectral energy distributions of the AGB stars with theoretical fluxes calculated from the synthetic spectra. A combination of the derived effective temperatures with the bolometric luminosities allows to derive precise population ages for a wide range of ages and metallicities over the large distance scales. This demonstrates that AGB stars can be employed very effectively for tracing star formation histories with GAIA, allowing to refine the global evolutionary scenarios of stellar populations in the Milky Way and the galaxies beyond. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

15.
Based on archival Hubble Space Telescope images, we have performed stellar photometry of several fields in the isolated spiral galaxies NGC 6503 and NGC 6946 with high peculiar velocities. Based on the TRGB method, we have determined the distances to the galaxies: D = 6.30 ± 0.10 Mpc for NGC 6503 and D = 6.72 ± 0.15 Mpc for NGC 6946. The current stellar content of the galaxies does not differ from that of other similar galaxies. The metallicity for young stars in NGC 6503 is Z = 0.02 (corresponding to the solar metallicity), while the metallicity for stars in NGC 6946 reaches Z = 0.05. Very few old globular clusters have been found in NGC 6946, while they have not been found at all in NGC 6503. The number density distribution of stars with different ages in NGC 6503 does not differ from the analogous distributions in other galaxies. The large sizes of the thick disk in NGC 6503, which is clearly seen up to 6 kpc from the galactic disk plane and whose possible extension is noticeable up to 8.6 kpc from the plane, are a difference. The sizes of the region occupied by red giants of the disk in NGC 6503 are 51 × 17 kpc, which are not much larger than the sizes of this galaxy from H I radio observations.  相似文献   

16.
Quantitative estimates of ionization sources that maintain the night-time E- and F-region ionosphere are given. Starlight (stellar continuum radiation in the spectral inverval 911–1026 Å) and resonance scattering of solar Ly-β into the night sector are the most important sources in the E-region and are capable of maintaining observable electron densities of order (1–4) × 103 cm?3. Starlight ionization rates have substantial variations (factors of 2–4) with latitude and time of year since the brightest stars in the night sky occur in the southern Milky Way and Orion regions. In the lower F-region the major O+ source in the equatorial ionosphere is 910 Å radiation from the O+ recombination in the F2-region, whereas in the extratropical ionosphere interplanetary 584 Å radiation only exceeds resonance scattering of solar 584 and 304 Å radiation as the dominant O+ source during the month of December.  相似文献   

17.
Stellar abundance pattern of n-capture elements such as barium is used as a powerful tool to infer how the star formation proceeded in dwarf spheroidal (dSph) galaxies. It is found that the abundance correlation of barium with iron in stars belonging to dSph galaxies orbiting the Milky Way, i.e., Draco, Sextans, and Ursa Minor have a feature similar to that in Galactic metal-poor stars. The common feature of these two correlations can be realized by our in homogeneous chemical evolution model based on the supernova-driven star formation scenario if dSph stars formed from gas with a velocity dispersion of ∼ 26 km s-1. This velocity dispersion together with the stellar luminosities strongly suggest that dark matter dominated dSph galaxies. The tidal force of the Milky Way links this velocity dispersion with the currently observed value ≲ 10 km s-1 by stripping the dark matter in dSph galaxies. As a result, the total mass of each dSph galaxy is found to have been originally ∼ 25 times larger than at present. In this model, supernovae immediately after the end of the star formation can expel the remaining gas over the gravitational potential of the dSph galaxy. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

18.
The goal of this work is to assess the expected scientific output from the photometric studies of globular clusters in the Large Magellanic Cloud with ESA's astrometric space mission GAIA. For this purpose we simulate GAIA photometry of individual stars in synthetic cluster populations, covering a large range of cluster ages and metallicities. We find that accurate effective temperatures (Δ T eff<10%) can be obtained from GAIA photometry down to V ∼ 18 for stars in populations within the studied metallicity range ([M/H] = -0.4 ... -1.7). GAIA will also provide photometric metallicities (Δ [M/H] ≲ 0.3 dex) for the cluster giants brighter than V ∼ 17.5. The knowledge of the effective temperature sand metallicities will allow to obtain accurate ages of stellar populations younger than about 1 Gyr using the usual procedure of main sequence turn-off point fitting. Ages of older stellar populations (≳ 1 Gyr) may be constrained from the isochrone fits to the giant branches in the observed CMDs. We conclude that GAIA will provide excellent opportunities for studying star formation histories far beyond the Milky Way, providing means for better understanding of stellar and galactic evolution in different astrophysical environments. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
We explore the predictions of the standard hierarchical clustering scenario of galaxy formation, regarding the numbers and metallicities of PopIII stars that are likely to be found within our Galaxy today. By PopIII we refer to stars formed at large redshift ( z >4), with low metallicities ([ Z /Z⊙]<−2.5) and in small systems (total mass ≲ 2×108 M⊙) that are extremely sensitive to stellar feedback, and which through a prescribed merging history end up becoming part of the Milky Way today. An analytic, extended Press–Schechter formalism is used to obtain the mass functions of haloes which will host PopIII stars at a given redshift, and which will end up in Milky Way sized systems today. Each of these is modelled as a mini-galaxy, with a detailed treatment of the dark halo structure, angular momentum distribution, final gas temperature and disc instabilities, all of which determine the fraction of the baryons that are subject to star formation. The use of new primordial metallicity stellar evolutionary models allows us to trace the history of the stars formed, and give accurate estimates of their expected numbers today and their location in L /L⊙ versus T /K Hertzsprung–Russell (HR) diagrams. A first comparison with observational data suggests that the initial mass function (IMF) of the first stars was increasingly high-mass weighted towards high redshifts, levelling off at z ≳9 at a characteristic stellar mass scale m s=10–15 M⊙.  相似文献   

20.
We argue that observations on Milky Way and dwarf spheroidals imply existence of individual haloes around dwarf spheroidals. If neutrinos (or any other ‘hot’ particle) provide the dark matter then we show that: (i) Embedding of visible matter inside large (∼ few Mpc) dark matter islands is observationally untenable. (ii) Dwarf spheroidals possess dark matter haloes of about 10 kpc radius around them, and have an (M/L) ratio of about 104. (iii) The haloes of spiral galaxies (e.g. Milky Way) extend to about 100 kpc in radius. If ‘cold’ dark matter makes up the haloes, then no significant constraints are obtained. We discuss briefly the effect of these constraints on larger scales.  相似文献   

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