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1.
Using high-resolution spectra, we study 31 yellow supergiants of the Large and Small Magellanic Clouds by the method of atmosphere models. Abundance values of 20 chemical elements are determined. It is shown that ??-elements are in a slight excess and neutron-capture elements have an excess up to 0.60 dex. Approbation of a new technique for the determination of absolute stellar magnitudes of late-type supergiants is performed. The technique is based on the use of the spectroscopic criterion, namely, depth-line ratios for iron. Absolute stellar magnitudes of nine supergiants of the Large Magellanic Cloud are calculated using this technique. A value of the distance modulus of the Large Magellanic Cloud is estimated: m ? M = 18.4 ± 0.3 m .  相似文献   

2.
Summary The Magellanic Clouds play a fundamental role in a number of fields of astronomical research. Their distances are most relevant to the extragalactic distance scale. Their relative proximity offers exceptional opportunities for detailed studies of their stellar and interstellar content. They serve therefore as testing grounds for modern astrophysical theories, in particular concerning the chemical evolution of stars and galaxies.In this review we will discuss recent attempts to determine accurate distances to the Magellanic Clouds. We will consider their stellar generations as the results of interactions between the Large and the Small Magellanic Cloud as well as between the Clouds and the Galaxy. Recent determinations of the chemical abundances of the various age groups will be presented. The fact that the evolution of the Clouds has been slower than that of our Galaxy gives us the opportunity to study the conditions in slightly metalpoor galaxies. Recent progress in observing techniques has added much to our knowledge about the interstellar medium of the Clouds.The Magellanic System, which comprises the Magellanic Clouds, the Inter-Cloud Region and the Magellanic Stream, will be described. We will in particular consider the complex structure of the Large and the Small Cloud and the kinematics of their populations.  相似文献   

3.
We have applied the near-infrared surface-brightness method to 111 Cepheids in the Milky Way and in the Large and the Small Magellanic Clouds determining distances and luminosities for the individual stars. We find that the K-band Period-Luminosity (PL-)relations for Milky Way and Large Magellanic Cloud Cepheids are almost identical, whereas the zero point of the Wesenheit relation depends significantly on metallicity, metal poor Cepheids being fainter.  相似文献   

4.
The Vista Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting K S -band time series photometry of the system formed by the two Magellanic Clouds (MC) and the “bridge” that connects them. These data are used to build K S -band light curves of the MC RR Lyrae stars and Classical Cepheids and determine absolute distances and the 3D geometry of the whole system using the K-band period luminosity (PLK S ), the period–luminosity–color (PLC) and the Wesenhiet relations applicable to these types of variables. As an example of the survey potential we present results from the VMC observations of two fields centered respectively on the South Ecliptic Pole and the 30 Doradus star forming region of the Large Magellanic Cloud. The VMC K S -band light curves of the RR Lyrae stars in these two regions have very good photometric quality with typical errors for the individual data points in the range of ∼0.02 to 0.05 mag. The Cepheids have excellent light curves (typical errors of ∼0.01 mag). The average K S magnitudes derived for both types of variables were used to derive PLK S relations that are in general good agreement within the errors with the literature data, and show a smaller scatter than previous studies.  相似文献   

5.
The Small Magellanic Cloud is a close, irregular galaxy that has experienced a complex star formation history due to the strong interactions occurred both with the Large Magellanic Cloud and the Galaxy. Despite its importance, the chemical composition of its stellar populations older than ∼ 1–2 Gyr is still poorly investigated. I present the first results of a spectroscopic survey of ∼ 200 Small Magellanic Cloud giant stars performed with FLAMES@VLT. The derived metallicity distribution peaks at [Fe/H] ∼ –0.9/–1.0 dex, with a secondary peak at [Fe/H] ∼ –0.6 dex. All these stars show [α /Fe] abundance ratios that are solar or mildly enhanced (∼+0.1 dex). Also, three metal‐poor stars (with [Fe/H] ∼ –2.5 dex and enhanced [α /Fe] ratios compatible with those of the Galactic Halo) have been detected in the outskirts of the SMC: These giants are the most metal‐poor stars discovered so far in the Magellanic Clouds. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

6.
A large and complete sample of stars with   K < 9.75  in the NGC 6522 Baade's Window towards the Galactic bulge is examined using light curves extracted from MACHO and IJK photometry from DENIS.
The improved statistics resulting from a sample of over 1000 variables allow all four of the sequences A, B, C and D in the   K S   , log  P diagram of the Large Magellanic Cloud to be seen in the Galactic bulge. The bulge sequences, however, show some differences from those in the Magellanic Clouds, possibly due to the effects of higher metallicity. These sequences may have value as distance indicators.
A new diagram of the frequency of late-type variables at a given amplitude is derived and compared with the old one from Payne-Gaposchkin. The catalogued semiregular variables of the solar neighbourhood are found to be a subset of the total of semiregulars, biased towards large amplitude.  相似文献   

7.
《New Astronomy Reviews》2004,48(9):727-730
We present results of our ongoing observing program on search and studies of massive stars (O type) in binary systems in our neighbour galaxies, the Magellanic Clouds. Radial velocity orbits are presented for two new binaries, one in the Small Magellanic Cloud and another in the Large Magellanic Cloud.  相似文献   

8.
《New Astronomy Reviews》2004,48(9):659-665
The average of 14 recent measurements of the distance to the Large Magellanic Cloud (LMC) implies a true modulus of 18.50 ± 0.02 mag, and demonstrates a trend in the past 2 years of convergence toward a standard value. The distance indicators reviewed are the red clump, the tip of the red giant branch, Cepheid, RR Lyrae, and Mira variable stars, cluster main-sequence fitting, supernova 1987A, and eclipsing binaries. The eclipsing binaries yield a consistent distance on average; however, the internal scatter is twice as large as the average measurement error. I discuss parameters of LMC structure that pertain to distance indicators, and speculate that warps discovered using the color of the clump are not really warps.  相似文献   

9.
A nearly complete sample of 24 Magellanic Cloud WC/WO subclass Wolf–Rayet stars is studied spectroscopically and photometrically to determine its binary frequency. Theory predicts the Roche lobe overflow produced Wolf–Rayet binary frequency to be 52±14 per cent in the Large Magellanic Cloud and 100 per cent in the Small Magellanic Cloud, not counting non-Roche lobe overflow Wolf–Rayet binaries. Lower ambient metallicity ( Z ) leads to lower opacity, preventing all but the most massive (hence luminous) single stars from reaching the Wolf–Rayet stage. However, theory predicts that Roche lobe overflow even in binaries of modest mass will lead to Wolf–Rayet stars in binaries with periods below approximately 200 d, for initial periods below approximately 1000 d, independent of Z . By examining their absolute continuum magnitudes, radial velocity variations, emission-line equivalent widths and full widths at half-maximum, a WC/WO binary frequency of only 13 per cent, significantly lower than the prediction, is found in the Large Magellanic Cloud. In the unlikely event that all of the cases with a less certain binary status actually turn out to be binary, current theory and observation would agree. (The Small Magellanic Cloud contains only one WC/WO star, which happens to be a binary.) The three WC+O binaries in the Large Magellanic Cloud all have periods well below 1000 d. The large majority of WC/WO stars in such environments apparently can form without the aid of a binary companion. Current evolutionary scenarios appear to have difficulty explaining either the relatively large number of Wolf–Rayet stars in the Magellanic Clouds, or the formation of Wolf–Rayet stars in general.  相似文献   

10.
Chemical evolution of the Magellanic Clouds: analytical models   总被引：1，自引：0，他引：1  
We have extended our analytical chemical evolution modelling ideas for the Galaxy to the Magellanic Clouds. Unlike previous authors (Russell &38; Dopita, Tsujimoto et al. and Pilyugin), we assume neither a steepened initial mass function nor selective galactic winds, since among the α-particle elements only oxygen shows a large deficit relative to iron and a similar deficit is also found in Galactic supergiants. Thus we assume yields and time delays identical to those that we previously assumed for the solar neighbourhood. We include inflow and non-selective galactic winds and consider both smooth and bursting star formation rates, the latter giving a better fit to the age–metallicity relations. We predict essentially solar abundance ratios for primary elements and these seem to fit most of the data within their substantial scatter. Our model for the Large Magellanic Cloud also gives a remarkably good fit to the anomalous Galactic halo stars discovered by Nissen &38; Schuster.   Our models predict current ratios of Type Ia supernova to core-collapse supernova rates enhanced by 50 and 25 per cent respectively relative to the solar neighbourhood, in fair agreement with ratios found by Cappellaro et al. for Sdm–Im relative to Sbc galaxies, but these ratios are sensitive to detailed assumptions about the bursts and a still higher enhancement in the Large Magellanic Cloud has been deduced from X-ray studies of remnants by Hughes et al. The corresponding ratios integrated over time up to the present are slightly below 1, but they exceed 1 if one compares the Magellanic Clouds with the Galaxy at times when it had the corresponding metallicities.  相似文献   

11.
We discuss the potential for using extragalactic eclipsing binaries with well-determined physical properties as standard candles to improve the extragalactic distance scale. The advent of high quantum efficiency/low noise CCDs has now made it possible to obtain high precision light and radial velocity curves for the more luminous OB-type eclipsing binaries in the Magellanic Clouds with even small to moderate size (1–2m) telescopes. This can lead to the determination of distance moduli (m-M)0 to the LMC and SMC with precisions of about 0m.15 for individual binaries.These distances are essentially free from the assumptions made using other distance indicators.  相似文献   

12.
The young blue populous cluster NGC 1866 in the Large Magellanic Cloud is an object which is well suited for a comparison of several basic distance indicators including ZAMS-fitting, the Cepheid period-luminosity-(colour) relation, Baade-Wesselink analysis of the Cepheids and luminosity determination for the B-stars from Strömgren'suvby-H-photometry.A progress report on a project aimed at exploring these possibilities will be presented here.  相似文献   

13.
Six stars out of a sample of ∼2300 carbon stars in the Magellanic Clouds have been identified as having strong C2 bands but CN bands that are very weak or absent. It is argued that five of these are likely to be R Coronae Borealis (RCB) stars on the basis of their spectral characteristics and peculiar colours. Most are variables and the Large Magellanic Cloud (LMC) members have extreme radial velocities that are more like the planetary nebula population than the carbon stars. This sample consists of four LMC members (only one of them previously recognized as an RCB star), one Small Magellanic Cloud (SMC) member (the first RCB star reported in the SMC) and one foreground Galactic star.  相似文献   

14.
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   

15.
We report the extragalactic radio-continuum detection of 15 planetary nebulae (PNe) in the Magellanic Clouds (MCs) from recent Australia Telescope Compact Array+Parkes mosaic surveys. These detections were supplemented by new and high-resolution radio, optical and infrared observations which helped to resolve the true nature of the objects. Four of the PNe are located in the Small Magellanic Cloud (SMC) and 11 are located in the Large Magellanic Cloud (LMC). Based on Galactic PNe the expected radio flux densities at the distance of the LMC/SMC are up to ∼2.5 and ∼2.0 mJy at 1.4 GHz, respectively. We find that one of our new radio PNe in the SMC has a flux density of 5.1 mJy at 1.4 GHz, several times higher than expected. We suggest that the most luminous radio PN in the SMC (N S68) may represent the upper limit to radio-peak luminosity because it is approximately three times more luminous than NGC 7027, the most luminous known Galactic PN. We note that the optical diameters of these 15 Magellanic Clouds (MCs) PNe vary from very small (∼0.08 pc or 0.32 arcsec; SMP L47) to very large (∼1 pc or 4 arcsec; SMP L83). Their flux densities peak at different frequencies, suggesting that they may be in different stages of evolution. We briefly discuss mechanisms that may explain their unusually high radio-continuum flux densities. We argue that these detections may help solve the 'missing mass problem' in PNe whose central stars were originally  1–8 M⊙  . We explore the possible link between ionized haloes ejected by the central stars in their late evolution and extended radio emission. Because of their higher than expected flux densities, we tentatively call this PNe (sub)sample –'Super PNe'.  相似文献   

16.
Narrow band-pass direct photographs have been secured of the central region of 30 Doradus and of several other nebulosities in the Magellanic Clouds. We have utilized an image tube camera attached to the Yale one-meter telescope at the Cerro Tololo Interamerican Observatory. Interference filters whose band passes were selected to allow for the radial velocities of the Magellanic Clouds have been utilized to record monochromatic images of [Nii] 6584, H, Hei 5876, and [Oiii] 5007. In 30 Doradus the main filamentary structures appear to be very similar in H, Hei, [Nii], and [Oiii] at least in the inner regions where most spectroscopic measurements have been made. The features appear to be material bounded rather than radiation bounded and the excitation differences are very small. Likewise, in NGC 346 in the Small Magellanic Cloud the [Oiii] and H images are very similar, but in N44 in the Large Magellanic Cloud excitation differences do appear. The implications of these observations for chemical compositions of nebulosities in the Magellanic Clouds would appear to be that spectroscopic and scanner studies should be supplemented by monochromatic photographs. Some nebulosities can be handled by simple models while for others excitation differences must be taken into account.Guest investigators at Cerro Tololo Interamerican Observatory operated by the Association of Universities for Research in Astronomy under contract with the National Science Foundation  相似文献   

17.
New methods are applied to samples of classical cepheids in the galaxy, the Large Magellanic Cloud, and the Small Magellanic Cloud to determine the interstellar extinction law for the classical cepheids, R B:R V:R I:R J:R H:R K= 4.190:3.190:1.884:0.851:0.501:0.303, the color excesses for classical cepheids in the galaxy, E(B-V)=-0.382-0.168logP+0.766(V-I), and the color excesses for classical cepheids in the LMC and SMC, E(B-V)=-0.374-0.166logP+0.766(V-I). The dependence of the intrinsic color (B-V)0 on the metallicity of classical cepheids is discussed. The intrinsic color (V-I)0 is found to be absolutely independent of the metallicity of classical cepheids. A high precision formula is obtained for calculating the intrinsic colors of classical cepheids in the galaxy: (<B>-<V>)0=0.365(±0.011)+0.328(±0.012)logP.  相似文献   

18.
A classification scheme for planetary nebulae in the Magellanic Clouds using four key criteria is suggested. All nebulae can then be divided into three classes. The features of physical parameters and evolution of the Magellanic Cloud planetary nebulae and the way in which they differ from galactic planetary nebulae are investigated separately for each class of nebulae.  相似文献   

19.
Excitation of radial pulsations in red supergiants of Magellanic Clouds is investigated using the stellar evolution calculations and the self-consistent solution of the equations of radiation hydrodynamics and turbulent convection. The stars with initial masses 6M ⊙ ≤ M ZAMS ≤ 28M ⊙ and the initial chemical composition X = 0.7, 0.004 ≤ Z ≤ 0.008 are shown to be unstable against fundamental mode oscillations with periods from 17 to 1200 days as they become helium burning red supergiants. The period-luminosity relation slightly depends on the mass loss rate varying with a factor of three, whereas its dependence on the metal abundance is given by δM bol = 0.89δ log Z. In comparison with galactic red supergiants the low metal abundances in red supergiants of Magellanic Clouds are responsible for their higher effective temperatures and substantially narrower ranges of evolutionary radius change during helium burning. Therefore on the period-mass diagram the red supergiants of Magellanic Clouds are located within the strip with width of δ logM ≈ 0.09, so that the uncertainty of mass evaluation of the red supergiant with the known pulsation period is nearly 25%.  相似文献   

20.
N-body simulations of the Magellanic stream   总被引：1，自引：0，他引：1  
A suite of high-resolution N -body simulations of the Magellanic Clouds–Milky Way system are presented and compared directly with newly available data from the H  i Parkes All-Sky Survey (HIPASS). We show that the interaction between Small Magellanic Clouds (SMC) and Large Magellanic Clouds results in both a spatial and kinematical bifurcation of both the stream and the leading arm. The spatial bifurcation of the stream is readily apparent in the HIPASS data, and the kinematical bifurcation is also tentatively identified. This bifurcation provides strong support for the tidal disruption origin for the Magellanic stream. A fiducial model for the Magellanic Clouds (MCs) is presented upon completion of an extensive parameter survey of the potential orbital configurations of the MCs and the viable initial boundary conditions for the disc of the SMC. The impact of the choice of these critical parameters upon the final configurations of the stream and leading arm is detailed.  相似文献   

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