Recent observational and theoretical studies on the three-dimensional (3D) space motions of the Large and the Small Magellanic Clouds (LMC and SMC, respectively) have strongly suggested that the latest proper motion measurements of the Magellanic Clouds (MCs) are consistent with their orbital evolution models in which the MCs have arrived in the Galaxy quite recently for the first time. The suggested orbital models appear to be seriously inconsistent with the tidal interaction models in which the Magellanic Stream (MS) can be formed as a result of the mutual tidal interaction between the MCs and the Galaxy for the last ~2 Gyr. Based on orbital models of the MCs, we propose that if the MCs have a common diffuse dark halo with the mass larger than ~ 2 * 10^{10} M_sun, the MCs can not only have the present 3D velocities consistent with the latest proper motion measurements but also interact strongly with each other and with the Galaxy for the last 2 Gyr.These results imply that if the observed proper motions of the MCs are true ones of the centers of mass for the MCs, the common halo of the MCs would need to be considered in constructing self-consistent MS formation models. We discuss whether the origin of the possible common halo can be closely associated either with the past binary formation or with the MCs having been in a small group.
We model the dynamics of Magellanic Stream with the ram-pressure scenario in the logarithmic and power-law galactic halo models and construct numerically the past orbital history of Magellanic clouds and Magellanic Stream. The parameters of models include the asymptotic rotation velocity of spiral arms, halo flattening, core radius and rising or falling parameter of rotation curve. We obtain the best fit parameters of galactic models through the maximum likelihood analysis, comparing the high resolution radial velocity data of HI in Magellanic Stream with that of theoretical models. The initia…
The properties of the Magellanic Stream constrain the density of coronal gas in the distant Galactic halo. We show that motion through ambient gas can strongly heat Stream clouds, driving mass loss and causing evaporation. If the ambient gas density is too high, then evaporation occurs on unreasonably short timescales. Since heating dominates drag, tidal stripping appears to be responsible for producing the Stream. Requiring the survival of the cloud MS IV for 500 Myr sets an upper limit on the halo gas density n_H< 10^{-5} cm^{-3} at 50 kpc, roughly a factor of 10 lower than that estimated fr…
Important problems to which we would like to find answers are: What are the distances to the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC)? What is the present distribution of stars, gas and dark matter in the Clouds, and how did it evolve? How, and where, did the Magellanic Clouds form, and how have their orbits evolved? Finally the recent discovery of numerous microlensing events in the Clouds provides answers to questions that we have only recently started to ask.
The oldest and most metal-poor Milky Way stars form a kinematically hot halo, which motivates the two major formation scenarios for our galaxy: extended hierarchical accretion and rapid collapse. RR Lyrae stars are excellent tracers of old and metal-poor populations. We measure the kinematics of 43 RR Lyrae stars in the inner regions of the nearby Large Magellanic Cloud (LMC) galaxy. The velocity dispersion, σ_{true}=53\pm10 km/s, indicates that a kinematically hot metal-poor old halo also exists in the LMC. This suggests that our galaxy and smaller late-type galaxies like the LMC have similar…
We present our catalog of U, B, V, and I stellar photometry of the central 64 sq. deg. area of the Large Magellanic Cloud. Internal and external astrometric and photometric tests using existing optical photometry (U, B, and V from Massey's bright star catalog and I from the near-infrared sky survey DENIS) are used to confirm our observational uncertainty estimates. We fit stellar atmosphere models to the optical data to check the consistency of the photometry for individual stars across the passbands and to estimate the line-of-sight extinction. Finally, we use the estimated line-of-sight exti…
In this paper, we investigate the intrinsic bias in detecting caustic crossings between Galactic halo and self-lensing events in the Magellanic Clouds. For this, we determine the region for optimal caustic-crossing detection in the parameter space of the physical binary separations, $\ell$, and the total binary lens mass, $M$, and find that the optimal regions for both populations of events are similar to each other. In particular, if the Galactic halo is composed of lenses with the claimed average mass of $<M>\sim 0.5 M_\odot$, the optimal binary separation range of Galactic halo events of $3…
The present status of our knowledge of the distances to the Magellanic Clouds is evaluated from a post-Hipparcos perspective. After a brief summary of the effects of structure, reddening, age and metallicity, the primary distance indicators for the Large Magellanic Cloud are reviewed: The SN 1987A ring, Cepheids, RR Lyraes, Mira variables, and Eclipsing Binaries. Distances derived via these methods are weighted and combined to produce final "best" estimates for the Magellanic Clouds distance moduli.
Some recent results on AGB research in the Magellanic Clouds are reviewed. Discussed are optical and IRAS based surveys, and recent results from the near-infrared DENIS survey, and ISO observations.
From an analysis of the sky and velocity distributions of the high-velocity clouds (HVCs) we show that the majority of the HVCs has a common origin. We conclude that the HVCs surround the Galaxy, forming a metacloud of 300 kpc in size and with a mass of 3 10^9 M_sun, and that they are the product of a powerful ``superwind'' (about 10^58 ergs), which occurred in the Magellanic Clouds about 570 Myr ago as a consequence of the interaction of the Large and Small Magellanic Clouds. The HVCs might be magnetic bubbles of semi-ionized gas, blown from the Magellanic Clouds around 570 Myr ago, that circ…
Aims : We study an unknown, or very poorly known, interstellar HII component in the Magellanic Clouds. This is the first study ever devoted to this class of objects, which we call Low-excitation blobs (LEBs). Methods : We used low-dispersion spectroscopy carried out at ESO to obtain emission line intensities of Ha, Hb, and [OIII] (4959+5007) for 15 objects in the Large Magellanic Cloud and 14 objects in the Small Magellanic Cloud. Results are displayed in excitation ([oiii]/Hb ratio) versus Hb luminosity diagrams. Results : We show the presence of an LEB component in the Magellanic Clouds and …
The flat rotation curve obtained for the outer star clusters of the Large Magellanic Cloud is suggestive of an LMC dark matter halo. From the composite HI and star cluster rotation curve, I estimate the parameters of an isothermal dark matter halo added to a `maximum disk.' I then examine the possibility of detecting high energy gamma-rays from non-baryonic dark matter annihilations in the central region of the Large Magellanic Cloud.
The Magellanic Clouds provide the ideal laboratory for the study of mass loss and molecule and dust formation in red giants as a function of luminosity and metal abundance. I present some recent observational work.
I present results with respect to the gamma-ray and synchrotron fluxes due to neutralino annihilation in the Large Magellanic Cloud based on Tasitsiomi et al., Astrop. Phys. 21, 637 (2004).
We present our catalog of U, B, V, and I stellar photometry of the central 18 sq. degree area of the Small Magellanic Cloud. We combine our data with the 2MASS and DENIS catalogs to provide, when available, U through K_S data for stars. Internal and external astrometric and photometric tests using existing optical photometry (U, B, and V from Massey's bright star catalog; B, V, and I from the microlensing database of OGLE and I from the near-infrared sky survey DENIS) are used to determine the observational uncertainties and identify systematic errors. We fit stellar atmosphere models to the o…
Regions of different metallicity have been identified in the Magellanic Clouds by using the ratio between Asymptotic Giant Branch stars of spectral type C and M. In the Large Magellanic Cloud the ratio appears to decrease radially while in the Small Magellanic Cloud (SMC) there is no clear trend, reflecting either the large extension of the SMC along the line of sight or a more complex star formation history. The distribution of the C/M ratio is clumpy and corresponds to a spread in [Fe/H] of 0.75 dex in both Clouds. There is an indication of increasing C/M ratio, thus decreasing metallicity, …
We report the results of our project devoted to study the chemical enrichment history of the field population in the Magellanic Clouds using Ca II triplet spectroscopy.
We present results from the combined Australia Telescope Compact Array (ATCA) aperture synthesis mosaic survey of HI emission in the Large Magellanic Cloud with 64m Parkes single dish telescope observations.
In this review we address the progress that has been made toward the understanding the population of Magellanic Cloud planetary nebulae since the last Magellanic Cloud Symposium. Planetary nebulae in the Clouds are not only important as key probes of stellar and ISM evolution in these galaxies, but also reflect the evolution of AGB stars and beyond in low-metallicity environments. We present the recent surveys results, including the wide fields ground-based search for PNe, the {\it HST} study of the resolves ejecta and their central stars, and the {\it Spitzer} analysis of the gas contents of …
Results obtained in the Magellanic Clouds using the latest near-IR DENIS survey are briefly revised. This sets the base to a similar study of AGB stars in other galaxies of the Local Group and in particular in NGC6822.
This review contains: (1) the scientific motivations for studying Planetary Nebulae in the Magellanic Clouds; (2) a review of this field of study, from the origins to the most recent results, focusing on the papers that have been published since the last IAU Symposium on Planetary Nebulae; (3) a review of the Hubble contribution to the field, from the early results to our own Magellanic Cloud Planetary Nebula program.
An extensive set of N-body simulations has been carried out on the gravitational interaction of the Small Magellanic Cloud (SMC) with the Galaxy and the Large Magellanic Cloud (LMC). The SMC is assumed to have been a barred galaxy with a disc-to-halo mass ratio of unity before interaction and modelled by a large number of self-gravitating particles, whereas the Galaxy and LMC have been represented by rigid spherical potentials. The best model we have found succeeded in reproducing the Magellanic Stream (MS), as well as a leading counterpart to the Magellanic Stream (the leading arm), on the op…
The spatial distribution of sources populating different regions of the colour-magnitude diagram (I-J, I) extracted from the DENIS catalogue towards the Magellanic Clouds (DCMC -- Cioni et al. 2000) reveal significantly different morphologies. Each region is associated to a different age group. The Large Magellanic Cloud (LMC) shows an extended circular shape with a prominent, off center bar, a nucleus and irregular spiral arms. The Small Magellanic Cloud shows a perturbated structure with a prominent central concentration of stars. Old and young populations are offset from one another.
We present a sample of 76 double-mode Cepheids detected in the 4.5 square degree area in the central part of the LMC. 19 stars from the sample pulsate in the fundamental mode and the first overtone while 57 objects are the first and second overtone pulsators. We analyze the period ratio of double-mode Cepheids and Fourier parameters of decomposition of the light curves of these objects. We also present location of different type Cepheids from the LMC in the color-magnitude diagram and show the distribution of their ${V-I}$ color indices.
We present our analysis of archival Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) observations in F450W (~B) and F555W (~V) of the intermediate- age populous star clusters NGC 121, NGC 339, NGC 361, NGC 416, and Kron 3 in the Small Magellanic Cloud. We use published photometry of two other SMC populous star clusters, Lindsay 1 and Lindsay 113, to investigate the age sequence of these seven populous star clusters in order to improve our understanding of the formation chronology of the SMC. We analyzed the V vs (B-V) and M_V vs (B-V)_0 color-magnitude diagrams of these populous Sm…
We present the first quantitative results explaining the presence in the Large Magellanic Cloud of some asymptotic giant branch stars that share the properties of lithium rich carbon stars. A self-consistent description of time-dependent mixing, overshooting, and nuclear burning was required. We identify a narrow range of masses and luminosities for this peculiar stars. Comparison of these models with the luminosities of the few Li-rich C stars in the Large Magellanic Cloud provides an independent distance indicator for the LMC
We use a numerical simulation of a loose group containing a Milky Way halo to probe that in the hierarchical universe the Magellanic Clouds and some dSphs have been accreted into the Milky Way halo from a late infalling group of dwarfs. Our simulations show that the tidal breakup of the Magellanic group occurs before it enters the Milky Way halo. Only half of the satellites contributed from the group are predicted to be inside the Milky Way virial radius. Half of its subhalos survive outside the current virial radius in the form of satellites, whereas the remaining material contributes to the …
We analyze the topical and demographic evolution of Magellanic Clouds research over the past five years based on submissions of abstracts of refereed papers to the electronic Magellanic Clouds Newsletter (http://www.astro.uiuc.edu/projects/mcnews/MCNews.html).
We have mapped two regions at the northern tip of the Magellanic Stream in neutral hydrogen 21-cm emission using the Arecibo telescope. The new data are used to study the morphology and properties of the Stream far away from the Magellanic Clouds, as well as to provide indirect constraints on the properties of the Galactic Halo. We investigate confinement mechanisms for the Stream clouds and conclude that these clouds cannot be gravitationally confined or in free expansion. The most likely mechanism for cloud confinement is pressure support from the hot Galactic Halo gas. This allows us to pla…
We discuss the young population of stars and clusters in the Magellanic Clouds. We present the discovery of pre-main sequence candidates in the nebula N~11 in the Large Magellanic Clouds using HST ACS photometry. The comparison of the Colour-Magnitude diagram with pre-main sequence tracks and the presence of Spitzer objects YSO I and II suggest that the star formation has been active for a long period in the region, from a few $10^5$ yrs to several Myr ago
Significant numbers of high-velocity HI clouds (HVCs) have now been detected in H-alpha, with a subset seen in low ionization lines (e.g. [NII]). It was originally hoped that the observed H-alpha strength would provide a distance constraint to individual clouds. This idea requires that a useful fraction (f_esc > 1%) of ionizing photons escape the Galaxy, and that the halo ionizing field is relatively smooth, as we discuss. Most HVCs which are known to be close to the Sun are H-alpha; the brightest clouds also show enhanced [NII] emission, in contrast to the Magellanic Stream where the low ioni…
The rotation curve of the Large Magellanic Cloud, which we have derived from high-resolution HI position-velocity diagrams observed by Kim et al (1998), shows a steep central rise and flat rotation with a gradual rise toward the edge. Using the rotation curve, we have calculated the distribution of surface mass density, and show that the LMC has a dark compact bulge, an exponential disk, and a massive halo. The bulge is 1.2 kpc away from the center of the stellar bar, and is not associated with an optical counterpart. This indicates that the "dark bulge" has a large fraction of dark matter, wi…
We performed an extended analysis of the parameter space for the interaction of the Magellanic System with the Milky Way (MW). The varied parameters cover the phase space parameters, the masses, the structure, and the orientation of both Magellanic Clouds, as well as the flattening of the dark matter halo of the MW. The analysis was done by a specially adopted optimization code searching for the best match between numerical models and the detailed HI map of the Magellanic System by Bruens et al. (2005). The applied search algorithm is a genetic algorithm combined with a code based on the fast,…
We present the first results of our study of stellar populations in the Large and Small Magellanic Clouds based on multi-band WFPC2 observations of "random" fields taken as part of the "pure parallel" programme carried out with the HST as a service to the community.
A review is given of the possibilities for the study of the kinematics and metallicities of the old populations in galaxies of the Local Group using SALT/PFIS observations of RR Lyrae variables.
There are a half-dozen or so young supernova remnants in the Magellanic Clouds that display one or more of the following characteristics: high velocity (>1000 km/s) emission, enhanced metallicity, or a rapidly rotating pulsar. I summarize the current state of knowledge of these remnants and present some recent results mostly from the new X-ray astronomy satellites.
We present V(RI)sub data for thirteen Cepheids in the Large Magellanic Cloud ans fifty-five in each wavelength band. The median uncertainty in the photometry iy Moffett, Gieren & Barnes (1998) which contained 1000 measures ($\pm 0.01$ mag) in each wavelength band on 22 variables with periods in the range 8--133 days.
Orbital periods and other parameters of symbiotic binaries in the LMC and SMC are presented and discussed. In particular, the symbiotic stars in the MCs are compared with those in the Milky Way.
Previous attempts at disturbing the galactic disk by the Magellanic Clouds relied on direct tidal forcing. However, by allowing the halo to actively respond rather than remain a rigid contributor to the rotation curve, the Clouds may produce a wake in the halo which then distorts the disk. Recent work reported here suggests that the Magellanic Clouds use this mechanism to produce disk distortions sufficient to account for both the radial location, position angle and sign of the HI warp and observed anomalies in stellar kinematics towards the galactic anticenter and LSR motion.
We show that HI clouds in the Magellanic Clouds are stripped by the ram-pressure due to the halo and disk gases of the Galaxy. Molecular clouds are swept to the edge of the LMC, showing an eccentric distribution. The stripped HI clouds form a narrow band on the sky, and mimics the Magellanic Stream, when the LMC takes a polar orbit. We point out that the Magellanic Stream will fall into the Galaxy, and will be finally accreted by the Galactic disk. The accretion may cause warping of the inner gas disk of the Galaxy. Some clouds are accreted by the nuclear disk, which could explain the peculiar…
A systematic survey of the Large and Small Magellanic Clouds for radio pulsars using the Parkes radio telescope and the 20-cm multibeam receiver has resulted in the discovery of 14 pulsars and the redetection of five of the eight previously known spin-powered pulsars believed to lie in the Magellanic Clouds. Of the 14 new discoveries, 12 are believed to lie within Clouds, three in the Small Cloud and nine in the Large Cloud, bringing the total number of known spin-powered pulsars in the Clouds to 20. Averaged over all positions within the survey area, the survey had a limiting flux density of …
(Abridged) A close scrutiny of the microlensing results towards the Magellanic clouds reveals that the stars within the Magellanic clouds are major contributors as lenses, and the contribution of MACHOs to dark matter is 0 to 5%. The principal results which lead to this conclusion are the following. (i) Out of the ~17 events detected so far towards the Magellanic Clouds, the lens locations have been determined for four events where the lenses are most likely within the Magellanic clouds. (ii) If caused by MACHOs, the event timescales would imply that the MACHOs in the direction of the LMC and …
We have carried out Wide Field Planetary Camera 2 F160BW, F555W and F656N imaging of four young populous clusters: NGC 330 in the Small Magellanic Cloud and NGC 1818, NGC 2004 and NGC 2100 in the Large Magellanic Cloud. We report photometric results for these four clusters, including identification using photometric colours of the cluster Be star population. We present theoretical WFPC2 and broad band colours and bolometric corrections for LMC and SMC metallicities. The use of the far-UV F160BW filter enables accurate determination of the effective temperatures for stars in the vicinity of the…
The results of the interaction between the Milky Way and the Magellanic Clouds are revealed through several high velocity complexes which are connected to the Clouds. The exact mechanism of their formation is under some debate, but they remain the only group of high-velocity clouds (HVCs) for which we have an origin and roughly a distance. Given that, the Magellanic HVCs can be used as a calibrator for other HVCs, while also providing an opportunity to closely investigate the remnants of an interacting system. These HVCs may hold the key to the star formation history, kinematic structure, and …
We present a new distance determination to the Large and Small Magellanic Clouds using the newly developed red clump stars method (Paczynski and Stanek 1998). This new, single-step, Hipparcos calibrated method seems to be one of the most precise techniques of distance determination with very small statistical error due to large number of red clump stars usually available. The distances were determined independently along four lines-of-sight located at opposite sides of each Magellanic Cloud. The results for each line-of-sight are very consistent. For the SMC we obtain the distance modulus: m-M…
We present a sample of 13 candidates for single-mode second overtone Cepheids discovered in the 2.4 square degree area of the SMC bar during the OGLE microlensing search. All candidates passed four photometric tests: analysis of Fourier parameters of the light curve, R_21 and ϕ_21, position in the period-luminosity diagram and location in the color-magnitude diagram. The stars form a very homogeneous group of objects with very similar light curves of low amplitude and almost sinusoidal shape. Their color indices B-V and V-I are also very similar and the objects determine the observational blue…
The satellite-disk interaction provides limits on halo properties in two ways: (1) physical arguments motivate the excitation of observable Galactic disk structure in the presence of a massive halo, although precise limits on halo parameters are scenario-dependent; (2) conversely, the Milky Way as a whole has significant dynamical effect on LMC structure and this interaction also leads to halo limits. Together, these scenarios give strong corroboration of our current gravitational mass estimates and suggests a rapidly evolving LMC.
The Hubble Space Telescope has provided the first clear evidence for weaker winds of metal-poor massive stars in the Small Magellanic Cloud, confirming theoretical predictions of the metallicity dependence of mass-loss rates and wind terminal velocities. For lower luminosity O-type stars however, derived mass-loss rates are orders of magnitude lower than predicted, and are at present unexplained.
We report about the stellar content and the luminosity and mass functions of three stellar associations and their field located on the north-east edge of the super-bubble LMC 4 in the Large Magellanic Cloud.
We present Cepheids located in the close neighborhood of star clusters from the Magellanic Clouds. 204 and 132 such stars were found in the LMC and SMC, respectively. The lists of objects were constructed based on catalogs of Cepheids and star clusters, recently published by the OGLE-II collaboration. Location of selected Cepheids on the sky indicates that many of them are very likely cluster members. Photometric data of Cepheids and clusters are available from the OGLE archive.
We investigate the dynamical and chemical evolution of the Large Magellanic Cloud (LMC) interacting with the Galaxy and the Small Magellanic Cloud (SMC) based on a series of self-consistent chemodynamical simulations. Our numerical models are aimed at explaining the entire properties of the LMC, i.e., the observed structure and kinematics of its stellar halo and disk components as well as the populations of the field stars and star clusters. The main results of the present simulations are summarized as follows. (1) Tidal interaction between the Clouds and the Galaxy during the last 9 Gyr trans…
The past decade has witnessed impressive progress in our understanding of the physical properties of massive stars in the Magellanic Clouds, and how they compare to their cousins in the Galaxy. I summarise new results in this field, including evidence for reduced mass-loss rates and faster stellar rotational velocities in the Clouds, and their present-day compositions. I also discuss the stellar temperature scale, emphasizing its dependence on metallicity across the entire upper-part of the Hertzsprung-Russell diagram.
Stellar pulsations in main-sequence B-type stars are driven by the $κ$-mechanism due to the Fe-group opacity bump. The current models do not predict the presence of instability strips in the B spectral domain at very low metallicities. As the metallicity of the Magellanic Clouds (MC) has been measured to be around $Z=0.002$ for the Small Magellanic Cloud (SMC) and $Z=0.007$ for the Large Magellanic Cloud (LMC), they constitute a very suitable objects to test these predictions. The aim of this work is to investigate the existence of B-type pulsators at low metallicities, searching for short-ter…
We observed five central stars of planetary nebulae (CSPN) in the Large Magellanic Cloud (LMC) and three in the Small Magellanic Cloud (SMC) with the Far Ultraviolet Spectroscopic Explorer (FUSE), in the range 905-1187 Ang. We performed a model-based analysis of these spectra in conjunction with Hubble Space Telescope (HST) spectra in the UV and optical range to determine stellar and nebular parameters. The signature of hot (T >~ 2000 K) circumstellar molecular hydrogen is found in the FUSE spectra of most objects. We also find evidence of X-rays in the wind of LMC-SMP 76.
EROS2 is a second generation microlensing experiment operating since mid-1996 at the European Southern Observatory (ESO) at La Silla (Chile). We present the two year analysis from our microlensing search towards the Small Magellanic Cloud (SMC) and report on the intensive observation of the caustic crossing event MACHO-SMC-98-1 and the limit derived on t he location of the lens. We also give preliminary results from our search towards the Large Magellanic Cloud (LMC); 25 square degrees are being analyzed and two candidates have been found. This allows us to set another limit on the halo mass f…
Superbubbles that result from the stellar winds and supernovae of OB associations probably play a fundamental role in the structure and energetics of the ISM in star-forming galaxies. Their influence may also dominate the relationship between the different interstellar gas phases. How do superbubbles form and evolve? How do they affect the local and global ISM? The Magellanic Clouds provide a superior opportunity to study this shell-forming activity, since both stellar content and gaseous structure can be examined in detail. Here, the results of recent studies of superbubbles in the Magellanic…
We have identified a candidate 1-2 x 10^5 year old luminous white dwarf in NGC 1818, a young star cluster in the Large Magellanic Cloud. This discovery strongly constrains the boundary mass M_c at which stars stop forming neutron stars and start forming white dwarfs, to M_c > 7.6 Msun.
We discuss how tidal interaction between the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC), and the Galaxy triggers galaxy-wide star formation in the Clouds for the last ~0.2 Gyr based on our chemodynamical simulations on the Clouds. Our simulations demonstrate that the tidal interaction induces the formation of asymmetric spiral arms with high gas densities and consequently triggers star formation within the arms in the LMC. Star formation rate in the present LMC is significantly enhanced just above the eastern edge of the LMC's stellar bar owing to the tidal interaction. The…
