Large Magellanic Cloud Disk Research Articles

LMC self-lensing from a new perspective

We present a new analysis on the issue of the location of the observed microlensing events in direction of the Large Magellanic Cloud (LMC). This is carried out starting from a recently drawn coherent picture of the geometrical structure and dynamics of the LMC disk and by considering different configurations for the LMC bar. In this framework it clearly emerges that the spatial distribution of the events observed so far shows a near--far asymmetry. This turns out to be compatible with the optical depth calculated for the LMC halo objects. In this perspective, our main conclusion, supported by a statistical analysis on the outcome of an evaluation of the microlensing rate, is that self lensing can not account for all the observed events. Finally we propose a general inequality to calculate quickly an upper limit to the optical depth along a line of view through the LMC center.

Surface Brightness and Stellar Populations at the Outer Edge of the Large Magellanic Cloud: No Stellar Halo Yet

We present a high-quality color-magnitude diagram (CMD) for a 36' × 36' field located 8° (7 kpc) from the Large Magellanic Cloud (LMC) center, as well as a precise determination of the LMC surface brightness derived from the resolved stellar population out to this large galactocentric radius. This deep CMD shows for the first time the detailed age distribution at this position, where the surface brightness is V 26.5 mag arcsec-2. At a radius R 474' the main sequence is well populated from the oldest turnoff at I 21.5 to the 2.5 Gyr turnoff at I 19.5. Beyond this radius, a relatively strong gradient in the density of stars with ages in the 2.5-4 Gyr range is apparent. There are some stars brighter and bluer than the main population, quite uniformly distributed over the whole area surveyed, which are well matched by a 1.5 Gyr isochrone and may be indicative of a relatively recent star formation, or merger, event. The surface brightness profile of the LMC remains exponential to this large galactocentric radius and shows no evidence of disk truncation. Combining the information on surface brightness and stellar population, we conclude that the LMC disk extends (and dominates over a possible stellar halo) out to a distance of at least 7 kpc. These results confirm that the absence of blue stars in the relatively shallow off-center CMDs of dwarf irregular galaxies is not necessarily evidence for an exclusively old stellar population resembling the halo of the Milky Way.

The Stellar Halo in the Large Magellanic Cloud: Mass, Luminosity, and Microlensing Predictions

Recently obtained kinematic data has shown that the Large Magellanic Cloud (LMC) possesses an old stellar halo. In order to further characterize the properties of this halo, parametric King models are fit to the surface density of RR Lyrae stars. Using data from both the MACHO and OGLE II microlensing surveys, the model fits yield the center of their distribution at RA = 05:21.1+-0.8, Dec = -69:45+-6 (J2000) and a core radius of 1.42+-0.12 kpc. As a check the halo model is compared with RR Lyrae star counts in fields near the LMC's periphery previously surveyed with photographic plates. These data, however, require a cautious interpretation. Several topics regarding the LMC stellar halo are discussed. First, the properties of the halo imply a global mass-to-light ratio of M/L_V = 5.3+-2.1 and a total mass of 1.6+-0.6 10^10 M_sun for the LMC in good agreement with estimates based on the rotation curve. Second, although the LMC's disk and halo are kinematically distinct, the shape of the surface density profile of the halo is remarkably similar to that of the young disk. For example, the best-fit exponential scale length for the RR Lyrae stars is 1.47+-0.08 kpc, which compares to 1.46 kpc for the LMC's blue light. In the Galaxy, the halo and disk do not resemble each other like this. Finally, a local maximum in the LMC's microlensing optical depth due to halo-on-disk stellar self-lensing is predicted. For the parameters of the stellar halo obtained, this maximum is located near MACHO events LMC-4 and LMC-23, and is large enough to possibly account for these two events, but not for all of the observed microlensing.

Geometry of the Large Magellanic Cloud Disk: Results from MACHO and the Two Micron All Sky Survey

We present a detailed study of the viewing angles and geometry of the inner LMC (ρ 4°) based on a sample of more than 2000 MACHO Cepheids with complete {VR}KC light curves and single-phase Two Micron All Sky Survey (2MASS) JHKs observations. The sample is considerably larger than any previously studied subset of LMC Cepheids and has an improved areal coverage. Single-epoch random-phase 2MASS photometry is corrected using MACHO V light curves to derive mean JHKs magnitudes. We analyze the resulting period-luminosity relations in VRJHKs to recover statistical reddening and distance to each individual Cepheid, with respect to the mean distance modulus and reddening of the LMC. By fitting a plane solution to the derived individual distance moduli, the values of LMC viewing angles are obtained: position angle θ = 1510 ± 24, inclination i = 307 ± 11. In the so-called ring analysis, we find a strong dependence of the derived viewing angles on the adopted center of the LMC, which we interpret as being due to deviations from planar geometry. Analysis of residuals from the plane fit indicates the presence of a symmetric warp in the LMC disk and the bar elevated above the disk plane. Nonplanar geometry of the inner LMC explains a broad range for values of i and θ in the literature and suggests caution when deriving viewing angles from inner LMC data.

Open Cluster LW 55 in the Large Magellanic Cloud

The field of the moderately old open cluster LW 55 in the outer parts of the Large Magellanic Cloud disk was monitored for detection of short-period variable stars over two nights. Eight variables were found; all but one (a detached eclipsing binary) are small-amplitude (ΔV ≤ 0.1 mag) pulsating stars of the δ Scuti, SX Phoenicis, or γ Doradus type. The BV color-magnitude diagram extends down to the solar-type stars at V = 24 (MV 5.2). The cluster age is estimated at 1.5 Gyr for Z = 0.004 ([Fe/H] = -0.67); the surrounding stellar field is older, with an age greater than 4 Gyr.

A new look at the large-scale H I structure of the Large Magellanic Cloud

We present a Parkes multibeam H I survey of the Large Magellanic Cloud (LMC). This survey, which is sensitive to spatial structure in the range 200 pc to 10 kpc, complements the Australia Telescope Compact survey, which is sensitive to structure in the range 15‐500 pc. With an rms column density sensitivity of 8 × 10 16 cm −2 for narrow lines and 4 × 10 17 cm −2 for typical linewidths of 40 km s −1 , emission is found to be extensive well beyond the main body of the LMC. Arm-like features extend from the LMC to join the Magellanic Bridge and the Leading Arm, a forward counterpart to the Magellanic Stream. These features, whilst not as dramatic as those in the Small Magellanic Cloud, appear to have a common origin in the Galactic tidal field, in agreement with recent 2MASS and DENIS results for the stellar population. The diffuse gas that surrounds the LMC, particularly at PAs of 90 ◦ ‐330 ◦ , appears to be loosely associated with tidal features, but loosening by the ram pressure of tenuous Galactic halo gas against the outer parts of the LMC cannot be discounted. High-velocity clouds, which lie between the Galaxy and the LMC in velocity and that appear in the ultraviolet spectra of some LMC stars, are found to be associated with the LMC if their heliocentric velocity exceeds approximately +100 km s −1 . They are possibly the product of energetic outflows from the LMC disc. The H I mass of the LMC is found to be (4.8 ± 0.2) × 10 8 M� (for an assumed distance of 50 kpc),

New Understanding of Large Magellanic Cloud Structure, Dynamics, and Orbit from Carbon Star Kinematics

We formulate a new and coherent understanding of the structure and dynamics of the Large Magellanic Cloud (LMC) and its orbit around and interaction with the Milky Way. Much of our understanding of these issues hinges on studies of the LMC line-of-sight kinematics. The observed velocity field includes contributions from the LMC rotation curve V(R'), the LMC transverse velocity vector vt, and the rate of inclination change di/dt. All previous studies have assumed di/dt = 0. We show that this is incorrect and that, combined with uncertainties in vt, this has led to incorrect estimates of many important structural parameters of the LMC. We derive general expressions for the velocity field that we fit to kinematic data for 1041 carbon stars. We calculate vt by compiling and improving LMC proper-motion measurements from the literature, and we show that for known vt, all other model parameters are uniquely determined by the data. The position angle of the line of nodes is Θ = 1299 ± 60, consistent with the value determined geometrically by van der Marel & Cioni in 2001. The rate of inclination change is di/dt = -0.37 ± 0.22 mas yr-1 = -103° ± 61° Gyr-1. This is similar in magnitude to predictions from N-body simulations by M. Weinberg, which predict LMC disk precession and nutation due to Milky Way tidal torques. The LMC rotation curve V(R') has amplitude 49.8 ± 15.9 km s-1. This is 40% lower than what has previously (and incorrectly) been inferred from studies of H I, carbon stars, and other tracers. The line-of-sight velocity dispersion has an average value σ = 20.2 ± 0.5 km s-1, with little variation as a function of radius. The dynamical center of the carbon stars is consistent with the center of the bar and the center of the outer isophotes, but it is offset by 12 ± 06 from the kinematic center of the H I. The enclosed mass inside the last data point is MLMC(8.9 kpc) = (8.7 ± 4.3) × 109 M⊙, more than half of which is due to a dark halo.

A Warp in the Large Magellanic Cloud Disk?

We present a study of the shape of the Large Magellanic Cloud (LMC) disk. We use the brightnesses of core helium burning red clump stars identified in V-I, I color-magnitude diagrams of 50 randomly selected LMC fields observed with the Cerro Tololo Inter-American Observatory 0.9 m telescope to measure relative distances to the fields. Random photometric errors and errors in the calibration are controlled to 1%. Following correction for reddening measured through the color of the red clump, we solve for the inclination and position angle of the line of nodes of the tilted plane of the LMC, finding i = 358 ± 24 and θ = 145° ± 4°. Our solution requires that we exclude 15 fields in the southwest of the LMC that have red clump magnitudes ~0.1 mag brighter than the fitted plane. On the basis of these fields, we argue that the LMC disk is warped and twisted, containing features that extend up to 2.5 kpc out of the plane. We argue that alternative ways of producing red clump stars brighter than expected, such as variations in age and metallicity of the stars, are unlikely to explain our observations.

The Global Content, Distribution, and Kinematics of Interstellar Oviin the Large Magellanic Cloud

We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of interstellar O VI absorption toward 12 early-type stars in the Large Magellanic Cloud (LMC). The observations have a velocity resolution of 20 km s-1 (FWHM) and clearly show O VI 1031.926 A absorption at LMC velocities toward all 12 stars. From these observations we derive column densities of interstellar O VI in this nearby galaxy; the observed columns are in the range log N(O VI) = 13.9-14.6, with a mean of 14.37 and a standard deviation of ±38% ( dex). The observations probe several sight lines projected onto known superbubbles in the LMC, but these show relatively little (if any) enhancement in O VI column density compared to sight lines toward relatively quiescent regions of the LMC. The observed LMC O VI absorption is broad, with Gaussian dispersions σ ≈ 30-50 km s-1. This implies temperatures T (2-5) × 106, indicating that much of the broadening is nonthermal because O VI has a very low abundance at such high temperatures. The O VI absorption is typically displaced ~-30 km s-1 from the corresponding low-ionization absorption associated with the bulk of the LMC gas. The general properties of the LMC O VI absorption are very similar to those of the Milky Way halo. The average column density of O VI and the dispersion of the individual measurements about the mean are identical to those measured for the halo of the Milky Way, even though the metallicity of the LMC is a factor of ~2.5 lower than the Milky Way. The velocity dispersion measured for the LMC material is also consistent with recent measurements of the Galactic halo. The striking similarities in these quantities suggest that much of the LMC O VI may arise in a vertically extended distribution similar to the Galactic halo. We discuss the measurements in the context of a halo composed of radiatively cooling hot gas and/or turbulent mixing layers. If the observed O VI absorption is tracing a radiatively cooling galactic fountain flow, the mass flow rate from one side of the LMC disk is of the order ~ 1 M☉ yr-1, with a mass flux per unit area of the disk /Ω ~ 2 × 10-2 M☉ yr-1 kpc-2.

The So-called “Bar” in the Large Magellanic Cloud

We propose that the off-centered bar in the Large Magellanic Cloud (LMC) is an unvirialized structure slightly misaligned with, and offset from, the plane of the LMC disk. The small displacement and misalignment are consequences of recent tidal interactions with the Small Magellanic Cloud and the Galaxy. This proposal, although radical, is consistent with the kinematics of the LMC and the near-infrared star count maps from the Deep Near-Infrared Survey and the 2 Micron All-Sky Survey and, in particular, with the reported 25°-50° inclination range of the LMC and the east-west gradient of distance moduli of standard candles. Contributions to LMC microlensing come mainly from the mutual lensing of stars in the disk and the The predicted microlensing optical depth is at levels comparable to observation, even without including contributions from MACHOs. Observational tests are suggested to discriminate between our misaligned offset bar model and the conventional picture of an off-centered planar bar.

The Rotation Curve of the Large Magellanic Cloud and the Implications for Microlensing

The rotation of the disk of the Large Magellanic Cloud (LMC) is derived from the radial velocities of 422 carbon stars. New aspects of this analysis include the propagation of uncertainties in the LMC proper motion with a Monte Carlo, and a self-consistent modeling of the rotation curve and disk kinematics. The rotation curve is well fit by a truncated, finite-thickness exponential disk model with no dark halo. The velocity dispersion in radial bins decreases from 22 to 15 km/s, then increases to 20 km/s at larger radii. Constant-thickness models in virial equilibrium cannot be reconciled with the data even if the effects of LMC or Galactic dark halos are included. If the disk is virialized, the LMC disk is flared. We model the velocity dispersion at large radii (R > 6 kpc) as a maximal flared disk under the influence of the Galactic dark halo, which favors a mean density for the latter of 0.00025 M_sol/pc^3 at the LMC distance. LMC stellar kinematics play an important role in elucidating the nature of MACHOs, a dark population inferred from LMC microlensing. We have constructed a truncated and flared maximal disk model for the LMC which is kinematically based. Our model does not include a nonvirialized component such as tidal debris. Our upper limit on the self-lensing optical depth is in good agreement with that obtained from less sophisticated models, and is an order of magnitude too small to account for the MACHO microlensing signal [Abridged].

Effect of the Milky Way on Magellanic Cloud Structure

A combination of analytic models and n-body simulations implies that the structural evolution of the Large Magellanic Cloud (LMC) is dominated by its dynamical interaction with the Milky Way. Although expected at some level, the scope of the involvement has significant observational consequences. First, LMC disk orbits are torqued out of the disk plane, thickening the disk and populating a spheroid. The torque results from direct forcing by the Milky Way tide and, indirectly, from the drag between the LMC disk and its halo resulting from the induced precession of the LMC disk. The latter is a newly reported mechanism that can affect all satellite interations. However, the overall torque can not isotropize the stellar orbits and their kinematics remains disk-like. Such a kinematic signature is observed for nearly all LMC populations. The extended disk distribution is predicted to increase the microlensing toward the LMC. Second, the disk's binding energy slowly decreases during this process, puffing up and priming the outer regions for subsequent tidal stripping. Because the tidally stripped debris will be spatially extended, the distribution of stripped stars is much more extended than the HI Magellanic Stream. This is consistent with upper limits to stellar densities in the gas stream and suggests a different strategy for detecting the stripped stars. And, finally, the mass loss over several LMC orbits is predicted by n-body simulation and the debris extends to tens of kiloparsecs from the tidal boundary. Although the overall space density of the stripped stars is low, possible existence of such intervening populations have been recently reported and may be detectable using 2MASS.

Magnitude Bias of Microlensed Sources toward the Large Magellanic Cloud.

There are lines of evidence suggesting that some of the observed microlensing events in the direction of the Large Magellanic Cloud (LMC) are caused by ordinary star lenses as opposed to dark MACHOs in the Galactic halo. Efficient lensing by ordinary stars generally requires the presence of one or more additional concentrations of stars along the line of sight to the LMC disk. If such a population behind the LMC disk exists, then the source stars (for lensing by LMC disk objects) will be drawn preferentially from the background population and will show systematic differences from LMC field stars. One such difference is that the (lensed) source stars will be farther away than the average LMC field stars, and this should be reflected in their apparent baseline magnitudes. We focus on red clump stars; these should appear in the color-magnitude diagram at a few tenths of a magnitude fainter than the field red clump. Suggestively, one of the two near-clump confirmed events, MACHO-LMC-1, is a few tenths of magnitude fainter than the clump.

The MACHO Project 9 Million Star Color-Magnitude Diagram of the Large Magellanic Cloud

We present a 9 million star color-magnitude diagram (9M CMD) of the Large Magellanic Cloud (LMC) bar. The 9M CMD reveals a complex superposition of different-age and -metallicity stellar populations, with important stellar evolutionary phases occurring over 3 orders of magnitude in number density. First, we count the nonvariable red and blue supergiants and the associated Cepheid variables and measure the stellar effective temperatures defining the Cepheid instability strip. Lifetime predictions of stellar evolution theory are tested, with implications for the origin of low-luminosity Cepheids. The highly evolved asymptotic giant branch (AGB) stars in the 9M CMD have a bimodal distribution in brightness, which we interpret as discrete old populations (≳1 Gyr). The faint AGB sequence may be metal-poor and very old. Comparing the mean properties of giant branch and horizontal-branch (HB) stars in the 9M CMD with those of clusters, we identify NGC 411 and M3 as templates for the admixture of old stellar populations in the bar. However, there are several indications that the old and metal-poor field population has a red HB morphology: the RR Lyrae variables lie preferentially on the red edge of the instability strip, the AGB bump is very red, and the ratio of AGB bump stars to RR Lyrae variables is quite large. If the HB second parameter is age, the old and metal-poor field population in the bar likely formed after the oldest LMC clusters. Lifetime predictions of stellar evolution theory lead us to associate a significant fraction of the ∼1 million red HB clump giants in the 9M CMD with the same old and metal-poor population producing the RR Lyrae stars and the AGB bump. In this case, compared with the age-dependent luminosity predictions of stellar evolution theory, the red HB clump is too bright relative to the RR Lyrae stars and AGB bump. Last, we show that the surface density profile of RR Lyrae variables is fitted by an exponential, favoring a disklike rather than a spheroidal distribution. We conclude that the age of the LMC disk is probably similar to the age of the Galactic disk.

Kepler Rotation Effects on the Binary-Lens Microlensing Events

We investigate the effects of the Kepler rotation of lens binaries on the binary-microlensing events towards the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). It is found that the rotation effects cannot always be neglected when the lens binaries are in the LMC disk or the SMC disk, i.e., when they are self-lensing. Therefore we suggest that it will be necessary to consider the rotation effects in the analyses of the coming binary events if the microlensing events towards the halo are self-lensing. As an example, we reexamine the MACHO LMC-9 event, in which the slow transverse velocity of the lens binary suggests a microlensing event in the LMC disk. From a simple analysis, it is shown that the lens binary with total mass $\sim 1M_{\odot}$ rotates by more than $\sim 60^{\circ}$ during the Einstein radius crossing time. However, the fitting of MACHO LMC-9 with an additional parameter, the rotation period, shows that the rotation effects are small, i.e., the projected rotation angle is only $\sim 5.9^{\circ} (M/M_{\odot})^{1/4}$ during the Einstein radius crossing time. This contradiction can be settled if the physical parameters, such as the mass and the velocity, are different in this event, the binary is nearly edge-on, or the binary is very eccentric, though definite conclusions cannot be drawn from this single event. If the microlensing events towards the halo are due to self-lensing, binary-events for which the rotation effects are important will increase and stronger constraints on the nature of the lenses will be obtained.

Structure and Kinematics of the Interstellar Medium in Front of SN 1987A

High-resolution (10 km s-1) [N II] echelle spectra, sampled every 13'' in a 6'×6' region around SN 1987A were obtained on the CTIO 4 m telescope. The map shows a complicated velocity structure consistent with that reported previously for the interstellar medium (ISM). Three components, Vhel=265, 277, and 285 km s-1 were identified as N157C (or the R1170 complex: see an earlier paper of Xu, Crotts, & Kunkel). The radius of this large superbubble was found to expand at 10 km s-1, with a lifetime of 6×106 yr and a total energy of 3×1051 ergs determined from its radius and velocity according to superbubble theory. The Vhel=235 km s−1 component corresponds to the near side of the 600 pc giant superbubble reported earlier. This bubble is over 107 years old, and has blown out of the Large Magellanic Cloud disk. Two other components, Vhel=255 and 245 km s-1 are identified as the inner major light echo ring (a double-shell structure) at about 130 pc in front of SN 1987A. There are also two high-velocity components, 300 and 313 km s-1, which are possibly the far side of a superbubble in which SN 1987A exploded. We also noticed that there are two components, at 279 and 301 km s-1, within 20'' of SN 1987A. These structures are probably due to the emission from the progenitor star's red supergiant wind. We find that the time it took the SN 1987A progenitor to move to the current location 300 pc behind N157C is comparable to the age of N157C as well as that of the progenitor itself.

Gravitational microlensing by the MACHOs of the Large Magellanic Cloud

view Abstract Citations (92) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gravitational Microlensing by the MACHOs of the Large Magellanic Cloud Wu, Xiang-Ping Abstract The expected microlensing events of the Large Magellanic Cloud (LMC) by the MACHOs of the LMC itself are calculated and compared with analog events by objects in the Galactic halo. The LMC matter distribution is modeled by a spherical halo and an exponential disk, while a face-on exponential disk is used for the stellar distribution of the LMC. Among the microlensing events discovered by the MACHO and EROS projects, a fraction of 22% could be caused by the lenses near the center of the LMC or 13% from lenses at 5^deg^ from the LMC center, provided that the halo of the Galaxy and of the LMC are composed of MACHOs. The LMC disk produces a relatively lower optical depth to microlensing of ~3 x 10^-8^ but contributes a fraction of ~40% of the observed microlensing events toward the LMC center, if the actual detection rate is taken to be (7-9) x 10^-8^. It is then likely that the presently detected microlensing events near the center of the LMC are due to some combination of the MACHOs of the Galactic halo, the Galactic spheroid, the LMC halo, and particularly the LMC disk. Therefore, any statistical study of these microlensing events must take the LMC lenses into account. Publication: The Astrophysical Journal Pub Date: November 1994 DOI: 10.1086/174794 arXiv: arXiv:astro-ph/9312059 Bibcode: 1994ApJ...435...66W Keywords: Astronomical Models; Galactic Halos; Gravitational Lenses; Magellanic Clouds; Mathematical Models; Optical Thickness; Star Distribution; Astronomy; COSMOLOGY: GRAVITATIONAL LENSING; GALAXIES: MAGELLANIC CLOUDS; Astrophysics E-Print: 12 pages, 6 figures (not included) by fax, ApJ submitted, DAEC-OPM-93 full text sources arXiv | ADS | data products SIMBAD (4) NED (1)

Probing the Large Magellanic Cloud halo for MACHOs

view Abstract Citations (32) References (6) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Probing the Large Magellanic Cloud Halo for MACHOS Gould, Andrew Abstract If galactic halos are composed of massive compact halo objects (MACHOs) in the mass range M <~ 0.01 M_sun_, then ongoing gravitational lensing experiments could be capable of detecting them in the Large Magellanic Cloud (LMC). The signature of LMC (as opposed to Galactic) MACHOs is a variation of the Optical depth to lensing as a function of sky position. Assuming that the LMC halo is spherical, the optical depth along lines of sight toward the far side of the LMC disk should be ~20% higher than those toward the near side because the former pass through more of the halo. If the LMC halo is oblate, the effect is diminished as the square of the halo flatness ratio. The amplitude of the spatial variation in the lensing rate can therefore provide information about the flattening of the LMC halo. Publication: The Astrophysical Journal Pub Date: February 1993 DOI: 10.1086/172298 Bibcode: 1993ApJ...404..451G Keywords: Galactic Halos; Gravitational Lenses; Magellanic Clouds; Dark Matter; Optical Thickness; Astrophysics; COSMOLOGY: GRAVITATIONAL LENSING; COSMOLOGY: DARK MATTER; GALAXIES: MAGELLANIC CLOUDS full text sources ADS | data products SIMBAD (3) NED (1)

Kinematics of the LMC CH-stars

Velocities have been measured for 74 CH stars in the direction of the Large Magellanic Cloud (LMC). These have been used to study the kinematics of the oldest stellar population. Velocities of these objects appear to reflect two distinct subgroups - one associated with the old globular cluster population and a second with the LMC disk.

The population structure of the large Magellanic Cloud bar

view Abstract Citations (77) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The population structure of the Large Magellanic cloud bar. Hardy, E. ; Buonanno, R. ; Corsi, C. E. ; Janes, K. A. ; Schommer, R. A. Abstract A combination of profile-deconvolution and automatized techniques of photographic photometry in crowded fields is used to construct a rich and deep color-magnitude diagram near the NW end of the Large Magellanic Cloud (LMC) bar. The morphology of the diagram and its analysis through the use of luminosity functions and evolutionary models for the core-helium-burning 'clump' red giants indicate that (1) stellar formation continues in the bar areas; (2) an old Population II in the Galaxy sense is not a significant contributor to the observed diagram, although stars of all ages are probably present in the LMC disk; (3) the bulk of star formation, which continues to date, started earlier than about one billion years ago but later than about three billion years ago, although the precise rate of star formation, including the possible presence of bursts, inside such an age range is not known from our data. The observed population is considerably younger and more metal deficient than that of the solar neighborhood. Publication: The Astrophysical Journal Pub Date: March 1984 DOI: 10.1086/161826 Bibcode: 1984ApJ...278..592H Keywords: Barred Galaxies; Galactic Structure; Magellanic Clouds; Stellar Evolution; Color-Magnitude Diagram; Main Sequence Stars; Red Giant Stars; Stellar Color; Stellar Magnitude; Astrophysics full text sources ADS | data products SIMBAD (8)