Large Magellanic Cloud Cluster NGC Research Articles

The age of the Large Magellanic Cloud cluster NGC 2193

The age of the LMC star cluster NGC 2193 is estimated as 2.2 + or - 0.6 Gyr from CCD photometry that reaches below the cluster main-sequence turnoff. The cluster is thus another member of the large set of LMC red clusters that have ages in the range of 1 to 3 Gyr. The principal cause of uncertainty in the estimated age is uncertainty in the LMC distance modulus; at (m - M)0 = 18.2, the age is estimated as 2.5 + or - 0.4 Gyr, while at (m - M)0 = 18.7, the age is 1.8 + or - 0.4 Gyr. A metal abundance of (Fe/H) = -0.5 + or - 0.3 dex is deduced for NGC 2193 from the color of the cluster giant branch. The C-M diagram for the LMC field near NGC 2193 shows the commonly found population of intermediate age stars but, in this case, the diagram is clearly dominated by a population of older stars. Isochrone fits indicate an age for this older population in excess of 7 Gyr, with some indication of ages perhaps as old as 13 Gyr. This latter population is the oldest LMC field population yet dated. 52 references.

VARIABLE STARS IN THE LARGE MAGELLANIC CLOUD CLUSTER NGC 1786.

ABSTRACT Twelve short-period variable stars have been identified in the Large Magellanic Cloud cluster NGC 1786. Periods have been obtained for ten stars. The period distribution is characteristic of a cluster of Oosterhoff type II. One variable is about a magnitude brighter than the others and may be a member of the class of anomalous Cepheids described by Zinn.

Luminosities and temperatures of the reddest stars in three LMC clusters

view Abstract Citations (120) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Luminosities and temperatures of the reddest stars in three LMC clusters. Frogel, J. A. ; Persson, S. E. ; Cohen, J. G. Abstract Infrared observations in the 1.2-2.2 micron region are presented for 12 of the reddest stars in the Large Magellanic Cloud (LMC) clusters NGC 1783, 1846, and 1978. Seven of the stars, which are carbon stars, are photometrically indistinguishable from carbon stars in the general field of the LMC. Bolometric magnitudes and temperatures are derived from the infrared data. The average bolometric magnitude of the carbon stars is -4.9, which is about two magnitudes fainter than previously published values, but still high enough to require that these stars are symptotic giant branch stars. The most luminous M-type stars in these clusters are warmer and perhaps more luminous than the giant branches of metal-rich Galactic globular clusters, in agreement with Hodge's results based on UBV photometry. The location of the M-type stars may present some problems for recent giant branch model calculations. Publication: The Astrophysical Journal Pub Date: July 1980 DOI: 10.1086/158133 Bibcode: 1980ApJ...239..495F Keywords: Infrared Astronomy; Late Stars; Magellanic Clouds; Red Giant Stars; Stellar Luminosity; Stellar Temperature; Bolometers; Carbon Stars; M Stars; Star Clusters; Astrophysics full text sources ADS | data products SIMBAD (13) GCPD (1)

Electronographic photometry of star clusters in the Magellanic Clouds - VII. The colour-magnitude diagram of NGC 2231

Electronographic magnitudes and colours of 134 stars in the field of NGC 2231 in the Large Magellanic Cloud have been measured to V = 22.2 on electrographs taken with a Spectracon image-converter attached to the focus of the 1.5-m (60-inch) Cerro Tololo reflector. The zero point of the electronographic photometry was provided by photoelectric observations of three stars in the cluster field using the same telescope. In addition, the electronographic observations of 32 of the stars have been used to reduce the photographic observations of this cluster by Hesser et al. to the BV system. The colour–magnitude diagram of the cluster consists of an evolved main sequence, whose termination point corresponds to an age of about 1.3 × 109 yr, but with a giant branch which is displaced blueward by about |$\Delta (B-V)_{0} = 0.24$| from the positions of the giant branches of open clusters of comparable ages in our Galaxy. This displacement probably results from a low metal abundance, although it could also be caused by an enriched He content. On the assumption that the displacement results from the metal abundance, [Fe/H] = – 0.9. Thus, NGC 2231 is slightly older and slightly more metal-deficient than the Large Magellanic Cloud cluster NGC 2209.

Electronographic photometry of star clusters in the Magellanic Clouds - VI. The colour-magnitude diagram of Hodge 11

Electronographic magnitudes and colours of 78 stars in the cluster Hodge 11 in the Large Magellanic Cloud have been measured to V = 21.5 on electrographs taken with a Spectracon image-converter attached to the focus of the 1.5-m (60-inch) Cerro Tololo reflector. The zero point of the electronographic photometry was provided by photoelectric observations of four stars in the cluster field using the same telescope. The colour–magnitude diagram of the cluster consists of an evolved main sequence, whose termination point corresponds to an age of about |$6 \times 10^8\enspace\text {yr}$|⁠, but with a giant branch which is displaced blueward by about |$\Delta (B-V)_0 = 0.4$| from the positions of the giant branches of open clusters of similar age in our Galaxy. This displacement probably results from a very low metal abundance, similar to that in the most metal-poor globular clusters such as M92. However, an enriched He content cannot presently be ruled out as a contributing factor. Hodge 11 thus appears to be similar to the Large Magellanic Cloud cluster NGC 2209, but is somewhat younger than this cluster and possesses a more abnormal chemical composition.

The Age and Chemical Composition of the LMC Cluster NGC 2209

A new color-magnitude diagram has been obtained for the populous Large Magellanic Cloud (LMC) cluster NGC 2209, together with DDO intermediate-band photometry of two stars on or near its giant branch. These data lead to the conclusion that NGC 2209 has an age approx.8 x 10/sup 8/ years, and a metal abundance (Fe/H)approx.-1.2. This cluster thus has no counterpart in our Galaxy. The LMC evidently contains, or has contained until recently, significant amounts of material which have experienced little metal enrichment from the initial stages of its formation, in contrast to the situation in the Galaxy. (AIP)

Chemical Composition and the Hertzsprung Gap

The effect of initial chemical composition on the size and position of the Hertzsprung gap is examined. Evolutionary sequences for stars in the mass range 0.8M/sub sun/ to 2.5M/sub sun/ with initial chemical composition ranging from X=0.7 to 0.9 and Z=0.001 to 0.04 have been computed with the Cox-Stewart opacities handled by bicubic interpolation. The models show that chemical composition does not affect the size and position of the Hertzsprung gap to the extent necessary to explain such peculiar color-magnitude diagrams as that of the Large Magellanic Cloud cluster NGC 2209. (AIP)

The RR Lyrae Stars in the Magellanic Clouds

AbstractThe characteristics of the RR Lyrae stars in the Magellanic Clouds are discussed. The existence of numerous RR Lyrae variables in the Large Magellanic Cloud (LMC) cluster NGC 1835 is noted. The variables indicate that this cluster is of Oosterhoff type I. No cluster of Oosterhoff type II has yet been recognized in the Clouds. Some new results of a study of the RRLyrae variables in an LMC field 1° x 1.°3 are discussed. Periods have been determined for 50 out of 72 probable RR lyraes in this field. RR Lyrae ab stars with periods less than 0.d46 are absent. The time averaged and are 19.m56 and 19.m20 with surprisingly small dispersion. First impressions of results for a similar field in the Small Magellanic Cloud (SMC) suggest that the old stellar population of the SMC may have a slightly lower metal abundance than that of the LMC. The best available distance moduli for the Magellanic Clouds indicate a mean absolute visual magnitude M of +0.m5 ±0.2 for the RR Lyrae stars in these systems.