Photometry of Magellanic Cloud clusters with the Advanced Camera for Surveys - II . The unique LMC cluster ESO 121 - SC 03
نویسنده
چکیده
We present the results of photometric measurements from images of the LMC cluster ESO 121-SC03 taken with the Advanced Camera for Surveys on the Hubble Space Telescope. Our resulting colour-magnitude diagram (CMD) reaches 3 magnitudes below the main-sequence turn-off, and represents by far the deepest observation of this cluster to date. We also present similar photometry from ACS imaging of the accreted Sagittarius dSph cluster Palomar 12, used in this work as a comparison cluster. From analysis of its CMD, we obtain estimates for the metallicity and reddening of ESO 121-SC03: [Fe/H] = −0.97± 0.10 and E(V − I) = 0.04± 0.02, in excellent agreement with previous studies. The observed horizontal branch level in ESO 121-SC03 suggests this cluster may lie 20 per cent closer to us than does the centre of the LMC. ESO 121-SC03 also possesses a significant population of blue stragglers, which we briefly discuss. Our new photometry allows us to undertake a detailed study of the age of ESO 121-SC03 relative to Pal. 12 and the Galactic globular cluster 47 Tuc. We employ both vertical and horizontal differential indicators on the CMD, calibrated against isochrones from the Victoria-Regina stellar models. These models allow us to account for the different α-element abundances in Pal. 12 and 47 Tuc, as well as the unknown run of α-elements in ESO 121-SC03. Taking a straight error-weighted mean of our set of age measurements yields ESO 121-SC03 to be 73 ± 4 per cent the age of 47 Tuc, and 91 ± 5 per cent the age of Pal. 12. Pal. 12 is 79 ± 6 per cent as old as 47 Tuc, consistent with previous work. Our result corresponds to an absolute age for ESO 121-SC03 in the range 8.3 − 9.8 Gyr, depending on the age assumed for 47 Tuc, therefore confirming ESO 121-SC03 as the only known cluster to lie squarely within the LMC age gap. We briefly discuss a suggestion from earlier work that ESO 121-SC03 may have been accreted into the LMC system.
منابع مشابه
Photometry of Magellanic Cloud clusters with the Advanced Camera for Surveys - I. The old LMC clusters NGC 1928, 1939 and Reticulum
We present the results of photometric measurements from images of the LMC globular clusters NGC 1928, 1939 and Reticulum taken with the Advanced Camera for Surveys on the Hubble Space Telescope. Exposures through the F555W and F814W filters result in high accuracy colour-magnitude diagrams (CMDs) for these three clusters. This is the first time that CMDs for NGC 1928 and 1939 have been publishe...
متن کاملBe star surveys with CCD photometry . II . NGC 1818 and its neighbouring cluster in the LMC ⋆
As part of an ongoing photometric survey of young Magellanic Cloud clusters we identified Be stars in NGC 1818 and a nearby smaller cluster in the Large Magellanic Cloud. The neighbouring cluster does not appear to contain any evolved stars, and its sparsely populated main sequence does not extend to stars as massive as in NGC 1818. Both clusters are younger than the surrounding field populatio...
متن کاملBe star surveys with CCD photometry II. NGC 1818 and its neighbouring cluster in the Large Magellanic Cloud?
As part of an ongoing photometric survey of young Magellanic Cloud clusters we identified Be stars in NGC 1818 and a nearby smaller cluster in the LargeMagellanic Cloud. The neighbouring cluster does not appear to contain any evolved stars, and its sparsely populated main sequence does not extend to stars as massive as in NGC 1818. Both clusters are younger than the surrounding field population...
متن کاملTight LMC massive star clusters R 127 and R 128 ?
We study the Large Magellanic Cloud (LMC) star clusters R 127 and R128 using imaging and spectroscopy obtained at the ESO NTT telescope. An advanced image restoration technique allows us to resolve these two clusters into at least 14 and 33 stars respectively and obtain their photometry. In particular, we show that the core of R 127 is composed of at least four stars and identify the Luminous B...
متن کاملThe last Magellanic collision: The formation of the off-center bar, asymmetric HI spirals, and young stars in the Large Magellanic Cloud
We first present the results of fully self-consistent numerical simulations of the Large and Small Magellanic Clouds (LMC and SMC), which show that the last collision between the Magellanic clouds about ∼ 0.2 Gyr ago can form the apparently off-center bar and peculiar HI spirals of the LMC. We also show that the present spatial distributions of young stars with ages less than ∼ 20 Myr in the LM...
متن کامل