Population I Cepheids and star formation history of the Large Magellanic Cloud

Abstract

In this paper we study the Cepheids distribution in the Large Magellanic Cloud (LMC) as a function of their ages using data from the OGLE III photometric catalogue. To determine age of the Pop I Cepheids, we derived a period -age (PA) relationship using the Cepheids found in the LMC star clusters. We find two peaks in the period distribution at log P = 0.49 ± 0.01 and log P = 0.28 ± 0.01 days which correspond to fundamental and first overtone pulsation modes, respectively. Ages of the Cepheids are used to understand star formation scenario in the LMC in last 30 -600 Myr. The age distribution of the LMC Cepheids is found to have a peak at log(Age)=8.2±0.1. This suggests that major star formation event took place at about 125-200 Myr ago which may have been triggered by a close encounter between the SMC and the LMC. Cepheids are found to be asymmetrically distributed throughout the LMC and many of them lie in clumpy structures along the bar. The frequency distribution of Cepheids suggests that most of the clumps are located to the eastern side of the LMC optical center.

Population I Cepheids and understanding star formation history of the Small Magellanic Cloud

“…Based on the evolutionary and pulsation models covering a broad range of stellar masses and chemical compositions, Bono et al (2005) derived a PA relation for the Cepheids with metallicity 0.004 as log(Age) = 8.49 − 0.79 log P . This is similar to the relation given by Joshi et al (2014). Bono et al (2005) did also present period-age-colour (PAC) relations apart from PA relations for F and 1O CCs.…”

“…It is quite evident that the Cepheids of longer periods are favoured over those with shorter periods. The period distribution for the SMC CCs deviates from the general pattern observed in the case of the LMC CCs as has been given by Joshi et al (2014). Unlike SMC, they found two peaks in the LMC when both the F and 1O CCs were combined together, a result similar to the galaxies like M31 and the MW (Antonello et al, 2002;Macri, 2004;Vilardell et al, 2007;Joshi et al, 2010).…”

“…Later, Efremov & Elmegreen (1998) and Efremov (2003) derived many PA relations considering different combinations of the 74 cluster Cepheids in 25 different open clusters in the LMC. Joshi et al (2014) made an attempt at improving the PA relation using the same sample of Cepheids given by the Efremov (2003) but taking ages of the clusters from the more recent study of Pandey et al (2010). They drew a linear square fit to the points by plotting the mean period against the clusters age in logarithmic scale and derived the following relation:…”

Reddening map and recent star formation in the Magellanic Clouds based on OGLE IV Cepheids

“…Recently Joshi & Joshi (2014) used mean periods of 74 LMC Cepheids found in 25 different open clusters and corresponding cluster ages taken from Pandey et al (2010) to draw an improved PA relation in the LMC. The empirical PA relation derived by Joshi & Joshi (2014) for the Cepheids in the LMC is given as log(t) = 8.60(±0.07) − 0.77(±0.08) log(P)…”

“…We used above PA relations to determine the age of each Cepheid in the LMC and SMC. As error in the period of Cepheids is reported to be less than 0.001%, we have not taken them into account in the subsequent age conversion but the typical average error in age is estimated to be ∼40 Myr due to uncertainty in the PA relations given by Bono et al (2005) and Joshi & Joshi (2014). Although resulting ages are in the range of log(t/yr) = 6.96 to 8.96 with a mean log(t/yr) of 8.21 for the LMC but three-fourth Cepheids population in the LMC are distributed between log(t/yr) of 8.0 to 8.4.…”