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      https://www.ias.ac.in/article/fulltext/joaa/034/04/0393-0429

    • Keywords

       

      Open clusters and associations: NGC 663, NGC 869, NGC 884, NGC 7380, Berkeley 86, IC 2602, Trumpler 18, Hogg15; stars: premain sequence; X-rays: massive stars, intermediate mass stars, low mass stars.

    • Abstract

       

      We present a detailed investigation of X-ray source contents of eight young open clusters with ages between 4 to 46 Myr using archival X-ray data from XMM-NEWTON. The probable cluster memberships of the X-ray sources have been established on the basis of multi-wavelength archival data, and samples of 152 pre-main sequence (PMS) low mass (< 2𝑀), 36 intermediate mass (2-10𝑀) and 16 massive (> 10𝑀) stars have been generated. X-ray spectral analyses of high mass stars reveal the presence of high temperature plasma with temperature < 2 keV, and mean 𝐿𝑋/𝐿bol of 10-6.9. In the case of PMS low mass stars, the plasma temperatures have been found to be in the range of 0.2 keV to 3 keV with a median value of ∼ 1.3 keV, with no significant difference in plasma temperatures during their evolution from 4 to 46 Myr. The X-ray luminosity distributions of the PMS low mass stars have been found to be similar in the young star clusters under study. This may suggest a nearly uniform X-ray activity in the PMS low mass stars of ages ∼ 4–14 Myr. These observed values of 𝐿𝑋/𝐿bol are found to have a mean value of 10-3.6 ± 0.4, which is below the X-ray saturation level. The 𝐿𝑋/𝐿bol values for the PMS low mass stars are well correlated with their bolometric luminosities, that implies its dependence on the internal structure of the low mass stars. The difference between the X-ray luminosity distributions of the intermediate mass stars and the PMS low mass stars has not been found to be statistically significant. Their 𝐿𝑋/𝐿bol values, however have been found to be significantly different from each other with a confidence level greater than 99.999% and the strength of X-ray activity in the intermediate mass stars is found to be lower compared to the low mass stars. However, the possibility of X-ray emission from the intermediate mass stars due to a low mass star in close proximity of the intermediate mass star can not be ruled out.

    • Author Affiliations

       

      Himali Bhatt1 J. C. Pandey2 K. P. Singh3 Ram Sagar2 Brijesh Kumar2

      1. Astrophysical Sciences Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085, India.
      2. Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263 129, India.
      3. Tata Institute of Fundamental Research, Mumbai 400 005, India.
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    • Supplementary Material

       
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