Abstract
King 2, one of the oldest clusters in the Milky Way, with an age of \(\sim \)6 Gyr and distance of \(\sim \)5700 pc, has been observed with UVIT payload on the AstroSat. With membership information derived from Gaia EDR3, the cluster is found to have 39 blue straggler stars (BSSs). We created multi-wavelength spectra-energy distributions (SED) of all the BSSs. Out of 10 UV detected BSSs, 6 bright ones were fitted with double component SEDs and were found to have hotter companions with properties similar to extreme horizontal branch (EHB)/subdwarf B (sdB) stars, with a range in luminosity and temperature, suggesting a diversity among the hot companions. We suggest that at least 15% of BSSs in this cluster are formed via mass-transfer pathway. When we compared their properties to EHBs and hotter companions to BSS in open and globular clusters, we suggest that EHB/sdBs like companions can form in binaries of open clusters as young as 6 Gyr.
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Notes
UOCS: UVIT Open Cluster Study
https://github.com/jikrant3/Binary_SED_FittingBinary_SED_Fitting is a python code which uses \(\chi ^2\) minimisation technique to fit two component SEDs.
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Acknowledgements
We thank the anonymous referee for their valuable comments and inputs. RS would like to thank the National Academy of Sciences, India (NASI), Prayagraj for the award the NASI Honorary Scientist; Alexander von Humboldt Foundation, Germany for the award of long-term group research linkage program and Director, IIA for hosting and making available facilities of the institute. This publication uses the data from the AstroSat mission of the Indian Space Research Organisation (ISRO), archived at the Indian Space Science Data Centre (ISSDC). This publication uses UVIT data processed by the payload operations centre at Indian Institute of Astrophysics (IIA). The UVIT is built in collaboration between IIA, Inter-University Centre for Astronomy and Astrophysics (IUCAA), Tata Institute of Fundamental Research (TIFR), ISRO and Canadian Space Agency (CSA). This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). This publication makes use of VOSA, developed under the Spanish Virtual Observatory project supported by the Spanish MINECO through grant AyA2017-84089.
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This article is part of the Special Issue on “AstroSat: Five Years in Orbit”.
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Jadhav, V.V., Pandey, S., Subramaniam, A. et al. UOCS. IV. Discovery of diverse hot companions to blue stragglers in the old open cluster King 2. J Astrophys Astron 42, 89 (2021). https://doi.org/10.1007/s12036-021-09746-y
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DOI: https://doi.org/10.1007/s12036-021-09746-y