UVIT Open Cluster Study. II. Detection of extremely low mass white dwarfs and post-mass transfer binaries in M67

Abstract

A detailed study of the ultraviolet (UV) bright stars in the old open star cluster, M67 is presented based on the far-UV observations using the {\it Ultra Violet Imaging Telescope} ({\it UVIT}) on {\it ASTROSAT}. The UV and UV-optical colour-magnitude diagrams (CMDs) along with overlaid isochrones are presented for the member stars, which include blue straggler stars (BSSs), triple systems, white dwarfs (WDs) and spectroscopic binaries (SB). The CMDs suggest the presence of excess UV flux in many members, which could be extrinsic or intrinsic to them. We construct multi-wavelength spectral energy distribution (SED) using photometric data from the {\it UVIT, Gaia} DR2, 2MASS and WISE surveys along with optical photometry. We fitted model SEDs to 7 WDs and find 4 of them have mass $>$ 0.5 \(M_\odot\) and cooling age of less than 200 Myr, thus demanding BSS progenitors. SED fits to 23 stars detect extremely low mass (ELM) WD companions to WOCS2007, WOCS6006 and WOCS2002, and a low mass WD to WOCS3001, which suggest these to be post mass transfer (MT) systems. 12 sources with possible WD companion need further confirmation. 9 sources have X-ray and excess UV flux, possibly arising out of stellar activity. This study demonstrates that UV observations are key to detect and characterise the ELM WDs in non-degenerate systems, which are ideal test beds to explore the formation pathways of these peculiar WDs. The increasing detection of post-MT systems among BSSs and main-sequence stars suggests a strong MT pathway and stellar interactions in M67.

29 pages, 13 figures, accepted in Astrophysical Journal

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Cited by in corpus (22)

• The ELM Survey. VIII. 98 Double White Dwarf Binaries
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• WIYN Open Cluster Study. LXXXVII. HST Ultraviolet Detection of Hot White Dwarf Companions to Blue Lurkers in M67
• UOCS.VI. UVIT/AstroSat detection of low-mass white dwarf companions to 4 more blue stragglers in M67
• UOCS. III. UVIT catalogue of open clusters with machine learning based membership using \textit{Gaia} EDR3 astrometry
• Characterization of hot populations of Melotte 66 open cluster using Swift/UVOT
• GlobULeS-IV. UVIT/AstroSat detection of extremely low mass white dwarf companions to blue straggler stars in NGC 362
• The White Dwarfs of the Old, Solar Metallicity Open Star Cluster Messier 67: Properties and Progenitors
• Discovery of double BSS sequences in the old Galactic open cluster Berkeley 17
• Hunting Down White Dwarf--Main Sequence Binaries Using Multi-Wavelength Observations
• UOCS-IX. AstroSat/UVIT study of the open cluster NGC 2818: Blue Stragglers, Yellow Stragglers, Planetary Nebula, and their membership
• M67 Blue Stragglers with High-resolution Infrared Spectroscopy
• UVIT Open Cluster Study. X. Rich Collection of Post Mass Transfer Systems in NGC 6791
• UOCS. XIV. Uncovering extremely low mass white dwarfs and blue lurkers in NGC 752
• The Blue Lurker WOCS 14020: A Long-Period Post-Common-Envelope Binary in M67 Originating from a Merger in a Triple System
• Dynamically Forming Extremely Low-Mass White Dwarf Binaries in Wide Orbits
• GlobULeS-V. UVIT/AstroSat studies of stellar populations in NGC 362: Detection of Blue Lurkers in a Globular Cluster
• Detection of a new sample of Galactic White Dwarfs in the direction of the Small Magellanic Cloud
• Photometric variability of blue straggler stars in M67 with TESS and K2
• A uvbyCaHbeta CCD Analysis of the Open Cluster Standard, M67,and its Relation to NGC 752
• A rotation-based census of blue lurker candidates in open clusters
• On the detectability and parameterisation of binary stars through spectral energy distributions