UVIT/AstroSat studies of blue straggler stars and post-mass transfer systems in star clusters: detection of one more blue lurker in M67

Subramaniam, Annapurni; Pandey, S. B.; Jadhav, Vikrant V.; Sahu, Snehalata

doi:10.1007/s12036-020-09668-1

Cited by 17 publications

(14 citation statements)

References 39 publications

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“…Similarly, stellar collisions and mergers are also expected to yield rapidly rotating stars (Sills et al 2001(Sills et al , 2005. Recently, Subramaniam et al (2020) found a correlation between T 𝑒 𝑓 𝑓 of WD and 𝑣 𝑠𝑖𝑛𝑖 of BSS. The BSSs with the hottest WD are fast rotators, whereas the slowest rotation is found for the BSS with the coolest WD (WOCS 5005).…”

Section: Discussionmentioning

confidence: 98%

“…A recent MT is expected to leave behind a hot companion to the BSS (and blue lurkers), whereas mergers leave behind a single BSS. UV investigations have revealed the presence of hot WD companions to the BSSs and MS stars (Knigge et al 2008;Gosnell et al 2015;Sindhu et al 2019;Leiner et al 2019;Jadhav et al 2019;Sahu et al 2019;Sindhu et al 2020;Subramaniam et al 2020).…”

Section: Discussionmentioning

confidence: 99%

“…Motivated by these results, we started a survey to understand BS systems in old open clusters using the Ultra Violet Imaging Telescope (UVIT) on AstroSat (UVIT Open Cluster Survey -UOCS). UVIT observation of M67 detected a WD companion <0.3M to a BSS and several post-MT systems (Sindhu et al 2019;Jadhav et al 2019;Sindhu et al 2020;Subramaniam et al 2020).…”

Section: Introductionmentioning

confidence: 98%

“…Ultraviolet (UV) observations have the potential to characterise the formation channels of BSSs and post-MT systems by detecting a possible hot companion to these stars (Landsman et al 1997;Knigge et al 2008;Gosnell et al 2015;Subramaniam et al 2016a;Sahu et al 2019;Sindhu et al 2019Sindhu et al , 2020Jadhav et al 2019;Subramaniam et al 2020). Landsman et al (1998) were able to detect 11 BSSs in M67 using Ultraviolet Imaging Telescope (UIT).…”

Section: Introductionmentioning

confidence: 99%

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UOCS.VI. UVIT/AstroSat detection of low-mass white dwarf companions to 4 more blue stragglers in M67

Pandey,

Subramaniam,

Jadhav

2021

Preprint

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Blue stragglers stars (BSSs) in M67 have attracted attention from observations and theory to unravel their formation mechanisms. In the series of Ultra Violet Imaging Telescope (UVIT on AstroSat) study of Open clusters (UOCS), here we report the detection of hot companions to 4 more BSSs (WOCS 2013, WOCS 3013, WOCS 4006 and WOCS 5005), using Far-UV photometry obtained in two epochs from UVIT. We characterise the hot companions to be low to extremely low mass (LM/ELM) white dwarfs (WDs) with T 𝑒 𝑓 𝑓 ∼ 13-23kK, R/R ∼ 0.035-0.051, M/M ∼ 0.19-0.3 and age ∼ 25-300 Myr using WD models. Two BSSs (WOCS 1025 and WOCS 3005) showed UV excess, and may have a hot companion, but we are unable to confirm/characterise. 13 BSSs are detected by UVIT in the two epochs of data, of the total 14 present in M67. We have performed detailed analysis on 10 BSSs, including our previous studies. Five BSSs are found to have LM/ELM WD companions, suggesting Case-B masstransfers (MT) to be prevalent in M67 (with a lower limit of 37.5%, 5/14), along with other mechanisms. Three BS+WD systems have orbital parameters outside the limit for stable MT as per the models. We speculate the following three possibilities -their orbits are altered due to cluster dynamics, some may be in triple systems with LM/ELM WDs in an unknown closer orbit, or a modified MT mechanism may be required to enable their formation.

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Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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UOCS.VI. UVIT/AstroSat detection of low-mass white dwarf companions to 4 more blue stragglers in M67

Pandey,

Subramaniam,

Jadhav

2021

Preprint

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“…However, depending upon the environment during merger or collision, the mass and age of BSs are slightly different from single star evolution (Sills et al 2009;Sun et al 2021). Due to their extremely large effective temperature, a UV imaging study is a powerful tool to identify and trace the properties of BSs in GCs (Ferraro 2000;Raso et al 2017;Ferraro et al 2018;Sindhu et al 2019;Sahu et al 2019a;Subramaniam et al 2020;Kumar et al 2021a).…”

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confidence: 99%

Study of UV bright sources in globular cluster NGC 4590 using Ultraviolet Imaging Telescope (UVIT) observations

Kumar,

Pradhan,

Parthasarathy

et al. 2022

Preprint

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We have studied ultraviolet (UV) bright sources in the Galactic globular cluster (GGC) NGC 4590 using Ultraviolet Imaging Telescope (UVIT) on-board the AstroSat satellite. Using UVoptical color-magnitude diagrams (CMDs), we have identified and characterized the sources of different evolutionary stages i.e., blue horizontal branch stars (BHBs), extremely blue horizontal branch stars (EHBs), blue straggler stars (BSs), variable stars, etc. We estimated effective temperature (T eff ), gravity (log(g)), luminosity (L bol ), and hence the radius (R) of these hot stars by fitting spectral energy distribution (SED) with the help of stellar atmosphere models. Two new far-UV (FUV) bright cluster member stars situated near the core of the cluster have been detected; one of them is an EHB star and the other one is either in its post-blue hook evolutionary phase or in white dwarf phase. The evolutionary status of all the hot stars, identified in the cluster, has been investigated by using various evolutionary models. We find the massive and younger BSs are concentrated at the center of the cluster whereas the older and less massive BSs are distributed though out the cluster. The BSs normalized radial distribution seems to be bi-modal with a minimum located at r min = 4.3 r c . We calculated A + parameter of the cluster which is obtained using cumulative normalized radial distribution of horizontal branch stars (HBs) and BSs. We measured this value up to half-mass radius of the cluster to be +0.13, which indicates that NGC 4590 is one of the youngest clusters among dynamically intermediate age GGCs with a dynamical age of 0.423 ± 0.096 Gyr.

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UOCS. IV. Discovery of diverse hot companions to blue stragglers in the old open cluster King 2

et al. 2021

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King 2, one of the oldest clusters in the Milky Way, with an age of $ 6 Gyr and distance of $ 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. Keywords. Open star clusters (1160)-blue straggler stars (168)-extreme horizontal branch stars (513)-B subdwarf stars (129)-ultraviolet astronomy (1736)-spectral energy distribution (2129)-binary stars (154).This article is part of the Special Issue on ''AstroSat: Five Years in Orbit''.

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UVIT/AstroSat studies of blue straggler stars and post-mass transfer systems in star clusters: detection of one more blue lurker in M67

Cited by 17 publications

References 39 publications

UOCS.VI. UVIT/AstroSat detection of low-mass white dwarf companions to 4 more blue stragglers in M67

UOCS.VI. UVIT/AstroSat detection of low-mass white dwarf companions to 4 more blue stragglers in M67

Study of UV bright sources in globular cluster NGC 4590 using Ultraviolet Imaging Telescope (UVIT) observations

UOCS. IV. Discovery of diverse hot companions to blue stragglers in the old open cluster King 2

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