arXiv subjects

Khushboo K Rao

Publications and source records attributed to Khushboo K Rao.

4 recordsLinked to original sources

arXiv2026

Investigating Extended Main-Sequence Turnoffs in Galactic Open Clusters

The extended main sequence (eMS) and extended main sequence turnoff (eMSTO) phenomena have been observed in some young and intermediate-age star clusters in the Milky Way and in the Magellanic Clouds. In this study, we conduct a survey of 53 galactic open clusters (OCs) to investigate the roles of stellar rotation, differential extinction, and cluster properties in the emergence of eMS and eMSTO. The projected rotational velocities are taken from the Gaia ESO spectroscopic survey and the Gaia DR3 line-broadening velocities. Stellar members of each OC are identified using the ML-MOC algorithm with Gaia DR3 astrometry. We divide clusters into four classes based on the color-rotation distribution, extinction, and MSTO morphology and report 14 clusters ($A_{\rm v} \lesssim 0.15$ mag, Class I) that exhibit split MS with fast and slow rotators populating the redder and bluer parts of MSTO. For the remaining clusters, differential extinction hampers the color-rotation distinction and also inflates MSTO width and therefore introduces a systematic offset in the MSTO-age relation. We also quantify the fraction of slow rotators among MSTO stars, finding a median value of $f_{\rm slow\, rot}^{v \sin i<100} \approx 0.41$ and the fraction reaching the spin-down limit, $f_{\rm slow\, rot}^{v \sin i<30}$, is $ \approx 0.08$. We find no statistically significant correlation between $f_{\rm slow\, rot}$ and either the binary fraction or cluster age.

astro-ph.GA↗

arXiv2025

Investigating Unusually Extended Main Sequence Turnoff of the Galactic Open Cluster NGC 3532

Extended main-sequence turnoffs are observed in the color-magnitude diagrams of some young and intermediate-age star clusters. Here we report the case study of NGC 3532. Among the cluster member candidates identified using the ML-MOC algorithm on Gaia DR3 sources, we found that fast rotators are significantly redder. Stars near the main-sequence turnoff exhibit a multi-modal distribution in the Gaia broadening velocity ($v_{\rm broad}$). A comparison with relevant literature suggests binaries being typically interspersed with fast rotators, often manifesting as slow to moderate rotators. Additionally, chemically peculiar stars are predominantly located in the bluer regions of the turnoff, with those in the fast-rotator region having large values of Gaia re-normalised unit weight error, indicating plausible companions. Our analysis suggests multiple channels responsible for angular momentum loss to account for the extended turnoff.

astro-ph.GA↗

arXiv2024

Dynamical Evolution of Four Old Galactic Open Clusters traced by their constituent stars with \textit{Gaia} DR3

We investigate the evolutionary stages of four open clusters, Berkeley 39, Collinder 261, NGC 6819, and NGC 7789, of ages ranging from 1.6 -- 6 Gyr. These clusters have previously been classified into dynamically young and intermediate age groups based on the segregation level of BSS with respect to red giant branch stars and main sequence stars, respectively. We identify members of these four clusters using the ML-MOC algorithm on Gaia DR3 data. To examine the relative segregation of cluster members of different evolutionary stages, we utilize cumulative radial distributions, proper motion distributions, and spatial distributions in galactocentric coordinates. Our analysis shows that Berkeley 39 and NGC 6819 exhibit moderate signs of population-wise segregation from evolved to less-evolved members. NGC 7789 shows signs of mass segregation only in the cumulative radial distributions. On the other hand, Collinder 261 exhibits high segregation of BSS in the cumulative radial distribution, while other populations show the same level of segregation.

astro-ph.GA↗

arXiv2022

Discovery of double BSS sequences in the old Galactic open cluster Berkeley 17

Blue straggler stars (BSS) are peculiar objects which normally appear as a single broad sequence along the extension of the main sequence. Only four globular clusters (GCs) have been observed to have two distinct and parallel BSS sequences. For the first time for any open cluster (OC), we report double BSS sequences in Berkeley 17. Using the machine-learning based membership algorithm ML-MOC on Gaia EDR3 data, we identify 627 cluster members, including 21 BSS candidates out to 15 arcmin from the cluster center. Both the BSS sequences are almost equally populated and parallel to one another in Gaia as well as in Pan-STARRS colour-magnitude diagram (CMD). We statistically confirm their presence and report that both BSS sequences are highly segregated compared to the reference population out to $\sim$5.5 arcmin and not segregated thereafter. The lower densities of OCs make BSS formation impossible via the collisional channel. Therefore, mass transfer seems to be the only viable channel for forming candidates of both sequences. The gap between the red and blue BSS sequences, on the other hand, is significant and presents a great opportunity to understand the connection between BSS formation and internal as well as external dynamics of the parent clusters.

astro-ph.GA↗