Astrometric and Spectroscopic Analysis of IC 2714: An Open Cluster Hosting a Lithium-Rich Giant

TL;DR

This paper presents a comprehensive astrometric and spectroscopic analysis of IC 2714, combining Gaia DR3 data with high-resolution spectra to refine cluster membership and deliver the most complete chemical inventory yet for the cluster, across 23 species and the $^{12}$C/$^{13}$C isotopic ratio for seven stars. The authors identify six bona fide members and classify two giants (#028 and #034) as non-members, deriving a mean metallicity of $ ext{[Fe/H]} = -0.07 \pm 0.09$ and an age of $ ext{log} t = 8.84$, consistent with a young open cluster at $R_{GC} \approx 7.95$ kpc. A standout result is the lithium-rich giant #087 with $ ext{log} \, \varepsilon\text{(Li)}_{NLTE} = 1.54$ dex, interpreted in the context of RC-phase evolution or possible enrichment scenarios (e.g., planetary engulfment or mergers). Overall, the study confirms solar-like abundances with modest scatter, supports Galactic chemical gradient trends for young clusters, and highlights the potential of chemical clocks, especially using $ ext{[C/N]}$, to constrain ages in open clusters.

Abstract

Open clusters serve as laboratories to study and evaluate stellar evolution and Galactic chemical evolution models. Chemical peculiarities, such as lithium-rich giants, are rarely observed in these stellar systems. This work focuses on eight red giants (#005, #028, #034, #053, #087, #121, #126, and #190) previously reported as members of the Galactic cluster IC 2714. We conducted a detailed investigation using high-resolution spectroscopy, supplemented with data from the Gaia DR3 catalog. Besides deriving the cluster's fundamental parameters, we provide the most thorough chemical characterization of IC 2714 to date, reporting the abundance of 23 species, including light elements (Li, C, N, O), odd-Z elements (Na, Al), $α$-elements (Si, Ca, Ti, Mg), iron-peak elements (Sc, Cr, Ni), $\textit{s}$-process-dominated elements (Y, Zr, Ba, La, Ce, Nd) and $\textit{r}$-process elements (Sm, Eu). We also present the carbon isotopic ratios $^{12}$C/$^{13}$C for the first time for seven stars. One particular star (#087) exhibits a high lithium abundance ($\log \varepsilon$(Li)$_{\rm NLTE}$ = $+$1.54 dex) and a slightly higher projected rotational velocity ($v \sin i$ = 6.7 km s$^{-1}$). Our results suggest that the analyzed stars are in the core-helium-burning phase of evolution, where the most lithium-rich giants are found. Combining astrometric probabilities and chemical abundances, we conclude that two giants (#028 and #034) might not be cluster members.

Figures (7)

• Figure 1: Proper-motion distribution of the extracted Gaia DR3 data around the center of IC 2714 (top left), with the color scale indicating probabilities computed using pyUPMASK; the star #034 is found outside the plot limits, as indicated by the green arrow. The top right panel shows the parallax versus G magnitude distribution. A color–magnitude diagram (bottom left) is presented, with an isochrone fit using PARSEC isochrones bressan2012; the fit was performed using the SIESTA code, considering stars with p $\geq$ 0.7. The bottom right panel displays the spatial distribution of stars around the center of the cluster. The red giants of our sample classified as members are shown in red circles, while the non-member stars #028 and #034 are shown in green circles. In the top left plot, the star #034 lies outside the plot limits, as indicated by the green arrow.
• Figure 2: Comparison between $T_{{\rm eff}}$ and $\log{g}$ spectroscopic results with those obtained by (V-K) photometry and LDR (top); and comparison between the parameters derived in this work with those from literature (middle and bottom): S09, santos2009; DM16, delgadomena2016; TS23, tsantaki2023; R24, ramos2024. The results for the non-member stars (#028 and #034) are highlighted in green. The literature comparison plots show only the star #034, as parameters for the #028 were not previously reported in the literature.
• Figure 3: Observed data (gray) and different synthetic spectra. The best fit is shown in red. The gray box shows the spectral region considered for the fit.
• Figure 4: $^{12}$C/$^{13}$C isotopic ratio (top) and [Na/Fe] ratio (bottom) in terms of the turn-off mass of giant stars in OCs. Our results for IC 2714 are shown in red, and the mean [Na/Fe] ratio was corrected by NLTE effects. The results for OCs previously studied by our team are also shown: penasuarez2018, in gray triangles; dasilveira2018, in blue diamonds; martinez2020, in blue circles; and holanda2019holanda2021holanda2022, in orange squares. Solid lines represent the predicted abundances at the first dredge-up from solar metallicity evolutionary models from CL10 charbonnel2010 and L12 lagarde2012. Dashed lines shows the prediction models for thermohaline and rotation-induced mixing (TH+V) from L12 (in blue), thermohaline extra-mixing from CL10 (orange), and TH+V from L12 (in blue), respectively.
• Figure 5: Abundance ratios [X/Fe] versus [Fe/H] for elements from carbon to europium. [$\alpha$/Fe], [odd/Fe], [peak/Fe], [s/Fe], and [r/Fe] represent the averages for $\alpha$-elements (Si, Ca, Ti, Mg), odd-Z elements (Na, Al), iron-peak elements (Sc, Cr, Ni), elements predominantly produced by the s-process (Y, Zr, Ba, La, Ce, Nd), and elements predominantly produced by the r-process (Sm, Eu), respectively. The results for the stars classified as members are shown in red, while those for the non-member stars are shown in green. In blue diamonds results by mishenina2006; in gray squares by luck2007; and in orange circles by bensby2014 and battistini2016. The intersection of the black dashed lines indicate solar values, while the intersection of the red lines indicate the average abundances of the members.