Vasiliki Fragkou

Planetary nebulae (PNs) that are physically associated with star clusters are rare but crucial for stellar-evolution studies because they allow their initial and final stellar properties to be determined independently, contributing to constraints on the initial-to-final-mass relation (IFMR), which traces stellar mass loss. Although the identification of such pairs is essential, most reported cases have been identified incidentally rather than through systematic searches. Here, we attempt to uncover new such associations in our Galaxy employing literature PN central stars (CSs) and star-cluster catalogues. Exploring relevant angular positions on the sky and kinematic Gaia DR3 data, we identify 38 candidate CS–cluster pairs. The components of eight of these pairs present consistent interstellar extinctions, and their CS properties are compatible with stellar-evolution models. Two of these candidate pairs are already reported in the literature as true associations. We evaluate separately the remaining six pairs using literature PN observational data, assessing the likelihood of each pair being a true association. The initial and final masses of our best candidates are mostly consistent with the latest IFMR predictions and confirmed cluster–PN points. An additional 46 CS–cluster pairs have components with compatible angular positions but lack kinematic CS data and are thus presented separately. More data are needed for a precise estimation of the physical parameters of most of our candidates and to confirm these associations, which will be addressed in future studies.

Stellar evolution studies of low-to-intermediate mass stars are hindered by the lack of a solid link that connects their initial and final properties. This problem can be resolved for stars that are members of star clusters and at the final stages of their evolution. In such cases, we can estimate their final properties from direct measurements and obtain the necessary information for the properties of their progenitors from independent cluster studies. Here, we focus on the study of planetary nebulae that are confirmed members of Galactic open star clusters. These rare instances provide us with a new additional sample of data, which contributes to the fundamental initial-to-final mass relation (IFMR). We examine the quality of this contribution and assess the efficacy of our method, showing that our approach is very promising with already significant initial results. Our data generally confirm the latest IFMR trends, filling important gaps in the process.

Planetary nebulae (PNs) studies are essential for understanding the late stellar evolution of low-to-intermediate mass stars. PNs in open clusters (OC) are rare but valuable since their study directly links their properties to those of their progenitors, something that cannot be achieved for field PNs. Here, we report the identification of one more OC-PN association to add to the small sample of, now, five pairs. The physical properties of the host cluster, PN, and its central star (CSPN) have been explored using high and intermediate-resolution spectral and deep photometric data. The close agreement of the radial velocities of the PN and host cluster, together with concordance of reddening and distance, shows that the PN PHR J1724-3859 is highly likely to be physically associated with the OC Trumpler 25. Deep photometric data allowed clear identification of the CSPN. We find a CSPN effective temperature of around 250 kK and a nebular kinematic age of 23 kyr, both at the extreme end, like the other members of this small class. The progenitor and final CSPN masses have been estimated to be 5.12 − 0.15 + 0.16 M _⊙ and 0.95 ± 0.12 M _⊙ respectively. These latest results agree with the emerging trend for our other OC-PNs, falling below, but approximately parallel to, the latest initial-to-final-mass relation estimates derived from cluster white dwarfs, and have important implications for stellar evolution models. All OC-PNs also possess some other common properties (e.g., all are Type I PNs and bipolars) to be explored in future studies.

Context. Achieving accurate photometric characterizations of central stars of planetary nebulae (CSPNe) toward the galactic plane is significantly hindered by the high levels of interstellar extinction in these regions. However, near-infrared (NIR) observations offer a more effective alternative, as extinction is substantially reduced at these wavelengths. Aims. By mitigating the effects of interstellar extinction via NIR observations of the Galactic disk and bulge, we seek to improve the identification and characterization of CSPNe in these regions, enabling a deeper understanding of their properties and evolutionary status. Methods. We used NIR photometry from the VISTA Variables in the Vía Láctea (VVV) survey and its extension VVVX to define the NIR photometry of a large sample of CSPNe recently identified with Gaia EDR3 data. We explored the optical and NIR properties of all CSPNe in our sample and searched for eclipsing binary candidates among them by employing relevant catalogs. Results. We present a homogeneous catalog of 1274 CSPNe, including their Z, Y, H, J, and K NIR magnitudes and errors. We also include our findings on the photometric properties of our sample. We report 14 CSPNe with a large IR excess indicating cool companions and/or surrounding discs and 56 eclipsing binary candidates. Conclusions. Based on the present VVVX CSPN catalog, we conclude that NIR photometry can prove valuable for further and in-depth studies of CSPNe. Subsequent studies ought to focus on exploring the true nature of the CSPNe that present IR excess as well as eclipsing-binary CSPNe candidates.

Achieving accurate photometric characterizations of central stars of planetary nebulae (CSPNe) toward the galactic plane is significantly hindered by the high levels of interstellar extinction in these regions. However, near-infrared (NIR) observations offer a more effective alternative, as extinction is substantially reduced at these wavelengths. By mitigating the effects of interstellar extinction via NIR observations of the Galactic disk and bulge, we seek to improve the identification and characterization of CSPNe in these regions, enabling a deeper understanding of their properties and evolutionary status. We used NIR photometry from the VISTA Variables in the Vía Láctea (VVV) survey and its extension VVVX to define the NIR photometry of a large sample of CSPNe recently identified with Gaia EDR3 data. We explored the optical and NIR properties of all CSPNe in our sample and searched for eclipsing binary candidates among them by employing relevant catalogs. We present a homogeneous catalog of 1274 CSPNe, including their Z, Y, H, J, and K NIR magnitudes and errors. We also include our findings on the photometric properties of our sample. We report 14 CSPNe with a large IR excess indicating cool companions and/or surrounding discs and 56 eclipsing binary candidates. Based on the present VVVX CSPN catalog, we conclude that NIR photometry can prove valuable for further and in-depth studies of CSPNe. Subsequent studies ought to focus on exploring the true nature of the CSPNe that present IR excess as well as eclipsing-binary CSPNe candidates.

We present the largest sample (∼13,000 candidates, ∼3000 of which are bona fide candidates) of globular cluster (GCs) candidates reported in the Fornax cluster so far. The survey is centered on the NGC 1399 galaxy, extending out to 5 virial radii (R _vir) of the cluster. We carried out a photometric study using images observed in the 12-band system of the Southern Photometric Local Universe Survey (S-PLUS), corresponding to 106 pointings, covering a sky area of ∼208 square degrees. Studying the properties of spectroscopically confirmed GCs, we have designed a method to select GC candidates using structural and photometric parameters. We found evidence of color bimodality in two broadband colors, namely (g − i)₀ and (g − z)₀, while, in the narrow bands, we did not find strong statistical evidence to confirm bimodality in any color. We analyzed the GCs luminosity functions (GCLF) in the 12 bands of S-PLUS, and we can highlight two points: (a) due to the relatively shallow depth of S-PLUS, it is only possible to observe the bright end of the GCLF and, (b) at that level, in all of the bands, it can be considered to be the log-normal distribution typical for GC systems. With the spatial coverage reached in this study, we are able, for the first time, to explore the large-scale distribution of GCs within and around a galaxy cluster. In particular, we noted that the GCs might be clustered along substructures, which trace the current cluster buildup.

Context. Planetary nebulae (PNe) that are physical members of open star clusters (OCs) provide us with highly valuable data for stellar evolution studies. Unfortunately, they are extremely rare, with only three such instances previously confirmed in our Galaxy. Aims. In this study, we confirm the physical association of PN NGC 2818 with OC NGC 2818A, an association long debated in literature studies. Hence, we add a fourth object to the sample of rare OC-PN pairs. The physical properties of the PN can then be linked to those of its progenitor star. Methods. Using GHOST at Gemini high-resolution nebular spectra, we measured the PN systemic radial velocity to compare it with that of the putative host cluster. This was well determined from Gaia. We estimated the physical parameters of both the OC NGC 2818A and the PN using our data, together with estimates from previous studies and theoretical cluster isochrones and evolutionary tracks to show they are compatible. Results. The highly precise, systemic radial velocity of the PN that was determined, is consistent to within the small errors with that of the cluster and its 1 km s⁻¹ associated velocity dispersion. This is a tight and primary requirement for cluster membership. We have determined other physical parameters of the PN and cluster, such as age and distance. These also match within the errors. Taken together, these results present compelling evidence for the physical association of the PN and cluster. The PN age was found to be around 11 kyr and the effective temperature of its central star was estimated as 130 kK. The initial and final masses of the progenitor star were determined to be 2.33 ± 0.10 M_⊙ and 0.58 ± 0.10 M_⊙, respectively. We plotted the resulting initial-to-final data point on the latest initial-to-final-mass relation and also include the data points from our other three OC-PN associations known. This new data point agrees with the published trends from previous studies and further delineates the ‘kink’ found at relatively low initial masses. Conclusions. We show that all four OC-PN associations, identified thus far, share a number of common properties. These rare cases merit detailed cluster-PN studies and work to further extend the sample.

Planetary nebulae (PNe) that are physical members of open star clusters (OCs) are valuable for stellar evolution studies. They are extremely rare, with only three such instances confirmed in our Galaxy. Here, we confirm the physical association of PN NGC 2818 with OC NGC 2818A, an association long debated in the literature, adding a fourth object to the sample of rare OC-PN pairs. The physical properties of the PN can then be linked to those of its progenitor star. Using GHOST/Gemini high-resolution nebular spectra, we measured the PN systemic radial velocity to compare it with that of the putative host cluster, determined from Gaia. We estimated the physical parameters of both the OC and the PN using our data, together with estimates from previous studies and theoretical cluster isochrones and evolutionary tracks to show they are compatible. The precise, systemic radial velocity of the PN that was determined, is consistent among the errors with that of the OC and its 1 km/s associated velocity dispersion, a primary requirement for cluster membership. We have determined other physical parameters of the PN and the OC, such as age and distance, which also match within the errors. These results present compelling evidence for the physical association of the PN and the OC. The PN age was found to be 11 kyr and the effective temperature of its central star was estimated as 130 kK. The initial and final masses of the progenitor star were determined to be 2.33$\pm$0.10 Msol and 0.58$\pm$0.10 Msol respectively. We plotted the resulting data point on the latest initial-to-final-mass relation. This new data point agrees with the previously published trends and further delineates the 'kink' found at relatively low initial masses. All four OC-PN associations, identified thus far, share a number of common properties. These rare cases merit detailed OC-PN studies and work to further extend the sample.

We have found strong evidence that an extended bipolar planetary nebula (PN), lying in the line-of-sight of the Galactic open cluster M37, is actually its physical member. We estimated both the PN physical properties and the properties of its progenitor from cluster studies. The progenitor mass has been found to be around 2.8 M_⊙. There are only a handful of such confirmed associations and each of them provides valuable additional data to the initial-to-final-mass relation. The nebula has a major axis of 445 arcsec and a kinematical age of around 80 kyrs -the largest ever determined for a PN- suggesting that PNe in clusters do not dissipate as fast as field PNe.