Posters

Posters

Mini-HAWKs: A pilot survey designed to discover new quiescient black holes

Gastón Escobar / Sara Navarro (Instituto de Astrofísica de Canarias, Spain)

Mini-HAWKs is a pilot photometric survey covering 50 square degrees of the Northern Galactic Plane, with 400 hours of guaranteed time, currently beeing carried out on the JAST80 telescope at the Observatorio de Javalambre. It uses three interference filters centered on H-alpha which allow to recover the full-width at half-maximum (FWHM) and equivalent widths of H-alpha lines from their flux ratios. We will show how this information can be used to efficiently identify candidate dormant black holes employing color-color diagrams and light curves constructed solely from the H-alpha measurements. This method is based on the idea that very broad H-alpha emission lines (FWHM ≳ 2200 km/s) are indicative of strong gravitational fields surrounding compact objects. This strategy is promising not only for discovering new black holes, but also for identifying a wide range of stellar populations, such as cataclysmic variables, Mira variables, Wolf-Rayet stars, among others, providing valuable data for many lines of research. We will present the preliminary results of the analysis from the first observed fields.

To be or not to be…a redback

María Alejandra De Vito (UNLP/Instituto de Astrofísica de La Plata - CONICET, Argentina)

Redbacks are binaries composed of an accreting neutron star and a giant low-mass donor star. These objects are considered to be in the recycling process of pulsars, before reaching their final state: a millisecond pulsar together with a white dwarf, or a black widow system. In the donor mass-orbital period plane, the region occupied by redbacks is defined as that of donor mass between 0.1 and 0.7 solar masses, and orbital period lower than 1 day. However, there are some systems that are not included in the redback group that behave as if they were. We present possible progenitors of a recent candidate, but whose orbital period is larger than that of the usually considered range for redbacks.

Characterization of a post-common envelope eclipsing binary hosting a peculiar white dwarf

Erin Motherway (University of Wisconsin-Madison, USA)

We provide a detailed characterization of 2M07515777+1807352, a post-common envelope eclipsing binary system with a 10.3 d, nearly circular orbit (e = 0.02). This system consists of a massive white dwarf (WD) (1.085 Msun) and a 4400 K main-sequence companion (0.66 Msun). This WD is among the most massive known within post-common envelope binary systems. We also find, through both spectral energy distribution and TESS light curve analyses, that the WD has a radius of 1.54 ± 0.07Rearth, roughly 12sigma larger than the expected value from WD mass-radius relationships. Both the Lomb-Scargle analysis and the vsini of the system indicate the main-sequence companion to be supersyncronously rotating at a period of ~6 days, which may suggest accretion occurred prior to CEE. This binary also interestingly shares similar physical characteristics with six other post-common envelope systems hosting massive WDs, which may point to a shared formation pathway. We model the history of this system with COSMIC and find that this system likely formed through an episode of common envelope evolution following the onset of mass transfer when the progenitor primary was on either the early or the thermally pulsing stages of the asymptotic giant branch. As a result of its interesting properties, the study of 2M07515777+1807352 can provide new insights regarding many key outstanding questions in our understanding of common envelope evolution.

Blue Lurkers Candidates across Open Clusters from UV excess and stellar rotation

Elisabetta Reggiani (Università di Firenze & INAF - Arcetri)

Blue lurkers (BLs) are a recently identified class of exotic stars, first characterized in the open cluster M67 as lower-mass counterparts of blue straggler stars, photometrically hidden along the main sequence of their host clusters. They have so far been recognized either through rapid rotation (Leiner et al. 2019) or ultraviolet excess indicative of recent mass transfer (Dattatrey et al., 2023; Jadhav et al., 2024). However, the number of confirmed BLs remains small, limiting our understanding of their formation pathways. Expanding the sample — both in size and across clusters of different ages and masses — is essential to constrain their evolutionary origins. In this work, we search for BL candidates in a large set of open clusters, identifying systems based on rotational and photometric peculiarities. We compare the efficiency of these methods and present new candidate BLs that, if followed up with detailed study and modeling, can serve as benchmarks for understanding mass transfer in low-mass binaries.

The Role of Mass Transfer Efficiency in Stability Criteria: A Study with SEVN

Maite Echeveste (INAF - Arcetri)

The fate of binary systems is largely determined by whether mass transfer proceeds stably or leads to a dynamical disruption. A standard approach to evaluate this stability compares how the donor star’s radius and its Roche lobe respond to mass loss. In reality, most population synthesis codes, including those based on Hurley’s prescriptions, assume fully efficient mass transfer, meaning that all the transferred mass is accreted by the companion, and no mass or angular momentum is lost from the system. In this work, we improve this prescription by introducing a new one that incorporates non-conservative mass transfer—allowing for mass and angular momentum loss—to calculate the Roche lobe’s response more realistically. This leads to a more physically consistent criterion for determining the stability of Roche lobe overflow. We implement this improved stability criterion in the SEVN population synthesis code and explore its impact on two distinct types of systems: blue straggler stars and binary black holes.

Nitrogen-rich field stars are not necessarily old

Ellen Leitinger (Bologna University & INAF - Arcetri)

Globular clusters (GCs) are important tracers of the early Galactic assembly process, with their stars showing distinct chemical abundance patterns. When such stars are found in the Galactic field rather than within GCs, they are considered remnant populations from clusters disrupted during the hierarchical assembly of our Milky Way. We expand the search for such chemically enriched stars in the Kepler field, targeting stars located in the halo, thin and thick disk, to show the potential in using asteroseismology to link asteroseismic properties with chemical abundances and kinematics. Using data from APOGEE DR17, Gaia DR3, and the Kepler asteroseismology mission, we identify primordial stars as those with chemical signatures typical of field stars, and enriched stars as those exhibiting strong nitrogen enrichment, with corresponding carbon and oxygen depletion. We present our sample of 151 red giant branch (RGB) and red clump (RC) stars, 100 of which have measured masses and inferred age estimations from asteroseismology. The asteroseismic ages indicate that many of the enriched stars found in the field are too young to have originated from globular clusters, prompting a search for alternative enrichment scenarios.

Survey of Surveys: expanding homogenized stellar parameters catalogue in the new release of SoS-Spectro

Aleksandra Avdeeva (INAF - Arcetri)

We present preliminary results that provide a framework for building the SoS-Spectro catalog, designed to combine spectroscopic surveys into a homogeneous dataset with reduced systematic biases. At this stage, our method has been applied to APOGEE, GALAH, and LAMOST surveys, where we have homogenized the key stellar parameters — effective temperature, surface gravity, and metallicity (Teff, logg, [Fe/H]) — and re-evaluated their uncertainties using a dedicated error analysis method. This improves the reliability of the parameters and enables consistent comparison across surveys. While the methodology is intended to be extended to additional spectroscopic datasets, here we report on the current status and first results. Looking ahead, applying the same approach to radial velocities will be crucial for identifying binary stars in large spectroscopic samples.

Eclipsing and contact binaries in star clusters: Insights from the Stetson database

Sneha Nedhath Divakaran (Università di Firenze & INAF - Arcetri)

Eclipsing and contact binaries in star clusters play a key role in tracing stellar evolution, cluster dynamics, and binary interaction processes. One of the major ways for their detection and characterization is long-term, high-precision photometric monitoring across diverse stellar populations. This can be accomplished using the Stetson photometric database - the largest existing collection of homogeneously and accurately calibrated photometric data of both open and globular clusters. Built from over a million public and proprietary CCD images, many stars in this database have been observed thousands of times, in some cases spanning over 30 years. This depth, longevity, and uniformity make it an unparalleled resource for studying stellar variability on cluster-wide scales. Within the framework of the ERC project StarDance: the non-canonical evolution of stars in clusters, my Ph.D. thesis focuses on a systematic exploration of variable stars, particularly binaries, across the entire set of open and globular clusters available in the Stetson database. By leveraging the extensive time coverage and photometric precision, this project aims to identify and classify variable stars, interpret their light-curve morphologies, and investigate links between variability and cluster properties in a homogeneous way. As a pilot study, I present the first results from the old, metal-rich open cluster NGC 6791. With its rich binary population and outstanding observational coverage in the database, NGC 6791 serves as an ideal test case to validate the methodology and illustrate the scientific potential of the project. These preliminary results pave the way for a comprehensive survey of variable stars in clusters, ultimately exploiting the full power of the Stetson database to probe binary evolution in different cluster environments.

The binary star inventory of Omega Centauri

Laurenz Steinbauer (Università di Firenze & INAF - Arcetri)

While globular clusters have long been considered simple stellar populations, observations have revealed anomalies such as chemical anti-correlations and multiple stellar populations. The discoveries suggest the presence of multiple populations of different compositions, contradicting the long-held assumptions. A particularly intriguing explanation for these anomalies is given by stellar interactions in binary star systems. Non-canonical stellar types such as blue stragglers, extrinsic S-type stars and the presence of short-period binaries such as W Ursa Majoris variables suggest that interactions like mass transfer or mergers are commonplace in the dense environments of globular cluster, and may provide a solution to the multiple population enigma. In this project, I work on identifying binary stars in NGC 5139 (Omega Centauri) by using archival data - including FLAMES@VLT GIRAFFE spectra and Gaia photometry - to determine radial velocities and important stellar parameters and RAVEN, a statistical method of identifying binary candidates based on their radial velocity distribution.