Galactic Stars Research Articles

The masses of open star clusters and their tidal tails and the stellar initial mass function

Unresolved binaries have a strong influence on the observed parameters of SC We quantify this influence and compute the resulting mass underestimates and MF N-body simulations of realistic SC were used to investigate the evolution of the binary population in a SC and its tidal tails. Together with an empirically gauged stellar mass-luminosity relation, the results were then used to determine how the presence of binaries changes the photometric mass and MF of the SC and its tails as deduced from observations. T1 which is the tidal tail caused by gas expulsion, contains a larger fraction of binaries than both the SC and T2 which forms after gas expulsion. Additionally T1 has a larger velocity dispersion. Using the luminosity of an unresolved binary, an observer would underestimate its mass. This bias sensitively depends on the companion masses due to the structure of the stellar mass-luminosity relation. Combining the effect of all binaries in the simulation, the total photometric mass of the SC is underestimated by 15<!PCT!>. Dark objects (black holes and neutron stars) increase the difference between the real and observed mass of the SC further. For both the SC and the tails, the observed power-law index of the MF between a stellar mass of 0.3 and 0.7 $M_ is smaller by up to 0.2 than the real one, the real IMF being steeper by this amount. This difference is larger for stars with a larger velocity dispersion or binary fraction. Since the stars formed in SC are the progenitors of the Galactic field stars, this work suggests that the binary fractions of different populations of stars in the Galactic disc will differ as a function of the velocity dispersion. However, the direction of this correlation is currently unclear, and a complete population synthesis will be needed to investigate this effect. Variations in the binary fractions of different clusters can lead to perceived variations of the deduced stellar MF

A Study of Stochastic Low-frequency Variability for Galactic O-type Stars

In order to explore how the ubiquitous stochastic low-frequency (SLF) variability of O-type stars is related to various stellar characteristics, we compiled a sample of 150 O-type stars observed via ground-based spectroscopic surveys, alongside photometric data obtained from the Transiting Exoplanet Survey Satellite (TESS). We analyzed 298 light curves obtained from TESS Sectors 1–65 for the stars in our sample. Leveraging the spectroscopic parameters, we used Bonnsai to determine masses, radii, fractional main-sequence ages, and mass-loss rates for stars of our sample. Subsequently, we identified possible correlations between the fitted parameters of SLF variability and stellar properties. Our analysis unveiled four significant correlations between the amplitude and stellar parameters, including mass, radius, fractional main-sequence ages, and mass-loss rate. For stars with ≳30 M ⊙, we observed a decrease in characteristic frequency and steepness with increasing radius. Finally, we compared various physical processes that may account for the SLF variability with our results. The observed SLF variability may arise from the combined effects of the iron convection zone (FeCZ) and internal gravity waves (IGWs), with IGWs potentially more dominant in the early stages of stellar evolution, and the contribution of FeCZ becoming more significant as stars evolve. Meanwhile, our results indicate that the SLF variability of O-type stars bears certain signatures of the line-driven wind instability and granulation.

JWST/NIRSpec spectroscopy of intermediate-mass quiescent galaxies at z ~ 3-4

ABSTRACT We present the analysis of three intermediate-mass quiescent galaxies (QGs) with stellar masses of ${\sim} 10^{10}\, \mathrm{M}_{\odot }$ at redshifts $z\sim 3\!-\!4$ using NIRSpec low-resolution spectroscopy. Utilizing the spectral energy distribution fitting code bagpipes, we confirm these target galaxies are consistent with quiescent population, with their specific star formation rates falling below 2 dex the star-forming main sequence at the same redshifts. Additionally, we identify these QGs to be less massive than those discovered in previous works, particularly prior to the JWST era. Two of our target galaxies exhibit the potentially blended $\mathrm{ H} \, {\alpha }$ + [N ii] emission line within their spectra with signal-to-noise ratio ${\gt} 5$. We discuss whether this feature comes from an active galactic nucleus (AGN) or star formation, although future high-resolution spectroscopy is required to reach a conclusion. One of the target galaxies is covered by JWST/NIRCam imaging of the Public Release IMaging for Extragalactic Research survey. Using the 2D profile fitting code galfit, we examine its morphology, revealing a disc-like profile with a Sérsic index of $n=1.1 \pm 0.1$. On the size–mass relation, we find a potential distinction between less massive ($\log _{10}{(M_*/\mathrm{M}_\odot)}\lt 10.3$) and massive ($\log _{10}{(M_*/\mathrm{M}_\odot)}\gt 10.3$) QGs in their evolutionary pathways. The derived quenching time-scales for our targets are less than $1 \, {\rm Gyr}$. This may result from these galaxies being quenched by AGN feedback, supporting the AGN scenario of the emission line features.

Boron depletion in Galactic early B-type stars reveals two different main sequence star populations

Context. The evolution and fate of massive stars are thought to be affected by rotationally induced internal mixing. The surface boron abundance is a sensitive tracer of this in early B-type main sequence stars. Aims. We test current stellar evolution models of massive main sequence stars which include rotational mixing through a systematic study of their predicted surface boron depletion. Methods. We construct a dense grid of rotating single star models using MESA, for which we employ a new nuclear network which follows all the stable isotopes up to silicon, including lithium, beryllium, boron, as well as the radioactive isotope aluminium-26. We also compile the measured physical parameters of the 90 Galactic early B-type stars with boron abundance information. We then compare each observed stars with our models through a Bayesian analysis, which yields the mixing efficiency parameter with which the star is reproduced the best, and the probability that it is represented by the stellar models. Results. We find that about two-thirds of the sample stars are well represented by the stellar models, with the best agreement achieved for a rotational mixing efficiency of ∼50% compared to the widely adopted value. The remaining one third of the stars, of which many are strongly boron depleted slow rotators, are largely incompatible with our models, for any rotational mixing efficiency. We investigate the observational incidence of binary companions and surface magnetic fields, and discuss their evolutionary implications. Conclusions. Our results confirm the concept of rotational mixing in radiative stellar envelopes. On the other hand, we find that a different boron depletion mechanism, and likely a different formation path, is required to explain about one-third of the sample stars. The large spread in the surface boron abundances of these stars may hold a clue to understanding their origin.

EROSITA (eRASS1) study of the Canis Major overdensity: Developing a multi-wavelength algorithm for classifying faint X-ray sources

Context. Using data from eROSITA (extended Roentgen Survey with an Imaging Telescope Array) on board Spektrum-Roentgen- Gamma (Spektr-RG, SRG) taken during the first eROSITAall-sky survey (eRASS1), we performed the first X-ray classification and population study in the field of the Canis Major overdensity (CMa OD), which is an elliptical-shaped stellar overdensity located at l = -240°, b = −80°. Aims. This study aims to identify the X-ray sources in CMa OD. We developed a classification algorithm using multi-wavelength criteria as a preliminary method for the classification of faint X-ray sources, specifically in regions with a high source number density. Methods. We used the brightness of the multi-wavelength counterparts (mainly from infrared and optical catalogues), along with the X-ray flux and X-ray hardness ratios (HRs) to classify the sources. Results. Out of a total number of 8311 X-ray sources, we classified 1029 sources as Galactic stars and binaries in the foreground, 946 sources as active galactic nuclei (AGNs) and galaxies in the background, and 435 sources with stellar counterparts that may belong to either the MW or CMa OD. Among the sources with a stellar counterpart, we identified 34 symbiotic star candidates, plus 335 sources, of which the infrared (IR) counterparts have properties of M-giants in CMa OD. Moreover, there is a known high-mass X-ray binary (HMXB, 4U 0728-25) in the field of our study; according to the Gaia parallax of its companion, it appears to be a member of CMa OD. There is also a recently detected transient low-mass X-ray binary (LMXB, SRGt J071522.1-191609) is also present; it may be a member of CMa OD based on its companion, which is most likely highly absorbed and is thus located behind the Galactic disk. In addition, we present the X-ray luminosity function (XLF) of members and candidate members of CMa OD. It is dominated by sources with luminosities of <2 × 1032–1033 erg s−1 in the energy range of 0.2–2.3 keV. These sources are expected to be either accreting white dwarfs or quiescent LMXBs.

The AMBRE Project: Lead abundance in Galactic stars

Context. The chemical evolution of neutron capture elements in the Milky Way is still a matter of debate. Although more and more studies investigate their chemical behaviour, there is still a lack of a significant large sample of abundances of a key heavy element: lead. Aims. Lead is the final product of the s-process nucleosynthesis channel and is one of the most stable heavy elements. The goal of this article is to present the largest catalogue of homogeneous Pb abundances, in particular for metallicities higher than −1.0 dex, and then to study the lead content of the Milky Way. Methods. We analysed high-resolution spectra from the ESO UVES and FEROS archives. Atmospheric parameters were taken from the AMBRE parametrisation. We used the automated abundance method GAUGUIN to derive lead abundances in 653 slow-rotating FGK-type stars from the 368.34 nm Pb I line. Results. We present the largest catalogue of Local Thermodynamic Equilibrium (LTE) and non-LTE lead abundances ever published with metallicities ranging from −2.9 to 0.6 dex and [Pb/Fe] from −0.7 to 3.3 dex. Within this sample, no lead-enhanced Asymptotic Giant Branch (AGB) stars were found, but nine lead-enhanced metal-poor stars ([Pb/Fe] > 1.5) were detected. Most of them were already identified as carbon-enhanced metal-poor stars with enrichments in other s-process species. The lead abundance of 13 Gaia Benchmark Stars are also provided. We then investigated the Pb content of the Milky Way disc by computing vertical and radial gradients and found a slightly decreasing [Pb/Fe] radial trend with metallicity. This trend together with other related ratios ([Pb/Eu], [Pb/Ba], and [Pb/α]) are interpreted thanks to chemical evolution models. The two-infall model closely reproduces the observed trends with respect to the metallicity. It is also found that the AGB contribution to the Pb Galactic enrichment has to be strongly reduced. Moreover, the contribution of massive stars with rather high rotational velocities should be favoured in the low-metallicity regime.

Combined Gemini-South and HST photometric analysis of the globular cluster NGC 6558

Context. NGC 6558 is a low-galactic-latitude globular cluster projected in the direction of the Galactic bulge. Due to high reddening, this region presents challenges in deriving accurate parameters, which require meticulous photometric analysis. We present a combined analysis of near-infrared and optical photometry from multi-epoch high-resolution images collected with Gemini-South/GSAOI+GeMS (in the J and KS filters) and HST/ACS (in the F606W and F814W filters). Aims. We aim to refine the fundamental parameters of NGC 6558, utilising high-quality Gemini-South/GSAOI and HST/ACS photometries. Additionally, we intend to investigate its role in the formation of the Galactic bulge. Methods. We performed a meticulous differential reddening correction to investigate the effect of contamination from Galactic bulge field stars. To derive the fundamental parameters – age, distance, reddening, and the total-to-selective coefficient – we employed a Bayesian isochrone fitting. The results from high-resolution spectroscopy and RR Lyrae stars were implemented as priors. For the orbital parameters, we employed a barred Galactic mass model. Furthermore, we analysed the age-metallicity relation to contextualise NGC 6558 within the Galactic bulge’s history. Results. We studied the impact of two differential reddening corrections on the age derivation. When removing as much as possible of the Galactic bulge field star contamination, the isochrone fitting combined with synthetic colour-magnitude diagrams gives a distance of 8.41−0.10+0.11 kpc, an age of 13.0 ± 0.9 Gyr, and a reddening of E(B − V) = 0.34 ± 0.02. We derived a total-to-selective coefficient of RV = 3.2 ± 0.2 thanks to the simultaneous near-infrared–optical synthetic colour-magnitude diagram fitting, which, aside from errors, agrees with the commonly used value. The orbital parameters showed that NGC 6558 is confined within the inner Galaxy and it is not compatible with a bar-shape orbit, indicating that it is a bulge member. Assembling the old and moderately metal-poor ([Fe/H] ∼ −1.1) clusters in the Galactic bulge, we derived their age-metallicity relation with star formation starting at 13.6 ± 0.2 Gyr and effective yields of ρ = 0.05 ± 0.01 Z⊙. Conclusions. The old age derived for NGC 6558 is compatible with other clusters with similar metallicity and a blue horizontal branch in the Galactic bulge, which constitute the moderately metal-poor globular clusters. The age-metallicity relation shows that the starting age of star formation is compatible with the age of NGC 6558, and the chemical enrichment is ten times faster than the ex situ globular cluster branch.

An `alien' called the Oosterhoff dichotomy?

In this Letter we investigate the origin of the Oosterhoff dichotomy in light of recent discoveries related to several ancient merging events of external galaxies with the Milky Way (MW). In particular, we aim to clarify if the subdivision in terms of the Oosterhoff type between Galactic globular clusters (GGCs) and field RR Lyrae (RRLs) can be traced back to one or more ancient galaxies that merged with the MW in its past. We first explored the association of GGCs with the past merging events according to different literature studies. Subsequently, we compiled the positions, proper motions, and radial velocities of 10,138 field RRL variables from Gaia Data Release 3. To infer the distances, we adopted the $M_G$-- Fe/H relation, with Fe/H values estimated via empirical relationships involving individual periods and Fourier parameters. We then calculated the orbits and the integrals of motion using the Python library Galpy for the whole sample. By comparing the location of the field RRLs in the energy--angular momentum diagram with that of the GGCs, we determined their likely origin. Finally, using Gaia G-band light curves, we determined the Oosterhoff types of our RRL stars based on their location in the Bailey diagram. The analysis of the Bailey diagrams for Galactic RRL stars and GGCs associated with an `in situ' versus `accreted' halo origin shows remarkable differences. The in situ sample shows a wide range of metallicities with a continuous distribution and no sign of the Oosterhoff dichotomy. Conversely, the accreted RRLs clearly show the Oosterhoff dichotomy and a significantly smaller dispersion in metallicity. Our results suggest that the Oosterhoff dichotomy was imported into the MW by the merging events that shaped the Galaxy.

Molecular Oxygen Abundance in Galactic Massive Star Formation Regions Based on SWAS Observations

Molecular oxygen abundance is a key parameter in understanding the chemical network of the interstellar medium. We estimate the molecular oxygen column density and abundance for a sample of Galactic massive star formation regions based on observations from the Submillimiter Wave Astronomy Satellite (SWAS) survey. We obtained an averaged O2 spectrum based on this sample using the (SWAS) survey data (O2, 487.249 GHz, N = 3–1, J = 3–2). No emission or absorption feature is seen around the supposed central velocity with a total integration time of t total = 8.67 × 103 hr and an rms noise per channel of 1.45 mK. Assuming a kinetic temperature T kin = 30 K, we derive the 3σ upper limit of the O2 column density to be 3.3 × 1015 cm−2, close to the lowest values reported in Galactic massive star formation regions in previous studies. The corresponding O2 abundance upper limit is 6.7 × 10−8, lower than all previous results based on SWAS observations and is close to the lowest reported value in massive star formation regions. On a galactic scale, our statistical results confirm a generally low O2 abundance for Galactic massive star formation regions. This abundance is also lower than results reported in extragalactic sources.

Period-luminosity and period-luminosity-metallicity relations for Galactic RR Lyrae stars in the Sloan bands

Context. RR Lyrae stars are excellent tracers of the old population II due to their period-luminosity (PL) and period-luminosity-metallicity (PLZ) relations. While these relations have been investigated in detail in many photometric bands, there are few comprehensive studies about them in Sloan-like systems. Aims. We present PL and PLZ relations (as well as their counterparts in Wesenheit magnitudes) in the Sloan–Pan-STARSS gP1rP1iP1 bands obtained for Galactic RR Lyrae stars in the vincinity of the Sun. Methods. The data used in this paper were collected with the network of 40 cm telescopes of the Las Cumbres Observatory, and geometric parallaxes were adopted from Gaia Data Release 3. Results. We derived PL and PLZ relations separately for RRab and RRc-type stars, as well as for the mixed population of RRab+RRc stars. Conclusions. To our knowledge, these are the first PL and PLZ relations in the Sloan bands determined using RR Lyrae stars in the Galactic field.

An all-sky catalogue of stellar reddening values

Context. When observing astronomical objects, we have to deal with extinction (i.e. the absorption and scattering of the emitted radiation by dust and gas between the source and the observer). Interstellar extinction depends on the location of the object and the wavelength. The different extinction laws describing these effects are difficult to estimate for a small sample of stars. Aims. Many sophisticated and automatic methods have recently been developed for estimating astrophysical parameters (age and metallicity, for example) depending on the reddening, which is normally treated as a free parameter within the corresponding estimations. However, many reddening values for stars have been published over the last few decades, most of which include observations in the ultraviolet, which are essential for a good estimation but are essentially no longer taken into account. Methods. We searched the literature through the end of 2022 for published independent reddening values of stellar objects based on various methods that exclude estimates from reddening maps. In addition, we present new reddening estimates based on the classical photometric indices in the Geneva, Johnson, and Strömgren-Crawford systems. These are based on well-established and reliable calibrations. Results. After a careful identification procedure and quality assessment of the data, we calculated the mean reddening values of 157 631 individual available measurements for 97 826 objects. We compared our results with the ones from recent automatic pipeline values, including those from the Gaia consortium. In addition, we chose star cluster members to compare their mean values with estimates for the corresponding aggregates. Within the different references, we find several statistically significant offsets and trends and discuss possible explanations for them. Conclusions. Our new catalogue can serve as a starting point for calibrating and testing automatic tools such as isochrone and spectral energy distribution fitting. Our sample covers the whole sky, including the Galactic field, star clusters, and Magellanic Clouds, and so can be used for a variety of astrophysical studies.

Element abundances of galactic RGB stars in the APO-K2 catalogue

Aims. We conducted an investigation on the chemical abundances of 4316 stars in the red giant branch (RGB) phase from the recently released APO-K2 catalogue. Our aim was to characterize the abundance trends of the single elements with [α/Fe], mainly focusing on C, N, and O, which are the most relevant for the estimation of stellar ages. Methods. The chemical analysis of the RGB sample involved cross-matching data from the APO-K2 catalogue with individual element abundances from APOGEE DR17. Results. The analysis detected a statistically significant difference in the [(C+N+O)/Fe]–[α/Fe] trend with respect to the simple α-enhancement scenario. This difference remained robust across different choices for the reference solar mixture and potential zero-point calibrations of C and N abundances. The primary discrepancy was a steeper increase in [O/Fe] with [α/Fe], reaching a 0.1 dex difference at [α/Fe] = 0.3. Notably, the impact on the evolutionary timescale of such oxygen over-abundance with respect to the commonly adopted uniform α-enhancement is rather limited. We verified that stellar models computed using an ad hoc O-rich mixture sped up the evolution by only 1% at [α/Fe] = 0.3, due to the counterbalancing effects of O enrichment on both the evolutionary timescale and the Z-to-[Fe/H] relationship.

Playing with FIRE: A Galactic Feedback-halting Experiment Challenges Star Formation Rate Theories

Stellar feedback influences the star formation rate (SFR) and the interstellar medium of galaxies in ways that are difficult to quantify numerically, because feedback is an essential ingredient of realistic simulations. To overcome this, we conduct a feedback-halting experiment starting with a Milky Way–mass galaxy in the second-generation Feedback In Realistic Environments (FIRE-2) simulation framework. By terminating feedback, and comparing to a simulation in which feedback is maintained, we monitor how the runs diverge. We find that without feedback, the interstellar turbulent velocities decay. There is a marked increase of dense material, while the SFR increases by over an order of magnitude. Importantly, this SFR boost is a factor of ∼15–20 larger than is accounted for by the increased freefall rate caused by higher densities. This implies that feedback moderates the star formation efficiency per freefall time more directly than simply through the density distribution. To probe changes at the scale of giant molecular clouds (GMCs), we identify GMCs using density and virial parameter thresholds, tracking clouds as the galaxy evolves. Halting feedback stimulates rapid changes, including a proliferation of new bound clouds, a decrease of turbulent support in loosely bound clouds, an overall increase in cloud densities, and a surge of internal star formation. Computing the cloud-integrated SFR using several theories of turbulence regulation, we show that these theories underpredict the surge in SFR by at least a factor of 3. We conclude that galactic star formation is essentially feedback regulated on scales that include GMCs, and that stellar feedback affects GMCs in multiple ways.

Constraints on Primordial Magnetic Fields from High Redshift Stellar Mass Density

Primordial magnetic fields (PMFs) play a pivotal role in influencing small-scale fluctuations within the primordial density field, thereby enhancing the matter power spectrum within the context of the ΛCDM model at small scales. These amplified fluctuations accelerate the early formation of galactic halos and stars, which can be observed through advanced high-redshift observational techniques. Therefore, stellar mass density (SMD) observations, which provide significant opportunities for detailed studies of galaxies at small scales and high redshifts, offer a novel perspective on small-scale cosmic phenomena and constrain the characteristics of PMFs. In this study, we compile 14 SMD data points at redshifts z > 6 and derive stringent constraints on the parameters of PMFs, which include the amplitude of the magnetic field at a characteristic scale of λ = 1 Mpc, denoted as B 0, and the spectral index of the magnetic field power spectrum, n B . At 95% confidence level, we establish upper limits of B 0 < 4.44 nG and n B < −2.24, along with a star formation efficiency of approximately f*0∼0.1 . If we fix n B at specific values, such as −2.85, −2.9, and −2.95, the 95% upper limits for the amplitude of the magnetic field can be constrained to 1.33, 2.21, and 3.90 nG, respectively. Finally, we attempt to interpret recent early observations provided by the James Webb Space Telescope using the theory of PMFs and find that by selecting appropriate PMF parameters, it is possible to explain these results without significantly increasing the star formation efficiency.

A Rare Cepheid-hosting Open Cluster Triad in Sagittarius

The following Galactic star clusters may constitute a rare Cepheid hosting triad in Sagittarius: M25, NGC 6716, and Collinder 394. The open clusters have comparable ages (τ ≃ 80 Myr) and nearly aligned main-sequences and turnoffs after accounting for differential extinction (A G , EBP−RP ). Gaia DR3 astrometry confirms an association between the three clusters, and importantly, the classical Cepheid U Sgr is a member (P ≃ 6.ͩ75, τ ≃ 80 Myr), while DR3 data indicate that the classical Cepheid BB Sgr (P ≃ 6.ͩ64, τ ≃ 80 Myr) could possibly be an escaped member traversing the background field.

New Wolf–Rayet wind yields and nucleosynthesis of Helium stars

ABSTRACT Strong metallicity-dependent winds dominate the evolution of core He-burning, classical Wolf–Rayet (cWR) stars, which eject both H and He-fusion products such as $^{14}$N, $^{12}$C, $^{16}$O, $^{19}$F, $^{22}$Ne, and $^{23}$Na during their evolution. The chemical enrichment from cWRs can be significant. cWR stars are also key sources for neutron production relevant for the weak s-process. We calculate stellar models of cWRs at solar metallicity for a range of initial Helium star masses (12–50 $\rm M_{\odot }$), adopting recent hydrodynamical wind rates. Stellar wind yields are provided for the entire post-main sequence evolution until core O-exhaustion. While literature has previously considered cWRs as a viable source of the radioisotope $^{26}$Al, we confirm that negligible $^{26}$Al is ejected by cWRs since it has decayed to $^{26}$Mg or proton-captured to $^{27}$Al. However, in Paper I, we showed that very massive stars eject substantial quantities of $^{26}$Al, among other elements including N, Ne, and Na, already from the zero-age-main-sequence. Here, we examine the production of $^{19}$F and find that even with lower mass-loss rates than previous studies, our cWR models still eject substantial amounts of $^{19}$F. We provide central neutron densities (N$_{n}$) of a 30 $\rm M_{\odot }$ cWR compared with a 32 $\rm M_{\odot }$ post-VMS WR and confirm that during core He-burning, cWRs produce a significant number of neutrons for the weak s-process via the $^{22}$Ne($\alpha$,n)$^{25}$Mg reaction. Finally, we compare our cWR models with observed [Ne/He], [C/He], and [O/He] ratios of Galactic WC and WO stars.

An Infrared Census of R Coronae Borealis Stars II—Spectroscopic Classifications and Implications for the Rate of Low-mass White Dwarf Mergers

We present results from a systematic infrared (IR) census of R Coronae Borealis (RCB) stars in the Milky Way, using data from the Palomar Gattini IR (PGIR) survey. RCB stars are dusty, erratic variable stars presumably formed from the merger of a He-core and a CO-core white dwarf (WD). PGIR is a 30 cm J-band telescope with a 25 deg2 camera that surveys 18,000 deg2 of the northern sky (δ > −28°) at a cadence of 2 days. Using PGIR J-band lightcurves for ∼60 million stars together with mid-IR colors from WISE, we selected a sample of 530 candidate RCB stars. We obtained near-IR spectra for these candidates and identified 53 RCB stars in our sample. Accounting for our selection criteria, we find that there are a total of ≈350−100+150 RCB stars in the Milky Way. Assuming typical RCB lifetimes, this corresponds to an RCB formation rate of 0.8–5 × 10−3 yr−1, consistent with observational and theoretical estimates of the He-CO WD merger rate. We searched for quasi-periodic pulsations in the PGIR lightcurves of RCB stars and present pulsation periods for 16 RCB stars. We also examined high-cadenced TESS lightcurves for RCB and the chemically similar, but dustless hydrogen-deficient carbon (dLHdC) stars. We find that dLHdC stars show variations on timescales shorter than RCB stars, suggesting that they may have lower masses than RCB stars. Finally, we identified 3 new spectroscopically confirmed and 12 candidate Galactic DY Per type stars—believed to be colder cousins of RCB star—doubling the sample of Galactic DY Per type stars.

Kinematic constraints on the ages and kick velocities of Galactic neutron star binaries

The systems creating binary neutron stars (BNSs) experience systemic kicks when one of the components goes supernova. The combined magnitude of these kicks is still a topic of debate and has implications for the eventual location of the transient resulting from the merger of the binary. For example, the offsets of short-duration gamma-ray bursts resulting from BNS mergers depend on BNS kicks. We investigated Galactic BNSs and traced their motion through the Galaxy. This enabled us to estimate their kinematic ages and construct a BNS kick distribution based on their Galactic trajectories. We used the pulsar periods and their derivatives to estimate the characteristic spin-down ages of the binaries. Moreover, we used a Monte Carlo estimation of their present-day velocity vector in order to trace back their trajectory and estimate their kinematic ages. These trajectories, in turn, were used to determine the eccentricity of their Galactic orbit. Based on simulations of kicked objects in the Galactic potential, we investigated the relationship between this eccentricity and the kick velocity in order to constrain the kicks imparted to the binaries at birth. We find that the Galactic BNSs are likely older than $ Myr, which means their current (scalar) galactocentric speeds are not representative of their initial kicks. However, we find a close relationship between the eccentricity of a Galactic trajectory and the experienced kick. Using this relation, we constrained the kicks of the Galactic BNSs, depending on the kind of isotropy assumed in estimating their velocity vectors. These kick velocities are well described by a log-normal distribution peaking around $ km/s and coincide with the peculiar velocities of the binaries at their last disc crossing. We conclude that BNSs receive kicks following a distribution that peaks at kick velocities lower than found in isolated pulsars. However, we find no tension between this distribution and literature on short-duration gamma-ray burst offsets.

Analysis of Gaia DR3 Data of Selected High Galactic Latitude Hα Emission Stars

Gaia DR3 data of 52 high galactic latitude Hα emission stars selected from the paper of Stephenson are analyzed. Ten new variable stars and eight new high velocity stars have been found. Details of six post-AGB stars and several other interesting stars are discussed. Many of the stars presented in this paper have Gaia DR3 light curves and spectra. A detailed study of these 52 stars is needed to derive their chemical composition and to further understand their binarity, circumstellar matter and evolutionary status. The astrophysical parameters from the Gaia DR3 data reveal several hot (OBA) and several F and G-type stars in this sample. Some of them are metal-poor stars.

A search for Galactic post-asymptotic giant branch stars in Gaia DR3

When low- and intermediate-mass stars leave the asymptotic giant branch (AGB) phase, and before they reach the planetary nebula stage, they enter a very brief and rather puzzling stellar evolutionary stage called post-AGB stage. The post-AGB phase lasts very briefly, about a few thousand years at most. The number of objects that are confirmed in this phase therefore is really small, and our understanding of this elusive stellar evolutionary stage is accordingly very limited. We provide a reliable catalogue of Galactic post-AGB stars together with their physical and evolutionary properties obtained through Gaia DR3 astrometry and photometry. As an added product, we provide information for a sample of other types of stellar objects, whose observational properties mimic those of post-AGB stars. Post-AGB stars are characterised by their infrared excesses and high luminosities. The publication of precise parallaxes in Gaia DR3 made it possible to calculate accurate distances and to revise the derivation of luminosities for post-AGB candidates, so that objects outside the expected luminosity range can be discarded. We started by identifying post-AGB stars or possible candidates from the bibliography, and we then searched for their Gaia DR3 counterpart sources. Using the available photometry, interstellar extinction, spectroscopically derived temperatures or spectral types and parallax-derived distances from the literature, we fitted their spectral energy distributions and estimated their luminosities and circumstellar extinctions. By a comparison to models, the luminosity values allowed us to determine which objects are likely post-AGB stars from other target types. Their position in the Hertzsprung-Russell diagram allows a direct comparison with updated post-AGB evolutionary tracks and an estimation of their masses and evolutionary ages. We obtained a sample of 69 reliable post-AGB candidates that meet our classification criteria, which provide their coordinates, distances, effective temperature, interstellar and circumstellar extinction, luminosity, mass, and evolutionary age. In addition, we provide similar data for other stellar objects in our initial compilation, such as supergiant stars and young stellar objects. Our identifications and parameters are compared with others found in the recent literature for the subject. We selected the data with the best precision in parallax and distance to obtain more accurate luminosities, which allowed us to confidently classify the objects of the sample in different stellar phases. In turn, this allowed us to provide a small but reliable sample of post-AGB objects. The derived mean evolutionary time and average mass values agree with theoretical expectations and with the mean mass value obtained in a previous work for the subsequent evolutionary stage, the planetary nebula stage.