Catherine A. Pilachowski

We measured lithium abundances and upper limits for 72 red clump stars in the old open cluster NGC 7789 to test the hypothesis that stars produce excess lithium when transitioning from the red giant stage to the helium-burning red clump. Stars were selected on the basis of their proper motion and radial velocity membership probabilities. Spectra of the 6707 Å Li i absorption feature were obtained with the Hydra multi-fiber spectrograph on the WIYN 3.5 m telescope, and lithium abundances were determined with spectrum synthesis. We find a range of lithium abundances from 0.0 < log ϵ (Li) < 1.4.

We present a detailed chemical abundance analysis of the eclipsing binary system V505 Per. High-resolution spectra were analyzed using the MOOG spectrum analysis code, we determined abundances not only for iron and lithium but also for Si, Na, Ca, Mn, and Ni—elements that have not previously been analyzed in detail for this system. Abundances were computed across 15 temperature points using model atmospheres, with stellar parameters refined by minimizing abundance trends with excitation potential. We determined effective temperatures of T _eff = 6650 ± 50 K for the primary and T _eff = 6550 ± 50 K, with iron abundances of [Fe/H] = −0.10 ± 0.06 and [Fe/H] = −0.19 ± 0.07, respectively. Most [X/Fe] ratios are consistent with solar values, though manganese is deficient. Our analysis of the effective temperatures shows that both stars lie on the hot edge of the lithium dip, consistent with G. Koenigsberger et al., which may help resolve the inconsistency noted of the stars lithium abundance within the dip by Baugh et al.

We present spectroscopic evidence for tidal debris associated with the bulge globular cluster NGC 6569, based on medium-resolution ( R ∼ 11,000) spectra of 303 stars obtained with the Anglo-Australian Telescope. Targets were selected using Blanco DECam Bulge Survey photometry with Gaia DR3 astrometry, and span ∼ 7 ′ – 3 0 ′ (i.e., 1–5 r _t , where r _t is the King-model tidal radius) from the cluster center. Theoretical modeling shows that the Jacobi radii can vary between 8 ′ – 1 1 ′ and 1 8 ′ – 2 2 ′ over the orbit, likely leaving stars around the cluster that are transitioning into the predicted leading and lagging tidal tails. We identify 40 stars in this sample that exhibit chemical and kinematic properties consistent with previous, or borderline, cluster membership. The seven best candidates have S/N > 30, with [Fe/H] = –0.83 ± 0.14 dex and [ α /Fe] = +0.38 ± 0.06 dex, consistent with NGC 6569’s bound population. Our findings provide evidence that NGC 6569 is actively losing stars through tidal stripping, contributing to the bulge field population at a present rate of 1.0–1.6 M _⊙ Myr ⁻¹ , which corresponds to ≈5.6% ± 1.3% of its present-day mass per Gyr. This work is part of the Milky Way Bulge Extra-Tidal Star Survey and represents our first detailed study of a massive bulge globular cluster in this context.

Observational astronomy has undergone a significant transformation driven by large-scale surveys such as the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) survey, the Sloan Digital Sky Survey, and the Gaia Mission. These programs yield large, complex data sets that pose significant challenges for conventional analysis methods, and as a result many different machine learning techniques are being tested and deployed. We introduce a new approach to analyzing multiband photometry by using a long short-term memory autoencoder. This model provides input-dependent reweighting of the passbands on a star-by-star basis, enabling it to encode patterns present in the stars’ spectral energy distributions (SEDs) into a two-dimensional latent space. We showcase this by using Pan-STARRS grizy mean magnitudes, and we use globular clusters, labels from SIMBAD, Gaia Data Release 3 parallaxes, and PanSTARRS images to aid our analysis and understanding of the latent space. For 3,112,259 stars in an annulus around the North Galactic Cap, 99.51% have their full SED shape reconstructed—that is, the absolute difference between the observed and the model-predicted magnitude in every band—within five-hundredths of a magnitude. We show that the model likely denoises photometric data, potentially improving the quality of measurements. Lastly, we show that the detection of rare stellar types can be performed by analyzing poorly reconstructed photometry.

We present the first fluorine measurements in 12 normal K giants belonging to the Galactic thin and thick disks using spectra obtained with the Phoenix infrared spectrometer on the 2.1 m telescope at Kitt Peak. Abundances are determined from the (1−0) R9 2.3358 μm feature of the molecule HF. Additionally, sodium abundances are derived in 25 giants in the thin disk, thick disk, and halo using the Na i line at 2.3379 μm. We report fluorine abundances for thin and thick disk stars in the metallicity range −0.7 < [Fe/H] < 0. We add two abundance measurements for stars with [Fe/H] < 0.5 dex, which are at a critical metallicity range to constrain models. We find a larger dispersion in fluorine abundances than sodium abundances despite both species having similar overall uncertainties due to atmospheric parameters, suggesting this dispersion is real and not observational. The dispersion is slightly larger in the thick disk than the thin. The thin and thick disk average [F/Fe] for our sample of stars combined with the literature differ by 0.03 dex. The observations are compared to available chemical evolution models.

The kinetic energy in tidal flows, when converted into heat, can affect the internal structure of a star and shift its location on a color–magnitude diagram from that of standard models. In this paper we explore the impact of injecting heat into stars with masses near the main-sequence turnoff mass (1.26 M _⊙) of the open cluster M67. The heating rate is obtained from the tidal shear energy dissipation rate, which is calculated from first principles by simultaneously solving the equations that describe orbital motion and the response of a star’s layers to the gravitational, Coriolis, centrifugal, gas pressure, and viscous forces. The stellar structure models are computed with MESA. We focus on the effects of injecting heat in pulses lasting 0.01 Gyr, a time frame consistent with the synchronization timescale in binary systems. We find that the location of the tidally perturbed stars in the M67 color–magnitude diagram is shifted to significantly higher luminosities and effective temperatures than predicted by the standard model isochrone and includes locations corresponding to some of the blue straggler stars. Because tidal heating takes energy from the orbit, causing it to shrink, blue straggler stars could be merger or mass transfer progenitors, as well as products of these processes.

The kinetic energy in tidal flows, when converted into heat, can affect the internal structure of a star and shift its location on a color-magnitude diagram from that of standard models. In this paper we explore the impact of injecting heat into stars with masses near the main sequence turnoff mass (1.26 $M_\odot$) of the open cluster M67. The heating rate is obtained from the tidal shear energy dissipation rate which is calculated from first principles by simultaneously solving the equations that describe orbital motion and the response of a star's layers to the gravitational, Coriolis, centrifugal, gas pressure and viscous forces. The stellar structure models are computed with MESA. We focus on the effects of injecting heat in pulses lasting 0.01 Gyr, a timeframe consistent with the synchonization timescale in binary systems. We find that the location of the tidally perturbed stars in the M67 color-magnitude diagram is shifted to significantly higher luminosities and effective temperatures than predicted by the standard model isochrone and include locations corresponding to some of the Blue Straggler Stars. Because tidal heating takes energy from the orbit causing it to shrink, Blue Straggler Stars could be merger or mass-transfer progenitors as well as products of these processes.

Context. The inner Galaxy is a complex environment, and the relative contributions of different formation scenarios to its observed morphology and stellar properties are still debated. The different components are expected to have different spatial, kinematic, and metallicity distributions, and a combination of photometric, spectroscopic, and astrometric large-scale surveys is needed to study the formation and evolution of the Galactic bulge. Aims. The Blanco DECam Bulge Survey (BDBS) provides near-ultraviolet to near-infrared photometry for approximately 250 million unique stars over more than 200 square degrees of the southern Galactic bulge. By combining BDBS photometry with the latest Gaia astrometry, we aim to characterize the chemodynamics of red clump stars across the BDBS footprint using an unprecedented sample size and sky coverage. Methods. Our field of view of interest is |ℓ| ≤ 10°, −10° ≤b ≤ −3°. We constructed a sample of approximately 2.3 million red clump giants in the bulge with photometric metallicities, BDBS photometric distances, and proper motions. Photometric metallicities are derived from a (u − i)₀ versus [Fe/H] relation; astrometry, including precise proper motions, is from the third data release (DR3) of the ESA satellite Gaia. We studied the kinematics of the red clump stars as a function of sky position and metallicity by investigating proper-motion rotation curves, velocity dispersions, and proper-motion correlations across the southern Galactic bulge. Results. By binning our sample into eight metallicity bins in the range of −1.5 dex < [Fe/H] < +1 dex, we find that metal-poor red clump stars exhibit lower rotation amplitudes, at ∼29 km s⁻¹ kpc⁻¹. The peak of the angular velocity is ∼39 km s⁻¹ kpc⁻¹ for [Fe/H] ∼ −0.2 dex, exhibiting declining rotation at higher [Fe/H]. The velocity dispersion is higher for metal-poor stars, while metal-rich stars show a steeper gradient with Galactic latitude, with a maximum dispersion at low latitudes along the bulge minor axis. Only metal-rich stars ([Fe/H] ≳ −0.5 dex) show clear signatures of the bar in their kinematics, while the metal-poor population exhibits isotropic motions with an axisymmetric pattern around Galactic longitude ℓ = 0. Conclusions. This work describes the largest sample of bulge stars with distance, metallicity, and astrometry reported to date, and shows clear kinematic differences with metallicity. The global kinematics over the bulge agrees with earlier studies. However, we see striking changes with increasing metallicity, and, for the first time, kinematic differences for stars with [Fe/H]> − 0.5, suggesting that the bar itself may have kinematics that depends on metallicity.

The Milky Way Bulge extra-tidal star survey is a spectroscopic survey with the goal of identifying stripped globular cluster stars from inner Galaxy clusters. In this way, an indication of the fraction of metal-poor bulge stars that originated from globular clusters can be determined. We observed and analyzed stars in and around BH 261, an understudied globular cluster in the bulge. From seven giants within the tidal radius of the cluster, we measured an average heliocentric radial velocity of 〈RV〉 = −61 ± 2.6 km s⁻¹ with a radial velocity dispersion of 〈σ〉 = 6.1 ± 1.9 km s⁻¹. The large velocity dispersion may have arisen from tidal heating in the cluster’s orbit about the Galactic center, or because BH 261 has a high dynamical mass as well as a high mass-to-light ratio. From spectra of five giants, we measure an average metallicity of 〈[Fe/H]〉 = −1.1 ± 0.2 dex. We also spectroscopically confirm an RR Lyrae star in BH 261, which yields a distance to the cluster of 7.1 ± 0.4 kpc. Stars with 3D velocities and metallicities consistent with BH 261 reaching to ∼0.°5 from the cluster are identified. A handful of these stars are also consistent with the spatial distribution of potential debris from models focusing on the most recent disruption of the cluster.

We report on the first detailed infrared chemical analysis of five binary members (S277, S997, S975, S1031, and S1195) in the open cluster M67 (NGC 2682). These stars are located outside (bluer and/or brighter than) the main-sequence turnoff region in M67. High-resolution (R ∼ 45,000) near-infrared spectra were obtained with the Immersion GRating INfrared Spectrograph (IGRINS) at the McDonald Observatory 2.7 m Harlan J. Smith Telescope, providing full spectral coverage of the H and K bands. The abundances of C, Na, Mg, Al, Si, S, Ca, Fe, and Ni are measured using neutral atomic absorption lines. We detect v sin i ≥ 25 km s⁻¹ in three of our program stars: S1031, S975, and S1195. We find our derived abundances to be in good agreement with turnoff star abundances, similar to published analyses of blue straggler stars in M67 from optical spectra. Detection of a carbon enhancement or depletion resulting from mass transfer is difficult due to the uncertainties in the carbon abundance and the relatively modest changes that may occur through red giant and asymptotic giant branch evolution.