Gemini South Research Articles

On the gravitational lensing interpretation of three gravitational wave detections in the mass gap by LIGO and Virgo

ABSTRACT We search for gravitational wave (GW) events from LIGO-Virgo’s third run that may have been affected by gravitational lensing. Gravitational lensing delays the arrival of GWs, and alters their amplitude – thus biasing the inferred progenitor masses. This would provide a physically well-understood interpretation of GW detections in the ‘mass gap’ between neutron stars and black holes, as gravitationally lensed binary neutron star (BNS) mergers. We selected three GW detections in LIGO-Virgo’s third run for which the probability of at least one of the constituent compact objects being in the mass gap was reported as high with low latency – i.e. candidate lensed BNS mergers. Our observations of powerful strong lensing clusters located adjacent to the peak of their sky localization error maps reached a sensitivity $\rm AB\simeq 25.5$ in the z′ band with the GMOS instruments on the Gemini telescopes, and detected no candidate lensed optical counterparts. We combine recent kilonova light-curve models with recent predictions of the lensed BNS population and the properties of the objects that we followed up to show that realistic optical counterparts were detectable in our observations. Further detailed analysis of two of the candidates suggests that they are a plausible pair of images of the same low-mass binary black hole merger, lensed by a local galaxy or small group of galaxies. This further underlines that access to accurate mass information with low latency would improve the efficiency of candidate lensed BNS selection.

The Roasting Marshmallows Program with IGRINS on Gemini South I: Composition and Climate of the Ultrahot Jupiter WASP-18 b

We present high-resolution dayside thermal emission observations of the exoplanet WASP-18 b using IGRINS on Gemini South. We remove stellar and telluric signatures using standard algorithms, and we extract the planet signal via cross-correlation with model spectra. We detect the atmosphere of WASP-18 b at a signal-to-noise ratio (S/N) of 5.9 using a full chemistry model, measure H2O (S/N = 3.3), CO (S/N = 4.0), and OH (S/N = 4.8) individually, and confirm previous claims of a thermal inversion layer. The three species are confidently detected (>4σ) with a Bayesian inference framework, which we also use to retrieve abundance, temperature, and velocity information. For this ultrahot Jupiter (UHJ), thermal dissociation processes likely play an important role. Retrieving abundances constant with altitude and allowing the temperature–pressure profile to adjust freely results in a moderately super-stellar carbon-to-oxygen ratio (C/O = ) and metallicity ([M/H] = ). Accounting for undetectable oxygen produced by thermal dissociation leads to C/O = and [M/H] = . A retrieval that assumes radiative–convective–thermochemical equilibrium and naturally accounts for thermal dissociation constrains C/O < 0.34 (2σ) and [M/H] = , in line with the chemistry of the parent star. Looking at the velocity information, we see a tantalizing signature of different Doppler shifts at the level of a few kilometers per second for different molecules, which might probe dynamics as a function of altitude and/or location on the planet disk. Our results demonstrate that ground-based, high-resolution spectroscopy at infrared wavelengths can provide meaningful constraints on the compositions and climate of highly irradiated planets. This work also elucidates potential pitfalls with commonly employed retrieval assumptions when applied to the spectra of UHJs.

A Decade of Linear and Circular Polarimetry with the POLISH2 Polarimeter

The POLISH2 optical polarimeter has been in operation at the Lick Observatory 3 m Shane telescope since 2011, and it was commissioned at the Gemini North 8 m in 2016. This instrument primarily targets exoplanets, asteroids, and the Crab Pulsar, but it has also been used for a wide variety of planetary, galactic, and supernova science. POLISH2's photoelastic modulators, employed instead of rotating wave plates or ferroelectric liquid crystal modulators, offer the unprecedented ability to achieve sensitivity and accuracy of order 1 ppm (0.0001%), which are difficult to obtain with conventional polarimeters. Additionally, POLISH2 simultaneously measures the intensity (Stokes I), linear polarization (Stokes Q and U), and circular polarization (Stokes V), which fully describe the polarization state of incident light. We document our laboratory and on-sky calibration methodology and our archival on-sky database, and we demonstrate the conclusive detection of circular polarization of certain objects.

A Census of the Taurus Star-forming Region and Neighboring Associations with Gaia* * Based on observations made with the Gaia mission, the Two Micron All Sky Survey, the Wide-field Infrared Survey Explorer, the LAMOST survey, the Sloan Digital Sky Survey IV, the NASA Infrared Telescope Facility, and Gemini Observatory.

I have used high-precision photometry and astrometry from the third data release of Gaia to perform a survey for members of the Taurus star-forming region and young associations in its vicinity. This work has produced a new catalog of 532 adopted members of Taurus, which has only minor changes relative to the previous catalog from Esplin & Luhman. I have used the Gaia astrometry to divide the Taurus members into 13 groups that have distinct kinematics. Meanwhile, I have identified 1378 candidate members of seven associations near Taurus. All of these associations have histograms of spectral types that peak near M5 (∼0.15 M ⊙), resembling other young populations in the solar neighborhood. For the Taurus groups and neighboring associations, I have estimated ages from their sequences of low-mass stars in Hertzsprung–Russell diagrams. Most of the Taurus groups have median ages of ∼1–3 Myr, while the associations have ages ranging from 13 to 56 Myr. I have used mid-infrared photometry from the Wide-field Infrared Survey Explorer to search for excess emission from circumstellar disks among the candidate members of the associations. Disks are detected for 51 stars, 20 of which are reported for the first time in this work. Some recent studies have proposed that samples of older stars (≳10 Myr) found in the vicinity of Taurus represent a distributed population that is associated with the Taurus cloud complex. However, I find that most of those stars have kinematics that are inconsistent with any relationship with Taurus.

Discovery of a resolved white dwarf–brown dwarf binary with a small projected separation: SDSS J222551.65+001637.7AB

ABSTRACT We present the confirmation of SDSS J222551.65+001637.7AB as a closely separated, resolved, white dwarf–brown dwarf binary. We have obtained spectroscopy from GNIRS and seeing-limited Ks-band imaging from NIRI on Gemini North. The target is spatially resolved into its constituent components: a 10926 ± 246 K white dwarf, with log g = 8.214 ± 0.168 and a mass of 0.66$^{+0.11}_{-0.06}$ M⊙, and an L4 brown dwarf companion, which are separated by 0.9498 ± 0.0022 arcsec. We derive the fundamental properties of the companion from the Sonora–Bobcat evolutionary models, finding a mass of 25–53 MJup and a radius of 0.101–0.128 R⊙ for the brown dwarf, at a confidence level of 1σ. We use wdwarfdate to determine the age of the binary as $1.97^{+4.41}_{-0.76}$ Gyr. A kinematic analysis shows that this binary is likely a member of the thick disc. The distance to the binary is 218$^{+14}_{-13}$ pc, and hence the projected separation of the binary is 207$^{+13}_{-12}$ au. Whilst the white dwarf progenitor was on the main sequence the binary separation would have been 69 ± 5 au. SDSS J222551.65+001637.7AB is the third closest spatially resolved white dwarf–brown dwarf binary after GD 165AB and PHL 5038AB.

Towards Powering Gemini South with Zero CO2 Emission

Towards Powering Gemini South with Zero CO2 Emission

Gaia-IGRINS synergy: Orbits of newly identified Milky Way star clusters

Context. The recent and exquisite astrometric, photometric, and radial velocity measurements of the Gaia mission resulted in a substantial advancement of the determination of the orbits for old star clusters, including the oldest Milky Way globular clusters (MW GCs). Aims. The main goal of the present paper is to use the new Gaia data release 3 (DR3) and the VISTA Variables in the Via Láctea Extended Survey (VVVX) measurements to obtain the orbits for nearly a dozen new MW GC candidates that have been poorly studied or previously unexplored. Methods. We use the Gaia DR3 and VVVX databases to identify bona fide MW GC candidates, namely VVV-CL160, Patchick 122, Patchick 125, Patchick 126, Kronberger 99, Kronberger 119, Kronberger 143, ESO 92-18, ESO 93-08, Gaia 2, and Ferrero 54. The relevant mean cluster physical parameters are derived (distances, Galactic coordinates, proper motions, radial velocities). We also measure accurate mean radial velocities for the GCs VVV-CL160 and Patchick 126 using observations acquired at the Gemini-South telescope with the Immersion GRating INfrared Spectrometer (IGRINS) high-resolution spectrograph. Orbits for each cluster are then computed using the GravPot16 model, assuming typical Galactic bar pattern speeds. Results. We reconstruct the orbits for these 11 star clusters for the first time. These include star clusters with retrograde and prograde orbital motions, both in the Galactic bulge and disk. We obtain orbital properties for this sample, such as the mean time-variations of perigalactic and apogalactic distances, eccentricities, vertical excursions from the Galactic plane, and Z-components of the angular momentum. Conclusions. Our main conclusion is that, based on the orbital parameters, Patchick 125 and Patchick 126 are genuine MW bulge or halo GCs; and Ferrero 54, Gaia 2, and Patchick 122 are MW disk GCs. In contrast, the orbits of Kronberger 99, Kronberger 119, Kronberger 143, ESO 92-18, and ESO 93-08 are more consistent with old MW disk open clusters, in agreement with previous results. VVV-CL160 falls very close to the Galactic centre, but reaches larger distances beyond the Solar orbit, and therefore its origin is still unclear.

Optimal Observational Scheduling Framework for Binary and Multiple Stellar Systems* *Based in part on observations obtained at the international Gemini Observatory, a program of NSF's NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership: the National Science Foundation (United

The optimal instant of observation of astrophysical phenomena for objects that vary on human timescales is an important problem, as it bears on the cost-effective use of usually scarce observational facilities. In this paper, we address this problem in the case of tight visual binary systems through a Bayesian framework based on the maximum entropy sampling principle. Our proposed information-driven methodology exploits the periodic structure of binary systems to provide a computationally efficient estimation of the probability distribution of the optimal observation time. We show the optimality of the proposed sampling methodology in the Bayes sense and its effectiveness through direct numerical experiments. We successfully apply our scheme to the study of two visual-spectroscopic binaries and one purely astrometric triple hierarchical system. We note that our methodology can be applied to any time-evolving phenomena, a particularly interesting application in the era of dedicated surveys, where a definition of the cadence of observations can have a crucial impact on achieving the science goals.

TNO or Comet? The Search for Activity and Characterization of Distant Object 418993 (2009 MS9)

The perihelion of the trans-Neptunian object (TNO) 2009 MS9 brings it close to the distance where some long-period comets are seen to become active. Knowing this, and the fact that this object appears to brighten in excess of its predicted nucleus brightness, suggests that 2009 MS9 has a delayed onset of activity brought on by the sublimation of a species more volatile than water. In this paper, we characterize 2009 MS9's physical properties and investigate potential outgassing through composite images, sublimation models, and measurements of spectral reflectivity. We find that deep composite images of the object at various epochs along its orbit show no evidence of dust yet place sensitive limits to the dust production. We estimate the nucleus radius to be 11.5 ± 3.5 km using thermal IR modeling from NEOWISE data and use this and data pre-perihelion to estimate a geometric albedo of 0.25. We compare a CO sublimation activity model to its post-perihelion heliocentric light curve and find that these data support an active fractional area of 5 × 10−6 assuming 2 μm–sized grains and other typical comet parameters. The spectral reflectivity of the surface materials obtained with the Gemini Observatory and CFHT at different epochs shows a reddening spectral slope. We compare the physical properties of 2009 MS9 to both TNO and comet populations and speculate that 2009 MS9's reddening may be due to the buildup of a dust mantle on the surface and could be an explanation of why TNOs exhibit a color bimodality.

Unveiling a new extragalactic structure hidden by the Milky Way

Context. The zone of avoidance (ZoA) does not allow for clear optical observations of extragalactic sources behind the Milky Way due to the meaningful extinction of the optical emission of these objects. Observations in near-infrared (NIR) wavelengths represent a potential source of astronomical discoveries that support the detection of new galaxies and potentially complete the picture of the large-scale structures in this as-yet poorly explored area of the sky. Aims. Our aim is to decipher the nature of the overdensity located behind the Milky Way in tile b204 of the VISTA Variables in Vía Láctea (VVV) survey. Methods. We studied an area of six arcmin around a galaxy concentration located at l = 354.82° and b = −9.81°. We selected five galaxies, taking into account the source distribution on the sky to optimise the requested time for the observations, and we obtained the spectra with Flamingos 2 long-slit spectrograph at Gemini South 8.1-meter telescope. To identify and characterise the absorption features, we fit the galaxies underlying spectrum using the STARLIGHT code together with the IRTF stellar library. In addition, the spectroscopic findings are reinforced using complementary photometric techniques such as red-sequence and photometric redshift estimation. Results. The mean spectroscopic redshift estimated from the NIR spectra is z = 0.225 ± 0.014. This value presents a good agreement with that obtained from photometric analysis, photoz = 0.21 ± 0.08, and the probability distribution function of the galaxies in the studied region. Also, the red-sequence slope is consistent with the one expected for NIR observations of galaxy clusters. Conclusions. The redshifts obtained from both, photometric and spectroscopic techniques are in good agreement, allowing for the confirmation of the nature of this structure at z = 0.225 ± 0.014, thereby unveiling a new galaxy cluster, VVVGCl-B J181435-381432, behind the Milky Way bulge.

A retrospective analysis of mid-infrared observations of the Comet D/Shoemaker-Levy 9 and Wesley impacts on Jupiter

We present a retrospective analysis of Earth-based mid-infrared observations of Jupiter capturing the aftermath of the impacts by Comet D/Shoemaker-Levy 9 (henceforth SL9) in July 1994 and the unknown object previously termed the “Wesley impactor” in July 2009. While the effects of both impacts on Jupiter’s atmosphere have been reported previously, we were motivated to re-examine both events using consistent data reduction and analysis methods to enable robust, quantitative comparisons. To study the aftermath of the SL9 impacts, we examined infrared (7.8–20.5μm) spectrophotometry of Jupiter measured by the MIRAC (Mid-Infrared Camera) on NASA’s Infrared Telescope Facility on July 20, 21 1994 and low-resolution (R = 100) N-band (7–13μm) spectroscopy measured by SpectroCam-10 on the Palomar Telescope on July 22 1994. To study the aftermath of the Wesley impact, we examined low-resolution (R = 100) N- and Q-band (R = 80, 17–25μm) spectroscopy recorded by Gemini South Telescope’s T-ReCS (Thermal-Region Camera Spectrograph). We analyzed the observations with two independent analyses: (1) a least-squares search over a grid of candidate mineral species to determine the composition of impact residue and (2) a radiative transfer analysis to derive atmospheric information. We observe that the SL9 impact sites are enhanced in stratospheric CH4 emissions at 7.9μm, due to shock heating and adiabatic compression from plume re-entry, and from 8.5–11.5μm due to stratospheric NH3 emission and non-gaseous cometary material, in agreement with previous work. In the G impact site, we derive NH3 concentrations of 5.7−2.8+4.5 ppmv at 30 mbar. In new findings, we find that the SL9 impact sites also exhibit a non-gaseous emission feature at 18–19μm. The non-gaseous emission at 8.5–11.5μm and 18–19μm emission result is best reproduced by predominantly amorphous olivine and (obsidian) silica at similar abundances. The Wesley impact site exhibits enhanced emissions from 8.8–11.5μm and 18–19μm. We found this could be reproduced by predominantly amorphous olivine and stratospheric gaseous NH3 at concentrations of 150−121+338 ppbv retrieved at 30 mbar. Stratospheric abundances of NH3 are a factor of ∼40 higher in the SL9 impacts compared to the Wesley impact, which confirms the former reached deeper, NH3-richer altitudes of Jupiter’s atmosphere compared to the latter. The absence of silicas in the Wesley impact would place an upper limit of 10 km/s on the incident angle and ∼9∘ on the entry angle of the impactor such that shock heating associated with the impact did not reach temperatures required for silicates to be converted.

Powerful Yet Lonely: Is 3C 297 a High-redshift Fossil Group?

The environment of the high-redshift (z = 1.408), powerful radio-loud galaxy 3C 297 has several distinctive features of a galaxy cluster. Among them, a characteristic halo of hot gas revealed by Chandra X-ray observations. In addition, a radio map obtained with the Very Large Array shows a bright hotspot in the northwestern direction, created by the interaction of the active galactic nucleus (AGN) jet arising from 3C 297 with its environment. In the X-ray images, emission cospatial with the northwestern radio lobe is detected, and peaks at the position of the radio hotspot. The extended, complex X-ray emission observed with our new Chandra data is largely unrelated to its radio structure. Despite having attributes of a galaxy cluster, no companion galaxies have been identified from 39 new spectra of neighboring targets of 3C 297 obtained with the Gemini Multi-Object Spectrograph. None of the 19 galaxies for which a redshift was determined lies at the same distance as 3C 297. The optical spectral analysis of the new Gemini spectrum of 3C 297 reveals an isolated Type II radio-loud AGN. We also detected line broadening in [O ii] λ3728 with a FWHM about 1700 km s−1 and possible line shifts of up to 500–600 km s−1. We postulate that the host galaxy of 3C 297 is a fossil group, in which most of the stellar mass has merged into a single object, leaving behind an X-ray halo.

FUMES. III. Ultraviolet and Optical Variability of M-dwarf Chromospheres

We obtained ultraviolet and optical spectra for nine M dwarfs across a range of rotation periods to determine whether they showed stochastic intrinsic variability distinguishable from flares. The ultraviolet spectra were observed during the Far Ultraviolet M-dwarf Evolution Survey Hubble Space Telescope program using the Space Telescope Imaging Spectrograph. The optical observations were taken from the Apache Point Observatory 3.5 m telescope using the Dual Imaging Spectrograph and from the Gemini South Observatory using the Gemini Multi-Object Spectrograph. We used the optical spectra to measure multiple chromospheric lines: the Balmer series from Hα to H10 and the Ca ii H and K lines. We find that after excising flares, these lines vary on the order of 1%–20% at minute-cadence over the course of an hour. The absolute amplitude of variability was greater for the faster rotating M dwarfs in our sample. Among the five stars for which we measured the weaker Balmer lines, we note a tentative trend that the fractional amplitude of the variability increases for higher-order Balmer lines. We measured the integrated flux of multiple ultraviolet emission features formed in the transition region: the N v, Si iv, and C iv resonance line doublets, and the C ii and He ii multiplets. The signal-to-noise ratio of the UV data was too low for us to detect nonflare variability at the same scale and time cadence as the optical. We consider multiple mechanisms for the observed stochastic variability and propose both observational and theoretical avenues of investigation to determine the physical causes of intrinsic variability in the chromospheres of M dwarfs.

Time-variable Jet Ejections from RW Aur A, RY Tau, and DG Tau* * Based on observations obtained at the Gemini Observatory, the European Southern Observatory (under ESO program 2100.C-5015), and the W. M. Keck Observatory.

We present Gemini-NIFS, Very Large Telescope-SINFONI, and Keck-OSIRIS observations of near-IR [Fe ii] emission that are associated with well-studied jets from three active T Tauri stars—RW Aur A, RY Tau, and DG Tau—taken from 2012 to 2021. We primarily cover the redshifted jet from RW Aur A and the blueshifted jets from RY Tau and DG Tau, in order to investigate long-term time variabilities that are potentially related to the activities of mass accretion and/or the stellar magnetic fields. All of these jets consist of several moving knots, with tangential velocities of 70–240 km s−1, which were ejected from the star with different velocities and at irregular time intervals. Via comparisons with the literature, we identify significant differences in the tangential velocities between 1985–2008 and 2008–2021 for the DG Tau jet. The sizes of the individual knots appear to increase with time, and, in turn, their peak brightnesses in the 1.644 μm emission decreased by up to a factor of ∼30 during the epochs of our observations. The variety of decay timescales measured in the [Fe ii] 1.644 μm emission could be attributed to different preshock conditions should the moving knots be unresolved shocks. However, our data do not exclude the possibility that these knots are due to nonuniform density/temperature distributions with another heating mechanism, or, in some cases, due to stationary shocks without proper motions. Spatially resolved observations of these knots with significantly higher angular resolutions will be necessary to better understand their physical nature.

NGC 7538 IRS 2 in [Ne ii]: shell and cavity kinematics of a compact H ii region

ABSTRACT NGC 7538 IRS 2 is a compact H ii region and recent star formation source, with a shell morphology, lying on the border of the visible H ii region NGC 7538. We present a spectral cube of the [Ne ii] 12.8 $\mu$m emission line obtained with the TEXES spectrometer on Gemini North with velocity resolution ∼4 km s−1 and angular resolution ∼0.3 arcsec. The kinematics of the data cube show ionized gas flowing along multiple cavity walls. We have simulated the kinematics and structure of IRS 2 with a model of superimposed cavities created by outflows from embedded stars in a cloud with density gradients. Most of the cavities, including the largest that dominates IRS 2 structure, are associated with B-type stars; the outflow of the bright ionizing O star binary IRS 2a/b is small in extent and lies in a high-density clump. The IRS 2 model shows that the behaviour of an H ii region is not a matter of only the most massive star present; cloud clumpiness and activity of lower mass stars may determine the structure and kinematics.

A low-mass companion desert among intermediate-mass visual binaries: The scaled-up counterpart to the brown dwarf desert

ABSTRACT We present a high-contrast imaging survey of intermediate-mass (1.75–4.5 M⊙) stars to search the most extreme stellar binaries, i.e. for the lowest mass stellar companions. Using adaptive optics at the Lick and Gemini observatories, we observed 169 stars and detected 24 candidates companions, 16 of which are newly discovered, and all but three are likely or confirmed physical companions. Despite obtaining sensitivity down to the substellar limit for 75 per cent of our sample, we do not detect any companion below 0.3 M⊙, strongly suggesting that the distribution of stellar companions is truncated at a mass ratio of qmin ≳ 0.075. Combining our results with known brown dwarf companions, we identify a low-mass companion desert to intermediate-mass stars in the range 0.02 ≲ q ≲ 0.05, which quantitatively matches the known brown dwarf desert among solar-type stars. We conclude that the formation mechanism for multiple systems operates in a largely scale-invariant manner and precludes the formation of extremely uneven systems, likely because the components of a protobinary accrete most of their mass after the initial cloud fragmentation. Similarly, the mechanism to form ‘planetary’ (q ≲ 0.02) companions likely scales linearly with stellar mass, probably as a result of the correlation between the masses of stars and their protoplanetary discs. Finally, we predict the existence of a sizable population of brown dwarf companions to low-mass stars and of a rising population of planetary-mass objects towards ${\approx}1\,M_\mathrm{Jup}$ around solar-type stars. Improvements on current instrumentation will test these predictions.

News in Astronomy &amp; Geophysics – December 2022

... Two tails of dust ejected from the Didymos-Dimorphos asteroid system are seen in recent images from NASA's Hubble Space Telescope (HST). Following the impact of NASA's Double Asteroid Redirection Test (DART) probe on 26 September, the second tail appears to have formed between 2 and 8 October. The twin tail is an unexpected development, although similar behaviour is commonly seen in comets and active asteroids. Current data show that DART shortened Dimorphos' original 11 hour and 55 minute orbit around Didymos by about 32 minutes. bit.ly/3TVwSJu A new study may have discovered the ancient chemical remains of Population III stars. A team led by Yuzuru Yoshii (University of Tokyo) observed distant quasar ULAS J1342+0928 with the Gemini North telescope. They found the clouds surrounding the quasar contained over 10 times more iron than magnesium, compared to the ratio of these elements found in the Sun. The most likely explanation for this striking feature is that the material was left behind by a Population III star that exploded as a ‘pair-instability supernova’. The study appears in The Astrophysical Journal. bit.ly/3DCnVjb

The Galactic chemical evolution of phosphorus observed with IGRINS

Context. Phosphorus (P) is considered to be one of the key elements for life, making it an important element to look for in the abundance analysis of spectra of stellar systems. Yet, only a select number of spectroscopic studies exist to estimate the phosphorus abundances and investigate its trend across a range of metallicities. This is due to the lack of good phosphorus lines in the optical wavelength region and the requirement of careful manual analysis of the blended phosphorus lines in near-infrared H-band spectra obtained with individual observations and surveys such as the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Aims. Based on a consistent and systematic analysis of high-resolution, near-infrared Immersion GRating INfrared Spectrograph (IGRINS) spectra of 38 K giant stars in the Solar neighborhood, we present and investigate the phosphorus abundance trend in the metallicity range of −1.2 dex &lt; [Fe/H] &lt; 0.4 dex. Furthermore, we compare this trend with the available chemical evolution models to shed some light on the origin and evolution of phosphorus. Methods. We have observed full H- and K-band spectra at a spectral resolving power of R = 45 000 with IGRINS mounted on the Gemini South telescope, the Discovery Channel Telescope, and the Harlan J Smith Telescope at McDonald Observatory. Abundances were determined from spectral lines by modeling the synthetic spectrum that best matches the observed spectrum by χ2 minimization. For this task, we used the Spectroscopy Made Easy (SME) tool in combination with one-dimensional (1D) Model Atmospheres in a Radiative and Convective Scheme (MARCS) stellar atmosphere models. The investigated sample of stars have reliable stellar parameters estimated using optical FIber-fed Echelle Spectrograph (FIES) spectra obtained in a previous study of a set of stars called Giants in the Local Disk (GILD). In order to determine the phosphorus abundances from the 16482.92 Å phosphorus line, we needed to take special care blending the CO(v = 7−4) line. With the stellar parameters known, we thus determined the C, N, and O abundances from atomic carbon and a range of nonblended molecular lines (CO, CN, and OH) which are plentiful in the H-band region of K giant stars, assuring an appropriate modeling of the blending CO(v = 7−4) line. Results. We present the [P/Fe] versus [Fe/H] trend for K giant stars in the metallicity range of −1.2 dex &lt; [Fe/H] &lt; 0.4 dex and enhanced phosphorus abundances for two metal-poor s-rich stars. We find that our trend matches well with the compiled literature sample of prominently dwarf stars and the limited number of giant stars. Our trend is found to be higher by ~0.05−0.1 dex compared to the theoretical chemical evolution trend resulting from the core collapse supernova (type II) of massive stars with the phosphorus yields arbitrarily increased by a factor of 2.75. Thus the enhancement factor might need to be ~0.05−0.1 dex higher to match our trend. We also find an empirically determined primary behavior for phosphorus. Furthermore, the phosphorus abundance is found to be elevated by ~0.6−0.9 dex in the two s-enriched stars compared to the theoretical chemical evolution trend.

Near-infrared observations of RR Lyrae and Type II Cepheid variables in the metal-rich bulge globular cluster NGC 6441

Context. NGC 6441 is a bulge globular cluster (GC) with an unusual horizontal branch morphology and a rich population of RR Lyrae (RRL) and Type II Cepheid (T2C) variables that is unexpected for its relatively high metallicity. Aims. Our goal is to characterize the pulsation properties of the population II RRL and T2C variables in this metal-rich GC and compare them with a sample of variables in more metal-poor clusters, as well as with theoretical predictions. Methods. We present JHKs time-series observations of 42 RRLs, eight T2Cs, and ten eclipsing binary candidate variables in NGC 6441 . The multi-epoch observations were obtained using the FLAMINGOS-2 instrument on the 8-m Gemini South telescope. Multiband data are used to investigate pulsation properties of the RRL and T2C variables, including their light curves, instability strip, period–amplitude diagrams, and period–luminosity and period–Wesenheit relations (PLRs and PWRs) in the JHKs filters. Results. The near-infrared (NIR) pulsation properties of RRL variables are well fitted with theoretical models that have canonical helium content and the mean-metallicity of NGC 6441 ([Fe/H] = −0.44 ± 0.07 dex). The helium-enhanced RRL models predict brighter NIR magnitudes and bluer colors than the observations of RRL in the cluster. We find that the empirical slopes of the RRL PLRs and PWRs in NGC 6441 are statistically consistent with those of RRLs in more metal-poor GCs, as well as the theoretical models. Therefore, we use theoretical calibrations of RRL period–luminosity–metallicity (PLZ) relations to simultaneously estimate the mean reddening, E(J − Ks)=0.26 ± 0.06 mag, and the distance, d = 12.67 ± 0.09 kpc, to NGC 6441. Our mean reddening value is consistent with an independent estimate from the bulge reddening map based on red clump stars. The RRL-based distance agrees well with similar literature measurements based on the PLZ relations, and the Gaia and other independent methods. Our distance and reddening values provide a very good agreement between the PLRs of T2Cs in NGC 6441 and those for RRLs and T2Cs in Galactic GCs that span a broad range of metallicity. Conclusions. We conclude that the NIR colour-magnitude diagrams, pulsation properties, and PLRs for RRLs and T2Cs in NGC 6441 are in good agreement with the predictions of RRL pulsation models with canonical helium content. This suggests that these population II variables are either not significantly helium enhanced, as previously thought, or the impact of such enhancement is smaller in NIR than the predictions of the pulsation models.

Global Extinction: Gemini North and South GMOS Combined Photometry Relative to the Gaia Catalog, and Long-term Atmospheric Change

Effects of long-term atmospheric change were looked for in photometry employing Gemini North and South twin Multi-Object Spectrograph (GMOS-N and GMOS-S) archival data. The whole GMOS imaging database, beginning from 2003, was compared against the all-sky Gaia object catalog, yielding ∼106 Sloan -filter samples, ending in 2021. These were combined with reported sky and meteorological conditions, and versus a simple model of the atmosphere plus cloud together with simulated throughputs. One exceptionally extincted episode in 2009 is seen, as is a trend (similar at both sites) of about 2 mmag worsening attenuation per decade. This is consistent with solar-radiance transmissivity records going back over six decades, aerosol density measurements, and more than 0.2°C/decade rise in air temperature, which has implications for the calibration of historic data sets or future surveys.