adsabs/SciX_UAT_keywords huggingface dataset:
TOI-1749: an M dwarf with a Trio of Planets including a Near-resonant Pair

We report the discovery of one super-Earth- (TOI-1749b) and two sub-Neptune-sized planets (TOI-1749c and TOI-1749d) transiting an early M dwarf at a distance of 100 pc, which were first identified as planetary candidates using data from the TESS photometric survey. We have followed up this system from the ground by means of multiband transit photometry, adaptive optics imaging, and low-resolution spectroscopy, from which we have validated the planetary nature of the candidates. We find that TOI-1749b, c, and d have orbital periods of 2.39, 4.49, and 9.05 days, and radii of 1.4, 2.1, and 2.5 R⊕, respectively. We also place 95% confidence upper limits on the masses of 57, 14, and 15 M⊕ for TOI-1749b, c, and d, respectively, from transit timing variations. The periods, sizes, and tentative masses of these planets are in line with a scenario in which all three planets initially had a hydrogen envelope on top of a rocky core, and only the envelope of the innermost planet has been stripped away by photoevaporation and/or core-powered mass-loss mechanisms. These planets are similar to other planetary trios found around M dwarfs, such as TOI-175b,c,d and TOI-270b,c,d, in the sense that the outer pair has a period ratio within 1% of 2. Such a characteristic orbital configuration, in which an additional planet is located interior to a near 2:1 period-ratio pair, is relatively rare around FGK dwarfs.

Keywords: transits; exoplanet detection methods; transit duration variation method; super earths; mini neptunes; m dwarf stars
The First Extensive Exploration of UV-bright Stars in the Globular Cluster NGC 2808

In this study, we identified and characterized the hot and luminous UV-bright stars in the globular cluster NGC 2808. We combined data from the Ultra Violet Imaging Telescope (UVIT) on board the Indian space satellite AstroSat with the Hubble Space Telescope UV Globular Cluster Survey data for the central region (within $\sim 2\buildrel{\,\prime}\over{.} 7\times 2\buildrel{\,\prime}\over{.} 7$ ) and Gaia and ground-based optical photometry for the outer parts of the cluster. We constructed the UV and UV-optical color-magnitude diagrams, compared the horizontal branch (HB) members with the theoretical zero- and terminal-age HB models, and identified 34 UV-bright stars. The spectral energy distributions of the UV-bright stars were fitted with theoretical models to estimate their effective temperatures (12,500-100,000 K), radii (0.13-2.2 R⊙), and luminosities (∼40-3000 L⊙) for the first time. These stars were then placed on the Hertzsprung-Russell diagram, along with theoretical post-HB evolutionary tracks, to assess their evolutionary status. The models suggest that most of these stars are in the asymptotic giant branch (AGB)-manqué phase, and all except three have evolutionary masses <0.53 M⊙. We also calculated the theoretically expected number of hot post-(early)-AGB stars in this cluster and found the range to match our observations. Seven UV-bright stars located in the outer region of the cluster, identified from the AstroSat/UVIT images, are ideal candidates for detailed follow-up spectroscopic studies.

Keywords: globular star clusters; post-asymptotic giant branch stars; ultraviolet photometry; hertzsprung russell diagram; horizontal branch stars
A Bayesian ILC Method for CMB B-mode Posterior Estimation and Reconstruction of Primordial Gravity Wave Signal

The cosmic microwave background (CMB) radiation B-mode polarization signal contains the unique signature of primordial metric perturbations produced during the inflation. The separation of the weak CMB B-mode signal from strong foreground contamination in observed maps is a complex task, and proposed new-generation low-noise satellite missions compete with the weak signal level of this gravitational background. In this paper, for the first time, we employ a foreground model-independent internal linear combination (ILC) method to reconstruct the CMB B-mode signal using simulated observations over large angular scales of the sky of six frequency bands of the future-generation CMB mission Probe of Inflation and Cosmic Origins (PICO). We estimate the joint CMB B-mode posterior density following the interleaving Gibbs steps of the B-mode angular power spectrum and cleaned map samples using the ILC method. We extend and improve the earlier reported Bayesian ILC method to analyze weak CMB B-mode reconstruction by introducing noise-bias corrections at two stages during the ILC weight estimation. By performing 200 Monte Carlo simulations of the Bayesian ILC method, we find that our method can reconstruct the CMB signals and the joint posterior density accurately over large angular scales of the sky. We estimate the Blackwell-Rao statistics of the marginal density of the CMB B-mode angular power spectrum and use them to estimate the joint density of the tensor-to-scalar ratio r and a lensing power spectrum amplitude ${A}^{{\rm{lens}}}$ . Using 200 Monte Carlo simulations of the delensing approach, we find that our method can achieve an unbiased detection of the primordial gravitational-wave signal r with more than 8σ significance for levels of $r\geqslant 0.01$ for input frequency maps with realistic lensing and foregrounds with constant spectral indices.

Keywords: cosmic microwave background radiation; extragalactic astronomy; cosmic inflation; principal component analysis
Colors of Irregular Satellites of Saturn with the Dark Energy Camera

We report g - r and r - i new colors for 21 Saturn Irregular Satellites; among them, four previously unreported. This is the highest number of Saturn Irregular satellites reported in a single survey. These satellites were measured by "stacking" their observations to increase their signal without trailing. This work describes a novel processing algorithm that enables the detection of faint sources under significant background noise and in front of a severely crowded field. Our survey shows these new color measurements of Saturn Irregular Satellites are consistent with other Irregular Satellites populations as found in previous works and reinforcing the observation that the lack of ultrared objects among the irregular satellites is a real feature that separates them from the trans-Neptunian objects (their posited source population).

Keywords: multi-color photometry; irregular satellites; saturnian satellites; astronomical techniques
Titan's North-South Haze Asymmetry Ratio and Boundary at Visible Wavelengths over the Cassini Mission

We document the evolution of the north-south asymmetry (NSA) of Titan's haze albedo during the Cassini mission between 2004 and 2017. We analyze coadded cube images taken at 96 distinct wavelengths between 0.35 and 1.05 μm by the Cassini Visual and Infrared Mapping Spectrometer (VIMS-V) instrument from 14 Titan flybys. Over half of a Titan year, we observe a near-complete transition in the NSA boundary latitude across the geographic equator from the southern to the northern hemisphere, including a 3 yr fading of the boundary for several years after the equinox. The fading transition of the NSA matches previous observations of a reversal of the NSA in Hubble Space Telescope images of Titan before the winter solstice between 1997 and 2000. A comparison of NSA images taken at similar times but different phase angles shows the NSA boundary is detectable, albeit with less contrast, at moderately high phase angles (~90°). Analysis of the NSA boundary in T61 and T67 VIMS images further supports a small tilt between the superrotating atmosphere and the solid body of Titan, as suggested in a previous analysis of 0.890 μm images from the Cassini Imaging Science Subsystem.

Keywords: astronomy data modeling; astronomy image processing; titan; atmospheric evolution; atmospheric dynamics; albedo; computational astronomy
A Second-order Moment of Microlensing Variability as a Novel Tool to Constrain Source Emission Size or Discrete Lens Demographics in Extragalactic Research

We define a second-order moment of the observational differential microlensing curves that can be used to impose constraints on physical properties of lensed quasars. We show that this quantity is sensitive both to variations in the source size and the deflector mass. We formulize a methodology to recover the source size from the observational measurements when the mass spectrum is fixed. As a case study, we test it with a sample of four quadruple lenses, both in simulated scenarios and with real data from the Chandra X-ray Observatory. In our simulations with a uniform stellar population the method works best to detect sources around 0.1 Einstein radii, giving correct upper/lower limits for much smaller/bigger sizes without requiring a big leap in additional computational effort as compared to a single-epoch approach, yet taking advantage of multi-epoch information. We apply the method to a small sample of X-ray data from four objects assuming a range of star masses, and obtain a degeneracy relation between the source size and deflector mass. Combined with previous estimates for the size of the X-ray corona, the degeneracy relation suggests that X-ray microlensing is mainly induced by planetary mass objects.

Keywords: accretion; black hole physics; gravitational lensing; quasar microlensing; quasars
Tidal Currents Detected in Kraken Mare Straits from Cassini VIMS Sun Glitter Observations

We present Cassini Visual and Infrared Mapping Spectrometer (VIMS) observations of sun glitter—wave-induced reflections from a liquid surface offset from a specular point—on Kraken Mare. sun glitter reveals rough sea surfaces around Kraken Mare, namely the coasts and narrow straits. The sun glitter observations indicate wave activity driven by the winds and tidal currents in Kraken Mare during northern summer. T104 Cassini VIMS observations show three sun glitter features in Bayta Fretum indicative of variegated wave fields. We cannot uniquely determine one source for the coastal Bayta waves, but we lean toward the interpretation of surface winds, because tidal currents should be too weak to generate capillary-gravity waves in Bayta Fretum. T105 and T110 observations reveal wave fields in the straits of Seldon Fretum, Lulworth Sinus, and Tunu Sinus that likely originate from the constriction of tidal currents. Coastlines of Bermoothes and Hufaidh Insulae adjoin rough sea surfaces, suggesting a complex interplay of wind-roughened seas and localized tidal currents. Bermoothes and Hufaidh Insulae may share characteristics of either the Torres Strait off Australia or the Åland region of Finland, summarized as an island-dense strait with shallow bathymetry that hosts complex surface circulation patterns. Hufaidh Insulae could host seafloor bedforms formed by tidal currents with an abundant sediment supply, similar to the Torres Strait. The coastlines of Hufaidh and Bermoothes Insulae likely host ria or flooded coastal inlets, suggesting that the Insulae may be local peaks of primordial crust isolated by an episode of sea-level rise or tectonic uplift.

Keywords: saturnian satellites; ocean-atmosphere interactions
Speckle Interferometry at SOAR in 2022

Results of the speckle-interferometry observations at the 4.1 m SOuthern Astrophysical Research Telescope obtained during 2022 are presented: 2508 measurements of 1925 resolved pairs or subsystems and 785 nonresolutions of 611 targets; 26 pairs are resolved here for the first time. This work continues our long-term effort to monitor orbital motion in close binaries and hierarchical systems. A large number of orbits have been updated using these measurements.

Keywords: interferometric binary stars
Orbital Alignment of the Eccentric Warm Jupiter TOI-677 b

Warm Jupiters lay out an excellent laboratory for testing models of planet formation and migration. Their separation from the host star makes tidal reprocessing of their orbits ineffective, which preserves the orbital architectures that result from the planet-forming process. Among the measurable properties, the orbital inclination with respect to the stellar rotational axis, stands out as a crucial diagnostic for understanding the migration mechanisms behind the origin of close-in planets. Observational limitations have made the procurement of spin-orbit measurements heavily biased toward hot Jupiter systems. In recent years, however, high-precision spectroscopy has begun to provide obliquity measurements for planets well into the warm Jupiter regime. In this study, we present Rossiter-McLaughlin (RM) measurements of the projected obliquity angle for the warm Jupiter TOI-677 b using ESPRESSO at the VLT. TOI-677 b exhibits an extreme degree of alignment (λ = 0.3 ± 1.3 deg), which is particularly puzzling given its significant eccentricity (e ≈ 0.45). TOI-677 b thus joins a growing class of close-in giants that exhibit large eccentricities and low spin-orbit angles, which is a configuration not predicted by existing models. We also present the detection of a candidate outer brown dwarf companion on an eccentric, wide orbit (e ≈ 0.4 and P ≈ 13 yr). Using simple estimates, we show that this companion is unlikely to be the cause of the unusual orbit of TOI-677 b. Therefore, it is essential that future efforts prioritize the acquisition of RM measurements for warm Jupiters.

Keywords: exoplanets; planetary alignment; exoplanet dynamics; exoplanet migration; radial velocity; transits
Principal-component Interferometric Modeling (PRIMO), an Algorithm for EHT Data. I. Reconstructing Images from Simulated EHT Observations

The sparse interferometric coverage of the Event Horizon Telescope (EHT) poses a significant challenge for both reconstruction and model fitting of black hole images. PRIMO is a new principal components analysis-based algorithm for image reconstruction that uses the results of high-fidelity general relativistic, magnetohydrodynamic simulations of low-luminosity accretion flows as a training set. This allows the reconstruction of images that are consistent with the interferometric data and that live in the space of images that is spanned by the simulations. PRIMO follows Monte Carlo Markov Chains to fit a linear combination of principal components derived from an ensemble of simulated images to interferometric data. We show that PRIMO can efficiently and accurately reconstruct synthetic EHT data sets for several simulated images, even when the simulation parameters are significantly different from those of the image ensemble that was used to generate the principal components. The resulting reconstructions achieve resolution that is consistent with the performance of the array and do not introduce significant biases in image features such as the diameter of the ring of emission.

Keywords: very long baseline interferometry; black hole physics; astronomy image processing; interferometry; principal component analysis; accretion
Identifying Bound Stellar Companions to Kepler Exoplanet Host Stars Using Speckle Imaging

The Kepler mission and subsequent ground-based follow-up observations have revealed a number of exoplanet host stars with nearby stellar companions. This study presents speckle observations of 57 Kepler objects of interest (KOIs) that are also double stars, each observed over a 3-8 yr period, which has allowed us to track their relative motions with high precision. Measuring the position angle and separation of the companion with respect to the primary can help determine if the pair exhibits common proper motion, indicating it is likely to be a bound binary system. We report on the motions of 34 KOIs that have close stellar companions, three of which are triple stars, for a total of 37 companions studied. Eighteen of the 34 systems are confirmed exoplanet hosts, including one triple star, while four other systems have been subsequently judged to be false positives and twelve are yet to be confirmed as planet hosts. We find that 21 are most likely to be common proper motion pairs, 4 are line-of-sight companions, and 12 are of an uncertain disposition at present. The fraction of the confirmed exoplanet host systems that are common proper motion pairs is approximately 86% in this sample. In this subsample, the planets are exclusively found with periods of less than 110 days, so that in all cases the stellar companion is found at a much larger separation from the planet host star than the planet itself. A preliminary period-radius relation for the confirmed planets in our sample suggests no obvious differences at this stage with the full sample of known exoplanets.

Keywords: visual binary stars; interferometric binary stars; planet hosting stars; speckle interferometry; astrometry
TONGS: A Treasury of Nearby Galaxy Surveys

The beginning of the 21st century marked the "modern era of galaxy surveys" in astronomy. Rapid innovation in observing technology, combined with the base built by galaxy catalogs and atlases dating back centuries, sparked an explosion of new observational programs driven by efforts to understand the different processes driving galaxy evolution. This review aims to answer the following science questions: (1) how have galaxy surveys evolved in the past 20 yr, and how have traditional observational programs been affected by the rise of large panoramic surveys, (2) can the term "nearby" be quantified in the context of galaxy surveys, and (3) how complete is the coverage of the nearby universe and what areas hold the largest opportunity for future work? We define a galaxy survey as a systematically obtained data set which aims to characterize a set of astronomical objects. Galaxy surveys can further be subdivided based on the methods used to select the objects to observe, the properties of the survey samples (e.g., distance or morphology), or the observing strategies used. We focus on pointed nearby galaxy surveys, which we define as surveys which observe a specific sample of target galaxies. Through a study of 43 nearby galaxy surveys, we find no standardized quantitative definition for "nearby" with surveys covering a wide range of distances. We observe that since 2003, traditional targeted galaxy surveys have undergone a dramatic evolution, transitioning from large, statistical surveys to small, ultra-specific projects which compliment the rise of large high resolution panoramic surveys. While wavelength regimes observable from the ground (such as radio or optical wavelengths) host numerous surveys, the largest opportunity for future work is within the less covered space-based wavelength regimes (especially ultraviolet and X-ray).

Keywords: history of astronomy; galaxies; galaxy photometry; galaxy spectroscopy; celestial objects catalogs; galaxy distances
Neon Cluster Formation and Phase Separation during White Dwarf Cooling

Recent observations of Galactic white dwarfs (WDs) with Gaia suggest there is a population of massive crystallizing WDs exhibiting anomalous cooling—the Q branch. While single-particle 22Ne sedimentation has long been considered a possible heat source, recent work suggests that 22Ne must separate into clusters, enhancing diffusion, in order for sedimentation to provide heating on the observed timescale. We show definitively that 22Ne cannot separate to form clusters in C/O WDs using molecular dynamics simulations, and we further present a general C/O/Ne phase diagram showing that strong 22Ne enrichment is not achievable for 22Ne abundance ≲30%. We conclude that the anomalous heating cannot be due to 22Ne cluster sedimentation and that Q branch WDs may have an unusual composition, possibly rich with heavier elements.

Keywords: stellar interiors; degenerate matter; n-body simulations
Mathematical Underpinnings of the Multiwavelength Structure of the Tip of the Red Giant Branch

We consider the application of the tip of the red giant branch (TRGB) in the optical and in the near-infrared for the determination of distances to nearby galaxies. We analyze ACS VI (F555W and F814W) data and self-consistently cross-calibrate WFC3-IR JH (F110W and F120W) data using an absolute magnitude calibration of MI = -4.05 mag as determined in the Large Magellanic Cloud using detached eclipsing binary star geometric parallaxes. We demonstrate how the optical and near-infrared calibrations of the TRGB method are mathematically self-consistent, and illustrate the mathematical basis and relations among these multiwavelength calibrations. We go on to present a method for determining the reddening, extinction, and the true modulus to the host galaxy using multiwavelength data. The power of the method is that with high-precision data, the reddening can be determined using the TRGB stars themselves, and decreases the systematic (albeit generally small) uncertainty in distance due to reddening for these halo stars.

Keywords: red giant branch; red giant tip; distance indicators; stellar distance
Periodic Fast Radio Bursts with Neutron Star Free Precession

The CHIME/FRB collaboration recently reported the detection of a 16 day periodicity in the arrival times of radio bursts from FRB 180916.J0158+65. We study the possibility that the observed periodicity arises from free precession of a magnetized neutron star, and put constraints on different components of the star's magnetic fields. Using a simple geometric model, where radio bursts are emitted from a rotating neutron star magnetosphere, we show that the emission pattern as a function of time can match that observed from FRB 180916.J0158+65.

Keywords: compact radiation sources; magnetospheric radio emissions; radio bursts; neutron stars; magnetars
A Superflare on YZ Canis Minoris Observed by the Seimei Telescope and TESS: Red Asymmetry of Hα Emission Associated with White-light Emission

Active M-type stars are known to often produce superflares on the surface. Radiation from stellar (super)flares is important for exoplanet habitability, but the mechanisms are not well understood. In this paper, we report simultaneous optical spectroscopic and photometric observations of a stellar superflare on an active M dwarf, YZ Canis Minoris, with the 3.8 m Seimei telescope and the Transiting Exoplanet Survey Satellite. The flare bolometric energy is ${1.3}_{-0.6}^{+1.6}\times {10}^{34}\,\mathrm{erg}$ and the Hα energy is ${3.0}_{-0.1}^{+0.1}\times {10}^{32}\,\mathrm{erg}$ . The Hα emission line profile shows red asymmetry throughout the flare, with a duration of 4.6-5.1 hr. The velocity of the red asymmetry is ~200-500 km s-1 and the line width of Hα broadens up to 34 ± 14 Å. The redshifted velocity and line width of Hα line decay more rapidly than the equivalent width, and their time evolutions are correlated with that of the white-light emission. This indicates the possibility of the white light, the Hα red asymmetry, and the Hα line broadening originating from nearly the same site, i.e., the dense chromospheric condensation region, heated by nonthermal electrons. On the other hand, the flux ratio of the redshifted excess components to the central components is enhanced one hr after the flare's onset. This may be due to the main source of the red asymmetry changing to post-flare loops in the later phase of the flare.

Keywords: stellar flares; stellar phenomena; optical flares; solar flares; magnetic variable stars; m dwarf stars; solar magnetic reconnection; solar magnetic fields; magnetic fields