focalinterest.net

Tag: Astrophysics & Stellar Science

  • Tomographic analysis identifies possible embedded planets in disk data

    Tomographic analysis identifies possible embedded planets in disk data

    What the study found

    The study found that tomographic analysis of molecular lines can reveal signatures associated with embedded planets in protoplanetary disks, including changes in gas motion and line shape. In the examples discussed, the authors report possible embedded planets in HD 135344B and structures in MWC 758 that fit other disk processes.

    Why the authors say this matters

    The authors suggest this matters because it extends analysis beyond line-centroid kinematics, meaning it uses more than just the position of spectral lines to study disk motion. They conclude that this approach can help separate planet-driven signatures from those caused by disk instabilities.

    What the researchers tested

    The researchers used synthetic observations of planet-disk interactions and disk instabilities to test a tomographic study of molecular lines. They then applied the method to ALMA (Atacama Large Millimeter/submillimeter Array) CO line data from the disks of HD 135344B and MWC 758.

    What worked and what didn't

    The results indicate that a few hours of ALMA integration at moderate angular resolution could identify key signatures from planets more massive than 0.1% of the stellar mass. These signatures included deviations from Keplerian motion, localized line broadening, and line skewness that can help distinguish planetary from instability-driven signals; in HD 135344B, the analysis suggested three massive planets at about 95 au, 41 au, and 73 au, while in MWC 758 the observed pattern was more consistent with vertical-velocity spirals linked to moderate disk eccentricities or warps.

    What to keep in mind

    The abstract does not describe uncertainties, sample size limits, or external validation beyond the two disk examples. The reported planet locations in HD 135344B are presented as a possibility, and the MWC 758 interpretation is described as consistency with models rather than a direct detection.

    • Tomographic molecular-line analysis was used to study embedded planet signatures in protoplanetary disks.
    • The method is reported to detect deviations from Keplerian motion, localized line broadening, and line skewness.
    • The authors say a few hours of ALMA observing time at moderate angular resolution may be enough to identify planets above 0.1% of stellar mass.
    • HD 135344B showed localized velocity and line-width perturbations that suggest three possible massive planets.
    • MWC 758 showed features more consistent with vertical-velocity spirals and possible moderate disk eccentricity or warps.
  • Tellurium atomic data support kilonova spectral modelling

    Tellurium atomic data support kilonova spectral modelling

    What the study found

    The study presents new atomic data for tellurium ions and uses them in spectral modelling of kilonovae, including AT2017gfo, a kilonova event. It also examines whether Te iv, meaning tellurium with a +3 charge, could contribute to the 1.08 micrometer emission feature seen in AT2017gfo.

    Why the authors say this matters

    The authors say kilonova spectral modelling needs large amounts of collisional excitation and photoionization data for lowly ionized heavy elements, and that much of the available data is currently based on approximate hydrogenic results or semi-empirical formulae. The study suggests the new tellurium data may help improve this modelling.

    What the researchers tested

    The researchers used the Multi-Configuration-Dirac–Hartree–Fock method to build model atomic structures and radiative rates. They then applied the R-matrix method to calculate electron-impact excitation and photoionization cross-sections for tellurium ions, and used the resulting rates in a collisional-radiative model to generate synthetic spectra for comparison with observations.

    What worked and what didn't

    The abstract states that atomic data were produced for tellurium ions, including excitation and photoionization information for Te i through Te iv, and additional radiative and thermal collision data for Te iv and Te v. It also says the authors investigated whether Te iv could contribute to the 1.08 micrometer emission feature alongside the established Sr ii P-Cygni feature, but it does not state the outcome of that investigation in the abstract.

    What to keep in mind

    The available summary does not give detailed numerical results or a clear conclusion about the Te iv contribution to the 1.08 micrometer feature. It also does not describe uncertainties, limitations, or how well the synthetic spectra matched the observations.

    • New atomic data were computed for tellurium ions using the R-matrix method.
    • The work includes electron-impact excitation and photoionization data for Te i through Te iv.
    • Radiative and thermal collision data were also produced for Te iv and Te v.
    • The data were used in a collisional-radiative model to make synthetic spectra for kilonovae.
    • The authors investigated whether Te iv could contribute to the 1.08 micrometer feature in AT2017gfo.

  • SLAM estimates M-dwarf stellar parameters from BOSS spectra

    What the study found

    The study found that the Stellar LAbel Machine (SLAM), a data-driven model using support vector regression, can estimate metallicity ([Fe/H]), effective temperature (T eff), and surface gravity (log g) for Sloan Digital Sky Survey V M dwarfs from low-resolution BOSS spectra. Its metallicity estimates showed no bias in M+M dwarf wide binaries, and its temperature and gravity estimates generally agreed with several external reference methods.

    Why the authors say this matters

    The authors suggest this work matters because it provides calibrated stellar parameters for M dwarfs, a type of cool dwarf star, using BOSS optical spectra. They also conclude that the study can be used to correct a bias in APOGEE ASPCAP metallicities through an equation they provide.

    What the researchers tested

    The researchers applied SLAM to low-resolution optical spectra from the BOSS spectrographs in SDSS-V DR19. They calibrated [Fe/H] using LAMOST F, G, or K dwarf companions, and calibrated T eff and log g using APOGEE Net.

    What worked and what didn't

    For [Fe/H], comparisons between the two stars in M+M dwarf wide binaries showed no bias and a scatter of 0.11 dex. Other comparisons gave biases of −0.06 ± 0.16 dex and 0.02 ± 0.14 dex, while T eff agreed well with interferometric angular-diameter calibrations (−27 ± 92 K) and LAMOST (−34 ± 65 K) but was lower than one color-based relation by 146 ± 45 K. The log g values aligned well with LAMOST (−0.01 ± 0.07 dex) and with values derived from stellar mass and radius (−0.04 ± 0.09 dex), and the bias versus APOGEE ASPCAP depended on ASPCAP [Fe/H] and T eff.

    What to keep in mind

    The abstract does not describe major limitations beyond the fact that the calibrations and comparisons are tied to the specific datasets and reference methods used here. The summary also notes that the ASPCAP metallicity correction depends on ASPCAP [Fe/H] and T eff, but it does not provide broader validation details in the abstract.

    • SLAM was used to estimate [Fe/H], T eff, and log g for SDSS-V M dwarfs from BOSS spectra.
    • M+M dwarf wide-binary comparisons showed no [Fe/H] bias and 0.11 dex scatter.
    • T eff matched interferometric and LAMOST-based values but was lower than one color-based estimate by 146 ± 45 K.
    • log g agreed well with both LAMOST and values derived from stellar mass and radius.
    • The authors provide an equation to correct a bias in APOGEE ASPCAP metallicities.

  • Magnetic charge alters periodic orbits and waveforms near regular black holes

    What the study found

    The study found that magnetic charge in a regular black hole changes periodic, zoom-whirl orbits and the gravitational waveforms produced by extreme mass ratio inspirals, or EMRIs, which are systems where a stellar-mass object spirals into a supermassive black hole. It also found that increasing the magnetic charge reduces the radii of the marginally bound orbit and the innermost stable circular orbit.

    Why the authors say this matters

    The authors conclude that future gravitational wave observations may constrain the properties of magnetically charged regular black holes, and they say this would deepen understanding of the gravitational imprint of regular black holes.

    What the researchers tested

    The researchers studied periodic geodesic orbits around a magnetically charged black hole within a regular black hole framework. They modeled a stellar-mass object as a timelike particle inspiraling into a supermassive black hole and analyzed the resulting orbital motion and gravitational waveforms with a semi-analytical approach.

    What worked and what didn't

    The calculations showed that the magnetic charge parameter reduces both the marginally bound orbit radius and the innermost stable circular orbit radius. The study also found that the charge parameter significantly changes zoom-whirl orbital dynamics and leads to notable changes in waveform structure.

    What to keep in mind

    The summary does not describe experimental data or observational tests; it describes a modeling and calculation study. Limits, caveats, and uncertainty estimates are not described in the available abstract.

    • Magnetic charge changes periodic zoom-whirl orbits around a regular black hole.
    • The marginally bound orbit radius and innermost stable circular orbit radius both decrease as magnetic charge increases.
    • The gravitational waveforms from EMRIs are altered by the charge parameter.
    • The authors say future gravitational wave observations may help constrain magnetically charged regular black holes.

  • Milky Way circular velocity curve measured from element abundances

    What the study found

    The study presents a new data-driven method for measuring the Milky Way’s circular velocity curve by using gradients in stellar element abundances. The authors report a circular velocity at the solar radius of 235.3 km s−1 from the [Mg/Fe] abundance ratio, along with estimates of the radial and azimuthal frequencies and the Oort constants.

    Why the authors say this matters

    The findings indicate that abundance ratios can trace stellar positions and motions in the Galactic disk, which the authors say enables an empirical measurement of the Galaxy’s circular velocity curve, epicyclic frequency, and azimuthal frequency. The study suggests this provides a way to study kinematic gradients across the Milky Way’s disk.

    What the researchers tested

    The researchers combined stellar surface abundances from the APOGEE survey with kinematic data from the Gaia mission. They tested a method that uses element abundance gradients in the plane of radial kinematics, focusing on average [Fe/H] and [Mg/Fe] patterns in the Milky Way disk.

    What worked and what didn't

    The results confirm ordered structure in the Milky Way’s disk in terms of average [Fe/H] and [Mg/Fe]. The authors suggest that 〈[Fe/H]〉 traces the radial positions of stars in the disk, while 〈[Mg/Fe]〉 traces orbital excursions around that radius. The method produced estimates of v_c,⊙ = 235.3−3.7+2.8 km s−1, κ0,R⊙ = 36.9−1.0+0.8 km s−1 kpc−1, Ω0,R⊙ = 28.5−0.1+0.4 km s−1 kpc−1, and Oort constants A = 16.5−0.1+0.1 km s−1 kpc−1 and B = −11.9−0.3+0.1 km s−1 kpc−1.

    What to keep in mind

    The abstract provided does not describe major limitations, but the reported measurements are tied to the solar radius and to the abundance ratio [Mg/Fe] as the most constraining tracer. The summary also stops before giving the full expression for the radial acceleration at the solar radius.

    • A new data-driven method uses stellar element abundance gradients to measure the Milky Way’s circular velocity curve.
    • APOGEE abundance data and Gaia kinematics were combined in the analysis.
    • Average [Fe/H] and [Mg/Fe] show ordered structure across the Milky Way’s disk.
    • The study reports v_c,⊙ = 235.3 km s−1 from [Mg/Fe] at the solar radius.
    • The authors also estimate the radial and azimuthal frequencies and the Oort constants.

  • Three ultra-faint Milky Way satellite candidates identified

    What the study found

    The study reports three Milky Way satellite candidates: Carina IV, Phoenix III, and DELVE 7. The authors describe all three as extremely faint systems made of old, metal-poor stars.

    Why the authors say this matters

    The authors note that Phoenix III is the faintest known satellite in the extreme outer stellar halo, and DELVE 7 is the faintest known satellite beyond 20 kiloparsecs from the Galactic center. They also say Carina IV appears unlikely to be associated with the Large Magellanic Cloud.

    What the researchers tested

    The candidates were identified in the third data release of the DECam Local Volume Exploration survey, or DELVE, by cross-matching results from two independent search algorithms. The team used Gaia proper motions and DECam CaHK photometry to examine Carina IV, and reported masses and sizes for all three systems.

    What worked and what didn't

    Carina IV has a half-light radius consistent with known dwarf galaxies, and Phoenix III does as well. DELVE 7 is very compact and seems more likely to be a star cluster, although its nature remains ambiguous without spectroscopic follow-up. The member stars in Carina IV are described as metal poor.

    What to keep in mind

    The abstract says DELVE 7 remains ambiguous without spectroscopic follow-up. It also presents these systems as candidates, so their classifications are not fully settled in the available summary.

    • Three Milky Way satellite candidates were reported: Carina IV, Phoenix III, and DELVE 7.
    • All three are described as extremely faint, old, and metal-poor systems.
    • Carina IV and Phoenix III have half-light radii consistent with dwarf galaxies.
    • DELVE 7 is very compact and may be a star cluster rather than a galaxy.
    • Phoenix III is reported as the faintest known satellite in the extreme outer stellar halo.
    • DELVE 7 is reported as the faintest known satellite beyond 20 kiloparsecs from the Galactic center.

  • Nonthermal line broadening confirmed in the DM Tau disk

    What the study found

    The study found a significant nonthermal contribution to the molecular line width in the DM Tau protoplanetary disk, around 0.4 times the sound speed. The authors report that this is inconsistent with purely thermal motion.

    Why the authors say this matters

    The authors conclude that this kind of analysis can directly extract disk structure and nonthermal broadening from molecular line data. They suggest the framework can be applied to other disks with high-quality observations.

    What the researchers tested

    The researchers used the radiative transfer code MCFOST in a Bayesian inference framework. They fit high-resolution 12CO J=3-2 observations from the exoALMA Large Program and evaluated over five million disk models to sample the parameter space. They then used the CO-based disk structure as a starting point to model CS J=7-6 emission.

    What worked and what didn't

    The CO data fit revealed a significant nonthermal contribution to the line width of about 0.4 times the sound speed. Using the CO-based disk structure, the authors reproduced the CS J=7-6 emission well, and the CS result agreed with the turbulence inferred from the CO fit. The abstract also says they identified residual structures in the moment maps that deviate from the expected emission and may trace forming planets.

    What to keep in mind

    The abstract does not describe specific limitations or uncertainties beyond what is implied by the modeling approach. The findings are reported for DM Tau and for the particular molecular lines and observations used in this study.

    • DM Tau shows a significant nonthermal contribution to its molecular line width.
    • The reported nonthermal broadening is about 0.4 times the sound speed.
    • The analysis used high-resolution 12CO J=3-2 observations and a Bayesian modeling framework.
    • CS J=7-6 emission was reproduced well using the CO-based disk structure.
    • Residual structures in the moment maps may trace forming planets.

  • Relaxed cool-core galaxy cluster studied at redshift 1.16

    What the study found

    The study reports new Chandra observations of SPT-CL J2215-3537, a galaxy cluster at redshift 1.16. The authors describe it as the second-most distant relaxed, cool-core cluster identified to date.

    Why the authors say this matters

    The authors say this cluster is a useful high-redshift benchmark for understanding how cool cores form and how massive galaxy clusters evolve. They also note that its resolved cool core provides context for the massive starburst seen in its central galaxy.

    What the researchers tested

    The researchers used Chandra X-ray observations to study the cluster’s total mass profile, thermodynamic profiles, scaling relations, and metal enrichment. They also compared its thermodynamic and cosmological properties with a sample of well-studied, lower-redshift relaxed clusters.

    What worked and what didn't

    The observations allowed the team to constrain the cluster’s total mass profile and resolve its cool core. They also investigated gas mass, average temperature, and X-ray luminosity, along with metal enrichment, in the cluster.

    What to keep in mind

    The abstract does not describe specific numerical results, detailed uncertainties, or methodological limitations. It also does not provide the full comparison outcomes with lower-redshift clusters.

    • SPT-CL J2215-3537 is described as a relaxed, cool-core galaxy cluster at redshift 1.16.
    • The cluster is said to be the second-most distant relaxed, cool-core cluster identified to date.
    • Chandra observations were used to constrain its total mass profile and study its thermodynamic properties.
    • The study examined gas mass, average temperature, X-ray luminosity, and metal enrichment.
    • The authors say the cluster can serve as a high-redshift benchmark for studying cool-core formation and cluster evolution.

  • Massive quiescent galaxies are common from redshift 2 to 5

    What the study found

    The study found that massive quiescent galaxies, meaning galaxies with little or no current star formation, are surprisingly common between redshift 2 and 5. The authors report number densities of at least about 10^-5 Mpc^-3 by 4 < z < 5.

    Why the authors say this matters

    The authors say these are the most complete spectroscopic estimates available before cosmic noon, a common term for the era when the universe's star formation activity was especially high. They also conclude that the results challenge most galaxy evolution simulations, which at z > 3 fail to make enough massive quiescent galaxies.

    What the researchers tested

    The researchers used JWST NIRSpec PRISM spectra from RUBIES, together with NIRCam photometry, to estimate the number density of massive galaxies with stellar mass above log(M*/M⊙) > 10.3. They identified quiescent candidates using principal component analysis and spectrophotometric fitting, then corrected for survey incompleteness by inverting the RUBIES selection function.

    What worked and what didn't

    The RUBIES spectra and targeting strategy allowed the authors to infer physical properties and number densities with high confidence, according to the abstract. Their inferred number densities are consistent with earlier JWST photometry-based studies and smaller-area surveys, but six state-of-the-art cosmological simulations generally underproduce these galaxies at z > 3.

    What to keep in mind

    The summary provided does not describe detailed limitations beyond the need to correct for survey incompleteness. The findings apply to massive quiescent galaxies at 2 < z < 5 and are based on the RUBIES sample and the methods described in the abstract.

    • The study estimates number densities for massive quiescent galaxies at 2 < z < 5.
    • By 4 < z < 5, the number density is reported as ≳10^-5 Mpc^-3.
    • The authors used JWST NIRSpec PRISM spectra from RUBIES plus NIRCam photometry.
    • Quiescent candidates were selected with principal component analysis and spectrophotometric fitting.
    • Most compared cosmological simulations fail to produce enough massive quiescent galaxies at z > 3.
  • VLBI and Gaia DR3 give broadly similar LPV astrometry

    VLBI and Gaia DR3 give broadly similar LPV astrometry

    What the study found

    The study found that very long baseline interferometry (VLBI) and Gaia Data Release 3 (DR3) give broadly consistent parallax measurements for about half of the 43 Galactic long period variable stars examined. The authors also report that Gaia DR3 parallaxes tend to be slightly smaller than VLBI values.

    Why the authors say this matters

    The authors conclude that the results show VLBI and Gaia astrometry are complementary for long period variable stars. They also note that this is relevant because accurate parallaxes are essential for determining distances and intrinsic properties, and because VLBI appears more effective for stars with parallaxes smaller than about 2 milliarcseconds, corresponding to distances beyond 500 parsecs.

    What the researchers tested

    The researchers compared astrometric measurements from VLBI and Gaia DR3 for 43 Galactic long period variable stars. They examined parallaxes and proper motions, and they also looked at how parallax uncertainties and residuals behaved across the sample.

    What worked and what didn't

    Parallaxes from the two methods were generally consistent within uncertainties for about half of the sample, but Gaia DR3 values were slightly smaller on average. VLBI parallax errors increased with increasing parallax, while Gaia DR3 errors stayed nearly constant; proper motions showed general agreement with a 2-sigma dispersion of about 13 km s−1, and the dispersion of parallax residuals was slightly larger for stars with pulsation periods around one year.

    What to keep in mind

    The study is limited to 43 Galactic long period variable stars. The abstract also notes that long period variables are difficult to measure because of their large stellar sizes, circumstellar matter, and time-variable surface brightness asymmetry.

    • The study compared VLBI and Gaia DR3 astrometry for 43 Galactic long period variable stars.
    • Parallaxes from the two methods were generally consistent within uncertainties for about half the sample.
    • Gaia DR3 parallaxes tended to be slightly smaller than VLBI parallaxes.
    • VLBI errors increased with parallax, while Gaia DR3 errors remained nearly constant.
    • VLBI was described as more effective for parallaxes below about 2 milliarcseconds, or distances beyond 500 parsecs.
    • Proper motions generally agreed, with a 2-sigma dispersion of about 13 km s−1.