Red Stars Research Articles

The evolution of continuum polarization in type II supernovae as a diagnostic of ejecta morphology

The linear polarization of the optical continuum of type II supernovae (SNe), together with its temporal evolution is a promising source of information about the large-scale geometry of their ejecta. To help access this information, we undertook 2D polarized radiative transfer calculations to map the possible landscape of type II SN continuum polarization (Pcont) from 20 to 300 days after explosion. Our simulations were based on crafted 2D axisymmetric ejecta constructed from 1D nonlocal thermodynamic equilibrium time-dependent radiative transfer calculations for the explosion of a red supergiant star. Following the approach used in our previous work on SN 2012aw, we considered a variety of bipolar explosions in which spherical symmetry is broken by material within ~30° of the poles that has a higher kinetic energy (up to a factor of two) and higher 56Ni abundance (up to a factor of about five, allowing for 56Ni at high velocity). Our set of eight 2D ejecta configurations produced considerable diversity in Pcont (λ ~ 7000 Å), although its maximum of 1–4% systematically occurs around the transition to the nebular phase. Before and after this transition, Pcont may be null, constant, rising, or decreasing, which is caused by the complex geometry of the depth-dependent density and ionization and also by optical depth effects. Our modest angle-dependent explosion energy can yield a Pcont of 0.5–1% at early times. Residual optical-depth effects can yield an angle-dependent SN brightness and constant polarization at nebular times. The observed values of Pcont tend to be lower than obtained here. This suggests that more complicated geometries with competing large-scale structures cancel the polarization. Extreme asymmetries seem to be excluded.

“Tektology”, VSM and the digital age

PurposeI examine Bogdanov’s notion of Tektology within the context of modern communication systems and political agendas.Design/methodology/approachThe practicality of Tektology from the perspective of 21st century sensibilities.FindingsI argue that, like the implications of creating a suitable environment in Red Star, the practicality of enabling tektology in the 21st century is unlikely.Research limitations/implicationsTektology was an idea created in the early 20th century and the social conditions of that era-especially in Russia. The work associated with it is Stafford Beers VSM – an idea of combining the two was suggested by Jackson in 2023. Clearly, the early ideas rely on the source material of that era which are taken within the context of now. A mixture of early 20th and 21st century references are referred to. To limit such a topic as this to the word limits of the journal necessitates reducing discussion, for example the link between Tektology and Happiness.Practical implicationsIt is not possible to test these ideas in a practical sense. The discussion relies upon what Tektology proposes and the way in which ICT is used in the 21 century. The only practical attempt of using technology as a major control system is that of Beer’s Chilean project but Tektolgy was more ambitious; it was aimed at creating a new society. The paper can only relate to observations about the way ICTs are used and controlled presentlySocial implicationsThe paper highlights the way that communication platforms are used and controlled in western society and elsewhere.Originality/valueWhile attempts have been made to link Tektology to modern communication technologies few consider it within the context of 21st century cultural, political and media experience.

The role of carbon in red giant spectro-seismology

ABSTRACT Although red clump stars function as reliable standard candles, their surface characteristics (i.e. Teff, log g, and [Fe/H]) overlap with those of red giant branch stars, which are not standard candles. Recent results have revealed that spectral features containing carbon (e.g. CN molecular bands) carry information correlating with the ‘gold-standard’ asteroseismic classifiers that distinguish red clump from red giant branch stars. However, the underlying astrophysical processes driving the correlation between these spectroscopic and asteroseismic quantities in red giants remain inadequately explored. This study aims to enhance our understanding of this ‘spectro-seismic’ effect by refining the list of key spectral features predicting red giant evolutionary state. In addition, we conduct further investigation into those key spectral features to probe the astrophysical processes driving this connection. We employ the data-driven The Cannon algorithm to analyse high-resolution (R ∼ 80 000) Veloce Rosso spectra from the Anglo-Australian Telescope for 301 red giant stars (where asteroseismic classifications from the TESS mission are known for 123 of the stars). The results highlight molecular spectroscopic features, particularly those containing carbon (e.g. CN), as the primary indicators of the evolutionary states of red giant stars. Furthermore, by investigating CN isotopic pairs (that is, 12C14N and 13C14N), we find suggestions of statistically significant differences in the reduced equivalent widths of such lines, suggesting that physical processes that change the surface abundances and isotopic ratios in red giant stars, such as deep mixing, are the driving forces of the ‘spectro-seismic’ connection of red giants.

Effect of nuclear reactions rates and core boundary mixing on the seismology of red clump stars

Context. Modeling of the stars in the red clump (RC), that is, core helium-burning stars that have gone through a He flash, is challenging because of the uncertainties associated with the physical processes in their core and during the helium flash. By probing the internal stellar structure, asteroseismology allows us to constrain the core properties of RC stars and eventually, to improve our understanding of this evolutionary phase. Aims. We aim to quantify the impact on the seismic properties of the RC stars of the two main core modeling uncertainties: core boundary mixing, and helium-burning nuclear reaction rates. Methods. Using the MESA stellar evolution code, we computed models with different core boundary mixing as well as different 3α and 12C(α, γ)16O nuclear reaction rates. We investigated the impact of these parameters on the period spacing ΔΠ, which is a probe of the region around the core. Results. We find that different core boundary mixing schemes yield significantly different period spacings, with differences of 30 s between the maximum ΔΠ value computed with semiconvection and maximal overshoot. We show that an increased rate of 12C(α, γ)16O lengthens the core helium-burning phase, which extends the range of ΔΠ covered by the models during their evolution. This results in a difference of 10 s between the models computed with a nominal rate and a rate multiplied by 2, which exceeds the observational uncertainties. The effect of changing the 3α reaction rate is comparatively small. Conclusions. The core boundary mixing is the main source of uncertainty in the seismic modeling of RC stars. Moreover, the effect of the 12C(α, γ)16O is non-negligible, even though it is difficult to distinguish from the effect of the mixing. This degeneracy could be seen more frequently in the future in the new seismic data from the PLATO mission and through theoretical constraints from numerical simulations.

Metallicity Distribution in the LMC and the SMC Based on the Tip-RGB Colors

The color index (J − K)0 of tip-red-giant branch (TRGB) is used to study the metallicity distribution in the Large and Small Magellanic Cloud. With the most complete and pure sample of red member stars so far, the areas are divided into 154 and 70 bins for the LMC and SMC, respectively, with similar number of stars by the Voronoi binning. For each bin, the position of TRGB on the near-infrared color–magnitude diagram, specifically (J − K)0/K 0, is determined by the poison-noise weighted method. Converting the color index of TRGB into metallicity, the metallicity gradients in the LMC and the SMC are obtained in four major directions. For the LMC, the gradient to the north is −0.006 ± 0.004 dex kpc−1, to the south −0.010 ± 0.005 dex kpc−1, to the east −0.006 ± 0.003 dex kpc−1, and to the west −0.010 ± 0.003 dex kpc−1. The farthest distance extends to 16 kpc. For the SMC, the gradients to the north, south, east, and west are −0.017 ± 0.031 dex kpc−1, −0.016 ± 0.007 dex kpc−1, −0.003 ± 0.002 dex kpc−1, and −0.004 ± 0.003 dex kpc−1, respectively. The farthest distance for the SMC extends to 27 kpc. The gradient is large from the center to 1 kpc.

The Blanco DECam Bulge Survey (BDBS)

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.

Convective-core overshooting and the final fate of massive stars

A massive star can explode in powerful supernova (SN) and form a neutron star, but it may also collapse directly into a black hole. Understanding and predicting the final fate of such stars is increasingly important, for instance, in the context of gravitational-wave astronomy. The interior mixing of stars (in general) and convective boundary mixing (in particular) remain some of the largest uncertainties in their evolution. Here, we investigate the influence of convective boundary mixing on the pre-SN structure and explosion properties of massive stars. Using the 1D stellar evolution code MESA, we modeled single, non-rotating stars of solar metallicity, with initial masses of 5 − 70 M⊙ and convective core step-overshooting of 0.05 − 0.50 pressure scale heights. Stars were evolved until the onset of iron core collapse and the pre-SN models were exploded using a parametric, semi-analytic SN code. We used the compactness parameter to describe the interior structure of stars at core collapse and we found a pronounced peak in compactness at carbon-oxygen core masses of MCO ≈ 7 M⊙, along with generally high compactness at MCO ≳ 14 M⊙. Larger convective core overshooting will shift the location of the compactness peak by 1 − 2 M⊙ to higher MCO. These core masses correspond to initial masses of 24 M⊙ (19 M⊙) and ≳40 M⊙ (≳30 M⊙), respectively, in models with the lowest (highest) convective core overshooting parameter. In both high-compactness regimes, stars are found to collapse into black holes. As the luminosity of the pre-supernova progenitor is determined by MCO, we predict black hole formation for progenitors with luminosities of 5.35 ≤ log(L/L⊙)≤5.50 and log(L/L⊙)≥5.80. The luminosity range of black hole formation from stars in the compactness peak is in good agreement with the observed luminosity of the red supergiant star N6946 BH1, which disappeared without a bright supernova, indicating that it had likely collapsed into a black hole. While some of our models in the luminosity range of log(L/L⊙) = 5.1 − 5.5 do indeed collapse to form black holes, this does not fully explain the lack of observed SN IIP progenitors at these luminosities. This case specifically refers to the “missing red supergiant” problem. The amount of convective boundary mixing also affects the wind mass loss of stars, such that the lowest black hole masses are 15 M⊙ and 10 M⊙ in our models, with the lowest and highest convective core overshooting parameter, respectively. The compactness parameter, central specific entropy, and iron core mass describe a qualitatively similar landscape as a function of MCO, and we find that entropy is a particularly good predictor of the neutron-star masses in our models. We find no correlation between the explosion energy, kick velocity, and nickel mass production with the convective core overshooting value, but we do see a tight relation with the compactness parameter. Furthermore, we show how convective core overshooting affects the pre-supernova locations of stars in the Hertzsprung–Russell diagram (HRD) and the plateau luminosity and duration of SN IIP light curves.

Measurements of visual double stars with PISCO2 at the Nice 76‐cm refractor in 2016–2017

AbstractWe present relative astrometric and photometric measurements of visual double stars made in 2016–2017, with PISCO2 installed at the 76‐cm refractor of Côte d'Azur Observatory in Nice (France). Our observing list contains orbital couples as well as double stars whose motion is still uncertain. Three different techniques were used for obtaining measurements: Lucky Imaging, Speckle Interferometry and the direct vector autocorrelation (DVA) method. From our observations of 1,510 multiple stars, we obtained 2,918 new measurements with angular separations in the range 0″.1–20″ and an average accuracy of . The mean error on the position angles is 1°.1. Most of the position angles were determined without the usual 180° ambiguity with the application of the DVA technique and/or by inspection of the Lucky images or the long integration files. We managed to routinely monitor faint systems () with large magnitude differences (up to ). We have thus been able to measure six systems containing red dwarf stars that had been poorly monitored since their discovery, from which we estimated the stellar masses thanks to Gaia measurements. We also measured the magnitude difference of the two components of 593 double stars with a mean error of 0.1 mag. Thanks to good seeing images and with the use of high‐contrast numerical filters, we have also been able to obtain 46 measurements with an angular separation smaller than the diffraction limit of our instrumentation. Except for a few objects that have been discussed, our measurements are in good agreement with the ephemerides computed with published orbital elements, even for the double stars whose separation is smaller than the diffraction limit. We also report the measurements of 205 new double stars that we found in the files obtained during the observations.

Induksi Kalus dari Hipokotil Belimbing Merah (Baccaurea angulata) dengan Penambahan 2,4-D (Dichlorophenoxy Acetic Acid) dan BAP (6-Benzyl Amino Purin)

Red starfruit is one of the endemic plants of Kalimantan which produces secondary metabolites which has been empirically used as antioxidant, antibacterial, and anticancer. This plant has a long reproductive period and seedless fruit is often found during the fruiting season, which is a problem for the sustainability of the red starfruit in nature. Conservation of red star fruit for propagation and production of secondary metabolites can be done in vitro through callus culture. This research aims to determine the effect of adding the growth regulators dichlorophenoxy acetic acid (2,4-D) and 6-benzyl amino purine (BAP) on callus induction time, percentage of callus forming explants, callus color and texture, and callus growth. This research used a Completely Randomized Design (CRD) with a factorial pattern consisting of two treatment factors, namely 2,4-D (0; 0.25; 0.5; 0.75; 1 ppm) and BAP (0; 0.25; 0.5; 0.75; 1 ppm). The percentage of explants forming callus (%), the time the callus appeared (days after planting), the color and texture of the callus, the wet weight and dry weight of the callus (g) were research observation parameters.The results showed that the single factor 2,4-D, single factor BAP, and the interaction of 2,4-D and BAP had a significant effect to callus appearance time. Single administration of 2,4-D and BAP had a significant effect on callus dry weight. The color variations of the callus produced are white, green and brown with a compact texture. The fastest callus emergence time was at 11.00 days after planting (DAP), namely in the combination treatment of 1 ppm 2,4-D and 0.75 ppm BAP, single treatment 0.75 ppm and 1 ppm 2,4- D. The highest average dry weight of 0.024 g was obtained in the single treatment of 0.75 ppm BAP.

Constraining stellar and orbital co-evolution through ensemble seismology of solar-like oscillators in binary systems

Context. Binary systems constitute a valuable astrophysics tool for testing our understanding of stellar structure and evolution. Systems containing at least one oscillating component are interesting in this regard because asteroseismology offers independent parameters for the oscillating component that aid in the analysis. Systems of particular interest include those with known inclinations. With ∼0.8 million binary candidates, the two-body orbit catalog (TBO) of Gaia Data Release 3 (DR3) substantially increases the number of known binaries and the quality of the astrometric data available for them. Aims. To enlarge the sample of these astrophysically valuable benchmark objects, we searched for new binary system candidates identified in the Gaia DR3 TBO, for which one component has a detection of solar-like oscillations reported in the literature. Methods. We cross-matched the TBO, the full non-single star (NSS) and eclipsing binary catalogs from Gaia DR3 with catalogs of confirmed solar-like oscillators in the main-sequence and red-giant phase from the NASA Kepler mission and stars in the Southern Continuous Viewing Zone of NASA TESS. The wealth of seismic information is used to characterize the oscillating primary. To test the completeness and robustness of the values reported in the TBO catalog, we performed a similar analysis on stars of the Ninth Catalog of Spectroscopic Binary Orbits (SB9). Results. The analysis of the SB9 reveals an overall completeness factor for the Gaia TBO catalog of up to ∼30% providing reliable orbital parameters for ≥90% of the systems below Porb, SB9 ≲ 250 d. We obtained new 954 unique binary system candidates from Gaia DR3, which host solar-like oscillators, of which we found 45 stars in binary candidates to be on the main sequence and 909 in the red giant phase. Additionally, we report 918 oscillators in potentially long-periodic systems. We present the seismic properties of the full sample and test whether the reported orbital periods are physically possible. For 146 giants, the evolutionary state has been determined from their mixed-mode period spacing, showing a clear trend to long periodic and less eccentric systems in the advanced phases of stellar evolution. Two new eclipsing binary systems, hosting a red-giant primary were found. For another 146 systems hosting oscillating stars, the values for the orbital inclination were found in the TBO. Of 181 TBO candidate systems observed multiple times with APOGEE, 149 (82%) are confirmed as binaries from radial-velocity (RV) measurement. Conclusions. We conclude that the grand majority of the orbital elements reported in the TBO catalog are physically reasonable and realistic. This finding increases the number included in the sample of known solar-like oscillators in binary systems by an order of magnitude. The large fraction of confirmed binaries from APOGEE RV measurements indicates that the TBO catalog is robust. We suggest that due to instrumental noise, the seismically inferred masses and radii of stars observed with the TESS satellite and with an excess of oscillation power of νmax ≲ 30 μHz could be significantly overestimated. The differences in the distributions of the orbital period and eccentricity are due to the accumulative effect of the equilibrium tide acting in these evolved binary systems.

New candidate hypervelocity red clump stars in the inner Galactic bulge

ABSTRACT We search for high-velocity stars in the inner region of the Galactic bulge using a selected sample of red clump stars. Some of those stars might be considered hypervelocity stars (HVSs). Even though the HVSs ejection relies on an interaction with the supermassive black hole (SMBH) at the centre of the Galaxy, there are no confirmed detections of HVSs in the inner region of our Galaxy. With the detection of HVSs, ejection mechanism models can be constrained by exploring the stellar dynamics in the Galactic centre through a recent stellar interaction with the SMBH. Based on a previously developed methodology by our group, we searched with a sample of preliminary data from version 2 of the Vista Variables in the Via Lactea (VVV) Infrared Astrometric Catalogue (VIRAC2) and Gaia DR3 data, including accurate optical and near-infrared proper motions. This search resulted in a sample of 46 stars with transverse velocities larger than the local escape velocity within the Galactic bulge, of which four are prime candidate HVSs with high-proper motions consistent with being ejections from the Galactic centre. Adding to that, we studied a sample of reddened stars without a Gaia DR3 counterpart and found 481 stars with transverse velocities larger than the local escape velocity, from which 65 stars have proper motions pointing out of the Galactic centre and are candidate HVSs. In total, we found 69 candidate HVSs pointing away from the Galactic centre with transverse velocities larger than the local escape velocity.

Uniting and APOGEE to unveil the cosmic chemistry of the Milky Way disc

The spatial distribution of Galactic stars with different chemical abundances encodes information on the processes that drove the formation and evolution of the Milky Way. Survey selection functions are indispensable for analysing astronomical catalogues produced by large-scale surveys. The use of these selection functions in data modelling is more complex when data from different surveys are to be modelled simultaneously. We introduce a procedure for constructing the selection function of a sample of red clump stars that have parallaxes and elemental abundances from the mission. We separately constructed the selection function of the APOGEE DR17 red clump stars, which depends on very different observables and has a very different spatial coverage. We combined the two surveys and accounted for their joint selection function to provide strong constraints on the radial and vertical density distribution of mono-abundance populations, with offering a dense coverage of the solar neighbourhood, while APOGEE reaches larger distances near the Galactic plane. We confirm that the radial density profile steepens with increasing metallicity. The combined sample also indicates a metallicity-dependent flaring of the alpha -poor disc. We provide the code for constructing the selection function we used in this study through the GaiaUnlimited Python package.

Evolved Massive Stars at Low Metallicity. VI. Mass-loss Rate of Red Supergiant Stars in the Large Magellanic Cloud

Mass loss is a crucial process that affects the observational properties, evolution path, and fate of highly evolved stars. However, the mechanism of mass loss is still unclear, and the mass-loss rate (MLR) of red supergiant stars (RSGs) requires further research and precise evaluation. To address this, we utilized an updated and complete sample of RSGs in the Large Magellanic Cloud (LMC) and employed the 2-DUST radiation transfer model and spectral energy distribution fitting approach to determine the dust-production rates (DPRs) and dust properties of the RSGs. We have fitted 4714 selected RSGs with over 100,000 theoretical templates of evolved stars. Our results show that the DPR range of RSGs in the LMC is 10−11 M ⊙ yr−1–10−7 M ⊙ yr−1, and the total DPR of all RSGs is 1.14 ×10−6 M ⊙ yr−1. We find that 63.3% RSGs are oxygen-rich, and they account for 97.2% of the total DPR. The optically thin RSG, which comprise 30.6% of our sample, contribute only 0.1% of the total DPR, while carbon-rich RSGs (6.1%) produce 2.7% of the total DPR. Overall, 208 RSGs contributed 76.6% of the total DPR. We have established a new relationship between the MLR and luminosity of RSGs in the LMC, which exhibits a positive trend and a clear turning point at logL/L⊙≈4.4 .

Discovery of new red stars with digitized plates of the μ Cephei range

The results of the spectral classification of 357 red stars observed in the Cepheus region are presented. 257 of the featured stars are included in the KP2001 catalogue. We found the remaining 100 red stars as a result of digitizing plates used in compiling the KP2001 catalog. All star data is taken from the GAIA DR3 database. These stars are most likely giants and supergiants. None of them were included in the catalog of variable stars. It has been suggested that further research may reveal variability in many of these.

Locked differential rotation in core-helium burning red giants

Context. Oscillation modes of a mixed character are able to probe the inner region of evolved low-mass stars and offer access to a range of information, in particular, the mean core rotation. Ensemble asteroseismology observations are then able to provide clear views on the transfer of angular momentum when stars evolve as red giants. Aims. Previous catalogs of core rotation rates in evolved low-mass stars have focussed on hydrogen-shell burning stars. Our aim is to complete the compilation of rotation measurements toward more evolved stages, with a detailed analysis of the mean core rotation in core-helium burning giants. Methods. The asymptotic expansion for dipole mixed modes allows us to fit oscillation spectra of red clump stars and derive their core rotation rates. We used a range of prior seismic analyses, complete with new data, to get statistically significant results. Results. We measured the mean core rotation rates for more than 1500 red clump stars. We find that the evolution of the core rotation rate in core-helium-burning stars scales with the inverse square of the stellar radius, with a small dependence on mass. Conclusions. Assuming the conservation of the global angular momentum, a simple model allows us to infer that the mean core rotation and envelope rotation are necessarily coupled. The coupling mechanism ensures that the differential rotation in core-helium-burning red giants is locked.

Blue Straggler Stars of NGC 7789 and NGC 2506 Using AstroSat/UVIT

Blue straggler stars are intriguing objects that seem to defy the standard theory of single-star evolution. They manage to elongate their main-sequence lifetimes by acquiring mass either in a direct stellar collision or through mass transfer in a binary or in mergers. We study the candidate blue straggler stars in two intermediate-age open clusters NGC 7789 and NGC 2506 using the far-UV and near-UV observations from the UV imaging telescope of AstroSat in combination with other multi-wavelength data. Around 45% of blue straggler star candidates show an excess in the UV wavelengths and are fitted with two-component spectral energy distributions. We detect most of these blue straggler stars to contain a low-mass or extremely low-mass white dwarf as a hot companion, whereas some yellow straggler stars and red clump stars with white dwarfs of normal mass or high mass as a companion. Based on our analysis, we infer that around 36% of blue straggler stars have likely formed via mass transfer by the Case-A/Case-B mechanism in these two clusters.

Mapping the Galactic Disk with the LAMOST and Gaia Red Clump Sample. VIII. Mapping the Kinematics of the Galactic Disk Using Mono-age and Mono-abundance Stellar Populations

We present a comprehensive study of the kinematic properties of the different Galactic disk populations, as defined by the chemical abundance ratios and stellar ages, across a large disk volume (4.5 ≤ R ≤ 15.0 kpc and ∣Z∣ ≤ 3.0 kpc), by using the LAMOST-Gaia red clump sample stars. We determine the median velocities for various spatial and population bins, finding large-scale bulk motions; for example, the wave-like behavior in radial velocity, the north–south discrepancy in azimuthal velocity and the warp signal in vertical velocity, and the amplitudes and spatial dependences of these bulk motions show significant variations for different mono-age and mono-abundance populations. The global spatial behaviors of the velocity dispersions clearly show a signal of spiral arms and a signal of the disk perturbation event within 4 Gyr, as well as disk flaring in the outer region (i.e., R ≥ 12 kpc), mostly for young or alpha-poor stellar populations. Our detailed measurements of age/[α/Fe]-velocity dispersion relations for different disk volumes indicate that young/α-poor populations are likely to originate from dynamic heating by both giant molecular clouds and spiral arms, while old/α-enhanced populations require an obvious contribution from other heating mechanisms, such as merger and accretion, or are born in the chaotic mergers of gas-rich systems and/or turbulent interstellar medium.

ALMA detection of CO rotational line emission in red supergiant stars of the massive young star cluster RSGC1

Context. The fate of stars largely depends on the amount of mass lost during the end stages of evolution. For single stars with an initial mass between ∼8–30 M⊙, most mass is lost during the red supergiant (RSG) phase, when stellar winds deplete the H-rich envelope. However, the RSG mass-loss rate (Ṁ) is poorly understood theoretically, and so stellar evolution models rely on empirically derived mass-loss rate prescriptions. However, it has been shown that these empirical relations differ largely, with differences up to 2 orders of magnitude. Aims. We aim to derive a new mass-loss rate prescription for RSGs that is not afflicted with some uncertainties inherent in preceding studies. Methods. We have observed CO rotational line emission towards a sample of RSGs in the open cluster RSGC1 that all are of a similar initial mass. The ALMA CO(2–1) line detections allowed us to retrieve the gas mass-loss rates (ṀCO). In contrast to mass-loss rates derived from the analysis of dust spectral features (ṀSED), the data allowed us a direct determination of the wind velocity and no uncertain dust-to-gas correction factor was needed. Results. Five RSGs in RSGC1 have been detected in CO(2–1). The retrieved ṀCO values are systematically lower than ṀSED. Although only five RSGs in RSGC1 have been detected, the data allow us to propose a new mass-loss rate relation for M-type red supergiants with effective temperatures between ∼3200 and 3800 K that is dependent on the luminosity and initial mass, and that is valid during the phase where nuclear burning determines the evolution along the RSG branch. The new mass-loss rate relation is based on the new ṀCO values for the RSGs in RSGC1 and on prior ṀSED values for RSGs in four clusters, including RSGC1. The new Ṁ-prescription yields a good prediction for the mass-loss rate of some well-known Galactic RSGs that are observed in multiple CO rotational lines, including α Ori, μ Cep and VX Sgr. Moreover, there are indications that a stronger, potentially eruptive, mass-loss process is occurring during some fraction of the RSG lifetime, suggesting that RSGs might experience a phase change in mass loss leading to the wind mass-loss rate dominating the RSG evolution at that stage. Conclusions. Implementing a lower mass-loss rate in evolution codes for massive stars has important consequences as to the nature of their end-state. A reduction of the RSG mass-loss rate implies that quiescent RSG mass loss is not enough to strip a single star’s hydrogen-rich envelope. Upon core collapse such single stars would explode as RSGs. Mass-loss rates of order ∼6 times higher would be needed to strip the H-rich envelope and produce a Wolf-Rayet star while evolving back to the blue side of the Hertzsprung–Russell diagram. Future observations of a larger sample of RSGs in open clusters should allow a more stringent determination of the ṀCO–luminosity relation and a sharper diagnostic as to when the phase change in mass loss is occurring.

Observation of significant photosynthesis in garden cress and cyanobacteria under simulated illumination from a K dwarf star

Abstract Stars with about 45 to 80% the mass of the Sun, so-called K dwarf stars, have previously been proposed as optimal host stars in the search for habitable extrasolar worlds. These stars are abundant, have stable luminosities over billions of years longer than Sun-like stars, and offer favourable space environmental conditions. So far, the theoretical and experimental focus on exoplanet habitability has been on even less massive, though potentially less hospitable red dwarf stars. Here we present the first experimental data on the responses of photosynthetic organisms to a simulated K dwarf spectrum. We find that garden cress Lepidium sativum under K-dwarf radiation exhibits comparable growth and photosynthetic efficiency as under Solar illumination on Earth. The cyanobacterium Chroococcidiopsis sp. CCMEE 029 exhibits significantly higher photosynthetic efficiency and culture growth under K dwarf radiation compared to Solar conditions. Our findings of the affirmative responses of these two photosynthetic organisms to K dwarf radiation suggest that exoplanets in the habitable zones around such stars deserve high priority in the search for extrasolar life.

Disentangling Stellar Age Estimates from Galactic Chemodynamical Evolution

Stellar ages are key for determining the formation history of the Milky Way, but are difficult to measure precisely. Furthermore, methods that use chemical abundances to infer ages may entangle the intrinsic evolution of stars with the chemodynamical evolution of the Galaxy. In this paper, we present a framework for making probabilistic predictions of stellar ages, and then quantify the contribution of both stellar evolution and Galactic chemical evolution to those predictions using SHapley Additive exPlanations. We apply this interpretable prediction framework to both a simulated Milky Way sample containing stars in a variety of evolutionary stages and an APOGEE-mocked sample of red clump stars. We find that in the former case, stellar evolution is the dominant driver for age estimates, while in the latter case, the more restricted evolutionary information causes the model to proxy ages through the chemical evolution model. We show that as a result of the use of nonintrinsic Galactic chemical information, trends estimated with the predicted ages, such as the age–metallicity relation, can deviate from the truth.