Early Stars Research Articles

The Effect of Warm Dark Matter on Early Star Formation Histories of Massive Galaxies: Predictions from the CROC Simulations

Abstract Several massive (M * > 108 M ⊙), high-redshift (z = 8–10) galaxies have recently been discovered to contain stars with ages of several hundred million years, pushing the onset of star formation in these galaxies back to z ∼ 15. The very existence of stars formed so early may serve as a test for cosmological models with suppressed small-scale power (and, hence, late formation of cosmic structure). We explore the ages of the oldest stars in numerical simulations from the Cosmic Reionization On Computers project with cold dark matter (CDM) and two warm dark matter (WDM) cosmologies with 3 and 6 keV particles. There are statistically significant differences of ∼5 Myr between average stellar ages of massive galaxies in CDM and 3 keV WDM, while CDM and 6 keV WDM are statistically indistinguishable. Even this 5 Myr difference, however, is much less than current observational uncertainties on the stellar population properties of high-redshift galaxies. The age distributions of all galaxies in all cosmologies fail to produce a substantial Balmer break, although uncertainties in dust attenuation are a potentially significant factor. Finally, we assess the convergence of our simulation predictions and find that the systematic uncertainties on individual galaxy properties are comparable to the differences between cosmologies, suggesting these differences may not be numerically robust.

Fundamental Parameters of the Eclipsing Binary DD CMa and Evidence for Mass Exchange

Abstract We present a detailed photometric and spectroscopic analysis of DD CMa, based on published survey photometry and new spectroscopic data. We find an improved orbital period of P o = 2.0084530(6) days. Our spectra reveal Hβ and Hα absorptions with weak emission shoulders, and we also find a color excess in the Wide-field Infrared Survey Explorer multiband photometry, interpreted as signatures of circumstellar matter. We model the V-band orbital light curve derived from the ASAS and ASAS-SN surveys, assuming a semidetached configuration and using the mass ratio and temperature of the hotter star derived from our spectroscopic analysis. Our model indicates that the system consists of a B2.5 dwarf and a B9 giant of radii 3.2 and 3.7 R ⊙, respectively, orbiting in a circular orbit of radius 6.75 R ⊙. We also found M c = 1.7 ± 0.1 M ⊙, T c = 11,350 ± 100 K, and M h = 6.4 ± 0.1 M ⊙, T h = 20,000 ± 500 K, for the cooler and hotter star, respectively. We find broad single emission peaks in Hα and Hβ after subtracting the synthetic stellar spectra. Our results are consistent with mass exchange between the stars and suggest the existence of a stream of gas being accreted onto the early B-type star.

These are not the Stars You are Looking for: On the Detection of X-Ray Emission from HD 143352

Abstract As part of a search for X-ray emission from RV Tau variable stars, we discovered a serendipitous X-ray detection of the closest RV Tau variable star, HD 143352. X-rays were detected in the 0.2–2.0 keV energy band, with most counts detected in the 0.5–1.0 keV band. The emission is consistent with a 106 K plasma and L X ∼ 2 × 1028 erg s−1. This would be the second RV Tau star detected in X-ray emission. However, after estimating the temperature (T eff ∼ 6000 K) and bolometric luminosity (L bol ∼ 4L ⊙) from the spectral energy distribution, we place HD 143352 on the main sequence. These stellar parameters suggest HD 143352 is neither an RV Tau variable nor a post-asymptotic giant branch star nor a super giant, but rather an early F-type main sequence star. The X-ray emission detected from HD 143352 is consistent with coronal-like emission with L X/L bol ∼ 10−6.

The Star Formation History of Eridanus II: On the Role of Supernova Feedback in the Quenching of Ultrafaint Dwarf Galaxies*

Abstract Eridanus II (Eri II) is an ultrafaint dwarf (UFD) galaxy (M V = −7.1) located at a distance close to the Milky Way virial radius. Early shallow color–magnitude diagrams (CMDs) indicated that it possibly hosted an intermediate-age or even young stellar population, which is unusual for a galaxy of this mass. In this paper, we present new Hubble Space Telescope/Advanced Camera for Surveys CMDs reaching the oldest main-sequence turnoff with excellent photometric precision and derive a precise star formation history (SFH) for this galaxy through CMD fitting. This SFH shows that the bulk of the stellar mass in Eri II formed in an extremely short star formation burst at the earliest possible time. The derived star formation rate profile has a width at half maximum of 500 Myr and reaches a value compatible with null star formation 13 Gyr ago. However, tests with mock stellar populations and with the CMD of the globular cluster M92 indicate that the star formation period could be shorter than 100 Myr. From the quantitative determination of the amount of mass turned into stars in this early star formation burst ( ∼2 × 105 M ⊙) we infer the number of supernova (SN) events and the corresponding energy injected into the interstellar medium. For reasonable estimates of the Eri II virial mass and values of the coupling efficiency of the SN energy, we conclude that Eri II could be quenched by SN feedback alone, thus casting doubts on the need to invoke cosmic reionization as the preferred explanation for the early quenching of old UFD galaxies.

Where Have All the Solar-like Stars Gone? Rotation Period Detectability at Various Inclinations and Metallicities

Abstract The plethora of photometric data collected by the Kepler space telescope has promoted the detection of tens of thousands of stellar rotation periods. However, these periods are not found to an equal extent among different spectral types. Interestingly, early G-type stars with near-solar rotation periods are strongly underrepresented among those stars with known rotation periods. In this study we investigate whether the small number of such stars can be explained by difficulties in the period determination from photometric time series. For that purpose, we generate model light curves of early G-type stars with solar rotation periods for different inclination angles, metallicities, and (magnitude-dependent) noise levels. We find that the detectability is determined by the predominant type of activity (i.e., spot or faculae domination) on the surface, which defines the degree of irregularity of the light curve, and further depends on the level of photometric noise. These two effects significantly complicate the period detection and explain the lack of solar-like stars with known near-solar rotation periods. We conclude that the rotation periods of the majority of solar-like stars with near-solar rotation periods remain undetected to date. Finally, we promote the use of new techniques to recover more periods of near-solar rotators.

Lithium depletion and angular momentum transport in solar-type stars

Context. Transport processes occurring in the radiative interior of solar-type stars are evidenced by the surface variation of light elements, in particular 7Li, and the evolution of their rotation rates. For the Sun, inversions of helioseismic data indicate that the radial profile of angular velocity in its radiative zone is nearly uniform, which implies the existence of angular momentum transport mechanisms that are efficient over evolutionary timescales. While there are many independent transport models for angular momentum and chemical species, there is a lack of self-consistent theories that permit stellar evolution models to simultaneously match the present-day observations of solar lithium abundances and radial rotation profiles. Aims. We explore how additional transport processes can improve the agreement between evolutionary models of rotating stars and observations for 7Li depletion, the rotation evolution of solar-type stars, and the solar rotation profile. Methods. Models of solar-type stars are computed including atomic diffusion and rotation-induced mixing with the code STAREVOL. We explore different additional transport processes for chemicals and for angular momentum such as penetrative convection, tachocline mixing, and additional turbulence. We constrain the resulting models by simultaneously using the evolution of the surface rotation rate and 7Li abundance in the solar-type stars of open clusters with different ages, and the solar surface and internal rotation profile as inverted from helioseismology when our models reach the age of the Sun. Results. We show the relevance of penetrative convection for the depletion of 7Li in pre-main sequence and early main sequence stars. The rotational dependence of the depth of penetrative convection yields an anti-correlation between the initial rotation rate and 7Li depletion in our models of solar-type stars that is in agreement with the observed trend. Simultaneously, the addition of an ad hoc vertical viscosity νadd leads to efficient transport of angular momentum between the core and the envelope during the main sequence evolution and to solar-type models that match the observed profile of the Sun. We also self-consistently compute for the first time the thickness of the tachocline and find that it is compatible with helioseismic estimations at the age of the Sun, but we highlight that the associated turbulence does not allow the observed 7Li depletion to be reproduced. The main sequence depletion of 7Li in solar-type stars is only reproduced when adding a parametric turbulent mixing below the convective envelope. Conclusions. The need for additional transport processes in stellar evolution models for both chemicals and angular momentum in addition to atomic diffusion, meridional circulation, and turbulent shear is confirmed. We identify the rotational dependence of the penetrative convection as a key process. Two additional and distinct parametric turbulent mixing processes (one for angular momentum and one for chemicals) are required to simultaneously explain the observed surface 7Li depletion and the solar internal rotation profile. We highlight the need of additional constraints for the internal rotation of young solar-type stars and also for the beryllium abundances of open clusters in order to test our predictions.

Statistical treatment of nuclear clusters in the continuum

The evaluation of the sub-saturation nuclear equation of state at finite temperature requires a proper state counting of the internal partition sum of nuclei which are immersed in the background of their continuum states. This classical statistical problem is addressed within the self-consistent mean-field approximation, which naturally accounts for isospin and effective mass effects in the nuclear density of states. The nuclear free energy is decomposed into bulk and surface terms, allowing a simple analytical prescription for the subtraction of gas states from the nuclear partition sum, that avoids double counting of unbound single particle states. We show that this correction leads to a sizeable effect in the composition of matter at high temperature and low proton fractions, such as it is formed in supernova collapse, early proto-neutron star evolution, as well as laboratory experiments. Specifically, the energy stored in the internal nuclear degrees of freedom is reduced, as well as the mass fraction of heavy clusters in the statistical equilibrium. The gas subtraction prescription is compared to different phenomenological methods proposed in the literature, based on a high energy truncation of the partition sum. We show that none of these methods satisfactorily reproduces the gas subtracted level density, if the temperature overcomes ~4 MeV.

Overview and reassessment of noise budget of starshade exoplanet imaging

High-contrast imaging enabled by a starshade in formation flight with a space telescope can provide a near-term pathway to search for and characterize temperate and small planets of nearby stars. NASA's Starshade Technology Development Activity to TRL5 (S5) is rapidly maturing the required technologies to the point at which starshades could be integrated into potential future missions. Here we reappraise the noise budget of starshade-enabled exoplanet imaging to incorporate the experimentally demonstrated optical performance of the starshade and its optical edge. Our analyses of stray light sources - including the leakage through micrometeoroid damage and the reflection of bright celestial bodies - indicate that sunlight scattered by the optical edge (i.e., the solar glint) is by far the dominant stray light. With telescope and observation parameters that approximately correspond to Starshade Rendezvous with Roman and HabEx, we find that the dominating noise source would be exozodiacal light for characterizing a temperate and Earth-sized planet around Sun-like and earlier stars and the solar glint for later-type stars. Further reducing the brightness of solar glint by a factor of 10 with a coating would prevent it from becoming the dominant noise for both Roman and HabEx. With an instrument contrast of 1E-10, the residual starlight is not a dominant noise; and increasing the contrast level by a factor 10 would not lead to any appreciable change in the expected science performance. If unbiased calibration of the background to the photon-noise limit can be achieved, Starshade Rendezvous with Roman could provide nearly photon-limited spectroscopy of temperate and Earth-sized planets of F, G, and K stars <4 parsecs away, and HabEx could extend this capability to many more stars <8 parsecs. (Abridged)

Cosmology, astrobiology and the RNA world: just add quintessential water

AbstractLaboratory generation of water nanoclusters from amorphous ice and strong terahertz (THz) radiation from water nanoclusters ejected from water vapour into a vacuum suggest the possibility of water nanoclusters ejected into interstellar space from abundant amorphous ice-coated cosmic dust produced by supernovae explosions. Water nanoclusters (section ‘Water nanoclusters’) offer a hypothetical scenario connecting major mysteries of our Universe: dark matter (section ‘Baryonic dark matter’), dark energy (section ‘Dark energy’), cosmology (section ‘Cosmology’), astrobiology (section ‘Astrobiology’) and the RNA world (section ‘The RNA world’) as the origin of life on Earth and habitable exoplanets. Despite their expected low density in space compared to hydrogen, their quantum-entangled diffuse Rydberg electronic states make cosmic water nanoclusters a candidate for baryonic dark matter that can also absorb, via the microscopic dynamical Casimir effect, the virtual photons of zero-point-energy vacuum fluctuations above the nanocluster cut-off vibrational frequencies, leaving only vacuum fluctuations below these frequencies to be gravitationally active, thus leading to a possible common origin of dark matter and dark energy. This picture includes novel explanations of the small cosmological constant, the coincidence of energy and matter densities, possible contributions of the red-shifted THz radiation from cosmic water nanoclusters at redshift z ≅ 10 to the cosmic microwave background (CMB) spectrum, the Hubble constant crisis, the role of water as a known coolant for rapid early star formation and ultimately, how life may have originated from RNA protocells on Earth and exoplanets and moons in the habitable zones of developed solar systems. Together, they lead to a cyclic universe cosmology – based on the proposed equivalence of cosmic water nanoclusters to a quintessence scalar field – instead of a multiverse based on cosmic inflation theory. Recent CMB birefringence measurements may support quintessence. Finally, from the quantum chemistry of water nanoclusters interacting with prebiotic organic molecules, amino acids and RNA protocells on early Earth and habitable exoplanets, this scenario is consistent with the anthropic principle that our Universe must have those properties which allow life, as we know it – based on water, to develop at the present stage of its history.

Gluon polarization measurements from longitudinally polarized proton-proton collisions at STAR

The gluon polarization contribution to the proton spin is an integral part to solve the longstanding proton spin puzzle. At the Relativistic Heavy Ion Collider (RHIC), the STAR experiment has measured jets produced in mid-pseudo-rapidity, |η| < 1.0, and full azimuth, ϕ, from longitudinally polarized pp collisions to study the gluon polarization in the proton. At center of mass energies = 200 and 510 GeV, jet production is dominated by hard QCD scattering processes such as gluon-gluon (gg) and quark-gluon (qg), thus making the longitudinal double-spin asymmetry (ALL ) sensitive to the gluon polarization. Early STAR inclusive jet ALL results at = 200 GeV provided the first evidence of the non-zero gluon polarization at momentum fraction x > 0.05. The higher center of mass energy = 510 GeV allows to explore the gluon polarization as low as x ∼ 0.015. In this talk we will present the recent STAR inclusive jet and dijet ALL results at = 510 GeV, and discuss the relevant new analysis techniques for the estimation of trigger bias and reconstruction uncertainty, the underlying event correction on the jet energy and its effect on jet ALL . Dijet results are shown for different topologies in regions of pseudo-rapidity, effectively scanning the x-dependence of the gluon polarization.

The magnetic early B-type stars – IV. Breakout or leakage? H α emission as a diagnostic of plasma transport in centrifugal magnetospheres

ABSTRACT Rapidly rotating early-type stars with strong magnetic fields frequently show H α emission originating in centrifugal magnetospheres (CMs), circumstellar structures in which centrifugal support due to magnetically enforced corotation of the magnetically confined plasma enables it to accumulate to high densities. It is not currently known whether the CM plasma escapes via centrifugal breakout (CB), or by an unidentified leakage mechanism. We have conducted the first comprehensive examination of the H α emission properties of all stars currently known to display CM-pattern emission. We find that the onset of emission is dependent primarily on the area of the CM, which can be predicted simply by the value BK of the magnetic field at the Kepler corotation radius RK. Emission strength is strongly sensitive to both CM area and BK. Emission onset and strength are not dependent on effective temperature, luminosity, or mass-loss rate. These results all favour a CB scenario; however, the lack of intrinsic variability in any CM diagnostics indicates that CB must be an essentially continuous process, i.e. it effectively acts as a leakage mechanism. We also show that the emission profile shapes are approximately scale-invariant, i.e. they are broadly similar across a wide range of emission strengths and stellar parameters. While the radius of maximum emission correlates closely as expected to RK, it is always larger, contradicting models that predict that emission should peak at RK.

Late Miocene to Late Pliocene (Hemphillian to Blancan) Borophagine Canids (Mammalia: Carnivora) from Idaho

While borophagine canids are known from numerous Tertiary faunas across North America, they have not been well documented from the Tertiary faunas of Idaho. Five species represented by 2 genera are now known from Idaho faunas ranging from the latest Clarendonian / earliest Hemphillian to the late Blancan. The earliest records of borophagines in Idaho are Epicyon haydeni from the early Hemphillian Star Valley fauna and Borophagus pugnator from the late Clarendonian / early Hemphillian Poison Creek Formation. Borophagus secundus is present in the late Hemphillian Chalk Hills Formation, and 2 species are present in the Blancan Glenns Ferry Formation: (1) B. hilli in the early Blancan Hagerman local fauna and (2) the terminal taxon of the subfamily, B. diversidens, in the late Blancan Grand View local fauna.

WASP-186 and WASP-187: two hot Jupiters discovered by SuperWASP and SOPHIE with additional observations by TESS

ABSTRACT We present the discovery of two new hot Jupiters identified from the Wide-Angle Search for Planets (WASP) survey, WASP-186b and WASP-187b (TOI-1494.01 and TOI-1493.01). Their planetary nature was established from SOPHIE spectroscopic observations, and additional photometry was obtained from Transiting Exoplanet Survey Satellite. Stellar parameters for the host stars are derived from spectral line, infrared flux method, and isochrone placement analyses. These parameters are combined with the photometric and radial velocity data in a Markov chain Monte Carlo method to determine the planetary properties. WASP-186b is a massive Jupiter (4.22 ± 0.18 MJ, 1.11 ± 0.03 RJ) orbiting a mid-F star on a 5.03-d eccentric (e = 0.327 ± 0.008) orbit. WASP-187b is a low-density (0.80 ± 0.09 MJ, 1.64 ± 0.05 RJ) planet in a 5.15-d circular orbit around a slightly evolved early F-type star.

Chromospheric activity of nearby Sun-like stars

Context.The chromospheric emission in the cores of the Ca IIH &amp; K lines of late-type dwarfs is a well known indicator of magnetic activity that decreases with increasing stellar age.Aims.I use this indicator to investigate the formation history of nearby G- and early K-type stars with origins at galactocentric distances similar to that of the region where the Sun was born.Methods.A parent sample of single main-sequence stars with near-solar metallicity and known magnetic activity levels is built from catalogues of stellar atmospheric parameters and chromospheric activity indices. A kinematical approach usesGaiaastrometric data to differentiate thin disc stars from thick disc stars. Measured distributions ofR′HKchromospheric activity indices are compared with Monte Carlo simulations based on an empirical model of chromospheric activity evolution.Results.The thin disc includes a significant fraction of Sun-like stars with intermediate activity levels (2 × 10−5≤R′HK≤ 6 × 10−5), while most early K- and G-type stars from the thick disc are inactive (R′HK&lt; 2 × 10−5). The chromospheric activity distribution among nearby Sun-like dwarfs from the thin disc can be explained by a combination of an old (&gt;6–7 Gyr) star formation event (or events) and a more recent (&lt;3 Gyr) burst of star formation. Such an event is not required to account for theR′HKindex distributions of nearby thick disc stars.Conclusions.The distribution of magnetic activity among local G- and early K-type stars with a near-solar metallicity bears the imprint of an important star formation event that occurred ~1.9–2.6 Gyr ago in the thin disc of the Milky Way.

Local group star formation in warm and self-interacting dark matter cosmologies

ABSTRACT The nature of the dark matter can affect the collapse time of dark matter haloes, and can therefore be imprinted in observables such as the stellar population ages and star formation histories of dwarf galaxies. In this paper, we use high-resolution hydrodynamical simulations of Local Group-analogue (LG) volumes in cold dark matter (CDM), sterile neutrino warm dark matter (WDM) and self-interacting dark matter (SIDM) models with the eagle galaxy formation code to study how galaxy formation times change with dark matter model. We are able to identify the same haloes in different simulations, since they share the same initial density field phases. We find that the stellar mass of galaxies depends systematically on resolution, and can differ by as much as a factor of 2 in haloes of a given dark matter mass. The evolution of the stellar populations in SIDM is largely identical to that of CDM, but in WDM early star formation is instead suppressed. The time at which LG haloes can begin to form stars through atomic cooling is delayed by ∼200 Myr in WDM models compared to CDM. It will be necessary to measure stellar ages of old populations to a precision of better than 100 Myr, and to address degeneracies with the redshift of reionization – and potentially other baryonic processes – in order to use these observables to distinguish between dark matter models.

Recombination Lines and Molecular Gas from Hypercompact H ii regions in W51 A

Abstract We present a detailed characterization of the population of compact radio-continuum sources in W51 A using subarcsecond Very Large Array and Atacama Large Millimeter/submillimeter Array observations. We analyze their 2 cm continuum, the recombination lines (RLs) H77α and H30α, and the lines of , , and . We derive diameters for 10/20 sources in the range D ∼ 10−3 to ∼10−2 pc, thus placing them in the regime of hypercompact H ii regions (HC H ii’s). Their continuum-derived electron densities are in the range n e ∼ 104 –105 cm−3, lower than typically considered for HC H ii’s. We combined the RL measurements and independently derived n e, finding the same range of values but significant offsets for individual measurements between the two methods. We find that most of the sources in our sample are ionized by early B-type stars, and a comparison of n e versus D shows that they follow the inverse relation previously derived for ultracompact (UC) and compact H ii’s. When determined, the ionized-gas kinematics is always (7/7) indicative of outflow. Similarly, 5 and 3 out of the 8 HC H ii’s still embedded in a compact core show evidence for expansion and infall motions in the molecular gas, respectively. We hypothesize that there could be two different types of hypercompact (D &lt; 0.05 pc) H ii regions: those that essentially are smaller, expanding UC H ii’s; and those that are also hyperdense (n e &gt; 106 cm−3), probably associated with O-type stars in a specific stage of their formation or early life.

Precise calibration of the dependence of surface brightness–colour relations on colour and class for late-type stars

Context. Surface brightness–colour relations (SBCRs) are used to derive the stellar angular diameters from photometric observations. They have various astrophysical applications, such as the distance determination of eclipsing binaries or the determination of exoplanet parameters. However, strong discrepancies between the SBCRs still exist in the literature, in particular for early and late-type stars. Aims. We aim to calibrate new SBCRs as a function of the spectral type and the luminosity class of the stars. Our goal is also to apply homogeneous criteria to the selection of the reference stars and in view of compiling an exhaustive and up-to-date list of interferometric late-type targets. Methods. We implemented criteria to select measurements in the JMMC Measured Diameters Catalog. We then applied additional criteria on the photometric measurements used to build the SBCRs, together with stellar characteristics diagnostics. Results. We built SBCRs for F5/K7–II/III, F5/K7–IV/V, M–II/III and M–V stars, with respective rms of σFV = 0.0022 mag, σFV = 0.0044 mag, σFV = 0.0046 mag, and σFV = 0.0038 mag. This results in a precision on the angular diameter of 1.0%, 2.0%, 2.1%, and 1.7%, respectively. These relations cover a large V − K colour range of magnitude, from 1 to 7.5. Our work demonstrates that SBCRs are significantly dependent on the spectral type and the luminosity class of the star. Through a new set of interferometric measurements, we demonstrate the critical importance of the selection criteria proposed for the calibration of SBCR. Finally, using the Gaia photometry for our samples, we obtained (G − K) SBCRs with a precision on the angular diameter between 1.1% and 2.4%. Conclusions. By adopting a refined and homogeneous methodology, we show that the spectral type and the class of the star should be considered when applying an SBCR. This is particularly important in the context of PLATO.

High-speed stars: Galactic hitchhikers

Context.The search for stars born in the very early stages of the Milky Way star formation history is of paramount importance in the study of the early Universe since their chemistry carries irreplaceable information on the conditions in which early star formation and galaxy buildup took place. The search for these objects has generally taken the form of expensive surveys for faint extremely metal-poor stars, the most obvious but not the only candidates to a very early formation.Aims.Thanks toGaiaDR2 radial velocities and proper motions, we identified 72 bright cool stars displaying heliocentric transverse velocities in excess of 500 km s−1. These objects are most likely members of extreme outer-halo populations, either formed in the early Milky Way build-up or accreted from since-destroyed self-gravitating stellar systems.Methods.We analysed low-resolution FORS spectra of the 72 stars in the sample and derived the abundances of a few elements. Despite the large uncertainties on the radial velocity determination, we derived reliable orbital parameters for these objects.Results.The stars analysed are mainly slightly metal poor, with a few very metal-poor stars. Their chemical composition is much more homogeneous than expected. All the stars have very eccentric halo orbits, some extending well beyond the expected dimension of the Milky Way.Conclusions.These stars can be the result of a disrupted small galaxy or they could have been globular cluster members. Age estimates suggest that some of them are evolved blue stragglers, now on the subgiant or asymptotic giant branches.

Dark photon dark matter in the presence of inhomogeneous structure

Dark photon dark matter will resonantly convert into visible photons when the dark photon mass is equal to the plasma frequency of the ambient medium. In cosmological contexts, this transition leads to an extremely efficient, albeit short-lived, heating of the surrounding gas. Existing work in this field has been predominantly focused on understanding the implications of these resonant transitions in the limit that the plasma frequency of the Universe can be treated as being perfectly homogeneous, i.e. neglecting inhomogeneities in the electron number density. In this work we focus on the implications of heating from dark photon dark matter in the presence of inhomogeneous structure (which is particularly relevant for dark photons with masses in the range 10−15 eV ≲ mA′ ≲ 10−12 eV), emphasizing both the importance of inhomogeneous energy injection, as well as the sensitivity of cosmological observations to the inhomogeneities themselves. More specifically, we derive modified constraints on dark photon dark matter from the Ly-α forest, and show that the presence of inhomogeneities allows one to extend constraints to masses outside of the range that would be obtainable in the homogeneous limit, while only slightly relaxing their strength. We then project sensitivity for near-future cosmological surveys that are hoping to measure the 21cm transition in neutral hydrogen prior to reionization, and demonstrate that these experiments will be extremely useful in improving sensitivity to masses near ∼ 10−14 eV, potentially by several orders of magnitude. Finally, we discuss implications for reionization, early star formation, and late-time y-type spectral distortions, and show that probes which are inherently sensitive to the inhomogeneous state of the Universe could resolve signatures unique to the light dark photon dark matter scenario, and thus offer a fantastic potential for a positive detection.

Eclipsing binaries in the OGLE variable star catalogue: long-period evolved systems

ABSTRACT Red giant stars are proving to be an exceptional source of information for testing models of stellar evolution, as photometric and spectroscopic analysis has opened up a window into their interiors, providing an exciting chance to develop highly constrained stellar models. In this study, we present a determination of precise fundamental physical parameters belonging to five detached, double-lined, eclipsing binary stars in the Large and Small Magellanic Clouds containing G- or early K-type giant stars with extended envelopes. We also derived the distances to the systems by using a temperature–colour relation and compared these distances with the measurements provided in the literature. The measured stellar masses are in the range 1.8–3.0 M⊙ and comparison with the PAdova and TRieste Stellar Evolution Code (PARSEC) isochrones gives ages between 0.4 and 1.1 Gyr. The derived uncertainties for individual masses and radii of components are better than 3 and 7 per cent, respectively, for these systems. Additionally, we performed atmospheric parameter determination and [M/H] analysis for each, where we disentangled the spectra.