Cepheid Research Articles

OGLE-IV Period–Luminosity Relation of the LMC: An Analysis Using Mean and Median Magnitudes

The Period–Luminosity (PL) relation for Cepheid variable stars in the LMC is crucial for distance measurements in astronomy. This study analyzes the impact of using the median rather than the mean of the PL relation’s slope and zero-point. It also examines the persistence of the break at approximately 10 days and addresses specification issues in the PL relation model. Using VI-band median and mean magnitudes from the OGLE-IV survey, corrected for extinction, we fit the PL relation employing robust MM-regression, which features a high breakdown point and robust standard errors. Statistical tests and residual analysis are conducted to identify and correct model deficiencies. Our findings indicate a significant change in the PL relation for Cepheids with periods of 10 days or longer, regardless of whether median or mean magnitudes are used. A bias in the zero-point and slope estimators is observed when using median magnitudes instead of mean magnitudes, especially in the V band. By identifying and correcting regression issues and considering the period break, our estimators for the slope and zero-point are more accurate for distance calculations. Comparative analysis of the models for each band quantifies the bias introduced by using median magnitudes, highlighting the importance of considering the Cepheids’ periods for accurate location measure results, similar to those obtained using mean magnitudes.

Exploring the dynamical evolution of Cepheid multiplicity in star clusters and its implications for B-star multiplicity at birth

Classical Cepheid variable stars provide a unique probe of binary evolution in intermediate-mass stars over the course of several tens to hundreds of Myr. In addition, understanding binary evolution with the inclusion of cluster dynamics is desirable for obtaining a more complete picture of these stars, especially as they play a vital role in distance determinations. We studied the binary and multiple properties of Cepheids, assuming that all mid-B stars form in binaries inside star clusters. We also estimated the birth multiplicity of mid-B stars by comparing the observed multiplicity statistics of Cepheids with models based on particular assumptions. The clusters were modelled with the code, including synthetic stellar and binary evolutionary tracks. The Cepheids were identified from their position on the Hertzsprung-Russell diagram. The dynamical cluster environment results in a higher binary fraction among the Cepheids that remain in star clusters ($ 60$<!PCT!>) than among the Cepheids which have escaped to the field ($ 35$<!PCT!>). The fraction of Cepheids in triples ($ 30$<!PCT!> and $ 10$<!PCT!> in clusters and field, respectively) follows the same trend. In clusters, the binary, triple, and multiple fraction decreases with increasing cluster mass. More massive clusters have binaries of shorter orbital periods than lower mass clusters and field Cepheids. Mergers are very common with $ 30$<!PCT!> of mid-B stars not evolving to Cepheids because of the interaction with their companion. Approximately $40$ <!PCT!> of Cepheids have merged with their companion, and the merger event impacts stellar evolution, so that $ 25$<!PCT!> of all Cepheids occur at an age by more than $40$<!PCT!> different than what would be expected from their mass and the current cluster age; the expected age of Cepheids can differ from the age of their host cluster. Our models predict that one in five Cepheids is the result of a merger between stars with mass below the lower mass limit for Cepheids; in clusters, these objects occur substantially later than expected from their mass. Approximately $10$<!PCT!> of binary Cepheids have a different companion from the zero-age main sequence (ZAMS) one, and $ 3$ to $5$<!PCT!> of all Cepheids have a compact companion ($ 0.15$ <!PCT!> of all Cepheids are accompanied by a black hole). The binary fraction derived from our simulations (42<!PCT!>) underestimates the observed binary Cepheid fraction by approximately a factor of 2. This suggests that the true multiplicity fraction of B-stars at birth could be substantially larger than unity and, thus, that mid-B stars may typically form in triple and higher order systems.

Small Magellanic Cloud Cepheids Observed with the Hubble Space Telescope Provide a New Anchor for the SH0ES Distance Ladder

We present phase-corrected photometric measurements of 88 Cepheid variables in the core of the Small Magellanic Cloud (SMC), the first sample obtained with the Hubble Space Telescope's (HST) Wide Field Camera 3, in the same homogeneous photometric system as past measurements of all Cepheids on the SH0ES distance ladder. We limit the sample to the inner core and model the geometry to reduce errors in prior studies due to the nontrivial depth of this cloud. Without crowding present in ground-based studies, we obtain an unprecedentedly low dispersion of 0.102 mag for a period–luminosity (P–L) relation in the SMC, approaching the width of the Cepheid instability strip. The new geometric distance to 15 late-type detached eclipsing binaries in the SMC offers a rare opportunity to improve the foundation of the distance ladder, increasing the number of calibrating galaxies from three to four. With the SMC as the only anchor, we find H 0 = 74.1 ± 2.1 km s−1 Mpc−1. Combining these four geometric distances with our HST photometry of SMC Cepheids, we obtain H 0 = 73.17 ± 0.86 km s−1 Mpc−1. By including the SMC in the distance ladder, we also double the range where the metallicity ([Fe/H]) dependence of the Cepheid P–L relation can be calibrated, and we find γ = −0.234 ± 0.052 mag dex−1. Our local measurement of H 0 based on Cepheids and Type Ia supernovae shows a 5.8σ tension with the value inferred from the cosmic microwave background assuming a Lambda cold dark matter (ΛCDM) cosmology, reinforcing the possibility of physics beyond ΛCDM.

Study of changes in the pulsation period of six Cepheids variable

We study the period change of six Cepheids using 19376 accurate flux observations of the Solar Mass Ejection Imager (SMEI) onboard the Coriolis spacecraft. All observations for the six Cepheids have been derived as templates for each star, independent of the specific sites utilized to establish and update the O–C values. Sometimes, sinusoidal patterns are superimposed on the star’s O–C changes, which cannot be regarded as random fluctuations in the pulsation period. Random period changes were detected and computed using Eddington’s and Plakidis’s approaches. A comparison of the observed and predicted period change reveals a good agreement with some published models and a very substantial divergence with others. Between the reported period change and that estimated by the current technique, a linear fit with a correlation coefficient of 90.08 percent was obtained. The temporal rate of period change in Cepheid stars might be connected to how well these stars’ mass losses are known today.

Energy flow of λ in Hořava-Lifshitz cosmology

Hořava-Lifshitz gravity has been proposed as a renormalizable and ghost-free quantum gravity model candidate with an anisotropic UV-scaling between space and time. We present here a cosmological background analysis of two different formulations of the theory, with particular focus on the running of the parameter λ. Using a large dataset consisting of cosmic microwave background data from , Pantheon+supernovae catalog, SH0ES Cepheid variable stars, baryon acoustic oscillations (BAO), cosmic chronometers, and gamma-ray bursts (GRB), we arrive at new bounds on the cosmological parameters, in particular λ, which runs logarithmically with energy and describes deviation from general relativity, which corresponds to λ=1 For the detailed balance scenario we arrive at the bound λ=1.0406±0.0023, and for beyond detailed balance the limit reads λ=1.0064±0.0002. We also study the influence of different datasets and priors, and we find that removing low-redshift data generally moves λ closer toward UV values, while simultaneously widening the error bars. In the detailed balance scenario, this effect is more noticeable, and without prior λ≥1 it takes on values that are significantly below unity. Published by the American Physical Society 2024

The VISTA Variables in the Vía Láctea eXtended (VVVX) ESO public survey: Completion of the observations and legacy

The ESO public survey VISTA Variables in the V\'ia L\'actea (VVV) surveyed the inner Galactic bulge and the adjacent southern Galactic disk from $2009-2015$. Upon its conclusion, the complementary VVV eXtended (VVVX) survey has expanded both the temporal as well as spatial coverage of the original VVV area, widening it from $562$ to $1700$ sq. deg., as well as providing additional epochs in s $ filters from $2016-2023$. With the completion of VVVX observations during the first semester of 2023, we present here the observing strategy, a description of data quality and access, and the legacy of VVVX. VVVX took sim \,$2000$ hours, covering about 4<!PCT!> of the sky in the bulge and southern disk. VVVX covered most of the gaps left between the VVV and the VISTA Hemisphere Survey (VHS) areas and extended the VVV time baseline in the obscured regions affected by high extinction and hence hidden from optical observations. VVVX provides a deep $JHK_ s $ catalogue of $ point sources, as well as a s $ band catalogue of sim \,$10^7$ variable sources. Within the existing VVV area, we produced a $5D$ map of the surveyed region by combining positions, distances, and proper motions of well-understood distance indicators such as red clump stars, RR Lyrae, and Cepheid variables. In March 2023 we successfully finished the VVVX survey observations that started in 2016, an accomplishment for ESO Paranal Observatory upon 4200 hours of observations for VVV+VVVX. The VVV+VVVX catalogues complement those from the Gaia mission at low Galactic latitudes and provide spectroscopic targets for the forthcoming ESO high-multiplex spectrographs MOONS and 4MOST.

Search for Classical Cepheids in Galactic Open Clusters and Calibration of the Period–Wesenheit–Metallicity Relation in the Gaia Bands

It is beneficial to calibrate the period–Wesenheit–metallicity relation (PWZR) of Delta Cephei stars (DCEPs), i.e., classical Cepheids, using accurate parallaxes of associated open clusters (OCs) from Gaia data release 3 (DR3). To this aim, we obtain a total of 43 OC–DCEPs (including 33 fundamental mode, 9 first overtone mode, and 1 multimode DCEPs) and calibrate the PWZR as WG=(−3.356±0.033)(logP−1)+(−5.947±0.025) + (−0.285 ± 0.064)[Fe/H]. The concurrently obtained residual parallax offset in OCs, zp = −4 ± 5 μas, demonstrates the adequacy of the parallax corrections within the magnitude range of OC member stars. By comparing the field DCEPs’ DR3 parallaxes with their photometric parallaxes derived by our PWZR, we estimated the residual parallax offset in field DCEPs as zp = −15 ± 3 μas. Using our PWZR, we estimate the distance modulus of the Large Magellanic Cloud to be 18.482 ± 0.040 mag, which aligns well with the most accurate published value obtained through geometric methods.

Analysis of the Hubble Tension and Modifications to the Standard Cosmological Model

The Hubble constant is crucial to the knowledge of the universe’s nature and expansion, remaining as an active area for research in the recent decades. Cosmological microwave background observations revealed a lower value of 67–69 km-1s-1Mpc for the Hubble constant, but local data showed a higher value of 73–75 km-1s-1Mpc. This study focuses on the Hubble constant and its measurement, systematic uncertainties, observed tension, and potential modifications to the standard cosmological model. To be specific, this paper aims to address the tension between different measurement methods, which are Cepheid variables and supernovae, Baryon Acoustic Oscillations, and Gravitational waves, and understand systematic uncertainties. Results show discrepancies in Hubble constant values, indicating potential modifications to the standard cosmological model. Prospects include exploring alternative cosmological components and enhanced detection and computation methods. The study's implications lie in advancing the understanding of the expanding universe and guiding future research directions regarding to Hubble tension measurement.

Cepheids with giant companions

Context. Binary Cepheids with giant companions are crucial for studying the physical properties of Cepheid variables, in particular providing the best means to measure their masses. Systems composed of two Cepheids are even more important, but to date, only one such system has been identified, in the Large Magellanic Cloud (LMC). Aims. Our current aim is to increase the number of these systems known tenfold and to provide their basic characteristics. The final goal is to obtain the physical properties of the component Cepheids, including their masses and radii, and to learn about their evolution in the multiple systems, also revealing their origin. Methods. We started a spectroscopic monitoring campaign of nine unresolved pairs of Cepheids from the OGLE catalog to check if they are gravitationally bound. Two of these so-called double Cepheids are located in the LMC, five are in the Small Magellanic Cloud (SMC), and two are in the Milky Way (MW). Results. We report a spectroscopic detection of the binarity of all nine of these double Cepheids with orbital periods ranging from 2 to 18 years. This increases the number of known binary double (BIND) Cepheids from 1 to 10 and triples the number of all confirmed double-lined binary (SB2) Cepheids. For five BIND Cepheids, the disentangled pulsational light curves of the components show anti-correlated phase shifts due to orbital motion. We show the first empirical evidence that typical period–luminosity relations (PLRs) are rather binary Cepheid PLRs, as they include light of the companion. Conclusions. The statistics of pulsation period ratios of BIND Cepheids do not agree with those expected for pairs of Cepheids of the same age. These ratios together with the determined mass ratios far from unity suggest a merger origin of at least one component for about half of the systems. The SMC and MW objects are the first found in SB2 systems composed of giants in their host galaxies. The Milky Way BIND Cepheids are also the closest such systems, being located at about 11 and 26 kpc.

An Asymmetric Galactic Stellar Disk Traced by OB-type Stars from LAMOST DR7

Using 9943 OB-type stars from LAMOST DR7 in the solar neighborhood, we fit the vertical stellar density profile with the model including a single exponential distribution at different positions (R, Φ). The distributions of the scale heights and scale length show that the young disk traced by the OB-type stars is not axisymmetric. The scale length decreases versus the azimuthal angle Φ, i.e., from 1.14−0.19+0.30 kpc with Φ = − 3° to 0.77−0.06+0.08 kpc with Φ = 9°. Meanwhile we find signal of non-symmetry in the distribution of the scale height of the north and south of the disk plane. The scale height in the north side shows signal of flaring of the disk, while that of the south disk stays almost constant around h s = 130 pc. The distribution of the displacement of the disk plane Z 0 also shows variance versus the azimuthal angle Φ, which displays significant differences with the warp model constrained by the Cepheid stars. We also test different values for the position of the Sun, and the distance between the Sun and the Galactic center affects the scale heights and the displacement of the disk significantly, but that does not change our conclusion that the disk is not axisymmetric.

Stellar Variability and Distance Indicators in the Near-infrared in Nearby Galaxies. I. RR Lyrae and Anomalous Cepheids in Draco Dwarf Spheroidal

The Draco Dwarf spheroidal (dSph) galaxy is one of the nearest and the most dark-matter-dominated satellites of the Milky Way. We obtained multiepoch near-infrared (NIR, JHK s ) observations of the central region of Draco dSph covering a sky area of ∼21′ × 21′ using the WIRCam instrument at the 3.6 m Canada–France–Hawaii Telescope. Homogeneous JHK s time-series photometry for 212 RR Lyrae (173 fundamental-mode, 24 first-overtone, and 15 mixed-mode variables) and five Anomalous Cepheids in Draco dSph are presented and used to derive their period–luminosity relations at NIR wavelengths for the first-time. The small scatter of ∼0.05 mag in these empirical relations for RR Lyrae stars is consistent with those in globular clusters and suggests a very small metallicity spread, up to ∼0.2 dex, among these centrally located variables. Based on empirically calibrated NIR period–luminosity–metallicity relations for RR Lyrae in globular clusters, we determined a distance modulus to Draco dSph of μ RRL = 19.557 ± 0.026 mag. The calibrated K s -band period–luminosity relations for Anomalous Cepheids in the Draco dSph and the Large Magellanic Cloud exhibit statistically consistent slopes but systematically different zero points, hinting at possible metallicity dependence of ∼ − 0.3 mag dex−1. Finally, the apparent magnitudes of the tip of the red-giant branch in I and J bands also agree well with their absolute calibrations with the adopted RR Lyrae distance to Draco. Our recommended ∼1.5% precise RR Lyrae distance, D Draco = 81.55 ± 0.98(statistical) ± 1.17(systematic) kpc, is the most accurate and precise distance to Draco dSph galaxy.

Bridging theory and observations in stellar pulsations: the impact of convection and metallicity on the instability strips of classical and type-II cepheids

ABSTRACT The effect of metallicity on the theoretical and empirical period–luminosity relations of Cepheid variables is not well understood and remains a highly debated issue. Here, we examine empirical colour–magnitude diagrams (CMDs) of Classical and Type-II Cepheids in the Magellanic Clouds and compare those with the theoretically predicted instability strip (IS) edges. We explore the effects of incorporating turbulent flux, turbulent pressure, and radiative cooling into the convection theory on the predicted IS at various metallicities using Modules for Experiments in Stellar Astrophysics – Radial Stellar Pulsations. We find that the edges become redder with the increasing complexity of convection physics incorporated in the fiducial convection sets, and are similarly shifted to the red with increasing metallicity. The inclusion of turbulent flux and pressure improves the agreement of the red edge of the IS, while their exclusion leads to better agreement with observations of the blue edge. About 90 per cent of observed stars are found to fall within the predicted bluest and reddest edges across the considered variations of turbulent convection parameters. Furthermore, we identify and discuss discrepancies between theoretical and observed CMDs in the low-effective temperature and high-luminosity regions for stars with periods greater than ∼20 d. These findings highlight the potential for calibrating the turbulent convection parameters in stellar pulsation models or the prediction of a new class of rare, long-period, ‘red Cepheids’, thereby improving our understanding of Cepheids and their role in cosmological studies.

Cepheid Metallicity in the Leavitt Law (C-MetaLL) survey

Context. The highly debated effect of metallicity on the absolute magnitudes of classical Cepheid variables needs to be properly quantified for determining accurate and precise distances based on their Leavitt Law. Aims. Our goal is to obtain homogeneous optical and near-infrared light curves of Milky Way Cepheid variables complementing their already collected high-resolution spectroscopic metallicities as part of the C-MetaLL survey. Together with Gaia parallaxes, we investigate period-luminosity-metallicity relations for Cepheid variables at multiple wavelengths. Methods. We present homogeneous multiband (grizJHKs) time-series observations of 78 Cepheids including 49 fundamental mode variables and 29 first-overtone mode variables. These observations were collected simultaneously using the ROS2 and REMIR instruments at the Rapid Eye Mount telescope. Multiwavelength photometric data were used to investigate pulsation properties of Cepheid variables and derive their period–luminosity (PL) and period–Wesenheit (PW) relations. Results. The Cepheid sample covers a large range of distances (0.5 − 19.7 kpc) with varying precision of parallaxes, and thus astrometry-based luminosity fits were used to derive PL and PW relations in optical Sloan (griz) and near-infrared (JHKs) filters. These empirically calibrated relations exhibit large scatter primarily due to larger uncertainties in parallaxes of distant Cepheids, but their slopes agree well with those previously determined in the literature. Using homogeneous high-resolution spectroscopic metallicities of 61 Cepheids covering −1.1 < [Fe/H] < 0.6 dex, we quantified the metallicity dependence of PL and PW relations which varies between −0.30 ± 0.11 (in Ks) and −0.55 ± 0.12 (in z) mag dex−1 in grizJHKs bands. However, the metallicity dependence in the residuals of the PL and PW relations is predominantly seen for metal-poor stars ([Fe/H] < −0.3 dex), which also have larger parallax uncertainties. The modest sample size precludes us from separating the contribution to the residuals due to parallax uncertainties, metallicity effects, and reddening errors. While this Cepheid sample is not optimal for calibrating the Leavitt law, upcoming photometric and spectroscopic datasets of the C-MetaLL survey will allow the accurate derivation of PL and PW relations in the Sloan and near-infrared bandpasses, which will be useful for the distance measurements in the era of the Vera C. Rubin Observatory’s Legacy Survey of Space and Time and upcoming extremely large telescopes.

Spectroscopic and photometric behavior of LP Ori

AbstractWe performed spectroscopic and photometric analyses on the early B‐type LP Ori young stellar object located in the Orion Nebula. The high‐resolution spectra of LP Ori was obtained at the Ankara University Kreiken Observatory in 2023, while all spectra recorded over the past 19 years were extracted from the ESO and ESPaDOnS archives. In these spectra of LP Ori, there is typically an emission observed in the core of the Balmer profile. This structure is accompanied by a 14‐year interval inverse P‐Cygni repetition superimposed on the Balmer profile. Additionally, an emission in the 5,875 He I line is visible in the spectra in the year 2023. When this emission is considered together with the inverse P‐Cygni structures, these observations suggest that LP Ori is a Herbig Ae/Be star. The abundance pattern of LP Ori is close to solar with the exception of a slightly rich helium and slightly poor aluminum abundance. Additionally, the spectral energy distribution of LP Ori was constructed to confirm the infrared excess caused by its circumstellar disk. Furthermore, the photometric analysis performed on the TESS observations of LP Ori shows significant photometric variability and the frequency analysis reveals a Cephei star in its forthcoming evolution.

Classical Cepheid pulsation properties in the Rubin-LSST filters

ABSTRACT Homogeneous multiwavelength observations of classical Cepheids from the forthcoming Rubin-LSST have the potential to significantly contribute to our understanding of the evolutionary and pulsation properties of these pulsating stars. Updated pulsation models for classical Cepheid stars have been computed under various assumptions about chemical compositions, including relatively low metallicity (Z = 0.004 with Y = 0.25 and Z = 0.008 with Y = 0.25), solar metallicity (Z = 0.02 with Y = 0.28), and supersolar metallicity environments (Z = 0.03 with Y = 0.28). From the predicted periods, intensity-weighted mean magnitudes, and colours, we have derived the first theoretical pulsation relations in the Rubin-LSST filters (ugrizy), including period–luminosity–colour, period–Wesenheit, and period–age–colour relations. We find that the coefficients of these relations are almost insensitive to the efficiency of superadiabatic convection but are significantly affected by the assumption of the mass–luminosity relation and the adopted chemical composition. Metal-dependent versions of these relations are also derived, representing valuable tools for individual distance determinations and correction for metallicity effects on the cosmic distance scale.

First spectroscopic investigation of anomalous Cepheid variables

Context. Anomalous Cepheids (ACEPs) are intermediate-mass metal-poor pulsators that are mostly discovered in dwarf galaxies of the Local Group. However, recent Galactic surveys, including the Gaia Data Release 3, found a few hundred ACEPs in the Milky Way. Their origin is only poorly understood. Aims. We aim to investigate the origin and evolution of Galactic ACEPs by studying the chemical composition of their atmospheres for the first time. Methods. We used UVES at the Very Large Telescope to obtain high-resolution spectra for a sample of nine ACEPs belonging to the Galactic halo. We derived the abundances of 12 elements, C, Na, Mg, Si, Ca, Sc, Ti, Cr, Fe, Ni, Y, and Ba. We complemented these data with literature abundances from high-resolution spectroscopy for an additional three ACEPs that were previously incorrectly classified as type II Cepheids. This increased the sample to a total of 12 stars. Results. All the investigated ACEPs have an iron abundance [Fe/H] < −1.5 dex, as expected from theoretical predictions for these pulsators. The abundance ratios of the different elements to iron show that the chemical composition of ACEPs is generally consistent with that of the Galactic halo field stars, with the exception of sodium, which is found to be overabundant in 9 out of the 11 ACEPs where it was measured. This is very similar to the situation for second-generation stars in Galactic globular clusters. The same comparison with dwarf and ultra-faint satellites of the Milky Way reveals more differences than similarities. It is therefore unlikely that the bulk of Galactic ACEPs originated in a galaxy like this that subsequently dissolved into the Galactic halo. The principal finding of this work is the unexpected overabundance of sodium in ACEPs. We explored several hypotheses to explain this feature, finding that the most promising scenario is the evolution of low-mass stars in a binary system with either mass transfer or merging. Detailed modelling is needed to confirm this hypothesis.

Why Mature Galaxies Seem to Have Filled the Universe Shortly After the Big Bang — A New Cosmological Model, that Predicted the JWST Observations

Recent observations from the first dataset, provided by NASA's James Webb Space Telescope (JWST) of six massive galaxies, at a time in the early universe, seem to defy conventional cosmological models, as they appear to be as mature and developed as our own local group. Such unexpected discoveries JUSTIFY A RADICALLY NOVEL MODEL OF COSMOLOGY. TO QUOTE JOEL LEJA, ASSISTANT PROFESSOR OF ASTRONOMY AND ASTROPHYSICS AT PENN STATE ''IT TURNS OUT WE FOUND SOMETHING SO UNEXPECTED IT ACTUALLY CREATES PROBLEMS FOR SCIENCE. IT CALLS THE WHOLE PICTURE OF EARLY GALAXY FORMATION INTO QUESTION''. This article provides an alternative mathematical model of cosmological redshifting (\(z\)), which actually predicted such mature galaxies in a 2022 preprint, prior to these recent observations. As well, this model also predicts discrepancies between theoretical and observed galaxy rotation curves with apparent increased energy density. The Azimuthal Projection Model of the Universe is conceptualized as an \(\mathbb{R}^5\) spacetime, with a four spatial dimensional hypersphere azimuthally projected onto a three-dimensional spatial sphere. This simple parsimonious model requires only a few assumptions, excluding dark energy to satisfy the Cosmological Constant \(\Lambda\), and is shown to match the Universal expansion rate, as established from supernova cosmology survey points. This novel model conceives the universe as a higher dimensional dynamic with spacetime as a projection, rather than as an arrow from the absolute beginning of the Big Bang. Redshifting is alternatively proposed as azimuthal angular projections of wavelengths \(\lambda\). Accelerated Universal Expansion is alternatively proposed as azimuthal projections of meridians, asymptotical to a horizon, and Lambert's cosine law of luminous intensity. A radical implication of this model is that azimuthal angular projections are positional dependent, and thus it's conceivable that apparent distances between galaxies vary with the location of the observer (see figure 4). Supportive mathematical evidence is described from the Hubble Tension; Discrepancies between visible spectra redshifting of cepheid variables (the most recent calculation is \(Ho=74.03 \pm 1.42km/sec/Mpc\)), and from temperature fluctuations in the Cosmic Microwave Background (CMB) (which are calculated to be \(Ho=68.7 \pm 1.3km/sec/Mpc\)), which resolves the discrepancy by recalibrating redshift data from supernova Cosmology survey points.

Stepped partially acoustic dark matter: likelihood analysis and cosmological tensions

We generalize the recently proposed Stepped Partially Acoustic Dark Matter (SPartAcous) model by including additional massless degrees of freedom in the dark radiation sector. We fit SPartAcous and its generalization against cosmological precision data from the cosmic microwave background, baryon acoustic oscillations, large-scale structure, supernovae type Ia, and Cepheid variables. We find that SPartAcous significantly reduces the H 0 tension but does not provide any meaningful improvement of the S 8 tension, while the generalized model succeeds in addressing both tensions, and provides a better fit than ΛCDM and other dark sector models proposed to address the same tensions. In the generalized model, H 0 can be raised to 71.4 km/s/Mpc (the 95% upper limit), reducing the tension, if the fitted data does not include the direct measurement from the SH0ES collaboration, and to 73.7 km/s/Mpc (95% upper limit) if it does. A version of CLASS that has been modified to analyze this model is publicly available at https://github.com/ManuelBuenAbad/class_spartacous.

Reeling in the Whirlpool galaxy: Distance to M 51 clarified through Cepheids and the type IIP supernova 2005cs

Context. The distance to the Whirlpool galaxy, M 51, is still debated, even though the galaxy has been studied in great detail. Current estimates range from 6.02 to 9.09 Mpc, and different methods yield discrepant results. No Cepheid distance has been published for M 51 to date. Aims. We aim to estimate a more reliable distance to M 51 through two independent methods: Cepheid variables and their period-luminosity relation, and an augmented version of the expanding photosphere method (EPM) on the type IIP supernova SN 2005cs, which exploded in this galaxy. Methods. For the Cepheid variables, we analysed a recently published Hubble Space Telescope catalogue of stars in M 51. By applying filtering based on the light curve and colour-magnitude diagram, we selected a high-quality sample of M 51 Cepheids to estimate the distance through the period-luminosity relation. For SN 2005cs, an emulator-based spectral fitting technique was applied, which allows for the fast and reliable estimation of the physical parameters of the supernova atmosphere. We augmented the established framework of EPM with these spectral models to obtain a precise distance to M 51. Results. The two resulting distance estimates are DCep = 7.59 ± 0.30 Mpc and D2005cs = 7.34 ± 0.39 Mpc using the Cepheid period-luminosity relation and the spectral modelling of SN 2005cs, respectively. This is the first published Cepheid distance for this galaxy. The obtained values are precise to 4–5% and are fully consistent within 1σ uncertainties. Because these two estimates are completely independent, they can be combined for an even more precise estimate, which yields DM 51 = 7.50 ± 0.24 Mpc (3.2% uncertainty). Conclusions. Our distance estimates agree with most of the results obtained previously for M 51, but they are more precise than the earlier counterparts. However, they are significantly lower than the TRGB estimates, which are often adopted for the distance to this galaxy. The results highlight the importance of direct cross-checks between independent distance estimates so that systematic uncertainties can be quantified. Because of the large discrepancy, this finding can also affect distance-sensitive studies and their discussion for objects within M 51, as well as the estimation of the Hubble constant through the type IIP standardizable candle method, for which SN 2005cs is a calibrator object.

A bias using the ages of the oldest astrophysical objects to address the Hubble tension

Recently different cosmological measurements have shown a tension in the value of the Hubble constant, H_0. Assuming the Lambda CDM model, the Planck satellite mission has inferred the Hubble constant from the cosmic microwave background (CMB) anisotropies to be H_0 = 67.4 pm 0.5 , text {km} , text {s}^{-1} , text {Mpc}^{-1}. On the other hand, low redshift measurements such as those using Cepheid variables and supernovae Type Ia (SNIa) have obtained a significantly larger value. For instance, Riess et al. reported H_0 = 73.04 pm 1.04 , text {km} , text {s}^{-1} , text {Mpc}^{-1}, which is 5sigma apart of the prediction from Planck observations. This tension is a major problem in cosmology nowadays, and it is not clear yet if it comes from systematic effects or new physics. The use of new methods to infer the Hubble constant is therefore essential to shed light on this matter. In this paper, we discuss using the ages of the oldest astrophysical objects (OAO) to probe the Hubble tension. We show that, although this data can provide additional information, the method can also artificially introduce a tension. Reanalyzing the ages of 114 OAO, we obtain that the constraint in the Hubble constant goes from slightly disfavoring local measurements to favoring them.