Distance Ladder Research Articles

Temporal and Spatial Variability Scales of Salinity at a Large Microtidal Estuary

The Río de la Plata is a large fluvial–estuarine–sea system discharging into the southwestern Atlantic Ocean, which has relevant features such as high fluvial discharge, microtidal astronomical tidal scales, a relevant meteorological tide, and a strong atmospheric forcing effect, due to its large width. The objective of this study is to advance the understanding of the estuarine hydrodynamics and salt transport, as well as discussing the main characteristics of the spatiotemporal variability of the salinity field. To achieve this, the results of a 3D model of the Río de la Plata and its maritime front were used, simulating an extensive period of 10 years. In this study, the model was validated using vertical salinity profiles collected at different locations in the estuary. The temporal variability of the salinity stratification was characterised at different temporal scales: annual, monthly, and storm. At the same time, the influences of fluvial flow and winds were determined. The correlation analysis between fluvial flow and the salinity field showed that high annual fluvial flows generate an extension of the freshwater area, with larger longitudinal salinity gradients and a shift of the salinity front towards the ocean. The tendency at the monthly scale is not as clear as that observed at the annual scale. The results show that the effect of a storm coming from the northwest is quite similar to that of storms coming from the southwest, especially in the central and southern zones of the Río de la Plata, where mixing increases and stratification decreases, according to the intensity of the storm. The effect of south–southeasterly storms increases the mixing process and reduces stratification; the opposite effect was identified with respect to northeasterly storms, under the influence of which the stratified area increases. Synthesising the obtained results, a global zonification of the vertical salinity stratification for the Río de la Plata is proposed.

TDCOSMO

Time-delay cosmography with gravitationally lensed quasars plays an important role in anchoring the absolute distance scale and hence measuring the Hubble constant, H0, independent of traditional distance ladder methodology. A current potential limitation of time-delay distance measurements is the mass-sheet transformation (MST), which leaves the lensed imaging unchanged but changes the distance measurements and the derived value of H0. In this work we show that the standard method of addressing the MST in time-delay cosmography, through a combination of high-resolution imaging and the measurement of the stellar velocity dispersion of the lensing galaxy, depends on the assumption that the ratio, Ds/Dds, of angular diameter distances to the background quasar and between the lensing galaxy and the quasar can be constrained. This is typically achieved through the assumption of a particular cosmological model. Previous work (TDCOSMO IV) addressed the mass-sheet degeneracy and derived H0 under the assumption of the ΛCDM model. In this paper we show that the mass-sheet degeneracy can be broken without relying on a specific cosmological model by combining lensing with relative distance indicators such as supernovae Type Ia and baryon acoustic oscillations, which constrain the shape of the expansion history and hence Ds/Dds. With this approach, we demonstrate that the mass-sheet degeneracy can be constrained in a cosmological model-independent way. Hence model-independent distance measurements in time-delay cosmography under MSTs can be obtained.

Is there really a Hubble tension?

The heliocentric redshifts (z hel) reported for 150 type Ia supernovae in the Pantheon compilation are significantly discrepant from their corresponding values in the JLA compilation. Both catalogues include corrections to the redshifts and magnitudes of the supernovae to account for the motion of the heliocentric frame relative to the ‘CMB rest frame’, as well as corrections for the directionally coherent bulk motion of local galaxies with respect to this frame. The latter is done employing modelling of peculiar velocities which assume the ΛCDM cosmological model but nevertheless provide evidence for residual bulk flows which are discordant with this model (implying that the observed Universe is in fact anisotropic). Until recently such peculiar velocity corrections in the Pantheon catalogue were made at redshifts exceeding 0.2 although there is no data on which to base such corrections. We study the impact of these vexed issues on the 4.4σ discrepancy between the Hubble constant of H 0 = 67.4 ± 0.5 km s−1 Mpc−1 inferred from observations of CMB anisotropies by Planck assuming ΛCDM, and the measurement of H 0 = 73.5 ± 1.4 km s−1 Mpc−1 by the SH0ES project which extended the local distance ladder using type Ia supernovae. Using the same methodology as the latter study we find that for supernovae whose redshifts are discrepant between Pantheon and JLA with Δz hel > 0.0025, the Pantheon redshifts favour H 0 ≃ 72 km s−1 Mpc−1, while the JLA redshifts favour H 0 ≃ 68 km s−1 Mpc−1. Thus the discrepancies between SNe Ia datasets are sufficient to undermine the claimed ‘Hubble tension’. We further note the systematic variation of H 0 by ∼6–9 km s−1 Mpc−1 across the sky seen in multiple datasets, implying that it cannot be measured locally to better than ∼10% in a model-independent manner.

The graviton Compton mass as Dark Energy

One of the greatest challenges of science is to understand the current accelerated expansion of the Universe. In this work we show that by considering the quantum nature of the gravitational field, its wavelength can be associated to an effective Compton mass. We propose that this mass can be interpreted as dark energy, with a Compton wavelength given by the size of the observable Universe, implying that the dark energy varies depending on this size. If we do so, we find that: 1.- Even without any free constant for dark energy, the evolution of the Hubble parameter is exactly the same as for the LCDM model, so this model has the same predictions as LCDM. 2.- The density rate of the dark energy is ΩΛ = 0.69 which is a very similar value as the one found by the Planck satellite ΩΛ = 0.684. 3.- The dark energy has this value because it corresponds to the actual size of the radius of the Universe, thus the coincidence problem has a very natural explanation. 4.- It is possible to find also a natural explanation to why observations inferred from the local distance ladder find the value H0 = 73 km/s/Mpc for the Hubble constant, we show that if we take the variability of the dark energy into account they should measure H0 = 67.3 km/s/Mpc as well. 5.- In this model the inflationary period contains a natural successful graceful exit.

$$\varvec{U\!BV\!I}$$ CCD photometry of Berkeley 55 open cluster

Fundamental astrophysical parameters have been derived for Berkeley 55 (Be 55) open cluster based on the UBVI charge-coupled device (CCD) photometric data observed using a AZT-22 1.5 m telescope at Maidanak Astronomical Observatory (MAO) in Uzbekistan. The mean reddening is obtained as \(E(B-V)=1.77\pm 0.10\,\mathrm {mag}\) from early-type members. The zero-age main sequence fitting in the \(Q_{V\lambda }\) – \(Q'\) diagrams indicates the distance modulus, \((V_{0}-M_{V})=12.4\pm 0.20\,\mathrm {mag}\,(d=3.02\pm 0.28\,\mathrm {kpc}\)). This photometric distance is consistent with the distances of Gaia EDR3 (\(d = 3.09 \pm 0.16\,\mathrm {kpc}\)) and period–luminosity relation (\(d =\) 2.78 ± 0.32 kpc) of its Cepheid S5 within the uncertainties. This distance also locates the cluster near the Perseus spiral arm. The Geneva isochrone fittings to the Hertzsprung–Russell diagram and observational colour–magnitude diagrams derive turn-off age, 85 ± 13 Myr, by taking care of five red supergiants/bright giants. The possible inconsistencies in the locations of the bright giants with the rotating/non-rotating isochrones may be due to both the age spread of stars in young open clusters and the diversity in rotational velocities.

On the Relation between the Astronomical and Visual Photometric Systems in Specifying the Brightness of the Night Sky for Mesopically Adapted Observers

ABSTRACT Due to the typical ambient light levels in inhabited places and light pollution of the night sky, most naked-eye astronomical observations are performed nowadays under mesopic conditions. The luminance (cd/m2) associated with the brightness of the night sky specified in the astronomical logarithmic scale of magnitudes per square arcsecond (mag/arcsec2) is strongly dependent on the spectrum of the sky, because the spectral sensitivity of the human visual system is not coincident with the standard photometric bands used in astronomy. The conversion between these two families of photometric systems was previously analyzed for observers presumed to be either fully photopically or scotopically adapted. In this work, we deduce the transformation equations between the astronomical and visual photometric systems for specifying and reporting the sky brightness in the mesopic range, within the framework of the MES-2 system for visual performance-based mesopic photometry. It is shown that the dependence of the conversion factors on the correlated color temperature of the night sky reaches a minimum spread for adaptation luminances of 0.5–1.0 cd/m2. The sky luminances corresponding to 22.0 mag/arcsec2 in the Johnson-Cousins V band (the assumed brightness of a natural night sky devoid of light pollution) span, for 1.0 cd/m2 adaptation, a relatively small range of ~195–215 μcd/m2 in the absolute (AB) magnitude system and ~210–225 μcd/m2 in the Vega-referenced one.

Stellar distance and velocity (III)

The use of parallax angles is one of the standard methods for determining stellar distance. The problem that arises in using this method is how to measure that angle. In order for the measurement to be correct, it is necessary for the object we are observing to be stationary in relation to the sun. This is generally not true. One way to overcome this problem is to observe the object from two different places at the same time. This would be technically possible but will probably never be realized. Another way to determine the distance is given in [1]. With certain assumptions, this is a mathematically completely correct method. After the publication of the third Gaia's catalog [2], we are now able to test the proposed method using real data. Unfortunately, for the majority of stars it is not possible to obtain the distance directly, but with the help of some additional measurements we would be able to indirectly determine the distance of such stars.

To H0 or not to H0?

ABSTRACT This paper investigates whether changes to late-time physics can resolve the ‘Hubble tension’. It is argued that many of the claims in the literature favouring such solutions are caused by a misunderstanding of how distance ladder measurements actually work and, in particular, by the inappropriate use of a distance ladder H0 prior. A dynamics-free inverse distance ladder shows that changes to late-time physics are strongly constrained observationally and cannot resolve the discrepancy between the SH0ES data and the base ΛCDM cosmology inferred from Planck. We propose a statistically rigorous scheme to replace the use of H0 priors.

Chameleon dark energy can resolve the Hubble tension

Values of the Hubble constant between the direct measurements from various independent local observations and that inferred from the cosmic microwave background with the $\mathrm{\ensuremath{\Lambda}}$-cold-dark-matter model are in tension with persistent significance. We propose a late-time inhomogeneous resolution suggesting that a chameleon field coupled to a local overdensity of matter could be trapped at a higher potential energy density as an effective cosmological constant driving the local expansion rate faster than that of the background with lower matter density. We illustrate this mechanism in a toy model in which a region with only 20% overdensity of matter is sufficient to resolve the Hubble tension, and the Hubble constant measured by the local distance ladders could be accommodated by the chameleon coupled to the observed overdensities from the large-scale structure surveys.

The peculiar nebula Simeis 57

Simeis 57 (HS 191) is an optically bright nebula in the Cygnus X region with a peculiar appearance that suggests an outflow from a rotating source. Newly obtained observations and archival data reveal Simeis 57 as a low-density (ne ~ 100 cm−3) nebula with an east-to-west excitation gradient. The extinction of the nebula is AV ≤ 2 mag. The nebula is recognizable but not prominent in mid- and far-infrared images. In its direction, half a dozen small CO clouds have been identified at VLSR = +5 km s−1. One of these coincides with both the optical nebula and a second CO cloud at the nebular velocity VLSR ≈−10 km−1. No luminous stars are embedded in these molecular clouds, nor are any obscured by them and no sufficiently luminous stars are found in the immediate vicinity of the nebula. Instead, all available data points to the evolved star HD 193793 = WR 140 (an O4-5 supergiant and WC7 Wolf–Rayet binary) as the source of excitation, notwithstanding its large separation of 50′, about 25 pc at the stellar distance of 1.7 kpc. Simeis 57 appears to be a part of a larger structure surrounding the HI void centered on HD 193793.

The graviton Compton mass as dark energy

One of the greatest challenges of science is to understand the current accelerated expansion of the Universe. In this work we show that by considering the quantum nature of the gravitational field, its wavelength can be associated to an effective Compton mass. We propose that this mass can be interpreted as dark energy, with a Compton wavelength given by the size of the observable Universe, implying that the dark energy varies depending on this size. If we do so, we find that: 1.- Even without any free constant for dark energy, the evolution of the Hubble parameter is exactly the same as for the LCDM model, so this model has the same predictions as LCDM. 2.- The density rate of the dark energy is ΩΛ = 0.69 which is a very similar value as the one found by the Planck satellite ΩΛ = 0.684. 3.- The dark energy has this value because it corresponds to the actual size of the radius of the Universe, thus the coincidence problem has a very natural explanation. 4.- It is possible to find also a natural explanation to why observations inferred from the local distance ladder find the value H0 = 73 km/s/Mpc for the Hubble constant, we show that if we take the variability of the dark energy into account they should measure H0 = 67.3 km/s/Mpc as well. 5.- In this model the inflationary period contains a natural successful graceful exit.

Starshade Imaging Simulation Toolkit for Exoplanet Reconnaissance

Starshade Imaging Simulation Toolkit for Exoplanet Reconnaissance (SISTER) is a versatile tool designed to provide accurate models of the images of exoplanet systems when observed with a starshade positioned to block the light from the host star. SISTER allows one to control a set of observational parameters including: (1) the starshade design, position, orientation, and glint properties; (2) the telescope and optical system pupil, aberrations, bandpass, and throughput including a detector model; (3) the exoplanetary system, including stellar distance and spectral type, parallax and proper motion, planet size, reflection properties, orbital parameters, and exozodiacal dust; and (4) background objects. Additionally, there is a substantial library of built-in plotting software added, but the simulations may be stored on disk and plotted with any other software. We describe SISTER’s algorithms, its operational modules, and how it can be used to generate starshade optical simulations with a high degree of fidelity. We include some imaging examples.

No H0 assistance from assisted quintessence

Early dark energy, as a proposed solution to the Hubble tension, faces an additional "why now" problem. Why should dark energy emerge just prior to recombination, billions of years before the onset of cosmic acceleration? Assisted quintessence explains this connection by positing that multiple scaling fields build up over time to drive the present-day cosmic acceleration. In this framework, early dark energy is inevitable. Yet, we show that scaling also leads to the demise of the scenario: the same feature that solves the coincidence problem then spoils a concordance of the Hubble constant inferred from the cosmic microwave background with that from the local distance ladder. The failure of the model offers a novel lesson on the ability of new physics to resolve the Hubble tension.

The Influence of Metallicity on the Leavitt Law from Geometrical Distances of Milky Way and Magellanic Cloud Cepheids

Abstract The Cepheid period–luminosity (PL) relation is the key tool for measuring astronomical distances and for establishing the extragalactic distance scale. In particular, the local value of the Hubble constant (H 0) strongly depends on Cepheid distance measurements. The recent Gaia Data Releases and other parallax measurements from the Hubble Space Telescope (HST) already enabled us to improve the accuracy of the slope (α) and intercept (β) of the PL relation. However, the dependence of this law on metallicity is still largely debated. In this paper, we combine three samples of Cepheids in the Milky Way (MW), the Large Magellanic Cloud (LMC), and the Small Magellanic Cloud (SMC) in order to derive the metallicity term (hereafter γ) of the PL relation. The recent publication of extremely precise LMC and SMC distances based on late-type detached eclipsing binary systems provides a solid anchor for the Magellanic Clouds. In the MW, we adopt Cepheid parallaxes from the early third Gaia Data Release. We derive the metallicity effect in V, I, J, H, K S , W VI , and W JK . In the K S band we report a metallicity effect of −0.221 ± 0.051 mag dex−1, the negative sign meaning that more metal-rich Cepheids are intrinsically brighter than their more metal-poor counterparts of the same pulsation period.

Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Cosmological implications from two decades of spectroscopic surveys at the Apache Point Observatory

We present the cosmological implications from final measurements of clustering using galaxies, quasars, and Ly$\alpha$ forests from the completed Sloan Digital Sky Survey (SDSS) lineage of experiments in large-scale structure. These experiments, composed of data from SDSS, SDSS-II, BOSS, and eBOSS, offer independent measurements of baryon acoustic oscillation (BAO) measurements of angular-diameter distances and Hubble distances relative to the sound horizon, $r_d$, from eight different samples and six measurements of the growth rate parameter, $f\sigma_8$, from redshift-space distortions (RSD). This composite sample is the most constraining of its kind and allows us to perform a comprehensive assessment of the cosmological model after two decades of dedicated spectroscopic observation. We show that the BAO data alone are able to rule out dark-energy-free models at more than eight standard deviations in an extension to the flat, $\Lambda$CDM model that allows for curvature. When combined with Planck Cosmic Microwave Background (CMB) measurements of temperature and polarization the BAO data provide nearly an order of magnitude improvement on curvature constraints. The RSD measurements indicate a growth rate that is consistent with predictions from Planck primary data and with General Relativity. When combining the results of SDSS BAO and RSD with external data, all multiple-parameter extensions remain consistent with a $\Lambda$CDM model. Regardless of cosmological model, the precision on $\Omega_\Lambda$, $H_0$, and $\sigma_8$, remains at roughly 1\%, showing changes of less than 0.6\% in the central values between models. The inverse distance ladder measurement under a o$w_0w_a$CDM yields $H_0= 68.20 \pm 0.81 \, \rm km\, s^{-1} Mpc^{-1}$, remaining in tension with several direct determination methods. (abridged)

High H 0 Values from CMB E-mode Data: A Clue for Resolving the Hubble Tension?

Abstract The E-mode (EE) CMB power spectra measured by Planck, ACTPol, and SPTpol constrain the Hubble constant to be 70.0 ± 2.7, , and km s−1 Mpc−1 within the standard ΛCDM model (posterior mean and central 68% interval bounds). These values are higher than the constraints from the Planck temperature (TT) power spectrum, and consistent with the Cepheid-supernova distance ladder measurement H 0 = 73.2 ± 1.3 km s−1 Mpc−1. If this preference for a higher value was strengthened in a joint analysis it could provide an intriguing hint at the resolution of the Hubble disagreement. We show, however, that combining the Planck, ACTPol, and SPTpol EE likelihoods yields H 0 = 68.7 ± 1.3 km s−1 Mpc−1, 2.4σ lower than the distance ladder measurement. This is due to different degeneracy directions across the full parameter space, particularly involving the baryon density, Ω b h 2, and scalar tilt, n s , arising from sensitivity to different multipole ranges. We show that the E-mode ΛCDM constraints are consistent across the different experiments within 1.4σ, and with the Planck TT results at 0.8σ. Combining the Planck, ACTPol, and SPTpol EE data constrains the phenomenological lensing amplitude, A L = 0.89 ± 0.10, consistent with the expected value of unity.

Interpretation of the Galactic gamma-ray excess with the dark matter indicated by 8Be and 4He anomalous transitions * *The work of T. Li was Supported by the the National Natural Science Foundation of China (11975129, 12035008) and “the Fundamental Research Funds for the Central Universities”, Nankai University (63196013). L.-B. Jia was Supported by the Longshan academic talent research supporting program

The long-standing Galactic center gamma-ray excess could be explained by GeV dark matter (DM) annihilation, but the DM interpretation seems to conflict with recent joint limits from different astronomical scale observations such as dwarf spheroidal galaxies, the Milky Way halo, and galaxy groups/clusters. Motivated by 8Be and 4He anomalous transitions with possible new interactions mediated by a vector boson X, we consider a small fraction of DM mainly annihilating into a pair of on-shell vector bosons followed by in this paper. The Galactic center gamma-ray excess is explained by this DM cascade annihilation. The gamma rays are mainly from inverse Compton scattering emission, and the DM cascade annihilation could be compatible with joint astrophysical limits and meanwhile be allowed by AMS-02 positron observation. The direct detection of this model is also discussed.

Method of star image identification based on robust perceptual hash feature

Traditional star image identification methods use adjacent stellar angular distances to form identification features. The missed detection of high-magnitude stars due to noise interference affects their identification accuracy. We propose a star image identification method based on perceptual hash features. The multiple Gaussian distribution superposition constructed by stars within a certain range around the center star forms the unique standard identification image of that star, in which the brightness distribution is determined by stellar magnitudes. The perceptual hash feature of the standard identification image is then used as a standard identification feature. The observation feature is extracted from the identification image as-constructed by the star points extracted from the star image. Finally, the observation feature is matched with the standard feature to identify the star image. Simulation results indicate that the proposed method can efficiently identify star images and effectively prevent missed stars from influencing the matching results.

Measurement of Hubble constant: were differences in secondary distance indicators apparent as early as the HST Key Project?

Different measurements of the Hubble constant (H 0) are not consistent, and a tension between the CMB based methods and cosmic distance ladder based methods has been observed. Measurements from various distance based methods are also inconsistent. To aggravate the problem, the same cosmological probe (Type Ia SNe for instance) calibrated through different methods also provides different values of H 0. We compare various distance ladder based methods through the already available unique data obtained from the Hubble Space Telescope (HST). Our analysis is based on parametric (t-test) as well as non-parametric statistical methods such as the Mann-Whitney U test and Kolmogorov-Smirnov test. Our results show that different methods provide different values of H 0 and the differences are statistically significant. The biases in the calibration would not account for these differences as the data have been taken from a single telescope with a common calibration scheme. The unknown physical effects or issues with the empirical relations of distance measurement from different probes could give rise to these differences.

On the Color–Metallicity Relation of the Red Clump and the Reddening toward the Magellanic Clouds

Abstract The zero point of the reddening toward the Large Magellanic Cloud (LMC) has been the subject of some dispute. Its uncertainty propagates as a systematic error for methods that measure the extragalactic distance scale through knowledge of the absolute extinction of LMC stars. In an effort to resolve this issue, we used three different methods to calibrate the most widely used metric to predict LMC extinction, the intrinsic color of the red clump, (V − I) RC,0, for the inner ∼3° of that galaxy. The first approach was to empirically calibrate the color zero points of the BaSTI isochrones over a wide metallicity range of Δ[Fe/H] ≈ 1.10 using measurements of red clump stars in 47 Tuc, the solar neighborhood, and NGC 6791. From these efforts, we also measure these properties of the solar neighborhood red clump, (V − I, G BP − K s , G − K s , G RP − K s , J − K s , H − K s , M I , M Ks ) RC,0 = (1.02, 2.75, 2.18, 1.52, 0.64, 0.15, −0.23, −1.63). The second and third methods were to compare the observed colors of the red clump to those of Cepheids and RR Lyrae in the LMC. With these three methods, we estimated the intrinsic color of the red clump of the LMC to be (V − I) RC,0,LMC = {≈0.93, 0.91 ± 0.02, 0.89 ± 0.02}, respectively, and similarly, using the first and third methods, we estimated (V − I) RC,0,SMC = {≈0.85, 0.84 ± 0.02}, respectively, for the Small Magellanic Cloud. We estimate the luminosities to be M I,RC,LMC = −0.26 and M I,RC,SMC = −0.37. We show that this has important implications for recent calibrations of the tip of the red giant branch in the Magellanic Clouds used to measure H 0.