TRGB Research Articles

Screened fifth forces lower the TRGB-calibrated Hubble constant too

The local distance ladder measurement of the Hubble constant requires a connection between geometric distances at low redshift and Type Ia supernovae in the Hubble flow, which may be achieved through either the Cepheid period--luminosity relation or the luminosity of the Tip of the Red Giant Branch (TRGB) feature of the Hertzsprung--Russell diagram. Any potential solution to the Hubble tension that works by altering the distance ladder must produce consistency of both the Cepheid and TRGB $H_0$ calibrations with the CMB. In this paper we extend our models of screened fifth forces (Desmond et al 2019) to cover the TRGB framework. A fifth force lowers TRGB luminosity, so a reduction in inferred $H_0$ requires that the stars that calibrate the luminosity---currently in the LMC---are on average less screened than those that calibrate the supernova magnitude. We show that even under pessimistic assumptions for the extinction to the LMC, full consistency with Planck can be achieved for a fifth force strength in unscreened RGB stars $\sim$0.2 that of Newtonian gravity. This is allowed by the comparison of Cepheid and TRGB distance measurements to nearby galaxies. Our results indicate that the framework of Desmond et al (2019) is more versatile than initially demonstrated, capable of ameliorating the Hubble tension on a second front.

Discovery of ubiquitous lithium production in low-mass stars

The vast majority of stars with mass similar to the Sun are expected to only destroy lithium over the course of their lives, via low-temperature nuclear burning. This has now been supported by observations of hundreds of thousands of red giant stars (Brown et al. 1989, Kumar et al. 2011, Deepak et al. 2019, Singh et al. 2019, Casey et al. 2019). Here we perform the first large-scale systematic investigation into the Li content of stars in the red clump phase of evolution, which directly follows the red giant branch phase. Surprisingly we find that all red clump stars have high levels of lithium for their evolutionary stage. On average the lithium content increases by a factor of 40 after the end of the red giant branch stage. This suggests that all low-mass stars undergo a lithium production phase between the tip of the red giant branch and the red clump. We demonstrate that our finding is not predicted by stellar theory, revealing a stark tension between observations and models. We also show that the heavily studied (Brown et al. 1989, Reddy et al. 2005, Kumar et al. 2011, Singh et al. 2019, Casey et al. 2019) very Li-rich giants, with A(Li) $> +1.5$ dex, represent only the extreme tail of the lithium enhancement distribution, comprising 3% of red clump stars. Our findings suggest a new definition limit for Li-richness in red clump stars, A(Li) $> -0.9$ dex, which is much lower than the limit of A(Li) $> +1.5$ dex used over many decades (Brown et al. 1989, Castilho et al. 1995, Reddy et al. 2005, Carlberg et al. 2016, Casey et al. 2019, Holanda et al. 2020).

Cosmic dissonance: are new physics or systematics behind a short sound horizon?

Context. Persistent tension between low-redshift observations and the cosmic microwave background radiation (CMB), in terms of two fundamental distance scales set by the sound horizon rd and the Hubble constant H0, suggests new physics beyond the Standard Model, departures from concordance cosmology, or residual systematics. Aims. The role of different probe combinations must be assessed, as well as of different physical models that can alter the expansion history of the Universe and the inferred cosmological parameters. Methods. We examined recently updated distance calibrations from Cepheids, gravitational lensing time-delay observations, and the tip of the red giant branch. Calibrating the baryon acoustic oscillations and type Ia supernovae with combinations of the distance indicators, we obtained a joint and self-consistent measurement of H0 and rd at low redshift, independent of cosmological models and CMB inference. In an attempt to alleviate the tension between late-time and CMB-based measurements, we considered four extensions of the standard ΛCDM model. Results. The sound horizon from our different measurements is rd = (137 ± 3stat. ± 2syst.) Mpc based on absolute distance calibration from gravitational lensing and the cosmic distance ladder. Depending on the adopted distance indicators, the combined tension in H0 and rd ranges between 2.3 and 5.1 σ, and it is independent of changes to the low-redshift expansion history. We find that modifications of ΛCDM that change the physics after recombination fail to provide a solution to the problem, for the reason that they only resolve the tension in H0, while the tension in rd remains unchanged. Pre-recombination extensions (with early dark energy or the effective number of neutrinos Neff = 3.24 ± 0.16) are allowed by the data, unless the calibration from Cepheids is included. Conclusions. Results from time-delay lenses are consistent with those from distance-ladder calibrations and point to a discrepancy between absolute distance scales measured from the CMB (assuming the standard cosmological model) and late-time observations. New proposals to resolve this tension should be examined with respect to reconciling not only the Hubble constant but also the sound horizon derived from the CMB and other cosmological probes.

MCR-TRGB: A Multiwavelength-covariant, Robust Tip of the Red Giant Branch Measurement Method*

Abstract We present a new method to measure colors and magnitudes of the tip of the red giant branch (TGRB) in multiple bandpasses simultaneously by fitting an n-dimensional Gaussian to photometry of candidate tip stars. We demonstrate that this method has several advantages over traditional edge detection, particularly in regimes where the TRGB magnitude is strongly color dependent, as is the case in the near-infrared (NIR). We apply this method to a re-reduction of a set of optical and NIR Hubble Space Telescope data originally presented in Dalcanton et al. (D12). The re-reduction takes advantage of the increased depth and accuracy in the NIR photometry enabled by simultaneous reduction with higher-resolution optical data in crowded fields. We compare three possible absolute calibrations of the resulting apparent TRGB measurements, one adopting the same distance moduli as in D12 and two based on predicted TRGB absolute magnitudes from two widely used, modern sets of model isochrones. We find systematic offsets among the model absolute calibrations at the ∼0.15 mag level, in line with previous investigations. The models also have difficulty reproducing the optical–NIR color–magnitude behavior of our measurements, making these observations a useful benchmark for future improvements.

A measurement of the Hubble constant from Type II supernovae

ABSTRACT Progressive increases in the precision of the Hubble-constant measurement via Cepheid-calibrated Type Ia supernovae (SNe Ia) have shown a discrepancy of ∼4.4σ with the current value inferred from Planck satellite measurements of the cosmic microwave background radiation and the standard $\Lambda $cold dark matter (ΛCDM) cosmological model. This disagreement does not appear to be due to known systematic errors and may therefore be hinting at new fundamental physics. Although all of the current techniques have their own merits, further improvement in constraining the Hubble constant requires the development of as many independent methods as possible. In this work, we use SNe II as standardisable candles to obtain an independent measurement of the Hubble constant. Using seven SNe II with host-galaxy distances measured from Cepheid variables or the tip of the red giant branch, we derive H$_0= 75.8^{+5.2}_{-4.9}$ km s−1 Mpc−1 (statistical errors only). Our value favours that obtained from the conventional distance ladder (Cepheids + SNe Ia) and exhibits a difference of 8.4 km s−1 Mpc−1 from the Planck + ΛCDM value. Adding an estimate of the systematic errors (2.8 km s−1 Mpc−1) changes the ∼1.7σ discrepancy with Planck +ΛCDM to ∼1.4σ. Including the systematic errors and performing a bootstrap simulation, we confirm that the local H0 value exceeds the value from the early Universe with a confidence level of 95 per cent. As in this work, we only exchange SNe II for SNe Ia to measure extragalactic distances, we demonstrate that there is no evidence that SNe Ia are the source of the H0 tension.

Beyond Gaia: Asteroseismic Distances of M Giants Using Ground-based Transient Surveys

Abstract Evolved stars near the tip of the red giant branch show solar-like oscillations with periods spanning hours to months and amplitudes ranging from ∼1 mmag to ∼100 mmag. The systematic detection of the resulting photometric variations with ground-based telescopes would enable the application of asteroseismology to a much larger and more distant sample of stars than is currently accessible with space-based telescopes such as Kepler or the ongoing Transiting Exoplanet Survey Satellite mission. We present an asteroseismic analysis of 493 M giants using data from two ground-based surveys: the Asteroid Terrestrial-impact Last Alert System (ATLAS) and the All-Sky Automated Survey for Supernovae (ASAS-SN). By comparing the extracted frequencies with constraints from Kepler, the Sloan Digital Sky Survey Apache Point Observatory Galaxy Evolution Experiment, and Gaia we demonstrate that ground-based transient surveys allow accurate distance measurements to oscillating M giants with a precision of ∼15%. Using stellar population synthesis models we predict that ATLAS and ASAS-SN can provide asteroseismic distances to ∼2 × 106 galactic M giants out to typical distances of 20–50 kpc, vastly improving the reach of Gaia and providing critical constraints for Galactic archeology and galactic dynamics.

TESS Asteroseismic Analysis of the Known Exoplanet Host Star HD 222076

Abstract The Transiting Exoplanet Survey Satellite (TESS) is an all-sky survey mission aiming to search for exoplanets that transit bright stars. The high-quality photometric data of TESS are excellent for the asteroseismic study of solar-like stars. In this work, we present an asteroseismic analysis of the red-giant star HD 222076 hosting a long-period (2.4 yr) giant planet discovered through radial velocities. Solar-like oscillations of HD 222076 are detected around 203 μHz by TESS for the first time. Asteroseismic modeling, using global asteroseismic parameters as inputs, yields a determination of the stellar mass ( ), radius ( ), and age (7.4 ± 2.7 Gyr), with precisions greatly improved from previous studies. The period spacing of the dipolar mixed modes extracted from the observed power spectrum reveals that the star is on the red-giant branch burning hydrogen in a shell surrounding the core. We find that the planet will not escape the tidal pull of the star and will be engulfed into it within about 800 Myr, before the tip of the red-giant branch is reached.

Tracing the anemic stellar halo of M 101

Models of galaxy formation in a cosmological context predict that massive disk galaxies should have structured extended stellar halos. Recent studies in integrated light, however, report that a few galaxies, including the nearby disk galaxy M 101, have no measurable stellar halos to the detection limit. We aim to quantify the stellar content and structure of M 101’s outskirts by resolving its stars. We present the photometry of its stars based on deepF606WandF814Wimages taken withHubbleSpace Telescope (HST) as part of the GHOSTS survey. The HST fields are placed along the east and west sides of M 101 out to galactocentric distance (R) of ∼70 kpc. The constructed color-magnitude diagrams of stars reach down to two magnitudes below the tip of the red giant branch. We derived radial number density profiles of the bright red giant branch (RGB) stars. The mean color of the RGB stars atR ∼ 40−60 kpc is similar to those of metal-poor globular clusters in the Milky Way. We also derived radial surface brightness profiles using the public image data provided by the Dragonfly team. Both the radial number density and surface brightness profiles were converted to radial mass density profiles and combined. We find that the mass density profiles show a weak upturn at the very outer region, where surface brightness is as faint asμg ≈ 33 mag arcsec−2. An exponential disk + power-law halo model on the mass density profiles finds the total stellar halo mass ofMhalo= 8.2−2.2+3.5× 107M⊙. The total stellar halo mass does not exceedMhalo = 3.2 × 108 M⊙when strongly truncated disk models are considered. In combining the halo mass with the total stellar mass of M 101, we obtain the stellar halo mass fraction ofMhalo/Mgal= 0.20−0.08+0.10% with an upper limit of 0.78%. We compare the halo properties of M 101 with those of six GHOSTS survey galaxies as well as the Milky Way and M 31 and find that M 101 has an anemic stellar halo similar to the Milky Way.

A Tip of the Red Giant Branch Distance to the Dark Matter Deficient Galaxy NGC 1052-DF4 from Deep Hubble Space Telescope Data

Abstract Previous studies have shown that the large, diffuse galaxies NGC 1052-DF2 and NGC 1052-DF4 both have populations of unusually luminous globular clusters as well as a very low dark matter content. Here we present newly obtained deep Hubble Space Telescope Advanced Camera for Surveys imaging of one of these galaxies, NGC 1052-DF4. We use these data to measure the distance of the galaxy from the location of the tip of the red giant branch (TRGB). We find a rapid increase in the number of detected stars fainter than m F814W ∼ 27.3, which we identify as the onset of the red giant branch. Using a forward modeling approach that takes the photometric uncertainties into account, we find a TRGB magnitude of . The inferred distance, including the uncertainty in the absolute calibration, is D TRGB = 20.0 ± 1.6 Mpc. The TRGB distance of NGC 1052-DF4 is consistent with the previously determined surface brightness fluctuation distance of D SBF = 18.7 ± 1.7 Mpc to NGC 1052-DF2 and is consistent with the distance of the bright elliptical galaxy NGC 1052. We conclude that the unusual properties of these galaxies cannot be explained by distance errors.

The Isaac Newton Telescope Monitoring Survey of Local Group Dwarf Galaxies. I. Survey Overview and First Results for Andromeda I

Abstract An optical monitoring survey in nearby dwarf galaxies was carried out with the 2.5 m Isaac Newton Telescope. Fifty-five dwarf galaxies and four isolated globular clusters in the Local Group were observed with the Wide Field Camera. The main aims of this survey are to identify the most evolved asymptotic giant branch (AGB) stars and red supergiants at the end-point of their evolution based on their pulsational instability, use their distribution over luminosity to reconstruct the star formation history, quantify the dust production and mass loss from modeling the multiwavelength spectral energy distributions (SEDs), and relate this to luminosity and radius variations. In this first of a series of papers, we present the methodology of the variability survey and describe the photometric catalog of the Andromeda I (And I) dwarf galaxy as an example of the survey, and we discuss the identified long period variable (LPV) stars. We detected 5581 stars and identified 59 LPV candidates within two half-light radii of the center of And I. The amplitudes of these candidates range from 0.2 to 3 mag in the i-band. Seventy-five percent of detected sources and 98% of LPV candidates are detected at mid-infrared wavelengths. We show evidence for the presence of dust-producing AGB stars in this galaxy including five extreme AGB (x-AGB) stars, and we model some of their SEDs. A distance modulus of 24.41 mag for And I was determined based on the tip of the red giant branch. Also, a half-light radius of 3.′2 ± 0.′3 was calculated.

Distance Measurements to Parent Galaxies of SNIa by the Tip of the Red-Giant Branch

Abstract—We use the archival data obtained with the Hubble space telescope to measure distances by the tip of the red-giant branch (TRGB) method to SNIa parent galaxies. Our sample consists of four galaxies: NGC2841, NGC4496A, NGC4535, and NGC4527. For three of them, we were able to determine only the lower bounds of the distance. For the galaxy NGC4527, we estimated the TRGB distance modulus: (m − M)0 = 30m.56 ± 0m.09. Combining our measurements with the published data, we compared the supernova distance moduli using the MLCS2k2 method and the host galaxies with the TRGB method. SNIa distance moduli show systematically higher value at 0m.15–0m.18 relative to the scale of the TRGB distances. This corresponds to overestimation of the luminosity of supernovae with the MLCS2k2 method. We estimated the luminosity of supernovae at the brightness maximum as MV = −19m.33 ± 0m.03 which allows one to accept the following Hubble constant: H0 = 70.4 ± 1.0 km s−1 Mpc−1.

Calibration of the Tip of the Red Giant Branch

Abstract The tip of the red giant branch (TRGB) method provides one of the most accurate and precise means of measuring the distances to nearby galaxies. Here we present a multi-wavelength, VIJHK absolute calibration of the TRGB based on observations of TRGB stars in the Large Magellanic Cloud (LMC), grounded on a geometric distance, determined by detached eclipsing binaries (DEBs). This paper presents a more detailed description of the method first presented by Freedman et al. for measuring corrections for the total line-of-sight extinction and reddening to the LMC. In this method, we use a differential comparison of the red giant population in the LMC, first with red giants in the Local Group galaxy IC 1613, and then with those in the Small Magellanic Cloud (SMC). As a consistency check, we derive an independent calibration of the TRGB sequence using the SMC alone, invoking its geometric distance also calibrated by DEBs. An additional consistency check comes from near-infrared observations of Galactic globular clusters covering a wide range of metallicities. In all cases we find excellent agreement in the zero-point calibration. We then examine the recent claims by Yuan et al., demonstrating that, in the case of the SMC, they corrected for extinction alone while neglecting the essential correction for reddening. In the case of IC 1613, we show that their analysis contains an incorrect treatment of (over-correction for) metallicity. Using our revised (and direct) measurement of the LMC TRGB extinction, we find a value of H 0 = 69.6 ± 0.8 (±1.1% stat) ± 1.7 (±2.4% sys) km s−1 Mpc−1.

The Strikingly Metal-rich Halo of the Sombrero Galaxy*

Abstract The nature of the Sombrero galaxy (M104 = NGC 4594) has remained elusive despite many observational studies at a variety of wavelengths. Here we present Hubble Space Telescope imaging of two fields at ∼16 and 33 kpc along the minor axis to examine stellar metallicity gradients in the extended spheroid. We use this imaging, extending more than 2 mag below the tip of the red giant branch, in combination with artificial star tests to forward model observed color–magnitude diagrams, measuring metallicity distribution functions (MDFs) at different radii along the minor axis. An important and unexpected result is that the halo of the Sombrero is strikingly metal-rich: even the outer field, located at ∼17 effective radii of the bulge, has a median metallicity [Z/H] ∼ −0.15, and the fraction of stars with [Z/H] < −1.0 is negligible. This is unprecedented among massive galaxy halos studied to date, even among giant ellipticals. We find significant radial metallicity gradients, characterized by an increase in the fraction of metal-poor stars with radius and a gradient in median metallicity of ∼0.01 dex kpc−1. The density profile is well fit by power laws with slopes that exhibit a dependence on metallicity, with flatter slopes for more metal-poor stars. We discuss our results in the context of recent stellar MDF studies of other nearby galaxies and potential formation scenarios for the Sombrero galaxy.

An Improved Distance to NGC 4258 and Its Implications for the Hubble Constant

Abstract NGC 4258 is a critical galaxy for establishing the extragalactic distance scale and estimating the Hubble constant ( ). Water masers in the nucleus of the galaxy orbit about its supermassive black hole, and very long baseline interferometric observations of their positions, velocities, and accelerations can be modeled to give a geometric estimate of the angular-diameter distance to the galaxy. We have improved the technique to obtain model parameter values, reducing both statistical and systematic uncertainties compared to previous analyses. We find the distance to NGC 4258 to be 7.576 ± 0.082 (stat.) ± 0.076 (sys.) Mpc. Using this as the sole source of calibration of the Cepheid-SN Ia distance ladder results in km s−1 Mpc−1, and in concert with geometric distances from Milky Way parallaxes and detached eclipsing binaries in the LMC we find km s−1 Mpc−1. The improved distance to NGC 4258 also provides a new calibration of the tip of the red giant branch of mag, with reduced systematic errors for the determination of compared to the LMC-based calibration, because it is measured on the same Hubble Space Telescope (HST) photometric system and through similarly low extinction as SN Ia host halos. The result is km s−1 Mpc−1, in good agreement with the result from the Cepheid route, and there is no difference in when using the same calibration from NGC 4258 and the same SN Ia Hubble diagram intercept to start and end both distance ladders.

Consistent Calibration of the Tip of the Red Giant Branch in the Large Magellanic Cloud on the Hubble Space Telescope Photometric System and a Redetermination of the Hubble Constant

Abstract We present a calibration of the tip of the red giant branch (TRGB) in the Large Magellanic Cloud (LMC) on the Hubble Space Telescope (HST)/ACS F814W system. We use archival HST observations to derive blending corrections and photometric transformations for two ground-based wide-area imaging surveys of the Magellanic Clouds. We show that these surveys are biased bright by up to ∼0.1 mag in the optical due to blending, and that the bias is a function of local stellar density. We correct the LMC TRGB magnitudes from Jang & Lee and use the geometric distance from Pietrzyński et al. to obtain an absolute TRGB magnitude of . Applying this calibration to the TRGB magnitudes from Freedman et al. in SN Ia hosts yields a value for the Hubble constant of H 0 = 72.4 ± 2.0 km s−1 Mpc−1 for their TRGB+SNe Ia distance ladder. The difference in the TRGB calibration and the value of H 0 derived here and by Freedman et al. primarily results from their overestimate of the LMC extinction, caused by inconsistencies in their different sources of TRGB photometry for the Magellanic Clouds. Using the same source of photometry (OGLE) for both Clouds and applying the aforementioned corrections yields a value for the LMC I-band TRGB extinction that is lower by 0.06 mag, consistent with independent OGLE reddening maps used by us and by Jang & Lee to calibrate TRGB and determine H 0.

The M101 Satellite Luminosity Function and the Halo–Halo Scatter among Local Volume Hosts

Abstract We have obtained deep Hubble Space Telescope (HST) imaging of 19 dwarf galaxy candidates in the vicinity of M101. Advanced Camera for Surveys HST photometry for two of these objects showed resolved stellar populations and tip of the red giant branch derived distances (D ∼ 7 Mpc) consistent with M101 group membership. The remaining 17 were found to have no resolved stellar populations, meaning they are either part of the background NGC 5485 group or are distant low surface brightness (LSB) galaxies. It is noteworthy that many LSB objects that had previously been assumed to be M101 group members based on projection have been shown to be background objects, indicating the need for future diffuse dwarf surveys to be very careful in drawing conclusions about group membership without robust distance estimates. In this work we update the satellite luminosity function of M101 based on the presence of these new objects down to M V = −8.2. M101 is a sparsely populated system with only nine satellites down to M V ≈ −8, as compared with 26 for M31 and 24.5 ± 7.7 for the median host in the Local Volume. This makes M101 by far the sparsest group probed to this depth, although M94 is even sparser to the depth at which it has been examined (M V = −9.1). M101 and M94 share several properties that mark them as unusual compared with the other Local Volume galaxies examined: they have a very sparse satellite population but also have high star-forming fractions among these satellites; such properties are also found in the galaxies examined as part of the Satellites around Galactic Analogs survey. We suggest that these properties appear to be tied to the wider galactic environment, with more isolated galaxies showing sparse satellite populations that are more likely to have had recent star formation, while those in dense environments have more satellites that tend to have no ongoing star formation. Overall, our results show a level of halo-to-halo scatter between galaxies of similar mass that is larger than is predicted in the lambda cold dark matter model.

The Carnegie-Chicago Hubble Program. VII. The Distance to M101 via the Optical Tip of the Red Giant Branch Method*

Abstract The Carnegie-Chicago Hubble Program (CCHP) is building a direct path to the Hubble constant (H 0) using Population II stars as the calibrator of the Type Ia supernova (SN Ia)-based distance scale. This path to calibrate the SNe Ia is independent of the systematics in the traditional Cepheid-based technique. In this paper, we present the distance to M101, the host to SN 2011fe, using the I-band tip of the red giant branch (TRGB) based on observations from the ACS/WFC instrument on the Hubble Space Telescope. The CCHP targets the halo of M101, where there is little to no host galaxy dust, the red giant branch is isolated from nearly all other stellar populations, and there is virtually no source confusion or crowding at the magnitude of the tip. Applying the standard procedure for the TRGB method from the other works in the CCHP series, we find a foreground-extinction-corrected M101 distance modulus of μ 0 = 29.07 ± 0.04stat ± 0.05sys mag, which corresponds to a distance of D = 6.52 ± 0.12stat ± 0.15sys Mpc. This result is consistent with several recent Cepheid-based determinations, suggesting agreement between Population I and II distance scales for this nearby SN Ia host galaxy. We further analyze four archival data sets for M101 that have targeted its outer disk to argue that targeting in the stellar halo provides much more reliable distance measurements from the TRGB method owing to the combination of multiple structural components and heavy population contamination. Application of the TRGB in complex regions will have sources of uncertainty not accounted for in commonly used uncertainty measurement techniques.

TESS Asteroseismology of the Known Red-giant Host Stars HD 212771 and HD 203949

Abstract The Transiting Exoplanet Survey Satellite (TESS) is performing a near all-sky survey for planets that transit bright stars. In addition, its excellent photometric precision enables asteroseismology of solar-type and red-giant stars, which exhibit convection-driven, solar-like oscillations. Simulations predict that TESS will detect solar-like oscillations in nearly 100 stars already known to host planets. In this paper, we present an asteroseismic analysis of the known red-giant host stars HD 212771 and HD 203949, both systems having a long-period planet detected through radial velocities. These are the first detections of oscillations in previously known exoplanet-host stars by TESS, further showcasing the mission’s potential to conduct asteroseismology of red-giant stars. We estimate the fundamental properties of both stars through a grid-based modeling approach that uses global asteroseismic parameters as input. We discuss the evolutionary state of HD 203949 in depth and note the large discrepancy between its asteroseismic mass (M * = 1.23 ± 0.15 M ⊙ if on the red-giant branch or M * = 1.00 ± 0.16 M ⊙ if in the clump) and the mass quoted in the discovery paper (M * = 2.1 ± 0.1 M ⊙), implying a change >30% in the planet’s mass. Assuming HD 203949 to be in the clump, we investigate the planet’s past orbital evolution and discuss how it could have avoided engulfment at the tip of the red-giant branch. Finally, HD 212771 was observed by K2 during its Campaign 3, thus allowing for a preliminary comparison of the asteroseismic performances of TESS and K2. We estimate the ratio of the observed oscillation amplitudes for this star to be , consistent with the expected ratio of ∼0.85 due to the redder bandpass of TESS.

Stellar Population and Structural Properties of Dwarf Galaxies and Young Stellar Systems in the M81 Group

We use Hyper Suprime-Cam on the Subaru Telescope to investigate the structural and photometric properties of early-type dwarf galaxies and young stellar systems at the center of the M81 Group. We have mapped resolved stars to $\sim2$ magnitudes below the tip of the red giant branch over almost 6.5 square degrees, corresponding to a projected area of $160\times160 \rm{kpc}$ at the distance of M81. The resulting stellar catalogue enables a homogeneous analysis of the member galaxies with unprecedented sensitivity to low surface brightness emission. The radial profiles of the dwarf galaxies are well-described by Sersic and King profiles, and show no obvious signatures of tidal disruption. The measured radii for most of these systems are larger than the existing literature values and we find the total luminosity of IKN ($\rm{M_{V,0}}=-14.29$) to be almost 3 magnitudes brighter than previously-thought. We identify new dwarf satellite candidates, d1006+69 and d1009+68, which we estimate to lie at a distance of $4.3\pm0.2$ Mpc and $3.5\pm0.5$ Mpc. With $\rm{M_{V,0}}=-8.91\pm0.40$ and $\rm{[M/H]}=-1.83\pm0.28$, d1006+69 is one of the faintest and most metal-poor dwarf satellites currently-known in the M81 Group. The luminosity functions of young stellar systems in the outlying tidal HI debris imply continuous star formation in the recent past and the existence of populations as young as 30 Myr old. We find no evidence for old RGB stars coincident with the young MS/cHeB stars which define these objects, supporting the idea that they are genuinely new stellar systems resulting from triggered star formation in gaseous tidal debris.

Tensions between the early and late Universe

The standard cosmological model successfully describes many observations from widely different epochs of the Universe, from primordial nucleosynthesis to the accelerating expansion of the present day. However, as the basic cosmological parameters of the model are being determined with increasing and unprecedented precision, it is not guaranteed that the same model will fit more precise observations from widely different cosmic epochs. Discrepancies developing between observations at early and late cosmological time may require an expansion of the standard model, and may lead to the discovery of new physics. The workshop "Tensions between the Early and the Late Universe" was held at the Kavli Institute for Theoretical Physics on July 15-17 2019 (More details of the workshop (including on-line presentations) are given at the website: https://www.kitp.ucsb.edu/activities/enervac-c19) to evaluate increasing evidence for these discrepancies, primarily in the value of the Hubble constant as well as ideas recently proposed to explain this tension. Multiple new observational results for the Hubble constant were presented in the time frame of the workshop using different probes: Cepheids, strong lensing time delays, tip of the red giant branch (TRGB), megamasers, Oxygen-rich Miras and surface brightness fluctuations (SBF) resulting in a set of six new ones in the last several months. Here we present the summary plot of the meeting that shows combining any three independent approaches to measure H$_0$ in the late universe yields tension with the early Universe values between 4.0$\sigma$ and 5.8$\sigma$. This shows that the discrepancy does not appear to be dependent on the use of any one method, team, or source. Theoretical ideas to explain the discrepancy focused on new physics in the decade of expansion preceding recombination as the most plausible. This is a brief summary of the workshop.