Period-luminosity Research Articles

Calibrating and Standardizing the Tip of the Red Giant Branch in the Small Magellanic Cloud Using Small-amplitude Red Giants

We investigate the absolute calibration of the tip of the red giant branch (TRGB) in the Small Magellanic Cloud (SMC) using small amplitude red giant stars (SARGs) classified by the Optical Gravitational Lensing Experiment (OGLE). We show that all stars near the SMC’s TRGB are SARGs. Distinguishing older and younger RGs near the tip according to two period–luminosity sequences labeled A and B, we show many similarities among SARG populations of the Large Magellanic Cloud (LMC) and the SMC, along with notable differences. In particular, SMC SARGs have shorter periods due to lower metallicity and smaller amplitudes due to younger ages than LMC SARGs. We discover two period–color relations near the TRGB that span all A-sequence and B-sequence stars in the OGLE-III footprints of the SMC and LMC, and we investigate using periods instead of color for TRGB standardization. Using variability-derived information only, we trace the SMC’s age and metallicity gradients and show the core to be populated by younger, more metal-rich RGs. The B-sequence yields the brightest and most accurate calibration (M F814W,syn = −4.057 ± 0.019(stat.) ± 0.029(syst.) mag), which we use to measure the distance modulus difference between the Clouds and investigate metallicity effects. Distance measurements not informed by variability should employ the SARG-based calibration based on all stars near the tip (M F814W,syn = −4.024 ± 0.041(stat.) ± 0.029(syst.) mag). Our work highlights the impact of RG population diversity on TRGB distance measurements. Further study is needed to unravel these effects and improve TRGB standardization.

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.

Period-luminosity and period-luminosity-metallicity relations for Galactic RR Lyrae stars in the Sloan bands

Context. RR Lyrae stars are excellent tracers of the old population II due to their period-luminosity (PL) and period-luminosity-metallicity (PLZ) relations. While these relations have been investigated in detail in many photometric bands, there are few comprehensive studies about them in Sloan-like systems. Aims. We present PL and PLZ relations (as well as their counterparts in Wesenheit magnitudes) in the Sloan–Pan-STARSS gP1rP1iP1 bands obtained for Galactic RR Lyrae stars in the vincinity of the Sun. Methods. The data used in this paper were collected with the network of 40 cm telescopes of the Las Cumbres Observatory, and geometric parallaxes were adopted from Gaia Data Release 3. Results. We derived PL and PLZ relations separately for RRab and RRc-type stars, as well as for the mixed population of RRab+RRc stars. Conclusions. To our knowledge, these are the first PL and PLZ relations in the Sloan bands determined using RR Lyrae stars in the Galactic field.

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.

A New Catalog of 100,000 Variable TESS A-F Stars Reveals a Correlation between δ Scuti Pulsator Fraction and Stellar Rotation

δ Scuti variables are found at the intersection of the classical instability strip and the main sequence on the Hertzsprung–Russell diagram. With space-based photometry providing millions of light curves of A-F type stars, we can now probe the occurrence rate of δ Scuti pulsations in detail. Using the 30 minutes cadence light curves from NASA's Transiting Exoplanet Survey Satellite's first 26 sectors, we identify variability in 103,810 stars within 5–24 cycles per day down to a magnitude of T = 11.25. We fit the period–luminosity relation of the fundamental radial mode for δ Scuti stars in the Gaia G band, allowing us to distinguish classical pulsators from contaminants for a subset of 39,367 stars. Out of this subset, over 15,918 are found on or above the expected period–luminosity relation. We derive an empirical red edge to the classical instability strip using Gaia photometry. The center where the pulsator fraction peaks at 50%–70%, combined with the red edge, agrees well with previous work in the Kepler field. While many variable sources are found below the period–luminosity relation, over 85% of sources inside of the classical instability strip derived in this work are consistent with being δ Scuti stars. The remaining 15% of variables within the instability strip are likely hybrid or γ Doradus pulsators. Finally, we discover strong evidence for a correlation between pulsator fraction and spectral line broadening from the Radial Velocity Spectrometer on board the Gaia spacecraft, confirming that rotation has a role in driving pulsations in δ Scuti stars.

Multimode δ Sct stars from the Zwicky Transient Facility Survey

We obtain the largest catalog of multimode δ Sct stars in the northern sky to date using the Zwicky Transient Facility (ZTF) Data Release 20. The catalog includes 2254 objects, of which 2181 are new to our study. Among these multimode δ Sct stars, 2142 objects are double-mode δ Sct, while 109 objects are triple-mode δ Sct and three are quadruple-mode δ Sct. By analyzing the light curves in the r and g bands of the ZTF, we determine the basic parameters of multimode δ Sct stars, including the periods and amplitudes. Periods are checked by comparison with the Optical Gravitational Lensing Experiment catalog of double-mode δ Sct stars. On the Petersen diagram, multimode δ Sct stars form six sequences. We find that in Galactic coordinates, the periods of 1O/F double-mode δ Sct stars at high latitudes are shorter than those of 1O/F double-mode δ Sct stars in the disk, due to metallicity variations. In the future, our catalog can be used to establish the period–luminosity relation and the period–metallicity relation of double-mode δ Sct stars, and to study the Galactic structure.

Signature of High-amplitude Pulsations in Seven δ Sct Stars via TESS Observations

The regular behavior of the pulsations of high-amplitude δ Sct (HADS) stars gives a greater chance to investigate the interiors of stars. We analyzed seven HADS stars showing peak-to-peak amplitudes of more than 0.3 mag that were newly observed by TESS. We obtained that TIC 374753270, TIC 710783, and TIC 187386415 pulsate in fundamental radial mode; also, TIC 130474019 and TIC 160120432 show double radial modes. On the other hand, TIC 148357344 and TIC 278119167 demonstrate triple-mode behavior. Our analysis shows that these seven stars are close to the red edge of the (inside) instability strip in the Hertzsprung–Russell diagram. The fundamental mode of these seven targets follows the period–luminosity (PL) relation for δ Sct stars. However, TIC 278119167 deviates slightly from the fundamental PL relation. The double-mode and triple-mode HADS stars (TIC 130474019, TIC 160120432, TIC 148357344, and TIC 278119167) are in agreement with the period ratio ranges (fundamental to first and second overtones). Using the information of 176 HADS stars (Netzel and Smolec), we find a scaling relation ( [Fe/H]∝log(M7.95±0.15L−1.83±0.11P00.79±0.14Teff0.047±0.02 )) between the metallicity ([Fe/H]) and mass (M), luminosity (L), effective temperature (T eff), and the fundamental period (P0). We estimate the metallicity of the seven newly identified HADS stars ranging from −0.62 to 0.37 dex.

Mid-infrared Period–Luminosity Relations of Gaia DR3 Long Period Variables

Long period variable (LPV) stars are very promising distance indicators in the infrared bands. We selected asymptotic giant branch (AGB) stars in the Large and Small Magellanic Cloud (LMC and SMC) from the Gaia Data Release 3 LPV catalog, and classified them into oxygen-rich (O-rich) and carbon-rich (C-rich) AGB stars. Using the Wide-field Infrared Survey Explorer database, we determined the W1- and W2-band period–luminosity relations (PLRs) for each pulsation-mode sequence of AGB stars. The dispersion of the PLRs of O-rich AGB stars in sequences C′ and C is relatively small, around 0.14 mag. The PLRs of LMC and SMC are consistent in each sequence. In the W2 band, the PLR of large-amplitude C-rich AGB stars is steeper than that of small-amplitude C-rich AGB stars, due to their more circumstellar dust. By two methods, we find that some PLR sequences of O-rich AGB stars in the LMC are dependent on metallicity. The coefficients of the metallicity effect are β = –0.533 ± 0.213 mag dex1 and β = –0.767 ± 0.158 mag dex1 for sequence C in W1 and W2 bands, respectively. The significance of the metallicity effect in W1 band for the four sequences is 2.2−3.5σ. Both of these imply that distance measurements using O-rich Mira may need to take the metallicity effect into account.

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.

Multiwavelength photometric study of RR lyrae variables in the globular cluster NGC 5272 (Messier 3)

ABSTRACT We present a comprehensive photometric study of RR Lyrae stars in the M3 globular cluster, utilizing a vast data set of 3140 optical (UBVRI) CCD images spanning 35 yr from astronomical data archives. We have successfully identified previously known 238 RR Lyrae stars from the photometric data, comprising 178 RRab, 49 RRc, and 11 RRd stars. Multiband periodogram was used to significantly improve the long-term periods of 65 per cent of RR Lyrae stars in our sample, thanks to the unprecedentedly long temporal coverage of the observations. The light curve templates were used to obtain accurate and precise mean magnitudes and amplitudes of all RR Lyrae variables. We combined optical (UBVRI) and near-infrared (NIR, JHKs) photometry of RR Lyrae variables to investigate their location in the colour-magnitude diagrams as well as the pulsation properties such as period distributions, Bailey diagrams and amplitude ratios. The period–luminosity relations in R and I bands and Period–Wesenheit relations were derived after excluding outliers identified in CMDs. The Period–Wesenheit relations calibrated via the theoretically predicted relations were used to determine a distance modulus of $\mu = 15.04 \pm 0.04 \, {\rm (stats)} \pm 0.19 \, {\rm {(syst.)}}$ mag (using metal-independent WBV Wesenheit) and $\mu = 15.03 \pm 0.04 \, {\rm (stats)} \pm 0.17 \, {\rm {(syst.)}}$ mag (using metal-dependent WVI Wesenheit). Our distance measurements are in excellent agreement with published distances to M3 in the literature. We also employed an artificial neural network based comparison of theoretical and observed light curves to determine physical parameters (mass, luminosity, and effective temperature) for 79 non-Blazhko RRab stars that agree with limited literature measurements.

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.

Asteroseismological Analysis of the Non-Blazhko RRab Star EPIC 248846335 in the LAMOST–Kepler/K2 Project

We conduct an asteroseismological analysis on the non-Blazhko ab-type RR Lyrae star EPIC 248846335, employing the Radial Stellar Pulsations module of the Modules for Experiments in Stellar Astrophysics based on the set of stellar parameters. The atmospheric parameters T eff = 6933 ± 70 K, log g = 3.35 ± 0.50, and [Fe/H] = −1.18 ± 0.14 are estimated from low-resolution spectra of LAMOST DR9. The luminosity L = 49.70−1.80+2.99 L ⊙ and mass M = 0.56 ± 0.07 M ⊙ are calculated, respectively, using the distance provided by Gaia and the metallicity estimated from the low-resolution spectra. The Fourier parameters of the light curves observed by K2 and radial velocity (RV) curves determined from the medium-resolution spectra of LAMOST DR10 are also calculated in this work. The period of the fundamental mode of the star and the residuals r of the Fourier parameters between the models and observations serve to select an optimal model, whose stellar parameters are T eff = 6700 ± 220 K, log g = 2.70, [Fe/H] = −1.20 ± 0.2, M = 0.59 ± 0.05 M ⊙, and L = 56.0 ± 4.2 L ⊙. The projection factors are constrained as 1.20 ± 0.02 and 1.59 ± 0.13 by the blue- and red-arm observed velocities with their corresponding RV curves derived from the best-fit model, respectively. The precise determination of stellar parameters in ab-type RR Lyrae stars is crucial for understanding the physical processes that occur during pulsation and for providing a deeper understanding of their period–luminosity relationship.

The candidates of long-periodic variable sources in 6.7 GHz methanol masers associated with four high-mass star-forming regions

Abstract Results of the long-term monitoring observations by the Hitachi 32 m radio telescope of the 6.7 GHz Class II methanol masers associated with four high-mass star-forming regions are presented. We detected periodic flux variability in G06.795−0.257, G10.472+0.027, G12.209−0.102, and G13.657−0.599 with the periods of 968, 1624, 1272, and 1266 d, respectively, although the detected period is tentative due to the short monitoring term relative to the estimated period. The facts that the flux variation patterns show the symmetric sine curves and that the luminosities of the central protostar and periods of maser flux variation are consistent with the expected period–luminosity (PL) relation suggest that the mechanisms of maser flux variability of G10.472+0.027 and G12.209−0.102 can be explained by protostellar pulsation instability. From the PL relation, the central stars of these two sources are expected to be very high-mass protostars with a mass of $\sim 40\, M_{\odot }$ and to have a mass accretion rate of $\sim 2 \times 10^{-2}\, M_{\odot }\:$yr−1. On the other hand, G06.795−0.257 and G13.657−0.599 have intermittent variation patterns and have luminosities that are an order of magnitude smaller than those expected from the PL relation, suggesting that the variation mechanisms of these sources originated from a binary system. Since almost all the maser features vary with the same period regardless of the geometry, periodic accretion models may be appropriate mechanisms for flux variability in G06.795−0.257 and G13.657−0.599.

The Cepheid Distance Scale: A Novel Method for Obtaining Mean Magnitudes from Single-epoch Observations

We present a novel technique for mapping single-phase observations of Cepheids in any given band into their time-averaged values, using strong priors on the known interrelations of the multiwavelength widths of Cepheid period–luminosity (PL) relations, combined with the physical ordering of individual Cepheids within and across the instability strip, as a function of temperature (or radius). The method is empirically calibrated and tested using high-precision published multiwavelength observations of Cepheids in the LMC. The example, given herein, takes a single-epoch B-band PL relation and transforms those random-phase observations to within ±0.05–0.06 mag of their time-averaged values. For high-precision single-phase data points, this method can transform single-phase magnitudes into mean magnitudes (without additional observations), bringing the statistical error budget for the PL relation at that wavelength down to the systematic floor. This technique is of particular importance for use with space-based facilities (e.g., Hubble Space Telescope or JWST) where limits on the availability of telescope time preclude dense phase coverage, often resulting in only single-epoch observations being available.

Discovery of the Longest-period Classical Cepheid in the Milky Way

We report the discovery of the classical Cepheid OGLE-GD-CEP-1884 (= GDS_J1535467-555656) with the longest pulsation period known in our Galaxy. The period of 78.14 days is nearly 10 days longer than that of the previous record-holding Cepheid, S Vulpeculae, and thus, OGLE-GD-CEP-1884 can be categorized as the first ultra-long-period Cepheid in the Milky Way. This star is present in the ASAS-SN and Gaia DR3 catalogs of variable stars, but it has been classified as a long-period variable in those catalogs. Based on more than 10 yr of the photometric monitoring of this star carried out by the OGLE project in the I and V bands and a radial velocity curve from the Gaia Focused Product Release, we unequivocally demonstrate that this object is a fundamental-mode classical Cepheid. By employing the mid-infrared period–luminosity relation, we determine the distance to OGLE-GD-CEP-1884 (4.47 ± 0.34 kpc) and place it on the Milky Way map, along with about 2400 other classical Cepheids. We also discuss the potential of finding additional ultra-long-period Cepheids in our Galaxy.

Galactic Archeology with Luminous Red Giant Oscillations in Gaia DR3 Photometry

Asteroseismology has significantly advanced the field of Galactic archeology, providing essential insights into the formation and evolution of our Galaxy. Here we present an asteroseismic analysis of 103 luminous red giant stars that were observed by Gaia in our Galaxy and the Large Magellanic Cloud. Leveraging a period–luminosity–amplitude relationship determined using data from the OGLE mission, we measure distances to these stars of up to 100 kpc, probing distances more than a factor of 2 beyond where Gaia parallaxes can be measured accurately. We have determined distance uncertainties of 8% or better for 80% of the stars in our sample and reduced known distance uncertainties for stars in this sample by more than a factor of 2 on average. Applying this approach to future Gaia data releases can provide more precise and accurate distances and constrain fundamental properties for 10,000+ stars across our Galaxy.

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.

Pulsation modeling of the Cepheid Y Ophiuchi with RSP/MESA

Context. Y Ophiuchi (Y Oph) is a classical Cepheid with a pulsation period of P = 17.12 days. This star is reported to be as dim as a Cepheid of about half its pulsation period and it exhibits a low radial velocity and light-curve amplitude. For these reasons, Y Oph is not used to calibrate period-luminosity (PL) relation and its distance remains uncertain. Aims. Our objective is to conduct hydrodynamical pulsation modeling of Y Oph to derive its distance and provide a physical insight into its low amplitude and luminosity, constrained by an extensive set of observations. Methods. We first performed a linear analysis on a grid of models using the hydrodynamical pulsation code MESA-RSP to find the combinations of mass, metallicity, effective temperature, and luminosity resulting in linear excitation of pulsations with period of about 17 days. Then, we performed non-linear computations to obtain the full-amplitude pulsations of these models. Last, we compare the results to a complete set of observations along the pulsation cycle, including the angular diameter obtained by interferometry, effective temperature, and radial velocity obtained by high-resolution spectroscopy, as well as the light curves in the VJHKSLM bands. We simultaneously adjusted the distance, the color excess and circumstellar envelope (CSE) model to fit the light curves and the angular diameter. Results. We find that all pulsation models at high effective temperatures are in remarkable agreement with the observations along the pulsation cycle. This result suggests that the low amplitude of Y Oph may be explained by proximal location to the blue edge of the instability strip (IS). We also find that a pulsational mass of about 7 − 8 M⊙ is consistent with a non-canonical evolutionary model with moderate overshooting, PL relation and Gaia parallax. However, a much lower mass below 5 M⊙ is required to match Baade-Wesselink (BW) distance measurements from the literature. We show that the combination of the impact of the CSE on the photometry, together with a projection factor of about 1.5, explains the discrepant distance and luminosity values obtained from BW methods. Conclusions. Our findings indicate that the small pulsation amplitude of Y Oph can be attributed to its proximity to the blue edge of the instability strip. Additionally, our analysis reveals that the distances obtained using the BW method are biased compared to Gaia, mainly due to the impact of circumstellar envelope on the photometries and a high p-factor close to 1.5. Despite these unique characteristics, Y Oph is a long-period classical Cepheid that holds potential for calibration of the PL relation in the Galaxy.

The Mira Distance to M101 and a 4% Measurement of H 0

The giant spiral galaxy M101 is host to the nearest recent Type Ia supernova (SN 2011fe) and thus has been extensively monitored in the near-infrared to study the late-time light curve of the SN. Leveraging this existing baseline of observations, we derive the first Mira-based distance to M101 by discovering and classifying a sample of 211 Miras with periods ranging from 240–400 days in the SN field. Combined with new Hubble Space Telescope (HST) WFC3/IR channel observations, our data set totals 11 epochs of F110W (HST YJ) and 13 epochs of F160W (HST H) data spanning ∼2900 days. We adopt absolute calibrations of the Mira period–luminosity relation based on geometric distances to the Large Magellanic Cloud and the water megamaser host galaxy NGC 4258, and find μ M101 = 29.10 ± 0.06 mag. This distance is in 1σ agreement with most other recent Cepheid and tip of the red giant branch distance measurements to M101. Including the previous Mira SN Ia host, NGC 1559, and SN 2005df, we determine the fiducial SN Ia peak luminosity, MB0=−19.27±0.09 mag. With the Hubble diagram of supernovae Ia, we derive H 0 = 72.37 ± 2.97 km s−1 Mpc−1, a 4.1% measurement of H 0 using Miras. We find excellent agreement with recent Cepheid distance ladder measurements of H 0 and confirm previous indications that the local universe value of H 0 is higher than the early universe value at ∼95% confidence. Currently, the Mira-based H 0 measurement is still dominated by the statistical uncertainty in the SN Ia peak magnitude.