Period-luminosity Research Articles

Three Ultra-short-period Contact Eclipsing Binary Systems Mined from Massive Astronomical Surveys

We present the photometric analysis of three ultra-short-period total eclipsing binaries in contact configuration, CRTS_J172718.0+431624, OGLE-BLG-ECL-000104, and OGLE-BLG-ECL-000012, mined from massive astronomical surveys. Using the available archival light curves (LCs) from Vista Variables in the Vía Láctea (VVV), Optical Gravitational Lensing Experiment (OGLE), Zwicky Transient Facility, and Catalina Sky Survey in different passbands and new multiband photometric observations with the 2.3 m Aristarchos telescope at Helmos Observatory, their relative physical parameters were derived. We explored the parameter space by using the PIKAIA genetic algorithm optimizer. The best photometric solution and error budget estimation were adopted for each system through Markov Chain Monte Carlo sampling of the global optimum. The approximate absolute parameters were derived for each contact system adopting an empirical mass–luminosity relation. All three systems have a mass ratio lower than 0.5. The exchange between the primary and secondary depths of CRTS_J172718.0+431624 during 2016–2022 may be due to spot activity. In addition, we present a detailed analysis of the first well-characterized shortest-period contact eclipsing binary with total eclipses known so far (OGLE-BLG-ECL-000104). Thanks to VVV and OGLE LCs, new distances were derived for OGLE-BLG-ECL-000104 and OGLE-BLG-ECL-000012 using empirical period–luminosity relations. The origin and evolutionary status of all three ultra-short-period contact binaries are thoroughly discussed in the context of the detached binary formation channel.

Cosmicflows-4

With Cosmicflows-4, distances are compiled for 55,877 galaxies gathered into 38,065 groups. Eight methodologies are employed, with the largest numbers coming from the correlations between the photometric and kinematic properties of spiral galaxies (TF) and elliptical galaxies (FP). Supernovae that arise from degenerate progenitors (type Ia SNe) are an important overlapping component. Smaller contributions come from distance estimates from the surface brightness fluctuations of elliptical galaxies and the luminosities and expansion rates of core-collapse supernovae (SNe II). Cepheid period–luminosity relation and tip of the red giant branch observations founded on local stellar parallax measurements along with the geometric maser distance to NGC 4258 provide the absolute scaling of distances. The assembly of galaxies into groups is an important feature of the study in facilitating overlaps between methodologies. Merging between multiple contributions within a methodology and between methodologies is carried out with Bayesian Markov chain Monte Carlo procedures. The final assembly of distances is compatible with a value of the Hubble constant of H 0 = 74.6 km s−1 Mpc−1 with the small statistical error of ±0.8 km s−1 Mpc−1 but a large potential systematic error of ∼3 km s−1 Mpc−1. Peculiar velocities can be inferred from the measured distances. The interpretation of the field of peculiar velocities is complex because of large errors on individual components and invites analyses beyond the scope of this study.

Detection of the longest periodic variability in 6.7 GHz methanol masers of G5.900−0.430

Abstract Long-term monitoring observations with the Hitachi 32 m radio telescope of the 6.7 GHz methanol masers associated with the high-mass star-forming region G5.900−0.430 are presented. A period of flux variability at approximately 1260 d is detected in the features at VLSR = 9.77 and 10.84 km s−1, while a secondary shorter period, 130.6 d, is determined for the 0.66 km s−1 feature. This is only the second source which has two different periods. The period of ∼1260 d is approximately twice as long as the longest known period of 6.7 GHz methanol masers. The variability pattern of the symmetric sine curves and the consistency with the expected period–luminosity relation suggest that the mechanism of the maser flux variability of the 9.77 and 10.84 km s−1 features in this source can be explained by protostellar pulsation instability. On the other hand, because the 0.66 km s−1 feature has an intermittent and asymmetric variability profile, we propose that this feature is explained by the colliding wind binary or spiral shock models. Obtaining the spatial distribution of the 0.66 km s−1 feature using very long baseline interferometry will lead to a better understanding of this source.

Relating peak optical luminosity and orbital period of stellar-mass black holes in X-ray binaries

ABSTRACT We compare the peak optical luminosity with the orbital period for a sample of 22 stellar-mass black hole candidates with good measurements of both quantities. We find that the peak absolute magnitude for the outbursts follows a linear relation with MV, peak = 3.48(± 0.85) − 3.89(± 0.91) logPorb, which corresponds to a $L_V \propto P_{orb}^{1.56\pm 0.36}$ power-law relation. Excluding V4641 Sgr which is a strong outlier and not likely to have outbursts produced by the standard disc instability model, in addition to BW Cir and V821 Ara – both of which have highly uncertain distances; the new correlation for the 19 sources is found to be MV, peak = 3.01 (± 0.93) − 3.21 (± 1.04) logPorb, which corresponds to $L_V \propto P_{orb}^{1.28 \pm 0.42}$. This is an analogous relationship to the ‘Warner relation’ between orbital period and peak luminosity found for cataclysmic variables. We discuss the implications of these results for finding black hole X-ray binaries in other galaxies and in our own Galaxy with the Large Synoptic Survey Telescope and other future large time domain surveys.

Period-luminosity relation of delta Sct stars from OGLE-IV and the CzeV catalogues

In this article, the period-luminosity (P-L) relation is determined of delta Sct stars, based on a strictly selected sample of 483 stars from the OGLE-IV Galactic bulge fileds, together with 547 delta Sct, of which 52 are high-amplitude delta Sct stars (HADS) from the CzeV catalogue using Gaia DR2 parallaxes and apparent magnitudes. Absolute magnitudes were corrected for interstellar extinction using the Planck thermal foreground dust maps and the 3D Bayestar probabilistic dust map. Where possible, the CzeV catalogue periods were compared with photometric measurements from the TESS mission.

Period–Luminosity Relations in the Local Group of Galaxies

AbstractLocal Group galaxies, particularly the Large and Small Magellanic Clouds, have historically played and continue to play a unique role in studies of the period–luminosity (PL), period–luminosity–color (PLC), and period–Wesenheit (PW) relations, not just for pulsating stars. In recent years, significant efforts have been devoted to calibrate the PL, PLC, and PW relationships at different wavelengths, including studies of the influence of metallicity and nonlinearities on the accuracy of measured distances. However, the PL diagram has many more astrophysical applications. It serves as a vital tool for classifying different types of pulsating stars and can even facilitate the discovery of new classes of variable stars. Moreover, it aids in distinguishing among various modes of pulsation, facilitates the identification of pulsating stars that are members of binary systems, and enables studies of the three-dimensional structures of neighboring galaxies. In this contribution, I present the latest results on the PL, PLC, and PW relations obeyed by various types of variable stars in Local Group galaxies – from δ Scuti stars to Mira variabless and from close binary systems to the mysterious long secondary periods exhibited by red giant and supergiant stars.

Double-mode RR Lyrae star — robust distance and metallicity indicators

AbstractRR Lyrae (RR Lyr) stars are a well-known and useful distance indicator for old stellar populations such as globular clusters and dwarf galaxies. Fundamental-mode RR Lyr (RRab) stars are commonly used to measure distances, and the accuracy of the determined distance is strongly constrained by metallicity. Here, we investigate the metallicity dependence in the period–luminosity (PL) relation of double-mode RR Lyr (RRd) stars. We find and establish a linear relation between metallicity and period or period ratio for RRd stars. This relation can predict the metallicity as accurately as the low-resolution spectra. Based on this relation, we establish a metallicity-independent PL relation for RRd stars. Combining the distance of the Large Magellanic Cloud and Gaia parallaxes, we calibrate the zero point of the derived PL relation to an error of 0.022 mag. Using RRd stars, we measure the distances of globular clusters and dwarf galaxies with an accuracy of 2-3% and 1-2%, respectively. In the future, RRd stars could anchor galaxy distances to an accuracy of 1.0% and become an independent distance ladder in the Local Group.

Period–Luminosity–Metallicity relations for Classical Pulsators at Near-infrared Wavelengths

AbstractClassical pulsating stars such as Cepheid and RR Lyrae variables exhibit well-defined Period–Luminosity relations at near-infrared wavelengths. Despite their extensive use as stellar standard candles, the effects of metallicity on Period–Luminosity relations for these pulsating variables, and in turn, on possible biases in distance determinations, are not well understood. We present ongoing efforts in determining accurate and precise metallicity coefficients of Period–Luminosity-Metallicity relations for classical pulsators at near-infrared wavelengths. For Cepheids, it is crucial to obtain a homogeneous sample of photometric light curves and high-resolution spectra for a wide range of metallicities to empirically determine metallicity coefficient and reconcile differences with the predictions of the theoretical models. For RR Lyrae variables, using their host globular clusters covering a wide range of metallicities, we determined the most precise metallicity coefficient at near-infrared wavelengths, which is in excellent agreement with the predictions of the horizontal branch evolution and stellar pulsation models.

Near-infrared observations of RR Lyrae and Type II Cepheid variables in the metal-rich bulge globular cluster NGC 6441

Context. NGC 6441 is a bulge globular cluster (GC) with an unusual horizontal branch morphology and a rich population of RR Lyrae (RRL) and Type II Cepheid (T2C) variables that is unexpected for its relatively high metallicity. Aims. Our goal is to characterize the pulsation properties of the population II RRL and T2C variables in this metal-rich GC and compare them with a sample of variables in more metal-poor clusters, as well as with theoretical predictions. Methods. We present JHKs time-series observations of 42 RRLs, eight T2Cs, and ten eclipsing binary candidate variables in NGC 6441 . The multi-epoch observations were obtained using the FLAMINGOS-2 instrument on the 8-m Gemini South telescope. Multiband data are used to investigate pulsation properties of the RRL and T2C variables, including their light curves, instability strip, period–amplitude diagrams, and period–luminosity and period–Wesenheit relations (PLRs and PWRs) in the JHKs filters. Results. The near-infrared (NIR) pulsation properties of RRL variables are well fitted with theoretical models that have canonical helium content and the mean-metallicity of NGC 6441 ([Fe/H] = −0.44 ± 0.07 dex). The helium-enhanced RRL models predict brighter NIR magnitudes and bluer colors than the observations of RRL in the cluster. We find that the empirical slopes of the RRL PLRs and PWRs in NGC 6441 are statistically consistent with those of RRLs in more metal-poor GCs, as well as the theoretical models. Therefore, we use theoretical calibrations of RRL period–luminosity–metallicity (PLZ) relations to simultaneously estimate the mean reddening, E(J − Ks)=0.26 ± 0.06 mag, and the distance, d = 12.67 ± 0.09 kpc, to NGC 6441. Our mean reddening value is consistent with an independent estimate from the bulge reddening map based on red clump stars. The RRL-based distance agrees well with similar literature measurements based on the PLZ relations, and the Gaia and other independent methods. Our distance and reddening values provide a very good agreement between the PLRs of T2Cs in NGC 6441 and those for RRLs and T2Cs in Galactic GCs that span a broad range of metallicity. Conclusions. We conclude that the NIR colour-magnitude diagrams, pulsation properties, and PLRs for RRLs and T2Cs in NGC 6441 are in good agreement with the predictions of RRL pulsation models with canonical helium content. This suggests that these population II variables are either not significantly helium enhanced, as previously thought, or the impact of such enhancement is smaller in NIR than the predictions of the pulsation models.

The Cepheid Extragalactic Distance Scale: Past, Present and Future

AbstractCepheids have been the cornerstone of the extragalactic distance scale for a century. With high-quality data, these luminous supergiants exhibit a small dispersion in their Leavitt (period–luminosity) relation, particularly at longer wavelengths, and few methods rival the precision possible with Cepheid distances. In these proceedings, we present an overview of major observational programs pertaining to the Cepheid extragalactic distance scale, its progress and remaining challenges. In addition, we present preliminary new results on Cepheids from the James Webb Space Telescope (JWST). The launch of JWST has opened a new chapter in the measurement of extragalactic distances and the Hubble constant. JWST offers a resolution three times that of the Hubble Space Telescope (HST) with nearly 10 times the sensitivity. It has been suggested that the discrepancy in the value of the Hubble constant based on Cepheids compared to that inferred from measurements of the cosmic microwave background requires new and additional physics beyond the standard cosmological model. JWST observations will be critical in reducing remaining systematics in the Cepheid measurements and for confirming if new physics is indeed required. Early JWST data for the galaxy, NGC 7250 show a decrease in scatter in the Cepheid Leavitt law by a factor of two relative to existing HST data and demonstrate that crowding/blending effects are a significant issue in a galaxy as close as 20 Mpc.

Detection of the longest periodic variability in 6.7 GHz methanol masers with iMet

AbstractLong-term monitoring observations of the 6.7 GHz methanol masers by Hitachi 32-m operated by Ibaraki University, which are named as “the Ibaraki 6.7 GHz Methanol Maser Monitor (iMet)”, have revealed that the periods of the flux variability of 6.7 GHz methanol masers in the five high-mass star-forming regions G05.900-0.430, G06.795-0.257, G10.472+0.027, G12.209-0.102 and G13.657-0.599 are over 1000 days. These periods are approximately twice the longest known period of 6.7 GHz methanol masers of 668 days for G196.45-1.68. The facts that the flux variation patterns show symmetric sine curves and that the luminosity of the central protostar and periods of maser flux variation are consistent with the expected period-luminosity (PL) relation suggest that the mechanism of maser flux variability of G05.900-0.430, G10.472+0.027 and G12.209-0.102 can be explained by protostellar pulsation instability. From the period-luminosity relation, central stars of these three sources are expected to be very high-mass protostars with a mass of : ∼40 M⊚ and a mass accretion rate of : ∼2×10-2M⊚yr-1. On the other hand, G06.795-0.257 and G13.657-0.599 have luminosities that are an order of magnitude smaller than that expected from PL relation, and the variation patterns are intermittent, suggesting a variation mechanism of these sources originated from binary system.

Sub-percent binary star masses and distances from interferometric observations

AbstractOur knowledge of stellar evolution relies on constraints provided by measurements of the physical stellar properties such as the mass, effective temperature, and radii. The most fundamental parameter, the stellar mass, is rarely available or has a low accuracy, providing poor constraints on the stellar structure and evolution. Observing binary stars combining astrometry and spectroscopy offers the unique opportunity to measure very precise masses. In addition, double-lined spectroscopic binaries provide independent distance measurements with an extreme accuracy, allowing to test the Gaia parallaxes and the period-luminosity (P-L) relations. I will show that masses and distances with an accuracy level as high as 0.05% can be obtained by combining interferometric and spectroscopic observations for different types of binary systems, i.e. binary Cepheids, eclipsing and non-eclipsing binaries.

A multi-wavelength analysis of BL Her stars: Models versus Observations

AbstractWe present new theoretical period–luminosity (PL) and period–radius (PR) relations at multiple wavelengths (Johnson–Cousins–Glass and Gaia passbands) for a fine grid of BL Herculis models computed using mesa-rsp. The non-linear models were computed for periods typical of BL Her stars, i.e. 1 ≤ P(days) ≤ 4, covering a wide range of input parameters: metallicity (−2.0 dex ≤ [Fe/H] ≤ 0.0 dex), stellar mass (0.5–0.8 ), luminosity (50–300 ) and effective temperature (full extent of the instability strip; in steps of 50K). We investigate the impact of four sets of convection parameters on multi-wavelength properties. Most empirical relations match well with theoretical relations from the BL Her models computed using the four sets of convection parameters. No significant metallicity effects are seen in the PR relations. Another important result from our grid of BL Her models is that it supports combining PL relations of RR Lyrae and Type II Cepheids together as an alternative to classical Cepheids for the extragalactic distance scale calibration.

Impact of the Gaia ESA mission on the primary Period–Luminosity Calibrators in the Milky Way: Cepheids and RR Lyrae

AbstractWe discuss the impact of Gaia, the cornerstone mission of the European Space Agency (ESA), on the calibration of the period–luminosity and luminosity–metallicity relations of Cepheids and RR Lyrae stars, with specific reference to data published as part of the most recent Gaia releases: Early Data Release 3 (EDR3), on 19 December 2020, and Data Release 3 (DR3) on 13 June 2022. We provide future perspectives for the Gaia mission, including extensions approved by ESA and a tentative schedule of the data releases that will take place in the next few years. We briefly present plans for cross-Coordination Unit processing of Gaia data of Cepheids and RR Lyrae stars for DR4 and conclude by outlining the expected improvement in astrometry at the end of the extended Gaia mission, which will help to further strengthen the calibration of the first rung of the cosmic distance ladder.

China Space Station Telescope and Variable Star Studies

AbstractIn the last five years, the number of periodic variable stars has increased by two million. We used the ZTF DR2 data to find and build a catalog that includes 780,000 periodic variable stars. These periodic variable stars were classified into 11 types, which greatly complemented the variable stars in Galactic disk. Based on the latest ZTF DR16 data, we found 2 million variable candidates. We trained a machine learner to classify variable stars, and the learner had a prediction accuracy of 94%. Using millions of variable stars, we carried out studies to optimize the period–luminosity relations and the Galactic structure and the extinction law. With the future China Space Station Telescope, millions of variable stars in the Local Group will be discovered. They help to study the structure of our Local Group and also to cross-check the distance ladders based on different variable stars.

Anomalous Cepheids: Updated Theoretical Period–Luminosity–Color and Period–Wesenheit Relations

AbstractIn the context of a project aimed to provide an updated theoretical scenario for various classes of radially pulsating stars, we present the first results obtained for anomalous Cepheids. By adopting reliable and updated evolutionary prescriptions concerning the luminosity levels for various core He-burning stellar models with masses suitable for entering the instability strip, we have computed nonlinear convective pulsation models for both fundamental and first-overtone mode anomalous Cepheids by exploring the impact of varying the metal abundance as well as the efficiency of super-adiabatic convection. These numerical simulations have allowed us to retrieve the boundaries of the instability strip and all relevant pulsation properties, namely period, amplitude, bolometric light and radial velocity curves. This theoretical scenario has been transformed into the Gaia photometric system to derive the first theoretical Period–Luminosity–Colour and Period–Wesenheit relations in the Gaia bands.

Primary Period–Luminosity-Relation Calibrators in the Milky Way: Cepheids and RR Lyrae Physical basis, Calibration, and Applications

AbstractIn this invited review I discuss the calibration and applications of the period–luminosity relation of classical Cepheid and RR Lyrae stars. After a brief introduction, starting with results from Hipparcos and discussing some post-Hipparcos era developments, I focus on recent results using Gaia Data Release 3 data. I present an overview of the most recent period–luminosity relations, a discussion and some new results on Cepheids in open clusters. I also discuss the effect of reddening and that the use of Wesenheit indices is actually an oversimplification to dealing with the problem of reddening.

Cepheids with giant companions: A new, abundant source of Cepheid astrophysics

AbstractWe present a progress report of our project aiming to increase the number of known Cepheids in double-lined binary (SB2) systems from six to 100 or more. This will allow us, among other goals, to accurately measure masses for a large sample of Cepheids. Currently, only six accurate Cepheid masses are available, which hinders our understanding of their physical properties and renders the Cepheid mass–luminosity relation poorly constrained. At the same time, Cepheids are widely used for essential measurements (e.g., extragalactic distances, the Hubble constant). To examine Cepheid period–luminosity relations, we selected as binary candidates Cepheids that are too bright for their periods. To date, we have confirmed 56 SB2 systems, including the detection of significant orbital motions of the components for 32. We identified systems with orbital periods up to five times shorter than the shortest reported period to date, as well as systems with mass ratios significantly different from unity (suggesting past merger events). Both features are essential to understand how multiplicity affects the formation and destruction of Cepheid progenitors and what effect this has on global Cepheid properties. We also present eight new systems composed of two Cepheids (only one such system was known before). Among confirmed SB2 Cepheids, there are also several wide-orbit systems. In the future, these may facilitate independent accurate geometric distance measurements to the Large and Small Magellanic Clouds.

A Segmented Period–Luminosity Relation for Nearby Extragalactic Delta Scuti Stars

The period–luminosity relations (PLRs) of Milky Way δ Scuti (δ Sct) stars have been described to the present day by a linear relation. However, when studying extragalactic systems such as the Magellanic Clouds and several dwarf galaxies, we notice for the first time a nonlinear behavior in the PLR of δ Sct stars. Using the largest sample of ∼3700 extragalactic δ Sct stars from data available in the literature—mainly based on the Optical Gravitational Lensing Experiment and the Super MAssive Compact Halo Object project in the Large Magellanic Cloud (LMC)—we obtain that the best fit to the period–luminosity (M V ) plane is given by the following piecewise linear relation with a break at logP = −1.03 ± 0.01 (or 0.093 ± 0.002 days) for shorter periods (sp) and longer periods (lp) than the break-point: Geometric or depth effects in the LMC, metallicity dependence, or different pulsation modes are discarded as possible causes of this segmented PLR seen in extragalactic δ Sct stars. The origin of the segmented relation at ∼0.09 days remains unexplained based on the current data.

An Improved Calibration of the Wavelength Dependence of Metallicity on the Cepheid Leavitt Law

The Cepheid period–luminosity (PL) relation (or Leavitt law) has served as the first rung of the most widely used extragalactic distance ladder and is central to the determination of the local value of the Hubble constant (H 0). We investigate the influence of metallicity on Cepheid brightness, a term that significantly improves the overall fit of the distance ladder, to better define its wavelength dependence. To this aim, we compare the PL relations obtained for three Cepheid samples having distinct chemical composition (in the Milky Way and Magellanic Clouds) and focusing on the use of improved and recent data while covering a metallicity range of about 1 dex. We estimate the metallicity effect (hereafter γ) in 15 filters from mid-IR to optical wavelengths, including five Wesenheit indices, and we derive a significant metallicity term in all filters, in agreement with recent empirical studies and models, in the sense of metal-rich Cepheids being brighter than metal-poor ones. We describe the contribution of various systematic effects in the determination of the γ term. We find no evidence of γ changing over the wavelength range 0.5–4.5 μm, indicating that the main influence of metallicity on Cepheids is in their luminosity rather than color. Finally, we identify factors that sharpen the empirical constraints on the metallicity term over past studies, including corrections for the depth of the Magellanic Clouds, better-calibrated Cepheid photometry, improved Milky Way extinction estimates, and revised and expanded metallicity measurements in the LMC.