RR Lyrae and Cepheids IV: Large-scale surveys as bridges between spectroscopy and photometry
La Palma, 26-30 September 2022
Volume 2 2022
Session 1a: Stellar models and HRD
Marconi Marcella, INAF-Osservatorio Astronomico di Capodimonte
Classical pulsating stars are important distance indicators and stellar population tracers. On this basis a comprehensive investigation of their properties based on both an observational and a theoretical approach is crucial. The most important theoretical tools and results obtained for both classical Cepheids and RR Lyrae are outlined and their reliability is tested against observed pulsation properties. Finally some open problems in the modeling of classical pulsators, mainly related to the treatment of convection, mass loss and rotation, as well as the adoption of static model atmospheres. are discussed together with the planned future development.
De Somma Giulia, INAF-Osservatorio Astronomico di Capodimonte
Modeling of radially pulsating stars, specifically Classical Cepheids, is fundamental to constrain the extragalactic distance scale. The various ingredients entering the theoretical calibration of the Classical Cepheid distance scale can affect the accuracy and reliability of the inferred distances and, as such, cast light on residual systematics in the local determination of the Hubble constant in the context of the debated topic on the so-called Hubble constant tension. By extending the set of nonlinear convective pulsation models published for solar metallicity (Z = 0.02 – De Somma et al. 2020) to Z = 0.004, Z = 0.008 and Z = 0.03, we provide a detailed homogeneous nonlinear model grid taking into account variations of the mass-luminosity (ML) relation, the efficiency of super-adiabatic convection and the chemical composition. A multiband light curve atlas was produced and in turn, period-luminosity-color (PLC) and period-Wesenheit (PW) relation for each assumed chemical composition, mass-luminosity relation, and efficiency of super-adiabatic convection were derived. The inclusion of the metallicity term in the derivation of PW relations allows us to properly predict the metallicity dependence of the Cepheid distance scale. The derived metal-dependent PW relations were then compared with similar results in the literature and applied to a sample of Gaia Early Data Release 3 Galactic Cepheids with known metal abundances so as to estimate their individual distances.By combining this updated pulsation scenario with self-consistent updated stellar evolutionary predictions, we also derived period-age (PA) and multi-band period-age-color (PAC) relations that take into account variations in the ML relation. These relationships have been used to investigate the metallicity effect when using Classical Cepheids as age indicators, and to finally estimate the age of a sample of Classical Cepheids in the Gaia EDR3 dataset.
Ziukowska Oliwia, Nicolaus Copernicus Astronomical Center
Contemporary one-dimensional stellar evolution codes, like MESA (Modules for Experiments in Stellar Astrophysics) come with a large quantity of free parameters that allow to model the physical processes in stellar interiors under many different assumptions.
Lub Jan, Leiden Observatory
Session 2: Spectroscopic Survey
Chiappini Cristina, Leibniz Institute for Astrophysics Potsdam – AIP
The focus of this talk will be to show how spectroscopic surveys can make the link between classical pulsators and galactic archaeology. I will first show the current mapping of the MW via spectroscopic surveys and what we expect to have in the near future.
Viviani Giordano, EPFL
We present the first data release of VELOCE, a project dedicated to measuring high-precision radial velocities (RVs) of Galactic classical Cepheids from both Hemispheres over up to 10 year baselines targeting dense phase coverage. VELOCE DR1 comprises more than 18,100 individual observations of 256 bona fide classical Cepheids spanning pulsation period and V-band magnitude ranges from 1.9-69d and 2-13mag. RV uncertainties are photon noise limited in most cases and the average per-observation RV uncertainty is 0.065 km/s. For bright stars, RV uncertainties can be as low as 2 m/s. Pulsation-averaged (vgamma) velocities of stars with more than 10 observations are measured to an average uncertainty of 0.42 km/s, reaching as low as 2 m/s uncertainty in some cases. VELOCE RVs are consistent with the IAU RV standard star system to within ~ 20m/s and we determine zero-point differences between VELOCE and 30 literature data sets by template fitting. Spectroscopic binaries identified using VELOCE data alone, or in conjunction with literature data, are presented in a companion paper (Shetye et al.). VELOCE data enable several new insights into the pulsational variability of Cepheids. Chiefly among these are: a high-definition view of the Hertzsprung progression in RVs, the identification of double-peaked bumps in the pulsation curve, and clear evidence that virtually all Cepheids observed in sufficient detail feature variance unexplained by periodic Fourier series models, that is, additional modulation signals are ubiquitous in Cepheids. We identify 4 previously unknown “modulators” that exhibit orbital motion in addition to RV amplitude variations and/or time-variable phase shifts. We will close by highlighting further features that elucidate systematic uncertainties involving Baade-Wesselink projection factor calibration.
Trentin Erasmo, PhD Student
Classical Cepheids (DCEPs) are the first fundamental step in the calibration of the cosmological distance ladder and represent powerful tracers in the context of Galactic studies. In the context of the C-MetaLL (Cepheids-Metallicity in the Leavitt Law) survey, we collected high-resolution spectroscopy with UVES@VLT for a sample of 65 DCEPs. Most of them are among the faintest DCEPs ever observed spectroscopically in the Milky Way (MW), out to Galactocentric radii as large as ∼20 Kpc. For each target we derived accurate atmospheric parameters, radial velocities, and abundances for 24 different species. The resulting iron abundances range between +0.3 and −1.1 dex, while the bulk of stars has [Fe/H]∼ −0.5 dex. We complemented our sample with literature data obtaining a total sample of 637 DCEPs. Taking advantage of the Gaia Early Data Release 3 (EDR3) and the 2MASS survey, we collected the photometry in V, I, G, GBP, GRP, J, H, Ks bands, which were also used to build a variety of reddening-free Wesenheit magnitudes. We use all these photometric and spectroscopic data, in conjunction with Gaia DR3 parallaxes to discuss the dependence on metallicity of the DCEPs Period-Luminosity and Period-Wesenheit relations, on a spectroscopically measured metallicity range never explored before
Hocdé Vincent, Nicolaus Copernic Astronomical Center
Estimating metallicity of classical Cepheids is of prime importance for studying chemical evolution of galaxies, metallicity effect on stellar evolution and ultimately its impact on period-luminosity relation used in the extragalactic distance scale.
Giuseppina Battaglia, IAC
The Gaia mission has already brought about a revolution in our understanding of the Milky Way system. Spectroscopic surveys obtaining accurate radial velocities and elemental abundances for stars that are too faint for Gaia’s Radial Velocity Spectrometer are however an essential complement to exploit the Gaia data in their full potential. In this presentation I will review the plans for Galactic Archaeology surveys with WEAVE, a wide-area multi-object survey spectrograph about the start operations on the 4.2-m William Herschel Telescope at the Observatorio del Roque de los Muchachos. I will give an introduction to the instrument, the various planned surveys and the modalities to ask for observing time. I will then describe the plans for the Galactic Archaeology surveys, in particular those that will target RRLyrae variable stars.
Britavskiy Nikolay, Liege University
Next-generation of multi-fiber spectrographs will provide huge spectroscopic datasets which require only an automatic tools to analyze them in a short timescale. For such purposes we developed the WEAVE Contributed Software in order to investigate the kinematic properties and physical parameters of RR Lyr variables. This tool was designed specifically for such types of variables by taking into account their phenomenological peculiarities. We will present our approach of analyzing the low- and high-resolution spectra within the scientific verification phase of the WEAVE Galactic Archeology survey. In our work, we will discuss how the different physical processes of RR Lyraes (shock phases, etc) could affect such spectroscopic analysis and what is the best strategy to make this analysis reliable for further in-depth study of the chemical composition of these stars.
Julio Olivares Carvajal, PUC/MAS
I will present the results of a spectroscopic analysis of more than 4000 APOGEE RRLs in the Milky Way bulge region (-8 < l < 8 and 1 < |b|< 6) aimed at characterizing the kinematics and spatial distribution of this old population. By combining APOGEE spectra with Gaia and VVV proper motions, we trace the orbits of the RRLs and further constrain the bulge 3D structure.Additionally, in an ongoing project, we use the PMs of more than 12000 new VVV RRLs at |b|<2.5 degrees to obtain the rotation curves in a region closer to the plane than in every previous study.
Ripepi Vincenzo, INAF-Osservatorio Astronomico di Capodimonte
Anomalous Cepheids (ACEPs) are intermediate-mass (1−2 M ☉), low-metallicity, core-He burning stars that are thought to ignite helium under partial electron-degeneracy conditions. They have been found preferentially in old, low metallicity dwarf galaxies of the local group as well as in the Large and Small Magellanic Clouds. Until recently, only a few ACs were known in the Milky Way (MW). However, the advent of large photometric surveys investigating the MW halo, disk and bulge (e.g. Catalina, OGLE, Gaia mission) allowed us to discover hundredts of ACs in our Galaxy. The investigation of the origin of Galactic ACs can help us in understing the details about the formatin of the MW. In this context, we used UVES@VLT to obtain high-resolution spectroscopy of nine Galactic ACEPs, obtaining the abundances for 13 species. This data is presented in combination with literature results for four stars and the implications for the nature of these pulsators as well as their role as stellar population tracers are discussed.
Session 1b:Stellar models and HRD
Montalban Josefina, University of Bologna
Modeling of radially pulsating stars, specifically Classical Cepheids, is fundamental to constrain the extragalactic distance scale. The various ingredients entering the theoretical calibration of the Classical Cepheid distance scale can affect the accuracy and reliability of the inferred distances and, as such, cast light on residual systematics in the local determination of the Hubble constant in the context of the debated topic on the so-called Hubble constant tension. By extending the set of nonlinear convective pulsation models published for solar metallicity (Z = 0.02 – De Somma et al. 2020) to Z = 0.004, Z = 0.008 and Z = 0.03, we provide a detailed homogeneous nonlinear model grid taking into account variations of the mass-luminosity (ML) relation, the efficiency of super-adiabatic convection and the chemical composition. A multiband light curve atlas was produced and in turn, period-luminosity-color (PLC) and period-Wesenheit (PW) relation for each assumed chemical composition, mass-luminosity relation, and efficiency of super-adiabatic convection were derived. The inclusion of the metallicity term in the derivation of PW relations allows us to properly predict the metallicity dependence of the Cepheid distance scale. The derived metal-dependent PW relations were then compared with similar results in the literature and applied to a sample of Gaia Early Data Release 3 Galactic Cepheids with known metal abundances so as to estimate their individual distances.
Matteuzzi Massimiliano, University of Bologna – DIFA
Asteroseismic constraints, coupled with information on photospheric chemical abundances and temperature, have given us the ability to measure radii and masses of tens of thousands of red-giant stars. Precise masses of red-giant stars enable a robust inference of their ages, given the strong relation between the initial mass of a star and the duration of the main-sequence phase, and hence its age on the red-giant branch. However, there are cases where the estimates of age can be highly precise yet very inaccurate. An example are giants that have undergone mass transfer events that have significantly altered their mass. In this context, stars with “apparent” ages significantly higher than the age of the Universe provide candidates stripped stars, or stars that have lost more mass than expected, most likely via interaction with a companion star or because of the poorly understood mass-loss mechanism along the RGB. These stars are present in the Kepler database, both in clusters and among field stars. In our study we look at these objects from an asteroseismic perspective, investigating potential specific signatures of their structure in the frequency spectra. We model the structure and pulsational properties of these stars using MESA+GYRE and we generate realistic artificial pulsation spectra representative of Kepler and K2 observations with AADG3. We find that these stars are characterised by a rather extreme coupling between the pressure-mode and gravity-mode cavities, leading to a large number of detectable dipolar and quadrupolar mixed modes. These peculiar spectra, if observed with sufficient frequency resolution, hold detailed information about the structural properties of likely products of mass stripping, hence can potentially shed light on their formation mechanism and on the transition from the Red horizontal branch (RHB) to the RR Lyrae instability strip. On the other hand, our tests highlight the difficulties associated with measuring reliably the large frequency separation in shorter datasets, with impact on the reliability of the inferred masses and ages of low-mass RHB stars with e.g. K2 or TESS data.
Benhida Abdelmajid, University Cad Ayyad-Oukaimeden Observatory
n this talk we will develop the study of the spectra from the star RR Lyr recorded at the OHP in France and at the Oukaimeden site in Morocco, out of a total of 2437 spectra spread over 21 years. The objective is to determine the physical origin of the emission of the hydrogen Hα line and that of helium D3 in correlation with the pulsation and Blazhko cycles as well as the shock waves which cross its atmosphere.
We were able to detect, for the first time, the statistical correlation on the evolution of the shock wave velocity with the Blazhko phase despite the large shock velocity fluctuations from one pulse cycle to another and the irregularities of the Blazhko cycle. Thus, the velocity increases from the Blazhko minimum to its maximum, then having reached a maximum shock velocity, gradually decreases to the Blazhko minimum to start growing again. This observation result is consistent with the shock wave model proposed by Gillet in 2013. The velocity of the shock wave front, the expression of which was determined by Fadeyev and Gillet, was estimated between 100 and 160 approximately kms-1 corresponding to a Mach number between 10 and 16.
Session 3: Rotation, Binarity, Dynamical and Blazhko
Nardetto Nicolas, Observatoire de la CÙte d’Azur (OCA)
Classical pulsators have long played a crucial role in the distance scale and the determination of the present value of the expansion rate of the universe. This is due to the relation which relates their period of pulsation to their intrinsic luminosity. In order to confirm the Hubble tension, it is mandatory to unveil all possible systematics in the calibration of the extragalactic distance scale, and also to find new roads. For this purpose, there is something important to keep in mind: correct astrophysics, correct cosmology. Classical pulsators are indeed fantastic laboratories to study stellar physics. In this review, we will illustrate how interferometry and spectroscopy have played a fundamental role in characterizing the photosphere/atmosphere/chromosphere of classical pulsators, as well as their close environment and binarity.
Hajdu Gergely, Nicolaus Copernicus Astronomical Center
The measurement of the mass of an RR Lyrae variable is a crucial step towards constraining models of stellar pulsation and evolution. With this aim, we have carried out a search for RR Lyrae variables in binary systems using the Light-Travel Time Effect (LTTE) in the light curves of bulge RR Lyrae published by the Optical Gravitational Lensing Experiment (OGLE). The detected 87 candidates allowed us to draw the first firm conclusions on the population of RR Lyrae stars in binary systems. Some, such as the approximately 1000 day lower limit on the binary periods, are easy to explain with natural selection effects imposed by binary (co-)evolution. Others, such as the large concentration of orbital eccentricities around 0.27, as well as the apparently trimodal distribution of companion masses (with modes of approximately 0.6, 0.2 and 0.067 solar masses) are lacking an explanation.Here we provide a brief update and the latest results on the search for RR Lyrae variables in binary systems, with special emphasis on the radial velocity follow-up efforts of our candidates.
Pilecki Bogumil, Nicolaus Copernicus Astronomical Center
Although Cepheids are widely used for essential measurements (galactic and extragalactic distances, the Hubble constant), such critical physical parameter as their mass is mainly known from theoretical calculations. Surprisingly, we could measure accurate masses of as few as 6 Cepheids only thanks to their membership in double-lined binary (SB2) systems. We recently proposed a photometric method for identifying Cepheids in SB2 systems and have already confirmed spectroscopically 52 new candidates in the LMC and SMC to show double lines. For half of them, we have detected the orbital motion, which is the ultimate proof of their binarity. Among the new SB2 Cepheids, there are such that have never been found in SB2 systems before, namely high-mass Cepheids, cluster Cepheids, double-mode Cepheids, and short-period Cepheids, whose existence is poorly explained by theory, as well as those for which eclipses were detected. The masses obtained for all these Cepheids will be later used to measure mass-luminosity relations.Surprisingly, one studied Cepheid resulted in residing in a system with an orbital period too short for the components to survive the evolution on the red giant branch. This Cepheid is probably on its first crossing, on the way to merging with its companion. We will describe the methods used, summarize the current discoveries, present the preliminary results for selected systems, including the orbital solutions, and finally draw the first conclusions from the study.
Salinas Ricardo, Gemini Observatory/NOIRLab
Despite being one of the most classical markers for old stellar populations, and holders of a widely used period luminosity relation, the actual mass of RR Lyrae stars (RRL) remains a mystery, predicted by stellar evolution models, but never actually measured. This is because of the surprising lack of RRL in binary systems, with currently only one confirmed RRL on such systems.
Shetye Shreeya, EPFL
For more than a century now, Classical Cepheid variable stars have been crucial calibrators of the extragalactic distance scale thanks to the famous period-luminosity (P-L) relation. Cepheid binaries are very common (~60% among bright cepheids) and have been intensively studied to understand the impact of the companion on the calibration of the P-L relationship. Accompanying the first data release of ‘VELOcities of CEpheids’ (VELOCE; 10 years long monitoring program of Cepheids), in my talk I will present our analysis of the single-lined spectroscopic binaries (SB1) as part of the VELOCE project.
Benko Jozsef, Konkoly Observatory
Using two years of data from the TESS space telescope, we have investigated the light curves of RRc stars on a 670-element, homogeneous sample. Our results show that the vast majority (88.3%) of stars contain pulsation modes beyond the main radial pulsation. The incidence rates of the frequencies associated with these modes (and their harmonics/sub-harmonics and linear combinations) were determined. We have identified a new frequency in many stars, probably belonging to the l=10 non-radial mode. The Galactic distributions of RRc stars with and without additional modes proved to be identical. The amplitude distribution of the additional frequencies can be described by Weibull distributions. Separating the quasi-periodic amplitude and phase variations (observed in most stars) from the classical Blazhko effect, we have determined a 10.3% incidence rate for the latter phenomenon. Analying the phase variation functions of 33 RRc stars around the continuous viewing zone (CVZ) of TESS we have offered a plausible explanation for the `phase jump’ phenomenon published in many RRc stars.
Netzel Henryka, Konkoly Observatory, CSFK
Pulsations in RR Lyrae stars and classical Cepheids were thought to be relatively simple since they typically pulsate only in one or two radial modes. This picture changes at a closer look when modulation or additional low-amplitude signals are detected. I will review different multi-periodic groups known among classical pulsators, including stars showing the Blazhko modulation.
Bobrick Alexey, Technion Institute
Despite the classical interpretation of RR Lyrae as old and metal-poor population II stars, it is well known that metal-rich (up to solar values) RR Lyrae stars exist in the solar vicinity. Some of these stars are also consistent with Sun-like kinematics, i.e. they likely belong to the thin-disc population.In this talk, I will present the results of the first comprehensive study of the chemo-kinematics of RR Lyrae stars in the Gaia DR2*. Thanks to the unprecedented Gaia capabilities, we found that the metal-rich RR Lyrae stars are present all over the Galactic disc, well beyond the Solar neighbourhood. The kinematics of these stars is consistent with a young (less than 5 Gyr) thin disc population, in particular for the first time I will show the Galactic rotation curve as traced by RR Lyrae stars. An age of only a few Gyrs would be very difficult to reconcile with the conventional scenarios of the RR Lyrae formation, for which more metal-rich stars are expected to be the oldest. At the same time, assuming that they are instead truly old implicates that they are tracing one of the oldest component of the Milky Way remained kinematically unperturbed. Alternative formation channels for RR Lyrae can be called into play to solve this conundrum. In particular, I will show that formation through binary evolution is theoretically capable to produce a population of metal-rich RR Lyrae with ages consistent with the thin-disc populations. It is plausible that almost all the metal-rich RR Lyrae in thin-disc have been formed through binary interactions. I will conclude my talk by describing how the next generation of spectroscopic surveys will be fundamental to shedding light on the nature of these peculiar pulsators.
Kovacs Geza, Konkoly Observatory
The discovery rate of low-amplitude and/or long-period modulations in periodic stellar pulsation signals can be seriously impaired by the quality of the data used in searching for the signal components causing the modulation. We use the amplitude and modulation period distributions derived from the short-survey data of the two-wheel Kepler (K2) mission and the long-survey data of the Optical Gravitational Lensing Experiment (OGLE) to assist in the estimation of the bias caused by observational noise and finite duration of target monitoring. When these two major bias sources are taken into account, reported modulation (i.e., Blazhko) rates for RR Lyrae stars are boosted up to 80-100%, indicating a high commonality of the Blazhko behavior
Session 4: Photometric Surveys
Catelan Marcio, Pontificia Universidad Cattolica de Chile
Photometric surveys have for many decades played a crucial role in the area of variable star research, bringing pulsating stars and their use as tracers of the structure and evolution of our cosmic vicinity, and indeed beyond, into the forefront of astrophysics. In this talk, I will provide an overview of the developments that have set the stage for the current generation of large-scale photometric surveys. I will highlight some results of particular interest that have been found along the way, and discuss some of the challenges that still await us, in the era of large étendue facilities as epitomized by the Vera C. Rubin Observatory’s Legacy Survey of Space and Time.
Baeza Villagra, Karina Pontificia Universidad Catolica
As part of the DECam Alliance for Transients (DECAT), a consortium of time-domain DECam programs, the DECam Deep Drilling Program (DDP) is being run at the Blanco 4m telescope, located at Cerro Tololo Inter-American Observatory, Chile. DDP fields include the so-called DECaPS East field, located in the Galactic bulge at coordinates (RA, DEC)(J2000) = (18:03:34, -29:32:02). We carried out two nights of high-cadence multi-band (griz) observations of the latter field, also using DECam. This dataset constitutes a treasure trove for studies of rapid stellar variability, and will provide, when combined with additional available DDP images of the same field, high-quality multi-band templates that can be used in the future to inform the variable star classifiers that are currently being developed for the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST). These data can also be used for studies of the structure, origin, and evolution of the Galaxy’s innermost regions, where most of its stars, dust, and gas are currently located. In this contribution, we present our first results on Cepheid and RR Lyrae stars using this combined dataset. These pulsating stars are excellent tracers of our galaxy’s old and young populations, respectively. We describe the steps we took in building our variability catalog, present the corresponding multi-band light curves, and use their respective period-luminosity and absolute magnitude-metallicity relations to analyze foreground extinction and distances, comparing our results with expectations based on Galactic 3D models and previous studies of the same region using different tracers.
Mullen Joseph, Iowa State University
The number of known RRL in the Milky Way and Local Group galaxies has significantly increased with the advent of large area photometric surveys. However, RRLs with known metal abundances remain limited due to the reliance on spectra, which require large amounts of telescope/analysis time to acquire. This talk presents the calibration of a quick and reliable method to derive [Fe/H] abundances solely from available photometric time series, as the shape of both RRab and RRc light curves are inherently tied to their metallic abundance. We present our newly published period-Fourier-metallicity relations at optical and, for the first time, mid-infrared wavelengths. Extension to the infrared will allow metallicity measurements to be readily made in both high-extinction environments and at much greater distances with large-aperture infrared space telescopes like Webb.
Pietrukowicz Pawel, Astronomical Observatory, University of Warsaw
I will describe the recently revealed huge collection of nearly 25,000 delta Scuti-type stars detected in OGLE fields toward the Galactic bulge and disk. I will present the variety of light curve shapes and observed properties of these pulsating stars. The collection contains dozens of unique objects, such as members of eclipsing binaries, stars with period and amplitude changes, members of Galactic stellar clusters and the Sagittarius Dwarf Spheroidal Galaxy. A detailed frequency analysis has led to the first identification of delta Scuti stars pulsating in the fundamental mode, first overtone, and third overtone simultaneously. Finally, I will report on the extension of the OGLE collection for two dozen spectroscopically confirmed multi-mode delta Scuti stars with ultra short periods in the range 20-60 min.
Plachy Emese, Konkoly Observatory CSFK
Nearly continuous, densely sampled space based photometry allows us to recover the finest details in the light variations of stars. The number of such light curves have been rapidly increasing in the last few years thanks to the extended mission of the Kepler space telescope and the launch of the TESS mission. This new era brings us new perspectives in RR Lyrae and Cepheid studies, where low amplitude phenomena can be studied in a wide range of individual stars and on a statistical basis. In this talk I review the recent investigations of the Kepler, K2 and TESS fields, as well as the challenges in accurately reducing high-quality photometry. Finally, I provide insights into some ongoing projects, as well.
Kalup Csilla, Konkoly Observatory, CSFK
Here we present the first detailed asteroseismic analysis of the RR Lyrae stars from clusters observed in Campaigns 11 and 15. We performed our own differential-aperture photometry to obtain the light curves, then applied K2SC systematics correction and PDM-optimized trend removal steps to increase the signal-to-noise ratio of the data. This allowed us to detect new, low-amplitude pulsational frequencies of the stars via Fourier analysis. We also report a discovery of a new RRc star in the cluster NGC5897, based on its position on the horizontal branch in the Gaia color-magnitude diagram. Overall, we extracted more than 30 light curves, which we compared both on a cluster-to-cluster basis and to the bulge and field RR Lyrae stars. We found that not only do the cluster variables have larger periods than the usual mean RRab or RRc periods, but their Fourier parameters, the distribution and abundance of the low-amplitude additional modes and the frequency of stars that show modulation are also considerably different from the bulge and field stars.
Molnar Laszlo, Konkoly Observatory, CSFK
RR Lyrae pulsations are easy to pick out from a sea of stars and they serve as distance markers throughout the Galaxy. What could then the TESS and Gaia missions, developed to measure the smallest light variations or the precise distances of stars, possibly tell us about them? A surprising number of things, as it turns out, starting from the simplest ones: whether all bright, cataloged RR Lyrae variables are truly pulsating stars. In this talk I will present our first results based on TESS observations of over a hundred nearby RR Lyrae stars, supplemented with measurements from the Gaia mission. We first revised the classification of all selected targets in TESS Sectors 1 and 2, and illustrate that eclipsing binaries and rotational variables can still lurk among the brightest pulsators. Gaia also allows us to put field stars onto a color-magnitude diagram accurately, matching the precision of globular cluster studies, but without the need of a common distance modulus. We carefully analyzed the TESS light curves of these field stars, which revealed an abundance of millimagnitude-level modes hiding behind the main radial pulsation. Many of these modes still lack proper identification or explanation. However, we are now starting to see the first connections between the appearance of the new modes and the effective temperature and metallicity of stars. Pure overtone stars, for example, appear to exist only at the blue edge of the instability strip, with virtually all of the rest displaying various low-amplitude modes. We also see indications for less extra modes towards the red edge, but this result is not yet significant. Metallicity differences also change the distribution of the extra modes in the Petersen diagram. Further, although TESS is not well-suited to study the Blazhko effect, we do see stars that are stable, single-mode pulsators, at least on month-long timescales. Our results showcase the power of combining TESS photometry with distances and colors from Gaia, both of which missions are currently precise enough down to about 15 mag for these kinds of analysis. The new developments may finally open up the possibility for a more detailed asteroseismic modeling of RR Lyrae stars, though the presence of a powerful radial mode still complicates this task.
Narloch Weronika, Universidad de Concepcion
Since the discovery of the period-luminosity (PL) relation of Cepheids by Henritta Leavitt in 1912, the classical pulsators became very important distance indicators. Moreover, the respective PL and period-Wesenheit relations have been calibrated for a wide range of wavelengths from optical to the near-infrared. Such relations, however, are still missing in the Sloan bands. With the impending start of the Legacy Survey of Space and Time (LSST), large amounts of pulsating variable stars, especially Cepheids and RR Lyrae stars, are going to be uncovered in the outer halo of the Milky Way, as well as in other galaxies of the Local Group. Accurate PL relations of various pulsating stars in the Sloan bands are necessary in order to take full advantage of it. Therefore, we have carried out a time-series photometric survey of the Magellanic Clouds in the Sloan gri(z) bands using three different classes of instruments and telescopes: the DECam instrument on the 4m Blanco telescope, OmegaCAM on the 2.6m VLT Survey Telescope, and the Sinistro cameras of the 1m telescopes of the Las Cumbres Observatory. The combination of data from different instruments allowed us to obtain fully covered, accurate light curves for variables of vastly different periods (below half a day to over 100 days) and mean magnitudes (from the faintest RR Lyrae to the brightest Cepheids) in a relatively short period of time (two years), making the above goal achievable.
Session 5: Milky Way
Grebel Eva, Heidelberg University
Exploring the structure of our Milky Way is a major challenge since our observations are necessarily limited to a fixed location within our Galaxy and furthermore subject to dust extinction. Pulsating variable stars such as Cepheids and RR Lyrae stars, which provide information on distances, ages, and metallicities are a valuable tool for uncovering the properties of the different Galactic components. Considerable progress has been made in recent years thanks to the growing number of massive ground-based optical and infrared imaging surveys, complemented by data from the Gaia mission as well as ground-based spectroscopy. These data are revealing the three-dimensional structure of the old bulge components and their metallicity and kinematics, help us to characterize Galactic spiral structure, metallicity gradients across the thin disk, the stellar Galactic warp, permit us to explore the nearby and the distant stellar halo, and allow us to uncover and characterize accretion features. I will attempt to review the current state of our knowledge.
Bobrick Alexey, Technion Institute
Despite the classical interpretation of RR Lyrae as old and metal-poor population II stars, it is well known that metal-rich (up to solar values) RR Lyrae stars exist in the solar vicinity. Some of these stars are also consistent with Sun-like kinematics, i.e. they likely belong to the thin-disc population.
Lemasle Bertrand, ARI, University of Heidelberg
Classical Cepheids are an ideal tool to study the distribution of abundances in the Milky Way disk. They are ubiquitous; their distances are derived with great accuracy, even at large Galactocentric distances (where Gaia parallaxes are uninformative) thanks to period-luminosity relations; the abundances of numerous alpha, iron-peak, and neutron-capture elements can be derived from their spectra.
Vivas Kathy, Cerro Tololo Inter-American Observatory / NOIRLab
We characterize the absolute magnitudes and colors of RR Lyrae stars in the globular cluster M5 in the ugriz filter system of the Dark Energy Camera (DECam), installed at the Blanco 4 m telescope at Cerro Tololo Inter-American Observatory, Chile. As expected from earlier studies by Sturch, the dispersion of the color at minimum light was found to be small, supporting the use of this parameter as a means to obtain accurate interstellar extinctions along the line of sight up to the distance of the RR Lyrae star. We found a trend of color at minimum light with pulsational period that, if taken into account, brings the dispersion in color at minimum light to <0.016 mag for the (r-i), (i-z), and (r-z) colors. Such color calibration was applied to observations of fundamental mode RR Lyrae stars of six fields toward the Galactic bulge made with the same instrument to derive maps of interstellar reddening. The resulting color-magnitude diagram corrected by extinction and reddening using such maps allows to study the stellar population of the Bulge with exquisite detail.
Kunder Andrea, Saint Martin’s University
The bulge RR Lyrae stars have been shown to be some of the oldest stars in the inner Galaxy, with ages of ~13.4 Gyr. The 3D motions of a sample of ~2500 RR Lyrae stars has been obtained by the BRAVA-RR survey. Here we derive new metallicities for a sub-sample of these stars and compare their chemodynamics with the younger, more metal-rich stars in the bulge/bar. We find that the inner Galaxy RR Lyrae star kinematics are complicated by a mix of a variety of Galactic components. After isolating only those RR Lyrae stars that are confined to the bulge, we find there are two different old and metal-poor populations in the bulge. The sample of stars closest to the Galactic plane have slower rotation and are less bared than the dominant bar/bulge. Old, metal-poor stars in the inner Galaxy need to be properly accounted for when discussing processes that gave rise to the formation of the inner Galaxy and the Galactic bar/bulge.
Vittorio Francesco Braga, IAC
The Halo is a purely old component of the Milky Way (MW), however its formation is due to at least two different processes (in-situ formation and accretion). Information on the merging events and on the formation of the MW itself are encoded in the complex chemo-dynamical properties of the Halo. Since Gaia DR2, the Halo has been dissected into tens of streams and at least three major merger events were detected. Since the Halo is so crucial to investigate the birth and assembly of the MW, we are interested in adopting RR Lyrae (RRLs) that, being strictly old, are ideal tracers of this component of the Galaxy. Therefore, we have built the largest catalog of MW RRLs (>285,000), based on Gaia DR2 and recently updated to Gaia DR3. The catalog also includes the largest sample of RRL spectroscopic chemical abundances (>9,000). This is the reference catalog for a series of works on Halo RRLs that addressed several open questions, like the Oosterhoff dichothomy, the evolutionary interpretation of the Bailey diagram, the gradients of iron, alpha and neutron-capture elements, detection of streams and photometric metallicity indicators. We have also built the first radial velocity templates for both fundamental and first-overtone pulsators and for seven diagnostics (Lyman alpha-to-delta lines, Iron, Magnesium and Sodium).
Prudil Zdenek, Astronomisches Rechen-Institut, Heidelberg University
In this work, we describe the MW stellar streams using population II pulsating variables of the RR~Lyrae class, which provide precise distances (down to 3 percent), and can be detected up to 100 kpc. The assembled chemo-dynamical sample combines spectroscopic metallicities and systemic velocities and the Gaia EDR3 astrometric products provide a 7D view of some MW streams. Our pilot study focused on the northern part of the Orphan stellar stream, where employing a probabilistic approach we identified 20 RR~Lyrae variables as likely members of the stream. The acquired sample allowed us to examine possible metallicity gradient within the stream, expand our sample with known and new non-variable objects, and assess and rule out possible Orphan progenitors, like the ultra-faint dwarf galaxy Grus II. Our analysis showed that if we consider Grus II as the progenitor of the Orphan stream it would be the first case of reversed metallicity gradient which is to date unseen in the Local Group. Contrary to this assumption any potential Orphan progenitor, if not yet dissolved, could be hidden behind the Galactic plane.
ala Hitesh, ARI, University of Heidelberg
We have created a carefully-curated catalog of ~245,000 RR Lyrae stars (RRab & RRc) and ~18,000 Cepheids (Classical, Type-II & Anomalous) containing 7-D information (positions, proper motions, distance, radial velocity, metallicity). In the process, we have homogeneously combined ten photometric and six spectroscopic surveys. We have ensured minimal contamination in our sample by cross-validating the classifications and periods across various surveys and also cleaning the sample by cross-matching against other variable stars whose light curve morphology is similar to our target stars. We have employed three independent calibrators for computing the distance to our stars: a. Astrometry-based Luminosity computed using Gaia (E)DR3 parallax; b. Large Magellanic Cloud population; c. Globular cluster members wrapped in a partially-pooled multi-level Hierarchical Bayesian model. The Period-Wesenheit laws obtained to get these three sets of distances were fit using Bayesian robust regression, which offers a complete treatment of uncertainties and is immune to outliers. After validation, we found these distances to be greater than 95% accurate (even at 150kpc) and have been estimated to a <5% precision. For our RR Lyrae sample (both RRab and RRc sub-types), we have also obtained photometric metallicity estimates on a new homogeneous scale creating the largest sample of RR Lyrae iron-abundances. Harnessing this catalog, we have discovered several new members of Galactic streams and over-densities. The re-discovery of already-identified members validates our distances, and metallicities, while the new ones enable precise measurement of these parameters for the very first time for many of these substructures.
Medina Toledo, Gustavo University of Heidelberg
In the current cosmological paradigm, the Milky Way was formed hierarchically through the accretion of smaller systems, and imprints of these interactions are visible in the present-day orbital and chemical properties of Galactic halo stellar populations. RR Lyrae stars are ideal tracers of these merger events, as their status of old and precise distance indicators removes distance as one of the biggest limitations in the study of the outer halo. However, deriving radial velocities and spectroscopic metallicities of remote RR Lyrae is challenging, owing to their variability in short time-scales and the need for dedicated time at large aperture telescopes. In this contribution, I will present the spectroscopic analysis of 20 outer halo RR Lyrae (with distances between 15 and 165 kpc) in the context of the Halo Outskirts With Variable Stars (HOWVAST) survey, conducted using medium-resolution spectra from the MIKE spectrograph. In combination with Gaia eDR3 data, we model the orbits of our stars considering the gravitational perturbation of the halo by the Large Magellanic Cloud, and determine atmospheric parameters and chemical abundance ratios (including alpha-elements, Fe, and neutron-capture elements) for a subsample of them. We search for associations between these distant RR Lyrae with known satellites and accretion events by studying their chemodynamics and speculate about their parent populations and origins (formed in-situ vs. accreted). We test the hypothesis that the accretion of sub-haloes largely contributes to the outer halo stellar populations, and report on the limitations of state-of-the-art distant halo RR Lyrae spectroscopic surveys. I will discuss the implications of our findings, and their impact on our preparation for the analysis of large samples of halo RR Lyrae in the upcoming era of large scale photometric and spectroscopic surveys.
Session 6: The Local Group
MartÌnez-Vazquez Clara, Gemini Observatory / NSF’s NOIRLab
Pulsating stars are considered standard candles because they obey well established period luminosity relations and, therefore, they are used very often to derive accurate and precise distances. By far, the most frequent and common pulsating stars found among Local Group dwarf galaxies are RR Lyrae stars. Since the discovery of the first RR Lyrae star by Wilhelmina Fleming at the beginning of the last century and thanks to their well-know period-luminosity relation (Henrietta Leavitt Law), the popularity of this kind of stellar pulsators has increased exponentially, specially over the past decades. The enormous amount of detections of RR Lyrae stars in surveys like ASAS, Catalina, DES, Gaia, OGLE, PanSTARRS, ZTF (and the future Vera Rubin LSST survey), and the fact that RR Lyrae stars are stellar tracers of old stellar populations makes them powerful archaeological tools. They have been used to detect/confirm new ultra-faint and ultra-diffuse dwarf galaxies and to obtain accurate distances to those systems, where the large contamination by field stars makes the determination of distances using isochrone fitting a challenging task. In addition, in those systems where the rate of RR Lyrae stars is large enough, RR Lyrae stars can be also used as metallicity tracers, and provide insight into the chemical evolution of the old population they belong to. Thus helping us not only to reveal their formation history and chemical evolutions but also to provide clues about the contribution of dwarf galaxies in the formation of the halo of the larger galaxies they are bound to.
Tantalo Maria, Universita di Roma Tor Vergata
We performed the deepest and widest optical photometric investigation of the nearby dwarf irregular NGC~6822 by using multi-band (g,r,i) images collected with Hyper Suprime-Cam at the Subaru Telescope. We ended up with a photometric catalog including more than one million stars covering more than two square degrees across the center of the galaxy. These data were complemented with images collected with wide field imagers at 2/4m telescopes (ING, CTIO, CFHT) and cover a time interval of two dozen years. We pian to discuss preliminary results concerning the identification of variable stars (hundreds) located inside the Cepheid instability strip (classical, Type II, Anomalous, RR Lyrae) and of Long Period Variables together with the comparison with similar investigations available in the literature. Finally, we will outilne peculiarities in the radial distribuzion of different stellar tracers and the 3D shape of the galaxy.
Marengo Massimo, Iowa State University
VV124 is an isolated dwarf in the outskirts of the Local Group of galaxies, yet close enough to allow for a detailed census of its variable stars. Despite its isolation, VV 124 hosts stellar populations with a wide range of ages (>10 Gyr to present), making it a home for all types of classical stellar pulsators, including Classical, Anomalous and Type II Cepheids, RR Lyrae and pulsating late-type giants. These unique characteristics allows this dwarf galaxy to be the ideal test case for stellar distance indicators based on pulsating stars. In this contribution we present our comprehensive analysis of the pulsating stars populat in VV 124 and we compare its distances derived with different methods based on its pulsating stars, using new data we have obtained with the Advanced Camera for Surveys onboard the Hubble space telescope.
Skowron Dorota, Astronomical Observatory, University of Warsaw
Since the first discoveries of classical Cepheids in the Large Magellanic Cloud over a century ago, the numbers of known pulsating stars in the Magellanic System have vastly increased. And so has our knowledge about the two galaxies, and about observational and physical properties of various classes of pulsating stars.
Session 7: Science with Gaia DE3
Clementini Gisella, INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna
The last couple of decades have seen a true revolution in the field of pulsating stars because of the increasing number of ground-based/space-borne surveys that have been collecting multi-epoch photometry over large portions of the celestial sphere.
Das Susmita, Konkoly Observatory, CSFK
We present new theoretical period-luminosity and period-Wesenheit, W=G-1.90*(GBP-GRP) relations in the Gaia bands for a fine grid of convective BL Herculis models computed using the non-linear radial stellar pulsation tool MESA-RSP. The non-linear models were computed for periods typical for BL Her stars, i.e. 1
Garro Elisa Rita, Universidad Andres Bello
RR Lyrae (RRL) variable stars, found in the Galactic halo and bulge, represent a very old population in the Milky Way (MW). These stars are considered powerful tools mainly for two reasons: first, because they are good distance indicators; second, they allow confirming the nature of GC candidate, because if detected in a stellar cluster, RRL guarantee the old age (>10 Gyr). We searched for these variables in many new GC candidates in the VVV/VVVX footprint. This allowed us to confirm the GC nature for Garro 01, Patchick 99, VVV-CL131, VVV-CL143, FSR1775, FSR1767, ESO393-12, ESO456-09, Patchick 125, and Riddle 15 in our Galaxy, and also for recently discovered GCs in the inner part of the Sagittarius dwarf galaxy. We also adopted the known period-luminosity-metallicity relations in order to derive the cluster distance as independent methods. In summary, we present the physical parameters for the 10 new Galactic GCs listed above.
Kovacs Gabor, ELTE, CSFK
Since the earliest success stories of the computational era in the sixties-seventies, one-dimensional pulsation calculations solved questions ranging from the driving mechanism of pulsation to the chaotic nature of given stars. However, stepping into the age of multi-dimensional calculations, some questions regarding these models are still unanswered.
In the presentation, we compare the two state-of-the-art 1D stellar pulsation codes, the Budapest-Florida and MESA-RSP codes, and show the calibration results of convection parameters. The codes are similar but implement slightly different convection models based on Stellingwerf, Kuhfuss, Gehmeyr, and Winkler’s works. Despite the similarities, they give different results questioning, e.g., the solution of the double-mode cepheids problem. Although they were effectively used several times, their eight convective parameters were never calibrated to the observations.
Ebenbichler Alexander, University of Innsbruck
The measurement of the expansion of the local universe depends on the correct calibration of the cosmic distance ladder which heavily relies on the period-luminosity relation of Cepheids. The metallicity dependence of this relation is still an open question and can contribute to the Hubble tension. Spectrum synthesis accounting for the effects of deviations from the assumption of local thermodynamic equilibrium (non-LTE) is the most reliable method to determine the metallicity of Cepheids, given the potential for non-LTE effects on diagnostic lines in these yellow supergiant stars. New generations of extremely large telescopes (ELTs) and advancements in adaptive optics will enable astronomers to observe Cepheids at much larger distances than possible currently, however diffraction-limited observations will be limited to near-infrared (NIR) wavelengths. Highly sensitive spectrographs like WINERED (Warm INfrared Echelle spectrograph to Realiz Extreme Dispersion and sensitivity) have enormous potential not only for groundbreaking spectroscopy of dust-obscured Cepheids in the Milky Way, but also to facilitate preparing spectroscopy of extragalactic Cepheids with the ELTs. A spectroscopic study of Cepheids at NIR wavelengths was conducted to test new analysis methods and non-LTE effects on the metallicity determination. A hybrid non-LTE spectral modelling approach was used for the analysis of WINERED spectra of 10 Cepheids in the Milky Way and the Large Magellanic Cloud. Atmospheric parameters were determined using purely spectroscopic indicators like the Stark-broadend hydrogen Paschen lines as effective temperature indicator, the Mg II ionization equilibrium as surface gravity indicator and numerous C I lines as indicator for the microturbulent velocity. Abundances were determined for several additional chemical species. Most diagnostic lines show pronounced non-LTE effects, implying systematic shifts in atmospheric parameters and leading to abundance deviations of up to 0.3,dex when compared to LTE results.
Session 8: Distance Scale
Anderson Richard, EPFL
Distance measurements are of fundamental importance for astronomy and astrophysics since they transform interpretations of apparent brightness to insights of luminosity, thereby offering insights into the physical nature of astronomical objects. In particular, classical Cepheids are pulsating stars whose luminosity can be calibrated, notably using individual trigonometic parallax measurements, thanks to the Leavitt law (period-luminosity relation). Thus, Cepheids are standard candles that light the way for determining distances well beyond the reach of direct, geometric distance measurements, for example to study Galactic structure on scales of 100 – 20000 kpc and to measure precise distances to galaxies as far as 70 Mpc. Thus, classical Cepheids form the basis of an extragalactic distance ladder that calibrates type Ia supernova luminosity, and allows to measure the local expansion rate of the Universe, Hubble’s constant H0, to a current precision of 1 km/s/Mpc.
Recent developments have shown that the late-Universe value of H0 differs systematically from the early-Universe value inferred from the cosmic microwave background interpreted in the flat LambdaCDM paradigm. The significance of this so-called Hubble Tension is currently quantified at the 5.3 sigma level, rendering the need for modifications of the concordance cosmological model increasingly likely.
Musella Ilaria, Italian National Institute for Astrophysics (INAF)
Ultra Long Period Cepheids are becoming a very interesting and important topic thanks to the contribution they can give to understanding the current tension existing between the early-universe and local Hubble constant measurements. These bright pulsating variables are hypothesized to be the counterparts at higher luminosity and mass of the Classical Cepheids. They are observable up to cosmological distances (larger than 100 Mpc) allowing us, in principle, to measure the Hubble constant without the need for secondary indicators, thus reducing the possible systematic errors in the calibration of the extragalactic distance scale. The Ultra Long Period Cepheids also represent a useful tool to get information on the star formation history of the host galaxy and a challenge for the evolutionary and pulsation models in particular in the very metal poor regime.
Karczmarek Paulina, Universidad de Concepcion
Classical Cepheids – famous for their period-luminosity relation (PLR) – are the most extensively used distance indicators, and a crucial rung in the cosmic distance ladder, enabling the determination of the Hubble constant. The majority of classical Cepheids are binary stars, yet the contribution of companions’ light has been long assumed negligible and lacked thorough, quantitative evaluation. I present a comprehensive collection of synthetic populations of binary Cepheids for the Milky Way and the Magellanic Clouds, which serves as a tool to quantify the contribution of companions’ light to the total brightness of the systems. This light excess shifts the zero point of the PLR, which now can be recognised as a systematic error associated with the Cepheid PLR, and, by extension, with the Hubble constant.
Breuval Louise, Johns Hopkins University
Cepheid variables are the best calibrated primary standard candles: they are used to standardize the brightness of Type Ia supernovae (SNIa) in nearby galaxies and therefore are central in the determination of the local value of the Hubble constant (H0). The empirical measurement of the Hubble constant obtained by the SH0ES team from the Cepheid-SNIa method is now in 5-sigma tension with the Planck prediction based on the lambda-CDM model. While both estimates have reached a great precision, the source of the Hubble tension remains unknown and suggests evidence of new physics beyond the standard model. In this talk I will describe recent progress on the Cepheid distance scale involving Gaia parallaxes and HST photometry and I will identify the remaining issues and systematics associated with the calibration of their period-luminosity relation. In particular, differences in Cepheid metallicities between the Milky Way, Magellanic Clouds and nearby galaxies hosting SNIa must be corrected in order to provide a consistent distance calibration. Finally I will discuss how future missions and promising techniques are expected to improve again the precision of the empirical H0 value.
Wielgurski Piotr, Nicolaus Copernicus Astronomical Center, PAS
Type II Cepheids are old population pulsating stars which lies about 2mag below Classical Cepheids on the period-luminosity diagram. I will show recent results of the Araucaria project where we use Gaia EDR3 parallaxes of nearby Type II Cepheids and photometry obtained in the Cerro Armazones Observatory in order to improve the accuracy of distance measurements with these old stars. First, I will show our calibration of the period-luminosity relations in the near-infrared J, H and Ks passbands (Wielgorski et al, 2022, ApJ, 927, 89) and compare it to calibrations in the other stellar systems. The influence of the metallicity on Type II Cepheids absolute magnitudes will be also discussed. The second method which can be applied to measure the distance of a radially pulsating star is the so-called Baade-Wesselink method. I will show the very first calibration of the projection factor, parameter required in the Baade-Wesselink analysis, for a sample of BL Herculis and W Virginis stars in the solar neighbourhood. Precision calibration of the projection factor will allow to measure geometrical distances of Type II Cepheids in e.g. globular clusters and dwarf spheroidal galaxies.
Madore Barry, Carnegie Observatories
In the context of their application to the extragalactic distance scale, three distinct groups of old and intermediate-aged stars will be discussed.
Bhardwaj Anupam, NAF – Osservatorio Astronomico di Capodimonte
RR Lyrae variables are sensitive probes for the precision stellar astrophysics and also for the distance scale thanks to their tight Period-Luminosity-Metallicity (PLZ) relations at infrared wavelengths. Theoretical models of RR Lyrae predict a significant metallicity coefficient of their PLZ relations, but the metallicity term is relatively smaller and not well-constrained in most empirical calibrations. Despite the improvements in Gaia parallaxes, the precision of the absolute calibration of Galactic PLZ relations is limited due to inhomogeneous photometry and spectroscopy of field RR Lyrae variables. We present new NIR time-series observations of RR Lyrae in 8 globular clusters with CFHT-WIRCam and Gemini-F2 covering a wide metallicity range (-0.4<[Fe/H]<-2.4). Combining with literature NIR data and Gaia parallaxes, RR Lyrae variables in 10 globular clusters are used to derive JHK_S PLZ relations with unprecedented precision. Our preliminary results show a good agreement with theoretical predictions. We discuss the implications of RR Lyrae PLZ relations for the independent calibration of the first rung of the population II distance ladder with our ongoing NIR observations of nearby dwarf spheroidal galaxies.
Zgirski Bartomiej, Nicolaus Copernicus Astronomical Center
RR Lyrae stars are important distance indicators that serve us to test the calibration of the cosmic distance ladder in the direct neighborhood of the Milky Way.
Spetsieri Zoi, Tzogia EPFL, Lausanne
We aim at measuring directly for the first time the stellar association bias caused by the physical association of Cepheids with their natal environments in order to validate and improve the stellar association bias corrections applied to the late-Universe Ho measurement. For this purpose, we quantify the occurrence of Cepheids in (or near) open clusters in the SNeIa host anchor M101.
Session 9: Future facilities
Ivezic Zeljko, University of Washington
The Legacy Survey of Space and Time (LSST), the first project to be undertaken at the new Vera C. Rubin Observatory, will be the most comprehensive optical astronomical sky survey ever undertaken. Starting in a couple of years, Rubin Observatory will obtain panoramic images covering the sky visible from its location in Chile every clear night for ten years. Close to a thousand observations of each position across half of the celestial sphere will represent an excellent observational material to study variable faint sky, including hundreds of millions of variable stars. I will briefly describe scientific goals behind this project, illustrate the progress of its ongoing construction, and finish by showing a few results from simulated LSST cadence analysis relevant for periodic variables.
Bono Giuseppe, University of Rome Tor Vergata
LSST is going to be a game changer concerning the accuracy and the homogeneity of multi-band time series data of variable stars. The difference is driven by a) entire southern hemiphere, b) photometric accuracy, c) cadence of the observations and ) time interval of the experiment. This means the unique opportunity to use several pulsation (luminosity amplitude, multi-periodicity, shape of the light curves, modal stability, period distribution) and evolutionary (star counts, luminosity function, evolutionary timescale, mass loss, age distribution) diagnostics to investigate resolved stellar populations. We plan to adress several key issues concerning individual metallicity estimates of Cepheids (classical, anomalous, type II) using photometric indices. Moreover, we also plan to discuss recent finings concerning the Hertzsprung progression, and in particular, its depenence on the metallicity.
Dall’Ora Massimo, INAF-OACN
Rubin-LSST will represent the giant leap in the time-domain astronomy for the next decade. The enormous amount of expected data will be both an unprecedented scientific opportunity and technical challenge. The Galactic Bulge and similar heavily crowded environments will pose even harder challenges, because of the combined effects of the crowding and dust, that will affect our efficiency in detecting and characterizing variable stars. It is therefore crucial to test the available techniques and tools, and eventually develop new ones, to effectively extract the scientific information from the data. Here we present the results of a pilot project started within the Rubin-LSST Transient and Variable Stars Science Collaboration, based on archive DECam data and focused on the characterization of the periodic stars in the field of the Bulge globular cluster NGC 6569.