arXiv subjects

P. Wielgórski

Publications and source records attributed to P. Wielgórski.

At least 19 recordsLinked to original sources

arXiv2026

Reddening maps of the Magellanic Clouds using spectral energy distribution fitting of red giants

Robust reddening maps of the Large and Small Magellanic Clouds (LMC/SMC) are crucial for a wide range of astrophysical studies, including the calibration of the cosmic distance ladder, investigations of stellar populations in low-metallicity environments, and the characterization of interstellar dust properties. We aim to construct reddening maps of the Magellanic Clouds using spectral energy distribution (SED) fitting, and to investigate the impact of different stellar atmosphere models on the resulting maps. We combined optical ($ugriz$) photometry from the SMASH survey with near-infrared ($YJK_{\rm s}$) photometry from the VMC survey for red giant branch (RGB) stars. Observed SEDs were matched to synthetic photometry derived from three atmosphere model grids. Our maps cover 34.5 deg$^2$ of the LMC and 24.5 deg$^2$ of the SMC at 4 arcmin resolution. We find mean reddening values of $E(B-V)=0.076 \pm 0.022$ mag for the LMC and $0.058 \pm 0.024$ mag for the SMC. We found that employing different atmospheric models results in differences up to 0.03 mag in the mean reddening. Canonical $R_V$ values for the Magellanic Clouds (3.41 for LMC and 2.74 for SMC, Gordon et al. 2003) provide results consistent with previous studies. We confirm higher and more structured reddening in the LMC compared to the SMC, with 30 Doradus standing out as the dominant high-reddening region. Our results show that the absolute reddening scale depends on the choice of stellar atmosphere models, while the relative spatial structure of the reddening maps remains stable.

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arXiv2026

Finding the elusive RR Lyrae companions via speckle imaging

Despite their key role in astrophysics, the binary properties of RR Lyrae stars (RRL) remain almost completely unknown since only a single RRL is confirmed as belonging to a binary system. Finding companions to RRL is difficult since most of them will be at wider orbits, given that close orbits will likely ensue mass transfer disrupting the conditions to develop stellar pulsations. These wide orbits open the possibility that RRL companions may be more easily found by high-resolution imaging. We observed 81 RRL with the speckle interferometers Zorro and 'Alopeke at the Gemini telescopes, reaching the diffraction limit of $\sim$20 mas of these 8m-class telescopes, and therefore exploring a new parameter space around RRL. We have detected 10 newly identified companions around these 81 RRL, with projected separations between 20 AU to 220 AU. An analysis of the field contamination shows that all of these detected companions are most likely gravitationally bound binaries. From these observations we can estimate an RRL binary fraction higher than 12%, ruling out a binary fraction higher than 25% at the 99% confidence level. These numbers are significantly more elevated than previous estimations which were close to a binary fraction of only 1%, albeit derived with methods exploring a different parameter space. For RRL with thin disc kinematics, we find that the binary fraction is significantly lower, at around 6%, with a single thin disc RRL having a companion out of the 16 observed. The nature of the companions, found to be stars in the lower red giant branch and upper main sequence, is also studied via the measurement of the minimum light colors of the RRL, which appears as a useful method for the search and analysis of RRL in binary systems.

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arXiv2026

Toward a Comprehensive Grid of Cepheid Models with MESA. III. Evolutionary and Pulsation Relations for Models with Core and Envelope Overshooting

Evolutionary tracks for 2-8M$_\odot$ models, covering a [Fe/H]=$-$1.0 ($Z=0.0014$) to [Fe/H]=+0.2 ($Z=0.02$) metallicity range are computed with Modules for Experiments in Stellar Astrophysics, MESA, to investigate evolutionary and pulsation properties of classical, fundamental mode Cepheids. We examine in detail the effects of convective overshooting from the Main Sequence core, as well as from the convective envelope on the Red Giant Branch. Mass loss is also included in a few model sets. Linear pulsation properties are derived consistently with a module of MESA, Radial Stellar Pulsation, RSP. We provide edges of the classical Instability Strip, as well as ages, crossing times through the Instability Strip and period change rates. Period-Luminosity, Mass-Luminosity, Period-Radius and Period-Age relations are provided, both in analytical and tabular form. Their dependence on metallicity, crossing number and overshooting parameters are investigated. Qualitative comparisons with classical Cepheids in the Milky Way and Magellanic Clouds as well as other theoretical relations are presented. We find satisfactory agreement for most of the observables and good match with other theoretical work, however reproducing short-period Cepheids in the Small Magellanic Cloud as well as Cepheid mass discrepancy pose a challenge for the presented models. Considering metallicity effect of the Period-Luminosity relation, we find $γ\approx -0.20$ mag dex$^{-1}$, nearly independent on photometric pass band and in good agreement with recent observational studies. The magnitude of this effect depends on the underlying mass-luminosity relation, being stronger for relations that predict higher luminosities at a given mass.

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arXiv2026

Reconstruction of Cepheid Radial Velocity Curves from the shape of the V-band Light Curves

This paper aims to develop the first method to reconstruct the shape of the RV curves of short-period fundamental-mode Cepheids, based exclusively on their pulsation period and the morphology of their $V$-band light curves (LCs). We compiled a dataset of high-quality spectroscopic and photometric measurements from the literature for 81 short-period fundamental-mode Galactic Cepheids up to a pulsation period of 8\,days, enabling precise determination of the Fourier parameters and their uncertainties. We investigated correlations between LC and RV Fourier parameters and used these relations to reconstruct the RV curves. We further assessed the accuracy of these reconstructions by examining potential metallicity effects with an additional dataset of 23 metal-poor Cepheids. For pulsation periods between 3.5 and 7.0\,days, we found tight correlations between different combinations of LC and RV Fourier parameters up to order 7, in particular $R_{21}(RV)/R_{21}(LC)$ and $R_{31}(RV)/R_{31}(LC)$ are correlated with the pulsation period. These relationships enable the reconstruction of RV curves of Cepheids with their LC. The reconstructed curve has an uncertainty of about 0.60${\rm km\,s}^{-1}$ relative to the Fourier fit of true spectroscopic RV measurements. For individual Cepheids, the reconstructed RV curves integrated along the pulsation cycle (i.e. the linear radius variations) are accurate to less than 1\% and precise to within 4.16\% in comparison to the integrated true spectroscopic RV curves. This approach provides a valuable tool for the reconstruction of RV curves for extragalactic Cepheids through photometric data alone. It opens the road to a purely photometric parallax-of-pulsation method in the context of photometric surveys, such as the Vera Rubin Telescope.

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arXiv2024

Circumstellar emission of Cepheids across the instability strip: Mid-infrared observations with VLTI/MATISSE

The circumstellar envelopes (CSE) of Cepheids are still not well characterized despite their potential impact on distance determination via both the period-luminosity relation and the parallax-of-pulsation method. This paper aims to investigate Galactic Cepheids across the instability strip in the mid-infrared with MATISSE/VLTI in order to constrain the geometry and physical nature (gas and/or dust) of their CSEs. We secured observations of eight Galactic Cepheids from short up to long period of pulsation, with MATISSE/VLTI in $L$, $M$ and $N$-bands. The SED analysis in the mid-IR confirms the absence of dust spectral signature for all the star sample. For each star in $L$, $M$ and $N$-band we observe closure phases which are consistent with centro-symmetric geometry for the different targets. Finally, the visibilities in $L$, $M$ and $N$ bands are in agreement with the expected star angular diameter, although the observations are compatible with the presence of compact CSEs within the uncertainties. We provide 2$\,σ$ upper limits on the CSE flux contribution based on model residuals for several CSE radius, which yield to exclude models simultaneously large and bright ($R_\mathrm{CSE}\approx10\,R_\star$ and $f_\mathrm{CSE}\approx10\%$) for all the stars of the sample. Last, the visibilities in the $N$-band rule out CSE models with significant amount of different type of dust. The MATISSE observations of eight Cepheids with different pulsation period (from 7 up to 38$\,$day) and evolution stage, provide for the first time a comprehensive picture of Cepheids from mid-IR interferometry. We present additional evidences that circumstellar dust emission is negligible or absent around Cepheids for a wide range of stellar parameters in the instability strip. Further interferometric observations in the visible and the near-infrared will be necessary to disentangle the star and the CSE.

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arXiv2024

Precise physical parameters of three late-type eclipsing binary giant stars in the Large Magellanic Cloud

Detached eclipsing binaries (DEBs) allow for the possibility of precise characterization of its stellar components. They offer a unique opportunity to derive their physical parameters in a near-model-independent way for a number of systems consisting of late-type giant stars. Here we aim to expand the sample of low-metallicity late-type giant stars with precise parameters determined. We aim to determine the fundamental parameters like the mass, radius, or effective temperature for three long-period late-type eclipsing binaries from the Large Magellanic Cloud: OGLE-LMC-ECL-25304, OGLE-LMC-ECL-28283, and OGLE-IV LMC554.19.81. Subsequently we aim to determine the evolutionary stages of the systems. We fit the light curves from the OGLE project and radial velocity curves from high resolution spectrographs using the Wilson-Devinney code. The spectral analysis was performed with the GSSP code and resulted in the determination of atmospheric parameters such as effective temperatures and metallicities. We used isochrones provided by the MIST models based on the MESA code to derive evolutionary status of the stars. We present the first analysis of three DEBs composed of similar He-burning late-type stars passing through the blue loop. Estimated masses for OGLE-LMC-ECL-29293 (G4III + G4III) are $M_1=2.898\pm0.031$ and $M_2=3.153\pm0.038$ $M_\odot$, stellar radii are $R_1=19.43\pm0.31$ and $R_2=19.30\pm0.31$ $R_\odot$. OGLE-LMC-ECL-25304 (G4III + G5III) has stellar masses of $M_1=3.267\pm0.028$ and $M_2=3.229\pm0.029$ $M_\odot$, radii of $R_1=23.62\pm0.42$ and $R_2=25.10\pm0.43$ $R_\odot$. OGLE-IV LMC554.19.81 (G2III + G2III) have masses of $M_1=3.165\pm0.020$ and $M_2=3.184\pm0.020$ $M_\odot$, radii of $R_1=18.86\pm0.26$ and $R_2=19.64\pm0.26$ $R_\odot$. All masses were determined with a precision better than 2\% and radii better than 1.5\%. The ages of the stars are in the range of 270-341 Myr.

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arXiv2023

The Araucaria Project: Improving the cosmic distance scale

The book consists of a number of short articles that present achievements of the Araucaria members, collaborators, and friends, in various aspects of distance determinations and related topics. It celebrates the 20-year anniversary of the Araucaria Project, acknowledges the people who worked for its success, and popularises our methods and results among broader readership. This book is a part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 695099.

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arXiv2022

Metallicities and ages for star clusters and their surrounding fields in the Large Magellanic Cloud

We study 147 star clusters in the Large Magellanic Cloud (LMC) in order to determine their mean metallicities and ages, as well as the mean metallicities of 80 surrounding fields. We construct an age-metallicity relation (AMR) for the clusters in the LMC. For this purpose, we used Strömgren photometry obtained with the SOI camera on the 4.1 m SOAR telescope. We found the mean metallicity and age for 110 star clusters. For the remaining 37, we provide an age estimation only. To the best of our knowledge, for 29 clusters from our sample, we provide both the metallicity and age for the first time, whereas for 66 clusters, we provide a first determination of the metallicity, and for 43 clusters, the first estimation of the age. We also calculated the mean metallicities for stars from 80 fields around the clusters. The old, metal-poor star clusters occur both in and out of the LMC bar region, while intermediate-age clusters are located mostly outside of the bar. The majority of star clusters younger than 1 Gyr are located in the bar region. We find a good agreement between our AMR and theoretical models of the LMC chemical enrichment, as well as with AMRs for clusters from the literature. Next, we took advantage of 26 stellar clusters from our sample which host Cepheid variables and used them as an independent check of the correctness of our age determination procedure. We used period-age relations for Cepheids to calculate the mean age of a given cluster and compared it with the age obtained from isochrone fitting. We find good agreement between these ages, especially for models taking into account additional physical processes (e.g., rotation). We also compared the AMR of the LMC and Small Magellanic Cloud (SMC) derived in a uniform way and we note that they indicate possible former interaction between these two galaxies.

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arXiv2022

Evolved eclipsing binary systems in the Galactic bulge: Precise physical and orbital parameters of OGLE-BLG-ECL-305487 and OGLE-BLG-ECL-116218

Our goal is to determine, with high accuracy, the physical and orbital parameters of two double-lined eclipsing binary systems, where the components are two giant stars. We also aim to study the evolutionary status of the binaries, to derive the distances towards them by using a surface brightness-colour relation, and to compare these measurements with the measurements presented by the Gaia mission. In order to measure the physical and orbital parameters of the systems, we analysed the light curves and radial-velocity curves with the Wilson-Devinney code. We used V band and I-band photometry from the OGLE catalogue and near-infrared photometry obtained with the New Technology Telescope (NTT) equipped with the SOFI instrument. The spectroscopic data were collected with the HARPS spectrograph mounted at the ESO 3.6m telescope and the MIKE spectrograph mounted at the 6.5m Clay telescope. We present the first analysis of this kind for two evolved eclipsing binary systems from the OGLE catalogue: OGLE-BLG-ECL-305487 and OGLE-BLG-ECL-116218. The masses of the components of OGLE-BLG-ECL-305487 are $M_1$ = 1.059 $\pm$ 0.019 and $M_2$ = 0.991 $\pm$ 0.018 $M_\odot$, and the radii are $R_1$ = 19.27 $\pm$ 0.28 and $R_2$ = 29.99 $\pm$ 0.24 R$_\odot$. For OGLE-BLG-ECL-116218, the masses are $M_1$= 0.969 $\pm$ 0.012 and $M_2$= 0.983 $\pm$ 0.012 $M_\odot$, while the radii are $R_1$= 16.73 $\pm$ 0.28 and $R_2$= 22.06 $\pm$ 0.26 $R_\odot$. The evolutionary status of the systems is discussed based on the PARSEC and MIST isochrones. The ages of the systems were established to be between 7.3-10.9 Gyr for OGLE-BLG-ECL-305487 and around 10 Gyr for OGLE-BLG-ECL-116218. We also measured the distances to the binaries. For OGLE-BLG-ECL-305487, $d$= 7.80 $\pm$ 0.18 (stat.) $\pm$ 0.19 (syst.) kpc and for OGLE-BLG-ECL-116218, $d$= 7.57 $\pm$ 0.28 (stat.) $\pm$ 0.19 (syst.) kpc.

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arXiv2022

Surface brightness-colour relations of dwarf stars from detached eclipsing binaries -- I. Calibrating sample

Surface brightness -- colour relations (SBCRs) are very useful tools for predicting the angular diameters of stars. They offer the possibility to calculate very precise spectrophotometric distances by the eclipsing binary method or the Baade-Wesselink method. Double-lined Detached Eclipsing Binary stars (SB2 DEBs) with precisely known trigonometric parallaxes allow for a calibration of SBCRs with unprecedented precision. In order to improve such calibrations, it is important to enlarge the calibration sample of suitable eclipsing binaries with very precisely determined physical parameters. We carefully chose a sample of ten SB2 DEBs in the solar neighbourhood which contain inactive main-sequence components. The components have spectral types from early A to early K. All systems have high-precision parallaxes from the Gaia mission. We analysed high precision ground- and space-based photometry simultaneously with the radial velocity curves derived from HARPS spectra. We used spectral disentangling to obtain the individual spectra of the components and used these to derive precise atmospheric parameters and chemical abundances. For almost all components, we derived precise surface temperatures and metallicities. We derived absolute dimensions for 20 stars with an average precision of 0.2% and 0.5% for masses and radii, respectively. Three systems show slow apsidal motion. One system, HD 32129, is most likely a triple system with a much fainter K6V companion. Also three systems contain metallic-line components and show strong enhancements of barium and ittrium. The components of all systems compare well to the SBCR derived before from the detached eclipsing binary stars. With a possible exception of HD 32129, they can be used to calibrate SBCRs with a precision better than 1% with available Gaia DR3 parallaxes.

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arXiv2021

Metallicities and ages for 35 star clusters and their surrounding fields in the Small Magellanic Cloud

In this work we study 35 stellar clusters in the Small Magellanic Cloud (SMC) in order to provide their mean metallicities and ages. We also provide mean metallicities of the fields surrounding the clusters. We used Strömgren photometry obtained with the 4.1 m SOAR telescope and take advantage of $(b - y)$ and $m1$ colors for which there is a metallicity calibration presented in the literature. The spatial metallicity and age distributions of clusters across the SMC are investigated using the results obtained by Strömgren photometry. We confirm earlier observations that younger, more metal-rich star clusters are concentrated in the central regions of the galaxy, while older, more metal-poor clusters are located farther from the SMC center. We construct the age-metallicity relation for the studied clusters and find good agreement with theoretical models of chemical enrichment, and with other literature age and metallicity values for those clusters. We also provide the mean metallicities for old and young populations of the field stars surrounding the clusters, and find the latter to be in good agreement with recent studies of the SMC Cepheid population. Finally, the Strömgren photometry obtained for this study is made publicly available.

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arXiv2021

The surface brightness - colour relations based on eclipsing binary stars and calibrated with Gaia EDR3

The surface brightness -- colour relation (SBCR) is a basic tool in establishing precise and accurate distances within the Local Group. Detached eclipsing binary stars with accurately determined radii and trigonometric parallaxes allow for a calibration of the SBCRs with unprecedented accuracy. We analysed four nearby eclipsing binary stars containing late F-type main sequence components: AL Ari, AL Dor, FM Leo and BN Scl. We determined very precise spectroscopic orbits and combined them with high precision ground- and space-based photometry. We derived the astrophysical parameters of their components with mean errors of 0.1% for mass and 0.4% for radius. We combined those four systems with another 24 nearby eclipsing binaries with accurately known radii from the literature for which $Gaia$ EDR3 parallaxes are available, in order to derive the SBCRs. The resulting SBCRs cover stellar spectral types from B9 V to G7 V. For calibrations we used Johnson optical $B$ and $V$, $Gaia$ $G_{\rm BP}$ and $G$ and 2MASS $JHK$ bands. The most precise relations are calibrated using the infrared $K$ band and allow to predict angular diameters of A-, F-, and G-type dwarf and subgiant stars with a precision of 1%.

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arXiv2019

Candidates for non-pulsating stars located in the Cepheid instability strip in the Large Magellanic Cloud based on Strömgren photometry

We present candidates for non-pulsating stars lying in the classical Cepheid instability strip based on OGLE photometric maps combined with Strömgren photometry obtained with the 4.1-m SOAR telescope, and Gaia DR2 data in four fields in the Large Magellanic Cloud. We selected 19 candidates in total. After analysis of their light curves from OGLE surveys we found that all these stars appear to be photometrically stable at the level of a few mmag. Our results show that non-pulsating stars might constitute to about 21%-30% of the whole sample of giant stars located in the classical instability strip. Furthermore, we identified potential candidates for classical Cepheids with hot companions based on their Strömgren colours.

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arXiv2019

Towards early-type eclipsing binaries as extragalactic milestones: I. Physical parameters of OGLE-LMC-ECL-22270 and OGLE-LMC-ECL-06782

In this first paper of the series we describe our project to calibrate the distance determination method based on early-type binary systems. The final objective is to measure accurate, geometrical distances to galaxies beyond the Magellanic Clouds with a precision of 2%. We start with the analysis of two early-type systems for which we have collected all the required spectroscopic and photometric data. Apart from catalog publications, these systems have not been studied yet, and it is the first time the modeling of light and radial velocity curves is performed for them. From the analysis we obtained precise physical parameters of the components, including the masses measured with precision of 0.6-1% and radii with precision of 0.4-3%. For one system we determined the $(V-K)$ color and estimated the distance using the bolometric flux scaling method (DM=18.47 $\pm$ 0.15 mag), which agrees well with our accurate determination of the distance to the LMC from late-type giants. For the same system we determined the surface brightness of individual stars using our model, and checked that it is consistent with a recent surface brightness -- color relation. We compared our results with evolution theory models of massive stars and found they agree in general, however, models with higher overshooting values give more consistent results. The age of the system was estimated to from 11.7 to 13.8 Myr, depending on the model.

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arXiv2019

Accurate stellar parameters and distance to two evolved eclipsing binary systems, OGLE-BLG-ECL-123903 and OGLE-BLG-ECL-296596, towards the Galactic bulge

Aim: Our aim is to obtain high-accuracy measurements of the physical and orbital parameters of two evolved eclipsing binary systems, and to use these measurements to study their evolutionary status. We also aim to derive distances to the systems by using a surface brightness - colour relation and compare these distances with the measurements provided by GAIA. Methods: We measured the physical and orbital parameters on both systems based on V-band and I-band photometry from OGLE, near-infrared photometry obtained with the NTT telescope and the instrument SOFI, as well as high-resolution spectra obtained at ESO 3.6m/HARPS and Clay 6.5/MIKE spectrographs. The light curves and radial-velocity curves were analysed with the Wilson-Devinney code. Results: We analysed two double-lined eclipsing binary systems OGLE-BLG-ECL-23903 and OGLE-BLG-ECL-296596 from the Optical Gravitational Lensing Experiment (OGLE) catalogue. Both systems have a configuration of two well-detached giant stars. The masses of the components ofOGLE-BLG-ECL-123903 are M_1= 2.045 $\pm$ 0.027 and M_2=2.074 $\pm$ 0.023 $M_\odot$ and the radii are R_1=9.540 $\pm$ 0.049 and R_2=9.052 $\pm$ 0.060 $R_\odot$. For OGLE-BLG-ECL-296596, the masses are M_1=1.093 $\pm$ 0.015 and M_2=1.125 $\pm$ 0.014 $M_\odot$, while the radii are R_1=18.06 $\pm$ 0.28 and R_2=29.80 $\pm$ 0.33 $R_\odot$. Evolutionary status was discussed based on the isochrones and evolutionary tracks from PARSEC and MESA codes. The ages of the systems were establishes to be around 1.3 Gyr for the OGLE-BLG-ECL-123903 and 7.7 Gyr for the OGLE-BLG-ECL-296596. We also determined the distance to both systems. For OGLE-BLG-ECL-123903 this is equal to d=2.95 $\pm$ 0.06 (stat.) $\pm$ 0.07 (syst.) kpc, while for the OGLE-BLG-ECL-296596 it is d=5.68 $\pm$ 0.07 (stat.) $\pm$ 0.14 (syst.) kpc. This is the first analysis of its kind for these unique evolved eclipsing binary systems.

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arXiv2018

The effect of metallicity on Cepheid Period-Luminosity relations from a Baade-Wesselink analysis of Cepheids in the Milky Way and Magellanic Clouds

The extragalactic distance scale builds on the Cepheid period-luminosity (PL) relation. In this paper, we want to carry out a strictly differential comparison of the absolute PL relations obeyed by classical Cepheids in the Milky Way (MW), LMC and SMC galaxies. Taking advantage of the substantial metallicity difference among the Cepheid populations in these three galaxies, we want to establish a possible systematic trend of the PL relation absolute zero point as a function of metallicity, and determine the size of such an effect in optical and near-infrared photometric bands. We are using the IRSB Baade-Wesselink type method as calibrated by Storm et al. to determine individual distances to the Cepheids in our samples in MW, LMC and SMC. For our analysis, we use a greatly enhanced sample of Cepheids in the SMC (31 stars) as compared to the small sample (5 stars) available in our previous work. We use the distances to determine absolute Cepheid PL relations in optical and near-infrared bands in each of the three galaxies.} {Our distance analysis of 31 SMC Cepheids with periods from 4-69 days yields tight PL relations in all studied bands, with slopes consistent with the corresponding LMC and MW relations. Adopting the very accurately determined LMC slopes for the optical and near-infrared bands, we determine the zero point offsets between the corresponding absolute PL relations in the 3 galaxies. We find that in all bands the metal-poor SMC Cepheids are intrinsically fainter than their more metal-rich counterparts in the LMC and MW. In the $K$ band the metallicity effect is $-0.23\pm0.06$~mag/dex while in the $V,(V-I)$ Wesenheit index it is slightly stronger, $-0.34\pm0.06$~mag/dex. We find some evidence that the PL relation zero point-metallicity relation might be nonlinear, becoming steeper for lower metallicities.

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arXiv2015

The Araucaria Project: The distance to the Carina Dwarf Galaxy from infrared photometry of RR Lyrae stars

We obtained single-phase near-infrared (NIR) magnitudes in the $J$- and $K$-band for a sample of 33 RR Lyrae stars in the Carina dSph galaxy. Applying different theoretical and empirical calibrations of the NIR period-luminosity-metallicity relation for RR Lyrae stars, we find consistent results and obtain a true, reddening-corrected distance modulus of 20.118 $\pm$ 0.017 (statistical) $\pm$ 0.11 (systematic) mag. This value is in excellent agreement with the results obtained in the context of the Araucaria Project from NIR photometry of Red Clump stars (20.165 $\pm$ 0.015) and Tip of Red Giant Branch (20.09 $\pm$ 0.03 $\pm$ 0.12 mag in $J$-band, 20.14 $\pm$ 0.04 $\pm$ 0.14 mag in $K$-band), as well as with most independent distance determinations to this galaxy. The near-infrared RR Lyrae method proved to be a reliable tool for accurate distance determination at the 5 percent level or better, particularly for galaxies and globular clusters that lack young standard candles, like Cepheids.

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arXiv2015

Total eclipse of the heart: The AM CVn Gaia14aae / ASSASN-14cn

We report the discovery and characterisation of a deeply eclipsing AM CVn-system, Gaia14aae (= ASSASN-14cn). Gaia14aae was identified independently by the All-Sky Automated Survey for Supernovae (ASAS-SN; Shappee et al. 2014) and by the Gaia Science Alerts project, during two separate outbursts. A third outburst is seen in archival Pan-STARRS-1 (PS1; Schlafly et al. 2012; Tonry et al. 2012; Magnier et al. 2013) and ASAS-SN data. Spectroscopy reveals a hot, hydrogen-deficient spectrum with clear double-peaked emission lines, consistent with an accreting double degenerate classification. We use follow-up photometry to constrain the orbital parameters of the system. We find an orbital period of 49.71 min, which places Gaia14aae at the long period extremum of the outbursting AM CVn period distribution. Gaia14aae is dominated by the light from its accreting white dwarf. Assuming an orbital inclination of 90 degrees for the binary system, the contact phases of the white dwarf lead to lower limits of 0.78 M solar and 0.015 M solar on the masses of the accretor and donor respectively and a lower limit on the mass ratio of 0.019. Gaia14aae is only the third eclipsing AM CVn star known, and the first in which the WD is totally eclipsed. Using a helium WD model, we estimate the accretor's effective temperature to be 12900+-200 K. The three out-burst events occurred within 4 months of each other, while no other outburst activity is seen in the previous 8 years of Catalina Real-time Transient Survey (CRTS; Drake et al. 2009), Pan-STARRS-1 and ASAS-SN data. This suggests that these events might be rebrightenings of the first outburst rather than individual events.

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