Abstract We present the results from a complex study of an eclipsing O-type binary (Aa+Ab) with the orbital period of P A = 3.2254367 days that forms part of a higher-order multiple system in a ...configuration of (A+B)+C. We derived masses of the Aa+Ab binary of M 1 = 19.02 ± 0.12 and M 2 = 17.50 ± 0.13 M ⊙ , the radii of R 1 = 7.70 ± 0.05 and R 2 = 6.64 ± 0.06 R ⊙ , and temperatures of T 1 = 34,250 ± 500 K and T 2 = 33,750 ± 500 K. From the analysis of the radial velocities, we found a spectroscopic orbit of A in the outer A+B system with P A+B = 195.8 days ( P A+B / P A ≈ 61). In the O − C analysis, we confirmed this orbit and found another component orbiting the A+B system with P AB+C = 2550 days ( P AB+C / P A+B ≈ 13). From the total mass of the inner binary and its outer orbit, we estimated the mass of the third object, M B ≳ 10.7 M ⊙ . From the light travel time effect fit to the O − C data, we obtained the limit for the mass of the fourth component, M C ≳ 7.3 M ⊙ . These extra components contribute about 20%–30% (increasing with wavelength) to the total system light. From the comparison of model spectra with the multiband photometry, we derived a distance modulus of 18.59 ± 0.06 mag, a reddening of 0.16 ± 0.02 mag, and an R V of 3.2. This work is part of our ongoing project, which aims to calibrate the surface brightness–color relation for early-type stars.
Abstract
We present new period–luminosity and period–luminosity–metallicity relations for Galactic RR Lyrae stars based on a sample of 28 pulsators located at distances of up to 1.5 kpc from the Sun. ...Near-infrared photometry was obtained at the Cerro Armazones Observatory, and parallaxes were taken from the Gaia Early Data Release 3. Relations were determined for the 2MASS
JHK
s
bands and the
W
JK
Wesenheit index. We compare our results with other calibrations available in the literature and obtain very good agreement with the photometry of RR Lyraes from the Large Magellanic Cloud (LMC) anchored using the distance to the Cloud, which is based on detached eclipsing binaries. We find that the dependence of absolute magnitudes on metallicity of 0.070 ± 0.042 (
J
band) to 0.087 ± 0.031 (
W
JK
index) mag dex
−1
for the population of fundamental pulsators (RRab) is in agreement with previously published phenomenological works. We perform a refined determination of distance to the LMC based on our new calibration and photometry from Szewczyk et al. We study the dependence of the fitted parameters of the fiducial relations and the LMC distance on the systematic parallax offset.
Context. In unified models, different types of active galaxy nuclei (AGN) correspond to a single class of objects, where their observed differences are solely due to the different orientations of the ...obscuring material around the central inner regions. Recent studies also show that this obscuring material can even extend at galactic scales due to debris from galaxy interactions and/or mergers. In standard unified models the different AGN types are expected to show similar galaxy environments. Aims. We aim to investigate properties and environment of obscured and unobscured AGNs selected from mid-infrared (MIR) bands from the Multiwavelength Survey by Yale-Chile (MUSYC), in order to test the unified model and evolutionary scenarios. Methods. The sample of AGNs was selected from images obtained with the Infrared Array Camera (IRAC) mounted on the Spitzer Space Telescope, based on their MIR colors centered at wavelengths 3.6, 4.5, 5.8 and 8.0 microns. We selected two samples of AGNs with redshifts in the range 1 ≤ z ≤ 2 and rest-frame absolute magnitudes Mv ≤ −21: obscured and unobscured AGNs by means of a simple optical-MIR color cut criterion (R− 4.5 = 3.05.) Results. We find that obscured AGNs are intrinsically optically faint in the R band, suggesting that luminous IR-selected AGNs have a significant dust extinction. From a cross-correlation with several X-ray surveys, we find that the majority of the AGNs in our sample have X-ray luminosities similar to those found in Seyfert-like galaxies. We study the properties of galaxies surrounding these two samples. Neighbouring galaxies located close to (~200 kpc) obscured AGNs tend to have redder colors, compared to the local environment of unobscured AGNs. Results obtained from a KS test show that the two color distributions are different at ~95% confidence level. We find that obscured AGNs are located in denser local galaxy environments compared to the unobscured AGN sample. Conclusions. Our results suggest that AGN obscuration can occur at galactic scales, possibly due to galaxy interactions or mergers, and that the simple unified model based solely on the local torus orientation may not be sufficient to explain all the observations.
Our main goal is to establish a firm empirical calibration of the surface brightness vs. (V-K) color relation for early type stars based on high quality spectroscopic and infrared observations of ...early-type detached eclipsing systems in the Large Magellanic Cloud (LMC). Our calibration of this relation will allow distance determinations accurate to about 2.5% to a single object located well beyond the Magellanic Clouds. This will let us calibrate other distance indicators, including period-luminosity relations for Cepheids. The first step of the project is to determine precise parameters for a sample of B-type systems in the LMC. We have already made a preliminary analysis of light and radial velocity curves for selected objects and measured their masses and radii. Here we present the results for one such system.
We present reddening maps of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC), based on color measurements of the red clump. Reddening values of our maps were obtained by calculating ...the difference of the observed and intrinsic color of the red clump in both galaxies. To obtain the intrinsic color of the red clump, we used reddenings obtained from late-type eclipsing binary systems, measurements for blue supergiants and reddenings derived from Strömgren photometry of B-type stars. We obtained intrinsic color of the red clump (V − I)0 = 0.838 0.034 mag in the LMC, and (V − I)0 = 0.814 0.034 mag in the SMC. We prepared our map with 3′ resolution, covering the central part of the LMC and SMC. The mean value of the reddening is E(B − V)LMC = 0.127 mag and E(B − V)SMC = 0.084 mag for the LMC and SMC, respectively. The systematic uncertainty of the average reddening value assigned to each field of our maps is 0.013 mag for both Magellanic Clouds. Our reddening values are on average higher by 0.061 mag for the LMC and 0.054 mag for the SMC, compared with the maps of Haschke et al. We also compared our values with different types of reddening tracers. Cepheids, RR Lyrae stars, early-type eclipsing binaries, and other reddening estimations based on the red clump color on average show reddenings consistent with our map to within a few hundredths of magnitude.
Using a sample of 81 galactic, detached eclipsing binary stars we investigated the global zero-point shift of their parallaxes with the Gaia Data Release 2 (DR2) parallaxes. The stars in the sample ...lay in a distance range of 0.04-2 kpc from the Sun. The photometric parallaxes ϖPhot of the eclipsing binaries were determined by applying a number of empirical surface brightness-color (SBC) relations calibrated on optical-infrared colors. For each SBC relation we calculated the individual differences and then we calculated unweighted and weighted means. As the sample covers the whole sky we interpret the weighted means as the global shifts of the Gaia DR2 parallaxes with respect to our eclipsing binary sample. Depending on the choice of the SBC relation the shifts vary from −0.094 to −0.025 mas. The weighted mean of the zero-point shift from all colors and calibrations used is dϖ = −0.054 0.024 mas. However, the SBC relations based on (B − K) and (V − K) colors, which are the least reddening dependent and have the lowest intrinsic dispersions, give a zero-point shift of dϖ = −0.031 0.011 mas in full agreement with results obtained by Lindegren et al. and Arenou et al. Our result confirms the global shift of Gaia DR2 parallaxes of dϖ = −0.029 mas reported by the Gaia team, but we do not confirm the larger zero-point shift reported by a number of follow-up papers.
Abstract
Masses of classical Cepheids of 3–11
M
⊙
are predicted by theory but those measured clump between 3.6–5
M
⊙
. As a result, their mass–luminosity relation is poorly constrained, impeding our ...understanding of basic stellar physics and the Leavitt Law. All Cepheid masses come from the analysis of 11 binary systems, including only five that are double lined and well suited for accurate dynamical mass determination. We present a project to analyze a new, numerous group of Cepheids in double-lined binary (SB2) systems to provide mass determinations in a wide mass interval and study their evolution. We analyze a sample of 41 candidate binary LMC Cepheids spread along the
P
–
L
relation, which are likely accompanied by luminous red giants, and present indirect and direct indicators of their binarity. In a spectroscopic study of a subsample of 18 brightest candidates, for 16 we detected lines of two components in the spectra, already quadrupling the number of Cepheids in SB2 systems. Observations of the whole sample may thus lead to quadrupling all the Cepheid mass estimates available now. For the majority of our candidates, erratic intrinsic period changes dominate over the light-travel-time effect due to binarity. However, the latter may explain the periodic phase modulation for four Cepheids. Our project paves the way for future accurate dynamical mass determinations of Cepheids in the LMC, Milky Way, and other galaxies, which will potentially increase the number of known Cepheid masses even 10-fold, hugely improving our knowledge about these important stars.
Abstract
Based on new observations and improved modeling techniques, we have reanalyzed seven Cepheids in the Large Magellanic Cloud. Improved physical parameters have been determined for the exotic ...system OGLE LMC-CEP-1718 composed of two first-overtone Cepheids and a completely new model was obtained for the OGLE LMC-CEP-1812 classical Cepheid. This is now the shortest period Cepheid for which the projection factor is measured. The typical accuracy of our dynamical masses and radii determinations is 1%. The radii of the six classical Cepheids follow period–radius relations in the literature. Our very accurate physical parameter measurements allow us to calculate a purely empirical, tight period-mass–radius relation that agrees well with theoretical relations derived from non-canonical models. This empirical relation is a powerful tool to calculate accurate masses for single Cepheids for which precise radii can be obtained from Baade–Wesselink-type analyses. The mass of the type-II Cepheid
κ
Pav, 0.56 ± 0.08
M
⊙
, determined using this relation is in a very good agreement with theoretical predictions. We find large differences between the
p
-factor values derived for the Cepheids in our sample. Evidence is presented that a simple period–
p
-factor relation shows an intrinsic dispersion, hinting at the relevance of other parameters, such as the masses, radii, and radial velocity variation amplitudes. We also find evidence that the systematic blueshift exhibited by Cepheids is primarily correlated with their gravity. The companion star of the Cepheid in the OGLE LMC-CEP-4506 system has a very similar temperature and luminosity, and is clearly located inside the Cepheid instability strip, yet it is not pulsating.
Abstract
We present the results of a study of the type II Cepheid (
P
puls
= 4.974 days) in the eclipsing binary system OGLE-LMC-T2CEP-098 (
P
orb
= 397.2 days). The Cepheid belongs to the peculiar ...W Vir group, for which the evolutionary status is virtually unknown. It is the first single-lined system with a pulsating component analyzed using the method developed by Pilecki et al. We show that the presence of a pulsator makes it possible to derive accurate physical parameters of the stars even if radial velocities can be measured for only one of the components. We have used four different methods to limit and estimate the physical parameters, eventually obtaining precise results by combining pulsation theory with the spectroscopic and photometric solutions. The Cepheid radius, mass, and temperature are
,
, and
, respectively, while its companion has a similar size (
), but is more massive (
) and hotter (9500 K). Our best estimate for the
p
-factor of the Cepheid is
. The mass, position on the period–luminosity diagram, and pulsation amplitude indicate that the pulsating component is very similar to the Anomalous Cepheids, although it has a much longer period and is redder in color. The very unusual combination of the components suggest that the system has passed through a mass-transfer phase in its evolution. More complicated internal structure would then explain its peculiarity.
Abstract
Our work presents an independent calibration of the
J
-region Asymptotic Giant Branch (JAGB) method using Infrared Survey Facility photometric data and a custom luminosity function profile ...to determine JAGB mean magnitudes for nine galaxies. We determine a mean absolute magnitude of carbon stars of
M
LMC
= −6.212 ± 0.010 (stat.) ±0.030 (syst.) mag. We then use near-infrared photometry of a number of nearby galaxies, originally obtained by our group to determine their distances from Cepheids using the Leavitt law, in order to independently determine their distances with the JAGB method. We compare the JAGB distances obtained in this work with the Cepheid distances resulting from the same photometry and find very good agreement between the results from the two methods. The mean difference is 0.01 mag with an rms scatter of 0.06 mag after taking into account seven out of the eight analyzed galaxies that had their distances determined using Cepheids. The very accurate distance to the Small Magellanic Cloud based on detached eclipsing binaries is also in very good agreement with the distance obtained from carbon stars.
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