We have analyzed the data on 16,836 RR Lyrae (RR Lyr) variables observed toward the Galactic bulge during the third phase of the Optical Gravitational Lensing Experiment (OGLE-III), which took place ...in 2001-2009. Using these standard candles, we show that the ratio of total-to-selective extinction toward the bulge is given by RI = AI/E(V - I) = 1.080 + or - 0.007 and is independent of color. We demonstrate that the bulge RR Lyr stars form a metal-uniform population, slightly elongated in its inner part. The photometrically derived metallicity distribution is sharply peaked at Fe/H = -1.02 + or - 0.18, with a dispersion of 0.25 dex. In the inner regions (|l| < 3degrees, |b| < 4degrees) the RR Lyr tend to follow the barred distribution of the bulge red clump giants. The distance to the Milky Way center inferred from the bulge RR Lyr is R sub(0) = 8.54 + or - 0.42 kpc. We report a break in the mean density distribution at a distance of ~0.5 kpc from the center indicating its likely flattening. Using the OGLE-III data, we assess that (4-7) x 10 super(4) type ab RR Lyr variables should be detected toward the bulge area of the ongoing near-IR VISTA Variables in the Via Lactea (VVV) survey, where the uncertainty partially results from the unknown RR Lyr spatial density distribution within 0.2 kpc from the Galactic center.
We report the discovery of a new subclass of double-mode RR Lyrae stars in the Large and Small Magellanic Clouds. The sample of 22 pulsating stars has been extracted from the latest edition of the ...Optical Gravitational Lensing Experiment collection of RR Lyrae variables in the Magellanic System. The stars pulsating simultaneously in the fundamental (F) and first-overtone (1O) modes have distinctly different properties than regular double-mode RR Lyrae variables (RRd stars). The P sub( 1O)/P sub( F) period ratios of our anomalous RRd stars are within a range of 0.725-0.738, while 'classical' double-mode RR Lyrae variables have period ratios in the range of ...0.742-0.748. In contrast to the typical RRd stars, in the majority of the anomalous pulsators, the F-mode amplitudes are higher than the 1O-mode amplitudes. The light curves associated with the F-mode in the anomalous RRd stars show different morphology than the light curves of, both, regular RRd stars and single-mode RRab stars. Most of the anomalous double-mode stars show long-term modulations of the amplitudes (Blazhko-like effect). Translating the period ratios into the abundance parameter, Z, we find for our stars Z ... (0.002, 0.005) -- an order of magnitude higher values than typical for RR Lyrae stars. The mass range of the RRd stars inferred from the W sub( I) versus P sub( F) diagram is (0.55-0.75)...M... These parameters cannot be accounted for with single star evolution assuming a Reimers-like mass-loss. Much greater mass-loss caused by interaction with other stars is postulated. We blame the peculiar pulsation properties of our stars to the parametric resonance instability of the 1O-mode to excitation of the F- and 2O-modes as with the inferred parameters of the stars ... (ProQuest: ... denotes formulae/symbols omitted.)
We present the results from the Optical Gravitational Lensing Experiment II (OGLE-II) survey (1996–2000) towards the Large Magellanic Cloud (LMC), which has the aim of detecting the microlensing ...phenomena caused by dark matter compact objects in the Galactic halo massive compact halo objects (MACHOs). We use high-resolution Hubble Space Telescope images of the OGLE fields and derive the correction for the number of monitored stars in each field. This also yields blending distributions which we use in ‘catalogue-level’ Monte Carlo simulations of the microlensing events in order to calculate the detection efficiency of the events. We detect two candidates for microlensing events in the All Stars Sample, which translates into an optical depth of 0.43 ± 0.33 × 10−7. If both events were due to MACHO, the fraction of mass of compact dark matter objects in the Galactic halo would be 8 ± 6 per cent. This optical depth, however, along with the characteristics of the events seems to be consistent with the self-lensing scenario, i.e. self-lensing alone is sufficient to explain the observed microlensing signal. Our results indicate the non-detection of MACHOs lensing towards the LMC with an upper limit on their abundance in the Galactic halo of 19 per cent for M= 0.4 M⊙ and 10 per cent for masses between 0.01 and 0.2 M⊙.
The Magellanic Quasars Survey (MQS) has now increased the number of quasars known behind the Magellanic Clouds by almost an order of magnitude. All survey fields in the Large Magellanic Cloud (LMC) ...and 70% of those in the Small Magellanic Cloud (SMC) have been observed. The targets were selected from the third phase of the Optical Gravitational Lensing Experiment (OGLE-III) based on their optical variability, mid-IR, and/or X-ray properties. We spectroscopically confirmed 758 quasars (565 in the LMC and 193 in the SMC) behind the clouds, of which 94% (527 in the LMC and 186 in the SMC) are newly identified. The MQS quasars have long-term (12 yr and growing for OGLE), high-cadence light curves, enabling unprecedented variability studies of quasars. The MQS quasars also provide a dense reference grid for measuring both the internal and bulk proper motions of the clouds, and 50 quasars are bright enough (I <, ~ 18 mag) for absorption studies of the interstellar/intergalactic medium of the clouds.
ABSTRACT We present the first space-based microlens parallax measurement of an isolated star. From the striking differences in the lightcurve as seen from Earth and from Spitzer ( to the west), we ...infer a projected velocity , which strongly favors a lens in the Galactic Disk with mass and distance . An ensemble of such measurements drawn from our ongoing program could be used to measure the single-lens mass function including dark objects, and also is necessary for measuring the Galactic distribution of planets since the ensemble reflects the underlying Galactic distribution of microlenses. We study the application of the many ideas to break the four-fold degeneracy first predicted by Refsdal 50 years ago. We find that this degeneracy is clearly broken, but by two unanticipated mechanisms: a weak constraint on the orbital parallax from the ground-based data and a definitive measurement of the source proper motion.
We present the most extensive and detailed reddening maps of the Magellanic Clouds (MCs) derived from the color properties of Red Clump (RC) stars. The analysis is based on the deep photometric maps ...from the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV), covering approximately 670 deg2 of the sky in the Magellanic System region. The resulting maps provide reddening information for 180 deg2 in the Large Magellanic Cloud (LMC) and 75 deg2 in the Small Magellanic Cloud (SMC), with a resolution of 1 7 × 1 7 in the central parts of the MCs, decreasing to approximately 27′ × 27′ in the outskirts. The mean reddening is E(V − I) = 0.100 0.043 mag in the LMC and E(V − I) = 0.047 0.025 mag in the SMC. We refine methods of calculating the RC color to obtain the highest possible accuracy of reddening maps based on RC stars. Using spectroscopy of red giants, we find the metallicity gradient in both MCs, which causes a slight decrease of the intrinsic RC color with distance from the galaxy center of ∼0.002 mag/deg in the LMC and between 0.003 and 0.009 mag/deg in the SMC. The central values of the intrinsic RC color are 0.886 and 0.877 mag in the LMC and SMC, respectively. The reddening map of the MCs is available both in downloadable form and as an interactive interface.
ABSTRACT
We use photometric and spectroscopic observations of the eclipsing binary E32 in the globular cluster 47 Tuc to derive the masses, radii, and luminosities of the component stars. The system ...has an orbital period of 40.9 d, a markedly eccentric orbit with e = 0.24, and is shown to be a member of or a recent escaper from the cluster. We obtain $M_{\rm p} = 0.862\pm 0.005 \, \mathrm{M}_\odot$, $R_{\rm p} = 1.183\pm 0.003 \, \mathrm{R}_\odot$, $L_{\rm p} = 1.65\pm 0.05 \, \mathrm{L}_\odot$ for the primary and $M_{\rm s} = 0.827\pm 0.005 \, \mathrm{M}_\odot$, $R_{\rm s} = 1.004\pm 0.004 \, \mathrm{R}_\odot$, $L_{\rm s} = 1.14\pm 0.04\, \mathrm{L}_\odot$ for the secondary. Based on these data and on an earlier analysis of the binary V69 in 47 Tuc, we measure the distance to the cluster from the distance moduli of the component stars, and, independently, from a colour – surface brightness calibration. We obtain 4.55 ± 0.03 and 4.50 ± 0.07 kpc, respectively – values compatible within 1$\, \sigma$ with recent estimates based on Gaia DR2 parallaxes. By comparing the M–R diagram of the two binaries and the colour–magnitude diagram of 47 Tuc to Dartmouth model isochrones we estimate the age of the cluster to be 12.0 ± 0.5 Gyr, and the helium abundance of the cluster to be Y ≈ 0.25.
The dusty aftermath of the V1309 Sco binary merger Nicholls, C. P; Melis, C; Soszy ski, I ...
Monthly notices of the Royal Astronomical Society. Letters,
05/2013, Letnik:
431, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present mid-IR photometry and spectra of the merged binary V1309 Sco taken between 18 and 23 months after outburst. Strong mid-IR emission and a solid-state absorption feature indicate the ...presence of a significant amount of dust in the circumstellar environment. The absence of detectable mid-IR emission before the outburst suggests that this dust was produced in the eruptive merger event.
Model fits to the solid-state absorption feature constrain the constituent species and column density of the dust around V1309 Sco. We find that the absorption feature can be reproduced by large (3 μm) amorphous pyroxene grains at a temperature of 800 K. This grain size, if confirmed with longer wavelength spectroscopy and modelling, would be suggestive of dust processing in the circumstellar environment. The data in hand do not allow us to discriminate between disc or shell configurations for the dusty material.
We report the discovery of a period doubling behaviour in a 2.4-d BL Herculis type variable of the Galactic bulge. Another bulge BL Her type star (P = 2.25 d) is a strong period doubling candidate. ...Both objects have been identified with the Optical Gravitational Lensing Experiment (OGLE) photometry. Possibility of period doubling in this type of pulsators has been predicted almost 20 yr ago by Buchler & Moskalik. Our finding is the first observational confirmation of their theoretical results.
Discovery of the first BL Herculis star showing the period doubling effect motivates a new theoretical investigation with the state-of-the-art convective pulsation codes. We present the results of initial model survey, specifically aimed at studying the observed period-doubled BL Her variable. All of our non-linear models have P = 2.4 d. The computations confirm that the period doubling effect is caused by the 3:2 resonance between the fundamental mode and the first overtone, as indicated by earlier radiative models of Buchler & Moskalik. Comparison of the computed and the observed light curves allows us to constrain the parameters of the star, in particular its metallicity, which appears to be high, Z ≈ 0.01. The recent evolutionary tracks put also constraint on the mass of the star, which is close to M = 0.50 M⊙.
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