January 2020
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16 Reads
Monthly Notices of the Royal Astronomical Society
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January 2020
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16 Reads
Monthly Notices of the Royal Astronomical Society
November 2019
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14 Reads
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8 Citations
Monthly Notices of the Royal Astronomical Society
We present candidates for non-pulsating stars lying in the classical Cepheid instability strip based on the Optical Gravitational Lensing Experiment (OGLE) photometric maps combined with Strömgren photometry obtained with the 4.1-m Southern Astrophysical Research (SOAR) telescope, and Gaia Data Release 2 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 $21\!-\!30\, {\rm per\, cent}$ 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.
August 2019
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12 Reads
We present candidates for non-pulsating stars lying in the classical Cepheid instability strip based on OGLE photometric maps combined with Str\"omgren 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 Str\"omgren colours.
July 2016
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34 Reads
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58 Citations
The Astrophysical Journal
We present the discovery of the first Neptune analog exoplanet or super-Earth with a Neptune-like orbit, MOA-2013-BLG-605Lb. This planet has a mass similar to that of Neptune or a super-Earth and it orbits at 9 ∼ 14 times the expected position of the snow line, a snow, which is similar to Neptune's separation of 11 a snow from the Sun. The planet/host-star mass ratio is q = (3.6 ± 0.7) × 10⁻⁴ and the projected separation normalized by the Einstein radius is s = 2.39 ± 0.05. There are three degenerate physical solutions and two of these are due to a new type of degeneracy in the microlensing parallax parameters, which we designate "the wide degeneracy." The three models have (i) a Neptune-mass planet with a mass of Mp = 21-7⁺⁶M⊕ orbiting a low-mass M-dwarf with a mass of Mh = 0.19-0.06+0.05M⊙, (ii) a mini-Neptune with Mp = 7.9-1.2+1.8M⊕ orbiting a brown dwarf host with Mh = 0.068-0.011+0.019M⊙, and (iii) a super-Earth with Mp = 3.2-0.3+0.5MM⊕ orbiting a low-mass brown dwarf host with Mh = 0.025-0.0004+0.005M⊙, which is slightly favored. The 3D planet-host separations are 4.6-1.2+4.7au, 2.1-0.2+1.0au, and 0.94-0.02+0.67au, which are 8.9-1.4+10.5, 12-1⁺⁷, or 14⁻¹⁺¹¹ times larger than a snow for these models, respectively. Keck adaptive optics observations confirm that the lens is faint. This discovery suggests that low-mass planets with Neptune-like orbits are common. Therefore processes similar to the one that formed Neptune in our own solar system or cold super-Earths may be common in other solar systems. © 2016. The American Astronomical Society. All rights reserved.
November 2015
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194 Reads
We present the discovery of the first Neptune analog exoplanet, MOA-2013-BLG-605Lb. This planet has a mass similar to that of Neptune or a super-Earth and it orbits at $9\sim 14$ times the expected position of the snow-line, $a_{\rm snow}$, which is similar to Neptune's separation of $ 11\,a_{\rm snow}$ from the Sun. The planet/host-star mass ratio is $q=(3.6\pm0.7)\times 10^{-4}$ and the projected separation normalized by the Einstein radius is $s=2.39\pm0.05$. There are three degenerate physical solutions and two of these are due to a new type of degeneracy in the microlensing parallax parameters, which we designate "the wide degeneracy". The three models have (i) a Neptune-mass planet with a mass of $M_{\rm p}=21_{-7}^{+6} M_{\rm earth}$ orbiting a low-mass M-dwarf with a mass of $M_{\rm h}=0.19_{-0.06}^{+0.05} M_\odot$, (ii) a mini-Neptune with $M_{\rm p}= 7.9_{-1.2}^{+1.8} M_{\rm earth}$ orbiting a brown dwarf host with $M_{\rm h}=0.068_{-0.011}^{+0.019} M_\odot$ and (iii) a super-Earth with $M_{\rm p}= 3.2_{-0.3}^{+0.5} M_{\rm earth}$ orbiting a low-mass brown dwarf host with $M_{\rm h}=0.025_{-0.004}^{+0.005} M_\odot$. The 3-D planet-host separations are 4.6$_{-1.2}^{+4.7}$ AU, 2.1$_{-0.2}^{+1.0}$ AU and 0.94$_{-0.02}^{+0.67}$ AU, which are $8.9_{-1.4}^{+10.5}$, $12_{-1}^{+7}$ or $14_{-1}^{+11}$ times larger than $a_{\rm snow}$ for these models, respectively. The Keck AO observation confirm that the lens is faint. This discovery suggests that Neptune-like planets orbiting at $\sim 11\,a_{\rm snow}$ are quite common. They may be as common as planets at $\sim 3\,a_{\rm snow}$, where microlensing is most sensitive, so processes similar to the one that formed Uranus and Neptune in our own Solar System may be quite common in other solar systems.
May 2015
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202 Reads
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30 Citations
The Astrophysical Journal
We report the discovery of a Jupiter-mass planet orbiting an M-dwarf star that gave rise to the microlensing event OGLE-2011-BLG-0265. Such a system is very rare among known planetary systems and thus the discovery is important for theoretical studies of planetary formation and evolution. High-cadence temporal coverage of the planetary signal combined with extended observations throughout the event allows us to accurately model the observed light curve. The final microlensing solution remains, however, degenerate yielding two possible configurations of the planet and the host star. In the case of the preferred solution, the mass of the planet is $M_{\rm p}$ = 1.0 $\pm$ 0.3 $M_{\rm J}$, and the planet is orbiting a star with a mass $M$ = 0.23 $\pm$ 0.07 $M_\odot$.The second possible configuration (2\sigma away) consists of a planet with $M_{\rm p}$ = 0.6 $\pm$ 0.2 $M_{\rm J}$ and host star with $M$ = 0.15 $\pm$0.06 $M_{\odot}$. The system is located in the Galactic disk 3-4 kpc towards the Galactic bulge. In both cases, with an orbit size of 2 AU, the planet is a "cold Jupiter" -- located well beyond the "snow line" of the host star. Currently available data make the secure selection of the correct solution difficult, but there are prospects for lifting the degeneracy with additional follow-up observations in the future, when the lens and source star separate.
February 2015
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118 Reads
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49 Citations
Monthly Notices of the Royal Astronomical Society
We present optical observations of the peculiar Type Ibn supernova (SN Ibn) OGLE-2012-SN-006, discovered and monitored by the OGLE-IV survey, and spectroscopically followed by PESSTO at late phases. Stringent pre-discovery limits constrain the explosion epoch with fair precision to JD = 2456203.8 +- 4.0. The rise time to the I-band light curve maximum is about two weeks. The object reaches the peak absolute magnitude M(I) = -19.65 +- 0.19 on JD = 2456218.1 +- 1.8. After maximum, the light curve declines for about 25 days with a rate of 4 mag per 100d. The symmetric I-band peak resembles that of canonical Type Ib/c supernovae (SNe), whereas SNe Ibn usually exhibit asymmetric and narrower early-time light curves. Since 25 days past maximum, the light curve flattens with a decline rate slower than that of the 56Co to 56Fe decay, although at very late phases it steepens to approach that rate. An early-time spectrum is dominated by a blue continuum, with only a marginal evidence for the presence of He I lines marking this SN Type. This spectrum shows broad absorptions bluewards than 5000A, likely O II lines, which are similar to spectral features observed in super-luminous SNe at early epochs. The object has been spectroscopically monitored by PESSTO from 90 to 180 days after peak, and these spectra show the typical features observed in a number of SN 2006jc-like events, including a blue spectral energy distribution and prominent and narrow (v(FWHM) ~ 1900 km/s) He I emission lines. This suggests that the ejecta are interacting with He-rich circumstellar material. The detection of broad (10000 km/s) O I and Ca II features likely produced in the SN ejecta (including the [O I] 6300A,6364A doublet in the latest spectra) lends support to the interpretation of OGLE-2012-SN-006 as a core-collapse event.
December 2014
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320 Reads
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166 Citations
The Astrophysical Journal
We have analyzed a sample of 27,258 fundamental-mode RR Lyrae variable stars (type RRab) detected recently toward the Galactic bulge by the OGLE survey. The data support our earlier claim that these metal-poor stars trace closely the barred structure formed of intermediate-age red clump giants. The distance to the Galactic center (GC) inferred from the bulge RR Lyrae stars is R_0=8.27+/-0.01(stat)+/-0.40(sys) kpc. We show that their spatial distribution has the shape of a triaxial ellipsoid with the major axis located in the Galactic plane and inclined at an angle i=20+/-3 deg to the Sun-GC line of sight. The obtained scale-length ratio of the major axis to the minor axis in the Galactic plane, and to the axis vertical to the plane is 1:0.49(2):0.39(2). We do not see the evidence for the bulge RR Lyrae stars forming an X-shaped structure. Based on the light curve parameters, we derive metallicities of the RRab variables and show that there is a very mild but statistically significant radial metallicity gradient. About 60% of the bulge RRab stars form two very close sequences on the period-amplitude (or Bailey) diagram, which we interpret as two major old bulge populations: A and B. Their metallicities likely differ. Population A is about four times less abundant than the slightly more metal-poor population B. Most of the remaining stars seem to represent other, even more metal-poor populations of the bulge. The presence of multiple old populations indicates that the Milky Way bulge was initially formed through mergers.
December 2014
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50 Reads
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1 Citation
Acta Astronomica -Warsaw and Cracow-
We report the discovery of two distinct types of ellipsoidal binary systems occupying, so called, sequence E on the period-luminosity (P-L) diagram. We propose that steeper P-L relation is composed of giant-dwarf binaries, while the other consists of giant-giant binary systems. Analysis is based on a sample of 5334 objects, which we select from the OGLE-III survey data toward the the Large Magellanic Cloud. We show that one of the components of ellipsoidal binaries is typically either a Red Clump or a Red Giant Branch star, which leads to clear separation split of the sequence E at P = 40 d. In its short-period part, we identify two subsequences corresponding to the two types of binary systems (E2 and E3), while in the longer-period part the two groups merge forming a single subsequence E1. We extract a group of 271 ellipsoidal systems with eccentric orbits, from our sample. We present the period-luminosity relation they follow.
December 2014
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7 Reads
... M. Breger suggested that probably all stars inside the classical instability strip show oscillations but some of them have a very low amplitude which could not be detected from the ground-based observations because of the accuracy of the observations (Breger 1969). However, recent studies with space-based photometric data showed that there are non-pulsators inside the instability strips of these variables (Guzik et al., 2013;Murphy et al., 2015;Narloch et al., 2019). In a recent study, Murphy et al., (2019), examined the fraction of pulsators inside the δ Scuti instability strip. ...
November 2019
Monthly Notices of the Royal Astronomical Society
... The orbital motion of the planet can often produce effects similar to microlensing parallax (Bennett et al. 2010b;Sumi et al. 2016), so most of the planets in the Suzuki et al. (2016) sample with microlensing parallax measurements also have had planetary orbital motion included in their models (Gaudi et al. 2008;Dong et al. 2009b;Batista et al. 2011;Muraki et al. 2011;Bachelet et al. 2012;Furusawa et al. 2013;Skowron et al. 2015;Bennett et al. 2016Bennett et al. , 2018b. Thus, the orbital motion of the planetary (and possible stellar companions) to the host star should generally be included in the modeling to ensure an unbiased π E measurement. ...
July 2016
The Astrophysical Journal
... The most common method to distinguish the O-rich and C-rich Miras in the LMC is using NIR photometry (J-K) from the 2MASS (Skrutskie et al., 2006). However, due to the large depth of the Galactic disk and bulge along the line of sight (Soszyński et al., 2013), the same method could not be used for Miras in the Milky Way. In order to classify O-rich and C-rich Miras in our sample, we adopted a so-called Gaia-2MASS diagram (Lebzelter et al., 2018;Abia et al., 2020Abia et al., , 2022 which combines Gaia and 2MASS photometry. ...
April 2013
... However, some of the events like SN 2014av display a longer rise time of ≈ 10 days, which we struggle to reproduce with our light curve model. Another slowlyevolving SN Ib with signatures of interaction is OGLE-2012-SN-006 (Pastorello et al. 2015c), which has a rise time of ∼ 10 days in the I band. The decline rate in the late phase matches the expectation from 56 Co decay, although this match is coincident and the flattening of the light curve after peak in I band is likely caused by dust formation (Gan et al. 2021). ...
February 2015
Monthly Notices of the Royal Astronomical Society
... As lower-mass counterparts to Cepheid variables, RR Lyrae stars have a long history of use as standard candles for mapping the structure, kinematics, and formation history of the Milky Way (e.g. Vi v as et al. 2008 ;Braga et al. 2015 ;Pietrukowicz et al. 2015 ;Minniti et al. 2016 ;Dong et al. 2017 ;Mateu, Read & Kawata 2017 ). They include the subtype ab, which pulsates in the fundamental mode; subtype c, which pulsates in the first o v ertone mode; and subtype d, which pulsates in both modes. ...
December 2014
The Astrophysical Journal
... Because of their resemblance to a cardiogram, this type of objects are called heartbeat stars (Thompson et al., 2012). OGLE found large numbers of ellipsoidal binaries, and Pawlak et al. (2014) identified more than 2,000 such systems towards the Large Magellanic clouds. ...
December 2014
Acta Astronomica -Warsaw and Cracow-
... The orbital motion of the planet can often produce effects similar to microlensing parallax (Bennett et al. 2010b;Sumi et al. 2016), so most of the planets in the Suzuki et al. (2016) sample with microlensing parallax measurements also have had planetary orbital motion included in their models (Gaudi et al. 2008;Dong et al. 2009b;Batista et al. 2011;Muraki et al. 2011;Bachelet et al. 2012;Furusawa et al. 2013;Skowron et al. 2015;Bennett et al. 2016Bennett et al. , 2018b. Thus, the orbital motion of the planetary (and possible stellar companions) to the host star should generally be included in the modeling to ensure an unbiased π E measurement. ...
May 2015
The Astrophysical Journal
... It started in 1992 with the original aim of detecting microlensing events towards the Galactic bulge (Udalski et al., 1992). Since then, OGLE has detected and classified about one million new variable stars (e.g., Soszyński et al., 2013Soszyński et al., , 2014Soszyński et al., , 2016Mróz et al., 2015). In its current fourth phase, OGLE-IV monitors about one billion stars over 3500 deg 2 of the Galactic bulge, Galactic disc, and Magellanic System (Udalski et al., 2015). ...
October 2014
Acta Astronomica -Warsaw and Cracow-
... The Optical Gravitational Lensing Experiment (OGLE; Udalski et al. 2015) also runs a transient search (Wyrzykowski et al. 2014). The survey is focused on an area of the sky around the Magellanic Clouds, but this includes many background galaxies. ...
September 2014
Acta Astronomica -Warsaw and Cracow-
... Among the 81 confirmed planets orbiting a VLM dwarf, 29 of them were found by the microlensing method. Ho we ver, only seven such microlens planetary systems have unambiguous mass measurements: MOA-2007-BLG-192 (Bennett et al. 2008Kubas et al. 2012 ), MOA-2010-BLG-073 (Street et al. 2013 ), OGLE-2012-BLG-0358 (Han et al. 2013 ), OGLE-2013-BLG-0102 (Jung et al. 2015 ), OGLE-2013-BLG-0341 (Jung et al. 2015 ), MOA-2013-BLG-605 (Sumi et al. 2016 ), OGLE-2016-BLG-1195(Bond et al. 2017Shv artzv ald et al. 2017 ), while other systems require a Bayesian analysis based on a Galactic model to estimate the mass of the planetary systems. ...
July 2014
The Astrophysical Journal