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News Article | May 23, 2017
Site: phys.org

Gravitational microlensing is an invaluable method of detecting new extrasolar planets and brown dwarfs, regardless of the light they emit. This technique is therefore sensitive to the mass of the objects, rather than their luminosity, which allows astronomers to study objects that emit little or no light at all. Hence, due to their extremely low luminosities, brown-dwarf systems seem to be ideal targets for microlensing observations. Now, a team of astronomers led by Cheongho Han of the Chungbuk National University in Cheongju, South Korea, reports the detection of a new brown-dwarf binary system from the analysis of the microlensing event OGLE-2016-BLG-1469. The discovery is the result of a joint effort of over 50 scientists working in three microlensing research groups. The team consists of researchers from the Korea Microlensing Telescope Network (KMTNet), the Optical Gravitational Lensing Experiment (OGLE) and the Microlensing Observations in Astrophysics (MOA). "In this paper, we present the microlensing discovery of another binary system composed of brown dwarfs," the astronomers wrote in the paper. For their observations of OGLE-2016-BLG-1469, MOA researchers employed the 1.8m telescope at the Mt. John University Observatory in New Zealand, while OGLE scientists used the 1.3m telescope located at the Las Campanas Observatory in Chile. When it comes to KMTNet, the astronomers utilized three identical 1.6m telescopes located at the Cerro Tololo Inter-American Observatory in Chile, the South African Astronomical Observatory in South Africa, and the Siding Spring Observatory in Australia. All these ground-based observatories located worldwide allowed the team to find that the light curve of the microlensing event showcased a short-term central anomaly. This irregularity turned out to be produced by a binary companion with a mass roughly equal to the primary. More importantly, the researchers were able to determine the mass of both brown dwarfs and estimate their projected separation. They found that the mass of one of the newly discovered objects is about 0.05 solar masses, while the second one has approximately 0.01 the mass of the sun. The projected separation between the binary components was estimated to be 0.33 AU. Moreover, the study revealed that the system is located about 14,670 light years away from the Earth. "By measuring both the angular Einstein radius and the microlens parallax, we could uniquely determine the masses and identified the substellar nature of the lens components," the paper reads. According to the authors of the paper, their discovery shows the importance of the microlensing technique when it comes to finding new brown-dwarf binary systems. "The lens was the third microlensing brown-dwarf binary with measured mass, demonstrating the usefulness of the microlensing method in detecting field brown-dwarf binaries," the researchers concluded. Explore further: Astronomers discover new substellar companion using microlensing Abstract We report the discovery of a binary composed of two brown dwarfs, based on the analysis of the microlensing event OGLE-2016-BLG-1469. Thanks to detection of both finite-source and microlens-parallax effects, we are able to measure both the masses M1∼0.05 M⊙, M2∼0.01 M⊙, and distance DL∼4.5 kpc, as well as the projected separation a⊥∼0.33 au. This is the third brown-dwarf binary detected using the microlensing method, demonstrating the usefulness of microlensing in detecting field brown-dwarf binaries with separations less than 1 au.


News Article | May 8, 2017
Site: phys.org

The planets were discovered by researchers working as part of the Optical Gravitational Lensing Experiment (OGLE) group and the Microlensing Observations in Astrophysics (MOA) collaboration. OGLE uses the 1.3-m Warsaw Telescope located at Las Campanas Observatory in Chile, while MOA utilizes the 1.8-m MOA-II telescope at the Mount John University Observatory, located in New Zealand. The main goal of these two microlensing surveys is to study the planet formation around late-type stars. Gravitational microlensing is an invaluable method of detecting new extrasolar planets circling their parent stars relatively closely. This technique is sensitive to planets orbiting beyond the so-called "snow line" around relatively faint host stars like M dwarfs or brown dwarfs. It is a location in the proto-planetary disk where the water ice may condense and where gas giant planets are believed to be formed. Therefore, understanding the distribution of exoplanets in this region could offer important clues to how planets form. Recently, OGLE and MOA scientists led by Przemek Mróz of the Warsaw University Observatory in Poland, have found planetary anomalies in two faint microlensing events designated OGLE-2013-BLG-0132 and OGLE-2013-BLG-1721. "Both events showed clear deviations from the simple point-source point-lens model, caused by the presence of a second body with well-measured planet-to-host mass ratios of (5.15 ± 0.28) x 10-4 and (13.18 ± 0.72) x 10-4, respectively," the researchers wrote in the paper. The newly discovered planets received designation OGLE-2013-BLG-0132b and OGLE-2013-BLG-1721b. Both planets likely belong to a group of sub-Jupiter-mass planets orbiting M dwarfs beyond the snow line distance. According to the research, OGLE-2013-BLG-0132b has a mass of about 0.29 Jupiter masses and orbits its parent star at a distance of 3.6 AU. The planet's host is located about 12,700 light years away and has a mass of approximately 0.54 solar masses. With a mass of about 0.64 Jupiter masses, OGLE-2013-BLG-1721b is circling its host (0.46 solar masses) at a distance of 2.6 AU. This planetary system is located some 20,500 light years away from the Earth. The researchers estimated the masses of the planets using the Bayesian analysis as both events were short and faint, which prevented them from measuring a reliable parallax signal. "Both events were too short and too faint to measure a reliable parallax signal and hence the lens mass. We therefore used a Bayesian analysis to estimate masses of both planets," the paper reads. The team noted that in order to uncover more properties of the two newly discovered planetary systems, follow-up high-resolution imaging observations should be conducted in the future. In particular, the Near InfRared Camera (NIRCam) on the James Webb Space Telescope (JWST) that will be launched into space in late 2018, could reveal important insights about these new Saturn-mass exoworlds. More information: OGLE-2013-BLG-0132Lb and OGLE-2013-BLG-1721Lb: Two Saturn-mass Planets Discovered around M-dwarfs, arXiv:1705.01058 [astro-ph.EP] arxiv.org/abs/1705.01058 Abstract We present the discovery of two planetary systems consisting of a Saturn-mass planet orbiting an M-dwarf, which were detected in faint microlensing events OGLE-2013-BLG-0132 and OGLE-2013-BLG-1721. The planetary anomalies were covered with high cadence by OGLE and MOA photometric surveys. The light curve modeling indicates that planet-host mass ratios are (5.15±0.28)×10−4 and (13.18±0.72)×10−4, respectively. Both events were too short and too faint to measure a reliable parallax signal and hence the lens mass. We therefore used a Bayesian analysis to estimate masses of both planets: 0.29+0.16−0.13 MJup (OGLE-2013-BLG-0132Lb) and 0.64+0.35−0.31 M (OGLE-2013-BLG-1721Lb). Thanks to a high relative proper motion, OGLE-2013-BLG-0132 is a promising candidate for the high-resolution imaging follow-up. Both planets belong to an increasing sample of sub-Jupiter-mass planets orbiting M-dwarfs beyond the snow line.


Adam C.,University Observatory | Mugrauer M.,University Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2014

We report the detection of a new low-mass stellar companion to the white dwarf HIP 3678 A, the central star of the planetary nebula NGC 246. The newly found companion is located about 1 arcsec (at projected separation of about 500 au) north-east of HIP 3678 A, and shares a common proper motion with the white dwarf and its known comoving companion HIP 3678 B. The hypothesis that the newly detected companion is a non-moving background object can be rejected on a significance level of more than 8σ, by combining astrometricmeasurements from the literature with follow-up astrometry, obtained withWide Field Planetary Camera 2/Hubble Space Telescope andNACO/Very Large Telescope. From our deepNACOimaging data, we can rule out additional stellar companions of the white dwarf with projected separations between 130 up to 5500 au. In the deepest high-contrast NACO observation, we achieve a detection limit in the Ks band of about 20 mag, which allows the detection of brown dwarf companions with masses down to 36Mjup at an assumed age of the system of 260 Myr. To approximate the masses of the companions HIP 3678 B and C, we use the evolutionary Baraffe et al. models and obtain about 0.85 M for HIP 3678 B and about 0.1 M for HIP 3678 C. According to the derived absolute photometry, HIP 3678 B should be a early to mid-K dwarf (K2-K5), while HIP 3678 C should be a mid M dwarf with a spectral type in the range between M5 and M6. © 2014 The Authors.


Kramm U.,University of Rostock | Nettelmann N.,University of Rostock | Fortney J.J.,University of California at Santa Cruz | Neuhauser R.,University Observatory | Redmer R.,University of Rostock
Astronomy and Astrophysics | Year: 2012

Context. Transit and radial velocity observations continuously discover an increasing number of exoplanets. However, when it comes to the composition of the observed planets the data are compatible with several interior structure models. Thus, a planetary parameter sensitive to the planet's density distribution could help constrain this large number of possible models even further. Aims. We aim to investigate to what extent an exoplanet's interior can be constrained in terms of core mass and envelope metallicity by taking the tidal Love number k 2 into account as an additional, possibly observable parameter. Methods. Because it is the only planet with an observationally determined k 2, we constructed interior models for the Hot Jupiter exoplanet HAT-P-13b by solving the equations of hydrostatic equilibrium and mass conservation for different boundary conditions. In particular, we varied the surface temperature and the outer temperature profile, as well as the envelope metallicity within the widest possible parameter range. We also considered atmospheric conditions that are consistent with nongray atmosphere models. For all these models we calculated the Love number k 2 and compared it to the allowed range of k 2 values that could be obtained from eccentricity measurements of HAT-P-13b. Results. We use the example of HAT-P-13b to show the general relationships between the quantities temperature, envelope metallicity, core mass, and Love number of a planet. For any given k 2 value a maximum possible core mass can be determined. For HAT-P-13b we find M core < 27 M ⊕, based on the latest eccentricity measurement. We favor models that are consistent with our model atmosphere, which gives us the temperature of the isothermal region as ∼2100 K. With this external boundary condition and our new k 2-interval we are able to constrain both the envelope and bulk metallicity of HAT-P-13b to 1-11 times stellar metallicity and the extension of the isothermal layer in the planet's atmosphere to 3-44 bar. Assuming equilibrium tidal theory, we find lower limits on the tidal Q consistent with 10 3-10 5. Conclusions. Our analysis shows that the tidal Love number k 2 is a very useful parameter for studying the interior of exoplanets. It allows one to place limits on the core mass and estimate the metallicity of a planet's envelope. © 2012 ESO.


Gadallah K.A.K.,Al - Azhar University of Egypt | Gadallah K.A.K.,University Observatory | Mutschke H.,University Observatory | Jager C.,Friedrich - Schiller University of Jena
EAS Publications Series | Year: 2012

Hydrogenated amorphous carbons (HACs) are considered as laboratory analogues to cosmic carbonaceous nanoparticles in the interstellar medium (ISM). The optical properties of nano-sized HACs may be influenced by the UV processing. The variation of the internal structure leads to dramatic changes in the spectral properties in the FUV-VIS range. This scenario can explain some astronomical features such as the interstellar UV bump at 4.6 μm -1. The spectrum of HACs, irradiated by a dose of UV irradiation that corresponds to 21-33% of the average dose of the UV radiation in diffuse ISM, exhibits a new band centered at 4.6 μm-1. This result confirms, for the first time, the suggestion by Mennella et al. (1996) that irradiated HACs might be considered as the carriers of the interstellar UV bump at 4.6 μm-1. However, the amount of carbon needed to reproduce this band is higher than that available for interstellar carbon dust grains. So the ideal structure of irradiated HACs that would produce a band of sufficient strength has still to be searched for. © The Author(s) 2013.


News Article | August 22, 2016
Site: phys.org

(Phys.org)—A team of researchers affiliated with the Warsaw University Observatory has captured for the first time the events that led to a classical nova exploding, the explosion itself and then what happened afterwards. In their paper published in the journal Nature, the team describes how they happened to capture the star activity and why they believe it may help bolster the theory of star hibernation.


News Article | November 8, 2016
Site: physicsworld.com

Astronomy in the City is a series of (free) public events, each packed with astrophysics; stargazing, and tea and biscuits. Evenings begin with talks covering astronomical highlights and recent research, and a question-and-answer session (for everything from beginner's questions about the night sky to the latest work done here in Birmingham). Afterwards, if the weather cooperates, we have observing with telescopes on campus with members of the University's AstroSoc and the Birmingham Astronomy Society. A lucky few will be taken out to the University's Observatory and our powerful telescope. Each Astronomy in the City event features a talk on a different astrophysical topic connected to the research done at the University of Birmingham. This month, our new Observatory Director Sean McGee will talk about his research on galaxy formation. The first talk begins at 6:00 pm, in the Large Lecture Theatre of the Poynting Physics Building (R13 on the campus map) on the University's Edgbaston campus. The ballot for trips to the University Observatory close at 5:55 pm. For more details, including a preliminary program, please see the event website.


Astronomers have found the first direct evidence that prove the nova hibernation hypothesis, a theory that posits binary star systems undergo cyclical explosion that repeat itself over a period of time. In a new study published in the journal Nature on Aug. 17, Przemek Mróz, from the Warsaw University Observatory in Poland, and colleagues reported the explosion of a hibernating star. They observed mini outbursts leading up to the classical nova, the final explosion of a white dwarf, the remains of sun-like star that has exhausted its nuclear fuel. Compared with more powerful supernova explosion which means the death of stars, nova eruptions do not necessarily result in the destruction of the stellar parents. The nova that astronomers call V1213 Cen, or Nova Centauri 2009 erupted in 2009 but they have been observing its source star since 2003. Using data that were collected years before and after the eruption, researchers were able to learn about the evolution of this particular type of nova. Classical novas such as the Nova Centauri 2009 happen in binary systems, which consist of two stars orbiting each other. The nova occurs when a white dwarf stars gains matter from the other star over a period of time. The cycle starts with the hibernation phase, wherein the companion star sends mass in the form of hydrogen to the white dwarf star. The white dwarf cyclically gets brighter, dims and then awakes erupting in a big explosion, an event that creates significant increase in brightness. The process is slow but eventually starts all over again. Although astronomers observe several classical novae in the Milky Way per year, most of them are faint due to interstellar gas and dust that hide them. Long term observations with this particular nova, however, showed that the white dwarf star experienced periodic brightening since 2003 before the explosion. The fluctuation in brightness means that during this time, a low mass-transfer occurred between the two stars. Mass transfer rate also increased after the explosion. The system is currently bright but is slow fading. This will continue for a while before the process starts all over again. "Within the six years before the explosion, the system revealed dwarf nova outbursts indicative of a low mass-transfer rate," the researchers wrote. "The post-nova is two orders of magnitude brighter than the pre-nova at minimum light with no trace of dwarf nova behaviour, implying that the mass-transfer rate increased considerably as a result of the nova explosion." © 2016 Tech Times, All rights reserved. Do not reproduce without permission.

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