South African Astronomical Observatory

Cape Town, South Africa

South African Astronomical Observatory

Cape Town, South Africa
SEARCH FILTERS
Time filter
Source Type

News Article | May 4, 2017
Site: phys.org

The new giant planet was detected by a team of astronomers led by Lorna Temple of Keele University in Newcastle, U.K. The discovery is the result of two exoplanet surveys, namely the Wide Angle Search for Planets (WASP) and the Kilodegree Extremely Little Telescope (KELT). WASP observations, using the WASP-South telescope of the South African Astronomical Observatory (SAAO) in South Africa were carried out between May 2006 and June 2012. The KELT observing campaign, utilizing SAAO's KELT-South telescope, started in March 2010 and lasted till August 2013. WASP-167/KELT-13 is a 1.3 billion-year-old F1V star with a rotation period estimated to be shorter than 1.8 days. With a radius of about 1.79 solar radii, this star is approximately 60 percent more massive than our sun. WASP-167/KELT-13 was observed by WASP and KELT teams independently from each other, and resulted in the detection of a planet-like transit signal. Later follow-up observations of this star conducted in March 2016 using the European Southern Observatory's (ESO) 3.6-m/HARPS spectrograph provided the teams Doppler tomographic data. The new set of data revealed the planetary shadow, thus confirming the presence of an exoworld orbiting the star. "In this work, we present the joint WASP/KELT discovery of a transiting hot Jupiter dubbed WASP-167b/KELT-13b. The 1.5 R planet was confirmed by Doppler tomography of the stellar line profiles during transit," the researchers wrote. According to the paper, WASP-167b/KELT-13b has a radius of about 1.51 Jupiter radii and its maximum mass is estimated to be eight Jupiter masses. The planet is in a retrograde orbit with a sky-projected spin-orbit angle of –165 degrees. Given the fact that the newly found exoworld also has a short orbital period, it was classified as a so-called "hot Jupiter". Exoplanets of this type are similar in characteristics to Jupiter, with orbital periods of less than 10 days. They have high surface temperatures, as they orbit their parent stars very closely. In addition to revealing basic parameters of the newly detected planet, the researchers also provided some new insights into the nature of the host star. The study finds that WASP-167/KELT-13 has an effective temperature of 6,900 K and experiences non-radial stellar pulsations. These pulsations appear to have a timescale of about four hours, which is longer compared to similar stars with detected pulsations (like WASP-33 and HAT-P-2) that are near the borderline between Delta Scuti and Gamma Doradus variables. Therefore, the scientists are unable to definitely classify WASP-167/KELT-13 at the moment. The researchers emphasized the significance of their discovery, concluding that the WASP-167/KELT-13 system is one of the few detected so far with a stellar rotation period less than the planetary orbital period. Moreover, WASP-167/KELT-13 is one of the hottest and most rapidly rotating stars known to host a "hot Jupiter" exoplanet. Abstract We report the joint WASP/KELT discovery of WASP-167b/KELT-13b, a transiting hot Jupiter with a 2.02-d orbit around a V = 10.5, F1V star with [Fe/H] = 0.1 ± 0.1. The 1.5 RJup planet was confirmed by Doppler tomography of the stellar line profiles during transit. We place a limit of


News Article | May 15, 2017
Site: www.eurekalert.org

Fifth-graders making styrofoam solar system models may have the right idea. Researchers at Lehigh University have discovered a new planet orbiting a star 320 light years from Earth that has the density of styrofoam. This "puffy planet" outside our solar system may hold opportunities for testing atmospheres that will be useful when assessing future planets for signs of life. "It is highly inflated, so that while it's only a fifth as massive as Jupiter, it is nearly 40 percent larger, making it about as dense as styrofoam, with an extraordinarily large atmosphere," said Joshua Pepper, astronomer and assistant professor of physics at Lehigh University, who led the study in collaboration with researchers from Vanderbilt University and Ohio State University, along with researchers at universities and observatories and amateur astronomers around the world. The research, "KELT-11b: A Highly Inflated Sub-Saturn Exoplanet Transiting the V+8 Subgiant HD 93396," is published online in The Astronomical Journal. The planet's host star is extremely bright, allowing precise measurement of the planet's atmosphere properties and making it "an excellent testbed for measuring the atmospheres of other planets," Pepper said. Such observations help astronomers develop tools to see the types of gases in atmospheres, which will be necessary in the next 10 years when they apply similar techniques to Earthlike exoplanets with next-generation telescopes now under construction. The planet, called KELT-11b, is an extreme version of a gas planet, like Jupiter or Saturn, but is orbiting very close to its host star in an orbit that lasts less than five days. The star, KELT-11, has started using up its nuclear fuel and is evolving into a red giant, so the planet will be engulfed by its star and not survive the next hundred million years. The KELT (Kilodegree Extremely Little Telescope) survey uses two small robotic telescopes, one in Arizona and the other in South Africa. The telescopes scan the sky night after night, measuring the brightness of about five million stars. Researchers search for stars that seem to dim slightly at regular intervals, which can indicate a planet is orbiting that star and eclipsing it. Researchers then use other telescopes to measure the gravitational "wobble" of the star - the slight tug a planet exerts on the star as it orbits - to verify that the dimming, called a "transit," is due to a planet and to measure the planet's mass. Pepper built the two telescopes used in the KELT survey, which he runs with researchers at Vanderbilt University, Ohio State University, Fisk University and the South African Astronomical Observatory. Among the more than 30 contributors to the research are partners at NASA, Harvard University, University of Pennsylvania, Princeton University and University of California at Berkeley. Lehigh University physics graduate student Jonathan Labadie-Bartz is a member of the KELT team and a co-author on the paper. Some 40 "citizen scientists" in 10 countries across four continents have also contributed to the KELT project and several contributed directly to the discovery of KELT-11b and are co-authors on the paper. While several projects using small robotic telescopes have found hundreds of planets orbiting other stars - and space telescopes like the NASA Kepler mission have discovered thousands - most of those planets orbit faint stars, making it difficult to measure the planets' properties precisely. "The KELT project is specifically designed to discover a few scientifically valuable planets orbiting very bright stars, and KELT-11b is a prime example of that," Pepper said. The star, KELT-11, is the brightest in the southern hemisphere known to host a transiting planet by more than a magnitude and the sixth brightest transit host discovered to date. Planets discovered by the KELT survey will be observed in detail by large space telescopes such as Hubble and Spitzer and the James Webb Space Telescope, scheduled to launch in 2018, to understand how planets form and evolve and how their atmospheres behave, Pepper said. The KELT researchers set out to discover gas giant planets orbiting bright stars, but did not expect to find planets with such low mass and large sizes. Located in the southern sky, the "extraordinarily inflated" KELT-11b is the third-lowest density planet with a precisely measured mass and radius that has been discovered. "We were very surprised by the amazingly low density of this planet," Pepper said. "It's extremely big for its mass. It's got a fifth of the mass of Jupiter but is puffed up into this really underdense planet." Though researchers are debating the cause of KELT-11b's inflation, further study of the planet could provide additional information about the mechanism that causes inflated planets, Pepper said. The planet's large atmosphere also provides good opportunities for developing techniques needed to identify chemicals in planets' atmospheres to assess habitability or products of life in the atmospheres of other planets. "We don't know of any real Earthlike planets or stars for which we can measure their atmospheres, though we expect to discover more in future years," Pepper said. "These (giant gas) planets are the gold standards or testbeds for learning how to measure the atmospheres of planets." The research was supported by the National Science Foundation, NASA and a variety of universities and foundations.


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.


Balona L.A.,South African Astronomical Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2014

Kepler photometry of A stars shows that a considerable fraction (about 19 per cent) have a peculiar feature in the periodogram. This feature consists of a broad peak, thought to be due to differential rotation in a spotted star, and a sharp peak at slightly higher frequency. The pattern clearly involves some widespread stellar property and the sharp peak implies a strictly coherent periodicity. We investigate the possibility that the periodicity is due to rotation, pulsation or an orbital effect.We argue that neither rotation nor pulsation can provide a suitable, testable, explanation. We suggest that the sharp feature could be due to a planet in synchronous orbit around the rapidly rotating, spotted A star, not necessarily in transit. Spectroscopic observations of sufficient precision are required to falsify this hypothesis. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.


Balona L.A.,South African Astronomical Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2014

We consider the high mode density reported in the δ Scuti star HD 50844 observed by CoRoT. Using simulations, we find that extracting frequencies down to a given false alarm probability by means of successive pre-whitening leads to a gross overestimate of the number of frequencies in a star. This is due to blending of the peaks in the periodogram due to the finite duration of the time series. Pre-whitening is equivalent to adding a frequency to the data which is carefully chosen to interfere destructively with a given frequency in the data. Since the frequency extracted from a blended peak is not quite correct, the interference is not destructive with the result that many additional fictitious frequencies are added to the data. In data with very high signal-to-noise ratio, such as the CoRoT data, these spurious frequencies are highly significant. Continuous pre-whitening thus causes a cascade of spurious frequencies which leads to a much larger estimate of the mode density than is actually the case. The results reported for HD 50844 are consistent with this effect. Direct comparison of the power in the raw periodogram in this star with that in δ Scuti stars observed by Kepler shows that HD 50844 has a typical mode density. © 2014 The Author.


Balona L.A.,South African Astronomical Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2014

A method is presented whereby the orbital parameters of a pulsating star in a binary ormultiple system can be determined using the time delay due to the changing distance of the pulsating star. The method differs from previously published methods in that a direct periodogram of the orbital frequency is derived using all possible information to extract the time delay from the stellar pulsations. The method is easy to use provided the pulsation frequencies are known. The method is tested using various simulations and applied to two stars which have been previously analysed in the literature. Application to 34 Kepler objects of interest which are also δ Sct variables resulted in the detection of five stars which are binaries. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.


Balona L.A.,South African Astronomical Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2013

Two years of Kepler data are used to investigate low-frequency variations in A-type stars. In about 875 (40 per cent) A-type stars, the periodogram shows a simple peak and its harmonic. If we assume that the photometric period is the period of rotation, we can derive the equatorial rotational velocity from a suitable radius estimate. It turns out that the distribution of equatorial velocities derived in this way is similar to the distribution of equatorial velocities of A-type main-sequence stars in the general field derived from spectroscopic line broadening, verifying our initial assumption. We suggest that the light variation is due to rotational modulation caused by starspots or some other corotating structure. In many stars the rotation peak in the periodogram has a characteristic shape which is not understood. The light amplitudes are highly variable.We deduce from the amplitude distribution that the sizes of starspots in A-type stars are similar to the largest sunspots. From the widths of the peaks in the periodogram we deduce that differential rotation in these stars is similar to that in the Sun. We find that the period-colour relationship used for gyrochronology in late-type stars extends to early F-type and probably late A-type stars as well. Flares in A-type stars have been recently detected. We add 13 additional A-type flare stars to this sample, which means that about 1.5 per cent of A-type stars in the Kepler field show flares. We conclude that A-type stars are active and, like cooler stars, have starspots and flares. © 2013 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Balona L.A.,South African Astronomical Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2012

We consider the possible use of combination frequencies seen in high-amplitude δ Scuti stars for mode identification. For this purpose, we extend a previous theory to obtain expressions for the relative amplitudes and phases of combination frequencies for the case where radius and surface normal variations are important. Although a term is present which is sensitive to the pulsation mode, this term is always combined with another one which depends on the physics of the outer layers. Whereas the terms can be separated in DA and DB white dwarfs using suitable assumptions, these assumptions are not valid in pulsating main-sequence stars. We also discuss the strong correlation of relative phase of the combination frequencies with frequency. We show that this correlation is a result of the non-sinusoidal nature of the dominant pulsation mode. © 2012 The Author Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Balona L.A.,South African Astronomical Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2012

Optical flares on early F- and A-type stars have never been observed with certainty. Inspection of several thousands of these stars in the Kepler public archives resulted in the discovery of flares in 25 G-type and 27 F-type stars. Because A-type stars are thought not to be active, the detection of flares on 19 A-type stars from a sample of nearly 2000 A stars is particularly noteworthy. The flares have relative intensities in the range 1-100 parts per thousand and typical durations of a few minutes to several hours. The mean interval between flares varies between 1 and 120days. We estimate the typical energy of flares to be around 10 35 erg in the F-type stars and about 10 36 erg in the A-type stars. Nearly all these stars vary at a low level with a period which is most likely the rotational period of the star. Comparison of the relative flare intensities with those in cool red stars observed by Kepler shows that flares in these stars, and certainly in the A-type stars, cannot easily be ascribed to cool flare-star companions. The huge energy released in the flares is difficult to understand. This is especially the case for A-type stars since these stars are thought to have very weak magnetic fields. The flare energy may possibly originate in magnetic reconnection of field lines between the primary star and a companion. © 2012 The Author Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Balona L.A.,South African Astronomical Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2011

We analyse the light curves of over 9000 A-F stars in the first public release of Kepler data and examine the noise properties in constant or nearly constant stars. For the A stars, we find a correlation between the excess power in certain frequency regions and the effective temperature which may be due to granulation. The majority of A-F stars vary with low frequencies (<5d-1) and low amplitudes (40-150 ppm). The low-frequency variation extends to the hottest A-type stars where the typical amplitude is about 40 ppm. We find that about 8 per cent of A8-A0 stars have light curves resembling those usually attributed to starspots in cool stars, including a few exhibiting travelling waves usually interpreted as differentially rotating starspots. A further 20 per cent of A stars have dominant low frequencies which are visible in the periodogram. If we assume that the dominant low frequency in A-F stars is the rotation frequency, we can calculate the distribution of equatorial rotational velocities given the stellar radii. The resulting distribution matches the distribution of equatorial rotational velocities in field stars of the same spectral type and luminosity class. However, the A8-A0 stars have an excess of slow rotators which can be explained as contamination from horizontal-branch stars. We conclude that the light variations in A-type stars may possibly be due to starspots or other corotating structures and that A-star atmospheres may not be quiescent as previously supposed. We also analyse low frequencies in Kepler A-type δ Sct stars which are too hot to be due to γ Dor pulsations. These do not appear to be due to simple combinations of high-frequency δ Sct modes. Unlike normal A-type stars, the dominant low frequency is close to twice the rotational frequency. In a significant proportion of δ Sct stars there is, in fact, a frequency of smaller amplitude at exactly half the dominant low frequency. There is clearly a quadrupole surface brightness distribution in a significant fraction of these stars, but the amplitudes seem to be too low to be explained as a proximity effect in a binary. © 2011 The Author Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Loading South African Astronomical Observatory collaborators
Loading South African Astronomical Observatory collaborators