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News Article | November 8, 2016
Site: www.eurekalert.org

In a study published last Friday in the journal Astronomy & Astrophysics, scientists of the international collaboration of the MAGIC telescopes (Major Atmospheric Gamma Imaging Cherenkov Telescope), located at the Roque de los Muchachos Observatory, in Garafía (La Palma), and among which are researchers of the Instituto de Astrofísica de Canarias (IAC), have announced the discovery of gamma-ray emission more distant than any previous detection. The discovery was made possible by the gravitational lensing caused by a massive galaxy between the quasar and Earth, that "repeated" the light produced by the source. According to Einstein's General Relativity, light is deflected passing close to a large mass. To a distant observer the mass focuses light like a giant lens. The result is a much brighter, although distorted, image of the source and a chance to see distant objects that might otherwise be far too faint to detect. And just like a lens, light can pass through the lens with slightly different path lengths. On cosmic scales, this means photons -- parcels of light -- traveling along different lines of sight arrive at slightly different times. If, in addition, the source is variable, this is "imprinted" on the light with a time delay relative to a fixed first arrival. And this should not depend on the energy of the photons, according to the theory. That makes such observations especially important. QSO B0218+357 harbors a supermassive black hole in a galaxy located halfway across the Universe from Earth. Over 7 billion years ago a gigantic explosion occurred in this object, which led to the emission of an intense flare of gamma rays, which is the highest-energy form of light. In its long journey toward Earth, these photons passed in the vicinity of a foreground -- still distant -- galaxy, B0218+357G, over one billion years later. In passing and being deflected, those photons traveling along the shorter path finally arrived at Earth on July 14th, 2014 and were observed by the Large Area Telescope on board the orbiting Fermi satellite, which scans the entire sky every 3 hours. The detection of this gamma-ray outburst alerted the astronomical community, and many telescopes worldwide were immediately pointed at QSO B0218+357 to learn more from this distant cosmic explosion. Researchers operating the MAGIC telescopes, located on La Palma in the Canary Islands, became excited about the possible observation of this object in very-high-energy gamma rays. These could provide the most extreme perspective of this outburst, but, unfortunately, at that time there was full moon in La Palma, which prevented the operation of the MAGIC telescopes. The MAGIC telescopes measure very-high-energy gamma rays, which are a thousand times more energetic than those measured by Fermi, and a hundred billion times more energetic than any light we see from our Sun. From the earlier measurements of this object in 2012 by Fermi and by radio telescopes the scientists knew that photons arriving along the longer path should arrive about 11 days later. "In other words, Nature could award us with a replay, a second chance to look at the same interesting phenomenon." says the MAGIC Collaboration member Julian Sitarek (University of ?ódz, Poland and IFAE former member of the Institut de Fisica d'Altes Energies in Barcelona, Spain, when he started this project) who led this study, and continues: "When the time came, the MAGIC telescopes were pointed at QSO B0218+357, and, in accordance with the prediction, a flare of very-high-energy gamma rays was observed, making QSO B0218+357 the most distant object detected in the very-high-energy gamma-ray domain to date." These very-high-energy gamma-rays from any distant source have a high chance to interact with the numerous low-energy photons emitted by galaxies and stars, being lost in the process. With this observation, MAGIC has doubled the previously known visibility range of the Universe in very-high-energy gamma rays. Observation of the delayed signal from QSO B0218+357 by MAGIC showed for the first time that these very energetic photons are also deflected in agreement with General Relativity, a result that is both striking and potentially profound. The signal arriving at the predicted time may rule out some theories of the structure of the vacuum. That awaits further analysis. For the moment, this observation demonstrates a new capability of the very-high-energy gamma-ray observatories and highlights what awaits the next generation of such telescopes, the Cherenkov Telescope Array (CTA) project. MAGIC is a ground-based gamma-ray instrument located on the Canary island of La Palma, Spain. The system of two 17m diameter Cherenkov telescopes is currently one of the three major imaging atmospheric Cherenkov instruments in the world. It is designed to detect gamma rays tens of billions to tens of trillions times more energetic than visible light. MAGIC has been built with the joint efforts of a largely European collaboration that includes about 160 researchers from Germany, Spain, Italy, Switzerland, Poland, Finland, Bulgaria, Croatia, India and Japan. The Observatories of the Instituto de Astrofísica de Canarias (IAC) are part of the Unique Scientific And Technical Infraestructures (ICTS) network.


News Article | November 16, 2016
Site: www.sciencedaily.com

Doctoral student Alejandro Suárez Mascareño, of the Instituto de Astrofísica de Canarias (IAC) and the University of La Laguna (ULL), and his thesis directors at the IAC Rafael Rebolo and Jonay Isaí González Hernández, have discovered a "super-Earth" type planet, GJ 536 b, whose mass is around 5.4 Earth masses, in orbit around a nearby very bright star. The study has been accepted for publication in the journal Astronomy & Astrophysics. Researchers from several countries are involved. This exoplanet -- the planet orbiting the star GJ 536 -- is not within the star's habitable zone, but its short orbital period of 8.7 days and the luminosity of its star, a red dwarf which is quite cool and near to our Sun, make it an attractive candidate for investigating its atmospheric composition. During this research a cycle of magnetic activity similar to that of the Sun has been found, but with a shorter period, 3 years. "So far the only planet we have found is GJ 536 b but we are continuing to monitor the star to see if we can find other companions," says Alejandro Suárez Mascareño, who is the first author on the article. "Rocky planets are usually found in groups," he explains, "especially round stars of this type, and we are pretty sure that we can find other low mass planets (other 'super-Earths') on orbits further from the star, with periods from 100 days up to a few years. We are preparing as programme of monitoring for transits of this new exoplanet to determine its radius and mean density." "This rocky exoplanet is orbiting a star much smaller and cooler than the Sun," comments Jonay Isaí González, "but, sufficiently nearby and bright. It is also observable from both the northern and southern hemispheres, so that it is a very interesting for future high stability spectrographs and in particular for the possible detection of another rocky planet in the habitability zone of the star." "To detect the planet," states Rafael Rebolo, "we had to measure the velocity of the star with an accuracy of the order of a metre per second. With the construction of the new instrument ESPRESSO, co-directed by the IAC, we will improve this accuracy by a factor of ten, and will be able to extend our search to planets with conditions very similar to Earth, around this and many other nearby stars." The planet has been detected in a joint effort between the IAC and the Geneva Observatory, using the HARPS (High Accuracy Radial velocity Planet Seeker) spectrograph on the 3.6M ESO Telescope at La Silla (Chile) and HARPS North, on the Telescopio Nacional Galileo (TNG) at the Roque de los Muchachos Observatory, Garafia (La Palma). This planet was discovered during the preparation of the doctoral thesis of Alejandro Suárez Mascareño, within the programme of Training of Research Personnel of the Ministry of Economy, Industry, and Competitivity (MINECO). The Observatories of the Instituto de Astrofísica de Canarias (IAC) are part of the Unique Scientific And Technical Infraestructures (ICTS) network.


Griffin R.F.,The Observatories | Fuhrmann K.,Ruhr University Bochum | Fuhrmann K.,Isaac Newton Group of Telescopes
Monthly Notices of the Royal Astronomical Society | Year: 2013

HD 75767 is a nearby solar-type star. It has an unseen companion with which it is in an orbit that is very slightly off-circular and has a period of about 10 d. In addition, it has a faint visual companion. Wraight et al., in a recent paper, have built a considerable edifice on the idea that the orbital period has shown a perceptible change within the last 100 yr. We point out that the phase shift that constitutes their evidence for such a change arises only from their use of their own, relatively inaccurate, value for the period. Rotational-velocity measurements for HD 75767, published independently by each of the authors and by others, have all been smaller than would correspond to the equatorial velocity if the star's rotation were synchronized to the orbital revolution. Each of the present authors has accordingly proposed (explicitly on the assumption of synchronism) an inclination corresponding to his favoured value of v sin i. There is, therefore, implicit surprise at the discovery by Wraight et al. that the system exhibits eclipses and therefore the orbital inclination must be close to 90° The logical conclusion must be that the star is rotating more slowly than would correspond to synchronism with the orbit.2013 The Authors.


Griffin R.F.,The Observatories | Stroe A.,The Observatories
Journal of Astrophysics and Astronomy | Year: 2012

The 'Redman K stars' are a group of 80-odd seventh-magnitude late-type stars, nearly all giants, distributed along the Galactic equator between approximate longitudes 50° and 150° (roughly Sagitta to Cassiopeia). Their radial velocities have been measured systematically once per season in 30 of the 45 seasons from 1966 to 2010/11. At least 26 of them (30%) have proved to vary in velocity. Orbits have been derived for all but one of the 26, many of them having longer periods than have normally been associated with spectroscopic binaries; several are comparable with, or longer than, the present duration of the observing campaign. Also reported here are radial-velocity measurements made casually of stars seen in the fields of some of the Redman stars. Two of the companions have proved to vary in velocity on long time-scales, and (somewhat preliminary) orbits are given for them. © 2012 Indian Academy of Sciences.


Griffin R.F.,The Observatories
Journal of Astrophysics and Astronomy | Year: 2012

Spectroscopic orbits are presented for 52 stars in the Hyades field, of which 41 prove to be actual members of the Hyades (with some reservations in two cases). Most of the stars concerned have not had orbits published for them previously. Three of them are of higher multiplicity. The already-known double-lined eclipsing system van Bueren 22 is demonstrated to be a triple system, as was obliquely announced 25 years ago; its 'outer' orbit, which has a period of about 8 years, is now determined. Van Bueren 75 is already known to be triple, but here the visual secondary is shown to be the (single-lined) spectroscopic sub-system, and an independent spectroscopic solution is given for the 40-year orbit of what has hitherto been regarded as the 'visual' pair. Van Bueren 102, for which a close visual companion was discovered comparatively recently, is a single-lined binary whose γ -velocity has shown a steady drift over at least the last 30 (probably 50) years. Three stars, vB 39, 50 and 59, have notably high eccentricities of 0.85, 0.98 and 0.94, respectively; they have quite long periods (especially vB 50, which is over 100 years), and every one of them contrived to pass the whole of its recent periastron passage (about 180° of true anomaly) between seasons, at the time of year when the Hyades are unobservable! © 2012 Indian Academy of Sciences.


Griffin R.F.,The Observatories | Filiz Ak N.,Erciyes University | Filiz Ak N.,Pennsylvania State University
Astrophysics and Space Science | Year: 2010

We present spectroscopic orbits for the active stars HD 82159 (GS Leo), HD 89959, BD +39° 2587 (a visual companion to HD 112733), HD 138157 (OX Ser), HD 143705, and HD 160934. This paper is a sequel to one published in this journal in 2006, with similar avowed intention, by Gálvez et al. They showed only graphs, and gave no data, and no orbital elements apart from the periods (only two of which were correct) and in some cases the eccentricities. Here we provide full information and reliable orbital elements for all the stars apart from HD 160934, which has not completed a cycle since it was first observed for radial velocity. © 2010 Springer Science+Business Media B.V.


Griffin R.F.,The Observatories
Journal of Astrophysics and Astronomy | Year: 2012

The 'Redman K stars' project, described more particularly in the paper immediately following this one, involved the repeated measurement on a quasi-annual basis of the radial velocities of a group of 86 seventh-magnitude late-type stars over an interval of 45 years. Certain of the stars proved to vary in velocity and were then transferred to a different observing programme, in which they were measured more frequently with a view to determining their orbits. Orbits have already been published for 18 of the stars. Presented here (and summarized in Table 9) are the results on six more; all are single-lined. One of them (HD 191046, a star which has a literature coverage about ten times as rich as that of any of the others, probably on account of its high space velocity which includes a γ-velocity of nearly -100 km s -1) has a good orbit with a period of about 8000 days (22 years). Five others (HD 3345, 15728, 20509, 188058 and 191084) have orbits that are perfectly secure in principle, but their periods range between 40 and perhaps 70 years, and (particularly in some cases) their radial velocities have not been observed well enough for long enough to establish either the periods or the orbits very accurately. One star, HD 9354, has exhibited a monotonic variation of velocity throughout the duration of the observing programme; it is possible to draw a Keplerian velocity curve that does justice to the measurements, but it cannot be expected to have much predictive power. © 2012 Indian Academy of Sciences.


Griffin R.F.,The Observatories
AIP Conference Proceedings | Year: 2011

This contribution is about the application of spectroscopic techniques to the study of binary stars. Some examples analyzed by the author are shown. © 2011 American Institute of Physics.

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