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  • richardmitnick 2:26 pm on September 12, 2017 Permalink | Reply
    Tags: , , , , , Leiden MASCARA at Cerro La Silla, Stellar Fingerprints: Using Exoplanets to See the Surfaces of Stars   

    From ESOblog: “Stellar Fingerprints: Using Exoplanets to See the Surfaces of Stars” 

    ESO 50 Large

    ESOblog

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    The Universe is absolutely teeming with stars — at least 100 billion populate our Milky Way galaxy alone. Yet because most stars are very far away, it’s incredibly hard for astronomers to observe them as anything more than just points of light. But thanks to a clever method involving transiting exoplanets, astronomers might have found a solution that allows us to actually see what’s happening on stellar surfaces. We’ve asked Dainis Dravins of Lund University in Sweden for the details.

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    Examples of images of computer-predicted patterns of small portions on stellar surfaces: a tiny white-dwarf star (left) and a huge supergiant (right). Credit: H. G. Ludwig

    Q: Dainis, tell us more about the surfaces of stars and what motivated your team to develop a new method to study these surfaces.

    A: Stars are not smooth spheres; rather their surfaces are violent boiling oceans of glowing gas. Most of what we know about the Universe relies on light emitted from these very surfaces, and precise studies of stars and their planets require us to understand this starlight. It’s now possible to compute models of such boiling stellar surfaces. While solar models are checked by comparing them to structures we observe on the Sun, this isn’t really an option for distant stars, because they’re only visible as specs of light. But if we can’t test these models, how can we know if they’re correct? So together with a team of astronomers from Sweden and Germany, we developed what at first seemed a far-fetched idea: a technique by which we can see the structures on the surfaces of nearby stars using transiting exoplanets.

    Q: How can exoplanets help us look at stars? Is it not the other way round: stars help us to discover and characterise exoplanets?!

    A: True. Exoplanets are planets orbiting other stars, but they’re trillions of kilometres away and their light is extremely faint compared to their parent stars, so we’ve had to come up with clever ways to detect and study them. One method is called transit photometry, which is when a planet passes in front of its parent star and blocks a fraction of the light, causing the star to dim slightly. It’s similar to what happens during a solar eclipse as seen on Earth. If the dimming lasts for a fixed interval of time and is repeated periodically, that tells us a planet is orbiting the star.

    And indeed a transit can tell us a lot of interesting things about the planet itself, like its size and the composition of its atmosphere, but the planet can also reveal information about the parent star. Since we can’t yet obtain detailed images of stellar surfaces, we can use transiting exoplanets to indirectly deduce the appearance of stellar surfaces.

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    This illustration shows how subtracting observations of a stellar surface during an exoplanet transit from observations of the star when the planet is not present can give us detailed information about the stellar surface obscured by the exoplanet.
    Credit: D. Dravins

    Here’s how it works: imagine a distant skyscraper at night with hundreds of illuminated windows in various colours. From far away, we only see the whole building as one unresolved blob of light. Now, suppose a hot-air balloon floats between us and this building. As it slowly moves across, the balloon gradually hides the light from some windows, uncovering light from others. We can now measure the light and colour from this distant building and watch it change as the balloon slowly drifts by. These gradual changes in brightness and colour allow us to figure out the light patterns of the skyscraper windows, determine what fraction of them are lit up, and whether all of them are the same colour or not.

    In the same way, an exoplanet that happens to be seen transiting across the disc of its parent star gradually covers part of the star’s surface and blocks the light from behind. By watching the changes in brightness and in colour (the latter in the form of spectra), we can deduce the properties of the fine structure on stellar surfaces. Then, we can compare these deductions to 3D models we’ve made of the stellar surface, and make synthesised images and videos of stellar structures and the movements of the surface.

    Q: Tell us about how you made your observations.

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    This graph from one of the papers shows changes in iron spectral lines at different locations and moments during the transit of exoplanet HD 209458 b. It’s packed with information needed to infer small details of far-away star surfaces. Credit: D. Dravins

    A: We carried out our project by diving into ESO’s rich data archive and using observations made by other astronomers in the past, for a different scientific purpose. Researchers like us can reuse data for new applications that weren’t known or foreseen when the original observations were made, so the data archives are kind of like a broadly-available virtual observatory!

    Q: What were you doing to come up with the idea to use exoplanet data to study stellar surfaces?

    Actually, as is the case with a lot of research, it started from a somewhat different angle. Several years ago, I prepared some ideas for future observations with ESO’s Extremely Large Telescope. One conceptual observing proposal would be to begin resolving the surfaces of nearby giant or supergiant stars using the ELT’s advanced technology. Exploring the details of this and similar concepts, it suddenly became clear that one would not have to wait for the ELT since exoplanets could be used as probes to study the surfaces of at least smaller stars, such as the Sun.

    The interest in such an ELT project remains undiminished, however, since it concerns giant stars, which cannot be probed by the current exoplanet technique. Since any planet covers only a tiny fraction of any giant star, the signal would be much too small to measure precisely.

    Q: What applications does this technique have for studies of stars and exoplanets? What could it help us discover?

    A: After developing this technique, we demonstrated its application to a well-known star called HD 209458. This star is host to the exoplanet HD 209458 b, nicknamed Osiris, which is an exoplanet of firsts for many observations — it was the first exoplanet discovered transiting its star, the first with a detected atmosphere, and the first exoplanet found to contain oxygen and carbon in its atmosphere. By watching this planet as it transited across its star, we obtained high-resolution spectra of small areas of the star’s surface.

    But this technique could take us even further, perhaps helping us find Earth-like planets. So far, no truly Earth-like planet has been found — i.e., a planet with a size comparable to ours, moving around a Sun-like star with a period of about one year. To find a planet like this is a major challenge because we’d have to identify very tiny changes in the light of the host star, which is difficult because the turbulent surface of a star causes its starlight to fluctuate much more than the minuscule effects caused by a planet. But we can get around this. By developing and testing more precise models for stellar surfaces, we might be able to separate the signatures caused by a planet from the effects caused by the star, allowing us to find Earth’s siblings. Our current project is one possible route towards this exciting goal.


    This model simulates the surface structures (granular convection) on a star similar the Sun. This is a 2D view of the stellar surface from above. At the top right is the scale and time. The scale is measured in 5000km while time is measured in seconds.
    Credit: H. G. Ludwig

    Q: What are the limitations of this technique? Can it be improved?

    A: Our method appears straightforward in principle, but it demands very precise measurements. To work, it requires a bright star with a large exoplanet transiting in front of it. Faint stars can’t be measured precisely enough, and if the planet is tiny then its effect on the starlight will be small and so our measurements will be uncertain. Fortunately, many projects are underway to search for various types of suitably bright targets, including the newly operating MASCARA exoplanet hunter at ESO’s La Silla Observatory!

    Leiden MASCARA cabinet at ESO Cerro la Silla located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    Leiden MASCARA instrument, La Silla, located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    Q: Are you excited for the future of this technique?

    A: Of course I have to say that, but I am actually very excited. Not long ago, the moons of the outer planets in our Solar System were just mere point sources of light — and now we know they are a plethora of different worlds. And imagine what a meager state extragalactic astronomy would be in if we only observed galaxies as pinpricks of light instead of rich and complex neighbourhoods of stars.

    These techniques start to reveal new worlds. Stars will now become more real to us once we see their irregularities, the magnetic or thermal spots on their surfaces, and their distorted shapes from their rapid rotation. Tantalising results have already been obtained with facilities like the VLTI interferometer but now we can start to examine stellar surfaces in greater detail.

    ESO VLT Interferometer image, Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

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    Links

    This research is presented in two papers by D. Dravins et. al. entitled “Spatially resolved spectroscopy across stellar surfaces. I. Using exoplanet transits to analyze 3-D stellar atmospheres; and II. High-resolution spectra across HD 209458 (G0 V)” in the journal Astronomy & Astrophysics. H. G. Ludwig (Zentrum für Astronomie der Universität Heidelberg, Germany), E. Dahlén (Lund Observatory, Sweden), and H. Pazira (AlbaNova University Center, Sweden) also contributed to the studies.
    Research Paper I (PDF 2.9 MB): Using exoplanet transits to analyze 3-D stellar atmospheres
    Research Paper II (PDF 5.8 MB): High-resolution spectra across HD 209458 (G0 V)
    Find more about Dravins here.

    See the full article here .

    Please help promote STEM in your local schools.
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    ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

    ESO LaSilla
    ESO/Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres.

    ESO VLT
    VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level.

    ESO Vista Telescope
    ESO/Vista Telescope at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level.

    ESO NTT
    ESO/NTT at Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres.

    ESO VLT Survey telescope
    VLT Survey Telescope at Cerro Paranal with an elevation of 2,635 metres (8,645 ft) above sea level.

    ALMA Array
    ALMA on the Chajnantor plateau at 5,000 metres.

    ESO E-ELT
    ESO/E-ELT to be built at Cerro Armazones at 3,060 m.

    ESO APEX
    APEX Atacama Pathfinder 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert.

    Leiden MASCARA instrument, La Silla, located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    Leiden MASCARA cabinet at ESO Cerro la Silla located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

     
  • richardmitnick 8:31 am on July 17, 2017 Permalink | Reply
    Tags: , , , , , Leiden MASCARA at Cerro La Silla,   

    From ESO: “Eyes Wide Open for MASCARA in Chile” 

    ESO 50 Large

    European Southern Observatory

    19 July 2017
    Ignas Snellen
    Leiden Observatory
    Postbus 9513, 2300 RA Leiden, The Netherlands
    snellen@strw.leidenuniv.nl

    Richard Hook
    ESO Public Information Officer
    Garching bei München, Germany
    Tel: +49 89 3200 6655
    Cell: +49 151 1537 3591
    rhook@eso.org

    Leiden MASCARA cabinet at ESO Cerro la Silla located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    Leiden MASCARA instrument, La Silla, located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    The Leiden/MASCARA (Multi-site All-Sky CAmeRA) station at ESO’s La Silla Observatory in Chile has achieved first light. This new facility will seek out transiting exoplanets as they pass in front of their bright parent stars and create a catalogue of targets for future exoplanet characterisation observations.

    Planet transit. NASA/Ames

    In June 2016, ESO reached an agreement with Leiden University to site a station of MASCARA at ESO’s La Silla Observatory in Chile, taking advantage of the excellent observing conditions of the southern hemisphere skies. This station is now made its first successful test observations.

    The MASCARA station in Chile is the second to begin operations; the first station is in the northern hemisphere on the Roque de los Muchachos Observatory, on the island of La Palma in the Canary Islands.

    Roque de los Muchachos Observatory located in the municipality of Garafía on the island of La Palma in the Canary Islands. The observatory site is operated by the Instituto de Astrofís

    Each station contains a battery of cameras in a temperature-controlled enclosure which will monitor almost the entire sky visible from its location [1].

    “Stations are needed in both the northern and southern hemisphere to obtain all-sky coverage,” says Ignas Snellen, of Leiden University and the MASCARA project lead. “With the second station at La Silla now in place, we can monitor almost all the brighter stars over the entire sky.”

    Built by Leiden University in the Netherlands, MASCARA is a planet-hunting instrument. Its very compact and low-cost design appears unassuming, but is innovative, flexible and highly reliable. Consisting of five digital cameras with off-the-shelf components, this small planet-hunter takes repeated measurements of the brightnesses of thousands of stars and uses software to hunt for the slight dimming of a star’s light as a planet crosses the face of the star.

    This exoplanet discovery method is called transit photometry. The planet’s size and orbit can be directly determined through this method, and in very bright systems the planet’s atmosphere can also be characterised by further observations with large telescopes such as ESO’s Very Large Telescope.

    The main purpose of MASCARA is to find exoplanets around the brightest stars in the sky, currently not probed either by space or ground-based surveys. The target population for MASCARA consists mostly of “hot Jupiters” — large worlds that are physically similar to Jupiter but orbit very close to their parent star, resulting in high surface temperatures and orbital periods of only a few hours. Dozens of hot Jupiters have been discovered with the radial velocity exoplanet detection method, as they exert a noticeably gravitational influence on their host stars.

    “Not much can yet be learned from the planets discovered via the radial velocity method, as they require significantly better direct imaging techniques to separate the light of these cool, old planets from that of their host stars,” comments Snellen. “In contrast, planets that transit their host stars can readily be characterised.”

    MASCARA also has the potential to discover super-Earths and Neptune-sized planets. The project is expected to provide a catalogue of the brightest nearby targets for future exoplanet characterisation observations, particularly for detailed planetary atmosphere observations.
    Notes

    [1] MASCARA can monitor stars down to about magnitude 8.4 — roughly ten times fainter than can be seen with the naked eye on a clear dark night. Due to its design, MASCARA is less sensitive to weather condition than other observing instruments, and so observations may be made even when the sky is partially cloudy, thus extending observation times.

    Read more about MASCARA on the ESO website
    MASCARA website at Leiden University
    Agreement to site MASCARA station at La Silla
    Science paper on the design and operation of MASCARA

    See the full article here .

    Please help promote STEM in your local schools.
    STEM Icon

    Stem Education Coalition
    Visit ESO in Social Media-

    Facebook

    Twitter

    YouTube

    ESO Bloc Icon

    ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

    ESO LaSilla
    ESO/Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres

    ESO VLT
    VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    ESO Vista Telescope
    ESO/Vista Telescope at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    ESO NTT
    ESO/NTT at Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres

    ESO VLT Survey telescope
    VLT Survey Telescope at Cerro Paranal with an elevation of 2,635 metres (8,645 ft) above sea level

    ALMA Array
    ALMA on the Chajnantor plateau at 5,000 metres

    ESO E-ELT
    ESO/E-ELT to be built at Cerro Armazones at 3,060 m

    ESO APEX
    APEX Atacama Pathfinder 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert

    Leiden MASCARA instrument, La Silla, located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    Leiden MASCARA cabinet at ESO Cerro la Silla located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

     
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