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  • richardmitnick 5:58 pm on July 18, 2017 Permalink | Reply
    Tags: Ancient Impacts Shaped the Structure of the Milky Way, , , , , SDSS,   

    From Universe Today: “Ancient Impacts Shaped the Structure of the Milky Way” 

    universe-today

    Universe Today

    1
    Accroding to new research, the Milky Way may still bear the marks of “ancient impacts”. Credit: NASA/Serge Brunier.

    18 July , 2017
    Matt Williams

    Understanding how the Universe came to be is one of the greater challenges of being an astrophysicist. Given the observable Universe’s sheer size (46.6 billion light years) and staggering age (13.8 billion years), this is no easy task. Nevertheless, ongoing observations, calculations and computer simulations have allowed astrophysicists to learn a great deal about how galaxies and larger structures have changed over time.

    For example, a recent study by a team from the University of Kentucky (UK) has challenged previously-held notions about how our galaxy has evolved to become what we see today. Based on observations made of the Milky Way’s stellar disk, which was previously thought to be smooth, the team found evidence of asymmetric ripples. This indicates that in the past, our galaxy may have be shaped by ancient impacts.

    The study, titled “Milky Way Tomography with K and M Dwarf Stars: The Vertical Structure of the Galactic Disk“, recently appeared in the The Astrophysical Journal. Led by Deborah Ferguson, a 2016 UK graduate, the team consisted of Professor Susan Gardner – from the UK College of Arts and Sciences – and Brian Yanny, an astrophysicist from the Fermilab Center for Particle Astrophysics (FCPA).

    This study evolved from Ferguson’s senior thesis, which was overseen by Prof. Gardner. At the time, Ferguson sought to expand on previous research by Gardner and Yanny, which also sought to understand the presence of ripples in our galaxy’s stellar disk. For the sake of this new study, the team relied on data obtained by the Sloan Digital Sky Survey‘s (SDSS) 2.5m Telescope, located at the Apache Point Observatory in New Mexico.

    SDSS Telescope at Apache Point Observatory, NM, USA

    See the full article here .

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  • richardmitnick 3:38 pm on July 11, 2017 Permalink | Reply
    Tags: , , , , , , Extreme variability quasars, , SDSS   

    From astrobites: “Extreme variability quasars” 

    Astrobites bloc

    Astrobites

    Jul 11, 2017
    Suk Sien Tie

    Title: Extreme variability quasars from the Sloan Digital Sky Survey and the Dark Energy Survey
    Authors: Nick Rumbaugh, Yue Shen, Eric Morganson et al.
    First Author’s Institution: National Center for Supercomputing Applications, IL.
    1
    Status: Submitted to ApJ, open access

    Active galactic nuclei (AGNs), the central active regions of supermassive black holes, have many masks. They span a large range of luminosities from roughly ten billion to ten thousand Milky Ways (even at their dimmest, they are still one of the brightest objects in the Universe). They have varying radio brightnesses and the presence of radio jets is not a luxury to be had by all. When scrutinized with a spectrograph, they reveal telltale signs of different anatomies. Some exhibit broad emission lines, others narrow, and still others both. Therefore, AGNs carry a myriad of different names, such as Seyferts, blazars, and quasars. However, the multifaceted appearances of AGNs are deceiving — the AGN unification theory postulates that which type of AGN you see depends on your viewing angle and the wavelength of light you’re looking in. Otherwise, you’re simply looking at one and the same object, the central bright region of a supermassive black hole.

    All AGNs have one thing in common: they vary in brightness. In (not quite) the (exact) words of Shakespeare, an AGN by any other name would always vary. In particular, quasars (the highest redshift and most luminous subclass of AGN and the main focus of the paper) are known to vary by 10%-30%, corresponding to ~0.1 mag to ~0.3 mag, over the course of many years. The physical mechanism for their variability is still an open question, with the leading theory being temperature fluctuations in the black hole accretion disk driven by an X-ray source near the central black hole. The authors of this paper are not interested in regular varying quasars, instead they are interested in quasars that vary by 1 magnitude or more — the extreme variability quasars.

    There is a hint of such a population from previous studies, such as a joint PanStarrs-SDSS search that uncovered ~40 quasars that vary by more than 1.5 magnitudes.

    U Hawaii Pann-STARRS1 Telescope, located at Haleakala Observatory, Hawaii

    SDSS Telescope at Apache Point Observatory, NM, USA

    Extreme variability quasars are thought to be the larger class of an intriguing group of quasars that has only recently been discovered (oh no, not another group), known as changing look quasars (see this for an example). Changing look quasars pose a significant challenge to the AGN unification model, because they change from one AGN type to another over the course of several decades. More often than not, these changes are accompanied by a large magnitude variation. Aside from studying the properties of the extreme variability quasars, the authors also hope to build a larger sample of changing look quasars in order to probe their origin(s).

    Using both SDSS and the Dark Energy Survey (DES) to construct a search baseline of ~15 years, the authors found ~1000 spectroscopically confirmed quasars that vary by 1 magnitude or more.

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam

    They also recovered all previously known changing look quasars that fall within their footprint. Figure 1 shows the light curves and spectrum for one of their objects. In addition to finding that extreme variability quasars have stronger emission line strengths compared to regular quasars with similar redshifts and luminosities, their Eddington ratios are also lower. The Eddington ratio is a ratio of the quasar luminosity, which depends on the accretion rate, to the Eddington luminosity, which is the theoretical maximum luminosity. Figure 2 shows the relation between the maximum variability of the extreme variability quasars and their Eddington ratios. There is a trend of decreasing Eddington ratios with variability, leading to the interpretation that the extreme variabilities are connected to the Eddington ratios. By extension, the authors attribute the reason changing-look quasars change types to their varying accretion rates caused by internal accretion disk processes.

    2
    An example extreme variability quasar discovered in this study. The top and middle panels show its light curves in two different filter bandpasses at different wavelengths, both of which have dimmed by more than 1 magnitude over ~15 years. The bottom panel shows its SDSS spectrum, which contains the usual broad emission lines associated with quasars. [Figure 2 in paper]

    3
    Fig. 2: Eddington ratio as a function of maximum variability for the extreme variability quasars (red) and regular quasars with similar redshifts and luminosities (black). The blue points are the median Eddington ratio in bins of maximum variability. There is a trend of decreasing Eddington ratio with increasing variability. [Figure 11 in paper]

    Using a simple model, the authors estimated the intrinsic fraction of extreme variability quasars to be between ~30-50%, which is much higher than the observed fraction of 10%. With more frequent searches over a wider area and longer period, we should discover more of these exotic objects to help shed light on the physical mechanism of quasar variability and the phenomena of the quasar population as a whole.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 1:46 pm on July 5, 2017 Permalink | Reply
    Tags: , , , , , , , SDSS,   

    From U Cambridge: “Fastest stars in the Milky Way are ‘runaways’ from another galaxy” 

    U Cambridge bloc

    Cambridge University

    05 Jul 2017
    Sarah Collins
    sarah.collins@admin.cam.ac.uk

    1
    Artist’s impression of a runaway star. Credit: Amanda Smith, Institute of Astronomy.

    A group of astronomers have shown that the fastest-moving stars in our galaxy – which are travelling so fast that they can escape the Milky Way – are in fact runaways from a much smaller galaxy in orbit around our own. A group of astronomers have shown that the fastest-moving stars in our galaxy – which are travelling so fast that they can escape the Milky Way – are in fact runaways from a much smaller galaxy in orbit around our own.

    The researchers, from the University of Cambridge, used data from the Sloan Digital Sky Survey and computer simulations to demonstrate that these stellar sprinters originated in the Large Magellanic Cloud (LMC), a dwarf galaxy in orbit around the Milky Way.

    SDSS Telescope at Apache Point Observatory, NM, USA

    Large Magellanic Cloud. Adrian Pingstone December 2003

    These fast-moving stars, known as hypervelocity stars, were able to escape their original home when the explosion of one star in a binary system caused the other to fly off with such speed that it was able to escape the gravity of the LMC and get absorbed into the Milky Way. The results are published in the Monthly Notices of the Royal Astronomical Society, and will be presented today (5 July) at the National Astronomy Meeting in Hull.

    Astronomers first thought that the hypervelocity stars, which are large blue stars, may have been expelled from the centre of the Milky Way by a supermassive black hole. Other scenarios involving disintegrating dwarf galaxies or chaotic star clusters can also account for the speeds of these stars but all three mechanisms fail to explain why they are only found in a certain part of the sky.

    To date, roughly 20 hypervelocity stars have been observed, mostly in the northern hemisphere, although it’s possible that there are many more that can only be observed in the southern hemisphere.

    “Earlier explanations for the origin of hypervelocity stars did not satisfy me,” said Douglas Boubert, a PhD student at Cambridge’s Institute of Astronomy and the paper’s lead author. “The hypervelocity stars are mostly found in the Leo and Sextans constellations – we wondered why that is the case.”

    An alternative explanation to the origin of hypervelocity stars is that they are runaways from a binary system. In binary star systems, the closer the two stars are, the faster they orbit one another. If one star explodes as a supernova, it can break up the binary and the remaining star flies off at the speed it was orbiting. The escaping star is known as a runaway. Runaway stars originating in the Milky Way are not fast enough to be hypervelocity because blue stars can’t orbit close enough without the two stars merging. But a fast-moving galaxy could give rise to these speedy stars.

    The LMC is the largest and fastest of the dozens of dwarf galaxies in orbit around the Milky Way. It only has 10% of the mass of the Milky Way, and so the fastest runaways born in this dwarf galaxy can easily escape its gravity. The LMC flies around the Milky Way at 400 kilometres per second and, like a bullet fired from a moving train, the speed of these runaway stars is the velocity they were ejected at plus the velocity of the LMC. This is fast enough for them to be the hypervelocity stars.

    “These stars have just jumped from an express train – no wonder they’re fast,” said co-author Rob Izzard, a Rutherford fellow at the Institute of Astronomy. “This also explains their position in the sky, because the fastest runaways are ejected along the orbit of the LMC towards the constellations of Leo and Sextans.”
    Astronomers first thought that the hypervelocity stars, which are large blue stars, may have been expelled from the centre of the Milky Way by a supermassive black hole. Other scenarios involving disintegrating dwarf galaxies or chaotic star clusters can also account for the speeds of these stars but all three mechanisms fail to explain why they are only found in a certain part of the sky.

    To date, roughly 20 hypervelocity stars have been observed, mostly in the northern hemisphere, although it’s possible that there are many more that can only be observed in the southern hemisphere.

    “Earlier explanations for the origin of hypervelocity stars did not satisfy me,” said Douglas Boubert, a PhD student at Cambridge’s Institute of Astronomy and the paper’s lead author. “The hypervelocity stars are mostly found in the Leo and Sextans constellations – we wondered why that is the case.”

    An alternative explanation to the origin of hypervelocity stars is that they are runaways from a binary system. In binary star systems, the closer the two stars are, the faster they orbit one another. If one star explodes as a supernova, it can break up the binary and the remaining star flies off at the speed it was orbiting. The escaping star is known as a runaway. Runaway stars originating in the Milky Way are not fast enough to be hypervelocity because blue stars can’t orbit close enough without the two stars merging. But a fast-moving galaxy could give rise to these speedy stars.

    The LMC is the largest and fastest of the dozens of dwarf galaxies in orbit around the Milky Way. It only has 10% of the mass of the Milky Way, and so the fastest runaways born in this dwarf galaxy can easily escape its gravity. The LMC flies around the Milky Way at 400 kilometres per second and, like a bullet fired from a moving train, the speed of these runaway stars is the velocity they were ejected at plus the velocity of the LMC. This is fast enough for them to be the hypervelocity stars.

    “These stars have just jumped from an express train – no wonder they’re fast,” said co-author Rob Izzard, a Rutherford fellow at the Institute of Astronomy. “This also explains their position in the sky, because the fastest runaways are ejected along the orbit of the LMC towards the constellations of Leo and Sextans.”

    The researchers used a combination of data from the Sloan Digital Sky Survey and computer simulations to model how hypervelocity stars might escape the LMC and end up in the Milky Way. The researchers simulated the birth and death of stars in the LMC over the past two billion years, and noted down every runaway star. The orbit of the runaway stars after they were kicked out of the LMC was then followed in a second simulation that included the gravity of the LMC and the Milky Way. These simulations allow the researchers to predict where on the sky we would expect to find runaway stars from the LMC.

    “We are the first to simulate the ejection of runaway stars from the LMC – we predict that there are 10,000 runaways spread across the sky,” said Boubert. Half of the simulated stars which escape the LMC are fast enough to escape the gravity of the Milky Way, making them hypervelocity stars. If the previously known hypervelocity stars are runaway stars it would also explain their position in the sky.

    Massive blue stars end their lives by collapsing to a neutron star or black hole after hundreds of millions of years and runaway stars are no different. Most of the runaway stars in the simulation died ‘in flight’ after being kicked out of the LMC. The neutron stars and black holes that are left behind just continue on their way and so, along with the 10,000 runaway stars, the researchers also predict a million runaway neutron stars and black holes flying through the Milky Way.

    “We’ll know soon enough whether we’re right,” said Boubert. “The European Space Agency’s Gaia satellite will report data on billions of stars next year, and there should be a trail of hypervelocity stars across the sky between the Leo and Sextans constellations in the North and the LMC in the South.”

    ESA/GAIA satellite

    See the full article here .

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    U Cambridge Campus

    The University of Cambridge (abbreviated as Cantab in post-nominal letters) is a collegiate public research university in Cambridge, England. Founded in 1209, Cambridge is the second-oldest university in the English-speaking world and the world’s fourth-oldest surviving university. It grew out of an association of scholars who left the University of Oxford after a dispute with townsfolk. The two ancient universities share many common features and are often jointly referred to as “Oxbridge”.

    Cambridge is formed from a variety of institutions which include 31 constituent colleges and over 100 academic departments organised into six schools. The university occupies buildings throughout the town, many of which are of historical importance. The colleges are self-governing institutions founded as integral parts of the university. In the year ended 31 July 2014, the university had a total income of £1.51 billion, of which £371 million was from research grants and contracts. The central university and colleges have a combined endowment of around £4.9 billion, the largest of any university outside the United States. Cambridge is a member of many associations and forms part of the “golden triangle” of leading English universities and Cambridge University Health Partners, an academic health science centre. The university is closely linked with the development of the high-tech business cluster known as “Silicon Fen”.

     
  • richardmitnick 7:38 am on May 19, 2017 Permalink | Reply
    Tags: , , , Baryonic Oscillation Spectroscopic Survey [BOSS], , , , SDSS   

    From EPFL: “Astronomers make the largest map of the Universe yet” 

    EPFL bloc

    École Polytechnique Fédérale de Lausanne EPFL

    19.05.17
    Nik Papageorgiou

    1
    One of the SDSS telescopes at Apache Point Observatory in New Mexico (USA) ©SDSS

    Astronomers of the extended Baryonic Oscillation Spectroscopic Survey [BOSS], led by EPFL Professor Jean-Paul Kneib, used the Sloan telescope to create the first map of the Universe based entirely on quasars.

    BOSS Supercluster Baryon Oscillation Spectroscopic Survey (BOSS)

    Quasars are incredibly bright and distant points of light powered by supermassive black holes. As matter and energy fall into the black hole, they heat up to incredible temperatures and begin to glow with excessive brightness. By observing this cosmic glow, the scientists of the multi-institutional Sloan Digital Sky Survey (SDSS), which includes EPFL, have constructed the largest map of the distant Universe to-date. The work will be published in the Monthly Notices of the Royal Astronomical Society.

    Quasars are supermassive black holes at the centers of galaxies and they radiate huge amounts of electromagnetic energy. “Because quasars are so bright, we can see them all the way across the Universe,” says study co-leader Ashley Ross (Ohio State University). “That makes them the ideal objects to use to make the biggest map yet.”

    “These quasars are so far away that their light left them when the Universe was between 3 and 7 billion years old, long before the Earth even existed,” adds Gongbo Zhao from the National Astronomical Observatory of China, the study’s other co-leader.

    To construct the map, the scientists used the SDSS telescopes at New Mexico to measure accurate 3D positions for an unprecedented sample of over 147,000 quasars. This work took place during the first two years of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), one of the component research projects of SDSS led by Jean-Paul Kneib, Professor of Astrophysics at EPFL. The SDSS telescope observations gave the astronomers the quasars’ distances, which they then used to pinpoint the quasars’ positions in a 3D map.

    But the scientists didn’t stop there; they wanted to use to understand the expansion history of the Universe. For this they went a step further and used a clever technique that involves “baryon acoustic oscillations” (BAOs). These are the present-day imprint of sound waves that travelled through the early Universe, when it was much hotter and denser than it is now. But when the Universe was 380,000 years old, conditions changed suddenly and the sound waves became “frozen” in place, imprinted in the 3D structure of the Universe we see today.

    The process that produced these frozen BAOs is simple, which means that scientists can have a very good idea of what BAOs must have looked like in the early Universe. So when we look at the 3D structure of the Universe today, it contains these ancient BAOs, but massively stretched out by the expansion of the universe.

    The astronomers used the observed size of a BAO as “standard ruler” to measure distances in their 3D map, the way we can estimate the length of a football field by measuring the apparent angle of a meter rule on one side. “You have meters for small units of length, kilometres or miles for distances between cities, and we have the BAO scale for distances between galaxies and quasars in cosmology,” says Pauline Zarrouk, a PhD student at Irfu/CEA (University Paris-Saclay) who measured the projected BAO scale.

    Working backwards in time, the SDSS astronomers covered a range of time periods never observed before. The study measured the conditions when the Universe was just 3 to 7 billion years old, more than 2 billion years before the Earth formed.

    See the full article here .

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    EPFL campus

    EPFL is Europe’s most cosmopolitan technical university with students, professors and staff from over 120 nations. A dynamic environment, open to Switzerland and the world, EPFL is centered on its three missions: teaching, research and technology transfer. EPFL works together with an extensive network of partners including other universities and institutes of technology, developing and emerging countries, secondary schools and colleges, industry and economy, political circles and the general public, to bring about real impact for society.

     
  • richardmitnick 3:58 pm on March 29, 2017 Permalink | Reply
    Tags: , , , , , SDSS,   

    From SDSS: “Seeing the whole galaxy with a “second eye on the sky”” Press Release 

    SDSS Telescope

    Sloan Digital Sky Survey

    March 29, 2017

    Earlier this month, the Sloan Digital Sky Survey (SDSS) reached an important milestone by opening its “second eye on the sky” – a new instrument called the “APOGEE South spectrograph.”

    1
    UVA APOGEE-South Team Installs Spectrograph | Department of Astronomy, U.Va

    This new instrument at Las Campanas Observatory in Chile is the twin of the APOGEE North spectrograph, and will let astronomers study stars across the whole Milky Way like never before.


    Carnegie Las Campanas Observaory in the southern Atacama Desert of Chile in the Atacama Region approximately 100 kilometres (62 mi) northeast of the city of La Serena

    The name APOGEE is short for the Apache Point Observatory Galaxy Evolution Experiment, based on the location of the experiment’s first “eye” at Apache Point Observatory, New Mexico.


    Apache Point Observatory,Apache Point Observatory, NM, USA

    “The original APOGEE made history by measuring extremely detailed properties of more stars than ever before,” said Steven Majewski of the University of Virginia, Principal Investigator of the APOGEE experiment. “But we always wanted a more complete view, especially because the center of the Galaxy is best seen from the Southern Hemisphere. With the APOGEE South spectrograph, we are finally realizing that vision.” Data collected by the twin instruments will help astronomers make a map of the entire Milky Way, with an unprecedented combination of size and detail.

    2
    The “first light” observations for the APOGEE South spectrograph. The dots show stars whose spectra were observed by APOGEE. Some example spectra are shown (colors are representative only, as APOGEE spectra are in the infrared).

    The first light observations included spectra of supermassive stars in the Tarantula Nebula. This nebula in the Large Magellanic Cloud is forming stars more rapidly than any other region in our Local Group of galaxies. It can only be seen from the Southern Hemisphere, underscoring the importance of APOGEE South’s location. The spectrograph will allow us to study the chemistry and evolution of the stars in the nebula in greater detail than ever before. Image Credit: SDSS collaboration; Tarantula Nebula image from ESA/Herschel and NASA/Spitzer.

    The APOGEE South spectrograph in Chile is identical to the original APOGEE spectrograph in New Mexico. Both work by spreading starlight into detailed rainbow patterns called “spectra.” Astronomers use these spectra to determine the chemical compositions of those stars, and also to find subtle shifts due to the Doppler Effect created by the stars’ motion through space. These pieces of information – composition and velocity – are combined with the known stellar positions to create an incredibly detailed map of our Galaxy.

    5
    Three instrument team members work on the APOGEE South instrument, before the top was closed. It was then cooled down and placed under vacuum ready for observing. Left to right: Garrett Ebelke, Matt Hall, and Mita Tembe (all from the University of Virginia). Image Credit: John Wilson (University of Virginia)

    John Wilson of the University of Virginia, APOGEE’s Instrument Scientist, explains the decision to build identical instruments in two hemispheres: “If the two spectrographs are exactly the same, then the spectra we collect from them will also be the same. We don’t need to worry that differences we see are due to differences in instrument design. We can directly compare the parts of our Galaxy we can see from the Northern and Southern Hemispheres.”

    The APOGEE experiment to date has measured more than one million spectra of 277,000 individual stars, making it the largest high-resolution, near-infrared spectroscopic sample of stars ever observed. By working in infrared light, the APOGEE instruments can peer through the thick clouds of dust that obscure the inner Milky Way. By the end of APOGEE South’s mission, the number of stars observed will double, resulting in the most complete map of the Milky Way ever created.

    7
    With the installation of the APOGEE South spectrograph on the du Pont telescope at Las Campanas Observatory in Chile, the SDSS can now view the whole night sky from both Northern and Southern Hemispheres. This new view gives us an unprecedented, homogeneous, and complete view of the entire Milky Way Galaxy, as well as its satellites the Large and Small Magellanic Clouds (shown just below the Milky Way in this image). The Tarantula Nebula, where APOGEE South took its first data, is visible as a bright pink spot in the Large Magellanic Cloud. Image Credit: Dana Berry/SkyWorks Digital Inc.; SDSS collaboration

    The new APOGEE South spectrograph is located at the Irénée du Pont Telescope at Las Campanas Observatory, located at an elevation of 2,400 meters (8,000 feet) in the Atacama Desert of Northern Chile — about the same distance south of the equator as the New Mexico site of the original APOGEE spectrograph is to the north.


    Carnegie Las Campanas Dupont telescope, Atacama Desert, approximately 100 kilometres (62 mi) northeast of the city of La Serena,Chile

    “Looking from the Southern Hemisphere will allow us to study the innermost regions of our Galaxy,” said Manuela Zoccali of Pontifica Universidad Católica de Chile and the Millennium Institute of Astrophysics, the chair of the SDSS Chilean Participation Group. “This is the first time that a large team of Chileans has worked with colleagues around the world on such an ambitious project. We are pleased we can now work together on the first data.”

    The director of the SDSS-IV project, Michael Blanton of New York University, agrees. “Working with our colleagues in Chile has helped us extend our survey in exciting new ways. Ever since we began in 2000, people have asked us when we would go to the Southern Hemisphere. We are delighted to have found a second home at Las Campanas.”

    About the Sloan Digital Sky Survey

    Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS web site is http://www.sdss.org.

    SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration including the Brazilian Participation Group, the Carnegie Institution for Science, Carnegie Mellon University, the Chilean Participation Group, the French Participation Group, Harvard-Smithsonian Center for Astrophysics, Instituto de Astrofísica de Canarias, The Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU) / University of Tokyo, Lawrence Berkeley National Laboratory, Leibniz Institut für Astrophysik Potsdam (AIP), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Max-Planck-Institut für Astrophysik (MPA Garching), Max-Planck-Institut für Extraterrestrische Physik (MPE), National Astronomical Observatories of China, New Mexico State University, New York University, University of Notre Dame, Observatório Nacional / MCTI, The Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, United Kingdom Participation Group, Universidad Nacional Autónoma de México, University of Arizona, University of Colorado Boulder, University of Oxford, University of Portsmouth, University of Utah, University of Virginia, University of Washington, University of Wisconsin, Vanderbilt University, and Yale University.
    About the Chilean Participation Group of SDSS-IV

    The infrastructure for the APOGEE South instrument has been developed and will be operated in a partnership with seven universities in Chile: Pontificia Universidad Católica, Universidad Andres Bello, Universidad de Antofagasta, Universidad de Chile, Universidad de Concepción, Universidad de La Serena, and Universidad de Valparaíso.

    See the full article here.

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    The Sloan Digital Sky Survey has created the most detailed three-dimensional maps of the Universe ever made, with deep multi-color images of one third of the sky, and spectra for more than three million astronomical objects. Learn and explore all phases and surveys—past, present, and future—of the SDSS.

    The SDSS began regular survey operations in 2000, after a decade of design and construction. It has progressed through several phases, SDSS-I (2000-2005), SDSS-II (2005-2008), SDSS-III (2008-2014), and SDSS-IV (2014-). Each of these phases has involved multiple surveys with interlocking science goals. The three surveys that comprise SDSS-IV are eBOSS, APOGEE-2, and MaNGA, described at the links below. You can find more about the surveys of SDSS I-III by following the Prior Surveys link.

    Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS- IV acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS web site is http://www.sdss.org.

    SDSS-IV is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration including the Brazilian Participation Group, the Carnegie Institution for Science, Carnegie Mellon University, the Chilean Participation Group, the French Participation Group, Harvard-Smithsonian Center for Astrophysics, Instituto de Astrofísica de Canarias, The Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU) / University of Tokyo, Lawrence Berkeley National Laboratory, Leibniz Institut für Astrophysik Potsdam (AIP), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Max-Planck-Institut für Astrophysik (MPA Garching), Max-Planck-Institut für Extraterrestrische Physik (MPE), National Astronomical Observatory of China, New Mexico State University, New York University, University of Notre Dame, Observatório Nacional / MCTI, The Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, United Kingdom Participation Group, Universidad Nacional Autónoma de México, University of Arizona, University of Colorado Boulder, University of Oxford, University of Portsmouth, University of Utah, University of Virginia, University of Washington, University of Wisconsin, Vanderbilt University, and Yale University.

     
  • richardmitnick 10:54 am on February 23, 2017 Permalink | Reply
    Tags: , , SDSS, SDSS Summer Interns Apply SDSS Science to Small Telescopes   

    From SDSS: “SDSS Summer Interns Apply SDSS Science to Small Telescopes” 

    SDSS Science blog bloc

    Science Blog from the SDSS

    February 23, 2017
    Rita Tojeiro

    By Kate Meredith. Kate is the Director of Education Outreach at the University of Chicago Yerkes Observatory. Kate began working with SDSS data while still a high school science teacher and continued that work in her role with SDSS as lead educator for formal education. She is the primary developer of the SDSS Voyages website. In her first year as Education Director at Yerkes, Kate launched a summer intern program. In this post, Kate describes one of the projects interns lead during the summer of 2016.

    Rebecca Chen and Lindsay Berkhout are sophomore physics majors at the University of Chicago. Both chose the astronomy specialization, and both spent the summer of 2016 as interns at Yerkes Observatory . They were two of the 12 undergraduates that helped launch the first ever Yerkes Education Outreach internship program. Their goal was to take precise photometric measurements of targets (how bright objects are) with instruments including the 24-inch telescope at Yerkes, as well as Stone Edge Observatory’s 20-inch telescope, located in Sonoma, California.

    1
    Image of a 24-inch reflector telescope used in watching a comet in its first stages, at the Yerkes Observatory at Williams Bay Wisconsin

    2
    Rebecca Chen positioning new SDSS filters for use with the 24 inch reflecting telescope at Yerkes Observatory.

    “We both came in, and we didn’t know anything,” Berkhout laughs. But they soon got up to speed, and ended the summer with a tested methodology that allows not only them, but students following in their footsteps, to use the telescopes to measure the brightness of objects to within 5% the value obtained by the venerable Sloan Digital Sky Survey (SDSS).

    The long-term goal on Yerkes’ side is to be able to extend SDSS catalog to bright stars. The survey, designed to measure many faint targets, has gaps when it comes to measuring the brightest stars. But the Yerkes and Stone Edge telescopes—large for small observatories, but tiny compared to SDSS’ 100-inch mirror—can tackle the bright stars with ease. The trick is being able to compare data using the very different instruments of SDSS and the observatory telescopes.Chen and Berkhout were interested in more dramatic events; they wanted to measure the lightcurves of recent supernovae. But both projects rely on being able to precisely measure the brightness of targets. And figuring out how to reliably attain such precision with the Stone Edge and Yerkes telescopes became the students’ summer objective.

    Richard Kron, a professor at the University of Chicago and former director of Yerkes Observatory, worked closely with the students. But he says he was mostly there to answer their technical questions, and let them guide the direction of the work themselves—something Chen and Berkhout handled with aplomb, though he notes that other students might desire a more hands-on approach to mentoring.

    He introduced the pair to software packages—Aperture Photometry Tool and Topcat—to help them in their work, and advised on details such as calculating uncertainty in their measurements. He admits that his first instinct is often to push through and rush to big results. And students likewise often want to do something novel and exciting—like observing supernovae.

    3
    Intern Lindsay Berkhout installs SDSS filters in CCD camera at Yerkes Observatory.

    But Kron says it’s important to remember how much time new students take to assimilate the big concepts at play: operating the telescopes, learning new software routines, finding and measuring the targets, understanding uncertainty. “Make sure the student feels really in command,” he suggests. “It’s okay if you don’t cover quite as much as your original dreams had suggested.”

    “There’s still a lot of work to do,” Berkhout acknowledges. Steep learning curves, but also telescope downtime, contributed to the sometimes slow pace. “The next step is actually taking data and using this methodology to get results,” she says, something they ran out of time for in the short summer. “I think that if someone else takes the project they could go wherever they want with it, whether it’s bright stars or variable stars, or supernovae.”
    Berkhout and Chen left behind a detailed guide of the work they did, summarizing the technical details of how to take observations, run them through the software, measure sources’ photometry, and compare it to SDSS values. They also left suggestions for ways future interns might improve from 5% down to within 2% of the SDSS values. And they took with them many more lessons in how to plan and tackle such a project.

    “I felt like it was a really nice internship for summer after first year,” Berkhout says. “It was a good way to get involved in a research project that taught us a lot so now we can go to other people and be able to say that we’ve done something. That we learned a lot and we’re competent and can be involved in bigger research projects in the future.”

    Chen reflects that, “While we were working it was frustrating, because at times it felt like we weren’t getting anywhere. But at the end of the summer, looking back on all the things we had done, I was like, ‘Oh that’s pretty cool. That’s a project. We did a real project.’”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    After nearly a decade of design and construction, the Sloan Digital Sky Survey saw first light on its giant mosaic camera in 1998 and entered routine operations in 2000. While the collaboration and scope of the SDSS have changed over the years, many of its key principles have stayed fixed: the use of highly efficient instruments and software to enable astronomical surveys of unprecedented scientific reach, a commitment to creating high quality public data sets, and investigations that draw on the full range of expertise in a large international collaboration. The generous support of the Alfred P. Sloan Foundation has been crucial in all phases of the SDSS, alongside support from the Participating Institutions and national funding agencies in the U.S. and other countries.

    The Sloan Digital Sky Survey has created the most detailed three-dimensional maps of the Universe ever made, with deep multi-color images of one third of the sky, and spectra for more than three million astronomical objects.

    In its first five years of operations, the SDSS carried out deep multi-color imaging over 8000 square degrees and measured spectra of more than 700,000 celestial objects. With an ever-growing collaboration, SDSS-II (2005-2008) completed the original survey goals of imaging half the northern sky and mapping the 3-dimensional clustering of one million galaxies and 100,000 quasars. SDSS-II carried out two additional surveys: the Supernova Survey, which discovered and monitored hundreds of supernovae to measure the expansion history of the universe, and the Sloan Extension for Galactic Understanding and Exploration (SEGUE), which extended SDSS imaging towards the plane of the Galaxy and mapped the motions and composition of more than a quarter million Milky Way stars.

    SDSS-III (2008-2014) undertook a major upgrade of the venerable SDSS spectrographs and added two powerful new instruments to execute an interweaved set of four surveys, mapping the clustering of galaxies and intergalactic gas in the distant universe (BOSS), the dynamics and chemical evolution of the Milky Way (SEGUE-2 and APOGEE), and the population of extra-solar giant planets (MARVELS).

    The latest generation of the SDSS (SDSS-IV, 2014-2020) is extending precision cosmological measurements to a critical early phase of cosmic history (eBOSS), expanding its revolutionary infrared spectroscopic survey of the Galaxy in the northern and southern hemispheres (APOGEE-2), and for the first time using the Sloan spectrographs to make spatially resolved maps of individual galaxies (MaNGA).

    This is the “Science blog” of the SDSS. Here you’ll find short descriptions of interesting scientific research and discoveries from the SDSS. We’ll also update on activities of the collaboration in public engagement and other arenas. We’d love to see your comments and questions about what you read here!

    You can explore more on the SDSS Website.

     
  • richardmitnick 2:45 pm on February 4, 2017 Permalink | Reply
    Tags: , , , , , SDSS, The Sloan Digital Sky Survey: A Legacy   

    From astrobites:”The Sloan Digital Sky Survey: A Legacy” 

    Astrobites bloc

    Astrobites

    Feb 3, 2017
    Gourav Khullar

    Title: The Sloan Digital Sky Survey: Technical Summary
    Authors: Donald G. York, J. Adelman, John E. Anderson, Jr., et al.
    First Author’s Institution: Department of Astronomy and Astrophysics, University of Chicago, USA
    U Chicago bloc
    Status: Submitted to The Astronomical Journal [open access]

    The story today begins with the Princeton astronomer James Gunn, who in the 1980s was well aware of the advancements in optical detector technologies and processing power in computers that could analyse gigabytes of data. Gunn, who was famous for predicting the Gunn-Peterson trough in the spectra of distant quasars, dreamt of a next generation telescope that would point to the sky and look at the ensemble of objects that adorn it – the cosmic web of galaxies! This dream would bring together physicists, engineers, computer scientists and astrophysicists in a rapidly changing community to create a legacy that was going to change the field as we knew it.

    The product? The Sloan Digital Sky Survey.

    1
    SDSS Telescope at Apache Point Observatory, NM, USA

    SDSS has been an integral part of the reshaping of astrophysics in the last two decades. Today’s astrophysicists are embracing the challenge of simultaneously appreciating all elements of research in astrophysics – from data structures to modern engineering, from servers hosting n-body simulations to groundbreaking phenomenological studies. It can safely be said that SDSS was a pioneer project that enabled astrophysicists to do exactly that – look at the universe at the grandest scale with unlimited potential and possibilities.

    From the support of the Alfred P. Sloan foundation and various agencies in the US and beyond, SDSS materialized into a project in the early 1990s, and saw first light in 1999 as part of a commissioning phase. This 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, USA started its data run in 2000, taking spectra and images of about 35% of the night sky, with 3 million spectra and 500 million images coming together to form the most comprehensive astrophysical catalog in the world. This catalog contains millions of galaxies upto z = 1, bright quasars upto z=6, with images in five major filter bands – u,g,r,i and z.

    SDSS was divided into multiple surveys/projects :

    SDSS I (2000-2005)
    SDSS II (2005-2008), including the Sloan Supernova Survey
    SDSS III (2008-2014), including the APO Galactic Evolution Experiment (APOGEE), Baryon Oscillation Spectroscopic Survey (BOSS)
    BOSS Supercluster Baryon Oscillation Spectroscopic Survey (BOSS)
    BOSS Supercluster Baryon Oscillation Spectroscopic Survey (BOSS)
    SDSS IV (2014-2020), including the Mapping Nearby Galaxies at APO (MaNGA)
    5
    Manga | Science Blog from the SDSS

    Today’s widely cited paper was the first technical summary of the project with discussions on survey characteristics and early science data.

    6
    Sky projection in Galactic coordinates, of the northern (left) and southern (right – three stripes) SDSS surveys.

    The Survey

    The telescope has different modes – imaging and spectroscopic. The imaging detectors are CCD-based, SDSS being one of the first major telescopes to ever use them. The rough resolution of the camera is ~0.4″, with the camera sweeping the sky in great circles in all five filters i.e. each point in the sky is seen by the camera 5 times. The dimmest objects that the initial cameras were expected to see were of AB magnitude ~23 in the g,r bands. The imaging survey at the time of initiation was planned to cover 10,000 square degrees of the northern Galactic cap, along with three stripes in the southern Galactic cap.

    Once objects were detected and stored by SDSS, extended objects were identified and classified as galaxies. The galaxy candidates then became part of the sample whose spectra were taken. Strong absorption lines in red galaxies and brightest cluster galaxies were targeted for measuring redshifts. This enabled SDSS to create a 3-D map of the universe up to a certain sensitivity limit, with a mean redshift of z~0.2-0.3. About 650 spectra were taken at a time, with spectroscopic masks being designed based on the imaging surveys. Moreover, this was one of the first projects to implement photometric redshift calculations of objects beyond z=0.2, because of the efficient characterization of its filters and the sheer amount of data that SDSS would generate!

    7
    This is a simulated galaxy distribution in a 6 degree slice of the SDSS. Small dots are the main galaxy sample, the redder dots are a special sample of luminous red galaxies.

    Early Science, circa 2000

    As mentioned before, the fundamental focus of this survey – whose data is still extremely relevant and competitively analysed, 17 years later – was to characterize the largest structures in the universe. This could be the largest galaxy clusters, or the cosmic filamentary structures predicted in cosmological simulations. Using photometric redshifts, statistics of large datasets and efficient reddening correction for galaxies, the SDSS collaboration planned to take about 2000 square degrees worth of test data and about 20,000 spectra (in the year 2000!). Weak lensing of background galaxies by foreground objects had already been detected, and a 150 RR Lyrae stars (which had never been seen before in the Galactic Halo) had been identified.

    8
    An updated 3-d map of the local universe (z~0.15), constructed using SDSS spectra that inform us of a galaxy’s redshift. The filamentary structures of the cosmic web can be clearly seen.

    As all SDSS data is residing in public archives, it is being extensively used by the community for research and teaching. The World Wide Telescope uses SDSS images for its characterization of the night sky. On the other hand, citizen science projects like Galaxy Zoo employ astronomy enthusiasts who help classify millions of galaxies in the SDSS data and churn out good science, from their homes! The future looks promising. The Dark Energy Survey (DES), the Large Synoptic Survey Telescope (LSST) and the Dark Energy Spectroscopic Instrument(DESI) are worthy successors that will take billions of images and spectra, with petabytes of data left to be analysed by the next generation of astronomers. It’s interesting to note that several bites on our website every month are about SDSS data and analysis, which makes this ‘beyond’ bite our way of paying homage to this amazing telescope.

    Dark Energy Icon
    Dark Energy Camera [DECam],  built at FNAL
    Dark Energy Camera [DECam], built at FNAL
    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile
    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile

    LSST
    LSST/Camera, built at SLAC
    LSST/Camera, built at SLAC
    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.
    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes

    LBNL/DESI spectroscopic instrument on the Mayall 4-meter telescope at Kitt Peak National Observatory starting in 2018
    LBNL/DESI spectroscopic instrument on the Mayall 4-meter telescope at Kitt Peak National Observatory starting in 2018

    NOAO/Mayall 4 m telescope at Kitt Peak, Arizona, USA
    NOAO/Mayall 4 m telescope at Kitt Peak, Arizona, USA

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 3:11 pm on January 18, 2017 Permalink | Reply
    Tags: , , , , , Galaxy Murder Mystery, , SDSS   

    From ICRAR: “Galaxy Murder Mystery” 

    ICRAR Logo
    International Centre for Radio Astronomy Research

    January 17, 2017
    Mr Toby Brown (ICRAR-UWA, Swinburne University of Technology)
    E: toby.brown@icrar.org
    M: +61 6488 7753

    Dr Barbara Catinella (ICRAR-UWA)
    E: barbara.catinella@icrar.org
    Tel: +972 89346511

    Pete Wheeler—Media Contact, ICRAR
    E: pete.wheeler@icrar.org
    M: +61 423 982 018

    1
    This artist’s impression shows the spiral galaxy NGC 4921 based on observations made by the Hubble Space Telescope. Credit: ICRAR, NASA, ESA, the Hubble Heritage Team (STScI/AURA)

    It’s the big astrophysical whodunnit. Across the Universe, galaxies are being killed and the question scientists want answered is, what’s killing them?

    New research published today by a global team of researchers, based at the International Centre for Radio Astronomy Research (ICRAR), seeks to answer that question. The study reveals that a phenomenon called ram-pressure stripping is more prevalent than previously thought, driving gas from galaxies and sending them to an early death by depriving them of the material to make new stars.

    The study of 11,000 galaxies shows their gas—the lifeblood for star formation—is being violently stripped away on a widespread scale throughout the local Universe.

    Toby Brown, leader of the study and PhD candidate at ICRAR and Swinburne University of Technology, said the image we paint as astronomers is that galaxies are embedded in clouds of dark matter that we call dark matter halos.

    Dark matter is the mysterious material that despite being invisible accounts for roughly 27 per cent of our Universe, while ordinary matter makes up just 5 per cent. The remaining 68 per cent is dark energy.

    “During their lifetimes, galaxies can inhabit halos of different sizes, ranging from masses typical of our own Milky Way to halos thousands of times more massive,” Mr Brown said.

    “As galaxies fall through these larger halos, the superheated intergalactic plasma between them removes their gas in a fast-acting process called ram-pressure stripping.

    “You can think of it like a giant cosmic broom that comes through and physically sweeps the gas from the galaxies.”

    Mr Brown said removing the gas from galaxies leaves them unable to form new stars.

    “It dictates the life of the galaxy because the existing stars will cool off and grow old,” he said.

    “If you remove the fuel for star formation then you effectively kill the galaxy and turn it into a dead object.”

    ICRAR researcher Dr Barbara Catinella, co-author of the study, said astronomers already knew ram-pressure stripping affected galaxies in clusters, which are the most massive halos found in the Universe.

    “This paper demonstrates that the same process is operating in much smaller groups of just a few galaxies together with much less dark matter,” said Mr. Brown. “Most galaxies in the Universe live in these groups of between two and a hundred galaxies,” he said.

    “We’ve found this removal of gas by stripping is potentially the dominant way galaxies are quenched by their surrounds, meaning their gas is removed and star formation shuts down.”

    The study was published in the journal Monthly Notices of the Royal Astronomical Society. It used an innovative technique combining the largest optical galaxy survey ever completed—the Sloan Digital Sky Survey—with the largest set of radio observations for atomic gas in galaxies —the Arecibo Legacy Fast ALFA survey.

    SDSS Telescope at Apache Point, NM, USA
    SDSS Telescope at Apache Point, NM, USA
    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey
    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    NAIC/Arecibo Observatory, Puerto Rico, USA
    NAIC/Arecibo Observatory, Puerto Rico, USA
    3
    The Arecibo Legacy Fast ALFA Survey

    Mr Brown said the other main process by which galaxies run out of gas and die is known as strangulation.

    “Strangulation occurs when the gas is consumed to make stars faster than it’s being replenished, so the galaxy starves to death,” he said.

    “It’s a slow-acting process. On the contrary, what ram-pressure stripping does is bop the galaxy on the head and remove its gas very quickly—of the order of tens of millions of years—and astronomically speaking that’s very fast.”

    See the full article here .

    Please help promote STEM in your local schools.
    STEM Icon

    Stem Education Coalition

    ICRAR is an equal joint venture between Curtin University and The University of Western Australia with funding support from the State Government of Western Australia. The Centre’s headquarters are located at UWA, with research nodes at both UWA and the Curtin Institute for Radio Astronomy (CIRA).
    ICRAR has strong support from the government of Australia and is working closely with industry and the astronomy community, including CSIRO and the Australian Telescope National Facility, iVEC, and the international SKA Project Office (SPO), based in the UK.

    ICRAR is:

    Playing a key role in the international Square Kilometre Array (SKA) project, the world’s biggest ground-based telescope array.

    SKA Square Kilometer Array
    Attracting some of the world’s leading researchers in radio astronomy, who will also contribute to national and international scientific and technical programs for SKA and ASKAP.
    Creating a collaborative environment for scientists and engineers to engage and work with industry to produce studies, prototypes and systems linked to the overall scientific success of the SKA, MWA and ASKAP.

    SKA Murchison Widefield Array
    A Small part of the Murchison Widefield Array

    Enhancing Australia’s position in the international SKA program by contributing to the development process for the SKA in scientific, technological and operational areas.
    Promoting scientific, technical, commercial and educational opportunities through public outreach, educational material, training students and collaborative developments with national and international educational organisations.
    Establishing and maintaining a pool of emerging and top-level scientists and technologists in the disciplines related to radio astronomy through appointments and training.
    Making world-class contributions to SKA science, with emphasis on the signature science themes associated with surveys for neutral hydrogen and variable (transient) radio sources.
    Making world-class contributions to SKA capability with respect to developments in the areas of Data Intensive Science and support for the Murchison Radio-astronomy Observatory.

     
  • richardmitnick 12:44 pm on January 10, 2017 Permalink | Reply
    Tags: , , , Origin of the Elements in the Solar System, SDSS   

    From SDSS: “Origin of the Elements in the Solar System” 

    SDSS Science blog bloc

    Science Blog from the SDSS

    January 9, 2017
    Jennifer Johnson

    “The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.” — Carl Sagan

    This is an evocative statement. It gets at the heart of the matter. However, it leaves out all the different ways that stars make the elements. It is not just collapsing stars, it is merging stars, burping stars, exploding stars, and the start of the Universe itself.

    Below is the latest version of an evolving periodic table color-coded by the origin of the elements in the Solar System. An original version of this was made by Inese Ivans and me in 2008 and refined and improved by Anna Frebel. Versions highlighting different aspects of the physical processes are available on Inese Ivans’ website.

    1
    My current version of the periodic table, color-coded by the source of the element in the solar system. Elements with more than one source have the approximate amount due to each process indicated by the amount of area. Tc, Pm, and the elements beyond U do not have long-lived or stable isotopes. I have ignored the elements beyond U in this plot, but not including Tc and Pm looked weird, so I have included them in grey.

    For this version, I tried to avoid the technical terms and jargon used in the origin. I also updated the sources of the heavy elements to reflect the current semi-consensus. This graphic draws on an enormous amount of labor from astronomers and physicists. In an upcoming blog post, I will give details on my sources and assumptions for interested parties. Note that this is for the solar system. There will be additional versions showing what this plot would look like if you were in the early Universe, or if you consider the origin of the elements on the Earth, etc.

    However, the main point of this blog post is to present the chart and address the following question:

    Why does your version have different information than the well-known Wikipedia entry?

    3
    Wikipedia version, based on the original from Northern Arizona Meteorite Laboratory.

    Here is a discussion of the some of the differences between the Wikipedia version and mine. In many cases, the Wikipedia graphic is presenting information that is flat-out wrong. I am trying to avoid going into all details in this single blog post. The underlined phrases below represent possible topics for future blog posts where I (or colleagues I coerce bribe ask) in more detail, including why we think we are on the right track.

    I will assume that “Large Stars” and “Small Stars” are “High-Mass Stars” and “Low-Mass Stars”, respectively. It does not make sense to think of nucleosynthesis origin having to do with the radius of the stars. As this wonderful graphic from NASA’s Chandra website shows, all stars at the end of their lives swell up to red giant and supergiant stars.

    5
    Wonderful graphic from NASA’s Chandra website

    In its death throes, a low-mass star can have a much larger radius than normal high-mass star. Note that the original source cited by the Wikipedia article just has the chart, with no additional information or links that I can find.

    High-mass stars end their lives (at least some of the time) as core-collapse supernovae. Low-mass stars usually end their lives as white dwarfs. But sometimes white dwarfs that are in binary systems with another star get enough mass from the companion to become unstable and explode as so-called Type-Ia supernovae. Which “supernova” is being referred to in the Wikipedia graphic is not clear. The interpretation that makes the graphic the least wrong is the “supernova” here means “Type Ia Supernovae” or “exploding white dwarfs” as I call them. I will assume that “Large Stars” refers to the production in high-mass stars both during their lives and during the explosion that spews products of their nuclear fusion into the interstellar gas. It would also be possible to think that “Supernovae” refers to both massive star core-collapse supernovae and exploding white dwarfs. In this case, “Large Stars” could mean that massive stars make it before they explode and the supernovae is just the mechanism for kicking out. These categories are therefore 1) confusing and 2) incorrect no matter how you slice it.

    Dying low-mass stars (aka “Small Stars”) make substantial amounts of the heavy elements, including most of the Pb in the solar system. There should be a lot of yellow in the bottom half of the diagram. I don’t understand agree that Cr and Mn are made only in “Large Stars”, but Fe is made in both “Large Stars” and “Supernovae”. Basically all the iron in the Universe is made in explosive nucleosynthesis. The iron that massive stars make right before they explode as supernova is all destroyed/collapsed in the remnant. And so on.
    The information for Li is incorrect. 6Li is indeed made by cosmic rays (fast-moving nuclei) hitting other nuclei and breaking them apart. But most of the far more common 7Li isotope is without question made in low-mass stars and spewed out out into the Universe as the star dies. Some 7Li is also made in the Big Bang and a small fraction by cosmic ray fission.
    This post does not need to be any longer, but I would like to end by pointing out a difference between the Wikipedia graphic and my graphic caused by the fact that we still don’t know everything. A fraction of the heavy elements, including most of the Au, are formed in the “rapid neutron-capture process“. Where that happens is currently in dispute. It could be in massive star supernovae close to the forming neutron-star. More recently, there is compelling evidence that most of the r-process happens when two neutron stars spiral together and merge. That is why “merging neutron stars” is a category in my chart, but “Supernovae” takes the role in the Wikipedia chart.

    The Source of it all

    Here is the original version, done with markers:

    6
    This is what happens when you give two astronomers who are tired of reminding everyone about which elements go with which process a periodic table, a set of markers, and time when they should have been listening to talks. A heartful thanks to Inese Ivans for coming up with this idea.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    After nearly a decade of design and construction, the Sloan Digital Sky Survey saw first light on its giant mosaic camera in 1998 and entered routine operations in 2000. While the collaboration and scope of the SDSS have changed over the years, many of its key principles have stayed fixed: the use of highly efficient instruments and software to enable astronomical surveys of unprecedented scientific reach, a commitment to creating high quality public data sets, and investigations that draw on the full range of expertise in a large international collaboration. The generous support of the Alfred P. Sloan Foundation has been crucial in all phases of the SDSS, alongside support from the Participating Institutions and national funding agencies in the U.S. and other countries.

    The Sloan Digital Sky Survey has created the most detailed three-dimensional maps of the Universe ever made, with deep multi-color images of one third of the sky, and spectra for more than three million astronomical objects.

    In its first five years of operations, the SDSS carried out deep multi-color imaging over 8000 square degrees and measured spectra of more than 700,000 celestial objects. With an ever-growing collaboration, SDSS-II (2005-2008) completed the original survey goals of imaging half the northern sky and mapping the 3-dimensional clustering of one million galaxies and 100,000 quasars. SDSS-II carried out two additional surveys: the Supernova Survey, which discovered and monitored hundreds of supernovae to measure the expansion history of the universe, and the Sloan Extension for Galactic Understanding and Exploration (SEGUE), which extended SDSS imaging towards the plane of the Galaxy and mapped the motions and composition of more than a quarter million Milky Way stars.

    SDSS-III (2008-2014) undertook a major upgrade of the venerable SDSS spectrographs and added two powerful new instruments to execute an interweaved set of four surveys, mapping the clustering of galaxies and intergalactic gas in the distant universe (BOSS), the dynamics and chemical evolution of the Milky Way (SEGUE-2 and APOGEE), and the population of extra-solar giant planets (MARVELS).

    The latest generation of the SDSS (SDSS-IV, 2014-2020) is extending precision cosmological measurements to a critical early phase of cosmic history (eBOSS), expanding its revolutionary infrared spectroscopic survey of the Galaxy in the northern and southern hemispheres (APOGEE-2), and for the first time using the Sloan spectrographs to make spatially resolved maps of individual galaxies (MaNGA).

    This is the “Science blog” of the SDSS. Here you’ll find short descriptions of interesting scientific research and discoveries from the SDSS. We’ll also update on activities of the collaboration in public engagement and other arenas. We’d love to see your comments and questions about what you read here!

    You can explore more on the SDSS Website.

     
  • richardmitnick 10:09 pm on January 7, 2017 Permalink | Reply
    Tags: , , , , , SDSS   

    From SDSS: “The Elements of Life Mapped Across the Milky Way by SDSS/APOGEE 

    SDSS Telescope

    Sloan Digital Sky Survey Telescope at Apache Point, NM, USA

    January 5, 2017

    Jon Holtzman, New Mexico State University, holtz@nmsu.edu, 575-646-8181
    Sten Hasselquist, New Mexico State University, sten@nmsu.edu, 575-646-4438
    Jennifer Johnson, The Ohio State University, johnson.3064@osu.edu, 614-893-2132,
    Twitter: @jajohnson51 / @APOGEEsurvey
    Jonathan Bird, Vanderbilt University, jonathan.bird@vanderbilt.edu, 615-292-5403,
    Twitter: @galaxyhistorian
    Karen Masters, SDSS Scientific Spokesperson, University of Portsmouth (UK), karen.masters@port.ac.uk, +44 (0)7590 526600,
    Twitter: @KarenLMasters / @SDSSurveys
    Jordan Raddick, SDSS Public Information Officer, Johns Hopkins University, raddick@jhu.edu, 1-443-570-7105,
    Twitter: @raddick

    1
    The six most common elements of life on Earth (including more than 97% of the mass of a human body) are carbon, hydrogen, nitrogen, oxygen, sulphur and phosphorus.
    The colors in the spectra show dips, the size of which reveal the amount of these elements in the atmosphere of a star. The human body on the left uses the same color coding to evoke the important role these elements play in different parts of our bodies, from oxygen in our lungs to phosphorous in our bones (although in reality all elements are found all across the body).
    In the background is an artist’s impression of the Galaxy, with cyan dots to show the APOGEE measurements of the oxygen abundance in different stars; brighter dots indicate higher oxygen abundance.
    Image Credit: Dana Berry/SkyWorks Digital Inc.; SDSS collaboration

    To say “we are stardust” may be a cliche, but it’s an undeniable fact that most of the essential elements of life are made in stars.

    “For the first time, we can now study the distribution of elements across our Galaxy,” says Sten Hasselquist of New Mexico State University. “The elements we measure include the atoms that make up 97% of the mass of the human body.”

    The new results come from a catalog of more than 150,000 stars; for each star, it includes the amount of each of almost two dozen chemical elements. The new catalog includes all of the so-called “CHNOPS elements” – carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur – known to be the building blocks of all life on Earth. This is the first time that measurements of all of the CHNOPS elements have been made for such a large number of stars.

    How do we know how much of each element a star contains? Of course, astronomers cannot visit stars to spoon up a sample of what they’re made of, so they instead use a technique called spectroscopy to make these measurements. This technique splits light – in this case, light from distant stars – into detailed rainbows (called spectra). We can work out how much of each element a star contains by measuring the depths of the dark and bright patches in the spectra caused by different elements.

    Astronomers in the Sloan Digital Sky Survey have made these observations using the APOGEE (Apache Point Observatory Galactic Evolution Experiment) spectrograph on the 2.5m Sloan Foundation Telescope at Apache Point Observatory in New Mexico.

    SDSS  APOGEE spectrograph
    SDSS APOGEE spectrograph

    This instrument collects light in the near-infrared part of the electromagnetic spectrum and disperses it, like a prism, to reveal signatures of different elements in the atmospheres of stars. A fraction of the almost 200,000 stars surveyed by APOGEE overlap with the sample of stars targeted by the NASA Kepler mission, which was designed to find potentially Earth-like planets. The work presented today focuses on ninety Kepler stars that show evidence of hosting rocky planets, and which have also been surveyed by APOGEE.

    While the Sloan Digital Sky Survey may be best known for its beautiful public images of the sky, since 2008 it has been entirely a spectroscopic survey. The current stellar chemistry measurements use a spectrograph that senses infrared light – the APOGEE (Apache Point Observatory Galactic Evolution Experiment) spectrograph, mounted on the 2.5-meter Sloan Foundation Telescope at Apache Point Observatory in New Mexico.

    Jon Holtzman of New Mexico State University explains that “by working in the infrared part of the spectrum, APOGEE can see stars across much more of the Milky Way than if it were trying to observe in visible light. Infrared light passes through the interstellar dust, and APOGEE helps us observe a broad range of wavelengths in detail, so we can measure the patterns created by dozens of different elements.”

    The new catalog is already helping astronomers gain a new understanding of the history and structure of our Galaxy, but the catalog also demonstrates a clear human connection to the skies. As the famous astronomer Carl Sagan said, “we are made of starstuff.” Many of the atoms which make up your body were created sometime in the distant past inside of stars, and those atoms have made long journeys from those ancient stars to you.

    While humans are 65% oxygen by mass, oxygen makes up less than 1% of the mass of all of elements in space. Stars are mostly hydrogen, but small amounts of heavier elements such as oxygen can be detected in the spectra of stars. With these new results, APOGEE has found more of these heavier elements in the inner Galaxy. Stars in the inner galaxy are also older, so this means more of the elements of life were synthesized earlier in the inner parts of the Galaxy than in the outer parts.

    While it’s fun speculate what impact the inner Galaxy’s composition might have on where life pops up, we are much better at understanding the formation of stars in our Galaxy. Because the processes producing each element occur in specific types of stars and proceed at different rates, they leave specific signatures in the chemical abundance patterns measured by SDSS/APOGEE. This means that SDSS/APOGEE’s new elemental abundance catalog provides data to compare with the predictions made by models of galaxy formation.

    Jon Bird of Vanderbilt University, who works on modelling the Milky Way, explains that “these data will be useful to make progress on understanding Galactic evolution, as more and more detailed simulations of the formation of our galaxy are being made, requiring more complex data for comparison.”

    “It’s a great human interest story that we are now able to map the abundance of all of the major elements found in the human body across hundreds of thousands of stars in our Milky Way,” said Jennifer Johnson of The Ohio State University. “This allows us to place constraints on when and where in our galaxy life had the required elements to evolve, a sort ‘temporal Galactic habitable zone’”.

    The catalog of chemical abundances from which these maps were generated has been publicly released as part of the Thirteenth Data release of the SDSS, and is available freely online to anyone at http://www.sdss.org.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The Sloan Digital Sky Survey has created the most detailed three-dimensional maps of the Universe ever made, with deep multi-color images of one third of the sky, and spectra for more than three million astronomical objects. Learn and explore all phases and surveys—past, present, and future—of the SDSS.

    The SDSS began regular survey operations in 2000, after a decade of design and construction. It has progressed through several phases, SDSS-I (2000-2005), SDSS-II (2005-2008), SDSS-III (2008-2014), and SDSS-IV (2014-). Each of these phases has involved multiple surveys with interlocking science goals. The three surveys that comprise SDSS-IV are eBOSS, APOGEE-2, and MaNGA, described at the links below. You can find more about the surveys of SDSS I-III by following the Prior Surveys link.

    Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS- IV acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS web site is http://www.sdss.org.

    SDSS-IV is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration including the Brazilian Participation Group, the Carnegie Institution for Science, Carnegie Mellon University, the Chilean Participation Group, the French Participation Group, Harvard-Smithsonian Center for Astrophysics, Instituto de Astrofísica de Canarias, The Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU) / University of Tokyo, Lawrence Berkeley National Laboratory, Leibniz Institut für Astrophysik Potsdam (AIP), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Max-Planck-Institut für Astrophysik (MPA Garching), Max-Planck-Institut für Extraterrestrische Physik (MPE), National Astronomical Observatory of China, New Mexico State University, New York University, University of Notre Dame, Observatório Nacional / MCTI, The Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, United Kingdom Participation Group, Universidad Nacional Autónoma de México, University of Arizona, University of Colorado Boulder, University of Oxford, University of Portsmouth, University of Utah, University of Virginia, University of Washington, University of Wisconsin, Vanderbilt University, and Yale University.

     
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