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  • richardmitnick 1:23 pm on January 5, 2018 Permalink | Reply
    Tags: , , , , , Galaxies Growing Up on the Edge of the Void, , SDSS-III   

    From AAS NOVA: “Galaxies Growing Up on the Edge of the Void” 



    5 January 2018
    Kerry Hensley

    Light distribution of galaxies generated in the Millennium Simulation. [Max Planck Institute for Astrophysics]


    As effective laboratories for studying the impact of nature on galaxy evolution without the influence of nurture, galaxies in cosmic voids stand alone. What does the dearth of galactic neighbors mean for the morphology of galaxies in cosmic voids?

    Bubbles on a Megaparsec Scale

    Cosmic voids are roughly spherical regions of the cosmic web with lower-than-average density of matter. Though far less populated than dense galaxy clusters, cosmic voids aren’t empty; delicate filaments beaded with galactic pearls cut across their centers, hosting sites of galaxy formation. Because of their low density, voids represent a laboratory within which galaxy properties and evolution are largely determined independent of the influence of neighboring galaxies.

    What is life like for a galaxy in the proximity of a cosmic void? To answer this question, Elena Ricciardelli (École Polytechnique Fédérale de Lausanne, Switzerland) and collaborators analyze the properties of galaxies residing in and around cosmic voids in the nearby (0.01 < z < 0.12) universe.

    Exploring Void Galaxy Morphology

    Fraction of elliptical and spiral galaxies as a function of absolute magnitude in and outside of voids. Voids contain a higher fraction of spirals and a lower fraction of ellipticals than the control sample. [Adapted from Ricciardelli et al. 2017]

    Ricciardelli and collaborators search for the effects cosmic voids have on galaxy morphology by analyzing a sample of galaxies drawn from the Sloan Digital Sky Survey.


    SDSS Telescope at Apache Point Observatory, NM, USA, Altitude 2,788 meters (9,147 ft)

    In total, they consider roughly 6,000 void galaxies and a control sample of 200,000 galaxies from environments of average density. They use the Galaxy Zoo morphological classification tool to identify the spiral and elliptical galaxies in their sample.

    Lastly, they calculate the fraction of spiral and elliptical galaxies present in their void and control samples, while correcting for the fact that faint spiral galaxies are more likely to be misclassified as ellipticals than their bright counterparts. They find that galaxies near voids are more likely to be spirals than galaxies far from voids, indicating that nearby cosmic voids have a marked effect on galaxy evolution.

    Life in and Around the Void

    Clockwise from top left: elliptical fraction, spiral fraction, star-forming fraction, and stellar mass for galaxies in and around voids out to a redshift of z = 0.065. The dashed line marks the median value for each variable for the control galaxies. The dotted lines indicate the boundaries of the zone of influence of the voids. [Ricciardelli et al. 2017]

    The authors find that not only does a galaxy’s distance from the void affect its properties, but the size of the adjacent void has a measurable impact as well. Within the voids, they find a larger fraction of spiral galaxies compared to the control sample. This effect persists after removing the mass bias due to the fact that the low-density void environments are preferentially populated with low-mass galaxies; for a given mass or absolute magnitude, voids contain a higher proportion of spiral galaxies than the control sample.

    This effect is not limited to the volume within the voids; Ricciardelli and collaborators find that the properties of void-adjacent galaxies are altered out to twice the radius of the void, with a higher fraction of spiral galaxies found closer to voids. The size of a void has an effect as well; larger-than-average voids harbor a larger fraction of spiral galaxies than smaller-than-average voids.

    The authors caution that this final result depends on how the voids are defined; the effect disappears if the voids are defined using their dynamical properties rather than their size. Future research will help further disentangle the role that cosmic voids play in galaxy evolution.


    Elena Ricciardelli et al 2017 ApJL 846 L4. http://iopscience.iop.org/article/10.3847/2041-8213/aa84ad/meta

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    Further references with links at the full article.

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    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

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  • richardmitnick 5:21 pm on March 22, 2017 Permalink | Reply
    Tags: , , , , , , , Dark Energy Spectroscopic Instrument (DESI), , , New Study Maps Space Dust in 3-D, , SDSS-III   

    From LBNL: “New Study Maps Space Dust in 3-D” 

    Berkeley Logo

    Berkeley Lab

    March 22, 2017
    Glenn Roberts Jr

    Access mp4 video here .
    This animation shows a 3-D rendering of space dust, as viewed in a several-kiloparsec (thousands of light years) loop through and out of the Milky Way’s galactic plane. The animation uses data for hundreds of millions of stars from Pan-STARRS1 and 2MASS surveys, and is made available through a Creative Commons License. (Credit: Gregory M. Green/SLAC, KIPAC)

    Consider that the Earth is just a giant cosmic dust bunny—a big bundle of debris amassed from exploded stars. We Earthlings are essentially just little clumps of stardust, too, albeit with very complex chemistry.

    And because outer space is a very dusty place, that makes things very difficult for astronomers and astrophysicists who are trying to peer farther across the universe or deep into the center of our own galaxy to learn more about their structure, formation and evolution.

    Building a better dust map

    Now, a new study led by Edward F. Schlafly, a Hubble Fellow in the Physics Division at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), is providing a detailed, 3-D look at dust on a scale spanning thousands of light-years in our Milky Way galaxy. The study was published today in The Astrophysical Journal.

    This dust map is of critical importance for the Dark Energy Spectroscopic Instrument (DESI), a Berkeley Lab-led project that will measure the universe’s accelerating expansion rate when it starts up in 2019. DESI will build a map of more than 30 million distant galaxies, but that map will be distorted if this dust is ignored.

    “The light from those distant galaxies travels for billions of years before we see it,” according to Schlafly, “but in the last thousand years of its journey toward us a few percent of that light is absorbed and scattered by dust in our own galaxy. We need to correct for that.”

    Just as airborne dust in Earth’s sky contributes to the atmospheric haze that gives us brilliant oranges and reds in sunrises and sunsets, dust can also make distant galaxies and other space objects appear redder in the sky, distorting their distance and in some cases concealing them from view.

    Scientists are constantly developing better ways to map out this interstellar dust and understand its concentration, composition, and common particle sizes and shapes.

    The dark regions show very dense dust clouds. The red stars tend to be reddened by dust, while the blue stars are in front of the dust clouds. These images are part of a survey of the southern galactic plane. (Credit: Legacy Survey/NOAO, AURA, NSF)

    Once we can solve the dust problem by creating better dust maps and learning new details about the properties of this space dust, this can give us a much more precise gauge of distances to faraway stars in the Milky Way, like a galactic GPS. Dust maps can also help to better gauge the distance to supernovae events by taking into account the effects of dust in reddening their light.

    “The overarching aim of this project is to map dust in three dimensions—to find out how much dust is in any 3-D region in the sky and in the Milky Way galaxy,” Schlafly said.

    Combined data from sky surveys shed new light on dust

    Taking data from separate sky surveys conducted with telescopes on Maui and in New Mexico, Schlafly’s research team composed maps that compare dust within one kiloparsec, or 3,262 light-years, in the outer Milky Way—including collections of gas and dust known as molecular clouds that can contain dense star- and planet-forming regions known as nebulae—with more distant dust in the galaxy.

    Pan-STARRS2 and PanSTARS1 telescopes atop Haleakalā on the island of Maui, Hawaii. (Credit: Pan-STARRS)

    The resolution of these 3-D dust maps is many times better than anything that previously existed,” said Schlafly.

    This undertaking was made possible by the combination of a very detailed multiyear survey known as Pan-STARRS that is powered by a 1.4-gigapixel digital camera and covers three-fourths of the visible sky, and a separate survey called APOGEE that used a technique known as infrared spectroscopy.

    A compressed view of the entire sky visible from Hawaii by the Pan-STARRS1 Observatory. The image is a compilation of half a million exposures, each about 45 seconds in length, taken over a period of four years. The disk of the Milky Way looks like a yellow arc, and the dust lanes show up as reddish-brown filaments. The background is made up of billions of faint stars and galaxies. (Credit: D. Farrow/Pan-STARRS1 Science Consortium, and Max Planck Institute for Extraterrestrial Physics)

    Infrared measurements can effectively cut through the dust that obscures many other types of observations and provides a more precise measurement of stars’ natural color. The APOGEE experiment focused on the light from about 100,000 red giant stars across the Milky Way, including those in its central halo.

    SDSS Telescope at Apache Point Observatory, NM, USA

    What they found is a more complex picture of dust than earlier research and models had suggested. The dust properties within 1 kiloparsec of the sun, which scientists measure with a light-obscuring property known as its “extinction curve,” is different than that of the dust properties in the more remote galactic plane and outer galaxy.

    New questions emerge on the makeup of space dust

    The results, researchers found, appear to be in conflict with models that expect dust to be more predictably distributed, and to simply exhibit larger grain sizes in areas where more dust resides. But the observations find that the dust properties vary little with the amount of dust, so the models may need to be adjusted to account for a different chemical makeup, for example.

    “In denser regions, it was thought that dust grains will conglomerate, so you have more big grains and fewer small grains,” Schlafly said. But the observations show that dense dust clouds look much the same as less concentrated dust clouds, so that variations in dust properties are not just a product of dust density: “whatever is driving this is not just conglomeration in these regions.”

    He added, “The message to me that we don’t yet know what’s going on. I don’t think the existing (models) are correct, or they are only right at the very highest densities.”

    Accurate measures of the chemical makeup of space dust are important, Schlafly said. “A large amount of chemistry takes place on dust grains, and you can only form molecular hydrogen on the surface of dust grains,” he said—this molecular hydrogen is essential in the formation of stars and planets.

    Access mp4 video here .
    This animation shows a 3-D rendering of dust, as viewed from a 50-parsec (163-light-year) loop around the sun. The animation uses data for hundreds of millions of stars from Pan-STARRS1 and 2MASS surveys, and is made available through a Creative Commons License: https://creativecommons.org/licenses/by-sa/4.0/. (Credit: Gregory M. Green/SLAC, KIPAC)

    Even with a growing collection of dust data, we still have an incomplete dust map of our galaxy. “There is about one-third of the galaxy that’s missing,” Schlafly said, “and we’re working right now on imaging this ‘missing third’ of the galaxy.” A sky survey that will complete the imaging of the southern galactic plane and provide this missing data should wrap up in May, he said.

    APOGEE-2, a follow-up survey to APOGEE, for example, will provide more complete maps of the dust in the local galaxy, and other instruments are expected to provide better dust maps for nearby galaxies, too.

    While the density of dust shrouds our view of the center of the Milky Way, Schlafly said there will be progress, too, in seeing deeper and collecting better dust measurements there as well.

    Researchers at the Harvard-Smithsonian Center for Astrophysics and Harvard University also participated in this work.

    The planned APOGEE-2 survey area overlain on an image of the Milky Way. Each dot shows a position where APOGEE-2 will obtain stellar spectra. (Credit: APOGEE-2)

    APOGEE is a part of the Sloan Digital Sky Survey III (SDSS-III), with participating institutions including Berkeley Lab, the Alfred P. Sloan Foundation, and the National Science Foundation. PanSTARRS1 surveys are supported by the University of Hawaii Institute for Astronomy; the Pan-STARRS Project Office; the Max-Planck Society and its participating institutes in Germany; the Johns Hopkins University; the University of Durham, the University of Edinburgh, and the Queen’s University Belfast in the U.K.; the Harvard-Smithsonian Center for Astrophysics; the Las Cumbres Observatory Global Telescope Network Inc.; and the National Central University of Taiwan. Pan-STARRS is supported by the U.S. Air Force.

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  • richardmitnick 1:38 pm on July 14, 2016 Permalink | Reply
    Tags: Dark Energy Measured with Record-Breaking Map of 1.2 Million Galaxies, , SDSS-III   

    From LBL: “Dark Energy Measured with Record-Breaking Map of 1.2 Million Galaxies” 

    Berkeley Logo

    Berkeley Lab

    July 14, 2016
    Jon Weiner

    David Schlegel, Lawrence Berkeley National Laboratory

    Shirley Ho, Lawrence Berkeley National Laboratory and Carnegie Mellon University

    A team of hundreds of physicists and astronomers have announced results from the largest-ever, three-dimensional map of distant galaxies. The team constructed this map to make one of the most precise measurements yet of the dark energy currently driving the accelerated expansion of the Universe.

    “We have spent five years collecting measurements of 1.2 million galaxies over one quarter of the sky to map out the structure of the Universe over a volume of 650 cubic billion light years,” says Jeremy Tinker of New York University, a co-leader of the scientific team carrying out this effort. “This map has allowed us to make the best measurements yet of the effects of dark energy in the expansion of the Universe. We are making our results and map available to the world.”

    This is one slice through the map of the large-scale structure of the Universe from the Sloan Digital Sky Survey and its Baryon Oscillation Spectroscopic Survey. Each dot in this picture indi-cates the position of a galaxy 6 billion years into the past. The image covers about 1/20th of the sky, a slice of the Universe 6 billion light-years wide, 4.5 billion light-years high, and 500 million light-years thick. Color indicates distance from Earth, ranging from yellow on the near side of the slice to purple on the far side. Galaxies are highly clustered, revealing superclusters and voids whose presence is seeded in the first fraction of a second after the Big Bang. This image contains 48,741 galaxies, about 3% of the full survey dataset. Grey patches are small regions without survey data. Credit: Daniel Eisenstein and SDSS-III

    These new measurements were carried out by the Baryon Oscillation Spectroscopic Survey (BOSS) program of the Sloan Digital Sky Survey-III. Shaped by a continuous tug-of-war between dark matter and dark energy, the map revealed by BOSS allows scientists to measure the expansion rate of the Universe and thus determine the amount of matter and dark energy that make up the present-day Universe. A collection of papers describing these results was submitted this week to the Monthly Notices of the Royal Astronomical Society.

    BOSS measures the expansion rate of the Universe by determining the size of the baryonic acoustic oscillations (BAO) in the three-dimensional distribution of galaxies. The original BAO size is determined by pressure waves that travelled through the young Universe up to when it was only 400,000 years old (the Universe is presently 13.8 billion years old), at which point they became frozen in the matter distribution of the Universe. The end result is that galaxies have a slight preference to be separated by a characteristic distance that astronomers call the acoustic scale. The size of the acoustic scale at 13.4 billion years ago has been exquisitely determined from observations of the cosmic microwave background from the light emitted when the pressure waves became frozen. Measuring the distribution of galaxies since that time allows astronomers to measure how dark matter and dark energy have competed to govern the rate of expansion of the Universe.

    “We’ve made the largest map for studying the 95% of the universe that is dark,” noted David Schlegel, an astrophysicist at Lawrence Berkeley National Laboratory (Berkeley Lab) and principal investigator for BOSS. “In this map, we can see galaxies being gravitationally pulled towards other galaxies by dark matter. And on much larger scales, we see the effect of dark energy ripping the universe apart.”

    The Sloan Digital Sky Survey and its Baryon Oscillation Spectroscopic Survey has transformed a two-dimensional image of the sky (left panel) into a three-dimensional map spanning distances of billions of light years, shown here from two perspectives (middle and right panels). This map includes 120,000 galaxies over 10% of the survey area. The brighter regions correspond to the regions of the Universe with more galaxies and therefore more dark matter. Image credit: Jeremy Tinker and SDSS-III.

    Shirley Ho, an astrophysicist at Berkeley Lab and Carnegie Mellon University (CMU), co-led two of the companion papers and adds, “We can now measure how much the galaxies and stars cluster together as a function of time to such an accuracy we can test General Relativity at cosmological scales.”

    Ariel Sanchez of the Max-Planck Institute of Extraterrestrial Physics led the effort to estimate the exact amount of dark matter and dark energy based on the BOSS data and explains: “Measuring the acoustic scale across cosmic history gives a direct ruler with which to measure the Universe’s expansion rate. With BOSS, we have traced the BAO’s subtle imprint on the distribution of galaxies spanning a range of time from 2 to 7 billion years ago.”

    To measure the size of these ancient giant waves to such sharp precision, BOSS had to make an unprecedented and ambitious galaxy map, many times larger than previous surveys. At the time the BOSS program was planned, dark energy had been previously determined to significantly influence the expansion of the Universe starting about 5 billion years ago. BOSS was thus designed to measure the BAO feature from before this point (7 billion years ago) out to near the present day (2 billion years ago).

    Jose Vazquez of Brookhaven National Laboratory combined the BOSS results with other surveys and searched for any evidence of unexplained physical phenomena in the results. “Our latest results tie into a clean cosmological picture, giving strength to the standard cosmological model that has emerged over the last eighteen years.”

    Rita Tojeiro of the University of St. Andrews is the other co-leader of the BOSS galaxy clustering working group along with Tinker. “We see a dramatic connection between the sound wave imprints seen in the cosmic microwave background 400,000 years after the Big Bang to the clustering of galaxies 7-12 billion years later. The ability to observe a single well-modeled physical effect from recombination until today is a great boon for cosmology.”

    The map also reveals the distinctive signature of the coherent movement of galaxies toward regions of the Universe with more matter, due to the attractive force of gravity. Crucially, the observed amount of infall is explained well by the predictions of general relativity.

    “The results from BOSS provide a solid foundation for even more precise future BAO measurements, such as those we expect from the Dark Energy Spectroscopic Instrument (DESI),” says Natalie Roe, Physics Division director at Berkeley Lab. “DESI will construct a more detailed 3-dimensional map in a volume of space ten times larger to precisely characterize dark energy — and ultimately the future of our universe.”
    Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. For more on SDSS-III, visit http://www.sdss3.org/.

    To read the SDSS news release, go here.

    SDSS Telescope at Apache Point, NM, USA
    SDSS Telescope at Apache Point, NM, USA

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  • richardmitnick 8:19 pm on March 31, 2016 Permalink | Reply
    Tags: , , , , SDSS-III   

    From SDSS: “An Oasis in the Brown Dwarf Desert – Astronomers Surprised, Relieved” 

    SDSS Telescope

    Sloan Digital Sky Survey

    March 31, 2016
    Jordan Raddick

    A new paper published this month in The Astronomical Journal by astronomers from the Sloan Digital Sky Survey (SDSS) reports a wellspring of new brown dwarf stellar companions, throwing cold water on the entire idea of the “brown dwarf desert,” the previously mystifying lack of these sub-stellar objects around stars.

    Artist's concept of a Brown dwarf [not quite a] star. NASA/JPL-Caltech
    Artist’s concept of a Brown dwarf [not quite a] star. NASA/JPL-Caltech

    Most stars in our Galaxy have a traveling companion. Often, these companions are stars of similar mass, as is the case for our nearest stellar neighbors, the triple star system Alpha Centauri.

    Centauris Alpha Beta Proxima 27 February 2012 Skatebiker
    Centauris Alpha Beta Proxima, 27 February 2012 Skatebiker

    The “before” and “after” comparison of the number of known brown dwarfs orbiting other stars.

    For each of the 41 close-in brown dwarf companions detected previously, the left panel shows the distance to its host star. The right panel shows the 112 brown dwarfs discovered in the new study.

    In both panels, the sizes of the brown dwarfs indicate their masses, and the circle shows the distance to Earth’s orbit. The larger dot (yellow or red) in the center of each panel represents the host star (not to scale). All the companions were discovered in different systems; they are shown together for comparison only.

    Our Sun, of course, has companions of its own – the planets of our Solar System. Planetary companions are vastly different from stellar companions: they are much smaller, and they do not shine with their own light created through nuclear fusion. Even the largest planet in our Solar System, Jupiter, would need to be 80 times more massive to even begin to shine this way.

    Stuck in the middle are “brown dwarfs,” much bigger than Jupiter but still too small to be shining stars. These brown dwarfs give off merely a dim glow as they slowly cool. The Universe is full of stars, and now we know that it is full of planets too. Astronomers expected that the Universe would also be teeming with brown dwarfs.

    But strangely, that’s not what they had been finding. Although astronomers have found plenty of brown dwarfs floating through space on their own, they found very few as stellar companions. Even in recent years, as new and sensitive detection techniques have allowed them to discover thousands of extrasolar planets, brown dwarfs have remained elusive – in spite of the fact that they should be easier to find than planets.

    In fact, until recently, so few brown dwarfs have been found orbiting close to other stars that astronomers refer to the phenomenon as the “brown dwarf desert.” This in turn created a problem for theorists, who have been scrambling to explain why astronomers have found so few. Therefore when SDSS astronomers started sifting through their data looking for brown dwarf companions to stars, they were hoping not to come up completely dry.

    “We were shocked to find that so many of the stars in our sample have close-orbiting brown dwarf companions,” says Nick Troup of the University of Virginia, lead author of the paper. “We never expected to triple the total number of known brown dwarf companions with only a few years’ worth of observations.”

    The team’s success is due to an unlikely tool in the race to find low-mass stellar companions. The Apache Point Observatory Galactic Evolution Experiment (APOGEE) was designed as a substantial survey of stars in our Milky Way to make a large-scale map of their motions and chemical compositions. But the instrument built for the APOGEE project is so sensitive to small stellar motions that companions orbiting these stars can be detected with APOGEE data.

    SDSS APOGEE spectrograph
    SDSS APOGEE spectrograph

    When an object orbits a star, it [gravitationally] tugs at it, causing the star to move on a little orbit of its own. For example, Jupiter tugs on the Sun enough to make it wobble around in space by more than its own diameter. To a distant observer, this wobble can be detected — and the mass of the tugging object can be determined — through changes in the motion of the star. This motion is seen through the Doppler effect, the same phenomenon that is the basis of the patrol officer’s speed gun and the meteorologist’s Doppler radar rain map. While APOGEE was designed to measure the grand motions of stars speeding around the Galaxy, it was never intended to do so at the subtle precisions needed to detect the much tinier wobbles induced by small sub-stellar companions.

    “This level of precision was a serendipitous bonus of the design of the APOGEE spectrograph”, says John Wilson, University of Virginia astronomer and leader of the APOGEE instrument team. “The entire instrument has to be contained in a giant steel vessel in a vacuum at –320 degrees F, otherwise the instrument’s own heat would swamp the infrared signals from the stars.” It turns out that this tightly controlled environment makes it possible to use the APOGEE instrument to measure Doppler shifts reliably over the course of months or years, a feat not achievable by many other spectrographs.

    “Even with the first data obtained a few years ago, it was clear that we could use APOGEE to detect the motions of planet-sized objects around our target stars,” says David Nidever of the University of Arizona and the Large Synoptic Survey Telescope, who was responsible for writing much of the software that measures the Doppler motions in APOGEE spectra. “It definitely opened our eyes to the possibilities of doing a more systematic search for planets and brown dwarfs.”

    To undertake such a search, the team started with the 150,000 stars that APOGEE had observed. The astronomers winnowed that collection of stars down to a “prime sample” of about four hundred representing the best examples of stars with companions in the APOGEE data. Among these, they identified about 60 stars with evidence for planetary-mass candidates, which was already exciting. But the real surprise came with the researchers’ extraordinary haul of 112 brown dwarf candidates – twice as many than had been found in the previous 15 years.

    Why has the APOGEE team been so lucky in finding this oasis of brown dwarfs? Troup thinks it may have to do with the types of host stars that they are looking at. “Most people doing planet searches have been interested in finding the next Earth, so they’ve focused their efforts on stars similar to the Sun,” Troup says. “But we had to work with the stars that APOGEE surveyed, which are mostly giant stars.”

    The reasons why brown dwarf companions are more common around giant stars is just one of many new questions raised by this new study that the Sloan team is investigating. And the team will continue to test their results with the ever-growing flow of APOGEE data.

    “It’s completely unprecedented that this many brown dwarf companions have been found at once, so we are anxious to see if the trend persists as the APOGEE sample grows to several times larger,” Troup said.

    But for now, it looks like the brown dwarf desert might be a mirage after all.

    Companions to APOGEE stars. I. A Milky Way-spanning catalog of stellar and substellar companion candidates and their diverse hosts.” Astronomical Journal, 151(3), 85-109, doi:10.3847/0004-6256/151/3/85, arxiv.org/abs/1601.00688.

    The science team:
    Nicholas W. Troup1a, David L. Nidever2,3,24, Nathan De Lee4,5, Joleen Carlberg6, Steven R. Majewski1, Martin
    Fernandez7, Kevin Covey7, S. Drew Chojnowski8, Joshua Pepper9, Duy T. Nguyen1, Keivan Stassun4, Duy
    Cuong Nguyen10, John P. Wisniewski11, Scott W. Fleming12,13, Dmitry Bizyaev14,15, Peter M. Frinchaboy23, D.
    A. Garca-Hernandez20,21, Jian Ge16, Fred Hearty17,18, Szabolcs Meszaros19, Kaike Pan14, Carlos Allende
    Prieto20,21, Donald P. Schneider17,18, Matthew D. Shetrone22, Michael F. Skrutskie1, John Wilson1, Olga


    1 Department of Astronomy, University of Virginia, Charlottesville,
    VA 22904-4325, USA Anwt2de@virginia.edu
    2 University of Michigan, 1085 S University Ave, Ann Arbor,
    MI 48109, USA
    3 Large Synoptic Survey Telescope, 950 North Cherry Ave,
    Tuscon, AZ 85719, USA
    4 Department of Physics, Geology, and Engineering Tech,
    Northern Kentucky University, Highland Heights, KY 41099,
    5 Department of Physics and Astronomy, Vanderbilt University,
    Nashville, TN, USA
    6 NASA Goddard Space
    ight Center, Greenbelt, MD, USA
    7 Western Washington University, Bellingham, WA 98225,
    8 New Mexico State University, Las Cruces, NM, USA
    9 Lehigh University, Bethlehem, PA, USA
    10 University of Toronto, Toronto, Ontario, Canada
    11 University of Oklahoma, Norman, OK, USA
    12 Space Telescope Science Institute, Baltimore, MD, USA
    13 Computer Sciences Corporation, Baltimore, MD, USA
    14 Apache Point Observatory and New Mexico State University,
    P.O. Box 59, Sunspot, NM, 88349-0059, USA
    15 Sternberg Astronomical Institute, Moscow State University,
    Moscow, Russia
    16 Department of Astronomy, University of Florida,
    Gainesville, FL 32611, USA
    17 Department of Astronomy & Astrophysics, The Pennsylvania
    State University, University Park, PA 16802, USA
    18 Center for Exoplanets and Habitable Worlds, The Pennsylvania
    State University, University Park, PA 16802, USA
    19 ELTE Gothard Astrophysical Observatory, H-9704 Szombathely,
    Szent Imre Herceg st. 112, Hungary
    20 Instituto de Astrofsica de Canarias, Via Lactea s/n, 38205
    La Laguna, Tenerife, Spain
    21 Departamento de Astrofsica, Universidad de La Laguna,
    38206 La Laguna, Tenerife, Spain
    22 University of Texas, Austin, TX, USA
    23 Department of Physics & Astronomy, Texas Christian
    University, TCU Box 298840, Fort Worth, TX 76129
    24 Steward Observatory 933 North Cherry Ave, Tuscon, AZ
    85719, USA

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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 4:38 pm on December 21, 2015 Permalink | Reply
    Tags: , , SDSS-III,   

    From SDSS: “Building the APOGEE-2S Spectrograph: Putting Together All the Little Pieces” 

    SDSS Science blog bloc

    Science Blog from the SDSS

    December 21, 2015
    David Whelan

    Building a spectrograph is no mean feat — and an instrument like the APOGEE spectrograph, with high expectations of precision to meet its mighty science goals, takes time and effort. Today we want to share with you some of the many highlights of the ongoing, and exciting, work being done to make the APOGEE-2S spectrograph, the “twin” spectrograph that is going to perform survey operations on the du Pont Telescope at Las Campanas Observatory in Chile.

    Las Campanas Dupont telescope exterior
    Las Campanas Dupont telescope interior
    Las Campanas duPont telescope

    Spectrographs have several key components. The light collected by the telescope from a star is collimated by a great big lens before it strikes the diffraction grating, which splits the light into its constituent colors (it’s a fancy prism). The “split” light then travels through a camera so that it can be refocused onto the infrared array, which records the spectrum of the star.

    With that in mind, here’s a picture of a part of the collimator known as the collimator positioning actuator, which is the little piece of metal seen at the center of the test dewar (the large cylinder). Its role is to precisely position the collimator lens, to ensure precise collimation at all times.

    Josh Peebles from Johns Hopkins is seen here preparing the collimator positioning actuator inside of a dewar for cryogenic testing. No image credits.

    Next we have some fancy-looking lenses. Because APOGEE works with infrared wavelengths, the lenses have to be made out of substances that are transparent to infrared light, not visible light. As a result, they are actually opaque at visible wavelengths. In the picture below, the lens appears green to us, but this fused silicon lens would be see-through if we had infrared-sensitive eyes.

    This is one of the APOGEE-2S spectrograph’s lenses (there are six of them in total) up close. It is made of fused silicon, and is transparent to infrared light.

    New England Optical Systems installed these lenses into the camera barrels — the black cylinders shown below — which will be attached to form the spectrograph’s camera (see further below).

    In November, New England Optical Systems finished installing the lenses into the camera barrel.

    As of just a few days ago, the camera is now fully assembled, and is currently undergoing tests to ensure that it is working to specifications.

    The spectrograph camera is fully assembled, and undergoing a test called laser unequal path interferometry (LUPI for short).

    This little photojournal makes building a multi-million dollar spectrograph look so neat and tidy! One final picture to disillusion you. Below is Matt Hall, one of the technicians at the University of Virginia assisting with the build. In this picture, he is testing springs that are used to hold some of the lenses in place. It sounds strange that springs are part of a lens system; but because the APOGEE-2S spectrograph is going to be cooled cryogenically, the lenses will all shrink a little. These springs apply pressure to the edges of the lenses so that they stay in place when they shrink.

    This picture illustrates the secret to building instruments like the APOGEE-2S spectrograph: every big piece, like the collimator or camera, is made up of dozens or even hundreds of small, interconnected and interdependent pieces. And each little piece has to be built and tested to ensure that it does its job properly. So here’s to the people, both in Chile and in the U.S., who are currently dedicating their time and effort to build the best spectrograph possible. We look forward to making good use of it!

    Matt Hall (UVa) is seen here testing the spring constants of individual spring plungers. As with every small part of the build, it is dealt with meticulously and thoroughly so that the completed spectrograph works at the highest level possible.

    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 9:08 am on April 7, 2014 Permalink | Reply
    Tags: , , , , , SDSS-III   

    From Brookhaven Lab: “Astronomers from the Sloan Digital Sky Survey Make the Most Precise Measurement Yet of the Expanding Universe” 

    Brookhaven Lab

    April 7, 2014
    Contacts: Chelsea Whyte, (631) 344-8671 or Peter Genzer, (631) 344-3174

    Astronomers from the Sloan Digital Sky Survey have used 140,000 distant quasars to measure the expansion rate of the Universe when it was only one-quarter of its present age. This is the best measurement yet of the expansion rate at any epoch in the last 13 billion years.

    “Quasars in BOSS measure the expansion history of the universe just before the dark energy should have kicked in. If there is funny business going on in the universe at that time, we should be able to detect that!”
    — Anže Slosar

    The Baryon Oscillation Spectroscopic Survey (BOSS), the largest component of the third Sloan Digital Sky Survey (SDSS-III), pioneered the technique of measuring the structure of the young Universe by using quasars to map the distribution of intergalactic hydrogen gas. Today, new BOSS observations of this structure were presented at the April 2014 meeting of the American Physical Society in Savannah, GA.

    These latest results combine two different methods of using quasars and intergalactic gas to measure the rate of expansion of the Universe. The first analysis, by Andreu Font-Ribera (Lawrence Berkeley National Laboratory) and collaborators, compares the distribution of quasars to the distribution of hydrogen gas to measure distances in the Universe. A second analysis team led by Timothée Delubac (Centre de Saclay, France) focused on the patterns in the hydrogen gas itself to measure the distribution of mass in the young Universe. Together the two BOSS analyses establish that 10.8 billion years ago, the Universe was expanding by one percent every 44 million years.

    Brookhaven’s Role in the BOSS Findings

    Brookhaven cosmologists Erin Sheldon and Anže Slosar made significant contributions to the recent BOSS results.

    Erin Sheldon was instrumental in making sure that the experiment observed the correct objects in the sky. In every field of view of the telescope, there are hundreds of thousands of celestial objects that can be observed, but the instrument can look at only 1000 objects at a time. Sheldon and collaborators selected appropriate targets for the telescope, including galaxies and quasars that reside in the cosmos at a distance useful for determining what is driving the expansion of the universe.

    “It’s fun to see all our years of groundwork lead to such beautiful and interesting results,” Sheldon said.

    Anže Slosar is a senior author on both papers and led one of the two analyses that discovered the baryon acoustic oscillations a year ago.

    “These measurements are a real improvement over what we had only a few months ago, so it is amazing to see how fast the field progresses,” he said. “Everybody hopes that one day we will see definite evidence that dark energy is not a static vacuum energy, but something more dynamic.”

    Dark energy is the mysterious force that cosmologists hypothesize is driving the accelerating expansion of the universe. “Quasars in BOSS measure the expansion history of the universe just before the dark energy should have kicked in,” Slosar said. “If there is funny business going on in the universe at that time, we should be able to detect that!”

    “If we look back to the Universe when galaxies were three times closer together than they are today, we’d see that a pair of galaxies separated by a million light-years would be drifting apart at a speed of 68 kilometers per second as the Universe expands,” says Font-Ribera.

    Delubac explains that “we have measured the expansion rate in the young Universe with an unprecedented precision of 2 percent.” Measuring the expansion rate of the Universe over its entire history is key in determining the nature of the dark energy that is responsible for causing this expansion rate to increase during the past six billion years. “By probing the Universe when it was only a quarter of its present age, BOSS has placed a key anchor to compare to more recent expansion measurements as dark energy has taken hold,” says Delubac.

    BOSS determines the expansion rate at a given time in the Universe by measuring the size of baryon acoustic oscillations (BAO), a signature imprinted in the way matter is distributed, resulting from sound waves in the early Universe. This imprint is visible in the distribution of galaxies, quasars, and intergalactic hydrogen throughout the cosmos.

    “Three years ago, BOSS used 14,000 quasars to demonstrate we could make the biggest 3-D maps of the Universe,” says David Schlegel (Lawrence Berkeley National Laboratory), principal investigator of BOSS. “Two years ago, with 48,000 quasars, we first detected baryon acoustic oscillations in these maps. Now, with more than 140,000 quasars, we’ve made extremely precise measures of BAO.”

    As the light from a distant quasar passes through intervening hydrogen gas distributed throughout the Universe, patches of greater density absorb more light. Each absorbing patch absorbs light from the spectrum of the quasar at a characteristic wavelength of neutral hydrogen. As the Universe expands, the quasar spectrum is stretched out, and each subsequent patch leaves its absorption mark at a different relative wavelength. The quasar spectrum is finally observed on Earth by BOSS, and it contains the signatures of all the patches encountered by the quasar light. Astronomers then measure from the quasar spectrum how much the Universe has expanded since the light passed through each patch of hydrogen.

    With enough good quasar spectra, close enough together, the position of the gas clouds can be mapped in three dimensions. BOSS determines the expansion rate by using these maps to measure the size of the BAO pattern at different epochs of cosmic time. These new measurements provide key data for astronomers seeking the nature of the dark energy postulated to be driving the increase in the expansion rate of the Universe.

    David Schlegel remarks that when BOSS was first getting underway, precision measurements using quasars and the Lyman-alpha forest had been suggested, but “som\begin{equi}

    \end{equi}e of us were afraid it wouldn’t work. We were wrong. Our precision measurements are even better than we optimistically hoped for.”

    About SDSS-III

    Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy’s Office of Science. This research used resources of the National Energy Research Scientific Computing Center (NERSC), which is supported by the Office of Science. Visit SDSS-III at http://www.sdss3.org.

    SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, University of Cambridge, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University.
    Andreu Font-Ribera, Lawrence Berkeley National Laboratory, afont@lbl.gov, 1-510-332-0635
    Timothee Delubac, Ecole Polytechnique Federale de Lausanne (Switzerland), timothee.delubac@epfl.ch, +44 22 379 2474
    David Schlegel, Lawrence Berkeley National Laboratory, djschlegel@lbl.gov, 1-510-495-2595
    Michael Wood-Vasey, SDSS-III Spokesperson, University of Pittsburgh, wmwv@pitt.edu, 1-412-624-2751
    Jordan Raddick, SDSS-III Public Information Officer, Johns Hopkins University, raddick@jhu.edu, 1-410-516-8889

    See the full article here.

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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