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  • richardmitnick 7:02 am on September 26, 2017 Permalink | Reply
    Tags: , , , , , , Is S0-2 a Binary Star?   

    From astrobites: “Is S0-2 a Binary Star?” 

    Astrobites bloc


    Sep 26, 2017
    Philipp Plewa

    Title: Investigating the Binarity of S0-2: Implications for its Origins and Robustness as a Probe of the Laws of Gravity around a Supermassive Black Hole
    Authors: D. S. Chu, T. Do, A. Hees, A. Ghez, S. Naoz, G. Witzel, S. Sakai, S. Chappell, A. K. Gautam, J. R. Lu, K. Matthews
    First Author’s Institution: Department of Physics and Astronomy, University of California, Los Angeles

    Status: Submitted to The Astrophysical Journal, open access

    S0–102 is a star that is located very close to the centre of the Milky Way, near the radio source Sgr A*, orbiting it with an orbital period of 11.5 years. As of 2012 it is the star with the shortest known period orbiting the black hole at the centre of the Milky Way. This beat the record of 15 years previously set by S0–2. The star was identified by a University of California, Los Angeles team headed by Andrea M. Ghez.

    Andrea Ghez, UCLA

    At its periapsis, its speed exceeds 1% of the speed of light.[3] At that point it is 260 astronomical units (36 light hours, 38.9 billion km) from the centre, while the black hole radius is less than one thousandth of that size (11 million km). It passed that point in 2009 and will be there again in 2020.

    The most exciting discoveries in astronomy all have something in common: They let us marvel at the fact that nature obeys laws of physics. The discovery of S0-2 is one of them. S0-2 (also known as S2) is a fast-moving star that has been observed to follow a full elliptical, 16-year orbit around the Milky Way’s central supermassive black hole, precisely according to Kepler’s laws of planetary motion. Serving as a test particle probe of the gravitational potential, S0-2 provides some of the best constraints on the black hole’s mass and distance yet, being the brightest of the S-stars, which are a group of young main-sequence stars concentrated within the inner 1” (0.13 ly) of the nuclear star cluster.

    The next time S0-2 will reach its closest approach to the black hole, in 2018, there will exist a unique opportunity to detect a deviation from Keplerian motion, namely the relativistic redshift of S0-2’s radial (line-of-sight) velocity, in a direct measurement. In anticipation of this event, the authors of today’s paper investigate possible consequences of S0-2 not being a single star, but a spectroscopic binary, which would complicate this measurement.

    Figure 1: Top: Radial velocity measurements of S0-2 over time. Bottom: Residual velocities after subtraction of the best-fit model for the orbital motion.

    To search for any periodicity in S0-2’s radial velocity curve that would indicate the presence of a companion star, the authors combine their most recent velocity measurements with previous ones obtained as part of monitoring programs carried out at both the WMKO in Hawaii and the VLT in Chile.

    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft) above sea level

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

    The resulting data set consists of 87 measurements in total, which are spread over 17 years of observations and have a typical uncertainty of a few 10 km/s (Figure 1, top panel). When S0-2 passes the black hole, the relativistic redshift of its radial velocity is predicted to amount to roughly 200 km/s at closest approach, while the radial velocity is expected to change from +4000 to -2000 km/s. S0-2’s actual speed at this time will be close to 8000 km/s, about 2.7% of the speed of light.

    See more at the full article.

    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 6:34 am on September 26, 2017 Permalink | Reply
    Tags: Ageing Star Blows Off Smoky Bubble, , , , , , ,   

    From ALMA: “Ageing Star Blows Off Smoky Bubble” 

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    20 September 2017

    Nicolás Lira
    Education and Public Outreach Coordinator
    Joint ALMA Observatory, Santiago – Chile
    Phone: +56 2 2467 6519
    Cell: +56 9 9445 7726

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

    Francisco Rodríguez I.
    ESO Press Officer in Chile
    Santiago, Chile
    +56 2 24633019

    Astronomers have used ALMA to capture a strikingly beautiful view of a delicate bubble of expelled material around the exotic red star U Antliae. These observations will help astronomers to better understand how stars evolve during the later stages of their life-cycles.

    In the faint southern constellation of Antlia (The Air Pump) the careful observer with binoculars will spot a very red star, which varies slightly in brightness from week to week. This very unusual star is called U Antliae and new observations with the Atacama Large Millimeter/submillimeter Array (ALMA) are revealing a remarkably thin spherical shell around it.

    This image was created from ALMA data on the unusual red carbon star U Antliae and its surrounding shell of material. The colours show the motion of the glowing material in the shell along the line of sight to the Earth. Blue material lies between us and the central star, and is moving towards us. Red material around the edge is moving away from the star, but not towards the Earth.
    For clarity this view does not include the material on the far side of the star, which is receding from us in a symmetrical manner. Credit: ALMA (ESO/NAOJ/NRAO), F. Kerschbaum

    Astronomers have used ALMA to capture a strikingly beautiful view of a delicate bubble of expelled material around the exotic red star U Antliae. These observations will help astronomers to better understand how stars evolve during the later stages of their life-cycles.
    This short podcast takes a look at this important new result and what it means. Credit:ESO.
    Directed by: Nico Bartmann.
    Editing: Nico Bartmann.
    Web and technical support: Mathias André and Raquel Yumi Shida.
    Written by: Izumi Hansen and Richard Hook.
    Music: Colin Rayment & Stan Dart.
    Footage and photos: ESO, spaceengine.org, NASA, SDO, M.Kornmesser, ALMA (ESO/NAOJ/NRAO), F. Kerschbaum.
    Executive producer: Lars Lindberg Christensen.

    U Antliae [1] is a carbon star, an evolved, cool and luminous star of the asymptotic giant branch type. Around 2700 years ago, U Antliae went through a short period of rapid mass loss. During this period of only a few hundred years, the material making up the shell seen in the new ALMA data was ejected at high speed. Examination of this shell in further detail also shows some evidence of thin, wispy gas clouds known as filamentary substructures.

    This spectacular view was only made possible by the unique ability to create sharp images at multiple wavelengths that is provided by the ALMA radio telescope, located on the Chajnantor Plateau in Chile’s Atacama Desert, at 5,000 metres. ALMA can see much finer structure in the U Antliae shell than has previously been possible.

    The new ALMA data are not just a single image; ALMA produces a three-dimensional dataset (a data cube) with each slice being observed at a slightly different wavelength. Because of the Doppler Effect, this means that different slices of the data cube show images of gas moving at different speeds towards or away from the observer. This shell is also remarkable as it is very symmetrically round and also remarkably thin. By displaying the different velocities we can cut this cosmic bubble into virtual slices just as we do in computer tomography of a human body.

    Understanding the chemical composition of the shells and atmospheres of these stars, and how these shells form by mass loss, is important to properly understand how stars evolve in the early Universe and also how galaxies evolved. Shells such as the one around U Antliae show a rich variety of chemical compounds based on carbon and other elements. They also help to recycle matter, and contribute up to 70% of the dust between stars.

    [1] The name U Antliae reflects the fact that it is the fourth star that changes its brightness to be found in the constellation of Antlia (The Air Pump). The naming of such variable stars followed a complicated sequence as more and more were found and is explained here.
    More information

    This research was presented in a paper entitled Rings and filaments. The remarkable detached CO shell of U Antliae, by F. Kerschbaum et al., to appear in the journal Astronomy & Astrophysics.

    The team is composed of F. Kerschbaum (University of Vienna, Austria), M. Maercker (Chalmers University of Technology, Onsala Space Observatory, Sweden), M. Brunner (University of Vienna, Austria), M. Lindqvist (Chalmers University of Technology, Onsala Space Observatory, Sweden), H. Olofsson (Chalmers University of Technology, Onsala Space Observatory, Sweden), M. Mecina (University of Vienna, Austria), E. De Beck (Chalmers University of Technology, Onsala Space Observatory, Sweden), M. A. T. Groenewegen (Koninklijke Sterrenwacht van België, Belgium), E. Lagadec (Observatoire de la Côte d’Azur, CNRS, France), S. Mohamed (University of Cape Town, South Africa), C. Paladini (Université Libre de Bruxelles, Belgium), S. Ramstedt (Uppsala University, Sweden), W. H. T. Vlemmings (Chalmers University of Technology, Onsala Space Observatory, Sweden), and M. Wittkowski (ESO)

    The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

    ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

    See the full article here .

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    The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan.

    ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

    NRAO Small
    ESO 50 Large

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    ESO Bloc Icon

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

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

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

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

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

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

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

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

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

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

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

    ESO Next Generation Transit Survey at Cerro Paranel, 2,635 metres (8,645 ft) above sea level

    SPECULOOS four 1m-diameter robotic telescopes 2016 in the ESO Paranal Observatory, 2,635 metres (8,645 ft) above sea level

    ESO TAROT telescope at Paranal, 2,635 metres (8,645 ft) above sea level

  • richardmitnick 8:05 pm on September 25, 2017 Permalink | Reply
    Tags: , , , , , , , , , DM axions, , , , The origin of solar flares,   

    From CERN Courier: “Study links solar activity to exotic dark matter” 

    CERN Courier

    Solar-flare distributions

    The origin of solar flares, powerful bursts of radiation appearing as sudden flashes of light, has puzzled astrophysicists for more than a century. The temperature of the Sun’s corona, measuring several hundred times hotter than its surface, is also a long-standing enigma.

    A new study suggests that the solution to these solar mysteries is linked to a local action of dark matter (DM). If true, it would challenge the traditional picture of DM as being made of weakly interacting massive particles (WIMPs) or axions, and suggest that DM is not uniformly distributed in space, as is traditionally thought.

    The study is not based on new experimental data. Rather, lead author Sergio Bertolucci, a former CERN research director, and collaborators base their conclusions on freely available data recorded over a period of decades by geosynchronous satellites. The paper presents a statistical analysis of the occurrences of around 6500 solar flares in the period 1976–2015 and of the continuous solar emission in the extreme ultraviolet (EUV) in the period 1999–2015. The temporal distribution of these phenomena, finds the team, is correlated with the positions of the Earth and two of its neighbouring planets: Mercury and Venus. Statistically significant (above 5σ) excesses of the number of flares with respect to randomly distributed occurrences are observed when one or more of the three planets find themselves in a slice of the ecliptic plane with heliocentric longitudes of 230°–300°. Similar excesses are observed in the same range of longitudes when the solar irradiance in the EUV region is plotted as a function of the positions of the planets.

    These results suggest that active-Sun phenomena are not randomly distributed, but instead are modulated by the positions of the Earth, Venus and Mercury. One possible explanation, says the team, is the existence of a stream of massive DM particles with a preferred direction, coplanar to the ecliptic plane, that is gravitationally focused by the planets towards the Sun when one or more of the planets enter the stream. Such particles would need to have a wide velocity spectrum centred around 300 km s–1 and interact with ordinary matter much more strongly than typical DM candidates such as WIMPs. The non-relativistic velocities of such DM candidates make planetary gravitational lensing more efficient and can enhance the flux of the particles by up to a factor of 106, according to the team.

    Co-author Konstantin Zioutas, spokesperson for the CAST experiment at CERN, accepts that this interpretation of the solar and planetary data is speculative – particularly regarding the mechanism by which a temporarily increased influx of DM actually triggers solar activity.

    CERN CAST Axion Solar Telescope

    However, he says, the long persisting failure to detect the ubiquitous DM might be due to the widely assumed small cross-section of its constituents with ordinary matter, or to erroneous DM modelling. “Hence, the so-far-adopted direct-detection concepts can lead us towards a dead end, and we might find that we have overlooked a continuous communication between the dark and the visible sector.”

    Models of massive DM streaming particles that interact strongly with normal matter are few and far between, although the authors suggest that “antiquark nuggets” are best suited to explain their results. “In a few words, there is a large ‘hidden’ energy in the form of the nuggets,” says Ariel Zhitnitsky, who first proposed the quark-nugget dark-matter model in 2003. “In my model, this energy can be precisely released in the form of the EUV radiation when the anti-nuggets enter the solar corona and get easily annihilated by the light elements present in such a highly ionised environment.”

    The study calls for further investigation, says researchers. “It seems that the statistical analysis of the paper is accurate and the obtained results are rather intriguing,” says Rita Bernabei, spokesperson of the DAMA experiment, which for the first time in 1998 claimed to have detected dark matter in the form of WIMPs on the basis of an observed seasonal modulation of a signal in their scintillation detector.

    DAMA-LIBRA at Gran Sasso

    “However, the paper appears to be mostly hypothetical in terms of this new type of dark matter.”

    The team now plans to produce a full simulation of planetary lensing taking into account the simultaneous effect of all the planets in the solar system, and to extend the analysis to include sunspots, nano-flares and other solar observables. CAST, the axion solar telescope at CERN, will also dedicate a special data-taking period to the search for streaming DM axions.

    “If true, our findings will provide a totally different view about dark matter, with far-reaching implications in particle and astroparticle physics,” says Zioutas. “Perhaps the demystification of the Sun could lead to a dark-matter solution also.”

    Further reading

    S Bertolucci et al. 2017 Phys. Dark Universe 17 13. Elsevier


    See the full article here .

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    CERN CMS New

    CERN LHCb New II


    CERN LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles

  • richardmitnick 7:40 pm on September 25, 2017 Permalink | Reply
    Tags: Messier Monday, ,   

    From Universe Today: “Messier 57 – The Ring Nebula” 


    Universe Today

    25 Sept , 2017
    Tammy Plotner

    Hubble image of the Ring Nebula (aka. Messier 57). Credit: NASA/ESA/ Hubble Heritage (STScI/AURA) – ESA /Hubble Collaboration

    Welcome back to Messier Monday! We continue our tribute to our dear friend, Tammy Plotner, by looking at the the Big Ring itself, the planetary nebula known as Messier 57. Enjoy!

    In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. In time, he would come to compile a list of approximately 100 of these objects, with the purpose of making sure that astronomers did not mistake them for comets. However, this list – known as the Messier Catalog – would go on to serve a more important function.

    One of these objects is known as Messier 57, a planetary nebula that is also known as the Ring Nebula. This object is located about 2,300 light years from Earth in the direction of the Lyra constellation. Because of its proximity to Vega, the brightest star in Lyra and one of the stars that form the Summer Triangle, the nebula is relatively easy to find using binoculars or a small telescope.

    What You Are Looking At:

    Here you see the remainders of a sun-like star… At one time in its life, it may have had twice the mass of Sol, but now all that’s left is a white dwarf that burns over 100,000 degrees kelvin. Surrounding it is an envelope about 2 to 3 light years in size of what once was its outer layers – blown away in a cylindrical shape some 6000 to 8000 years ago. Like looking down the barrel of a smoking gun, we’re looking back in time at the end of a Mira-like star’s evolutionary phase.

    It’s called a planetary nebula, because once upon a time before telescopes could resolve them, they appeared almost planet-like. But, as for M57, the central star itself is no larger than a terrestrial planet! The tiny white dwarf star, although it could be as much as 2300 light years away, has an intrinsic brightness of about 50 to 100 times that of our Sun.

    Much more at the full article.

    See the full article here .

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  • richardmitnick 2:51 pm on September 25, 2017 Permalink | Reply
    Tags: , , , , , Discovery of Two More Runaway Stars   

    From AAS NOVA: “Discovery of Two More Runaway Stars” 


    American Astronomical Society

    25 September 2017
    Susanna Kohler

    Hubble has detected the fastest moving hypervelocity star, even faster than the blue stellar torpedoes caught in 2009. This one moves at 1,600,000mph (2.5 million km/h).

    Speeding stars running away from our galaxy pose an intriguing puzzle: where did these stars come from, and how were they accelerated to their great speeds? The recent discovery of two new runaway stars have increased the mystery.

    Unexplained Speeders

    Hypervelocity stars are rare objects that zip along at unusually high speeds — fast enough to escape the gravitational pull of our galaxy. More than 20 hypervelocity stars have been discovered since the first one was found serendipitously in 2005. But what accelerates these strange stars?

    One of the most commonly proposed scenarios is that these objects originated near the center of the Milky Way, and were flung out as a result of dynamical interactions with the central supermassive black hole. Other explanations exist, however — for instance, these stars could be the tidal debris of an accreted and disrupted dwarf galaxy, or they could be the surviving companion stars kicked out in Type Ia supernovae.

    Besides wanting to better understand the origin of hypervelocity stars, scientists also care about these speedy objects because of the information they provide about the Milky Way. Measuring the three-dimensional motions of hypervelocity stars can give us a detailed look at the mass distribution of our galaxy — thereby revealing the shape of the Milky Way’s dark matter halo.

    The radial velocities and locations of the three LAMOST-detected hypervelocity stars (red), compared to the other 24 known hypervelocity stars (blue). The dashed lines represent two models for the galactic escape velocity curve. [Huang et al. 2017]

    For these reasons, scientists have conducted a number of systematic searches for hypervelocity stars to build up our sample size. Results from the most recent of these searches, conducted by examining the spectroscopic survey data of 6.5 million stars from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST), have now been described in a publication led by Yang Huang (Yunnan University and Peking University).

    LAMOST telescope located in Xinglong Station, Hebei Province, China

    Huang and collaborators narrowed the LAMOST data down to 126 high-mass hypervelocity star candidates. Using distance measurements, they determined the stars’ velocities in the galactic rest frame and eliminated all stars not moving faster than the galactic escape speed. This left three true hypervelocity stars: one that had been previously found in another study, and two that are new discoveries.

    The spatial distribution of the confirmed hypervelocity stars, with the LAMOST detections shown in red and the other 24 known hypervelocity stars shown in blue. The great circles represent planes of young stellar structures near the galactic center. [Huang et al. 2017]

    Conflicting Results

    The authors show that the three detected hypervelocity stars are spatially associated with known young stellar structures near the galactic center, supporting a galactic-center origin for hypervelocity stars. But they also find that the time it would have taken two of these stars to travel to their current locations from the galactic center is longer than the stars’ expected lifetimes, posing a new puzzle.

    Huang and collaborators suggest that upcoming accurate proper motion measurements of these stars, expected in the next data release from the Gaia mission, will provide direct constraints on their origins.

    ESA/GAIA satellite

    In the meantime, continued systematic searches for hypervelocity stars such as that presented here will ensure that we have a large sample of these speeding objects ready for Gaia’s analysis.


    Y. Huang et al 2017 ApJL 847 L9. doi:10.3847/2041-8213/aa894b

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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.

    Adopted June 7, 2009

  • richardmitnick 12:08 pm on September 25, 2017 Permalink | Reply
    Tags: , , , , , Counting the Dwarf Galaxies of the Milky Way,   

    From astrobites: “Counting the Dwarf Galaxies of the Milky Way” 

    Astrobites bloc


    Sep 25, 2017
    Stacy Kim

    Title: The total satellite population of the Milky Way
    Authors: O. Newton, M. Cautum, A. Jenkins, C. S. Frenk and J. C. Helly
    First Author’s Institution: Institute of Computational Cosmology, Durham University, Durham, UK
    Status: Submitted to MNRAS, open access

    Our home galaxy, the Milky Way, is surrounded by small, “dwarf” galaxies. Astronomers are obsessed with counting how many exist. Why? In the 1990s, we realized that the prevailing view of the universe as one primarily composed of dark energy and dark matter, called LCDM for short, predicts that the Milky Way should be surrounded by a vast horde of at least a hundred. But perplexingly, we saw only 11 dwarf galaxies. This stark discrepancy has fueled much consternation and many papers, and has been dubbed the “missing satellites problem.”

    Since then, it’s been recognized that not all satellites found in simulations form bright galaxies that we can detect. The smallest satellites, in particular, can’t hold onto enough cold gas—the material from which stars are born—to form enough stars to make the galaxy detectable. In addition, bigger and better telescopes that scanned wide portions of the sky have turned up more dwarf galaxies. The Sloan Digital Sky Survey (SDSS) found almost 20 new satellites, bringing the total up to about 30.

    SDSS Telescope at Apache Point Observatory, NM, USA

    The ongoing survey called Dark Energy Survey (DES), which surveys the southern skies, has found almost 20 more, and promises to yield 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 at an altitude of 7200 feet

    Additional discoveries by other surveys have pushed the number up to about 55—a drastic increase from the 11 originally known, but still short of 100.

    But the surveys pointed to a solution. Both SDSS and DES only observed part of the sky—SDSS covered about a third, and DES will eventually cover a tenth of the sky—so what if there were more in the regions we hadn’t looked? And while both surveys were powerful, they could only see the faintest dwarfs only if they were close. While the Milky Way is about 300 kiloparsecs in size, we can only see the faintest dwarfs about 30-40 kiloparsecs away from us—only about 0.1% of the entire Milky Way volume. To determine the true number of dwarfs in the Milky Way, the authors of today’s paper attempted to correct for the number we can’t see. This is called a “completeness correction.”

    To do this, the authors turned to the Aquarius Project, a simulation suite with six realizations of the Milky Way, each run with dark matter only and thus without the bright disk of stars and gas that make up the familiar, visible portion of the galaxy (which only makes up about a fifth of the mass of the galaxy, anyway). For each realization, they made a list of all the satellite galaxies they could find. The authors corrected these lists for a couple pieces of physics the simulations did not include. Satellites orbiting the Milky Way are typically stripped of mass due to the Milky Way’s greater gravitational pull. This can cause satellites to drop below the resolution of the simulation, and artificially disappear. The un-simulated disk of the Milky Way can severely strip satellites of mass to the point where they are destroyed. The authors considered how to account for these physics, and carefully added or subtracted satellites to make up for them.

    With the satellite lists in hand, they could finally begin their completeness corrections. For each galaxy we’ve observed with SDSS and DES, the authors determined how much of the Milky Way volume we could see it out to, then asked, “How far down the list of satellites do we need to go before we’d see one in that volume?” After going through each observed galaxy, they got an overall total. The authors repeated this exercise, randomizing the list of simulated satellites each time for each of the 6 simulated Milky Ways in order to determine a reasonable range for the true number of satellites.

    Figure 1. The number of dwarf galaxies around the Milky Way. The number that’s been observed as a function of how bright the galaxies are is shown by the black dashed line, while the number the authors extrapolated using dwarfs observed in SDSS and DES are shown via the purple line. Extrapolations with only SDSS or only DES dwarfs are shown the dotted blue and green lines, respectively. Figure taken from today’s paper.

    And what did they find? The Milky Way should host about 108-195 total dwarfs. It thus looks like the missing satellites problem might not be so bad after all. With future surveys covering the entire sky, such as the Large Synoptic Survey Telescope coming online soon, we are close to being able to measure—instead of extrapolating—the total number of Milky Way satellites, and determine once and for all whether the missing satellites problem exists.


    LSST Camera, built at SLAC

    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.

    On its way to assembling the most detailed 3D map ever made of our Galaxy, ESA’s Gaia spacecraft has pinned down the precise position on the sky and the brightness of 1.142 billion stars, and in addition measured the velocity and distance of two million of them relative to the Sun. Image credit: ESA / Gaia / DPAC / A. Moitinho & M. Barros, CENTRA – University of Lisbon.

    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 11:29 am on September 25, 2017 Permalink | Reply
    Tags: , , , , , ,   

    From U Wisconsin IceCube: “Looking for new physics in the neutrino sector” 

    U Wisconsin IceCube South Pole Neutrino Observatory

    25 Sep 2017
    Sílvia Bravo

    ICECUBE neutrino detector

    Neutrinos are intriguing in more ways than one. And although the fact that they have such tiny mass explains their quirky behavior, their allure remains intact. The issue is that neutrino masses are not predicted by the Standard Model; thus, on its own, the existence of a neutrino with mass is an indication of new physics. And that’s what scientists around the world, including at IceCube, want to learn: what type of new physics are neutrinos pointing to?

    New physics could appear in the form of a new type of neutrino or it could help us understand the nature of dark matter. The possibilities are endless. In a new search for nonstandard neutrino interactions, the IceCube Collaboration has tested theories that introduce heavy bosons, such as some Grand Unified Theories. These heavy bosons would explain, for example, why neutrinos have masses much smaller than their lepton partners. The study resulted in new constraints on these models, which are among the world’s best limits for nonstandard interactions in the muon-tau neutrino sector. These results have just been submitted to Physical Review D.

    Confidence limits from this analysis are shown as solid vertical red lines. The light blue and light green vertical lines show previous limits by Super-Kamiokande and another study using IceCube data at higher energy. Credit: IceCube Collaboration.

    Super-Kamiokande experiment. located under Mount Ikeno near the city of Hida, Gifu Prefecture, Japan

    The flavor of neutrinos oscillates as they travel through matter or empty space, a quantum effect on macroscopic scales that proves that they have mass. When atmospheric neutrinos reach IceCube after crossing the Earth, they have often morphed from muon into tau neutrinos. If TeV-scale bosons predicted by nonstandard theories exist, they will modify the probability that a given type of neutrino oscillates into other types. The result is that the disappearance pattern of muon neutrinos in IceCube will change, with effects that span a large range of energies.

    In IceCube, for studies using atmospheric neutrinos that sail through the Earth, these nonstandard interactions (NSIs) can be parametrized in terms of the strength of muon neutrino to tau neutrino morphing due to an NSI, a parameter called .

    IceCube researchers have analyzed three years of data, using the same neutrino sample used for a recent measurement of the neutrino oscillation parameters, but with an additional selection criterion to improve the signal purity. The remaining 4,625 candidate neutrino events were used to fit the oscillation parameters, including the NSI contribution.

    The best fit of muon to tau NSI oscillations was consistent with no nonstandard interactions. “Even though no new physics was shown by this study, it narrows in on the possible existence of new neutrino interactions with regular matter” says Carlos Argüelles, an IceCube researcher from MIT. “It also showcases the advantages of having a very broad energy range, so experiments like IceCube can look for new oscillation physics with neutrinos, which are 10 to 1000 times more energetic than the average proton.”

    The 90% confidence level upper limit on the NSI parameter is consistent with previous measurements by Super-Kamiokande, which at that time had set the world’s best limits. The new IceCube measurement slightly improves Super-Kamiokande’s measurements, also extending the energy range. A more recent study using published IceCube data at even higher energies has also set limits on the parameter, which in turn were slightly more stringent than the ones of the present study.

    Albrecht Karle, a professor of physics at UW–Madison, comments that “the results shown here are based on only a relatively small set of muon neutrinos available.” IceCube is collecting more than 100,000 muon neutrinos per year, which are yet to be mined for physics beyond the Standard Model. “With almost a million atmospheric neutrinos, IceCube has an incredible data set for investigating even small deviations from Standard Model physics.”

    And keeping in mind that it’s not all about the detector, Melanie Day, another IceCube researcher and co-author on this paper, adds, “Not enough is said about the value of teamwork and collaboration over individual contributions to scientific results. But without that, this result would not have been possible.”

    See the full article here .

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    IceCube is a particle detector at the South Pole that records the interactions of a nearly massless sub-atomic particle called the neutrino. IceCube searches for neutrinos from the most violent astrophysical sources: events like exploding stars, gamma ray bursts, and cataclysmic phenomena involving black holes and neutron stars. The IceCube telescope is a powerful tool to search for dark matter, and could reveal the new physical processes associated with the enigmatic origin of the highest energy particles in nature. In addition, exploring the background of neutrinos produced in the atmosphere, IceCube studies the neutrinos themselves; their energies far exceed those produced by accelerator beams. IceCube is the world’s largest neutrino detector, encompassing a cubic kilometer of ice.

  • richardmitnick 11:07 am on September 25, 2017 Permalink | Reply
    Tags: , , Double-blind peer review, Nature Publishing Group (NPG) in London,   

    From Science: “Few authors choose anonymous peer review, massive study of Nature journals shows 


    Sep. 22, 2017
    Martin Enserink

    Scientists from India and China far more often ask Nature’s journals for double-blind peer review than those from Western countries. Emily Petersen

    Once you’ve submitted your paper to a journal, how important is it that the reviewers know who wrote it?

    Surveys have suggested that many researchers would prefer anonymity because they think it would result in a more impartial assessment of their manuscript. But a new study by the Nature Publishing Group (NPG) in London shows that only one in eight authors actually chose to have their reviewers blinded when given the option. The study, presented here at the Eighth International Congress on Peer Review, also found that papers submitted for double-blind review are far less likely to be accepted.

    Most papers are reviewed in single-blind fashion—that is, the reviewers know who the authors are, but not vice versa. In theory, that knowledge allows them to exercise a conscious or unconscious bias against researchers from certain countries, ethnic minorities, or women, and be kinder to people who are already well-known in their field. Double-blind reviews, the argument goes, would remove those prejudices. A 2007 study of Behavioral Ecology found that the journal published more articles by female authors when using double-blind reviews—although that conclusion was challenged by other researchers a year later. In a survey of more than 4000 researchers published in 2013, three-quarters said they thought double-blind review is “the most effective method.”

    But that approach also has drawbacks. Journals have checklists for authors on how to make a manuscript anonymous by avoiding phrases like “we previously showed” and by removing certain types of meta-information from computer files—but some researchers say they find it almost impossible to ensure complete anonymity.

    “If I am going to remove every trace that could identify myself and my coauthors there wouldn’t be much left of the paper,” music researcher Alexander Jensenius from the University of Oslo wrote on his blog. Indeed, experience shows that reviewers can sometimes tell who wrote a paper, based on previous work or other information. At Conservation Biology, which switched to double-blind reviews in 2014, reviewers who make a guess get it right about half of the time, says the journal’s editor, Mark Burgman of Imperial College London. “But that’s not the end of the world,” he says. Double-blind review, he says, “sends a message that you’re determined to try and circumvent any unconscious bias in the review process.”

    In 2013 NPG began offering its authors anonymous peer review as an option for two journals, Nature Geoscience and Nature Climate Change. Only one in five authors requested it, Nature reported 2 years later—far less than editors had expected. But the authors’ reactions were so positive that NPG decided to expand the option to all of its journals.

    At the peer review congress last week, NPG’s Elisa De Ranieri presented data on 106,373 submissions to the group’s 25 Nature-branded journals between March 2015 and February 2017. In only 12% of cases did the authors opt for double-blind review. They chose double-blind reviews most often for papers in the group’s most prestigious journal, Nature (14%), compared to 12% for Nature “sister journals” and 9% for the open-access journal Nature Communications.

    The data suggest that concerns about possible discrimination may have been a factor. Some 32% of Indian authors and 22% of Chinese authors opted for double-blind review, compared with only 8% of authors from France and 7% from the United States. The option was also more popular among researchers from less prestigious institutes, based on their 2016 Times Higher Education rankings. There was no difference in the choices of men and women, De Ranieri noted, a finding that she called surprising.

    Burgman suspects that the demand for double-blind review is suppressed by fears that it could backfire on the author. “There’s the idea that if you go double blind, you have something to hide,” he says. That may also explain why women were not more likely to demand double blind reviews than men, he says. Burgman says he thinks making double-blind reviews the standard, as Conservation Biology has done, is the best course. “It has not markedly changed the kind or numbers of submissions we receive,” he says. “But we do get informal feedback from a lot of people who say: ‘This is a great thing.’”

    Authors choosing double-blind review in hope of improving their chances of success will be disappointed by the Nature study. Only 8% of those papers were actually sent out for review after being submitted, compared to 23% of those opting for single-blind review. (Nature’s editors decide whether to send a paper for review or simply reject it, and the editors know the identity of the authors.) And only 25% of papers under double-blind review were eventually accepted, versus 44% for papers that went the single-blind route.

    See the full article here .

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  • richardmitnick 10:43 am on September 25, 2017 Permalink | Reply
    Tags: , , Stanford scholars discuss the benefits and risks of using talking software to address mental health,   

    From Stanford: “Stanford scholars discuss the benefits and risks of using talking software to address mental health” 

    Stanford University Name
    Stanford University

    September 25, 2017
    Milenko Martinovich

    Interacting with a machine may seem like a strange and impersonal way to seek mental health care, but advances in technology and artificial intelligence are making that type of engagement more and more a reality. Online sites such as 7 Cups of Tea and Crisis Text Line are providing counseling services via web and text, but this style of treatment has not been widely utilized by hospitals and mental health facilities.

    Conversational software programs are making it possible for people to seek mental health care online and via text, but the risks and benefits need further study, Stanford experts say. (Image credit: roshinio / Getty Images)

    Stanford scholars Adam Miner, Arnold Milstein and Jeff Hancock examined the benefits and risks associated with this trend in a Sept. 21 article in the The American Medical Association. They discuss how technological advances now offer the capability for patients to have personal health discussions with devices like smartphones and digital assistants.

    Stanford News Service interviewed Miner, Milstein and Hancock about this trend.

    Why would conversational agents – software programs that converse with users through voice or text – be effective for mental health care? Which aspects of mental health care could they be applied to?

    Miner: Talking to another person about mental health can be scary and often treatment is hard to access. Conversational agents may allow people to share experiences they don’t want to talk about with another person. If successful, this technology could recognize and respond to mental health needs. People may be more honest about their symptoms.

    Hancock: They also can be available when needed. Delivering health care when it’s most needed can make these conversational agents really effective for people.

    How could interacting with this technology be more beneficial to a patient than a human mental health professional?

    Hancock: I’m not sure that it could ever be more beneficial than interacting with a human mental health professional, but they could play a role in simply being available. That is, there are only so many mental health professionals, and they can’t be of assistance to all who need them all the time. So, these programs can at least play a role in helping to triage.

    Miner: Most people don’t like feeling judged. Talking to a machine may feel like a safer way to share experiences without feeling ashamed. Also, their value may not be in being “better” than a well-trained clinician, but in their accessibility and scalability.

    Are there risks associated with this technology?

    Miner: If a user has a negative experience disclosing mental health problems to a conversational agent, he or she may be less willing to seek help in the future. Also, human-to-human connection is an important part of healing. A balance must be struck between high-tech and high-touch treatment.

    Hancock: Yes, and importantly, we don’t even know what all the risks are because the psychological aspects are so understudied. One concern is what happens over longer interactions – does the benefits of interacting with a conversational agent fade or even become negative? Could interacting with a machine over time lead to a sense of loneliness or disconnection, or even become a crutch in the form of preferring to interact with a machine than other people?

    What are some of the dangers with regards to privacy?

    Miner: Privacy is incredibly important and we have to get it right to build trust. User expectations of privacy are unclear. A conversation may feel more private, but might have a higher risk of being remembered forever or shared in unexpected ways through social media or services that track online behavior.

    Your article mentions that hundreds of thousands of people have already engaged in similar technology-based interactions – for example, 7 Cups of Tea, Talkspace. What must occur for widespread adoption at hospitals, mental health facilities, etc.?

    Milstein: Mainstream health care organizations are unlikely to adopt this innovation until there is plausible evidence of therapeutic benefit and applicability of HIPAA privacy rules is clarified.

    Miner: There is a growing demand for safe, scalable and cost-effective mental health treatment. Clinical trials can address safety and efficacy, but clarity around user expectations and rules governing medical devices are needed.

    Hancock: The success of 7 Cups of Tea and others, like Crisis Text Line, indicates that mental health through text and with the phone or computer is viable. What’s needed next is improved technology along with the required research to understand what kind of conversational agent will be most beneficial and avoid harms. Some of our research suggests that people can get the same kind of psychological benefits disclosing to a machine as to another human – at least in a one-off interaction. We still don’t know about long-term interactions, however.

    Adam Miner is an AI psychologist and instructor in Stanford’s Department of Psychiatry and Behavioral Sciences. Arnold Milstein, a professor of medicine, is the director of Stanford’s Clinical Excellence Research Center. Jeff Hancock is a professor of communication and director of the Stanford Center for Computational Social Science.

    Media Contacts
    Adam Miner, Psychiatry and Behavioral Sciences: asmpysd@stanford.edu
    Milenko Martinovich, Stanford News Service: (650) 725-9281, mmartino@stanford.edu

    See the full article here .

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    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

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  • richardmitnick 5:37 am on September 25, 2017 Permalink | Reply
    Tags: , , Australian National University, , , New partnership advances Australia’s space mission capabilities, UNSW Canberra   

    From UNSW: “New partnership advances Australia’s space mission capabilities” 

    U NSW bloc

    University of New South Wales

    25 Sep 2017
    Nick Ellis

    A UNSW Canberra agreement with the Australian National University means Australia now has the facilities to come up to speed with the international space sector.

    UNSW Canberra scientists working on a Cubesat. Photo: UNSW Canberra

    UNSW Canberra and the Australian National University (ANU) will join forces to create end-­to-­end capability for the design, assembly and testing of spacecraft for future space missions.

    The collaboration between the two universities provides joint access to world-­class facilities at UNSW Canberra Space and ANU’s Advanced Instrumentation Technology Centre (AITC).

    UNSW Canberra brings to the agreement its space engineering expertise and Australia’s first Concurrent Design Facility while AITC hosts Australia’s most sophisticated space testing facilities and expertise in spacecraft instrument design and calibration.

    “Australia has been, until now, one of the few developed countries without the ability to professionally design and deliver space missions,” said Professor Russell Boyce, Director of UNSW Canberra Space.

    “The UNSW Canberra team includes 40 highly skilled Australian space professionals from the global space sector. This includes scientists, engineers, faculty staff, postdocs and PhD students, who bring more than 150 years of experience in organisations such as ESA and NASA –­ where they designed, developed and deployed spacecraft and space instrumentation for near-­Earth and deep space programs.”

    Dr Doug Griffin, Space Mission Lead at UNSW Canberra Space, said: “Space is a big industry, it is complicated and requires a diverse, yet unique set of skills. The UNSW Canberra agreement with ANU means Australia now has the facilities to come up to speed with the international space sector.”

    UNSW Canberra’s new Concurrent Design Facility, partly funded by the ACT Government, will also partner with the French space agency CNES. An Australian first, this facility allows the country to lead the design and operation of future space missions.

    “This is an exciting time for Australian space research and innovation,” said Professor Michael Frater, Rector of UNSW Canberra. “The combination of two Group of 8 universities in the heart of the nation’s capital, focussing on space missions, will see the ACT and Australia mature as serious players on the global space stage.”

    UNSW Canberra Space already provides valuable research and technology to support national services, including Defence. UNSW Canberra’s space program, with five satellites now confirmed, demonstrates what can be done in Australia.

    Professor Boyce said: “This agreement also helps create the right environment in the ACT for space engineering to grow and deliver commercial operations. The UNSW Canberra commercial spin-­off Skykraft will provide commercial services to a growing space sector, drawing on the research at UNSW Canberra Space.

    “So, our UNSW Canberra space partnerships will service not only our teaching and research, but will feed right through to supporting national needs and commercial opportunities.

    “These agreements provide new employment pathways for university graduates, while positioning Canberra right at the heart of the national space industry.”

    See the full article here .

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    U NSW Campus

    Welcome to UNSW Australia (The University of New South Wales), one of Australia’s leading research and teaching universities. At UNSW, we take pride in the broad range and high quality of our teaching programs. Our teaching gains strength and currency from our research activities, strong industry links and our international nature; UNSW has a strong regional and global engagement.

    In developing new ideas and promoting lasting knowledge we are creating an academic environment where outstanding students and scholars from around the world can be inspired to excel in their programs of study and research. Partnerships with both local and global communities allow UNSW to share knowledge, debate and research outcomes. UNSW’s public events include concert performances, open days and public forums on issues such as the environment, healthcare and global politics. We encourage you to explore the UNSW website so you can find out more about what we do.

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