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  • richardmitnick 12:42 pm on August 6, 2019 Permalink | Reply
    Tags: "Ghosts of Ancient Explosions Live on in Stars Today", , , , , , , , Zwicky Transient Facility at the 48-inch Samuel Oschin Telescope at Palomar   

    From Caltech: “Ghosts of Ancient Explosions Live on in Stars Today” 

    Caltech Logo

    From Caltech

    August 05, 2019

    Contact
    Lori Dajose
    (626) 395‑1217
    ldajose@caltech.edu

    The chemical composition of certain stars gives clues about their predecessors, stars that have long since exploded and faded.

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    Image of a Type Ia supernova. Credit: Zwicky Transient Facility

    Zwicky Transient Facility (ZTF) instrument installed on the 1.2m diameter Samuel Oschin Telescope at Palomar Observatory in California. Courtesy Caltech Optical Observatories

    Edwin Hubble at Caltech Palomar Samuel Oschin 48 inch Telescope, (credit: Emilio Segre Visual Archives/AIP/SPL)

    Caltech Palomar Intermediate Palomar Transient Factory telescope at the Samuel Oschin Telescope at Palomar Observatory,located in San Diego County, California, United States, altitude 1,712 m (5,617 ft)

    Caltech Palomar Samuel Oschin 48 inch Telescope, located in San Diego County, California, United States, altitude 1,712 m (5,617 ft)

    When small, dense stars called white dwarfs explode, they produce bright, short-lived flares called Type Ia supernovae. These supernovae are informative cosmological markers for astronomers—for example, they were used to prove that the universe is accelerating in its expansion.

    White dwarfs are not all the same, ranging from half of the mass of our sun to almost 50 percent more massive than our sun. Some explode in Type Ia supernovae; others simply die quietly. Now, by studying the “fossils” of long-exploded white dwarfs, Caltech astronomers have found that early on in the universe, white dwarfs often exploded at lower masses than they do today. This discovery indicates that a white dwarf could explode from a variety of causes, and does not necessarily have to reach a critical mass before exploding.

    A paper about the research, led by Evan Kirby, assistant professor of astronomy, appears in The Astrophysical Journal.

    Near the end of their lives, a majority of stars like our sun dwindle down into dim, dense white dwarfs, with all their mass packed into a space about the size of Earth. Sometimes, white dwarfs explode in what’s called a Type Ia (pronounced one-A) supernova.

    It is uncertain why some white dwarfs explode while others do not. In the early 1900s, an astrophysicist named Subrahmanyan Chandrasekhar calculated that if a white dwarf had more than 1.4 times the mass of our sun, it would explode in a Type Ia supernova. This mass was dubbed the Chandrasekhar mass. Though Chandrasekhar’s calculations gave one explanation for why some more massive white dwarfs explode, it did not explain why other white dwarfs less than 1.4 solar masses also explode.

    Studying Type Ia supernovae is a time-sensitive process; they flare into existence and fade back into darkness all within a few months. To study long-gone supernovae and the white dwarfs that produced them, Kirby and his team use a technique colloquially called galactic archaeology.

    Galactic archaeology is the process of looking for chemical signatures of long-past explosions in other stars. When a white dwarf explodes in a Type Ia supernova, it pollutes its galactic environment with elements forged in the explosion—heavy elements like nickel and iron. The more massive a star is when it explodes, the more heavy elements will be formed in the supernova. Then, those elements become incorporated into any newly forming stars in that region. Just as fossils today give clues about animals that have long ceased to exist, the amounts of nickel in stars illustrates how massive their long-exploded predecessors must have been.

    Using the Keck II telescope, Kirby and his team first looked at certain ancient galaxies, those that ran out of material to form stars in the first billion years of the universe’s life.

    Keck 2 telescope Maunakea Hawaii USA, 4,207 m (13,802 ft)

    Most of the stars in these galaxies, the team found, had relatively low nickel content. This meant that the exploded white dwarfs that gave them that nickel must have been relatively low mass—about as massive as the sun, lower than the Chandrasekhar mass.

    Yet, the researchers found that the nickel content was higher in more recently formed galaxies, meaning that as more time went by since the Big Bang, white dwarfs had begun to explode at higher masses.

    “We found that, in the early universe, white dwarfs were exploding at lower masses than later in the universe’s lifetime,” says Kirby.”It’s still unclear what has driven this change.”

    Understanding the processes that result in Type Ia supernovae is important because the explosions themselves are useful tools for making measurements of the universe. Regardless of how they exploded, most Type Ia supernovae follow a well-characterized relationship between their luminosity and the time it takes for them to fade.

    “We call Type Ia supernovae ‘standardizable candles.’

    Standard Candles to measure age and distance of the universe from supernovae NASA

    If you look at a candle at a distance, it will look dimmer than when it’s up close. If you know how bright it is supposed to be up close, and you measure how bright it is at a distance, you can calculate that distance,” says Kirby. “Type Ia supernovae have been very useful in calculating things like the rate of expansion of the universe. We use them all the time in cosmology. So, it’s important to understand where they come from and characterize the white dwarfs that generate these explosions.”

    The next steps are to study elements other than nickel, in particular, manganese. Manganese production is very sensitive to the mass of the supernova that produces it, and therefore gives a precise way to validate the conclusions drawn by the nickel content.

    The paper is titled Evidence for Sub-Chandrasekhar Type Ia Supernovae from Stellar Abundances in Dwarf Galaxies. In addition to Kirby, co-authors are Justin L. Xie and Rachel Guo of Harvard University, Caltech graduate student Mithi A. C. de los Reyes, Maria Bergemann and Mikhail Kovalev of the Max Planck Institute for Astronomy, Ken J. Shen of University of California Berkeley, and Anthony L. Piro and Andrew McWilliam of the Observatories of the Carnegie Institution for Science. Funding was provided by the National Science Foundation, a Cottrell Scholar award from the Research Corporation for Science Advancement, and Caltech.

    See the full article here .


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    Please help promote STEM in your local schools.


    Stem Education Coalition

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

    Caltech campus

     
  • richardmitnick 3:58 pm on February 7, 2019 Permalink | Reply
    Tags: , , , Catech, , Zwicky Transient Facility at the 48-inch Samuel Oschin Telescope at Palomar   

    From Caltech: “Zwicky Transient Facility Nabs Supernovae, Stars, and More” 

    Caltech Logo

    From Caltech

    02/07/2019

    Whitney Clavin
    (626) 395-1856
    wclavin@caltech.edu

    Zwicky 576-megapixel Transient Facility installed on the 48-inch Samuel Oschin Telescope at Palomar

    1
    A new, composite image of the Andromeda galaxy made by combining three bands of visible light captured by ZTF. The image covers 2.9 square degrees of sky, which is one-sixteenth of ZTF’s full field of view. Andromeda, also known as Messier 31, is the nearest major galaxy to our Milky Way galaxy, lying 2.5 million light-years away.
    Credit: ZTF/D. Goldstein and R. Hurt (Caltech)

    2
    The orbit of asteroid 2019 AQ3, discovered by ZTF, is shown in this diagram. The object has the shortest “year” of any recorded asteroid, with an orbital period of just 165 days.
    Credit: NASA/JPL-Caltech

    3
    Artwork showing a pair of white dwarfs in orbit around each other. The middle panel shows the two dense, dead stars in orbit, while the third panel illustrates what happens when one star begins to siphon material off its partner. Earth is shown for reference—while it is not much smaller than the white dwarfs, they are 200,000 times more dense. ZTF is well-suited to detect binary star systems like this one.
    Credit: Caltech

    The newest instrument at Palomar Observatory has its eye on our dynamic night skies

    The results are rolling in from Caltech’s newest state-of-the-art sky-surveying camera, which began operations at the Palomar Observatory in March 2018. Called the Zwicky Transient Facility, or ZTF, the new instrument has so far discovered 50 small near-Earth asteroids and more than 1,100 supernovae, and it has observed more than 1 billion stars in the Milky Way galaxy. One of the near-Earth asteroids discovered by ZTF, called 2019 AQ3, has an orbital period of just 165 days, the shortest known “year” for any asteroid.

    “It’s a cornucopia of results,” says Shri Kulkarni, the principal investigator of ZTF and the George Ellery Hale Professor of Astronomy and Planetary Science at Caltech. Recently, several new papers about early results and technical specifications for ZTF were accepted for publication in the journal Publications of the Astronomical Society of the Pacific. “We are up and running and delivering data to the astronomical community. Astronomers are energized.”

    ZTF uses the 48-inch Samuel Oschin Telescope at Palomar to survey the northern skies for anything that explodes, moves, or changes in brightness. Because the ZTF camera covers 240 times the size of the full moon in a single night-sky image, it is discovering the most fleeting, or short-lived, of cosmic events, which were impossible to catch before now.

    Caltech Palomar Samuel Oschin 48 inch Telescope

    “ZTF is surveying the whole northern sky every three nights,” says Kulkarni. “It’s already discovering a few supernovae a night, and we expect that rate to go up.”

    The cost to develop and run ZTF is about $24 million, with about $11 million of the funding coming from the U.S. government via the National Science Foundation (NSF) and the rest coming from an international collaboration of partners.

    The ZTF Collaboration

    Institutions participating in the development of ZTF include Caltech, the Weizmann Institute of Science, the Oskar Klein Center at Stockholm university, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Tawian, the University of Wisconsin-Milwaukee, and Lawrence Berkeley National Laboratory.

    Additional support comes from the Heising-Simons Foundation, along with Caltech itself.

    “The start of routine operations of ZTF marks a new era in our ability to capture the nightly and hourly changes transpiring in the universe,” says Anne Kinney, NSF assistant director for mathematical and physical sciences. “They are now recording real-time events from distant supernovae to nearby asteroids and are poised to discover the violent mergers and explosions generating gravitational-wave events.”

    Because nearly half of ZTF is paid for by the U.S. government, nearly half of its observations are shared publicly in near-real-time with the astronomy community. When varying, or transient, objects are detected, an automated alert system is activated, sending notices out to astronomers, who then quickly follow up on notable objects of interest using other telescopes, including the 60-inch and 200-inch Hale telescopes at Palomar. An NSF-funded program called GROWTH, with 18 international observatories in the Northern Hemisphere, also follows up on the ZTF alerts.

    Caltech Palomar 200 inch Hale Telescope, at Mt Wilson, CA, USA, Altitude 1,712 m (5,617 ft)

    Caltech Palomar 1.5 meter 60 inch telescope, Altitude 1,712 m (5,617 ft)

    All data from the ZTF camera are sent via a microwave network managed by UC San Diego to IPAC, an astronomy center at Caltech that processes and archives up to 4 terabytes of data each night. “This is the first time IPAC has generated real-time alerts from a survey and the first time a survey has made public up to hundreds of thousands of alerts per night,” says George Helou, ZTF co-investigator and executive director of IPAC. Ultimately, the detailed data are also made available to astronomers around the world through IPAC.

    “It takes only 10 to 20 minutes from the time a transient observation is made to the time the alert goes out,” says Matthew Graham, the ZTF project scientist at Caltech. Graham specializes in “big data,” and specifically how to handle and process large streams of astronomical data. “It’s like running a major newsroom. We’ve never operated at this scale before, and handling all the data is quite a feat,” he says.

    Discoveries from ZTF so far include not only new supernovae, binary stars, and asteroids but two black holes caught shredding stars. As stars wander too close to black holes, they can be “tidally disrupted” by the gravity of the black hole and stretched into oblivion. Graham says that he and the team working on the tidal disruption data, led by Suvi Gezari of the University of Maryland, got fed up with referring to the technical names for the objects, consisting of long strings of numbers. “We decided to nickname them Ned Stark and Jon Snow, after Game of Thrones characters,” he says.

    ZTF also caught two near-Earth asteroids, 2018 NX and 2018 NW, that zipped by Earth at distances of only 72,000 miles and 76,000 miles away, respectively, or approximately a third of the distance between Earth and the moon. These discoveries were enabled by the NSF-funded GROWTH program.

    On January 4, 2019, ZTF caught the near-Earth asteroid 2019 AQ3. “This is one of the largest asteroids with an orbit entirely within the orbit of Earth—a very rare species,” says Quanzhi Ye, a postdoctoral scholar at IPAC who first spotted the asteroid in the ZTF data.

    Tom Prince, one of the co-investigators of ZTF and the Ira S. Bowen Professor of Physics at Caltech, says that the instrument is particularly adept at identifying new gravitational-wave sources—in particular, pairs of compact stars like white dwarfs—that will be observed with future space-based gravitational-wave detectors.

    “Because we cover so much sky so often, we can find these rare exotic binary systems that contain two white dwarf stars, each about the size of Earth but about half the mass of our sun. Their orbits are predicted to become smaller and smaller because of the loss of energy due to gravitational waves.”

    ZTF is also laying the groundwork for the future NSF-funded Large Synoptic Survey Telescope (LSST), which will, in every exposure, scan a volume of sky 13 times larger than that scanned by ZTF. LSST is scheduled to begin operations in 2022.

    LSST


    LSST Camera, built at SLAC



    LSST telescope, currently under construction on the El Peñón peak 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.

    “The same alert techniques that ZTF is developing for international networks of observatories to follow up on its findings will be applied to LSST when it joins the search,” says Kinney.

    The newest ZTF papers are: “The Zwicky Transient Facility: System Overview, Performance, and First Results,” led by Eric Bellm of the University of Washington; “The Zwicky Transient Facility: Science Objectives,” led by Graham; “The Zwicky Transient Facility: Data Processing, Products, and Archive,” led by Frank Masci of IPAC; “Machine Learning for the ZTF,” led by Ashish Mahabal of Caltech; “The Zwicky Transient Facility Alert Distribution System,” led by Maria Patterson of the University of Washington; “The GROWTH Marshal: A Dynamic Science Portal for Time-domain Astronomy,” led by Mansi Kasliwal of Caltech; and “A Morphological Classification Model to Identify Unresolved PanSTARRS Sources: Application in the ZTF Real-Time Pipeline,” led by Yutaro Tachibana of Tokyo Institute of Technology and Caltech and Adam Miller of Northwestern University and the Adler Planetarium.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.


    Stem Education Coalition

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

    Caltech campus


    Caltech campus

     
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