THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 484 Jan 13th

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    THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 484 2019 January 13

    Here is the latest round-up of news from the Society for Popular
    Astronomy. The SPA is arguably Britain's liveliest astronomical
    society, with members all over the world. We accept subscription
    payments online at our secure site and can take credit and debit
    cards. You can join or renew via a secure server or just see how
    much we have to offer by visiting


    Using data from the Kepler space telescope, citizen scientists have
    discovered a planet roughly twice the size of the Earth located within its
    star's habitable zone (the range of orbital distances where liquid water may
    exist on the planet's surface). The new world, known as K2-288Bb, could be
    rocky or could be a gas-rich planet similar to Neptune. Its size is rare
    among exoplanets (planets beyond our Solar System). Located 226 light-years
    away in the constellation Taurus, the planet lies in a stellar system known
    as K2-288, which contains a pair of dim, cool M-type stars separated by
    about 8.2 billion kilometres — roughly six times the distance between
    Saturn and the Sun. The brighter star is about half as massive and large as
    the Sun, while its companion is about one-third the Sun's mass and size.
    The new planet, K2-288Bb, orbits the smaller, dimmer star every 31.3 days.
    Examining data from the fourth observing campaign of Kepler's K2 mission,
    the team noticed two probable planetary transits in the system. But
    scientists require a third transit before claiming the discovery of a
    candidate planet, and there wasn't a third signal in the observations they
    reviewed. As it turned out, though, the team wasn't actually analyzing all
    of the data. In Kepler's K2 mode, which ran from 2014 to 2018, the space-
    craft repositioned itself to point at a new patch of sky at the start
    of each three-month observing campaign. Astronomers were initially
    concerned that that repositioning would cause systematic errors in the
    measurements. To deal with that, early versions of the software that was
    used to prepare the data for planet-finding analysis simply ignored the
    first few days of observations — and that's where the initial transit was
    hiding. As scientists learned how to correct for the systematic errors,
    that trimming step was eliminated — but the early K2 data had been clipped.
    The re-processed data were posted directly to Exoplanet Explorers, a project
    where the public searches Kepler's K2 observations to locate new transiting
    planets. In 2017 May, volunteers noticed the third transit and began an
    excited discussion about what was then thought to be an Earth-sized
    candidate in the system, which caught the attention of the team. Estimated
    to be about 1.9 times the Earth's size, K2-288Bb is half the size of
    Neptune. That places it within a recently discovered category called the
    Fulton gap, or radius gap. Among planets that orbit close to their stars,
    there's a curious dearth of worlds between about 1.5 and two times the
    Earth's size. That is likely to be a result of intense starlight breaking
    up atmospheric molecules and eroding away the atmospheres of some planets
    over time, leaving behind two populations. Since K2-288Bb's radius places
    it in that gap, it may provide a case study of planetary evolution within
    that size range.

    Massachusetts Institute of Technology

    NASA's Transiting Exoplanet Survey Satellite, TESS, has discovered a third
    small planet outside our Solar System. The new planet, named HD 21749b,
    orbits a bright, nearby dwarf star about 53 light-years away, in the
    constellation Reticulum, and appears to have the longest orbital period of
    the three planets so far identified by TESS. HD 21749b journeys around its
    star in a relatively leisurely 36 days, compared to the two other planets —
    Pi Mensae b, a 'super-Earth' with a 6.3-day orbit, and LHS 3844b, a rocky
    world that speeds around its star in just 11 hours. All three planets were
    discovered in the first three months of TESS observations. The surface of
    the new planet is probably at around 150 C — relatively cool, given its
    proximity to its star, which is almost as bright as the Sun. The planet
    is about three times the size of the Earth. Surprisingly, it is also a
    whopping 23 times as massive as Earth. But it is unlikely that the planet
    is rocky and therefore habitable; it is more likely to be made of gas, of a
    kind that is much denser than the atmospheres of either Neptune or Uranus.
    Serendipitously, the researchers have also detected evidence of a second
    planet, though not yet confirmed, in the same planetary system, with a
    shorter, 7.8-day orbit. If it is confirmed as a planet, it could be the
    first Earth-sized planet discovered by TESS. Since it was launched in 2018
    April, TESS has been monitoring the sky, sector by sector, for momentary
    dips in the light of about 200,000 nearby stars. Such dips are likely to
    represent planets passing in front of the stars.

    W. M. Keck Observatory

    Astronomers have found a new exoplanet that could alter the standing theory
    of planet formation. With a mass that is between those of Neptune and
    Saturn, and its location beyond the 'snow line' of its host star, an alien
    world of that scale was supposed to be rare. Using the Near-Infrared
    Camera, second generation (NIRC2) instrument on the 10-m Keck II telescope
    on Mauna Kea, Hawaii, and the Wide-Field Camera 3 (WFC3) instrument on the
    Hubble Space Telescope, the researchers took simultaneous high-resolution
    images of the exoplanet, named OGLE-2012-BLG-0950Lb, allowing them to
    determine its mass. They were surprised to find the mass come out right in
    the middle of the predicted intermediate-giant-planet mass gap. In an
    uncanny timing of events, another team of astronomers published a
    statistical analysis at almost the same time showing that such sub-Saturn-
    mass planets are not rare after all. OGLE-2012-BLG-0950Lb was among the
    sub-Saturn planets in the statistical study; all were detected through
    microlensing, the only method currently sensitive enough to detect planets
    with less than Saturn's mass in Jupiter-like orbits. Microlensing arises as
    a consequence of Einstein's general theory of relativity: the bending and
    magnification of light near a massive object like a star, producing a
    natural lens in the sky. In the case of OGLE-2012-BLG-0950Lb, the light
    from a distant background star was magnified by OGLE-2012-BLG-0950L (the
    exoplanet's host star) over the course of two months as it passed close to
    perfect alignment in the sky with the background star. By carefully
    analyzing the light during the alignment, an unexpected dimming with a
    duration of about a day was observed, revealing the presence of
    OGLE-2012-BLG-0950Lb by its own influence on the lensing.
    What is unique about the microlensing method is its sensitivity to
    sub-Saturn planets like OGLE-2012-BLG-0950Lb that orbit beyond the 'snow
    line' of their host stars. The snow line, or frost line, is the distance in
    a young solar system, (a.k.a. a protoplanetary disc) at which it is cold
    enough for water to condense into ice. At and beyond the snow line there is
    a dramatic increase in the amount of solid material needed for planet
    formation. According to the core accretion theory, the solids are thought
    to build up into planetary cores first through chemical and then gravita-
    tional processes. A key process of the core-accretion theory is called
    'runaway gas' accretion. Giant planets are thought to start their formation
    process by collecting a core mass of about 10 times the Earth's mass in rock
    and ice. At that stage, a slow accretion of hydrogen and helium gas begins
    until the mass has doubled. Then, the accretion of hydrogen and helium is
    expected to speed up exponentially in a runaway gas-accretion process. That
    process stops when the supply is exhausted. If the supply of gas is stopped
    before runaway accretion stops, we get 'failed Jupiter' planets with masses
    of 10-20 Earth-masses (like Neptune). The runaway gas-accretion scenario of
    the core-accretion theory predicts that planets like OGLE-2012-BLG-0950Lb
    are expected to be rare. At 39 times the mass of the Earth, planets that
    size are thought to be continuing through a stage of rapid growth, ending in
    a much more massive planet. This new result suggests that the runaway-
    growth scenario may need revision. The discovery has not only called into
    question an established theory, it was made using a new technique that will
    be a key part of NASA's next big planet-finding mission, the Wide-Field
    Infra-Red Survey Telescope (WFIRST), which is scheduled to be launched into
    orbit in the mid-2020s.

    University of Michigan

    Researchers have long known that the Milky Way has about 10 smaller
    satellite galaxies surrounding it, each with at least a million stars, and
    up to more than a billion, such as the Magellanic Clouds. Now, with
    the Subaru telescope, astronomers can observe galaxies five or ten times the
    distance from the Milky Way, such as M94. They can then use the physics of
    how satellite galaxies form around the Milky Way to predict how many
    satellite galaxies a similar-sized galaxy such as M94 may have. When
    astronomers examined M94, they expected to find a similar number of
    satellite galaxies. However, they detected just two galaxies near M94, with
    very few stars each. The results have implications for the current
    understanding of how galaxies form — which is in much larger haloes of dark
    matter. Those halos of dark matter surrounding galaxies have immense
    gravitational force, and can pull in gas from their immediate vicinity.
    Large galaxies like the Milky Way generally form in haloes of about the same
    mass. But smaller satellite galaxies, which form in smaller 'subhaloes' are
    not nearly so dependable. The production rate of high-mass stars in such
    satellite galaxies actually modulates their growth. If, for example, the
    nascent satellite galaxy forms too many high-mass stars at one time, their
    eventual supernova explosions might expel all its gas and halt all further
    growth. But astronomers are unsure at what size halo such 'scatter' in
    galaxy formation becomes important. M94 indicates that galaxy formation in
    intermediate-sized dark haloes may be much more uncertain than previously
    thought. To observe the number of satellite dwarf galaxies around M94, the
    researchers took a composite image of the large galaxy. The image covered
    about 12 square degrees of the night sky. That kind of image includes
    layers and layers of 'noise', including cosmic rays and scattered light,
    which make faint dwarf galaxies difficult to detect. To make sure they
    weren't missing satellite galaxies, the team engineered artificial galaxies
    back into the image and recovered them using the same methods as for real
    satellites. With that technique, the researchers confirmed that there were
    no more than two galaxies around M94.

    Massachusetts Institute of Technology

    On 2014 Nov. 22, astronomers observed a rare event in the night sky: a
    supermassive black hole at the centre of a galaxy, nearly 300 million light
    years away, ripping apart a passing star. The event, known as a tidal-
    disruption flare, for the black hole's massive tidal pull that tears a star
    apart, created a burst of X-ray activity near the centre of the galaxy.
    Since then, many observatories have trained their sights on the event, in
    the hope of learning more about how black holes feed. Now researchers have
    pored through data from multiple telescopes' observations of the event, and
    discovered a curiously intense, stable, and periodic pulse, or signal, of
    X-rays, across all datasets. The signal appears to emanate from an area
    very close to the black hole's event horizon — the point beyond which
    material is swallowed inescapably by the black hole. The signal appears
    periodically to brighten and fade every 131 seconds, and persisted over at
    least 450 days. The researchers believe that whatever is emitting the
    periodic signal must be orbiting the black hole, just outside the event
    horizon, near the Innermost Stable Circular Orbit, or ISCO — the smallest
    orbit in which a particle can safely travel around a black hole. Given the
    signal's stable proximity to the black hole, and the black hole's mass,
    which researchers previously estimated to be about 1 million times that of
    the Sun, the team has calculated that the black hole is spinning at about
    half the speed of light. The findings are the first demonstration of a
    tidal-disruption flare being used to estimate a black hole's spin. Most
    supermassive black holes are dormant and do not usually emit much in the
    way of X-ray radiation. Only occasionally will they release a burst of
    activity, such as when stars get close enough for black holes to devour
    them. Such tidal-disruption flares can be used to estimate the spin of
    supermassive black holes — a characteristic that has been, up until now,
    incredibly tricky to pin down. Events where black holes shred stars that
    come too close to them could help us map out the spins of several super-
    massive black holes that are dormant and otherwise hidden at the centres of
    galaxies. That could ultimately help us understand how galaxies evolved
    over cosmic time.

    Theoretical models of tidal-disruption flares show that when a black hole
    shreds a star apart, some of that star's material may stay outside the event
    horizon, circling, at least temporarily, in a stable orbit such as the ISCO,
    and giving off periodic flashes of X-rays before ultimately being fed by the
    black hole. The periodicity of the X-ray flashes thus encodes key
    information about the size of the ISCO, which itself is dictated by how fast
    the black hole is spinning. Astronomers thought that if they could see such
    regular flashes very close to a black hole that had undergone a recent tidal
    disruption event, those signals could give them an idea of how fast the
    black hole was spinning. They focused their search on ASASSN-14li, the
    tidal-disruption event that astronomers identified in 2014 November, using
    the ground-based All-Sky Automated Survey for SuperNovae (ASASSN). The team looked through archived datasets from three observatories that collected
    X-ray measurements of the event since its discovery: the European Space
    Agency's XMM-Newton space observatory, and NASA's space-based Chandra and Swift observatories. On the basis of the properties of the signal, and the
    mass and size of the black hole, the team estimated that the black hole is
    spinning at at least half the speed of light. Once the team discovered the
    periodic signal, it was up to the theorists to find an explanation for what
    may have generated it. The team came up with various scenarios, but the one
    that seems the most likely to generate such a strong, regular X-ray flare
    involves not just a black hole shredding a passing star, but also a smaller
    white-dwarf star, orbiting close to the black hole. Such a white dwarf may
    have been circling the supermassive black hole, at ISCO — the innermost
    stable circular orbit — for some time. Alone, it would not have been
    enough to emit any sort of detectable radiation. For all intents and
    purposes, the white dwarf would have been invisible to telescopes as it
    circled the relatively inactive, spinning black hole. Sometime around 2014
    Nov. 22, a second star passed close enough to the system that the black hole
    tore it apart in a tidal-disruption flare that emitted an enormous amount of
    X-ray radiation, in the form of hot, shredded stellar material. As the
    black hole pulled that material inward, some of the stellar debris fell into
    the black hole, while some remained just outside, in the innermost stable
    orbit — the very same orbit in which the white dwarf circled. As the white
    dwarf came in contact with that hot stellar material, it probably dragged it
    along as a luminous overcoat of sorts, illuminating the white dwarf in an
    intense amount of X-rays each time it circled the black hole, every 131
    seconds. The scientists admit that such a scenario would be incredibly rare
    and would last only for several hundred years at most — a blink of an eye
    on the cosmic scale. The chances of detecting such a scenario would be
    exceedingly slim. Estimating spins of several black holes from the
    beginning of time to now would be valuable in terms of estimating whether
    there is a relationship between the spin and the age of black holes.


    A brief and unusual flash observed in the night sky on 2018 June 16 puzzled
    astronomers and astrophysicists across the globe. The event — called
    AT2018cow and nicknamed 'the Cow' after the coincidental final letters in
    its official name — is unlike any celestial outburst ever seen before,
    prompting multiple theories about its source. Over three days, the Cow
    produced a sudden explosion of light at least 10 times brighter than a
    typical supernova, and then it faded over the next few months. The unusual
    event occurred inside or near a star-forming galaxy known as CGCG 137-068,
    located about 200 million light-years away in the constellation Hercules.
    The object was first observed by the Asteroid Terrestrial-impact Last Alert
    System telescope in Hawaii. So exactly what is the Cow? Using data from
    multiple NASA missions, including the Neil Gehrels Swift Observatory and the
    Nuclear Spectroscopic Telescope Array (NuSTAR), two groups are publishing
    papers that provide possible explanations for the Cow's origins. One paper
    argues that the Cow is a monster black hole shredding a passing star. The
    second paper hypothesizes that it is a supernova that gave birth to a black
    hole or a neutron star. One potential explanation of the Cow is that a star
    has been ripped apart in what astronomers call a 'tidal disruption event'.
    Just as the Moon's gravity causes Earth's oceans to bulge, creating tides, a
    black hole has a similar but more powerful effect on an approaching star,
    ultimately breaking it apart into a stream of gas. The tail of the gas
    stream is flung out of the system, but the leading edge swings back round
    the black hole, collides with itself and creates an elliptical cloud of
    material. According to one research team using data spanning from infrared
    radiation to gamma rays from Swift and other observatories, that transform-
    ation best explains the Cow's behaviour.
    Other astronomers think that the shredded star was a white dwarf — a hot,
    roughly Earth-sized stellar remnant marking the final state of stars like
    our Sun. They also calculated that the black hole's mass ranges from
    100,000 to 1 million times the Sun's, almost as large as the central black
    hole of its host galaxy. It is unusual to see black holes of that scale
    outside the centre of a galaxy, but it is possible that the Cow occurred in
    a nearby satellite galaxy or a globular star cluster whose older stellar
    populations could have a higher proportion of white dwarfs than average
    galaxies. A third team of scientists was able to gather data on the Cow
    over an even broader range of wavelengths, spanning from radio waves to
    gamma rays. On the basis of those observations, the team suggests that a
    supernova could be the source of the Cow. When a massive star dies, it
    explodes as a supernova and leaves behind either a black hole or an
    incredibly dense neutron star. The Cow could represent the birth of one
    such stellar remnant. The team used high-energy X-ray data to show that the
    Cow has characteristics similar to a compact body like a black hole or
    neutron star consuming material. But on the basis of what we saw in other
    wavelengths, we think that this was a special case and that we may have
    observed — for the first time — the creation of a compact body in real
    time. The team analyzed data from multiple observatories, including NASA's
    NuSTAR, ESA's XMM-Newton and INTEGRAL satellites, and the National Science Foundation's Very Large Array. The team proposes that the bright optical and ultraviolet flash from the Cow signalled a supernova and that the X-ray emissions that followed shortly after the outburst arose from gas radiating
    energy as it fell onto a compact object. Typically, a supernova's expanding
    debris cloud blocks any light from the compact object at the centre of the
    blast. Because of the X-ray emissions, astronomers suggest that the
    original star in this scenario may have been relatively low in mass,
    producing a comparatively thinner debris cloud through which X-rays from the
    central source could escape. If we are seeing the birth of a compact object
    in real time, this could be the start of a new chapter in our understanding
    of stellar evolution.


    Scientists have found evidence that dark matter can be heated up and moved
    around, as a result of star formation in galaxies. The findings provide the
    first observational evidence for the effect known as 'dark matter heating',
    and give new clues as to what makes up dark matter. In the new work,
    scientists set out to hunt for evidence for dark matter at the centres of
    nearby dwarf galaxies. Dwarf galaxies are small, faint galaxies that are
    typically found orbiting larger galaxies like our own Milky Way. Dark
    matter is thought to make up most of the mass of the Universe. However,
    since it does not interact with light in the same way as normal matter, it
    can only be observed through its gravitational effects. The key to studying
    it may however lie in how stars are formed in these galaxies. When stars
    form, strong winds can push gas and dust away from the heart of the galaxy.
    As a result, the galaxy's centre has less mass, which affects how much
    gravity is felt by the remaining dark matter. With less gravitational
    attraction, the dark matter gains energy and migrates away from the centre,
    an effect called 'dark matter heating'. The team of astrophysicists
    measured the amount of dark matter at the centres of 16 dwarf galaxies with
    very different star-formation histories. They found that galaxies that
    stopped forming stars long ago had higher dark-matter densities at their
    centres than those that are still forming stars today. That supports the
    theory that the older galaxies had less dark-matter heating. The findings
    provide a new constraint on dark-matter models: dark matter must be able to
    form dwarf galaxies that exhibit a range of central densities, and those
    densities must relate to the amount of star formation. The team hopes to
    expand on that work by measuring the central dark-matter density in a larger
    sample of dwarfs, pushing to even fainter galaxies, and testing a wider
    range of dark-matter models.

    BBC Science

    Astronomers have revealed details of mysterious signals emanating from a
    distant galaxy, picked up by a telescope in Canada. The precise nature and
    origin of the blasts of radio waves is unknown. Among the 13 bursts of fast
    radio waves, known as FRBs, was a very unusual repeating signal, coming from
    the same source about 1.5 billion light-years away. Such an event has only
    been reported once before, by a different telescope. The CHIME observatory,
    located in British Columbia's Okanagan Valley, consists of four 100-metre
    semi-cylindrical antennae, which scan the entire northern sky each day. The
    telescope only got up and running last year, detecting 13 of the radio
    bursts almost immediately, including the repeater. FRBs are short, bright
    flashes of radio waves, which appear to be coming from almost halfway across
    the Universe. So far, scientists have detected about 60 single fast radio
    bursts and two that repeat. They believe there could be as many as a
    thousand FRBs in the sky every day. There are a number of theories about
    what could be causing them. They include a neutron star with a very strong
    magnetic field that is spinning very rapidly or two neutron stars merging

    Association of Universities for Research in Astronomy (AURA)

    Observations from Gemini Observatory identify a key fingerprint of an
    extremely distant quasar, allowing astronomers to sample light emitted from
    the dawn of time. Astronomers happened upon this deep glimpse into space
    and time thanks to an unremarkable foreground galaxy acting as a
    gravitational lens, which magnified the quasar's ancient light. The Gemini
    observations provide critical pieces of the puzzle in confirming the object
    as the brightest-appearing quasar so early in the history of the Universe,
    raising hopes that more sources like it will be found. Before the cosmos
    reached its billionth birthday, some of the very first cosmic light began
    a long journey through the expanding Universe. One particular beam of
    light, from a quasar, serendipitously passed near an intervening galaxy,
    whose gravity bent and magnified the quasar's light and refocused it in our
    direction, allowing telescopes like Gemini North to probe the quasar in
    great detail. The Gemini observations provided key pieces of the puzzle by
    filling a critical hole in the data. The Gemini North telescope on Mauna
    Kea, Hawaii, utilized the Gemini Near-InfraRed Spectrograph (GNIRS) to
    dissect a significant swath of the infrared part of the light's spectrum.
    The Gemini data contained the tell-tale signature of magnesium which is
    critical for determining how far back in time we are looking. The Gemini
    observations also led to a determination of the mass of the black hole
    powering the quasar. When astronomers combined the Gemini data with
    observations from multiple observatories on Mauna Kea, the Hubble Space
    Telescope, and other observatories around the world, they were able to paint
    a complete picture of the quasar and the intervening galaxy. That picture
    reveals that the quasar is located extremely far back in time and space —
    shortly after what is known as the Epoch of Reionization — when the very
    first light emerged from the Big Bang. This is one of the first sources to
    shine as the Universe emerged from the cosmic dark ages. Before then, no
    stars, quasars, or galaxies had been formed, until objects like this
    appeared like candles in the dark.
    The foreground galaxy that enhances our view of the quasar is especially
    dim, which is extremely fortuitous. If that galaxy were much brighter,
    astronomers would not have been able to differentiate it from the quasar.
    The intense brilliance of the quasar, known as J0439+1634, also suggests
    that it is fuelled by a supermassive black hole at the heart of a young
    forming galaxy. The broad appearance of the magnesium fingerprint captured
    by Gemini also allowed astronomers to measure the mass of the quasar's
    supermassive black hole at 700 million times that of the Sun. The
    supermassive black hole is most likely surrounded by a sizeable flattened
    disc of dust and gas. That torus of matter — known as an accretion disc —
    most likely continually spirals inward to feed the black hole powerhouse.
    Observations at sub-millimetre wavelengths with the James Clerk Maxwell
    Telescope on Mauna Kea suggest that the black hole is not only accreting gas
    but may be triggering star birth at a prodigious rate — which appears to be
    up to 10,000 stars per year; for comparison, our Milky Way Galaxy makes one
    star per year. However, because of the boosting effect of gravitational
    lensing, the actual rate of star formation could be much lower. Quasars are
    extremely energetic sources powered by huge black holes thought to have
    resided in the very first galaxies to form in the Universe. Because of
    their brightness and distance, quasars provide a unique glimpse into the
    conditions in the early Universe. This quasar has a redshift of 6.51, which
    translates to a distance of 12.8 billion light-years, and appears to
    shine with a combined light of about 600 million million Suns, boosted by
    the gravitational lensing magnification. The foreground galaxy which bent
    the quasar's light is about half that distance away, at a mere 6 billion
    light-years from us. The first follow-up spectroscopic observations,
    conducted with the Multi-Mirror Telescope in Arizona, confirmed the object
    as a high-redshift quasar. Subsequent observations with the Gemini North
    and Keck I telescopes in Hawaii confirmed the MMT's finding, and led to
    Gemini's detection of the crucial magnesium fingerprint — the key to
    nailing down the quasar's fantastic distance. However, the foreground
    lensing galaxy and the quasar appear so close that it is impossible to
    separate them with images taken from the ground owing to blurring by the
    Earth's atmosphere. It took the Hubble Space Telescope to reveal that the
    quasar image is split into three components by a faint lensing galaxy.
    The quasar is ripe for future scrutiny. Astronomers also plan to use the
    Atacama Large Millimetre/submillimetre Array, and eventually the James
    Webb Space Telescope, to look within 150 light-years of the black hole and
    directly detect the influence of the gravity from the black hole on gas
    motion and star formation in its vicinity. Any future discoveries of very
    distant quasars like J0439+1634 will continue to teach astronomers about the
    chemical environment and the growth of massive black holes in the early

    Bulletin compiled by Clive Down

    The Society for Popular Astronomy has been helping beginners in amateur
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    right now with a credit or debit card at our lively web site:

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