astrobites 2018

Find out the latest thinking about our universe.
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How did Pluto Settle in its Peculiar Orbit?

Post by bystander » Tue Apr 17, 2018 5:10 pm

Like a Captured Stone: How did Pluto Settle in its Peculiar Orbit?
astrobites | 2018 Apr 13
Vatsal Panwar wrote:
Investigating the history of planet formation in the solar system can be a lot like solving a devious jigsaw puzzle, except that there is more than one set of pieces that will let you arrive at the same final picture in case of the solar system. There is a good deal of debate on the physical mechanism governing the very early stages of formation of gas giants and it continues to be one of the important open questions in planetary science.

Today’s paper by Renu Malhotra, next in the series of astrophysical classics, focuses instead on the late stages of planet formation in the solar system when the dynamical interactions between the gas giants and planetesimals are believed to have played a key role in deciding the configuration of the solar system as we see it today. The vestiges of this dynamical evolution that can be observed today are the peculiar orbits (highly eccentric, inclined, and in orbital resonance with Neptune) of trans-Neptunian objects — especially that of Pluto. ...

The Origin of Pluto's Orbit: Implications for the Solar System Beyond Neptune - Renu Malhotra The Origin of Pluto's Peculiar Orbit - Renu Malhotra
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Dancing in the Dark

Post by bystander » Tue Apr 17, 2018 5:31 pm

Dancing in the Dark
astrobites | 2018 Apr 16
Mia de los Reyes wrote:
A few weeks ago, van Dokkum et al. published a paper in Nature about the ultra-diffuse galaxy NGC1052-DF2 (closed access, but you can read a great summary here). Using the spectra of globular clusters in this galaxy, the authors concluded that NGC1052-DF2 has a dynamical mass that is very close to the mass of its stars—suggesting that NGC1052-DF2 has much less dark matter than expected for its stellar mass!

This exciting result has generated a lot of buzz (including lots of Twitter debates and even some memes like the featured image), and astronomers have plenty of follow-up questions. First of all, how real is this result? And if NGC1052-DF2 really does lack dark matter, how could such a galaxy form? Finally, how do alternative theories that don’t include dark matter explain this galaxy (and any other galaxies that might be like it)?

It’s only been a few weeks, but already several scientists have begun to write papers in response to van Dokkum et al.’s paper. Today, we’ll watch a scientific debate unfold by taking a look at some of these responses. ...

As Carl Sagan once famously said, “extraordinary claims require extraordinary evidence.” A galaxy that has much less dark matter than expected is definitely an extraordinary claim. Is the evidence extraordinary enough to hold up? Today’s papers argue that it’s not; the authors of the original paper might argue otherwise (you can see P. van Dokkum’s response to some of these responses here). We may need more data to know for sure, but in the meantime you’ll have to decide for yourself.

Current velocity data on dwarf galaxy NGC1052-DF2 do not constrain it to lack dark matter - Nicolas F. Martin et al Measured and found wanting: reconciling mass-estimates of ultra-diffuse galaxies - Chervin F. P. Laporte et al MOND and the dynamics of NGC1052-DF2 - B. Famaey, S. McGaugh, M. Milgrom Dark Matter in Ultra-Diffuse Galaxies in the Virgo Cluster from their Globular Cluster Populations - Elisa Toloba et al
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Uncovering Triple Systems with Gravitational Waves

Post by bystander » Tue Apr 17, 2018 5:40 pm

Triple Threat: Uncovering Triple Systems with Gravitational Waves
astrobites | 2018 Apr 17
Lisa Drummond wrote:
The Laser Interferometer Gravitational-Wave Observatory (LIGO) collaboration has been receiving a lot of press in recent years, with a run of groundbreaking gravitational wave (GW) detections (most recently, a neutron star binary!), capturing the excitement of the astrophysics community and general public alike. All of the gravitational waves detected so far have been produced by compact binary mergers. This series of LIGO discoveries begs the question – where are the gravitational waves produced by triples? Triple systems are not uncommon in astrophysics – but how would we distinguish a standard compact binary coalescence signal from one produced by a tight binary in orbit around a triple companion? Todays’ paper tackles this question by identifying signatures of the triple that are apparent in the GW signal. ...

Detecting Triple Systems with Gravitational Wave Observations - Yohai Meiron, Bence Kocsis, Abraham Loeb
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Why Jupiter spins fast, but not really fast

Post by bystander » Mon Apr 23, 2018 3:48 pm

Why Jupiter spins fast, but not really fast
astrobites | 2018 Apr 19
Michael Hammer wrote:
Good luck getting any sleep on Jupiter! This humongous gas giant rotates faster than any other planet in the Solar System, completing a day in less than 10 hours! If you were to emigrate from Earth to the largest planet in our solar system and still aimed to get the daily 8 hours of sleep recommended for adults, that would leave you with less than two hours per day to eat, exercise, and study astrophysics. That’s not nearly enough time! Future inhabitants of Jupiter’s cloud cities should not complain, though.

When Jupiter formed, it accreted its atmosphere (over 95% of the planet’s total mass!) from the hydrogen and helium gas in the protoplanetary disk surrounding our Sun. As Jupiter ate up this gas mass, it must have begun to spin faster as it also ate up the gas’s angular momentum. Eventually, it would reach the break-up velocity, which is defined as the point when the upper layers of the atmosphere are rotating as fast as an object would if it were placed in orbit around the planet close to the surface. At these speeds, Jupiter could not possibly rotate any faster. Naively, we would expect Jupiter to still be rotating that fast today. However, if we calculate Jupiter’s rotation period based on its break-up velocity, we get that one Jovian day should not even last 3 hours!

Really, Jupiter’s inhabitants should be thankful that something was able to slow down the planet’s rotation enough for them to be able to watch the first four Harry Potter movies in one day instead of just one of them. But what?

We have long known that Saturn also rotates much slower than its break-up speed (11 hr compared to 4 hr). And as Eckhart summarized in his December astrobite, we now know gas giant exoplanets also rotate slower than expected. In today’s paper, Konstantin Batygin attempts to solve this widespread conundrum with the solution people would most expect: Jupiter’s magnetic field. ...

On the Terminal Rotation Rates of Giant Planets - Konstantin Batygin
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A ‘Breathing’ Comet

Post by bystander » Mon Apr 23, 2018 4:06 pm

A ‘Breathing’ Comet
astrobites | 2018 Apr 19
Jamila Pegues wrote:
In August 2014, the Rosetta orbiter met up with the comet known as 67P/Churyumov-Gerasimenko (aka, 67P/C-G). Rosetta stuck close by, watching and observing, as the comet orbited around the Sun. Now, nearly four years later, we’re still learning new science from everything Rosetta (and its lander Philae) discovered. In today’s astrobite, we focus on one comet discovery in particular: molecular oxygen.

Molecular oxygen (O2) is certainly important here on Earth. Plants breathe out O2 during photosynthesis, while other living creatures (like humans) breathe it in. But O2 isn’t only produced through life as we know it – which means that if we see molecular oxygen in the atmosphere of, say, an exoplanet, we shouldn’t automatically assume it came from a living source (as talked about in this article and this previous astrobite). 67P/C-G seems like an example of such a non-living, ‘breathing’ body.

67P/C-G is a comet, which means it’s a small icy body of rock, dust, and gas orbiting about the Sun. When a comet passes close to the Sun, the Sun warms up its ices, producing a coma – the iconic ‘tail’ of released gas that trails after a comet during its orbit, as seen in this gallery. With Rosetta, scientists have detected O2 abundance levels in 67P/C-G’s coma of some 1% to 10% with respect to water (which means 1% to 10% of water’s abundance). Scientists have also noted that the rate of O2 production in the coma is surprisingly correlated with the coma’s rate of water production; from this, they’ve concluded that both the O2 and the water must be coming from the same icy phase of the comet.

So how did all of this O2 get into 67P/C-G in the first place? To try and answer this question, today’s authors looked back to well before 67P/C-G formed. ...

Synthesis of Molecular Oxygen via Irradiation of Ice Grains in the Protosolar Nebula - O. Mousis et al
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Pinpointing star formation in distant active galaxies

Post by bystander » Mon Apr 23, 2018 4:18 pm

Same time, same place: Pinpointing star formation in distant active galaxies
astrobites | 2018 Apr 20
Joanna Ramasawmy wrote:
Active galactic nuclei — the growing supermassive black holes at the hearts of massive galaxies — are a puzzling element in galaxy evolution. These monsters ‘feeding back’ energy and momentum into their surroundings are thought to play a crucial role in shaping a galaxy, but the exact nature of how and what they do to their host galaxies is still rather controversial. They could be a mechanism for shutting down star formation and preventing galaxies from growing too large — an effect called for by cosmological simulations, which require this negative AGN feedback to reproduce the observed galaxy luminosity function. However, there is also evidence for positive AGN feedback, in which star formation is enhanced by AGN activity.

The authors of today’s astrobite are not as concerned about how AGN affect the star formation in their hosts, as where these two processes are happening. They exploit the highest resolution data available to spatially resolve the regions of star formation and the location of the accreting black hole. ...

Cospatial Star Formation and Supermassive Black Hole Growth
in z ~ 3 Galaxies: Evidence for In Situ Co-evolution
- W. Rujopakarn et al
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The Nuclear Physics of Exploding Stars

Post by bystander » Mon Apr 23, 2018 4:39 pm

The Nuclear Physics of Exploding Stars
Astrobites | 2018 Apr 23
Sara Ayoub wrote:
Classical novae are commonly observed in our galaxy. These powerful events happen when a white dwarf in a binary system accretes material from a hydrogen-rich main sequence companion, until temperatures and densities are high enough that it ignites thermonuclear explosive burning on the white dwarf surface. We know quite a bit about these objects, but some things still don’t match up to our calculations.

For the first time ever, this paper uses experiments – real nuclear reactions performed in the lab – to help address some of these problems. ...

Direct Measurement of Astrophysically Important Resonances in 38K(p,γ)39Ca - G. Christian et al
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Predicting the Number of Planets from TESS

Post by bystander » Fri Apr 27, 2018 3:32 pm

Predicting the Number of Planets from TESS
Astrobites | 2018 Apr 24
Emma Foxell wrote:
Exoplanet hunters around the world held their breath while NASA’s Transiting Exoplanet Survey Satellite (TESS) launched last Wednesday. Thankfully the launch was a success and after 60 days of orbit manoeuvring and engineering tests, TESS is expected to begin its initial two years of science observations. The question is: how many planets do we expect TESS to find?

The TESS mission will observe 90% of the sky to find nearby unknown planets. However, to get mission funding, astronomers need to predict how many planets they expect to identify.

The authors of today’s paper took on this challenge with their three step modelling plan: 1) predict which stars would be observed, 2) randomly assign planets around them and 3) test if they are detected. ...

A Revised Exoplanet Yield from the Transiting Exoplanet Survey Satellite (TESS) - Thomas Barclay, Joshua Pepper, Elisa V. Quintana
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Did Stripped Stars Re-ionize the Universe?

Post by bystander » Fri Apr 27, 2018 3:39 pm

Did Stripped Stars Re-ionize the Universe?
Astrobites | 2018 Apr 25
Mathieu Renzo wrote:
One long standing puzzle about the evolution of the Universe is the epoch of reionization. After the recombination of electrons and protons that created the cosmic microwave background, the universe was opaque and light could not get through. But roughly ~500 million years after the Big Bang, something turned on and started producing ionizing radiation, causing protons and electrons to re-separate. This ended the “cosmic dark ages” and made the universe transparent again.

It is generally believed that this “something” was the population of massive stars (although AGN are also considered). Most stars have a thick hydrogen-rich envelope, which absorbs the ionizing photons they produce, but stars more massive than ~30 solar masses can lose to stellar winds their entire hydrogen-rich envelope. By doing so, these stars reveal their hot helium-rich core and become Wolf-Rayet stars, which can release ionizing radiation. However, current estimates of the massive star populations in the early Universe can hardly produce enough ionizing photons from Wolf-Rayet stars to explain the epoch of re-ionization.

In today’s paper, Götberg et al. propose another way to remove the ionizing-radiation-blocking envelope from stars: mass transfer in binaries. In the local universe, the vast majority of massive stars are in binaries. Interactions with a companion can change the properties of stars. In particular, it is expected that ~30% of massive stars will lose their hydrogen-rich envelope to their companion after the end of their main sequence phase, when they expand to become giants. By losing their envelope, these stars also expose their helium core, and become “stripped stars”. Stripped stars might have contributed or even dominated the epoch of re-ionization, if massive stars preferred to be in binaries also in the early universe. ...

Ionizing spectra of stars that lose their envelope through interaction
with a binary companion: role of metallicity
- Y. Gotberg, S. E. de Mink, J. H. Groh
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How, what and when of neutron star-white dwarf mergers

Post by bystander » Fri Apr 27, 2018 3:45 pm

How, what and when of neutron star-white dwarf mergers
Astrobites | 2018 Apr 26
Sanjana Curtis wrote:
Gather around, because it’s time to talk about compact binary mergers again – but not the usual ones! Today’s paper focuses on neutron star – white dwarf mergers. White dwarfs (WDs), neutron stars (NSs) and black holes (BHs) are all endpoints of stellar evolution. While binary systems involving various combinations of NSs and BHs have been the focus of a lot of work, as have those involving two WDs, the binaries we will discuss here have not received the same amount of attention. This paper presents the first systematic study of the demographics of NS-WD mergers and makes a number of predictions – including their rates and properties. ...

The demographics of neutron star - white dwarf mergers:
rates, delay-time distributions and progenitors
- S. Toonen et al
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Snake (on a Plane) in the Clouds

Post by bystander » Thu May 03, 2018 2:48 pm

Snake (on a Plane) in the Clouds
Astrobites | 2018 Apr 30
Caitlin Doughty wrote:
The Magellanic Clouds are two prominent splotches of light visible in the sky of the Southern Hemisphere. Named for their relative sizes, the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are two dwarf galaxies, satellites of the Milky Way which are believed to have been pulled into the domain of our galaxy some several billion years ago. During this accretion event, gravitational interactions flung a wide field of debris from the Clouds. While studying the Magellanic Bridge between the two Clouds, the authors of today’s paper found another piece of the puzzle: an intriguing little dwarf galaxy occupying the bridge of debris. Dubbed Hydrus I after the constellation of sky it occupies, a preliminary investigation of this ultra-faint dwarf galaxy (UFD) is the focus of today’s paper. ...

Snake in the Clouds: A New Nearby Dwarf Galaxy in the Magellanic Bridge - Sergey E. Koposov et al
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A Hyper Quick Return to Hypervelocity Stars

Post by bystander » Thu May 03, 2018 3:02 pm

A Hyper Quick Return to Hypervelocity Stars
Astrobites | 2018 May 01
Tarini Konchady wrote:
Hypervelocity stars appear to be in a tearing hurry. While the sun moseys around the Milky Way with no intent of leaving, hypervelocity stars are raring to leave home with speeds greater than the escape velocity of our galaxy. While the existence of hypervelocity stars was predicted in 1988, the first one was discovered in 2005 traveling at about 3 million km/hr (for comparison, the sun has an orbital velocity of about 828,000 km/hr).

What could have sent these stars flying out and away from the galaxy? The most popular idea is that they came from binary stars that interacted with the supermassive black hole that lives in the center of the Milky Way. While one star in the pair was captured by the black hole the other was flung out at a high speed. Other possibilities are that the stars were kicked out of nearby star clusters such as the Large Magellanic Cloud, and that some of them might be supernova remnants that received a kick from the aforementioned supernova.

The Gaia mission aims to provide the most precise measurements of position and radial velocity for over a billion stars throughout and just beyond the Milky Way. The second Gaia data release (DR2) was on April 25, 2018. With measurements of 1.3 billion stars, it was a large step up from the first data release that covered about 2 million stars.

With this wealth of position and velocity data, the authors of this paper reckoned it would be interesting to return to hypervelocity star candidates and see what the Gaia DR2 has to say about them. ...

Revisiting Hypervelocity Stars after Gaia DR2 - Douglas Boubert et al
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Quantum kicks messing with primordial black holes

Post by bystander » Thu May 03, 2018 3:10 pm

How slow can you go? Quantum kicks messing with primordial black holes
Astrobites | 2018 May 02
Philippa Cole wrote:
Primordial black holes are on the cosmologist community’s most wanted list because they make promising dark matter candidates (see here for an astrobite that explains why). They’ve risen through the ranks recently because the gravitational waves that LIGO detected came from merging black holes. The black holes were relatively light and could have formed early enough to have been primordial.

This tantalising detection means that a lot of effort has been put into finding models of the early universe that produce enough black holes to make up all of the dark matter. Today’s authors have shown that we all need to be extra careful with how we come up with these models – it turns out that pesky quantum effects can mess around with the number of primordial black holes that could be around today. ...

Primordial Black Holes from Inflation and Quantum Diffusion - Matteo Biagetti et al
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Earth Twins and Imposters – Determining the Odds of Detection

Post by bystander » Sun May 06, 2018 2:26 pm

Earth Twins and Imposters – Determining the Odds of Detection
Astrobites | 2018 May 03
Mara Zimmerman wrote:
Direct imaging is one of the best ways to characterize exoplanet atmospheres, especially when it comes to Earth-sized exoplanets in the habitable zone of Sun-like stars. Unfortunately, direct imaging can be tricky and difficult for many planetary systems, which is why future missions will be dedicated to this form of detection. Looking towards future exoplanet characterization missions, like the proposed LUVOIR and HabEx, these authors use current knowledge of detection methods to determine how capable these mission will be at detecting Earth-like exoplanets, or Earth twins. ...

The direct imaging search for Earth 2.0: Quantifying biases and planetary false positives - Claire Marie Guimond, Nicolas B. Cowan
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A Stellar Review: Re-Analyzing the Kepler Stellar Radii with Gaia

Post by bystander » Sun May 06, 2018 2:35 pm

A Stellar Review: Re-Analyzing the Kepler Stellar Radii with Gaia
Astrobites | 2018 May 04
Jessica Roberts wrote:
One of the most important mantras in studying exoplanets is this: you only know your planet as well as you know your star. This is because almost 95% of exoplanets have been detected indirectly, relying on stellar measurements to infer the existence of a planet. Using the transit method, we search for small dips in star light as the planet passes in front of the star. From this dip, we can approximate the size of the planet, assuming we know the size of the star. For radial velocity detections, we measure the “wobble” in star light as the planet tugs on its host star. And from this wobble we can measure the approximate mass of the planet, but again this is assuming we know the mass of the star. Because we rely so heavily on the stellar characteristics to infer planetary properties, we must characterize and classify these stars to the best of our ability.

But determining the masses, sizes, and even temperatures of stars is a challenge. Stars only provide one observable – their light. It is only when we combine their spectrum with models that we are able to deduce their other physical properties. Yet, this is also difficult as we require their intrinsic luminosity, without effects of distance. A dim close object may appear brighter than a distant bright one. Therefore, to determine a star’s actual brightness we need to know its distance. Without a precise distance measurement, we cannot accurately obtain its intrinsic luminosity, and without this information, we cannot properly constrain any of its characteristics and may even potentially misclassify the star!

With the recent Gaia data release of new parallaxes, we now have accurate distance measurements to over a billion stars. In other words, we are now able to better characterize these billion stars, which is an essential step towards better understanding exoplanets. That is the goal of this paper. The authors use Gaia distances to improve the stellar radii measurements of nearly all of the stars observed by Kepler. From these updated radii, the authors are also able to better constrain the sizes of thousands of confirmed and potential exoplanets. ...

Revised Radii of Kepler Stars and Planets using Gaia Data Release 2 - Travis A. Berger et al
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Which Are The Brightest Gravitational Wave Sources In Our Galaxy?

Post by bystander » Thu May 10, 2018 3:28 pm

Which Are The Brightest Gravitational Wave Sources In Our Galaxy?
Astrobites | 2018 May 07
Matthew Green wrote:
A couple of weeks ago, the Gaia satellite released data that it has been collecting since its launch in 2013. Among these data were “parallax” measurements (a property we can use to measure how far away something is) for over a billion stars — a revolution for many fields of astronomy. A couple of astrobites last week talked about some results from this data. In today’s paper, the authors used the data from Gaia to look at a group of gravitational-wave-emitting binary stars, and see how visible they will be to the planned LISA mission. ...

LISA verification binaries with updated distances from Gaia Data Release 2 - T. Kupfer et al
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Stellar Streams & The Nature of Dark Matter

Post by bystander » Thu May 10, 2018 3:38 pm

Stellar Streams & The Nature of Dark Matter
Astrobites | 2018 May 08
Nora Shipp wrote:
The type of matter that makes up humans, the Earth, and all of the stars in the Universe is only a fraction of the matter that exists. The rest is made up of a mysterious dark matter that light passes straight through, leaving it invisible. Although we cannot see this dark matter, we know that it exists because of the effect that it has on things that we can see. For example, just like the wind reveals its presence by blowing the leaves on trees, dark matter gives itself away by its gravitational pull on stars and galaxies. Today’s paper explores how we might use future telescopes to study this gravitational pull on stellar systems to describe the dark matter in our Universe.

One type of astronomical system that is particularly susceptible to the effects of dark matter is stellar streams (Figure 1). Stellar streams and their interactions with clumps of dark matter have been previously discussed in this astrobite. Today’s piece delves deeper into this discussion. ...

Probing the nature of dark matter particles with stellar streams - Nilanjan Banik et al
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The Spin-Down Rate of AR Sco is Impossible to Know … Right Now

Post by bystander » Thu May 10, 2018 3:54 pm

The Spin-Down Rate of AR Sco is Impossible to Know … Right Now
Astrobites | 2018 May 09
Thankful Cromartie wrote:
Two years ago, the first white dwarf pulsar was discovered by scientists at the South African Astronomical Observatory. The white dwarf in AR Scorpii — a binary system also containing an M-type main sequence star — was found to exhibit regular, extremely strong pulsations. The periodic emission from the white dwarf (henceforth, AR Sco) spans almost the entire electromagnetic spectrum, despite the fact that white dwarfs are almost never detected in far-infrared or radio light. Pulsations can cause the system’s optical flux to increase by a factor of four in less than a minute, and show extreme linear polarization of up to 40%. For these reasons, AR Sco was dubbed the first white dwarf pulsar, owing to its similarity to the rapidly rotating, highly magnetized neutron stars we know and love.

Today’s astrobite revisits a specific feature of AR Sco that was reported in Marsh et al.’s original 2016 paper: its reported spin-down rate of -(2.86 ± 0.36) × 10-17 Hz s-1. Energy loss from a spinning dipole (like a pulsar; see Section 6.1.5 here) is proportional to the object’s moment of inertia times its spin frequency times the rate at which its spin is slowing (its spin-down rate). While the moment of inertia can be derived from known properties of white dwarfs, accurate measurements of the spin frequency and spin-down rate are critical in understanding the star’s properties. For example, measuring energy loss can help us understand the source of the system’s luminosity, which would shed light on how it evolved. The authors of today’s paper present two years of new observations that contradict AR Sco’s originally reported spin-down rate; in fact, the new observations yield a value consistent with zero (the “constant frequency solution”). The authors emphasize that more observations are necessary to determine the actual energy loss of AR Sco, though their new observations have allowed for a better understanding of the system. ...

A reevaluation of the proposed spin-down of the white dwarf pulsar in AR Scorpii - Stephen B. Potter, David A. H. Buckley
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Antineutrinos, Left-Handed Molecules, and You

Post by bystander » Sun May 13, 2018 2:25 pm

Antineutrinos, Left-Handed Molecules, and You
Astrobites | 2018 May 10
Kerrin Hensley wrote:
Scientists are enamored with the search for life. They’ve scoured spectra for hints of life-supporting gases in the atmospheres of exoplanets. They’ve assessed the friendliness of galaxies near and far, and found the universe to be an unforgiving place. They’ve plumbed the depths of the oceans and studied pristine Antarctic lakes to understand the harsh conditions life might be able to withstand elsewhere in the cosmos.

The search for life on other worlds has been guided by what we know about life on Earth. Life as we know it depends on amino acids to survive. Today’s paper explores the effects of exotic astrophysical settings on amino acids, which could tell us something about how life came to be on Earth — and where else in the universe life like Earth’s might be found. ...

Sites That Can Produce Left-Handed Amino Acids in the
Supernova Neutrino Amino Acid Processing Model
- Richard N. Boyd et al
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Probing the source of a mysterious line in the laboratory

Post by bystander » Thu May 17, 2018 3:55 pm

Probing the source of a mysterious (dark matter?) line in the laboratory
Astrobites | 2018 May 14
Aaron Tohuvavohu wrote:
Over the past several years a mysterious spectral line at 3.5 keV has been identified in deep exposures carried out by many X-ray observatories, including Chandra, XMM-Newton, Suzaku, and NuSTAR. With most known atomic emission candidates ruled out and no known astrophysical origin, a dark matter source was hypothesized as the culprit producing this line. Indeed, there exist some dark matter models that predict the monochromatic emission of photons as part of the process of dark matter decay. Most notably sterile neutrino dark matter, a model that proposes a fourth, weighty and ‘sterile‘, neutrino flavor as the dark matter, predicts the emission of a 3.5 keV photon in the decay of a 7 keV sterile neutrino particle. However, the tables listing atomic transitions and their corresponding energies are quite incomplete, and often based on theoretical models that can be unreliable. As such, any assumption that a spectral feature has a dark matter origin, that is based mostly on its absence in tables of spectral data, is tenuous at best.

As a solution to this problem the authors attempt to produce the 3.5 keV line in the laboratory, motivated by a theoretical prediction of Liyi Gu, Jelle Kaastra, et al. (2016), wherein S16+ ions can steal electrons from a neutral atom during collision, a process known as charge exchange. These newly formed excited states will then radiatively decay to the ground state, releasing X-ray photons of the appropriate energy in the process. Gu and Kaastra argued that this process is ubiquitous whenever a hot plasma interacts with a neutral medium, and so should be expected for galaxy clusters where the hot intracluster medium interacts with cold clouds around the central galaxies. In order to test whether the charge exchange process with Sulfur ions can indeed produce an X-ray line near 3.5 keV, the authors of today’s paper use the experimental apparatus shown in Figure 1. ...

Laboratory Measurements Compellingly Support a Charge-Exchange
Mechanism for the ’Dark Matter’ ~3.5 keV X-Ray Line
- Chintan Shah et al
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Optics to outrace them all

Post by bystander » Thu May 17, 2018 4:08 pm

Optics to outrace them all
Astrobites | 2018 May 15
Eckhart Spalding wrote:
In the 1970s and 80s, scientists working for the U.S. Department of Defense developed a secret technology for imaging Soviet spy satellites from the ground. One of the consultants, Claire Max, realized the technology could benefit astronomy and pushed for its declassification. The concept of adaptive optics with laser-powered guide stars was finally released to the public in 1991.

Adaptive optics (AO) involves the rapid deformation of a mirror to remove distortions from an image. Imagine seeing a rock at the bottom of a clear but fast-moving stream of water. Inverting the jittery, garbled image into a true image of the rock is a significant engineering and computational challenge. First, we need to observe a simple point source behind the same distorting medium.

This is where laser guide stars come in. One type of laser lights up a thin layer of sodium at about 90 km altitude. This creates a “guide star” that experiences much of the distortion seen in a true star. Using this information, a deformable mirror can correct the true star’s image in real-time.

But large AO systems are extremely unwieldy. They require lots of money and manpower, and lots of observing overhead— it can take several minutes to slew to a target, lock onto a guide star, and initialize a correction loop for deforming the mirror. And yet, in today’s era of “big data” astronomy, AO imaging has become ever more relevant for rapidly-growing datasets. There’s a niche for fast, robotic AO. Recently, the optical scientist Christoph Baranec has done just that by building… Robo-AO. ...

Robo-AO Kepler Survey IV: The Effect of Nearby Stars on 3857 Planetary Candidate Systems - Carl Ziegler et al
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A classic optics experiment, in space with asteroids and AGNs!

Post by bystander » Thu May 17, 2018 4:23 pm

A classic optics experiment, in space with asteroids and AGNs!
Astrobites | 2018 May 16
Samuel Factor wrote:
For decades astronomers have used occultations to study celestial bodies such as the moon, asteroids and even quasars. An occultation occurs when some foreground object—the moon, a planet, or an asteroid—crosses in front of a background object—the sun (in the case of an eclipse), a planet, a star or a quasar. While rare, these occurrences can tell us a lot about the foreground and/or background objects. For example they have been used to determine the positions of quasars (before radio interferometers were available), detect binary stars, study surface topography of the moon, the atmosphere of the outer planets, and the shapes and sizes of asteroids (including New Horizons‘s next target). Today’s paper uses an intriguing technique to analyze an occultation of an active galactic nucleus (AGN) by an asteroid observed with the Very Long Baseline Array (VLBA). ...

Radio interferometric observation of an asteroid occultation - Jorma Harju et al
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Choosing targets with TESS

Post by bystander » Sun May 20, 2018 6:56 pm

Choosing targets with TESS
Astrobites | 2018 May 18
Peter Sinclair wrote:
TESS, the Transiting Exoplanet Survey Satellite, is a follow-up to NASA’s wildly successful Kepler mission. TESS launched into orbit aboard a SpaceX Falcon 9 rocket on April 18, 2018. Over the course of the next two years, it will conduct an exoplanet survey covering nearly the whole sky. Unlike Kepler, TESS will be looking for planets around bright and nearby stars. These bright stars are ideal for follow-up observations with ground and space-based observatories. The follow-up observations will allow astronomers to learn more about these exoplanets. In particular, astronomers are hoping to determine their masses and atmospheric compositions. ...

TESS’s mission has specifically been designed to make sure that astronomers can have an easy time doing follow-up observations. But in order to maximize their potential results, astronomers have to carefully decide which targets have the highest priority for follow-up observations. In particular, JWST is scheduled for a five year mission, so time is of the essence.

In today’s paper, Kempton et al. outline a series of criteria for determining which targets are of the highest value for follow-up observations. They do so using statistical methods based on the expected results from TESS. They split up the expected planet yield into three samples. The first is a large statistical sample containing a wide range of planet sizes. The second is small planets in and near their star’s habitable zone (ideal for looking for biosignatures). The final group of planets are terrestrial planets which could be observed via emission spectroscopy. ...

A Framework for Prioritizing the TESS Planetary Candidates
Most Amenable to Atmospheric Characterization
- Eliza M.-R. Kempton et al
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Turning a Blind Eye

Post by bystander » Sat May 26, 2018 3:19 pm

Turning a Blind Eye: Fighting the Gender Gap in Telescope Proposal Success
Astrobites | 2018 May 21
Stephanie Hamilton wrote:
If you’re a woman, you probably wouldn’t be surprised to hear that men tend to receive more paper citations or better scores on proposals than women. As women in STEM, we’re outnumbered by men and often faced with prejudices and biases in our fields (check out these posts for previous Astrobites coverage of gender bias). So it’s probably not surprising either that these biases show up in the scores that a Time Allocation Committee (TAC) awards to competing telescope proposals. In fact, there have already been several studies examining this very phenomenon in proposals to the Hubble Space Telescope, European Southern Observatory, and National Radio Astronomy Observatory. Today’s authors systematically evaluate the success of proposals written by men vs. women for Canadian observatories, showing that in the period from 2012-2016 proposals written by women were rated significantly worse than those written by men.

The authors of today’s paper obtained their data from the National Research Council (NRC) of Canada for ten recent telescope proposal cycles. They divided the proposals according to whether the Principal Investigator was male or female (noting that gender identity is not binary, however this information was not available to the authors). Of the 751 proposals analyzed, 72.7% were submitted by men while 27.3% were submitted by women. These numbers change slightly when the sample is divided into faculty PIs (78.5/21.5) vs. non-faculty PIs (69.8/39.2). ...

Sex-Disaggregated Systematics in Canadian Time Allocation Committee
Telescope Proposal Reviews
- Kristine Spekkens, Nicholas Cofie, Dennis R. Crabtree
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New Frontiers in CCD Systematics

Post by bystander » Sat May 26, 2018 3:28 pm

New Frontiers in CCD Systematics
Astrobites | 2018 May 22
Daniel Berke wrote:
I’ve lost count of the number of people who assume my job as an astronomer involves peering through a giant telescope all night. This romanticized picture of astronomy is out of date by over a century now, as astronomers were quick to adopt the new technology of photography to make observations repeatable and objective. At first this involved dry plate photography, but since the 1970s virtually all astronomical research has been conducted using charge coupled devices, or CCDs.

CCDs are a remarkable technology, so important that their discoverers won the 2009 Nobel Prize in Physics for the discovery. They do however have some limitations, and astronomers have become very good over the years at correcting for many of the issues they can have. In today’s paper the authors identify a previously-unknown issue with CCDs and set about quantifying its effects in a number of popular instruments and figuring out how to correct for it. ...

A Binary Offset Effect in CCD Readout and Its Impact on Astronomical Data - K. Boone et al
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