astrobites 2017

Find out the latest thinking about our universe.
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The oldest dust bunnies in the universe

Postby bystander » Wed Aug 09, 2017 7:09 pm

The oldest dust bunnies in the universe
astrobites | 2017 Aug 02
Mia de los Reyes wrote:
Dust isn’t just something to sweep up under your bed. In fact, when we observe a galaxy outside the Milky Way, dust is everywhere, strongly affecting what we see. There’s dust between us and the galaxy (including dust in the Milky Way itself), which absorbs the light from the galaxy. We can correct for this using dust maps, which tell us how much dust is in the direction of the galaxy.

Then there’s dust within the galaxy itself, which is a bit trickier. All of the radiation produced within the galaxy—especially radiation from star formation—is susceptible to absorption by this dust. The dust then re-radiates the absorbed energy in the form of infrared light. Infrared light, therefore, traces both the amount of dust and the amount of star formation in a galaxy. ...

An amplified dusty star-forming galaxy at z=6: unveiling an elusive population of galaxies - Jorge A. Zavala et al
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The Generation Game

Postby bystander » Wed Aug 09, 2017 7:20 pm

The Generation Game
astrobites | 2017 Aug 03
Paddy Alton wrote:
Stars are a sociable bunch, by and large. They don’t like to be alone: some hang out in pairs, or sometimes in small groups of three or four. Others still are extreme extroverts, keeping company with hundreds of thousands of other stars, for example in densely packed globular clusters (GCs) ...

This isn’t be the first article on star clusters to feature on astrobites – and you can be pretty sure it won’t be the last. After all, we’ve been studying them since the seventeenth century and people are still publishing papers about them! ...

Young LMC clusters: the role of red supergiants and multiple stellar
populations in their integrated light and CMDs
- Randa S. Asa'd et al
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The mass of Kepler-10c revisited

Postby bystander » Fri Aug 11, 2017 3:47 pm

The mass of Kepler-10c revisited: upping the radial velocities game
astrobites | 2017 Aug 07
Leonardo dos Santos wrote:
Kepler-10 (or K-10 for the acquainted) is one of those exoplanet-hosting stars that keep on giving us more and more reasons to scratch our heads. A publication from 2014 claimed that K-10c was a weirdly massive planet, possibly of a new kind of extremely solid object. Cue another study two years later — using the same technique, mind you — and a 3-times lower mass was measured. It turns out that the key piece to solve this puzzle is not exactly more data, but a more careful analysis of the already available data. ...

Pinning down the mass of Kepler-10c: the importance of sampling
and model comparison
- Vinesh Rajpaul, Lars A. Buchhave, Suzanne Aigrain
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A (Sub-Millimetre) Galaxy Far, Far Away

Postby bystander » Fri Aug 11, 2017 4:06 pm

A (Sub-Millimetre) Galaxy Far, Far Away
astrobites | 2017 Aug 08
Matthew Green wrote:
Disclaimer: This paper was covered in a previous astrobite by Mia de los Reyes.

Today’s paper is about the discovery of G09 83808, a distant, dusty, and star-forming galaxy that might help us learn more about star formation in the early Universe. ...

An amplified dusty star-forming galaxy at z=6: unveiling an elusive population of galaxies - Jorge A. Zavala et al
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A Treasure Map of Massive Stars

Postby bystander » Fri Aug 11, 2017 4:16 pm

A Treasure Map of Massive Stars
astrobites | 2017 Aug 09
Benny Tsang wrote:
Charting a map of the densest gas clouds in the Milky Way will lead us to the hidden corners of our home galaxy where new stars form. It is not surprising as stars are basically extra-dense clouds of gas that shine with light produced by fusing hydrogen nuclei in their cores. Mapping the locations of the densest clouds is therefore equivalent to finding stars-to-be before their nuclear engines turn on. Creating detailed maps of gas and dust in the Universe is therefore crucial to outlining the environments in which stars and planets form (a vision that kept appearing in the recent 230th AAS meeting). ...

The ATLASGAL survey: The sample of young massive cluster progenitors - T. Csengeri et al

viewtopic.php?t=35673
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Somewhere in the Stratosphere

Postby bystander » Fri Aug 11, 2017 4:22 pm

Somewhere in the Stratosphere
astrobites | 2017 Aug 10
Elisabeth Matthews wrote:
Hot Jupiters are pretty weird. That’s unsurprising, given that they are planets the size of Jupiter, but are closer to their host stars than Mercury is to the Sun. This can produce some pretty wacky environments. Hot Jupiters can reach incredible temperatures (KELT-16b is 2500K), which can lead to extreme weather systems, such as rains made of glass. Meanwhile, some of these hot Jupiters are literally evaporating away, or dissipating onto their host stars. Astronomers are just beginning to learn what these alien worlds are like. A recent paper studied the atmosphere of 10 hot Jupiters, and was covered here on astrobites by Natasha Batalha. This paper marked the beginning of the period of so-called “comparative exoplanetology”. Enough exoplanets have now been observed that we can start to compare their different atmospheres and weather systems, and attempt to find trends and understand their formation and evolution.

Today we focus on one particularly weird hot Jupiter: WASP-121b. This planet is just 0.025AU from its host star, meaning that it orbits the star every 1.28 days. Any visitors to this planet get to celebrate a lot of birthdays! However, they would also have to survive the toasty ~2700K upper atmosphere, so I suggest you think twice before investing in party hats. ...

An ultrahot gas-giant exoplanet with a stratosphere - Thomas M. Evans et al

viewtopic.php?t=37447
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Predicting a 21cm AGN reionization signal

Postby bystander » Fri Aug 11, 2017 4:35 pm

Predicting a 21cm AGN reionization signal
astrobites | 2017 Aug 11
Joshua Kerrigan wrote:
It’s a generally accepted idea that the earliest galaxies reionized the universe, however it’s always interesting and fun to explore potentially rare sources, especially when they’re as cool as AGN. Now “what are AGN ?” you may ask. Active Galactic Nuclei, such as quasars, are a galaxy with a compact core that are thought to host supermassive black holes at their center. These central black holes accrete matter surrounding them, causing these galaxies to have an abnormally high luminosity across the electromagnetic spectrum. Initially it was thought that AGN at high redshift were uncommon and therefore could not be a primary source for reionization. Recent detections of high redshift AGN have changed that outlook and this motivates today’s astrobite about how AGN affect the 21cm signal from reionization. ...

Large 21-cm signals from AGN-dominated reionization - Girish Kulkarni et al
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Cosmology Results from The Dark Energy Survey!

Postby bystander » Tue Aug 15, 2017 3:12 pm

Cosmology Results from The Dark Energy Survey!
astrobites | 2017 Aug 14
Gourav Khullar wrote:
I must tell you, these survey results were a long time coming. With CMB telescopes vastly expanding our understanding of the early universe the past two decades, it was only a matter of time before we gained the capability to perform a census of the millions of galaxies at our disposal today using ground based telescopes. This is a very important step: studying today’s galaxies tells us whether the universe evolved after the CMB the way we think it did.

Today’s bite is not just about thanking the early universe for being kind in its evolution, but also an ode to the 400+ scientists working over the last two decades to bring this census to fruition!

The Dark Energy Survey (DES) is a 5-year long endeavor meant to map astrophysical objects over 1/8th of the total night sky visible from Earth (5000 square degrees!), making it one of the largest all-sky surveys ever undertaken from the Earth. DES, which has been in operation since 2013 and is being considered the natural successor to the Sloan Digital Sky Survey (SDSS), uses the 4m Blanco Telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile for its observations.

Attached to the Blanco telescope is the Dark Energy Camera ([url]DECam[/url]), the gift of the DES collaboration to the scientific community. DECam is a 570 megapixel camera (which until a couple years ago was the most powerful digital camera in the world) that captures millions of objects during every night of operation. Its objective? To put constraints on the cosmology of the universe, and to inform formation and evolution models by studying the distribution of galaxies. ...

Dark Energy Survey Year 1 Results:

    Cosmological Constraints from Galaxy Clustering and Weak Lensing - DES Collaboration: T. M. C. Abbott et al
    Photometric Data Set for Cosmology - A. Drlica-Wagner et al
    Redshift Distributions of the Weak Lensing Source Galaxies - B. Hoyle et al
    Weak Lensing Shape Catalogues - J. Zuntz et al
    The Impact of Galaxy Neighbours on Weak Lensing Cosmology with im3shape - S. Samuroff et al
    Curved-Sky Weak Lensing Mass Map - C. Chang et al
    Galaxy Clustering for Combined Probes - J. Elvin-Poole et al
    Galaxy-Galaxy Lensing - J. Prat et al
    Cosmological Constraints from Cosmic Shear - M. A. Troxel et al
    Multi-Probe Methodology and Simulated Likelihood Analyses - E. Krause et al

viewtopic.php?p=273025#p273025
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New twinkles in the sky

Postby bystander » Tue Aug 15, 2017 3:23 pm

New twinkles in the sky
astrobites | 2017 Aug 15
Ingrid Pelisoli wrote:
Has the Sun ever winked at you? It was probably too subtle for you to notice, but this definitely has happened. Our Sun’s brightness is constantly varying due to convective bubbles near its surface. Other stars similar to the Sun undergo the same process, forming a class of pulsating stars called solar-like oscillators. This is only one of many classes of pulsating stars. We are very lucky that stars pulsate and we are able to detect that: this is the only way we can explore the interior of stars. The frequency of the pulsations we can detect depends directly on the internal structure of the star, so this method allows us to probe stellar interiors and check if what we obtain from our stellar evolution models is correct.

Thus astronomers are constantly sweeping the sky in search of new pulsators. There are dedicated projects doing that, but sometimes data from projects with other scientific goals can be used. One project that has so far revealed the existence of almost 500,000 pulsating stars is the Optical Gravitational Lensing Experiment (OGLE). As the name suggests, the goal of the project is to study dark matter though microlensing phenomena. Matter, be it dark or not, bends the light, focusing it and acting as a magnifying glass. Identifying regions where this magnification occurs is a way to study objects that emit little or even no light. To achieve that, photometric data was obtained for about a billion stars over the years, allowing also the search for pulsators. With such a huge amount of data, there’s a good chance of finding something new and rare. That’s exactly what the authors of today’s paper spotted: an entirely new class of variables, with some properties which are kind of hard to explain.

Blue large-amplitude pulsators as a new class of variable stars - Pawel Pietrukowicz et al
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Re: astrobites 2017

Postby Ann » Wed Aug 16, 2017 5:18 am

BLUE twinkles! :D

(I know... I'm beyond predictable.)

One more thing, though. As expected, these variable and very blue stars have in all probability undergone mass loss. Stars not on the main sequence are blue because they are smaller than their red "cousins", and their surface is closer to their hot interior.

Ann
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Links in the Evolution Chain of Post-Starburst Galaxies

Postby bystander » Tue Aug 22, 2017 4:49 pm

Links in the Evolution Chain of Post-Starburst Galaxies
astrobites | 2017 Aug 16
Jamila Pegues wrote:
If you’ve ever spared a quick, casual glance at the night sky, you may have noticed a few bright stars, sparkling bravely alongside the Moon. But if you look long enough and deep enough, you’ll notice that there’s a lot more out there than just a few twinkling stars. Figure 1 shows a beautiful snapshot of the Hubble Ultra Deep Field, where we can see not just stars but galaxies – nearly 10,000 of them! – across an area that’s only about one-tenth the length of the full Moon. The galaxies that we see come in all sorts of shapes, sizes, ages, and colors, but astronomers, like the authors of today’s astrobite, believe that there are similarities and patterns in how each of these galaxies grow and evolve. ...

The Evolutionary Sequence of Post-Starburst Galaxies - C. L. Wilkinson, K. A. Pimbblet, J. P. Stott
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Sneaky pete baryons in gravitational lensing

Postby bystander » Tue Aug 22, 2017 4:57 pm

Sneaky pete baryons in gravitational lensing
astrobites | 2017 Aug 21
Suk Sien Tie wrote:
When a photon perilously escapes being engulfed by gases in its galaxy, it embarks on a long journey to reach our telescopes. Along the way, the combined gravitational field of nearby galaxies and galaxy clusters lures the photon away from sticking to a straight path. Occasionally, its path gets very bent when it passes very close to a galaxy, so much so that when the photon reaches our telescope, we see multiple images of the galaxy where the photon originates. This phenomenon of light bending due to the gravity of matter is known as gravitational lensing. ...

In the context of today’s paper, gravitational lensing is a tool to detect dark matter substructures in the halo of the lensing galaxy. Dark matter is that mysterious stuff that makes up nearly 85% of the Universe mass, does not emit light, and interacts only through gravity. The ratio of fluxes between any pair of lensed images is sensitive to the underlying mass distribution of the lens galaxy. In the absence of dark matter substructures, the flux ratios of the images are well predicted using a smooth lens model. But it does not work as well if dark matter substructures are present, resulting in anomalous flux ratios. Hence, flux ratio anomaly is a telltale sign of dark matter.

Or is it? ...

Flux-ratio anomalies from discs and other baryonic structures in the Illustris simulation - Jen-Wei Hsueh et al
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