astrobites 2018

Find out the latest thinking about our universe.
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astrobites 2018

Postby bystander » Tue Jan 02, 2018 4:14 pm

astrobites

Astrobites is a daily astrophysical literature journal written by graduate students in astronomy since 2010. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.

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No Escape from the Milky Way

Postby bystander » Tue Jan 02, 2018 4:24 pm

No Escape from the Milky Way
astrobites | 2018 Jan 01
Amber Hornsby wrote:
Back in 2002, an apparent overdensity of stars was uncovered by the Sloan Digital Sky Survey (SDSS). This so-called Monoceros ring is a long filament of stars which has wrapped itself around the Milky Way several times. In the first bite of the year, we look at the simulations undertaken by astronomers to explore one of many scenarios proposed to explain its much disputed origin.

The Milky Way, like many other galaxies in the universe, is surrounded by several streams of stars. For example, the impressive Sagittarius stream, shown in Figure 1, is composed of stars it stole from the Sagittarius dwarf elliptical galaxy during its merger with the Milky Way. From its shared stellar properties to the dwarf galaxy and the stream’s structure, astronomers were able to deduce its origin. ...

On the Origin of the Monoceros Ring - I: Kinematics, Proper Motions, and the Nature of the Progenitor - Magda Guglielmo et al
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A Recipe for Mini-Neptunes

Postby bystander » Tue Jan 02, 2018 4:38 pm

A Recipe for Mini-Neptunes
astrobites | 2018 Jan 02
Michael Hammer wrote:
To be a master chef, one must have an incredible amount of culinary expertise and creativity to create a wide variety of dishes. To be a computational astrophysicist building planets in simulations, it feels a lot more like going to the store and buying a box of pancake mix. Instead of buying all the ingredients, you start with a pre-made mixture. From there, all you have to do is just add water! ...

In today’s paper, Julia Venturini and Ravit Helled explore which planet and disk conditions are best for building planets that have just the right-sized atmosphere to be classified as Mini-Neptunes – the most common type of exoplanet (see Figure 2), even though there are none in our solar system. ...

The Formation of Mini-Neptunes - Julia Venturini, Ravit Helled
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Sensing a Pulsar’s Sense of Rotation

Postby bystander » Mon Jan 08, 2018 8:58 pm

Sensing a Pulsar’s Sense of Rotation
astrobites | 2018 Jan 03
Thankful Cromartie wrote:
In 2017, the field of pulsar astrophysics turned 50 years old. In those 50 years, we’ve learned a lot about these rapidly rotating neutron stars — and they’ve facilitated some of the most exciting scientific discoveries of the last century. It’s easy to assume that in the years since 1967 we’ve confirmed most of the basic assumptions we make about these compact objects (like their evolutionary history, motion, and composition). However, today’s astrobite reveals that we still have a lot to learn.

We use pulsars to do unfathomably cool science, from testing general relativity and detecting gravitational waves to enabling spacecraft navigation. With such an advanced understanding of these objects, you might expect us to be able to determine a property as basic as what direction a pulsar is rotating. Remarkably, we haven’t been able to — at least not with much certainty. This study from Pol et al. presents the first direct determination of a pulsar’s sense of rotation (i.e. if it’s rotating prograde or retrograde with respect to its orbit). It also provides support for the widely accepted rotating lighthouse model of pulsars, which describes pulsars as rotating neutron stars with radiation emitted from their magnetic poles. Their beams sweep across our line of sight, creating the rapid pulsing signals we detect.

The authors of this work exploited a one-of-a-kind system, called PSR J0737–3039 (the Double Pulsar). It is the only known binary that consists of two detectable radio pulsars, and its fast orbital period (~2.5 hours) makes it the most relativistic pulsar binary we know of. More subtle features (detailed below) make this system ideal for the determination of a pulsar’s sense of rotation. ...

A Direct Measurement of Sense of Rotation of PSR J0737-3039A - Nihan Pol et al
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Hot Jupiters are not really like layer-cakes

Postby bystander » Mon Jan 08, 2018 9:10 pm

Hot Jupiters are not really like layer-cakes
astrobites | 2018 Jan 04
Shang-Min Tsai wrote:
The phase curves of transit planets reveal the longitudinal (from day to night) variation. When observing with multiple-wavelengths, they further tell us the information in the radial direction. Different wavebands in principle probe different pressure depths in the atmosphere, since different wavelengths have different opacities (the ability to absorb and scatter photons). However, the opacity is determined by the local temperature, pressure, and gaseous composition, and there is no reason for the opacity to hold constant across the planet, as we will see later. In today’s paper, the authors address this important yet challenging issue when it comes to interpreting the multi-band phase curves. ...

Wavelength Does Not Equal Pressure: Vertical Contribution Functions and
Their Implications for Mapping Hot Jupiters
- Ian Dobbs-Dixon, Nicolas B. Cowan
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A new kind of animal in the exoplanet zoo

Postby bystander » Mon Jan 08, 2018 9:17 pm

A new kind of animal in the exoplanet zoo
astrobites | 2018 Jan 05
Kerrin Hensley wrote:
By now, exoplanet enthusiasts will be familiar with hot Jupiters, super-Earths, mini Neptunes, and even exo-Venuses, to name just a few. As the search continues, astronomers are finding colder and smaller planets, making possible the discovery of more Solar System analogs. In today’s paper, Lora et al. consider exoplanets similar to one of the most tantalizingly Earth-like yet alien bodies in the Solar System: Titan. ...

In today’s paper, Lora et al. use theoretical models to investigate the atmospheres of Titan-like exoplanets orbiting Sun-like stars as well as K and M dwarfs, which are smaller and redder than the Sun. Thanks to Cassini, we already have an idea of what Titan might look like masquerading as an exoplanet around a Sun-like star, but Titan takes about 30 years to orbit the Sun; that’s a long time to wait to detect and confirm an exoplanet! Around an M dwarf, a planet with the same effective temperature as Titan (~80 K) takes only about 2 years to complete an orbit—much easier and quicker to detect. Titan-like exoplanets don’t need to crowd M dwarfs as closely as Earth-like planets do, so they are less susceptible to the notoriously nasty space weather of cool stars and they are less likely to be tidally locked. Though neither issue immediately disqualifies M dwarf planets from the habitability contest, considering a cooler planet appears to solve both problems at once. ...

Atmospheric circulation, chemistry, and infrared spectra of Titan-like
exoplanets around different stellar types
- Juan M. Lora, Tiffany Kataria, Peter Gao
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor


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