Tagged: Astrobites Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 11:16 am on February 22, 2018 Permalink | Reply
    Tags: Astrobites, , , , , PEPSI technology   

    From astrobites: “Deep Spectra with PEPSI” 

    Astrobites bloc

    astrobites

    Title: PEPSI deep spectra III: A chemical analysis of the ancient planet-host star Kepler−444
    https://arxiv.org/abs/1712.06986
    Authors: C. E. Mack III, K. G. Strassmeier, I. Ilyin, S. C. Schuler, F. Spada, and S. A. Barnes
    First Author’s Institution: Leibnitz Institute for Astrophysics Potsdam
    1
    Status: In press in Astronomy & Astrophysics, open access

    More and more information can be squeezed out of spectra at ever higher resolutions and over longer wavelength ranges. Today, one cutting-edge spectrograph at visible wavelengths is the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) on Mt. Graham in Arizona. Cunningly, PEPSI was build to take data from three different telescopes on Mt. Graham. They include 1.) the LBT itself, with twin 8.4 m primary mirrors; 2.) the nearby 1.8 m Vatican Advanced Technology Telescope (VATT) through an underground cable; and 3.) a tiny, effectively 13 mm solar telescope on the LBT patio, right next to the barbeque.

    U Arizona Large Binocular Telescope, Mount Graham, Arizona, USA, Altitude 3,221 m (10,568 ft)

    Vatican Advanced Technology Telescope, U Arizona Steward Observatory, Altitude 792 meters (2,598 ft)

    The hydra-headed PEPSI can produce spectra with a resolution of up to around λ/Δλ=270,000 between wavelengths of about 380 to 910 nm. The first deep spectral data from PEPSI are just now coming out in a set of three papers, and we’ll look at one of them, a chemical analysis of a planet-hosting star.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. 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.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

    Advertisements
     
  • richardmitnick 1:47 pm on February 19, 2018 Permalink | Reply
    Tags: Astrobites, , , , ,   

    From astrobites: “Big light comes from small clusters” 

    Astrobites bloc

    astrobites

    Title: The Little Engines That Could? Globular Clusters Contribute Significantly to Reionization-era Star Formation
    Authors: Michael Boylan-Kolchin
    First Author’s Institution: University of Texas, Austin, TX, USA

    Status: Submitted to Monthly Notices of the Royal Astronomical Society, open access via arXiv

    This article was previously covered on Astrobites, but here is another Astrobiter’s take on it!

    When the lights went on.

    Reionization era and first stars, Caltech

    The Epoch of Reionization (EoR), as its name suggests, is the relic of a very ionizing (read exciting) time in the evolutionary history of our universe. It is the time when the first stars are thought to have lived and died, as light emerged in the darkness of the cosmos, for the first time after recombination. Leading up to this point, the universe had been unobservable for millions of years due to the presence of neutral hydrogen that blocks any high energy photons capable of ionizing the medium by absorbing them. However, something during the reionization epoch provided enough light to strip the electrons off of all the existing neutral atoms, making it possible to peer back into the formation of first stars and galaxies.

    Finding the culprit.

    Today, what exactly caused reionization remains a puzzle that many scientists are eager to solve. Sources such as supernovae, active galactic nuclei, binary mergers, and more recently, faint dwarf galaxies have all been posited as significant contributors of ionizing photons. Regrettably, constraining them with observations, especially in the case of faint sources, is far from easy and continues to render the pursuit inconclusive.

    In the wake of this situation, author Boylan-Kolchin turns his eye towards something that has long been a corner-stone of the study of early galaxies. These objects are tightly bound collection of stars a.k.a globular clusters (GCs), whose numerousness and ancient origin (coinciding with the EoR) make them important objects in the context of cosmic reionization. In his work, the author seeks to theoretically infer the contribution of GCs to reionization, and spell out its implications. Using the number density and stellar mass distribution of GCs from local observations, and a uniform rate of formation over 1 Gyr (redshift z ~ 4-10), he artificially synthesizes stellar populations characteristic of a GC to obtain its ultraviolet luminosity function (UVLF; the number distribution per unit volume and magnitude in ultraviolet wavelengths) at various epochs.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. 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.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 12:27 pm on February 8, 2018 Permalink | Reply
    Tags: Astrobites, , , , , How much does the Milky… weigh?   

    From astrobites: “How much does the Milky… weigh?” 

    Astrobites bloc

    astrobites

    Title: What galaxy masses perturb the local cosmic expansion?
    Authors: Jorge Penarrubia & Azadeh Fattahi
    First Author’s Institution: Institute for Astronomy, University of Edinburgh, Royal Observatory
    1
    Status: Published in MNRAS, open access

    Picture this: you’re at your local clinic for an annual physical, and your doctor asks to measure your weight. Simple, right? But now, imagine your doctor doesn’t have a scale, nor the ability to lift you, nor any understanding of what your body is made of. Oh, and you’re invisible, too. Not so simple anymore…

    This is (more or less) the challenge astrophysicists face when trying the measure the mass of the Milky Way, our humble galactic home. And even though this has been an active area of research for nearly 60 years, today’s best estimates still vary widely from one another (see figure 1 for a few recent examples). Back at your annual physical, it’s as if your doctor tells you, “I think you weigh about 150 lbs, give or take 80 lbs.”

    2
    Figure 1: Fourteen recent mass estimates of the Milky Way produced since 1999, obtained through a variety of different methods. Note how the estimates vary significantly from each other, by up to a factor of 5. Figure adapted from Table 8 in Hawthorn & Gerhard 2017.

    A guide to measuring heavy, invisible things

    Like other galaxies, much of the Milky Way’s mass comes in the form of dark matter, which is a bit of a bummer, because we can’t see it. What we can see are visible objects – like stars, gas clouds, or dust particles – whose motion is a tell-tale for the dark matter density around them (this Astrobite and this one provide a great overview of how this is done in practice). So in order to measure the total mass of the galaxy (often referred to as the galaxy’s virial mass), we need to find observable objects all the way out to the galaxy’s edge. The issue is that out at the fringes of our galaxy, visible tracers are few and hard to find. This is one of the main causes of the large uncertainty in our estimate of the Milky Way’s mass.

    Fortunately, there are a few other theoretical approaches to measuring the total mass of a galaxy. And these methods do not rely as heavily on observing faint objects at the outskirts of galaxies. Today’s paper discusses several of these, and specifically one that involves measuring the mass of a galaxy based on how it perturbs the local Hubble flow (or in other words, how its gravitational force affects the motion of other galaxies far beyond its own boundaries, where the expansion of the universe is the dominant effect). In theory, the mass derived from the perturbed Hubble flow is equal to the virial mass of the galaxy, which could be a big deal because we can theoretically calculate the mass of the Milky Way without needing to find faint objects at the edge of the galaxy!

    3
    Figure 2: 6 of the 12 APOSTLE simulations. The two dashed circles represent the boundaries of the galaxy equivalents of the Milky Way and Andromeda, and the solid circle represents a 3 Mpc radius around the pair of galaxies, inside of which one can measure their influence on the Hubble Flow. Figure 2 in the paper.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. 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.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 11:24 am on February 7, 2018 Permalink | Reply
    Tags: Astrobites, , , , , , The Deepest Rumblings of the Sun   

    From astrobites: “The Deepest Rumblings of the Sun” 

    Astrobites bloc

    astrobites

    Feb 7, 2018
    Avery Schiff

    Title: Asymptotic g modes: Evidence for a rapid rotation of the solar core
    Authors: Eric Fossat, Patrick Boumier, Thierry Corbard, et al.
    First Author’s Institution: Université Côte d’Azur, Observatoire Côte d’Azur, France
    1
    Status: Published in Astronomy and Astrophysics, open access

    Far below its surface, the Sun slowly breaths with invisible pulses. Blobs of plasma are launched upwards by buoyant forces, only to reach the peak of their trajectories and plunge back to the depths below. This motion is known as a g-mode oscillation, and until recently it was unseen by solar scientists. In today’s paper, Fossat et al. describe one of the most promising detections of the g-modes to date and the implications for the Sun’s deepest layers.

    Helioseismology

    While the Sun appears constant in brightness to the naked eye, careful telescope observations reveal that it periodically dims and brightens on a miniscule scale. Just as a song is made from many notes, the flickering occurs at countless different frequencies that create the “music” of the Sun. Helioseismology, an observation technique that tracks vibrations deep into the Sun, uses Fourier analysis to determine which frequencies are most important and study three potential sources of brightness fluctuations on the Sun: p-mode, g-mode, and f-mode oscillations. Since the brightness of plasma is strongly related to the density, each mode is associated with material compressing or decompressing in some way. P-mode and f-mode oscillations are frequently observed at the solar surface, but the g-modes lurk far beneath the surface of the Sun. By studying g-modes, we are studying the lowest depths of the Sun far below what is visible to us.

    2
    Figure 1: An illustration of the layers of the sun. While p-mode oscillations are able to travel from the surface all the way to the core, g-modes are unable to escape the radiative zone. Credit: ESA

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. 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.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 8:37 am on February 1, 2018 Permalink | Reply
    Tags: Astrobites, , , , , Post-starburst galaxies: the missing link in galaxy evolution?   

    From astrobites: “Post-starburst galaxies: the missing link in galaxy evolution?” 

    Astrobites bloc

    astrobites

    Feb 1, 2018
    Joanna Ramasawmy

    Title: Massive post-starburst galaxies at z > 1 are compact proto-spheroids
    Authors: Omar Almaini, Vivienne Wild, David T. Maltby, William G. Hartley, Chris Simpson, Nina A. Hatch, Ross J. McLure, James S. Dunlop, Kate Rowlands
    First Author’s Institution: School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, U.K
    1
    Status: Accepted for publication in MNRAS, open access

    2
    NGC 5090 and 5091, a pair of interacting galaxies which show two different morphologies, or galaxy shapes. NGC 5090 is an elliptical galaxy, whereas NGC 5091 is a disc-shaped spiral galaxy. Source: ESO.

    Surveys of the nearby universe show that we can divide galaxies into two types if we look at their colours — we find a “blue cloud” of star-forming galaxies, and “red sequence” of passive ellipticals without active star formation. Besides their colours, there is another important difference between these two types of galaxies: their shape, or morphology. It turns out that most blue galaxies have a disc shape, while red galaxies are spheroidal. The majority of massive galaxies we see around us are spheroidal passive galaxies. But how and when do galaxies evolve from star-forming discs to red-and-dead spheroids?

    In this paper, the authors investigate post-starburst galaxies (PSBs, or E+A galaxies as described in the astrobites galaxy classification guide), which are galaxies that have only recently stopped forming stars. One narrative of galaxy evolution suggests that galaxies move from the blue cloud to the red sequence following a rapid quenching of star formation. By shutting down star formation, the hot blue stars rapidly die out and the galaxy is left with an old red stellar population, explaining the transition in colour. However, this doesn’t explain the additional structural transformation that changes galaxies from a disc to a spheroid morphology. PSBs, rare galaxies caught in this transition phase, might hold the key.

    PSBs are traditionally identified by their spectral features, usually the strong absorption lines associated with the A-type stars that dominate these galaxies’ starlight. However, spectroscopy limits us to looking at nearby, bright galaxies. Very distant galaxies are much fainter and so require very long exposure times on the most expensive space telescopes. The authors of this paper use a novel technique, identifying “supercolours” that allow them to categorise galaxies using just photometric data — which is much cheaper as it can be done from the ground! This method allows them to obtain a large sample of galaxies at high redshifts (z > 1), investigating an earlier period in the history of the universe than other studies of PSBs. The authors are interested in two properties of PSBs: the size (or compactness), and the morphological shape. The authors then compare these properties of PSBs to those of the blue cloud and red sequence galaxy populations.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. 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.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 1:39 pm on January 24, 2018 Permalink | Reply
    Tags: Astrobites, , , , ,   

    From astrobites: “Hunting for new physics in a black hole’s shadow” 

    Astrobites bloc

    astrobites

    Jan 24, 2018
    Aaron Tohuvavohu

    Title: Event Horizon Telescope Observations as Probes for Quantum Structure of Astrophysical Black Holes
    Authors: Steven B. Giddings & Dimitrios Psaltis
    First Author’s Institution: University of California, Santa Barbara

    Status: Submitted to Phys Rev D, open access on the arXiv.

    For 5 days in April of 2017, 8 radio telescopes on 4 continents all pointed in concert at Sagittarius A*, the supermassive black hole at the center of our galaxy.

    SGR A* , the supermassive black hole at the center of the Milky Way. NASA’s Chandra X-Ray Observatory

    During this observing campaign these 8 telescopes effectively became one Earth-sized radio telescope, the Event Horizon Telescope (EHT).

    Event Horizon Telescope Array

    Arizona Radio Observatory
    Arizona Radio Observatory/Submillimeter-wave Astronomy (ARO/SMT)

    ESO/APEX
    Atacama Pathfinder EXperiment

    CARMA Array no longer in service
    Combined Array for Research in Millimeter-wave Astronomy (CARMA)

    Atacama Submillimeter Telescope Experiment (ASTE)
    Atacama Submillimeter Telescope Experiment (ASTE)

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

    IRAM NOEMA interferometer
    Institut de Radioastronomie Millimetrique (IRAM) 30m

    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA
    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array, Chile

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    NSF CfA Greenland telescope

    Greenland Telescope

    Using hydrogen maser atomic clocks to track the difference in the arrival times of the radio signal at the various telescopes, the far-flung array can emulate a single telescope with an effective diameter equal to that of our planet, a technique called very long baseline interferometry (VLBI).

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. 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.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 8:31 am on January 18, 2018 Permalink | Reply
    Tags: Astrobites, , , , Capturing neutrons in the thin disk,   

    From astrobites: “Capturing neutrons in the thin disk” 

    Astrobites bloc

    astrobites

    Jan 17, 2018
    Eckhart Spalding

    Title: Neutron-capture elements across the Galactic thin disk using Cepheids
    Authors: R. da Silva, B. Lemasle, G. Bono et al.
    First Author’s Institution: INAF/University of Rome
    1
    Status: Published in Astronomy & Astrophysics, open access

    The evolution of the Milky Way holds a place of special importance for us, because many aspects of it are easier to study than in other galaxies, and, after all, we live in it. From our vantage point, we can observe up-close the nitty-gritty of the galactic assembly process, and come to understand how the formation of our own solar system is intimately tied to the Galaxy’s long and storied dynamical and chemical history. In today’s bite, let’s focus on an aspect of the Milky Way’s chemical story.

    1
    A comparison of lines in the r-process-weak star HD122563 and the r-process-strong star HE 1523−0901. The narrow and crowded atomic lines often require high-resolution spectroscopy to disentangle the r- from s-process history of the star’s chemical makeup, which means large telescopes, long integration times, and consequentially small sample sizes of Cepheids. (Fig. 2 in Frebel, 2008.)

    In today’s paper, which was published before the observations of GW170817, the authors assemble a homogeneous data set to infer the spatial distribution of r- and s-process elements in the Galaxy. What’s a good way to map the distribution of elements in the Galaxy? Well, by measuring abundances in stars that are good distance indicators!

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. 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.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 7:37 am on January 16, 2018 Permalink | Reply
    Tags: Astrobites, , , , , How habitable is your galaxy?   

    From astrobites: “How habitable is your galaxy?” 

    Astrobites bloc

    astrobites

    Jan 16, 2018
    Matthew Green

    Title: Exploring the Cosmic Evolution of Habitability with Galaxy Merger Trees
    Authors: E. R. Stanway, M. J. Hoskin, M. A. Lane et al.
    First Author’s Institution: Department of Physics, University of Warwick, Coventry, UK

    Status: Accepted to MNRAS, open access

    1
    Figure 1: The Antennae Galaxies, two galaxies which are in the process of merging. The bright blue regions are undergoing bursts of star formation triggered by the merger. Source: ESO/L. Calçada

    When we talk about the habitability of a planet, astronomers are normally referring to one thing: whether a planet’s temperature is right for life. This comes down to a planet’s relationship to its host star — how hot the star is, and how far away the planet is from the star. Of course, there are a whole host of other factors at play regarding whether life could evolve on a planet or not — some that we know about and undoubtedly many that we don’t. As our understanding increases, the conversation is widening to include some of these other factors (for instance, what impact X-rays or flares from the host star will have). Today’s paper takes a broader view, by looking at habitability not on the level of stars and planets, but on the level of galaxies. It turns out that both the nature of the galaxy you’re in and where you are within it are important questions for any aspiring life-forms.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. 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.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 2:41 pm on January 4, 2018 Permalink | Reply
    Tags: Astrobites, , , , , Hot Jupiters are not really like layer-cakes   

    From astrobites: “Hot Jupiters are not really like layer-cakes” 

    Astrobites bloc

    astrobites

    Jan 4, 2018
    Shang-Min Tsai

    Title: Wavelength Does Not Equal Pressure: Vertical Contribution Functions and Their Implications for Mapping Hot Jupiters
    Authors: Ian Dobbs-Dixon and Nicolas B. Cowan
    First Author’s Institution: Department of Physics, NYU Abu Dhabi
    1
    Status: Published in APJL [open access]

    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.

    Trends do not fit with one-dimensional models

    When considering a one-dimensional atmosphere, as has been widely used in modeling, we can predict which wavelength will probe deeper into the atmosphere by examining their opacities. Water is one of the main infrared absorbers. Since water absorbs more radiation at 4.5 μm, the opacity at 4.5 μm should be larger than that at 3.6 μm. A larger mass of overlying gas at 3.6 μm is required to achieve the same absorption as at 4.6 μm. Hence, the photosphere (where photons are mostly absorbed and emitted) is deeper at 3.6 μm than at 4.6μm. The radiative cooling operates less efficiently as the pressure increases, hence we know that the day-night temperature contrast should be smaller in the deeper atmospheres. Therefore, one would expect the day-night temperature contrast, represented by the observed phase amplitude, to be also smaller at 3.6 μm than at 4.5 μm. In addition, the phase offset (how the hot spot being shifted) and normalized amplitude should be anti-correlated, with large amplitude phase variations having a small phase offset due to the inefficient heat transport. However, neither of these are observed.

    2
    Figure 1. Phase offset vs. normalized phase amplitude for seven hot Jupiters. Blue is 3.6 μm and green is 4.5 μm. Each planet is denoted by different symbols, and the two wavebands for a given planet are connected by a line to guide the eye. The normalized phase amplitude is always greater at 3.6 μm than at 4.5 μm.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. 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.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 1:37 pm on January 2, 2018 Permalink | Reply
    Tags: A Recipe for Mini-Neptunes, Astrobites, , , , , Kepler telescope doubles its count of known exoplanets   

    From astrobites: “A Recipe for Mini-Neptunes” 

    Astrobites bloc

    astrobites

    Jan 2, 2018
    Michael Hammer

    Title: The Formation of Mini-Neptunes
    Authors: Julia Venturini and Ravit Helled
    First Author’s Institution: University of Zurich

    Status: Accepted in ApJ [open access]

    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!

    Simulating planets can be quite similar. In place of the pancake mix, you can start out with a ball of rock. From there, all you have to do is just add gas (see Figure 1). When making pancakes, one thing to be careful about is how much water to add. If you add hardly any water, you will just end up with the same dried-out bowl you started out with. If you add way too much water, you will end up with pancake soup.

    Unlike in cooking, there’s no recipe to follow when building a planet; you do not get to decide how much gas to add! A planet must accumulate a particular-sized atmosphere based on its own properties and the properties of the surrounding protoplanetary disk in which it forms. Mini-Neptunes are the “perfect pancake” of planets. They ended up with just the right amount of gas. Any less and they would have stayed Earth-sized dried-out rock. Any more and they would have grown to Jupiter-sized gaseous soup.

    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.

    1
    Histogram showing the frequency of known planets of different sizes. Mini-Neptunes are the most common, followed by the slightly smaller Super-Earths. Credit: NASA Ames / W. Stenzel

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. 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.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: