astrobites: Daily Paper Summaries 2019

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The “Shocking” Mystery about Filaments

Post by bystander » Mon Dec 30, 2019 5:01 pm

The “Shocking” Mystery about Filaments
astrobites | Daily Paper Summaries | 2019 Dec 24
Michael Foley wrote:
Galaxies are built from black holes, stars, gas, and dust. While the stars and black holes may get most of the attention, the gas and dust play crucial roles in the evolution of a galaxy. Gas and dust are responsible for forming stars, feeding the central supermassive black hole, and regulating the chemical composition of the galaxy. Consequently, understanding the dynamics of the gas and dust is very important if we want to learn how galaxies work.

One critical mechanism in the workings of galaxies is shocks. Gas in galaxies can frequently become supersonic, such as when a supernova explodes, meaning that it travels faster than the local sound speed. This supersonic gas will generate shocks, just like an airplane traveling supersonically will produce a shockwave in the air that creates a sonic boom. The interactions of these shocks with other shocks or gas features can create turbulence or interesting substructures in the interstellar medium, potentially laying the fertile ground for stars to form.

Today’s paper looks at the interaction of these shocks with filaments of gas. Filaments are long, coherent structures that are found throughout the interstellar medium and that serve as the birthplaces of stars (Figure 1). We know that filaments can be destroyed by shocks, but the exact conditions necessary to destroy a filament remain a mystery. The authors of ran a number of simulations to try to recreate these crime scenes. ...

The isothermal evolution of a shock-filament interaction ~ K.J.A. Goldsmith, J.M. Pittard
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BDanielMayfield
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Re: Separated At Birth: Comparing Chemical Compositions of Binaries

Post by BDanielMayfield » Tue Dec 31, 2019 12:04 am

bystander wrote:
Mon Dec 30, 2019 4:48 pm
‘DNA’ of Twin Stars to Reveal Family History of the Milky Way
McDonald Observatory | University of Texas | 2019 Dec 20

Identical or fraternal twins? : The chemical homogeneity of wide binaries from Gaia DR2 ~ Keith Hawkins et al
Nice to see that an old workhorse, the 2.7-meter Harlan J. Smith Telescope at McDonald Observatory (which my wife and I saw up close on a tour once), is still helping produce cutting edge science. Go UT Astronomy!

Bruce
Just as zero is not equal to infinity, everything coming from nothing is illogical.

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Toughest Telescope in the West?

Post by BDanielMayfield » Tue Dec 31, 2019 5:17 am

BDanielMayfield wrote:
Tue Dec 31, 2019 12:04 am
bystander wrote:
Mon Dec 30, 2019 4:48 pm
‘DNA’ of Twin Stars to Reveal Family History of the Milky Way
McDonald Observatory | University of Texas | 2019 Dec 20

Identical or fraternal twins? : The chemical homogeneity of wide binaries from Gaia DR2 ~ Keith Hawkins et al
Nice to see that an old workhorse, the 2.7-meter Harlan J. Smith Telescope at McDonald Observatory (which my wife and I saw up close on a tour once), is still helping produce cutting edge science. Go UT Astronomy!

Bruce
I found out something interesting they didn't bother to mention in the tour:
The telescope was the victim of an act of vandalism in February 1970. A newly hired worker suffered a mental breakdown and brought a hand gun into the observatory. After firing one shot at his supervisor, the worker then fired the remaining rounds into the Primary Mirror. The holes effectively reduced the 107-inch (2.7 m) telescope to the equivalent of a 106-inch telescope (or about 2.5 centimeters less), but did not affect the quality of the telescope's images, only the amount of light it can collect.[1]
The telescope too tough to die. :cowboy:
Just as zero is not equal to infinity, everything coming from nothing is illogical.

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Making Blue Photons in Dwarf Galaxies

Post by bystander » Tue Dec 31, 2019 6:03 pm

Making Blue Photons in Dwarf Galaxies
astrobites | Daily Paper Summaries | 2019 Dec 25
Caitlin Doughty wrote:
How does star light escape from galaxies? It may seem like a simple question on its face, but it becomes more complicated the more you think about it. When you see a picture of a galaxy in optical wavelengths it seems to be very bright, but switching to a UV image you see less light. This decrease in the amount of light escaping for shorter wavelengths becomes worse as you progress into the far and extreme-UV (i.e. shorter wavelengths), where it becomes particularly prone to being absorbed by neutral hydrogen gas. Because of this tendency, when this short-wavelength radiation is created by stars, which are surrounded by dense clouds containing neutral hydrogen, much or even all of it gets absorbed and blocked from view.

The absorption of this light creates problems for understanding the reionization of hydrogen in the intergalactic medium (IGM) that took place more than 12 billion years ago. In short, this process consisted of ionizing radiation coming from…somewhere…and separating the IGM hydrogen atoms into individual protons and electrons. But if our observations indicate that not much hydrogen-ionizing light can escape from galaxies, then how can reionization even happen? Although there are alternative possible sources of radiation, galaxies are the current best candidate for causing reionization, and the fact that photon escape and this process can’t be reconciled would seem to indicate astronomers are missing something important about this portion of the Universe’s history.

This quandary motivates many experiments looking at how light escapes from galaxies, and today’s paper focuses on how efficiently galaxies, particularly dwarf galaxies, generate ionizing light and allow it to pass out into intergalactic space. ...

The Ionizing Photon Production Efficiency (ξion) of Lensed Dwarf Galaxies at z∼2 ~ Najmeh Emami et al
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TESS reveals HD118203 b transits after 13 years

Post by bystander » Tue Dec 31, 2019 6:22 pm

TESS reveals HD118203 b transits after 13 years
astrobites | Daily Paper Summaries | 2019 Dec 26
Emma Foxell wrote:
There are multiple ways to discover an exoplanet. The first exoplanet around a solar type star was discovered by radial velocity measurements, and earned the discoverers’ this year’s Nobel Prize. After the advent of wide field exoplanet surveys, from SuperWASP starting in 2006, to NGTS and TESS, most exoplanets have been discovered using the transit method and confirmed by radial velocity. However, the exoplanet in today’s article, HD118203 b, was detected by radial velocity back in 2006 and has been found to transit 13 years after its discovery.

HD118203 b was found in 2006 by using the radial velocity technique: measuring the amount the star’s spectrum ‘wobbles’ tugged by its orbiting planet. Spectra are red shifted as the planet tugs its star away from us and blue shifted as the star is tugged towards us over one orbit of the planet. Radial velocity measurements give us the planet’s orbital period as well as its eccentricity and the minimum mass of the planet. The true planet mass depends on the relative inclination between star and planet. 43 radial velocity measurements from ELODIE revealed HD118203 b as an eccentric planet with an orbital period of ~6.13 days, and a minimum mass of about 2 Jupiters (see Figure 1). ...

TESS Reveals HD 118203 b to be a Transiting Planet ~ Joshua Pepper et al
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A Pulsar’s Surface Map Gets a NICER Update

Post by bystander » Tue Dec 31, 2019 6:49 pm

A Pulsar’s Surface Map Gets a NICER Update
astrobites | Daily Paper Summaries | 2019 Dec 30
Kaitlyn Shin wrote:
Pulsars are rapidly rotating neutron stars with short and regular rotational periods, observed via their beams of electromagnetic radiation. These observed pulses are analogous to the light flashing on a lighthouse where observers can only see the light pulses once every rotation, when the beams are aligned along the line of sight. For rotation-powered pulsars, these light pulses are powered by the neutron stars’ rapid rotations and extremely strong magnetic fields; the canonical (standard) depiction of the magnetic fields that give rise to these pulses can be seen below in Figure 1. ...

The Neutron star Interior Composition ExploreR (NICER) is a NASA telescope installed aboard the International Space Station in 2017. With its high time resolution and unprecedented sensitivity in the soft X-ray band (0.2–12 keV), NICER has obtained some of the highest-quality pulse profiles (shape of observed pulses) of known X-ray pulsars. Today’s paper focuses on NICER data of one such pulsar, PSR J0030+0451. This pulsar is an isolated pulsar as well as a millisecond pulsar (since its rotation period is ~4.87 ms). It is one of the nearest observed millisecond pulsars, with a relatively well-constrained distance of 329 ± 9 parsecs (about 1070 ± 30 light years) away from Earth. ...

A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation ~ Thomas E. Riley et al
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A New Look into Cas A’s Past

Post by bystander » Tue Dec 31, 2019 7:06 pm

A New Look into Cas A’s Past
astrobites | Daily Paper Summaries | 2019 Dec 31
Charles Law wrote:
Ever wondered what a star looked like before it exploded? Today, with the existence of extensive archival data, we can always go back after a supernova (SN) explosion and search for pre-SN images of the progenitor star. However, this method does not work for those stars without such prior imaging and is certainly impossible for historical SN that are several centuries old and predate the era of telescopic astronomy. In these cases, we can take an alternative approach and study the material left behind after the stellar explosion. This material, more generally referred to as a supernova remnant (SNR), interacts with circumstellar material (CSM) that was ejected towards the end of the progenitor star’s lifetime. Thus, by studying the physical and chemical characteristics of this material, astronomers can learn more about how the progenitors of core collapse supernovae strip off their hydrogen/helium envelopes and the explosion process itself. Using such an approach, today’s authors report the exciting discovery of a pristine CSM knot in Cassiopeia A (Cas A), one of the most famous and well-studied SNRs in our Galaxy. ...

Using observations in the near-infrared (NIR), today’s authors detected a strong iron emission line toward a new QSF knot in the south of Cas A, as shown in Figure 1. The presence of emission from a heavy element such as iron is a telltale sign that this material originated deep inside the progenitor star and represents a mass-loss event prior to the SN explosions. ...

Detection of Pristine Circumstellar Material of the Cassiopeia A Supernova ~ Bon-Chul Koo et al
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Re: A New Look into Cas A’s Past

Post by BDanielMayfield » Fri Jan 03, 2020 2:15 pm

I wondered what QSF stands for, so from the astrobite:
The presence of dense, He- and N-enriched CSM knots in Cas A have been known since the 1950s and are often referred to as “quasi-stationary flocculi” (QSFs) due to their relatively low-velocity (~400 km/s) compared to the faster moving main ejecta (1000s of km/s). These QSFs are believed to be dense CNO-processed CSM clumps that have been recently shocked by the SN blast wave. As they likely originated from mass-loss from the SN progenitor star, they offer a rare window into the conditions deep inside the progenitor star. However, until now, no one had detected emission from an unprocessed CSM knot, which retains the original physical and chemical conditions of the stellar interior and has not been disrupted by the advancing SN shockwave.
So this is an unmixed clump of Cas A's SN progenitor. Ann will like what it was:
Implications for Cas A’s Stellar Progenitor

In order to deduce when the mass-loss event that ejected the QSFs occurred and what the evolutionary stage of the progenitor was, the authors also analyzed the proper motions of the QSFs. They find a systemic expansion with a velocity of 180 km/s and are able to determine a stellar radius and surface temperature that are 100x and 2x that of our Sun, respectively. Taken together with the high He and N abundances of these QSFs and the high fraction of gas phase Fe, the authors conclude that the Cas A QSFs were likely the result of mass-loss due to stellar winds from a blue supergiant with a thin hydrogen envelope.
Just as zero is not equal to infinity, everything coming from nothing is illogical.

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Re: A New Look into Cas A’s Past

Post by Ann » Fri Jan 03, 2020 6:21 pm

BDanielMayfield wrote:
Fri Jan 03, 2020 2:15 pm
So this is an unmixed clump of Cas A's SN progenitor. Ann will like what it was:
Implications for Cas A’s Stellar Progenitor

In order to deduce when the mass-loss event that ejected the QSFs occurred and what the evolutionary stage of the progenitor was, the authors also analyzed the proper motions of the QSFs. They find a systemic expansion with a velocity of 180 km/s and are able to determine a stellar radius and surface temperature that are 100x and 2x that of our Sun, respectively. Taken together with the high He and N abundances of these QSFs and the high fraction of gas phase Fe, the authors conclude that the Cas A QSFs were likely the result of mass-loss due to stellar winds from a blue supergiant with a thin hydrogen envelope.
Click to play embedded YouTube video.
You bet I like it! :shock: :D

Please note that the most famous supernova of recent times, SN1987A, also had a blue supergiant progenitor.


Perhaps we should be talking a little less about the red supergiants and start waiting for the blue supergiants to go pop?


Check out this interesting video. I apologize for them mixing up Bellatrix and Rigel. And no, I wouldn't say that blue supergiants are hard to see... I mean, Rigel, Deneb, Alnilam, Gamma Velorum?

Ann
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