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Sunday, May 29, 2016

Type Ia Supernovae, Recurrent Novae and Classical Novae

A Possible Symbiotic Relationship Between Type Ia Supernovae, Recurrent Novae, and Classical Novae: Do These Events Occur in the Same or Different Stellar Masses?

Astronomers are trying to determine the answer to the question of whether there is a direct relationship between Type Ia Supernovae (SNeIa), Classical Novae (CNe) and Recurrent Novae (RNe). Some evidence has been found to support a distinct relationship between catastrophic SNe events and RNe outbursts. There is evidence that tipping of the scale into a full-fledged Type Ia SN may be related to RNe, and though some evidence seems to point to this, all the particulars are not out regarding the three types. Do the three events occur within the same stellar mass, or are they separate events occurring in separate stellar masses. 

Las Cumbres Observatory Global Telescope Network
Las Cumbres Observatory Global Telescope Network.

The results of a study, led by Ben Dilday, a postdoctoral researcher in physics at UC Santa Barbara and at Las Cumbres Observatory Global Telescope Network (LCOGT), are surprising because previous indirect –– but strong –– evidence had pointed to the merger of two white dwarf stars as the originators of other Type Ia supernovae. One interesting subject is the planetary nebula NGC 5189. It has a unique, torqued-spiral shape, with peculiar patterns of knots around its periphery, possibly due to a wobbling in the stars' rotation, or, possibly, to the presence of a binary white dwarf system at its center.

Symbiotic binaries are systems containing both a white dwarf (WD) and a red giant component. Symbiotic novae are those systems in which thermonuclear eruptions occur on the WD component. These are to be distinguished from events are driven by accretion disk instabilities analogous to dwarf novae eruptions in cataclysmic variable outbursts. Another class of symbiotic system is that in which the WD is extremely luminous and it seems likely that quiescent nuclear burning is ongoing on the accreting WD. A fundamental question is the secular evolution of the WD. Do the repeated outbursts or quiescent burning in these accreting systems cause the WD to gain or lose mass? If it is gaining mass, can it eventually reach the Chandrasekhar Limit and become a supernova (a Type Ia SN if it can hide the hydrogen and helium in the system)? In order to better understand these systems, a new study has begun of the evolution of Thermonuclear Runaways (TNRs) in the accreted envelopes of WDs using a variety of initial WD masses, luminosities, and mass accretion rates. Astrophysicists have put into use a 1-D hydrocode, NOVA, which includes the new convective algorithm of Arnett, Meakin, and Young, the Hix and Thielemann nuclear reaction solver, the Iliadis reaction rate library, the Timmes equation of state, and the OPAL opacities. It is reported that (1) the WD grows in mass for all simulations so that canonical 'steady burning' does not occur, and, (2) that only a small fraction of the accreted matter is ejected in some (but not all) simulations. They have also found that the accreting systems, before thermonuclear runaway, are too cool to be seen in X-ray searches for Type Ia SN progenitors.

SN PTF 11kx Imaged by BJ Fulton Las Cumbres Global Telescope Network
SN PTF 11kx Imaged by BJ Fulton  
Las Cumbres Global Telescope Network.

The case of SN PTF 11kx, discovered by the Palomar Transient Factory, showed this relationship beyond further doubt. Astronomers could discern that the supernova was surrounded by shells of hydrogen gas that had likely been blown off in previous nova eruptions, decades before the supernova occurred. Novae are more frequent but weak explosions not catastrophic to the star. While similar shells of material had been seen before in a handful of Type Ia supernovae, their origin was debated and they had never before been firmly linked to novae - some doubted that the material was near to the supernova at all. SN PTF 11kx proved differently. The surrounding gas was moving too slowly to be from the supernova event itself, but too fast to be from a typical stellar wind. Lars Bildsten, director of UC Santa Barbara's Kavli Institute for Theoretical Physics, hypothesized that it was material shot out from a previous nova eruption, which had been slowed as it collided with the wind from the red giant star. UCSB graduate student Kevin Moore showed this hypothesis to be plausible and would lead to gas moving at speeds seen in the observations. Adding credence to the theory was the fact that the material moved at two different speeds -- faster-moving interior material to slower-moving exterior -- exactly as expected. The outer material had been slowing for decades, while the inner material had less time to slow. But if this was the case, the fast-moving supernova ejecta should have eventually collided with the nova material. About two months after the explosion, this is exactly what happened. New observations showed that the supernova ejecta was colliding with the interior shell of material. It was impossible to doubt that this gas was nearby the supernova. "This was the most exciting supernova I've ever studied," said Dilday, "For several months, almost every new observation showed something we'd never seen before."

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration; The Palomar Transient Factory at the California Institute of Technology; Baltic Astronomy, Vol 21, pages 76 - 87, 201arXiv:1211.6145v1 [astro-ph.SR]
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Friday, May 20, 2016

Digital Shoebox

A few weeks ago I found the equivalent of a shoebox full of old snapshots. As I was looking through an old backup of a filesystem from a computer I had long since parted with I ran across a directory, simply titled "CCD", circa 2003. A quick glance at the files of this lost directory I immediately knew what I had: these files, all FITS, and JPEG format, were astronomical image files, a reminder from the not so distant past when we first discovered the excitement of capturing night sky wonders with a CCD camera.

Mars - August 2003 - Image by Muir Evenden
Mars - August 2003 - Image by Muir Evenden.

Before the CCD revolution, Mike Petrasko and I tried our hand at imaging using traditional photographic processes by taking images on film, mostly wide-field views of the Milky Way, Orion, and other areas that fascinated us. Our friend and colleague Harry Hammond took this to the next level with prime focus photography, a much more demanding endeavor (please refer to Harry's article Old Dogs and New Tricks). When CCD's became available (and more affordable!) to the amateur market it was something we embraced wholeheartedly: there was a way to get "prime-focus" quality images but without the long hours spent in front of a guiding eyepiece. Once I had a job well paying enough to afford the equipment, you can bet I did not hesitate to start the adventure, starting with a Celestron 8 on a Losmandy G11 mount and a kit camera CCD and quickly evolve into a Celestron 14 on a Software Bisque Paramount and an Apogee camera.

NGC 6946 - August 2003 - Image by Muir Evenden
NGC 6946 - August 2003 - Image by Muir Evenden

So what I had here in our digital shoebox was a moment in time when we were getting our feet wet and honing our chops in the realm of CCD's and computers, and looking at these images now I think we can be rightly proud of our efforts. Of course compared to the achievements of what amateurs have been able to accomplish with the equipment available today our images may seem downright pedestrian, but that's OK as we don't expect to win a contest with these pictures but simply revel in the pleasure knowing that we captured this light from galaxies, nebulae, and planets, socking it away for future enjoyment. And what do you know, the future just arrived!
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Sunday, May 15, 2016

Students Observe the Mercury Transit

On Monday, May 9, 2016, close to 100 students from grades 7 thru 12 walked into the Kohout-Dingley Observatory located on the Sacred Heart High School campus to safely view the rare transit of the planet Mercury crossing the disk of the Sun. This was the first use of the new Baader solar filter manufactured by AstroZap recently purchased specifically for the event. The session, in partnership with the staff of Insight Observatory, hosted entire classes throughout the course of the school day as well as small groups of students visiting during their lunch session. All observers were treated not only to the Mercury transit event but were able to observe groups of sunspots as well.

Sacred Heart Students Observing the Mercury Transit - Photo by Joe Masi.
Sacred Heart Students Observing the Mercury Transit - Photo by Joe Masi.

The early morning hours of May, 9th brought a potential promise of clear observing conditions for the transit. However, just as I was leaving for the observatory to set up for the day, clouds started quickly rolling in. I checked in with the transit's live coverage feed from Sky and Telescope Magazine and J. Kelly Beatty, one of the publication's Cheif Editors, was reporting the same weather conditions from Cambridge, Massachusetts. Once I arrived at the school's campus around 8:10 am located in Kingston, Massachusetts, I noticed the clouds were starting to break up and scatter a bit. Joe Masi, a science teacher at the school, assisted me with opening the facility that houses the 11" Celestron Schmidt-Cassegrain Telescope. As the sky proceeded to clear up, we locked the solar filter onto place on the telescope and proceeded to slew the telescope towards the Sun. Remember, NEVER look directly at the Sun find it. As I focused the telescope I immediately detected a defined sharp black dot on the Sun's disk along with a few small groupings of sunspots. Mr. Masi wanted to get a quick peek before his 9:00 am class started. He quickly spotted the tiny planet as well.

A little after 9:00 am, Mr. Masi returned to the observatory with his first class. As the students in groups of 2 or 3 took turns viewing the Mercury transit upstairs at the telescope, the rest of the class below learned about the event taking place with a display set up by Insight Observatory on the first floor. The science teachers were discussing what was actually transpiring as well by using the display as an aide. While Mr. Masi's first class was enjoying the event, he suggested that the students image the transit on their smartphones. Some of the students attempted this throughout the day (as I did myself). However, it was very painstaking trying to hold the device steady enough to get an image in decent focus. A student from the first class, Nolan D., had the most successful image of the day. The morning classes that visited the observatory were treated to excellent views of the transit as the sky completely cleared up. However, the students that stopped by during their lunch period were challenged by fast-moving clouds. As they patiently waited, they were able to get a quick glimpse.

Mercury Transit at 9:15 am EDT - Image by Nolan D.
Mercury Transit at 9:15 am EDT - Image by Nolan D.

After the last class left around 2:10 pm, I sat in the observing chair at the telescope and took in the last part of this rare event. I watched the silhouette of the planet slowly disappear at the sun's limb exactly at 2:41 pm EDT. It was a great astronomy education experience and pleasure in sharing the transit of Mercury with the Sacred Heart students. Some of them are already looking forward to the next one in November of 2019.

Special thanks to Frank Lopez of the Stellarvision Astronomy and Science Shop located in Tucson, Arizona for his prompt delivery of the AstroZap Solar Filter allowing us to observe this special event.
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Sunday, May 8, 2016

May 9th 2016 Transit of Mercury

On Monday, May 9th, 2016, a transit of the planet Mercury will take place. The tiny planet will travel across the face of the Sun. Mercury transits are rare events which can be observed from much of the world, however, since they involve viewing the Sun, extreme caution must be taken when attempting to observe them. NEVER look directly at the sun with the unaided eye, binoculars or telescopes unless they are equipped with special solar filters and supervised by an educator or experienced amateur astronomer. One of the easiest and safest ways to observe this rare event is online via a live web feed. Insight Observatory will be broadcasting a live web of the transit courtesy of Sky and Telescope Magazine's Livestream channel. You can watch the progress of the planet Mercury crossing the Sun's disc on our website at http://www.insightobservatory.com/p/real-time-astronomical-event.html.

Sky and Telescope Magazine Diagram
Sky and Telescope Magazine Diagram.

During this transit, the planet Mercury is seen as a tiny black dot moving slowly in an East-to-West direction across the Sun. The 2016 transit begins on May 9th at 11:12 UT (Universal Time, which is equivalent to Greenwich Mean Time) and ends later that same day at 18:42 UT, with mid-transit taking place at 14:57 UT. Here in the northeast, the event begins at 7:22 am with the transiting midpoint at 10:57 am and ending at 2:42 pm. If you’re in western North America, the rising Sun will already display Mercury’s black dot. Easterners and many Western Europeans will be able to watch the entire transit, weather permitting, from Mercury’s first sign of visibility onto the Sun’s face to its final disappearance 7½ hours later.

For the rest of Europe, Africa, and most of Asia, the transit also begins in the daytime but will still be underway when the Sunsets. Observers in Australia and eastern Asia will just have to watch online as it will not be visible to those parts of the globe. For more detailed information on of the Mercury transit, please visit Sky and Telescope's article covering the event.

Mercury is the smallest planet, therefore, you'll need a telescope to observe its transit. The black silhouette will appear only 12 arcseconds wide even though Mercury is at inferior conjunction. That’s about 1⁄160 of the Sun’s width and only a fifth the diameter (and 4% of the area) of Venus’s dramatic black disk during the rare transits of Venus. When first viewing, you might mistake Mercury for a small sunspot. It’s precisely round and lacks a gray penumbra. As Mercury travels across the Sun’s vast expanse, how readily can you see its motion? If it passes near a sunspot, can you see that it’s darker than even the sunspot’s umbra? When Mercury departs at egress, the sequence of phenomena at ingress unwinds in reverse order.

Image from In-The-Sky.org
Image from In-The-Sky.org

After a May transit, a November transit always occurs 3.5 years later (for instance: May 9, 2016, and November 11, 2019). Transits recur on nearly the same date in cycles of 46 years (for instance: May 9, 2016, and May 10, 2062). November transits, which are more common than May transits, occasionally recur in periods of 7 years, and more frequently in periods of 13 and 33 years. If you simply can’t catch 2016’s Mercury madness, make sure to mark your calendar for the next mercury transit on November 11, 2019. After that, you’ll be waiting until 2032.

Sources: Sky and Telescope Magazine, NakedEyePlanets.com
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Sunday, May 1, 2016

Winging It!

Much observational astronomy is done with an itinerary in mind; be it sketches of deep-sky objects, planets, the moon, comets, etc., with time allotted for each object. Along with fellow astronomers, Mike Petrasko and Muir Evenden, I used to do galaxy scans of a number of galaxies, in search of extragalactic supernovae events, or, stellar explosions in other galaxies. This kind of observing requires a conventional star atlas and special galaxy charts at one’s side, along with an array of oculars, a red acetate-covered flashlight, Astro-goggles (dark-adaptation goggles) paper, pencils and such.

Amateur Astronomer Observing
Amateur Astronomer Observing.

But this kind of observing session is for more advanced amateurs, not something the beginning astronomer is looking at any time soon. And that’s alright. There are other ways of doing it. If you’re new to astronomy and have only recently acquired your first telescope - regardless of size - take it out into the backyard and set it up, otherwise equipment-less, if that should be the case (it would be nice to have some kind of atlas with you, for reference, and to save a little time, but it isn’t absolutely necessary).

Point your marvellous instrument toward the sky and just start scanning - randomly. In no time, you’ll be coming across all kinds of things. Look at each, take a mental note and move on. Spend an hour or two, just randomly aiming the telescope, or, do a more cohesive sweep of the sky, somewhat overlapping the field of view of the scope on each pass. Just enjoy the various objects that pop into view, make a mental note and continue.

When you’ve had enough of this, pack it up and go to bed. I guarantee you'll lie there, in bed, that night, running the various sights you’ve seen, over and over in your head. You’ll wonder what it was that had that tail-like thing sticking out of it, what gave that other smudge of light its unusual shape, color, etc.

A few observing sessions like this, and you’ll want to do more, know more and acquire more in no time. This is how it all started for me, with a 60mm Tasco® refractor telescope on a simple mount, at age 19, all those ages ago.

Dale Alan Bryant
Senior Contributing Science Writer
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