SOAR Telescope: A sharp eye on Southern binary stars

Click to view the animation demonstrating the orbit of the close binary pair Ba, Bb in the HIP 83716 Triple System. 

The orbit has been calculated from five observations (blue circles) taken between 2009, when the close binary was discovered at SOAR, and 2014, the date of the most recent observation. 

Animation Credit: M. A. Newhouse & NOAO/AURA/NSF

Unlike our sun, with its retinue of orbiting planets, many stars in the sky orbit around a second star.

These binary stars, with orbital periods ranging from days to centuries, have long been the primary tool for measuring basic quantities like the star's mass.

While masses of normal stars are now well determined, some binaries present special interest because their stars are unusual (e.g. very young) or because they may contain planets, gas clouds, or other stars.

Now, astronomers at the Cerro Tololo Inter-American Observatory (CTIO) and at the US Naval Observatory (USNO) are making use of the latest technology, speckle imaging, to measure the separation of close binary stars.

By observing them over a period of years, their obits have been determined with exquisite precision.

Using the new speckle camera at the 4.1-m Southern Astrophysical Research Telescope (SOAR) in Chile with its novel electron-multiplication CCD detector, the team is able to measure the angular separation of stars down to 25 milli arcseconds: this is equivalent to measuring the size of a quarter atop the Empire State building in New York - from Washington, DC.

This is over 2000 times better than the human eye can resolve. As Dr. Andrei Tokovinin, the lead author on the paper, said: "This camera surpasses adaptive-optics instruments at the 8-m telescopes, which work in the infrared and can only resolve binaries wider than 50 milli arcseconds."

The team, which includes astronomers from SOAR and from the USNO, has not only been observing previously known binary systems for which older data are very poor, but is also finding new double and multiple systems.

The attached animation shows the system HIP 83716, known to be double for over a century but until the SOAR camera examined it, nobody realized that the companion star was also a binary, making this a triple system.

The wide pair A,B orbit each other in about 520 years, while the newly discovered pair Ba, Bb orbit each other in just 6.5 years.

Over the past seven years, the speckle camera on SOAR has observed almost 2000 objects, both previously known and newly discovered binaries.

This is a unique dataset in terms of quantity and quality: prior to this project such measurements of southern binaries were made only occasionally by the team from the USNO.

More information: "Speckle Interferometry at SOAR in 2012 and 2013." Andrei Tokovinin, Brian D. Mason, and William I. Hartkopf, Andrei Tokovinin et al. 2014 The Astronomical Journal 147 123. DOI: 10.1088/0004-6256/147/5/123

NASA Aura Image: Antarctic ozone hole monitoring report

The Antarctic ozone hole reached its maximum single-day area for 2013 on Sept. 16. 

The ozone hole (purple and blue) is the region over Antarctica with total ozone at or below 220 Dobson units (a common unit for measuring ozone concentration). 

Image Credit: NASA's Goddard Space Flight Center

The ozone hole that forms each year in the stratosphere over Antarctica was slightly smaller in 2013 than average in recent decades, according to NASA satellite data.

The ozone hole is a seasonal phenomenon that starts to form during the Antarctic spring (August and September).

The September-October 2013 average size of the hole was 8.1 million square miles (21 million square kilometers).

For comparison, the average size measured since the mid-1990s when the annual maximum size stopped growing is 8.7 million square miles (22.5 million square kilometers).

However, the size of the hole in any particular year is not enough information for scientists to determine whether a healing of the hole has begun.

"There was a lot of Antarctic ozone depletion in 2013, but because of above average temperatures in the Antarctic lower stratosphere, the ozone hole was a bit below average compared to ozone holes observed since 1990," said Paul Newman, an atmospheric scientist and ozone expert at NASA's Goddard Space Flight Center in Greenbelt, Md.

The ozone hole forms when the sun begins rising again after several months of winter darkness.

Polar-circling winds keep cold air trapped above the continent, and sunlight-sparked reactions involving ice clouds and chlorine from manmade chemicals begin eating away at the ozone.

Most years, the conditions for ozone depletion ease before early December when the seasonal hole closes.

Levels of most ozone-depleting chemicals in the atmosphere have gradually declined as the result of the 1987 Montreal Protocol, an international treaty to protect the ozone layer by phasing out production of ozone-depleting chemicals.

As a result, the size of the hole has stabilized, with variation from year to year driven by changing meteorological conditions.



Daily images from Jul. 1 to Oct. 15 show the evolution of the 2013 ozone hole. The ozone hole maximum occurred on Sept. 16, 2013. 

Image Credit: NASA/Robert Simmon/Ozone Hole Watch

The single-day maximum area this year was reached on Sept. 16 when the maximum area reached 9.3 million square miles (24 million square kilometers), about equal to the size of North America.

The largest single-day ozone hole since the mid-1990s was 11.5 million square miles (29.9 million square kilometers) on Sept. 9, 2000.

Science teams from NASA and the National Oceanic and Atmospheric Administration (NOAA) have been monitoring the ozone layer from the ground and with a variety of instruments on satellites and balloons since the 1970s.

These ozone instruments capture different aspects of ozone depletion. The independent analyses ensure that the international community understands the trends in this critical part of Earth's atmosphere.

The resulting views of the ozone hole have differences in the computation of the size of the ozone hole, its depth, and record dates.

NASA observations of the ozone hole during 2013 were produced from data supplied by the Ozone Monitoring Instrument on NASA's Aura satellite and the Ozone Monitoring and Profiler Suite instrument on the NASA-NOAA Suomi National Polar-orbiting Partnership satellite.

Long-term satellite ozone-monitoring instruments have included the Total Ozone Mapping Spectrometer, the second generation Solar Backscatter Ultraviolet Instrument, the Stratospheric Aerosol and Gas Experiment series of instruments, and the Microwave Limb Sounder.

Uranus: Keck observations brings weather into sharp focus

A paired picture of Uranus, the sharpest, most detailed picture of the distant planet to date, reveals a raft of new details about the planet's enigmatic atmosphere. 

The north pole of Uranus (to the right in the picture) is characterised by a swarm of storm-like convective features, and an unusual scalloped pattern of clouds encircles the planet's equator. 

The infrared image was taken using the Keck II telescope in Hawaii. 

Credit: Lawrence Sromovsky, Pat Fry, Heidi Hammel, Imke de Pater

In 1986, when Voyager swept past Uranus, the probe's portraits of the planet were "notoriously bland," disappointing scientists, yielding few new details of the planet and its atmosphere, and giving it a reputation as the most boring planet of the solar system.

Now, however, thanks to a new technique applied at the Keck Observatory, Uranus is coming into sharp focus through high-resolution infrared images, revealing in incredible detail the bizarre weather of the seventh planet from the sun.

The images were released in Reno, Nev. today (Oct. 17, 2012) at a meeting of the American Astronomical Society's Division of Planetary Sciences and provide the best look to date of Uranus's complex and enigmatic weather.

The planet's deep blue-green atmosphere is thick with hydrogen, helium and methane, Uranus's primary condensable gas.

Larry Sromovsky

Winds blow mainly east to west at speeds up to 560 miles per hour, in spite of the small amounts of energy available to drive them.

Its atmosphere is almost equal to Neptune's as the coldest in our solar system with cloud-top temperatures in the minus 360-degree Fahrenheit range, cold enough to freeze methane.

Large weather systems, which are probably much less violent than the storms we know on Earth, behave in bizarre ways on Uranus, explains Larry Sromovsky, a University of Wisconsin-Madison planetary scientist who led the new study using the Keck II telescope.

"Some of these weather systems," Sromovsky notes, "stay at fixed latitudes and undergo large variations in activity. Others are seen to drift toward the planet's equator while undergoing great changes in size and shape. Better measures of the wind fields that surround these massive weather systems are the key to unraveling their mysteries."

Imke de Pater

To get a better picture of atmospheric flow on Uranus, Sromovsky and colleagues Pat Fry, also of UW-Madison, Heidi Hammel of the Association of Universities for Research in Astronomy (AURA), and Imke de Pater of the University of California at Berkeley, used new infrared techniques to detect smaller, more widely distributed weather features whose movements can help scientists trace the planet's pattern of blustery winds.

"We're seeing some new things that before were buried in the noise," says Sromovsky, a senior staff scientist at UW-Madison's Space Science and Engineering Center.

Heidi Hammel

"My first reaction to these images was 'wow' and then my second reaction was WOW," says AURA's Heidi Hammel, a co-investigator on the new observations and an expert on the atmospheres of the solar system's outer planets.

"These images reveal an astonishing amount of complexity in Uranus's atmosphere. We knew the planet was active, but until now much of the activity was masked by noise in our data."

The complexity of Uranus's weather is puzzling, Sromovsky explains. The primary driving mechanism must be solar energy because there is no detectable internal energy source.

"But the sun is 900 times weaker there than on Earth because it is 30 times further from the sun, so you don't have the same intensity of solar energy driving the system," explains Sromovsky.

"Thus the atmosphere of Uranus must operate as a very efficient machine with very little dissipation. Yet the weather variations we see seem to defy that requirement."

The new Keck II pictures of the planet, according to Sromovsky, are the "most richly detailed views of Uranus yet obtained by any instrument on any observatory.

No other telescope could come close to producing this result." Sromovsky and his colleagues used Keck II, located on the summit of Hawaii's 14,000-foot extinct volcano Mauna Kea, to capture a series of images that, when combined, help increase the signal to noise ratio and thus tease out weather features that are otherwise obscured.

In two nights of observing under superb conditions, Sromovsky's group was able to obtain exposures of the planet that provide a clear view of the planet's cloudy features, including several new to science.

The group used two different filters in an effort to characterize cloud features at different altitudes. "The main objective was to find a larger number of cloud features by detecting those that were previously too subtle to be seen, so we could better define atmospheric motions," Sromovsky notes.

New features found by the Wisconsin group include a scalloped band of clouds just south of Uranus's equator and a swarm of small convective features in the north polar regions of the planet, features that have never been seen in the southern polar regions.

"This is a very asymmetric situation," says the Wisconsin scientist. "There is certainly something different going on in those two polar regions." One possible explanation, is that methane is pushed north by an atmospheric conveyor belt toward the pole where it wells up to form the convective features observed by Sromovsky's group.

"The 'popcorn' appearance of Uranus's pole reminds me very much of a Cassini image of Saturn," adds de Pater.

Read more here