February 2010: ING direct

We have interviews with Dr. Rodríguez-Gil and Dr. Miguel Santander-García from the Isaac Newton Group of telescopes. As ever we have the latest astronomical news, and what you can see in the February night sky.

The News

In the news this month:

• Star formation is usually thought of as occurring mainly in the spiral arms of galaxies. In close encounters or collisions between galaxies, the orbits of these stars around the galactic disk can be disrupted, resulting in some stars being thrown out into intergalactic space. But new results from the Chandra X-ray Observatory suggest that, at least in some cases, stars can form outside the normal boundaries of galactic disks.

  A team led by Ming Sun at the University of Virginia used the orbiting Chandra telescope to observe galaxies in a nearby rich cluster known as Abell 3627. What they found were several enormous tails of X-ray emission, trailing behind galaxies located in the cluster. Tails like these are made up of X-ray emitting gas which is stripped from a galaxy as it moves through the cluster. One of these galaxies, ESO 137-001, was already known to have one X-ray tail which extends approximately 260 thousand light years from the galaxy itself, but in these observations the team found a second tail apparently associated with the same galaxy. This new tail is of a similar length to the first, but is both fainter and narrower. Both the widths and temperatures of the tails remain surprisingly constant over their entire lengths, and these properties present challenges to current models and simulations of such systems. A similar tail of about half the length was also detected behind ESO 137-002, another similar galaxy in the same cluster.

  Together with observations using telescopes operating in other parts of the electromagnetic spectrum, the research also shows the first unambiguous evidence of star formation in the material stripped from a galaxy. Rather than forming in the galactic disk as normal, these stars are forming in the gas stripped from the disk as the galaxy moves through the tenuous gas in the cluster.

  X-ray tails are rare, and double-tails are extremely rare, so one question is, why should there be two bright X-ray tails visible in the same cluster? In their paper, published in the Astrophysical Journal, the researchers suggest that (aside from coincidence) the high ambient pressure in this particular cluster could play a role, making the X-ray tails denser and more luminous. If this is the case, the high pressure environment would also be helping the process of extra-galactic star formation.

• Most of our knowledge of the processes and morphology of stellar coronae comes from observing our nearest star, the Sun. Coronal loops are associated with sunspot groups which affect the streams of charged particles leaving the Sun as the solar wind, so an understanding of the processes in these loops has implications for space weather predictions which can impact on satellite operations and the safety of astronauts. Studying the same processes in other stars is difficult due to the distances involved and the high resolution required to see any detail. Some of the highest resolution observations possible in astronomy are made using arrays of radio telescopes linked together in a process known as very long baseline interferometry; the more widely separated the telescopes in the array, the higher the resolution of the final images. Using this technique, a team led by William Peterson, a graduate student at the University of Iowa, have detected a large coronal loop on another star. Using a very sensitive array of radio telescopes which included the ten antennas of the Very Long Baseline Array in the US, the 100-m Green Bank Telescope in West Virginia, the Very Large Array in New Mexico and the 100-m Effelsberg telescope in Germany, the astronomers imaged the variable star Algol in Perseus. Algol is an eclipsing binary system consisting of a large main sequence B-class star and a cooler K-class sub-giant in orbit around each other. The two stars are very close, just 6% of the distance between the Earth and our own Sun, and orbit each other every 2.86 days. The results show a gigantic coronal loop stretching out from the surface of Algol B, the K-class sub-giant star, towards its companion Algol A, with the two ends of the loop located at the magnetic poles of the sub-giant star. Throughout the orbit, this loop continues to point towards Algol A. The researchers say that Algol B's coronal loop is similar to those seen on the Sun, but is much larger, and the magnetic field at Algol is about 1,000 times more powerful. The size of the coronal loop is larger than predicted by stellar models, and the suggestion is that this is probably due to the tidal effects of the companion star distorting the loop and stretching it.

  The results, the first time a coronal loop has been imaged on another star, were published in the journal Nature on February 14th.

• An international team, led by astronomers at the University of Hertfordshire have discovered what may be the coolest sub-stellar body ever found outside our own solar system. Using the United Kingdom Infrared Telescope (UKIRT) in Hawaii, the astronomers have discovered a type of object known as a brown dwarf, smaller than other stars but larger than gas giant planets such as Jupiter. The object, known as SDSS1416+13B, is only visible in infra-red light and is in a wide orbit around a somewhat brighter and warmer brown dwarf known as SDSS1416+13A. This discovery is "the fourth time in three years that UKIRT has made a record breaking discovery of the coolest known brown dwarf, with an estimated temperature not far above 200 degrees Celsius," said the University of Hertfordshire?s Dr Philip Lucas.

  The light detected from the star is rather unusual, it appears far bluer at near infra-red wavelengths than any other brown dwarf detected so far. A near infrared spectrum, taken with the Japanese Subaru Telescope in Hawaii, showed that it belongs to a class of objects known as T dwarfs, and that is has a lot of methane in its atmosphere but with peculiar features including a big gap at certain wavelengths. Using the Spitzer space telescope to measure its colour at mid-infrared wavelengths,the researchers found that it is also the reddest known brown dwarf at these wavelengths by some margin. A comparison with theoretical models of brown dwarf atmospheres results in a temperature estimate of just 500 Kelvin or 227 degrees Celsius. In comparison, our own Sun has a surface temperature of approximately 6000 Kelvin. Both stars are also lacking in heavy elements, an indication that they may be very old which fits in with the low temperature of the fainter star - fainter stars use up their fuel much slower and can last for many billions of years.

  The research has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

• And finally: The HiRISE instrument on board the Mars Reconnaissance Orbiter has been taking spectacular images since the probe entered orbit around the planet in 2006. One particular image, posted to Astronomy Picture of the Day on January 19th, caused something of a stir.

  The image shows a series of pinkish-coloured sand dunes covered with a light frost, located near the North pole of Mars, taken on the 7th of April 2008 during the Martian spring. As the Sun started to melt the carbon dioxide ice, the sand started to shift, cascading down the dunes in dark streaks which look uncannily like trees in the image taken by the HiRISE instrument on board the orbiter. The image covers an area of roughly one square kilometre and resolves objects as small as 25 cm. The colour variations in the ice around the streaks are thought to be caused by dust kicked up as the material shifts and settles on the surface.

Isaac Newton Group

In January 2010, while observing with the Isaac Newton Group's William Herschel Telescope on the island of La Palma, Dave Jones took some time out to interview a few members of ING staff working at the observatory. The ING operates three optical telescopes at the Spanish Roque de los Muchachos Observatory, on behalf of the astronomical communities of the UK, Spain and the Netherlands. Dave spoke to Dr Pablo Rodríguez-Gil about his work on compact binaries, systems of two stars held together by gravity where one star is of a much higher density than the Sun. Dr. Rodríguez-Gil tells us about the interesting processes that can be seen in these systems, including accretion where the denser star rips material away from its companion. We also hear about the application process by which astronomers get to use the ING's telescopes, and specifically how their 2.5m Isaac Newton Telescope is run.

While in La Palma, Dave also spoke to Dr Miguel Santander-García about his ground-breaking work on planetary nebulae. Planetary nebulae, a misnomer as they bear no relation to planets, are the final stage in the lives of stars similar to our own Sun when the star blows off its outer layers. These planetary nebulae are some of the most poorly understood and strikingly beautiful objects to be found in the night sky.

The Night Sky

Ian Morison tells us what we can see in the night sky during February 2010.

Northern Hemisphere

As night falls the constellations of Pegasus and Andromeda are setting towards the west. High in the south is Orion. The three stars of its belt point down to Sirius in Canis Major. Up to the right they point to Taurus the Bull with the Hyades and Pleiades. High above Orion is Auriga with the bright star Capella. Up to the left of Orion are the Twins - Gemini. Over towards the eastern sky is Procyon in Canis Minor and then a very faint area - the constellation of Cancer - which currently contains the planet Mars.

The Planets

• Jupiter is now beginning to set very soon after sunset.
• Saturn is becoming better, rising by about 9pm in the middle of the month. The rings are at about 5 degrees in tilt angle but will drop to 4 degrees by the end of the month.
• Venus was behind the Sun on January 11th. It is beginning to climb up into the evening sky.
• Mercury had a morning apparition last month and is now moving back towards the Sun. On the morning of the 12th February it is just to the lower right of a thin crescent Moon just above the horizon.
• Mars is still looking good. It is well up in the south by about 10 pm. It is now moving westwards through Cancer until about March 8th when it will turn around and head back towards Leo.

Highlights

• Between 14th - 17th February Venus and Jupiter can be seen together just after sunset. They are closest on 16th February.
• At magnitude +6.1, Vesta is the brightest minor planet or asteroid. It has a diameter of 530 km and is the second most massive asteroid in the "main belt" between Mars and Jupiter. It will probably be easiest to find as it passes between the stars Algieba and 40 Leonis on the 16th February.
• On February 21st the Moon occults the Pleaides Cluster at about 18:50 GMT.

Southern Hemisphere

The main stars of Sagittarius make up a teapot. Just above the teapot is a lovely region of luminosity called the Lagoon Nebula which is easily seen with binoculars. Centaurus has two bright stars - Alpha and Beta Centauri. Alpha Centaurus is actually three stars - two orbiting quite close. Curving around from Beta Centauri you find a fuzzy object named Omega Centauri.

Odds and Ends

EADS Astrium are developing the technology to get solar power from space.

Universe Today have put together a guide to the objects in the Messier catalogue. Dave also mentioned Stellarium.

The International Space Station has live internet access and have sent the first live tweet from space! Astronauts on board the ISS now can directly access the web which means that they can update their Twitter accounts themselves instead of sending the messages down to Earth for someone else to update the account on their behalf.

NASA have finally given up trying to "free Spirit" and have decided to keep the Mars Rover operating as a stationary science platform. Providing that it survives the Martian winter, it could continue to do science for a few more years.

Megan has been busy recently with an episode of 365 Days of Astronomy (January 21st), a Doctor Who supernova story and a paper in Nature (January 28th)! We'll let you decide the relative importance of each of those.

Jodcast listener OG has an episode of 365 Days of Astronomy on 15th February.

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