Observing at the GMRT

Astronomers often get to travel to exotic, far-flung places all in the name of science. To non-astronomers these may seem like free holidays but there often isn't much chance to do any sight-seeing or sunbathing as you are usually miles from anywhere, up a mountain. Being awake through the night, and asleep during the day certainly doesn't allow much chance for tourist activities either, although it does mean that you can email people at a reasonable hour back home (at least if you go sufficiently far east/west). Doing radio astronomy doesn't help too much as you can usually find things to observe during both day and night.

Megan is currently on an observing trip to the Giant Metrewave Radio Telescope (GMRT) in India so I thought I would drop her a line and find out what she was up to and what the GMRT was like. I caught her just as a huge two-day science festival had started at the telescope, and thousands of people had descended on the site with mobile phones just to annoy her.

What is the GMRT?

The GMRT (run by the National Centre for Radio Astrophysics, or NCRA) consists of thirty antennas arranged in a Y-shaped configuration near the village of Khodad, India. The central square kilometre contains 14 antennas, randomly arranged, while the rest are distributed in three approximately equal arms. The antennas themselves do not have solid surfaces like radio telescopes such as the Lovell. Instead the reflecting surface is made up of many thin wire "ropes". This works because at the long wavelengths we are using (21 cm and longer) the wires have the same effect as a solid surface. The use of wire instead of panels makes the telescopes lighter, cheaper and more stable in high winds.

What observations are you doing and why do you need to use the GMRT?

We are observing the first half of a sample of nearby Seyfert galaxies, looking for absorption caused by clouds of neutral hydrogen gas in front of the core of the galaxy. The GMRT is designed to work at low frequencies (1420 MHz and below) so it is perfect for doing this sort of project. The GMRT is nearer to the equator (latitude 19°rees; North) so we can see some objects here that never rise above the horizon for a more northern telescope like MERLIN. There is also less man-made interference here than there would be with MERLIN, as the site is a long way from the nearest large town.

One of our first sources was NGC4594 (M104), which is also known as the Sombrero galaxy.

Is it a busy site? Are there many observers there?

There are a few other observers here at the moment. For the last few days there were two Spanish astronomers using the telescope in the early morning, and an astronomer from the NRAO observing after us in the evening. About 100 people work here at the telescope site, most of them as telescope operators, engineers, technicians and other support staff. Most of the GMRT astronomers are based on the University campus in Pune, two hours drive south of the telescope, and spend a few days a month at the telescope making observations or helping visitors with theirs.

What is a typical day/night like?

Because this is a radio telescope, an observing run can be scheduled at any time of the night or day, depending on when the objects you want to observe are above the horizon. The length of a run can vary too, our shortest run was only four hours while the longest was 13. Before the run starts you have to create a command file which tells the telescope what to do. It lists all the commands to tell the telescope how long to spend on each source before moving on to the next. You also have to select some other parameters such as the frequency band in which you want to observe, the frequencies of two of the local oscillators and the bandwidth over which you want to observe. Once the run starts there isn't a lot to do as the command file does most of the work, so most of the run is spent in the computer room adjacent to the main control room which, in order to minimise interference caused by the computers, is situated inside a giant vault.

What is there to do between observations or when the equipment/telescope breaks?

Luckily it is very unlikely that enough will go wrong with the telescope to make observations impossible! Occasionally there are power cuts which mean that you might lose one (or more) of the outer arms for may be an hour or so, as happened to us on Sunday evening. The central square antennas can be run on a backup generator though, so generally you can continue observing, just with reduced sensitivity and a lower resolution.

The site is a long way from the nearest town, but the landscape is quite impressive so there's plenty to explore. There is a track which winds around the central square which you can walk round in under an hour. It does get very hot during the day though, even in winter, and there are apparently panthers around in the evening, so it's best to go early. The village of Khodad is about three kilometres away and the road passes through some suprisingly green farmland. It's a good walk to do if you want to take some pictures of the central square!

Posted in astro blog by Stuart on Monday 28th Feb 2005 (19:31 UTC) | Permalink

Methone and Pallene

Two moons of Saturn that were discovered last year, along with a tentative third, have been given provisional names. The two confirmed moons, discovered by Sebastien Charnoz at the University of Paris, have been named Methone and Pallene. The third, Polydeuces, was spotted by Professor Carl Murray at Queen Mary, University of London. All the new moons have been spotted using images taken by the Cassini mission. This brings the total number of confirmed moons for Saturn up to 33.

Posted in astro blog by Stuart on Sunday 27th Feb 2005 (21:19 UTC) | Permalink

Measuring the Distance of the LMC

How do astronomers measure the distances to the stars and other galaxies? That is a good question and has many answers. For nearby stars this can be done by measuring their apparent change in position with respect to more distant stars, as the Earth orbits the Sun - an effect known as parallax. Further away, we have to use standard candles such as Cepheids and RR Lyrae stars or cluster main sequence fitting. For these techniques, we assume the star to be emitting a certain amount of light and compare this to how much light we observe. Just as the light from a torch gets dimmer the further away it is, we can use the apparent brightness of the star to determine its distance.

For very distant galaxies, we can measure their velocity away from us via the Doppler effect due to the expansion of the universe. However, the velocities of nearby galaxies are largely determined by their own random motions. The Large Magellanic Cloud (LMC), a mid-sized irregular galaxy, is one of the closest to the Milky Way and is visible in the southern hemisphere. A future ESA space mission, GAIA, plans to map the structure of the LMC to the precision we currently have in the Milky Way. However, according to a paper on astro-ph (submitted to ApJ), another space mission could produce independent measurements on about the same time scale. That mission is the Laser Interferometer Space Antenna or LISA.

LISA is another joint mission between ESA and NASA but this doesn't take pretty pictures of stars. In fact LISA doesn't observe any part of the electromagnetic spectrum; this instrument will measure ripples in space-time itself. These ripples are called gravitational waves and are caused when massive objects are accelerated or disturbed. The ripples spread outwards, like the waves caused when you jump into a swimming pool, and can in theory be detected by the vibrations they create between widely separated objects. Lots of people are trying to detect gravitational waves from the Earth although none have been detected yet. That is because they are so small compared to all the other vibrations around us. LISA plans to get around these issues by going into space.

The paper claims that LISA could detect as many as 22 white dwarf binaries in the LMC, via gravitational waves. This could determine the distance of the LMC to an accuracy of around 5% which is pretty good going in astronomy.

Posted in astro blog by Stuart on Saturday 26th Feb 2005 (17:31 UTC) | Permalink

Slacker Astronomy Podcasts

Here is another heads up to an astronomy podcast. This time it is Slacker Astronomy. The trio behind the podcasts are Aaron Price a PhD student at AAVSO, Tavis Searle also at AAVSO and Dr Pamela Gay of the Harvard University Science Centre.

They haven't officially launched the podcasts yet - that will probably be in March - so they are currently at show -3. Trust astronomers to start counting at negative numbers. They promise to hunt down and interview astronomers in the future as well as feature a 'phantom astronomer' segment; anonymous opinions from professional astronomers. The shows are created "for fun, for you, for the voices in our head". I think it might be one to look out for.

Posted in astro blog by Stuart on Saturday 26th Feb 2005 (16:07 UTC) | Permalink

Lets Talk Stars

Did you know that David Levy - of comet Shoemaker-Levy-9 fame - has an audio webcast? The show is called Let's Talk Stars and is webcast once a week. It seems to have been fairly regular since 2001. The current show interviews Mario Motta, a cardiologist and avid amateur astronomer with his own 20 ft dome. They talk about domes, deep sky images, telescope designs and amateur observations of GRBs.

Posted in astro blog by Stuart on Saturday 26th Feb 2005 (15:33 UTC) | Permalink

The 28th closest star

In 2000, astronomers from IoA on the Canary Islands and the Canada-France-Hawaii Telescope discovered a faint (apparent magnitude 17.39) star in the direction of Antlia. The star, named DENIS 1048-39, has been calculated to be 13.2 (0.1) light-years from Earth. The distance was calculated from parallax measurements with the 0.9 meter telescope at Cerro Tololo Inter-American Observatory in Chile. That makes it the 28th closest star to Earth.

Posted in astro blog by Stuart on Thursday 24th Feb 2005 (13:53 UTC) | Permalink

Water and Life on Mars?

Mars has certainly managed to make the news over the last week or so. ESA's Mars Express has released news of a possible frozen water sea on the surface of Mars at latitude 5° North and longitude 150° East. This uses data from the High Resolution Stereo Camera (HRSC) to compare the 'blocky' structures with rafts of fragmented sea ice in the Antarctic. Using cratering statistics, the claim is that this area flooded only 5 million years ago. To stop the water/ice sublimating into the atmosphere, it is suggested that volcanic activity could have covered the ice in a layer of volcanic ash. Water has been found on Mars before but that was at the polar regions not so near to the equator.

This frozen sea has also thrown up a debate about the evidence for life on Mars (again). Vittorio Formisano, chief scientist for Mars Express's Planetary Fourier Spectrometer (PFS) announced that there are high methane levels above the frozen sea. Although methane can be produced by natural processes, it is easy to explain it by the presence of microbial life. Kenneth Nealson of the University of Southern California says that the detected level could also be produced by geological activity especially with all those volcanos in the region.

In a second claim for life on Mars, space.com claimed that two NASA scientists had found life on Mars. The story seems to have been made-up and Carol Stoker, one of the scientists attributed with the claim, is not happy about the fabricated article.

Posted in astro blog by Stuart on Thursday 24th Feb 2005 (13:24 UTC) | Permalink

Dark Matter Galaxy

Cardiff astronomers, using the Lovell telescope at Jodrell Bank, claim to have found the first 'dark matter galaxy'. It is currently thought (unless you play with MOND) that when we look at galaxies, we only see about 10% of the matter; we can see stars, hydrogen and dust but the rotation of a galaxy - as measured via the doppler effect - seems to imply that there should be about 10 times as much mass. The matter that we can't see with telescopes is termed dark matter for obvious reasons.

The new galaxy was first seen in 2000 during the multibeam measurements with the 76m Lovell telescope. The folks down at Cardiff have spent the last five years ruling out all the other possible explanations they can think of. They used the Issac Newton Telescope in La Palma to check if they could see a visible galaxy (i.e. stars) but nothing showed up in the location of the radio galaxy. The total hydrogen content is quoted as 100 million Suns which is equivalent to about a 1000th the mass of our galaxy. The explanation for no star formation is that the density is too low.

Posted in astro blog by Stuart on Wednesday 23rd Feb 2005 (15:10 UTC) | Permalink

Hitchhiker's Guide Trailer

The official trailer was released today with some good shots of the Lovell Telescope in it. I wondered how much of the Lovell they would show in the film so it was great to see it in the trailer. There are also some pictures of the Vogons which vaguely resemble Patrick Moore - even down to the monocle. Sir Patrick even writes Vogon standard poetry. The film release date has been moved forward a week to the 29th April.

Posted in astro blog by Stuart on Wednesday 16th Feb 2005 (17:33 UTC) | Permalink

What is it?

What is the strange, slowly moving object visible in today's astronomy picture of the day? The frames were taken by ConCams on Mauna Kea and Haleakala in Hawii. The object takes quite a lot of time to pass over the camera position and seems to move in a straight line. That doesn't necessarily mean that the object was moving in a straight line due to the fisheye projection; only objects moving radially would follow straight lines and all others would move in curved ones. There is quite a lot of discussion - up to eight pages already - over at the NightSkyLive fora.

Posted in astro blog by Stuart on Tuesday 08th Feb 2005 (18:11 UTC) | Permalink


ESA's Mars Express arrived at Mars over a year ago now but the MARSIS experiment (Mars Advanced Radar for Subsurface and Ionosphere Sounding) has not yet been deployed. That is because they are a bit worried that it may whip back and strike the spacecraft. Despite the worries, officials at ESA have taken the decision to deploy the 20 metre long arms possibly this April in order to take advantage of Mars Express's closer passes to Mars from April to June.

Posted in astro blog by Stuart on Tuesday 08th Feb 2005 (17:52 UTC) | Permalink

Asteroid 2004 MN4

Dont panic! Just after Christmas asteroid 2004 MN4 gained a rating on the Torino scale of 4, making it the highest ever rating. The Torino scale measures the likelihood of a comet/asteroid hitting the Earth. This was interesting, as the probability of a hit got as high as 1 in 45. However, after more observations the orbit was refined and it was calculated that it will miss us by about 6 million km on 13th April 2029. It currently has a probability of impact of 0.016%.

Posted in astro blog by Stuart on Friday 04th Feb 2005 (18:31 UTC) | Permalink

V838 Monocerotis

The Hubble Space Telescope (HST) have released another frame to the really great looking animation of V838 Monocerotis (Quicktime). This is thought to be a young binary star system in the constellation of Monoceros, where the larger star has had a short outburst. As well as making astronomy picture of the day, it even made the front page of the Independent newspaper.

The press release claims that the individual frames are presented as if they had the same exposure time but it doesn't look like that to me; the central stars get brighter as time goes on. I don't think there should be any physical interaction between the expanding light echo and the foreground stars to make them brighter so my best guesses are that either the exposure correction isn't too good or it is a touched-up PR image made with Photoshop. At least it looks nice.

Posted in astro blog by Stuart on Friday 04th Feb 2005 (16:44 UTC) | Permalink

Astronomy from the Moon

The idea of building radio telescopes on the far side of the Moon has been around for a long time and we commented on it a few months ago.

It seems that a workshop titled 'Towards a European Infrastructure for Lunar Observatories' is being organised this March in Bremen, Germany. It will be sponsored by EADS, ASTRON, and Radionet but will be restricted to 30 people. The point of the workshop is to "bring together representatives from science and industry to discuss the various options, time scales, and scientific justifications for scientific experiments on the Lunar surface". Possible observatories on the lunar surface might study a range of frequencies from low-frequency radio (they don't say how low, low is) through submm-wave, optical and X-ray. There could also be a network of seismic sensors and other detectors as well.

This has come to the fore with ESA's plan for more missions, some manned, to the Moon and Mars. If you think this sounds familiar you'd be right; NASA have their own, well publicised plan called Earth, Moon, Mars and beyond.

I can't wait to see the results of the workshop and see if any of the recommendations get put into use.

Posted in astro blog by Stuart on Friday 04th Feb 2005 (13:28 UTC) | Permalink

Beagle 2 Inquiry

The joint Commission of Inquiry into the failure of Beagle 2 has released its report. The Commission's view was that "the SPC Science Programme Committee should not have confirmed the selection of Beagle 2, given the failure of the project to comply with the recommendations of the PRC". They also said that the mission was too big for a single university team to take on.

Posted in astro blog by Stuart on Thursday 03rd Feb 2005 (17:52 UTC) | Permalink
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