A collaboration between astronomers at the University of Arizona's Steward Observatory and at the National Astronomical Observatory of China has led to a better camera for one of the UA's telescopes on Kitt Peak, and better pictures of the sky for the Chinese astronomers.
"Chinese science and astronomy are expanding very rapidly, so in order to train and to give facilities to their scientists, at the moment anyway, they need to seek places outside of China," said Edward Olszewski, an astronomer at the UA's Steward Observatory.
"The Chinese built a very large telescope near Beijing that can take light spectra of objects in the sky to measure the distance of the galaxies or the age or the compositions of the stars," said Olszewski. "It's the biggest telescope of that kind in the world right now."
Before using their new telescope, astronomers at the National Astronomical Observatory of China need detailed digital images of the area of sky they want to investigate – images that can be taken with the 90Prime camera on the 90-inch UA telescope on Kitt Peak.
"They need these pictures to decide what objects to observe," said Olszewski. The digital images show objects in several different colors of light. Based on how bright the objects appear in the different colors, astronomers can predict whether the objects are stars, distant galaxies or other objects, and can decide which objects are worth investigating more closely.
While the 90-inch telescope on Kitt Peak had been used to take many of the type of digital images that the Chinese astronomers needed, it was in need of some repair. "Ninety-prime was built between 1998 to 2003," said Olszewski. "The detectors that were in it were very experimental, and over time they degraded."
UA astronomy professor Xiaohui Fan was attending a conference in China when the question arose about what to do when the new Chinese telescope was finished. The astronomers mentioned the need for specialized digital images in order to use the new telescope.
"I thought: We have a telescope, we have a camera that in principle can be used," said Fan. "And the people in China thought that might be interesting to collaborate on. That's how it started. They had a need to support the national facility by using a very large camera to take digital pictures."
"And we had a need to refurbish our camera," said Olszewski.
The UA and Chinese astronomers worked out a trade: the Chinese would gain access to the Kitt Peak telescope to take the digital images of the sky that they required, and in return they would contribute to the upkeep of the telescope and the refurbishment of the 90Prime camera.
"They get access to a certain number of nights as a result of their contributions to the refurbishment of the camera and the operation of the telescope," said Fan.
"They get seven or eight nights every dark of the moon in September, October, November and December, which is when their objects are visible," said Olszewski. "Dark of the moon" refers to the time of month around new moon, when the sky is darkest. This is the best time for the astronomers to take images of the sky, because the moon's light does not interfere with the image exposures.
The Chinese astronomers are looking for images of an area known as the south polar cap of the Milky Way galaxy. The north and south polar caps of the Milky Way galaxy are defined relative to the Earth's north and south poles. The plane of the Earth's orbit around the sun is in relatively close alignment with the plane of the galaxy.
If you were looking down on the Milky Way and the Earth's north pole, you could define "up" as the general direction of Earth's north pole, and "down" as the general direction of Earth's south pole, explained Olszewski. From Tucson and Beijing, which are on nearly the same latitude, the southern cap of the Milky Way is best observed in the autumn, when the Earth's Northern hemisphere is tilted away from the sun.
The images taken with the UA's 90Prime camera will enable the Chinese astronomers to get the information they need about the objects in order to select the best ones for further observation with the telescope at the Chinese National Observatory.
The data gathered during this collaboration are shared among the Chinese and American scientists, leading to potential new astronomical discoveries and new sources of data for future studies of this relatively unexplored area of the sky.
"The data are not just for one purpose," said Olszewski. "You could probably think of 10 or 20 different ways to use the data."
The project represents a major step forward for international astronomy collaborations. It is the largest of several collaborations between Steward Observatory and Chinese astronomers.
"For most of our telescopes, past collaborations have not been international," said Olszewski. "We're learning how to do this."
"Other fields have probably done it," said Fan. "But in astronomy, they haven't really done this before. There are bureaucracies that we have to go through to actually make it work."
The Chinese will finish up their project at the end of 2012 or in the fall of 2013, said Olszewski, and there is a possibility of extending this collaboration to additional astronomy projects where both groups could benefit from shared resources and data.
"The collaboration worked very well this year," said Olszewski. "In the first year we still had differing levels of expectations, and in the second year each of us figured out what the other was able to offer. It's worked out very well."
"And the weather was better too," added Fan. Which for astronomers, whose work depends on clear skies, is no trivial detail.