Institute of Astronomy

Astronomy News

Part of infant Earth survived moon's shocking birth

10 June 2014 - 5:33pm
Earth held on to a part of its past – a layer of rock seems to have resisted the catastrophic melting caused by the collision that spawned the moon

NASA Instruments Begin Science on European Spacecraft Set to Land on Comet

10 June 2014 - 5:00pm
Three NASA science instruments aboard the European Space Agency's (ESA) Rosetta spacecraft, which is set to become the first to orbit a comet and land a probe on its nucleus, are beginning observations and sending science data back to Earth.

Extreme checklist to look for odd life on other worlds

9 June 2014 - 8:00pm
Snow algae and light-shunning seaweed are some of the weird life forms that may rule on habitable exoplanets, according to criteria from a NASA astrobiologist

Pluto and its moon snuggle under a shared atmosphere

6 June 2014 - 3:38pm
Nitrogen from Pluto's atmosphere could be flowing over to its moon Charon – something we've never seen in a planet and moon before

XMM-Newton:Cosmic collision in the Bullet Group

6 June 2014 - 1:59pm
Galaxies are not as isolated as they at first glance may seem; on a cosmic scale they congregate in clumps along with dark matter and hot gas. The colourful blob in this new composite image, based on data from several telescopes including ESA's XMM-Newton, is the group of galaxies known as the Bullet Group. Its components appear to be clearly separated, with the hot gas partitioned from the rest of the mass within the group. This is the smallest object ever found to show such an effect, which was caused by a merger in the group's past.

Trace of another world found on Moon

5 June 2014 - 7:00pm
Researchers find evidence of the world that crashed into Earth billions of years ago to form the Moon.

Ancient exoplanet may have the right stuff for life

5 June 2014 - 4:26pm
A possibly rocky world snared from another galaxy is thought to be 11.5 billion years old and may still be warm enough to be friendly to life

Venus death dive to unlock secrets of Earth's evil twin

5 June 2014 - 4:00pm
On its final plunge, the Venus Express probe will fly deeper than ever before. But only a return mission will tell us about climate change and alien life

Gaia takes science measurements

5 June 2014 - 1:04pm

As part of the on-going commissioning tests, we are happy to be able to report on the first spectroscopy observations made by Gaia.

You will have seen the ‘first light’ images from the early phases of commissioning already, but as part of these activities we have also started taking test spectroscopic measurements of known stars.

While astrometric measurements will determine the positions and motions of stars, Gaia will use spectroscopy to measure key physical properties, such as brightness, temperature, mass, age, and chemical composition.

This is achieved by studying stellar spectra – the fingerprints of stars. Typically, a star’s spectrum includes a broad continuum spanning a wide range of wavelengths coming from the hot gas at the surface of the star. This is then interspersed with dips at specific wavelengths, where cooler atoms and molecules in the ‘atmosphere’ of the star absorb some of the continuum light. Occasionally, brighter emission lines can also be seen. The absorption and emission lines provide an indication of the elements present in the object and under what temperature and pressure conditions they exist.

In addition, the lines can all be shifted from their normal wavelengths – that is, the corresponding wavelength at which the same line is observed in the laboratory – if the star is moving towards us or away from us. These stellar radial velocities can be used to determine the velocity of stars with respect to the Sun, and are therefore essential to understand stellar motions in our Galaxy.

The two plots shown here give an idea of the kind of spectroscopic information that Gaia will return over its 5-year mission.

Gaia RVS data (top) compared with high-res ground-based observations (bottom) for the star HIP 86564.
Credits: ESA/Gaia/DPAC/Airbus DS

The first (above) is a radial velocity spectrum for a bright star (HIP 86564), with key elements identified. The RVS only covers a very narrow spectral range at wavelengths centred near 860nm, just beyond the visible red, but provides high enough spectral resolution to make it possible to measure stellar velocities to within a few kilometres per second. The most prominent spectral lines correspond to iron (labelled Fe), titanium (Ti), and calcium (Ca). The ‘triplet’ of calcium lines is particularly important, as they appear in almost all stars. The Gaia plot (top) is compared with high-resolution ground-based observations of the same star, by the NARVAL instrument at the Pic-du-Midi Observatory (bottom), showing that the Gaia RVS is working as expected.

The second plot (below) shows temperature information for seven different bright stars (labelled, along with their spectral types – click here for background on stellar types). This information is extracted from Gaia’s photometric instrument, which generates two low-resolution spectra, one covering blue wavelengths and the other red wavelengths. The blue photometer (BP) receives light with shorter wavelengths (from 330 nm to 680 nm), and the red photometer (RP) receives light with longer wavelengths (from 640 to 1050 nm). The photometers record the total intensity of each star across these wavelengths, and also make it possible to determine the stellar temperatures.

Gaia BP/RP data for seven bright stars.
Credits: ESA/Gaia/DPAC/Airbus DS

A pair of red and blue spectra is shown here for each of the seven stars. The plot is arranged with cool stars (approximately 3000ºC) at the top, to hotter stars (around 8000ºC) at the bottom. As expected, the hottest stars are relatively stronger in Gaia’s blue photometer, and weaker in the red photometer. Conversely, the cooler stars are brighter in the red photometer. Data like these will be used to determine the temperatures for millions of stars in the Milky Way that have not yet been studied in detail.

More details and original spectra are available here.

Within the next few days we will provide an update on the stray light issues discussed in previous blog posts. 

Posted on behalf of the Gaia Project Team