Institute of Astronomy

Astronomy News

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 


Eye of Sauron star spotted by planet-hunting camera

4 June 2014 - 9:30pm
An exoplanet-hunting add-on for the Very Large Telescope has taken its first images, revealing a stunning ringed star with unprecedented clarity

First Light for SPHERE Exoplanet Imager

4 June 2014 - 11:00am
SPHERE — the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument — has been installed on ESO’s Very Large Telescope (VLT) at the Paranal Observatory in Chile and has achieved first light. This powerful new facility for finding and studying exoplanets uses multiple advanced techniques in combination. It offers dramatically better performance than existing instruments and has produced impressive views of dust discs around nearby stars and other targets during the very first days of observations. SPHERE was developed and built by a consortium of many European institutes, led by the Institut de Planétologie et d'Astrophysique de Grenoble, France, working in partnership with ESO. It is expected to revolutionise the detailed study of exoplanets and circumstellar discs.

History: Moon mapped by an artist's impression

4 June 2014 - 1:00am

History: Moon mapped by an artist's impression

Nature 510, 7503 (2014). doi:10.1038/510035d

Author: José Rafael Martínez Enríquez

Thomas Harriot mapped the Moon before Galileo (J.RamplingNature508, 39–40; 201410.1038/508039a). Unlike Galileo, he did not interpret what he saw as craters, mountains and valleys (see S.PumfreyNotes Rec. R. Soc.63, 163–

Astrophysics: The MAD world of black holes

4 June 2014 - 1:00am

Astrophysics: The MAD world of black holes

Nature 510, 7503 (2014). doi:10.1038/510042a

Authors: Denise Gabuzda

An analysis of optical and radio observations has revealed how powerful jets are launched from the centres of active galaxies, where supermassive black holes accrete matter through magnetically arrested disks, or MADs. See Letter p.126

Dynamically important magnetic fields near accreting supermassive black holes

4 June 2014 - 1:00am

Dynamically important magnetic fields near accreting supermassive black holes

Nature 510, 7503 (2014). doi:10.1038/nature13399

Authors: M. Zamaninasab, E. Clausen-Brown, T. Savolainen & A. Tchekhovskoy

Accreting supermassive black holes at the centres of active galaxies often produce ‘jets’—collimated bipolar outflows of relativistic particles. Magnetic fields probably play a critical role in jet formation and in accretion disk physics. A dynamically important magnetic field was recently found near the Galactic Centre black hole. If this is common and if the field continues to near the black hole event horizon, disk structures will be affected, invalidating assumptions made in standard models. Here we report that jet magnetic field and accretion disk luminosity are tightly correlated over seven orders of magnitude for a sample of 76 radio-loud active galaxies. We conclude that the jet-launching regions of these radio-loud galaxies are threaded by dynamically important fields, which will affect the disk properties. These fields obstruct gas infall, compress the accretion disk vertically, slow down the disk rotation by carrying away its angular momentum in an outflow and determine the directionality of jets.

Hubble:Hubble unveils a colourful view of the Universe [heic1411]

3 June 2014 - 7:15pm
Astronomers using the Hubble Space Telescope have captured the most comprehensive picture ever assembled of the evolving Universe – and one of the most colourful. The study is called the Ultraviolet Coverage of the Hubble Ultra Deep Field (UVUDF) project.

Hubble Team Unveils Most Colorful View of Universe Captured by Space Telescope

3 June 2014 - 7:15pm

Get larger image formats

Astronomers using the Hubble Space Telescope have assembled a comprehensive picture of the evolving universe among the most colorful deep space images ever captured by the 24-year-old telescope. This study, which includes ultraviolet light, provides the missing link in star formation.

Rosetta Comet Comes Alive

3 June 2014 - 5:07pm
Later this year, Europe's Rosetta probe will orbit and land on comet 67P/Churyumov--Gerasimenko. New images of the comet show that it will be a lively place when Rosetta arrives.

Hubble Team Unveils Most Colorful View of Universe Captured by Space Telescope

3 June 2014 - 5:00pm
Astronomers using NASA's Hubble Space Telescope have assembled a comprehensive picture of the evolving universe – among the most colorful deep space images ever captured by the 24-year-old telescope.

XMM-Newton:Pulsating X-rays allow XMM-Newton to unmask a mysterious star

3 June 2014 - 4:00pm
XMM-Newton has revealed a unique star. It is a celestial chimera with the body of a normal massive star yet the magnetic field of a dead, stellar dwarf. This makes it a singular object among the billions of known stars.

NASA Begins Testing of New Spectrograph on Agency's Airborne Observatory

3 June 2014 - 3:51pm
Astronomers are eagerly waiting to begin use of a new instrument to study celestial objects: a high-resolution, mid-infrared spectrograph mounted on NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA), the world's largest flying telescope.

Fireball meteors emit unique radio wave signals

3 June 2014 - 3:37pm
After 50 years of trying, physicists have tuned into the radio waves given off by fireballs streaking through Earth's atmosphere

Big Bang finding challenged

3 June 2014 - 1:00am

Big Bang finding challenged

Nature 510, 7503 (2014).

Author: Ron Cowan

Signal of gravitational waves was too weak to be significant, studies suggest.

Big Bang blunder bursts the multiverse bubble

3 June 2014 - 1:00am

Big Bang blunder bursts the multiverse bubble

Nature 510, 7503 (2014).

Author: Paul Steinhardt

Premature hype over gravitational waves highlights gaping holes in models for the origins and evolution of the Universe, argues Paul Steinhardt.

Impossibly heavy planet is the first 'mega-Earth'

2 June 2014 - 6:40pm
Twice the size of Earth and with 17 times our planet's mass, Kepler-10c is so unusual that it has been placed in a brand new class of exoplanet

'Godzilla of Earths' identified

2 June 2014 - 6:17pm
There is a new class of planet out there that astronomers are calling the "mega-Earth".