Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Cepheids and their ’Cocoons’

01.03.2006


Interferometry Helps Discover Envelopes Around Supergiant Stars



Using ESO’s Very Large Telescope Interferometer (VLTI) at Cerro Paranal, Chile, and the CHARA Interferometer at Mount Wilson, California, a team of French and North American astronomers has discovered envelopes around three Cepheids, including the Pole star. This is the first time that matter is found surrounding members of this important class of rare and very luminous stars whose luminosity varies in a very regular way. Cepheids play a crucial role in cosmology, being one of the first "steps" on the cosmic distance ladder.

The southern Cepheid L Carinae was observed with the VINCI and MIDI instrument at the VLTI, while Polaris (the Pole Star) and Delta Cephei (the prototype of its class) were scrutinised with FLUOR on CHARA, located on the other side of the equator. FLUOR is the prototype instrument of VINCI. Both were built by the Paris Observatory (France).


For most stars, the observations made with the interferometers follow very tightly the theoretical stellar models. However, for these three stars, a tiny deviation was detected, revealing the presence of an envelope.

"The fact that such deviations were found for all three stars, which however have very different properties, seems to imply that envelopes surrounding Cepheids are a widespread phenomenon", said Pierre Kervella, one of the lead authors.

The envelopes were found to be 2 to 3 times as large as the star itself. Although such stars are rather large - about fifty to several hundreds of solar radii - they are so far away that they can’t be resolved by single telescopes. Indeed, even the largest Cepheids in the sky subtend an angle of only 0.003 arc second. To observe this is similar to viewing a two-storey house on the Moon.

Astronomers have thus to rely on the interferometric technique, which combines the light of two or more distant telescopes, thereby providing the angular resolution of a unique telescope as large as the separation between them. With the VLTI, it is possible to achieve a resolution of 0.001 arc second or less.

"The physical processes that have created these envelopes are still uncertain, but, in analogy to what happens around other classes of stars, it is most probable that the environments were created by matter ejected by the star itself", said Antoine Mérand, lead-author of the second paper describing the results.

Cepheids pulsate with periods of a few days. As a consequence, they go regularly through large amplitude oscillations that create very rapid motions of its apparent surface (the photosphere) with velocities up to 30 km/s, or 108 000 km/h! While this remains to be established, there could be a link between the pulsation, the mass loss and the formation of the envelopes.

Henri Boffin | alfa
Further information:
http://www.eso.org/outreach/press-rel/pr-2006/pr-09-06.html

More articles from Physics and Astronomy:

nachricht Hope to discover sure signs of life on Mars? New research says look for the element vanadium
22.09.2017 | University of Kansas

nachricht Calculating quietness
22.09.2017 | Forschungszentrum MATHEON ECMath

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Rainbow colors reveal cell history: Uncovering β-cell heterogeneity

22.09.2017 | Life Sciences

Penn first in world to treat patient with new radiation technology

22.09.2017 | Medical Engineering

Calculating quietness

22.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>