Supergiant star with a thick dust disc

Jan 26, 2011
3D images of HD 62623, obtained with the VLTI (left), compared to the model of a rotating disk (right). In the boxes, the gas kinematics is shown (3rd dimension): blue-coloured gas approaches the observer, while red-coloured gas recedes from the observer. The size of the inner gas disk of approx. 2 milli-arcseconds corresponds to 1.3 astronomical units (distance Earth-Sun), while the dust ring seen in the images has a radius corresponding to 4 astronomical units, assuming 2100 light years as thedistance to HD 62623. Credit: F. Millour et al.

How is it possible that HD 62623, a hot super-giant star on the verge of death, is surrounded by a disc, generally only associated with infant stars? Using long-baseline stellar interferometry at ESO's VLT interferometer, a team led by Florentin Millour from Observatoire de la Cote d'Azur and Anthony Meilland from Max Planck Institute for Radio Astronomy could generate for the first time a three-dimensional high angular and high spectral resolution image of this star and its closest environment. They conclude that a solar-mass companion star is the key to this mystery. To attain their goal, the researchers adapted an imaging technique from radio astronomy which uses interferometric datasets.

HD 62623 is an exotic hot . Contrary to its well-known twin, the bright star Deneb in the summer triangle, and almost all with the same spectral class, this star is surrounded by a dense and complex zone composed of plasma and dust. Hot supergiant stars are very bright stars, so bright, that they push their strong wind with their own photons. Such a wind would normally prevent matter from condensing as dust next to the star. So as to understand processes in the harsh environment of such stars better, it is highly desirable to disentangle the geometry of the gas and dust in the surroundings of the central source, but also to access the kinematics of this close environment.

"Thanks to our interferometric observations with AMBER we could synthesize a 3D image of HD 62623 as seen through a virtual 130 metre diameter telescope", says Florentin Millour, leading author of the study. "The resolution is of an order of magnitude higher when compared with the world's largest optical telescopes of 8-10 metres diameter." The AMBER instrument is located at the Very Large (VLTI) in Chile. The scientists significantly improved the image quality by adapting the so-called "self-calibration" method, which is well-known from radio interferometry. The image obtained by this method combines spatial and velocity information, showing not only the shape of the close environment of HD 62623, but also its kinematics or motion. Up until now the necessary kinematics information was missing in such images.

Four domes of the 1.8 metre Auxiliary Telescopes(AT), utilized for the Very Large Telescope Interferometer (VLTI). ESO, Cerro Paranal, Chile. Credit: F. Millour, OCA, Nice, France

"Our new 3D image locates the dust-forming region around HD 62623 very precisely, and it provides evidence for the rotation of the gas around the central star," explains Anthony Meilland. "This rotation is found to be Keplerian, the same way the Solar system planets rotate around the Sun." A nearby , with approximately the mass of our Sun, could be the reason for such a disc around HD 62623. This companion, though not directly detected due to its brightness being thousands of times lower than the primary star, is betrayed by a central cavity between the gas disk and the central star. The presence of the companion could explain the exotic characteristics of HD 62623, exactly like the monster among the old stars within our Galaxy, Eta Carinae.

The new 3D imaging technique presented in this work is equivalent to integral-field spectroscopy, but gives access to a 15 times larger angular resolution or capacity to detect fine details in the images. "With these new capacities, the VLTI will be able to provide a better comprehension of many sky targets, too small to be resolved by the largest telescopes", concludes Florentin Millour. "We can use this approach to study young stellar disks or jets, or even the central regions of active galaxies."

The European Southern Observatory (ESO): is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor.

The Very Large Telescope Interferometer (VLTI): utilizes telescopes at ESO's Paranal site, either the 8.2 m UTs or the 1.8m ATs (Auxiliary Telescopes). AMBER (Astronomical Multi-BEam Recombiner) is one of the science instruments of the VLTI. It is an interferometric beam combiner, sensitive in the near-infrared wavelength range (from 1 to 2.5 microns), built in collaboration with institutes from Grenoble (Laboratoire d'Astrophysique de Grenoble), Nice (Laboratoire d'Astrophysique Universitaire de Nice und Observatoire de la Côte d'Azur), Florence (Observatorio Astrofisico di Arcetri) and Bonn (Max Planck Institute for Radio Astronomy).

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More information: Florentin Millour, et al. Imaging the spinning gas and dust in the disc around the supergiant A[e] star HD62623, Astronomy & Astrophysics, DOI:10.1051/0004-6361/201016193 , 26. January 2011

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Charles_Rovira
not rated yet Jan 26, 2011
Curious layman question follows: "Why are objects distant in time/space point sources?"

There is something which has never been explained to my satisfaction about the apparent size of stars/galaxies.

If the universe was created by a big bang, as most evidence supports, why are the earliest stars/galaxies seen as point sources, without any spreading of the light in three dimensions?

Take a balloon, put a dot on it with a marker. Now blow it up, and it is spread. It would be spread whether one was inside of a balloon or not.

Either inflation was instantaneous which means that it has stopped, or it wasn't which means that the apparent size of stars/galaxies would be larger, like the dot on the balloon.

Given dark energy blowing things up, that probably has some effect too so why are objects distant in time/space point sources?

Just asking if anybody knows what I need to learn to see the explanation...
Skeptic_Heretic
5 / 5 (4) Jan 26, 2011
If the universe was created by a big bang, as most evidence supports, why are the earliest stars/galaxies seen as point sources, without any spreading of the light in three dimensions?
Because it's far away.

It does spread in three dimensions but that doesn't change the fact that you're still very distant from it.
saporis
not rated yet Jan 26, 2011
@Charles
...


The universe is expanding, but not the stars / planets themselves due to gravity that acts upon them. For example, stars may drift apart (as the universe expands), but not the stars and planets themselves as there is gravity holding everything together. Holding the molecules together is a strong force (and I forgot what it was called).
DamienS
5 / 5 (2) Jan 27, 2011
Either inflation was instantaneous which means that it has stopped, or it wasn't

Inflation was very nearly instantaneous, but not quite, and while it lasted for a relatively short period of time at the birth of the universe, the magnitude of the expansion was vast.
PinkElephant
5 / 5 (3) Jan 27, 2011
@Charles_Rovira,

You see any such distant object as a point source, because of the way optics works. Light travels in straight lines through space, so you can only perceive those photons that traveled straight to your eye (or to your telescope's mirror) from the object in question. Because these objects are so far away from you, they subtend only a tiny angle across the sky. And so all the photons you can perceive from them, appear to you as if they're coming from that tiny angular interval.

Note however, that those aren't the only photons being emitted. In fact, the photons emitted by a distant galaxy are about equally distributed on a surface of a sphere whose radius is the distance from that galaxy to you. If you could position yourself at any point on that sphere, you could still see the galaxy in question (perhaps from a different angle.) But you'd still only see those photons that traveled straight from the sphere's center through the patch you happen to subtend.
eachus
5 / 5 (2) Feb 02, 2011
"Why are objects distant in time/space point sources?"

There is something which has never been explained to my satisfaction about the apparent size of stars/galaxies.

If the universe was created by a big bang, as most evidence supports, why are the earliest stars/galaxies seen as point sources, without any spreading of the light in three dimensions?

Take a balloon, put a dot on it with a marker. Now blow it up, and it is spread. It would be spread whether one was inside of a balloon or not.

Either inflation was instantaneous which means that it has stopped, or it wasn't which means that the apparent size of stars/galaxies would be larger, like the dot on the balloon.


Early inflation was extremely rapid, with the universe doubling in size thousands of times in the first picosecond or so. Inflation quickly slowed down and for billions of years the expansion almost stood still. Now it is accelerating again, but won't reach anything like the original rate.
eachus
5 / 5 (1) Feb 02, 2011
I remember back when astronomers were trying to figure out if the expansion of the universe would continue forever, slow to a stop, or even reverse and shrink in size. Only in the last ten years or so has it been shown that, at least in the local ten billion light years or so, the inflation is accelerating, not slowing.

Could this be a local effect? Yes, but very unlikely. There could be massive galaxy clusters all around us at a distance where we can't see them, but close enough to affect the acceleration of clusters we can see. However, we would have to be in a very special area of the universe for that to be true, since the effect is very uniform in all directions.
frajo
5 / 5 (1) Feb 02, 2011
Early inflation was extremely rapid, with the universe doubling in size thousands of times in the first picosecond or so.
One picosecond is 10**(-12) sec while the inflationary period is assumed to have taken place from 10**(-36) to 10**(-32) sec.
See hyperphysics.phy-astr.gsu.edu/hbase/astro/planck.html#c1

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