Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Astronomers’ first direct evidence: young low-mass objects are twice as heavy as predicted

20.01.2005


Although mass is the most important property of stars, it has proved very hard to measure for the lowest mass objects in the universe. Thanks to a powerful new camera, a very rare, low-mass companion has finally been photographed.



The discovery suggests that, due to errors in the models, astronomers have overestimated the number of young "brown dwarfs" and "free floating" extrasolar planets. An international team of astronomers lead by University of Arizona Associate Professor Laird Close reports the discovery in today’s (Jan 20.) issue of Nature.

The image has allowed the team to directly measure the mass of a young, very low mass object for the first time. The object, more than 100 times fainter than its close primary star, is 93 times as massive as Jupiter -- almost twice as heavy as theory predicts it should be. Their findings challenge current ideas about the astronomical brown dwarf population and the existence of widely publicized free-floating extrasolar planets.


Brown dwarfs are objects 75 times more massive than Jupiter but not massive enough to burn as stars. If young objects identified as brown dwarfs are twice as massive as has been thought, many actually are low mass stars. Objects recently identified as ’free-floating’ planets are in turn likely just low mass brown dwarfs.

Close of the UA’s Steward Observatory and his international colleagues detected the faint, very-low-mass companion, named AB Dor C, which orbits the very young star AB Doradus A (AB Dor A) at only 2.3 times the distance between the Earth and the sun, or about the distance between the sun and the asteroids beyond Mars.

Astronomers searching for very low mass objects look at young nearby stars because low mass companion objects will be brightest when young, before they contract and cool. Astronomers had suspected since the early 1990s that well-known AB Dor A -- a star 48 light years (14.9 parsecs) from Earth and only 50 million years old -- has a low-mass companion because its position ’wobbles’ as it’s pulled by an unseen companion. But even the Hubble Space Telescope tried and failed to detect the companion because it was too faint and too close to the glare of the primary star.

Close and his colleagues from Germany (Rainer Lenzen, Wolfgang Brandner), Spain (Jose C. Guirado), Chile (Markus Hartung, Chris Lidman), and the United States (Eric Nielsen, Eric Mamajek, and Beth Biller) succeeded in photographing the elusive companion. They used Close and Lenzen’s novel high-contrast camera on the European Southern Observatory’s 8.2-meter Very Large Telescope in Chile in February 2004.

Close and Lenzen developed the new high-contrast adaptive optics camera, the NACO Simultaneous Differential Imager, or NACO SDI, for hunting extrasolar planets. The SDI camera enhances the ability of the powerful 8.2-meter VLT telescope and its existing adaptive optics system to detect faint companions that normally would be lost in the glare of the primary star.

Close and his team are the first to image a companion so faint – 120 times fainter than its star -- and so near its star. The tiny distance between the star and the faint companion (0.156 arcseconds) is the same as the width of a dime (1.5 centimeters) seen 8 miles (13 kilometers) away. Once they located the companion, they observed it at near infrared wavelengths to measure its temperature and luminosity.

"We were surprised to find that the companion was 400 degrees Celsius cooler and 2.5 times fainter than the latest models predicted," Close said.

"We used our discovery of the companion’s exact location, along with the star’s known ’wobble’, to accurately determine the companion’s mass," team member Jose Guirado said.

"Theory predicts that this low-mass, cool object would be about 50 Jupiter masses," Close said. "But theory is incorrect: This object is between 88-98 Jupiter masses. This discovery will force astronomers to rethink what masses of the smallest objects produced in nature really are."

"Objects like AB Dor C are very rare," Wolfgang Brandner said. "Only one percent of stars have close very low mass companions -- and only about one percent of nearby stars are young. Hence, we are very lucky to be able to accurately measure the mass of even a single low mass companion that is accurately known to be young."

The NACO SDI camera is a unique type of camera using adaptive optics, which removes the blurring effects of Earth’s atmosphere to produce extremely shape images. SDI splits light from a single star into four identical images, then passes the resulting beams through four slightly different methane-sensitive filters. When the filtered light beams hit the camera’s detector array, astronomers can subtract the images so the bright star disappears, revealing a fainter, lower-mass methane-rich object otherwise hidden in the star’s scattered light halo.

The National Science Foundation awarded Close a prestigious 5-year, $545,000 Faculty Early Career Development award that supports his search for extrasolar planets using SDI cameras on the European Southern Observatory’s 8.2-meter VLT in Chile and on the UA/Smithsonian 6.5-meter MMT on Mount Hopkins, Ariz. This research was also supported by NASA.

Authors of the Jan. 20 Nature letter, "A dynamical calibration of the mass-luminosity relation at very low stellar masses and young ages," are: Laird Close of the UA Steward Observatory, Rainer Lenzen of the Max Planck Institute for Astronomy in Heidelberg, Jose C. Guirado of the University of Valencia (Spain), Eric L. Nielsen of UA Steward Observatory, Eric E. Mamajek of the Harvard-Smithsonian Center for Astrophysics, Wolfgang Brandner of the Max Planck Institute for Astronomy in Heidelberg, Markus Hartung and Chris Lindman of the European Southern Observatory (Chile), and Beth Biller of the UA Steward Observatory.

Laird M. Close | EurekAlert!
Further information:
http://www.arizona.edu

More articles from Physics and Astronomy:

nachricht A better way to weigh millions of solitary stars
15.12.2017 | Vanderbilt University

nachricht A chip for environmental and health monitoring
15.12.2017 | Friedrich-Alexander-Universität Erlangen-Nürnberg

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: First-of-its-kind chemical oscillator offers new level of molecular control

DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.

Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Engineers program tiny robots to move, think like insects

15.12.2017 | Power and Electrical Engineering

One in 5 materials chemistry papers may be wrong, study suggests

15.12.2017 | Materials Sciences

New antbird species discovered in Peru by LSU ornithologists

15.12.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>