Featured Research

from universities, journals, and other organizations

Astronomers' First Direct Evidence: Young Low-mass Objects Are Twice As Heavy As Predicted

Date:
January 29, 2005
Source:
University Of Arizona
Summary:
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.

An enhanced false color infrared image of AB Dor A and C. The faint companion "AB Dor C" -- seen as the pink dot at 8 O'clock -- is 120 times fainter than its primary star. The tiny 0.156 arcsec separation between A and C is smaller than a dime seen from 8 miles away. Nevertheless, the new NACO SDI camera was able to distinguish it as a "redder" dot surrounded by the "bluer" light from AB Dor A. The orbit of AB Dor C around AB Dor A is shown as a yellow ellipse. It takes 11.75 years for the 93 Jupiter mass companion to complete this orbit.
Credit: Photo Laird Close, Steward Observatory

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.

Related Articles


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.

###

More information and images are available on the Web sites: http://exoplanet.as.arizona.edu/~lclose/talks/ins/SDI_NACO.html and http://athene.as.arizona.edu/~lclose/.


Story Source:

The above story is based on materials provided by University Of Arizona. Note: Materials may be edited for content and length.


Cite This Page:

University Of Arizona. "Astronomers' First Direct Evidence: Young Low-mass Objects Are Twice As Heavy As Predicted." ScienceDaily. ScienceDaily, 29 January 2005. <www.sciencedaily.com/releases/2005/01/050125084544.htm>.
University Of Arizona. (2005, January 29). Astronomers' First Direct Evidence: Young Low-mass Objects Are Twice As Heavy As Predicted. ScienceDaily. Retrieved November 28, 2014 from www.sciencedaily.com/releases/2005/01/050125084544.htm
University Of Arizona. "Astronomers' First Direct Evidence: Young Low-mass Objects Are Twice As Heavy As Predicted." ScienceDaily. www.sciencedaily.com/releases/2005/01/050125084544.htm (accessed November 28, 2014).

Share This


More From ScienceDaily



More Space & Time News

Friday, November 28, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Scientists Find Invisible Space Shield Protecting Earth

Scientists Find Invisible Space Shield Protecting Earth

Newsy (Nov. 27, 2014) An invisible barrier is keeping dangerous super fast electrons from interfering with our atmosphere, but scientists aren't entirely sure how. Video provided by Newsy
Powered by NewsLook.com
NASA's First 3-D Printer In Space Creates Its First Object

NASA's First 3-D Printer In Space Creates Its First Object

Newsy (Nov. 26, 2014) The International Space Station is now using a proof-of-concept 3D printer to test additive printing in a weightless, isolated environment. Video provided by Newsy
Powered by NewsLook.com
Feast Your Eyes: Lamb Chop Sent Into Space from UK

Feast Your Eyes: Lamb Chop Sent Into Space from UK

Reuters - Light News Video Online (Nov. 25, 2014) Take a stab at this -- stunt video shows a lamb chop's journey from an east London restaurant over 30 kilometers into space. Rough Cut (no reporter narration). Video provided by Reuters
Powered by NewsLook.com
Soyuz Spacecraft Docks With International Space Station: NASA

Soyuz Spacecraft Docks With International Space Station: NASA

AFP (Nov. 24, 2014) A Russian Soyuz spacecraft carrying Italy's first female astronaut safely docks with the International Space Station, according to NASA. Duration: 00:40 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins