Featured Research

from universities, journals, and other organizations

Hottest White Dwarf In Its Class

Date:
December 15, 2008
Source:
Journal Astronomy and Astrophysics
Summary:
Astronomers have identified a white dwarf that is among the hottest stars known so far, with a temperature of 200,000 K at its surface. It is so hot that its photosphere exhibits emission lines in the ultraviolet spectrum, a phenomenon that has never been seen before.

White dwarfs in the globular cluster M4. In this picture, only the faintest stars are white dwarfs.
Credit: NASA and H. Richer (University of British Columbia)

Astronomy & Astrophysics is publishing spectroscopic observations with NASA's space-based Far-Ultraviolet Spectroscopic Explorer (FUSE) of the white dwarf KPD 0005+5106. The team of German and American astronomers who present these observations show that this white dwarf is among the hottest stars known so far, with a temperature of 200 000 K at its surface.

It is so hot that its photosphere exhibits emission lines in the ultraviolet spectrum, a phenomenon that has never been seen before. These emission features stem from extremely ionized calcium (nine-fold ionized, i.e., CaX), which is the highest ionization stage of a chemical element ever discovered in a photospheric stellar spectrum.

Stars of intermediate mass (1-8 solar masses) terminate their life as an Earth-sized white dwarf after the exhaustion of their nuclear fuel. During the transition from a nuclear-burning star to the white dwarf stage, the star becomes very hot. Many such objects with surface temperatures around 100 000 Kelvin are known. Theories of stellar evolution predict that the stars can be much hotter. However, the probability of catching them in such an extremely hot state is low, because this phase is rather short-lived.

Since its discovery as a faint blue star in 1985, KPD 0005+5106 attracted much attention because optical spectra taken with ground-based telescopes suggested that this white dwarf is very hot. In addition, it belongs to a particular class of rare white dwarfs whose atmospheres are dominated by helium. A detailed analysis of these spectra, combined with ultraviolet observations performed with the Hubble Space Telescope (HST), had led to the conclusion that KPD 0005+5106 has a temperature of 120 000 Kelvin, which made it the hottest member of its class. It was, however, rivaled by other similarly hot white dwarfs, discovered a few years ago in the Sloan Digital Sky Survey.

The FUSE observatory performed spectroscopy in the far-ultraviolet wavelength range, which is inaccessible to HST. During its lifetime (1999-2007), FUSE frequently observed KPD 0005+5106 because it was used as a calibration target to track the telescope's performance. The team of astronomers, including K. Werner, T. Rauch, and J.W. Kruk, made use of all accumulated data and obtained a dataset of outstanding quality. Close inspection revealed the presence of two emission lines from calcium, and detailed stellar atmosphere modeling confirmed their photospheric origin. The analysis proves that the temperature must be 200 000 Kelvin, for the presence of these emission lines to be possible.

Although theory predicted the existence of such hot white dwarfs, the star nevertheless represents a challenge to our concepts of stellar evolution because of its composition. The measured calcium abundance (1-10 times the solar value) in combination with the helium-rich nature of its atmosphere represents a chemical surface composition that is not predicted by stellar evolution models.


Story Source:

The above story is based on materials provided by Journal Astronomy and Astrophysics. Note: Materials may be edited for content and length.


Journal Reference:

  1. K. Werner, T. Rauch, and J.W. Kruk. Discovery of photospheric CaX emission lines in the far-UV spectrum of the hottest known white dwarf (KPD 0005 5106). Astronomy & Astrophysics Letteres, vol. 492-3, pp. L43

Cite This Page:

Journal Astronomy and Astrophysics. "Hottest White Dwarf In Its Class." ScienceDaily. ScienceDaily, 15 December 2008. <www.sciencedaily.com/releases/2008/12/081212081540.htm>.
Journal Astronomy and Astrophysics. (2008, December 15). Hottest White Dwarf In Its Class. ScienceDaily. Retrieved August 1, 2014 from www.sciencedaily.com/releases/2008/12/081212081540.htm
Journal Astronomy and Astrophysics. "Hottest White Dwarf In Its Class." ScienceDaily. www.sciencedaily.com/releases/2008/12/081212081540.htm (accessed August 1, 2014).

Share This




More Space & Time News

Friday, August 1, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

New Study Says The Moon Was Deformed Early In Its History

New Study Says The Moon Was Deformed Early In Its History

Newsy (July 31, 2014) Scientists say when the moon was young, it was deformed by the Earth's gravitational pull, which gave it a lemon-like shape. Video provided by Newsy
Powered by NewsLook.com
Supply Ship Takes Off for International Space Station

Supply Ship Takes Off for International Space Station

AFP (July 30, 2014) The European Space Agency's fifth Automated Transfer Vehicle (ATV-5) is takes off to the International Space Station on an Ariane 5 rocket from French Guiana. Duration: 00:34 Video provided by AFP
Powered by NewsLook.com
Raw: Rocket Launches Into Space With Cargo Ship

Raw: Rocket Launches Into Space With Cargo Ship

AP (July 30, 2014) Arianespace launched a rocket Tuesday from French Guiana carrying a robotic cargo ship to deliver provisions to the International Space Station. (July 30) Video provided by AP
Powered by NewsLook.com
In Virginia, the Rise of a New Space Coast

In Virginia, the Rise of a New Space Coast

AP (July 30, 2014) Every summer, tourists make the pilgrimage to Chincoteague Island, Va. to see wild ponies cross the Assateague Channel. But, it's the rockets sending to supplies to the International Space Station that are making this a year-round destination. (July 30) Video provided by AP
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:
from the past week

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