NASA missions harvest “pumpkin” stars

84
pumpkin stars
This artist's concept illustrates how the most extreme 'pumpkin star' found by Kepler and Swift compares with the sun. Both stars are shown to scale. KSw 71 is larger, cooler and redder than the sun and rotates four times faster. Rapid spin causes the star to flatten into a pumpkin shape, which results in brighter poles and a darker equator. Rapid rotation also drives increased levels of stellar activity such as starspots, flares and prominences, producing X-ray emission over 4,000 times more intense than the peak emission from the sun. KSw 71 is thought to have recently formed following the merger of two sun-like stars in a close binary system.

In a recent study, astronomers using observations from NASA’s Kepler and Swift missions discover a batch of rapidly spinning stars. These stars produce X-rays at more than 100 times the peak levels ever seen from the sun.

The stars, which spin so fast they’ve been squashed into pumpkin-like shapes, are thought to be the result of close binary systems where two sun-like stars merge.

Researchers from NASA said that these 18 stars rotate in just a few days on average, while the sun takes nearly a month.

The rapid rotation amplifies the same kind of activity they see on the sun, such as sunspots and solar flares, and essentially sends it into overdrive.

The most extreme member of the group, a K-type orange giant dubbed KSw 71, is more than 10 times larger than the sun, rotates in just 5.5 days, and produces X-ray emission 4,000 times greater than the sun does at solar maximum.

These rare stars were found as part of an X-ray survey of the original Kepler field of view, a patch of the sky comprising parts of the constellations Cygnus and Lyra.

From May 2009 to May 2013, Kepler measured the brightness of more than 150,000 stars in this region to detect the regular dimming from planets passing in front of their host stars.

The mission was immensely successful, netting more than 2,300 confirmed exoplanets and nearly 5,000 candidates to date.

An ongoing extended mission, called K2, continues this work in areas of the sky located along the ecliptic, the plane of Earth’s orbit around the sun.

A side benefit of the Kepler mission is that its initial field of view is now one of the best-studied parts of the sky.

For example, NASA’s Wide-field Infrared Survey Explorer observed the entire area in infrared light, and NASA’s Galaxy Evolution Explorer observed many parts of it in the ultraviolet.

Using the X-ray and ultraviolet/optical telescopes aboard Swift, the researchers conducted the Kepler-Swift Active Galaxies and Stars Survey (KSwAGS).

They imaged about six square degrees, or 12 times the apparent size of a full moon, in the Kepler field.

For the brightest sources, the team obtained spectra using the 200-inch telescope at Palomar Observatory in California.

These spectra provide detailed chemical portraits of the stars and show clear evidence of enhanced stellar activity, particularly strong diagnostic lines of calcium and hydrogen.

A paper detailing the findings will be published in the Nov. 1 edition of the Astrophysical Journal and is now available online.

Follow Knowridge Science Report on Facebook, Twitter and Flipboard.


News source: NASA.
Figure legend: This Knowridge.com image is credited to NASA’s Goddard Space Flight Center/Francis Reddy.