It’s Halloween and even the cosmos is celebrating it with Earthlings by putting up a show in the form of ‘pumpkin’ stars, which have been spotted by NASA’s Kepler and Swift missions.
Astronomers at NASA has used data from the two missions to spot quite a few pumpkin stars in a patch of sky comprising parts of the constellations Cygnus and Lyra, which was part of an X-ray survey of the original Kepler field of view. The data was collected during the period between May 2009 and 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.Using the X-ray and ultraviolet/optical telescopes aboard Swift, the researchers conducted the Kepler-Swift Active Galaxies and Stars Survey (KSwAGS), imaging about six square degrees, or 12 times the apparent size of a full Moon, in the Kepler field.
Researchers found 93 new X-ray sources using KSwAGS, many of which have never been observed before in X-rays or ultraviolet light. 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.
These ‘pumpkin’ stars are so named because of the shape they attain due to their fast rotation speeds. Our Sun completes one rotation in just under a month, while these pumpkin stars complete one rotation in matter of days. Some are so fast that they complete one rotation in just 8-10 days and in the process emit x-rays up to 4,000 times greater than the Sun does at solar maximum. NASA notes that the most extreme of these group of stars a K-type orange giant dubbed KSw 71, is more than 10 times larger than the Sun and rotates in just 5.5 days. Astronomers are of the opinion that such stars are a result of close binary systems where two Sun-like stars merge.
The researchers used Kepler measurements to determine the rotation periods and sizes for 10 of the stars, which range from 2.9 to 10.5 times larger than the Sun. Their surface temperatures range from somewhat hotter to slightly cooler than the Sun, mostly spanning spectral types F through K. Astronomers classify the stars as subgiants and giants, which are more advanced evolutionary phases than the Sun’s caused by greater depletion of their primary fuel source, hydrogen. All of them eventually will become much larger red giant stars.
A paper detailing the findings will be published in the Nov. 1 edition of the Astrophysical Journal and is now available online. Check out the video below: