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Astronomers identify 21 more stars with erratic dimming as Tabby's Star

Astronomers identify 21 more stars with erratic dimming as Tabby’s Star

The KIC 8462852, fondly recognized as Tabby’s Star made news when spotted in 2015. Over time its brightness decreased in a manner defying all explanations. A new sky survey research has identified a group of 15 stars that show similar dimming behavior like KIC 8462852 and a further six which are more extreme. The work appears in The Astrophysical Journal Letters.

Tabetha Boyajian, astronomer at Louisiana State University and co-workers first published the uncommon behavior of KIC 8462852 in 2015. One of the main ways to detect exoplanets is with the help of dimming stars. Exoplanets passing between the star and us generally reduce the brightness of the star by less than 1 percent. Dimming behavior KIC 8462852 is peculiar although it appears to be a normal yellow-white dwarf.

The dimming of KIC 8462852 is entirely random and unpredictable and the extent of light blocked varies from 1 percent to 22 percent, unlike the planetary dips that are usually on a standard time-frame and dim the star by the same amount in every transit. These dimming durations have varying time limits that are not caused by planets. Researchers said that some wavelengths of light are blocked more than others ruling out a large, solid opaque object such as an alien megastructure. Identifying more stars exhibiting the same behavior in the same kind of environment could provide further clues.

Edward Schmidt, astronomer and physicist of the University of Nebraska-Lincoln combined the information collected between April 1999 and March 2000 by the Northern Sky Variable Survey to find such stars with irregular variability excluding the stars with explicable dimming. This resulted in 21 stars. He downloaded the light curve data from the All-Sky Automated Survey for Supernovae (ASAS-SN) for the 21 stars, then compared against KIC 8462852’s light curve. Some interesting similarities were obtained.

Schmidt said that he found no periodicity and inconsistent depths of dips in the candidate stars similar to KIC 8462852. This irregularity is a crucial differentiation since KIC 8462852 isn’t the only strangely dimming star. EPIC 204376071 was observed dimming to a depth of 80 percent like an abnormally large, ringed planet had passed in front of it. EPIC 249706694 has unevenly synchronized dips in light that have similar depth.

Schmidt divided the stars into two categories, slow and rapid dippers. 15 “slow dippers” were recognized which were similar to KIC 8462852 in terms of the timing and also six “rapid dippers”, which had similar dips, but with greater frequency. This indicates that the dimming behavior shows a series of characteristics and the event that causes it has a range into which KIC 8462852 could fall. Besides their behavior, they occupy the same area of the temperature-luminosity diagram as KIC 8462852 i.e. they are the same type of star.

However, he has not yet checked whether the dips of the 21 new stars block precise wavelengths which shows that there is still work to be done. Based on archival data, KIC 8462852 was determined to be gradually fading – between 1890 and 1989, by 0.193 magnitudes.

To decide whether these newly recognized 21 stars are Tabby-alike or not these factors have to be studied along with the cause of dimming. Schmidt thinks that it is most likely that the dips are caused by moving objects which are likely dust based on the color changes although it does not explain the long-term dimming.

Journal Reference: The Astrophysical Journal Letters.