Why WD 1145+017 is Important White dwarf stars provide us with time-travel views of our solar system's future. Almost all stars become white dwarfs after their supply of hydrogen fuel in the core is exhausted. For decades astronomers have wondered if a star's solar system survives the transition from a normal star through an expansion phase to a red giant, followed by a shrinking phase to an earth-sized white dwarf. The answer came slowly, and the first hint of it was from spectroscope measurements of white dwarf atmospheres; it was found that 1/3 of white dwarfs were "polluted" with minerals that had to come from planets or asteroids generating dust that continually fell upon the white dwarf atmosphere. So "Yes, some stars retain part of their solar system after becoming white dwarfs." But the ultimate proof came when WD1145 was discovered: it had dust clouds in orbit around it that would block the white dwarf's starlight every orbit. This discovery hinged on the good fortune that the WD1145 system was oriented favorably, presenting an edge-on view to Earth. The dust cloud orbit periods ranged from 4.5 to 4.9 hours, which required that the orbiting objects have densities of at least 6 g/cc. This density can only be found in planetary cores, so this was evidence that a planet had survived the transition to a white dwarf. This was evidence that "For most stars their asteroids and planets will survive and accompany them on their eternal journeys as white dwarfs - for billions, if not trillions, of years." Our sun and solar system are 4.5 billion years old. In another 4 or 5 billion years our sun will undergo the transition to a white dwarf. Afterward, our sun will remain a white dwarf forever – for 100 billion years, or however long the universe lasts. Our sun, like most stars, will therefore spend most of it total lifetime as a white dwarf accompanied by most of our present solar system of planets and asteroids. This is an amazing discovery!

Status & Summary of Results for this Observing Season: 

The level of dip activity during this observing season is the lowest for all ground-based observations during the past 8 years, and similar to what was observed by Kepler in 2014. However, since late 2023 February activity has begun to increase. In late February a two-dip structure appeared and lasted for the week that observations were possible. The deeper dip was fixed in phase using the A-system period of 4.4955 hours while the smaller dip shifted in phase corresponding to it being in a larger orbit. When observations resumed in late March (after a long stretch of cloudy weather) a single dip was observed. It was present for a total of 5 days and varied in depth with a "time scale" of 3 days.


Activity Plots

The next 4 graphs show the level of "dust production dip activity" vs. date:


Activity for a 6-month interval for this season's observations using a  linear scale for activity.


Activity for the last nine years, using a linear scale for activity.


Activity for the last nine years, using a log scale for activity.



Activity for the last nine years, showing a smooth "eyeball fit."


A possible "model" for activity based on collisions as triggers for increased activity. Only two actual measurement of dip activity has been achieved this season (the other symbols are estimattes, based on 1/2 of max). Kepler K2 data is represented by two symbols,the lower one is for the A-system periodicity and the upper one is the sum of EW for each of the A through F periodicities. The A-system EW is more appropriate for comparison with the other data since they are exclusively for the A-system (which dominated activity after the 2015 outburst). If duration of phase "A" is twice the duration of the combined phase "B" and "C" then it could be said that WD1145 is "active" 1/3 of the time. Does "1/3" call to mind anything (hint: fraction of WDs that are "polluted.")? 

Dara Group Averages: link 

Data exchange file for activity values: link

List of observing sessions   

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