Our Second Paper and a New Kind of M Dwarf Disk

Our second paper just got published! Steven Silverberg, the lead author on the paper, tells up more:

More kudos to us! Our second paper was published by The Astrophysical Journal Letters over the weekend. It will be going up on astro-ph later today. In it, we discuss a potential new kind of disk we’ve found, around an M dwarf.

M dwarfs are really valuable targets to look for. They’re smaller and less massive than the Sun, which makes it easy to find planets around them with the most common detection methods used, radial velocity and transit searches. There are more of these stars in the solar neighborhood than any other kind of star, too. Our nearest neighbor star, Proxima Centauri, is an M dwarf; you may recognize the name from the recent discovery that it has a planet orbiting it <with link to story on it from somewhere>. Since we expect disks to appear about as often as planets appear, we would expect to see lots of M dwarf disks, too, but we haven’t observed that many. The largest survey of M dwarf debris disks to date only found ~175 new disks, and most of those were quite old, over 1 billion years old. Young disks are in some ways more interesting, since any planets around the star would be young enough and therefore warm enough to observe via direct imaging (like the planets around Beta Pictoris).

One method we have of determining the age of a star is seeing if it is a member of a Young Moving Group (YMG). These are groups of stars whose position and motions through the galaxy, along with age indicators in their spectra, suggest that they were born in about the same place at about the same time. Using the online tool BANYAN II by Jonathan Gagne, we can test the likelihood that a star is a member of a moving group, based solely on its observable astrometics (its coordinates, its parallax, its proper motion, and its velocity directly toward or away from us). And you all have found…

…the oldest M dwarf in a YMG! You first met this object at AWI0005x3s, and flagged it as good. We ran its astrometry data through BANYAN II, and found that it has a 93.9% chance of being a member of the ~45 Myr-old Carina association. Very cool, right?

Well, that’s not all. Because it’s a very unusual disk, too.

As stars form, their circumstellar material is mostly gas and dust that settles into a YSO disk. As time goes on, the gas usually accretes onto the star, forms gas giants, or is blown out of the system, leaving the dust behind as a debris disk. Since there’s more material, the gas disk is usually hotter and more massive than the dusty debris disk. This usually occurs in the first 20 Myr or so of the system’s existence.

This star, however, shows a large infrared excess in both the W3 and W4 bands, which suggests that it’s warm (~263 K) and massive. That implies that there’s still a lot of gas in the system, but there’s not enough data yet to tell us *why* that is. It could be an unusually old YSO disk, or it could be something we’ve never seen before.

To help us get a sense of what the system might look like from an artist’s perspective, we enlisted the help of one of our Disk Detectives, Jonathan Holden. Jonathan put together this rather stunning depiction of what this system might look like, that we’ll be using in press releases about this discovery.

You’ll also notice that there are eight citizen scientists listed as co-authors on the paper: Joseph R. Biggs, Milton Bosch, Katharina Doll, Hugo A. Durantini-Luca, Alexandru Enachioaie, Phillip Griffith, Sr., Michiharu Hyogo, and Fernanda Piniero. These fellow Disk Detectives on the Advanced User team helped collect the kinematic data from online astronomical catalogs that we used to test each object with BANYAN II. If you’ve done more than 300 classifications and you would like to join the group, email us at diskdetectives@gmail.com.

Great work, everyone! Two papers accepted in the space of four months is excellent progress for the project, and there’s more on the way. Stay tuned, and keep classifying!