Fall is just around the corner here in the northern hemisphere, so it’s the time of year when we write observing proposals! And last week, we submitted the first Backyard Worlds: Planet 9 proposal of the season–to follow up some of our brown dwarf candidates using the Astrophysical Research Consortium (ARC) 3.5 meter telescope at Apache Point Observatory. We asked for half a night of time on Near-Infrared Camera & Fabry-Perot Spectrometer (NIC-FPS), to perform J band photometry of 10 objects. Photometry means you take a picture of the object and sometimes a picture of a reference star, and you use the image to figure out how bright your object is. J band corresponds to a wavelength of light of about 1.25 microns, about the size of a virus or a particle of soot.
Here’s why we we need these brightness measurements (the photometry). While many of our brown dwarfs have infrared photometry from surveys like 2MASS and Pan-STARRS, the reddest, coldest, and probably the most interesting objects are too faint for these surveys! 2MASS went as faint as about 16th magnitude in J band. Pan-STARRS data goes down to about 21st magnitude in y band (a wavelength of around 1.02 microns). But ultracool brown dwarfs are faint, faint, faint. So we need to make our own measurements.
Once we have the new photometry, we will be able to do two new things. First, we will be able to get much better estimates of the spectral types of these objects. As you may recall, the spectral type of the coldest brown dwarfs is Y. Only 25 Y dwarfs are presently known. T dwarfs are the next coldest, but hundreds of T dwarfs are have already been discovered, so Y dwarfs are much more exciting. So far, all we know about the targets we have in mind is that they have WISE colors that are similar to those of Y dwarfs (i.e. brighter in W2 than W1 by at least 2.5 magnitudes). But they might still turn out to be late T dwarfs. The near infrared photometry will help make that distinction.
Second, we will be able to apply for time on still larger telescopes to get their near-infrared spectra. The photometry will tell us what instrument we will need, and how long we need to keep the shutter open while were are collecting the spectra. These spectra will tell us for sure what the spectral type is (Y or T?), and maybe even lead to a big discovery.
Here’s a link to the full proposal, if you are curious: APO_BWs The final target list is not set yet, but the 10 targets that meet our cutoff of W1-W2 > 2.5 were found by Guillaume Colin, Sam Goodman and Dan Caselden. Nice work, guys!
I’m sure we’ll be writing several more telescope proposals over the next month—stay tuned!