Want a quick summary of what my research is all about?
This is a word cloud generated using Wordle.net of the 120 most common words I used in my dissertation (singulars and plurals were grouped together and common English words were eliminated).
Young Stars Near the Earth
Young, late-type stars have chromospheres and coronae that are more active than older stars. This implies that these stars may produce larger amounts of X-rays and UV than their older counterparts and as such, these stars will stand out in X-ray and UV observations of the sky.
In collaboration with Ben Zuckerman (UCLA), Joel Kastner (RIT), and Mike Bessell (ANU), I am searching for stars that may be part of the nearby young stellar associations we presently know of. My work involves searching through GALEX, XMM, ROSAT, and Chandra data in addition to the 2MASS and WISE near-IR point source catalogs to search for these stars. Our results for a UV search in the TWA and ScoCen regions are presented here. This work has also been featured as part of GALEX press release.
Hunting the Coolest Subdwarfs
Ben Zuckerman, Carl Melis (UC, San Diego), Inseok Song (Univ. of Georgia), and I are searching for the coolest class of substellar objects. These so called Y Dwarfs are expected to be around 500K in temperature and should contain water clouds in their atmosphere. To search for these objects we have selected a set of nearby, old, high-proper motion white dwarfs. As a star losses mass, any companions (or planets) will drift outward. So some white dwarfs could potentially have companions at very large separations.
We are acquiring near-IR wide field images of these white dwarfs with instruments like ISPI and NEWFIRM at CTIO, WIRC at Palomar, and FLAMINGOS at KPNO. By comparing images of a wide field (since they are nearby) taken a year apart (since they have high-proper motion) we will be able to find companions to these white dwarfs (if they have any). Because these objects are old (~Gyrs), any companions will also be old and thus a substellar companion will have had enough time to cool to these low temperatures. We additionally look at Spitzer data we have for these fields. These wavelengths (3 and 4 microns) will allow us to make a color selection which can then be followed up more deeply with our ground-based survey.
While we have yet to detect a conclusive companion, we have deeper J-band imaging for the recently discovered GJ 3483B (Luhman et al. 2011). Results are presented here. This could be the very first Y-dwarf companion known, as its 4.5 micron photometry and red color (J-[4.5]>5) suggest a temperature as cool as 350 K.
Animation of our submillimeter data (carbon monoxide) for the circumbinary disk V4046 Sgr. The video steps through separate velocity channels which are color-coded by velocity. Notice that the fastest moving gas is closest to the center, where the binary stars are.
V4046 Sagitarii is the second closest classical T Tauri star to the Earth (distance of 72 parsecs; TW Hydra is the closest at ~50 pc). Additionally this star is in the Beta Pic Moving Group making it about 12 million years old, a very old age for a T Tauri. As if that weren't enough, this 'star' is actually a 2.4 day spectroscopic binary. Because of its unique nature, V4046 Sgr can help us understand the late stages of planetary formation (as Jovian-type planets are expected to form in around 10 Myr) and planetary systems around close binary stars.
In collaboration with Joel Kastner (RIT), David Wilner (CfA), and Ben Zuckerman (UCLA), we have acquired submillimeter data using the Submillimeter Array on Mauna Kea. We have detected the disk in 12CO and 13CO; it exhibits Keplerian motion and is quite extended. Subsequent modeling allowed us to constrain properties of the disk such as its inclination. Studying systems like these help us understand the early epochs of planet formation.
We've had a press release about this star (click here to find out more) and our results are published in ApJ- click here to see the paper.
Debris Disks Among Binary Stars
One of my research projects with Ben Zuckerman involves searching for binary stars among known debris disk systems.
By debris disk systems, we mean those stars with infrared excess that are too old for them to be remnants of protoplanetary disks. These debris disks are believed to be formed by the collisions of planetesimals residing somewhere like the Kuiper belt in our own star system. The dust produced by these collisions is detectable via infrared instruments such as those on IRAS or Spitzer. This dust dissipates rather quickly so the formation process must be recent collisions. Some well known stars with debris disks are Vega, Fomalhaut, Beta Pictoris, and Epsilon Eridani.
Now, perhaps 15% of stars or more are contain debris disks. We also know that many stars, perhaps 50% or higher, are part of multiple systems. It is reasonable to expect then that binary stars will have debris disks, but how often? Are binaries more or less likely to contain debris disks? Does the presence of a companion star affect the development of the disk and possibly planet formation/evolution? Are Tatooine-like worlds, with two suns, the norm or the exception?
Some preliminary results of this work were presented in the Spitzer Conference New Light on Young Stars: Spitzer's View of Circumstellar Disks held October 26-30 2008. We have published these results in ApJ, click here for the arxiv entry.
BP Piscium (center)
Lick Observatory 3-m telescope
Credit: Marshall Perrin (UCLA)
and James Graham (UC Berkeley)
Another project I'm involved in is the study of the unusual star BP Piscium. This is work done with Bruce Macintosh (LLNL) and Marshall Perrin (UCLA).
This star emits about 75% of its energy in the infrared and has evidence for gas accretion and bipolar jets. Because of these properties, among others, it was originally classified as a T Tauri star. The story could have ended there, but it didn't. T Tauri stars are young stars near to star forming regions. Analysis of lithium lines and a lack of a nearby birthplace seem to show that BP Psc is older than we previously thought. So BP Psc could actually be a first-ascent giant several Gyrs old. Is BP Psc a very old (10 Myr) T Tauri star or a giant star with jets? If only we had the distance to this star...
My particular work with this stars involves the analysis of HST NICMOS and WFPC2 data. Some preliminary results of our work were presented at the 213th AAS meeting in Long Beach, CA.
In addition, you can check out this paper for more information on BP Piscium and this one to learn about its X-ray detection (I am 3rd author).
Emission Line Properties of Seyfert Galaxies
This work, done with Matt Malkan, formed my second-year project, before switching over to stellar astronomy.
Seyfert galaxies are local, active galaxies. These type of galaxies are believed to contain supermassive blackholes, whose accretion disks illuminate clouds of matter around them. This results in emission lines, some of which can be of very high ionization states. The study of the emission lines provide clues as to the environment close to the blackhole. Seyfert galaxies come in two main types- Seyfert 2's with narrow lines and Seyfert 1's with both broad lines and narrow lines.
In my work, I compared many optical and ultraviolet line ratios to see what differences, if any, they showed for Seyfert 1 and 2 galaxies.