Tuesday, July 19, 2016

Research at Rochester Institute of Technology (RIT)

The search for exoplanets is an active and evolving area of research in astronomy. According to the NASA website for exoplanet exploration, there are currently 3,368 confirmed exoplanets, 2,416 candidate planets, 2,506 solar systems, and 232 of which are terrestrial planets. In our search for exoplanets we gain knowledge about the evolution of solar systems as well as planets like our earth, information that can give us clues as to the fate of our own solar system and earth. 

Young stellar moving groups represent some of the most viable targets for investigating young stellar objects and the conditions and evolution of circumstellar disks, subsequently leading to the study of the evolution of planetary systems. Planets form around stars within 10 Myr of a star’s birth, thus stellar age is vital knowledge for exoplanet research. 

Young stellar moving groups form inside of what many people think of as "stellar nurseries", also known to scientists as molecular clouds. These clouds are dense areas of gas and dust found in the interstellar medium. Molecular clouds are compressed via gravity and pressure interactions that cause the more dense regions to fall in on themselves, giving way to the formation of a protostars. Protostars are stars that have not yet begun hydrogen fusion, also known as a pre-main sequence (pre-MS) stars. Small molecular clouds can form magnitudes of tens of stars, where giant molecular clouds can give rise to hundreds of thousands of stars, that like the giant molecular cloud found in the Orion constellation. 

These pre-MS stars spend the beginning portions of their lives traveling the galaxy together (young stellar moving groups, aka; moving associations, open clusters) and are loosely bound by mutual gravity that can keep most the group together for a few hundred million years. As the stars age, gravity from other moving groups and impacts with stellar bodies can pull/knock stars out of their association, causing stars to join new associations, or leave the stars to endure life in the galaxy on their own.

Protostar evolution involves the acquisition of an accretion disk, formed from angular momentum via the infall of material after the initial formation of the star. This disk continues to feed into the mass of the protostar until the gas cools. At this stage of evolution, known as the T Tauri stage, with a cooled circumstellar disk surrounding the protostar, planetesimals can begin to form around the star from aggregated dust and ice grains. These planetesimals are the beginnings of a solar system.

In the Laboratory for Multiwavelength Astrophysics (LAMA) at Rochester Institute of Technology (RIT) one of the missions of the faculty, graduate students, and undergraduate students is to work to analyze and model multiwavelength astronomical and astrophysical data in order to make determinations about young stellar objects inside and outside our galaxy. 

My role in this lab has been to aide in the evolutionary determination of a known galactic variable star in the constellation Pisces. RZ Piscium (Psc) is an enigmatic variable star whose evolutionary status lies somewhere between a pre-MS star that is on it's way to hydrogen burning, and a post-MS star that is swelling up to become a red giant

RZ Psc shows as a bright X-ray point source when imaged by ESA’s Multi-Mirror Mission (XMM-Newton) space telescope. Any potential members of a group associated with RZ Psc should have similar ages (within a few million years), thus a survey of stellar association candidates is being conducted to try and resolve the question of the stars evolutionary status. 

The search includes looking for X-ray bright sources using XMM-Newton in conjunction with infrared source catalogs, the Wide-field Infrared Survey Explorer (WISE) All-Sky Data Release and the Two Micron All Sky Survey (2MASS), as well as optical images from the WIYN 0.9m National Observatory in Kitt Peak, Arizona. 

Using many wavelengths to image star fields allows our team to gain different kinds information about the ages and properties of the stars of interest. Bright x-ray sources are suggestive of youth as young stars rotate rapidly and throw off x-rays as they fling themselves about their center of gravity. Infrared observation tells us about possible accretion disks around stars causing a "reddening" in the color of the star, also known as stellar extinction. These disks are also indicators of youth as older stars tend to either blow their disks away with solar wind, or their disks have been transformed into planetesimals. Optical images allow astronomers to perform photometry, a science of using pixel intensity from point sources in various wavelengths to measure apparent magnitudes of the stars. These apparent magnitudes are converted into flux's and then fit to Spectral Energy Distributions (SEDs) in order to make an assumption about spectral type. 

Candidate matches that show in these images are analyzed against field stars using color-color plots, used to determine star color as we don't know their distances, color-magnitude plots, showing position on the evolutionary Herztsprung-Russell diagram, and then fit to SED's to tighter fit a spectral type. 

                                            Herztsprung-Russell Diagram  (picture source)

By the end of our survey we hope to either show an association related to RZ Psc and use those stars as age determinants for the variable, or show that RZ Psc has no association, which will also tell us something about its age. 

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