L. Clark Seelye Professor of Astronomy
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Stars are formed deep within molecular clouds in the galaxy. The gravitational collapse of rotating, denser–than–average "cores" within a molecular cloud results in the creation of a central proto–star surrounded by a flattened spinning disk of gaseous material, with dimensions comparable to the Solar System. At first the circumstellar disk is in a phase called an accretion disk, where mass is transported inward toward the star and angular momentum is transported outward. Planet formation likely occurs primarily during the accretion era.
My work has been focused on studying star formation in the accretion disk phase, particularly for low mass protostars that are progenitors of sun–like stars. The accretion phase is intriguing because it is always accompanied by the simultaneous presence of a high velocity ejection of material into collimated, bipolar jets that emerge perpendicular to the plane of the disk. Although we know that accretion disks and jets of expelled material are always seen together, exactly how this pairing happens is a mystery.
Lately, I have been using spectroscopic techniques to explore the complex interface region where the star meets the disk, since it is a likely location for the jets to originate. The inner disk is spinning rapidly, and it probably has a magnetic field. With these two ingredients, it is possible to launch outflowing material off the disk. But this is not all! The star itself is known to have a strong (kilogauss) magnetic field, which is capable of interrupting the inner disk. Many permitted atomic emission lines from this region show kinematic signatures of mass infall, demonstrating that mass from the truncated inner edge of the disk is lifted up along magnetic funnel flows and falls ballistically toward the star. We also see spectroscopic evidence for atomic features that appear to be formed in accretion shocks where the funnel flow meets the stellar surface. Amidst this chaos, we are searching for spectroscopic evidence for outflowing gas that might come from the launching point and acceleration region of the wind. This might be on the stellar surface, at the truncation zone in the accretion disk, or further out in the disk beyond the reach of the stellar magnetic field. This work is being carried out in collaboration with John Kwan, Will Fischer, and Lynne Hillenbrand.
Starport article on Suzan Edwards.
"Characterizing the IYJ Excess Continuum Emission in T Tauri Stars'' Fischer, W, Edwards, S., Hillenbrand, L, and Kwan, J. 2011 Astrophysical Journal 730, 73
"Winds and Accretion in Young Stars" Edwards, S. 2009, Proceedings of the 15th Workshop of Cool Stars, Stellar Systems, and the Sun, AIP Conference Proceedings, Volume 1094, pp. 29-38
"Redshifted Absorption at He I 10830 as a Probe of the Accretion Geometry of T Tauri Stars" Fischer, W., Kwan, J., Edwards, S. and Hillenbrand, L. 2008, Astrophysical Journal 687,1117.
"Spectroscopic Diagnostics of T Tauri Inner Winds" Edwards, S. 2007, Star–Disk Interaction in Young Stars, Proceedings of the International Astronomical Union, IAU Symposium, Volume 243, ed. J. Bouvier and I. Appenzeller (Cambridge University Press) pp. 171–182.
"Stellar Jets: Clues to the Process of Star and Planet Formation" Edwards, S. 2007, Jets from Young Stars II, Clues to High Angular Resolution Observations, Lecture Notes in Physics, ed. E. Whelan (Springer-Verlag) pp. 3–13.
"Modeling T Tauri Winds from He I 10830 Profiles" Kwan, J., Edwards, S. Fischer, W., 2007 Astrophysical Journal, 567, 897.
"Probing T Tauri Accretion and Outflow with 1 Micron Spectroscopy" Edwards, S. Fischer, W., Hillenbrand, L. Kwan, J. 2006, Astrophysical Journal.
"Going Slitless: Images of Forbidden Line Emission Regions of Classical T Tauri Stars Observed with the Hubble Space Telescope" Hartigan, P., Edwards, S. and Pierson, R. 2004, Astrophysical Journal 609, 261.
"Helium I 10830 as a Probe of Winds in Accreting Young Stars" Edwards, S., Fischer, W., Kwan, J., Hillenbrand, L. and Dupree A.K. 2003, Astrophysical Journal Letters, 599, L41.
"Observations of the Star–Disk Interface: A Search for Wind Origins" Edwards, S. 2004, Jets in Young Stellar Objects: Theory and Observations, ed. A. Fernandez, P. Garcia, J. Lima (Kluwer).
"Helium Emission from Classical T Tauri Stars: Dual Origin in Magnetospheric Infall and Hot Wind" Beristain, G., Edwards, S. and Kwan, J. 2001, Astrophysical Journal, 551, 1037.
"Spectroscopic Probes of Inner Accretion Disks and the Star–Disk Interface," Najita, J., Edwards, S., Basri, G. and Carr, J. 2000, Protostars and Planets IV, University of Arizona Press, editors V. Mannings and A. Boss, 457.
"Near–Infrared Classification Spectroscopy: H–band Spectra of Fundamental MK Standards," Meyer, M., Edwards, S., Hinkle, K. and Strom, S.E. 1998, The Astrophysical Journal, 508, 397.
"Permitted Iron Emission Lines in the Classical T Tauri Star DR Tauri" Beristain, G., Edwards, S. and Kwan, J. 1998, The Astrophysical Journal, 488, 828.