Suzan Edwards

Research Interests: Star Formation

Recent Preprints

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. Eventually, presumably around the time newly formed planets inhibit accretion, the disk moves into a phase known as a debris disk, where the whole disk resembles something not so different from our own asteroid belt, with lots of dust and planetismals that reprocess stellar radiation into the infrared spectral region.

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, graduate student Will Fischer, Lynne Hillenbrand, and Andrea Dupree.

Selected Publications

• ``Spectroscopic Diagnostics of T Tauri Inner Winds" Edwards, S. 2007, in 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) p. 171-182

• ``Stellar Jets: Clues to the Process of Star and Planet Formation'' Edwards, S. 2007, in Jets from Young Stars II, Clues to High Angular Resolution Observations, Lecture Notes in Physics, ed. E. Whelan (Springer-Verlag) in press

• "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, July 20, 2006

• "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. 2003, in Jets 2002: Theory and Observations in Young Stellar Objects, ed. A. Fernandez, P. Garcia, J. Lima (Kluwer), in press.

• "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 p. 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.

• "Magnetospherically Mediated Accretion in Classical T Tauri Stars", Edwards, S. 1997, IAU Symposium 182 on Herbig-Haro Flows and the Birth of Low Mass Stars, ed. B. Reipurth and C. Bertout (Kluwer), pp. 433-440.

• "Disk Accretion and Mass Loss From Young Stars", Hartigan, P., Edwards, S. and Ghandour, L. 1995, Astrophysical Journal, 452,736.

• "Observational Evidence for the Importance of Magnetospheres in the Evolution of T Tauri Accretion Disk Systems", Edwards, S. 1995, Proceedings of the Circumstellar Disks, Outflows, and Star Formation Conference, Cozumel, Mexico, Revista Mexicana de Astronomia y Astrofisica, 1995, editors Susana Lizano and Jose M. Torrelles

• "Spectroscopic Evidence for Magnetospheric Accretion in Classical T Tauri Stars" ,
  Edwards, S., Hartigan, P., Ghandour, L. and Andrulis, C., The Astronomical Journal, 104, 1056

• " The Role of Accretion Disks in Establishing the Initial Angular Momentum of Low Mass Stars" , Edwards, S., 1995, in Revista Mexicana Astronomia and Astrophysica. 29, 35

• "Angular Momentum Regulation in Low Mass Young Stars Surrounded by Accretion Disks", Edwards, S. Strom, S., Hartigan, P., Strom, K., Hillenbrand, L., Herbst, W., Attridge, J., Merrill, M., Probst, R., and Gatley, I., The Astronomical Journal, July, 1993.

• "Energetic Mass Outflows From Young Stars," Edwards, S., Ray, T. and Mundt, R. (1993), Protostars and Planets, III., editors E. Levy and J. Lunine, University of Arizona Press.

Last Update: 8/5/2003