Nicole M. Silvestri, Research Associate
This site is currently under construction, in flux, a work in progress...you get the point. Please feel free to contact me with questions until I'm finished!
Last updated: May 12, 2009.
Office : C325
Phone : 206.543.9487
Fax : 206.685.0403
GTalk : nmkelly21
Dept. of Astronomy
University of Washington
Seattle, WA 98195-1580
3910 15th Ave NE
Seattle, WA 98195-1580
I am an observational astronomer specializing in the evolution of binary systems, primarily those comrised of a low mass star and a white dwarf. I arrived at UW for my first post-doc position in January 2003 to work with Dr. Suzanne Hawley, after completing my dissertation work at the Florida Institute of Technology under Dr. Terry Oswalt.
My work focuses on the properties of M dwarf stars in close binary systems with white dwarf companions found spectroscopically in the Sloan Digital Sky Survey. This work was an extension of my dissertation work, which focused primarily on the properties of M dwarf stars, such as chromospheric activity and age, in wide, common proper motion binary (CPMB) systems with white dwarf companions, first discovered by W. Luyten (1963). The publications resulting from this work can be found through the publications link at the right.
In addition to my research, I work with SSG member Andy Becker and Russell Owen, under the guidance of Dr. Andrew Connolly, as part of the Large Synoptic Survey's Data Management team at UW. My primary responsibilities involve the development and support of the software for the image processing pipelines for the LSST, UML and our SSG webpages. You can read in more detail about UW's involvement in LSST on our SSG LSST links.
Current Research Interests
Below, I list the current research projects I have underway at the University of Washington. I give a brief description of each project here, but you can read more about the details of these projects on our Research Pages under Variable Stars.
Close Binary M Dwarf-White Dwarf Systems
Chromospheric Activity and Ages of M Dwarf stars
Pre-CVs and the missing magnetic Pre-CV problem.
Common Proper Motion Binary M Dwarf-White Dwarf Systems
White Dwarf Star Ages and Kinematics
Bergeron, P., Saumon, D., & Wesemael, F. 1995, ApJ, 443, 764
My current research the University of Washington involves the study of the evolution of dMs in close WD+dM binary systems, often referred to as pre-cataclysmic variables (pre-CVs), drawn from the Sloan Digital Sky Survey (SDSS). The ultimate goal of this project is to fully understand how the close binary environment influences the evolution of the low mass secondary and to compare these results to a variety of recent low mass star studies in the literature (Reid et al. 1995, Hawley et al. 1996, West et al. 2004, to name a few) and to the evolution of low mass stars in wide binaries as discussed below.
We obtain the effective temperatures and log(g) estimates of the separated WD spectra from the atmospheric models of D. Koester and rough ages from WD evolutionary models (Bergeron et al. 1995). We use the TiO bandhead ratios of the dMs to determine the spectral type (mass, Hawley et al. 1996), activity level (Halpha EW and L_Halpha/L_bol), and distance. We measure the radial velocities and full space motions (U, V, W) of each system to determine the population membership of the sample. We have approached the study of these systems from several avenues, the full results of which was presented at the 2005 SDSS Special Session of the January AAS meeting in San Diego and in (Lemagie et al. 2005, Silvestri et al. 2005b) and in two publications (Silvestri et al. 2005c,d). We have found some interesting and surprising results. I highlight a few here:
This is the most surprising outcome of the project. While assessing our growing number of WD+dM pre-CV pairs we have discovered that very few of the WDs in these pairs appear to be magnetic (see Lemagie et al. 2005, Silvestri et al. 2005b). Less than 10 out of over 600 DA+dM pre-CVs fitted with magnetic hydrogen WD models were determined to have a magnetic field, and in all cases the field was small (< 10 MG). It is intriguing that nearly 25% of all known CV systems harbor a magnetic WD with an appreciable magnetic field (~30-50 MG) and yet we see very few pre-CVs with magnetic WDs.
For my thesis work as a graduate student at Florida Tech we used common proper motion binary (CPMB) systems first identified by W. Luyten (1963) to study activity in low mass stars. The goal was to develop a chromospheric activity-age relation for low mass M dwarfs (dMs; see Silvestri et al. 2001; Silvestri 2002; Silvestri et al. 2002, 2005a) similar to the one for F, G,and K dwarf stars (Skumanich 1972), though due in part to structural differences in the M dwarf sequence is significantly more complex than the current relation (F(Ca K) = At^-1/2). We aimed to extend these relations to ages much larger than those determined by studies of dMs in open clusters (see Reid et al. 1995, Hawley et al. 1996, and references therein).
The wide binaries in this study are comprised of a white dwarf (WD) star and dM (WD+dM) with average separations of ~100's AU. The binaries are coeval, therefore age of the WD, as determined from WD evolutionary models (Bergeron et al. 1995), is the age of the dM companion. Using a sample of approximately 200 WD+dM CPMBs we were able to confirm that dMs remain active for a longer time at later spectral type, a trend established in studies of dMs in clusters. We were also successful at extending these relations to ages much older than can be examined using dMs in open clusters. Our study revealed a tremendous amount of complexity in assigning age based on activity alone (Silvestri et al. 2005a).
de Kool, M. & Ritter, H. 1993, A&A, 267, 397
Hawley, S.L. et al. 2002, AJ, 123, 3409
Hawley, S.L., Gizis, J.E., & Reid, I.N. 1996, AJ, 112, 2799
Kleinman, S. et al. 2004, ApJ, 607, 426
Lemagie, M.P., Silvestri, N.M., Hawley, S.L. et al. 2005, BAAS
Liebert, J. et al. 2005, AJ,
Liebert, J., Bergeron, P., Holberg, J.B 2005, ApJS
Luyten, W.J. 1963, in Proper Motion Survey with the Forty-Eight Inch Telescope (U. of Minnesota, Minneapolis Press)
Raymond S.N. et al. 2003, AJ, 125, 2621
Reid, I.N., Hawley, S.L., & Gizis, J.E. 1995, AJ, 110, 1838
Saffer, R.A., Livio, M., & Yungelson, L.R. 1998, ApJ, 502, 394
Schmidt, G.D. et al. 2003, ApJ, 595, 1101
Silvestri, N.M., Hawley, S.L., & Oswalt, T.D. 2005a, AJ
Silvestri, N.M., Hawley, S.L., Szkody, P. et al. 2004, BAAS
Silvestri, N.M., Hawley, S.L., Szkody, P. et al. 2005b, BAAS
Silvestri, N.M., Hawley, S.L., Szkody, P. et al. 2005c, AJ
Silvestri, N.M., Lemagie, M.P., Hawley, S.L. et al. 2005d, AJ
Silvestri, N.M. et al. 2001, AJ, 121, 503
Silvestri, N.M., Oswalt, T.D., & Hawley, S.L. 2002, AJ, 124, 1118
Silvestri, N.M., Oswalt, T.D., Wood, M.A. et al. 2001, AJ, 121, 503
Skumanich, A. 1972, ApJ, 171, 565
West, A.A. et al. 2004, AJ, 128, 426
Willems, B. & Kolb, U. 2004, A&A, (astro-ph/0403090)
Wood, M.A. 1995, in White Dwarfs, eds. D. Koester & K. Werner (New York: Springer), 41
Future Survey Science Research