Using Molecular Bands to Measure Starspot Properties
James E. Neff (College of Charleston),
Douglas O'Neal (Allegheny College),
and Steve Saar (Center for Astrophysics)
View a copy of our IAU Division 5 Presentation
We are using spectra obtained at Penn State, Kitt Peak, and McDonald
Observatory to directly measure the total area and the temperature of
magnetic "spots" in the photospheres of active stars. The observed
spectrum of an active star (top) is composed mostly of emission from
the non-spotted photosphere, which is much warmer than the starspots.
The starspots are cool enough that molecular TiO bands form in them,
producing a radically different spectrum. The spectrum of an active
star (II Peg) is reproduced here by a suitably weighted sum of a K
dwarf star (Gl 688) to represent the non-spotted photosphere plus an M
dwarf star (FS Com) to represent the spots.
We have observed a ``grid'' of comparison stars spanning all possible
temperatures along with our sample of active stars. We have observed
bandheads with different temperature sensitivity. The absolute depth
of the bands is a measure of starspot area, while the ratio of band
depths independently constrains the starspot temperature. Given the
total area and temperature of spots, Doppler imaging can provide a
unique map of the surface distrution of those spots.
We are studying the variation of these parameters on rotational and on
stellar cycle timescales. This involves repeated observations of our
target stars on approximately uniform intervals from several days to
several weeks (for rotational variation; over many years for the cycle
variation).
PUBLICATIONS:
- Spot
Temperatures and Area Coverages on Active Dwarf Stars, S.H.
Saar and J.E. Neff, in Cool Stars, Stellar Systems, and the Sun, ed. G.
Wallerstein, (ASP Conf. Series), p. 171, 1990.
- Absolute
Measurements of Starspot Area and Temperature, J.E. Neff, D.
O'Neal, S.H. Saar, in Inside The Stars, ed. W.W. Weiss and A. Baglin,
(ASP Conf. Series), p. 193, 1993.
- Measurements
of Starspot Area and Temperature on II Pegasi, D. O'Neal,
J.E. Neff, S.H. Saar, in Cool Stars, Stellar Systems, and the Sun,
ed. J.-P. Caillault, (ASP Conf. Series), p. 726, 1994.
-
Measurements of Starspot Area and Temperature on II Pegasi In 1989
October, J.E. Neff, D. O'Neal, S.H. Saar, Astrophys. J., 452,
879, 1995.
- Using TiO
Spectroscopy To Further Constrain Doppler Imaging, D. O'Neal,
J.E. Neff, S.H. Saar, N.E. Piskunov, in Stellar Surface Structure:
Poster Proceedings, ed. K.G. Strassmeier, (Vienna Obs.), p. 32,
1995.
- A Possible
Relationship Between Surface Gravity and Temperature Deficit in Stellar
Spots, S.H. Saar, D. O'Neal, J.E. Neff, in Stellar Surface
Structure: Poster Proceedings, ed. K.G. Strassmeier, (Vienna Obs.),
p. 105, 1995.
-
Multiwavelength Observations of Two Moderate Rotation RS CVn Systems:
V815 Hercules and IM Pegasi, R.C. Dempsey, J.E. Neff, D.
O'Neal, K. Olah, Astron. J., 111, 1356, 1996.
-
Measurements of Starspot Area and Temperature on Four Active, Evolved
Stars, D. O'Neal, S.H. Saar, J.E. Neff, Astrophys. J., 463,
766, 1996.
- TiO
Band Measurement of Starspot Temperature and Area on Active
Stars, D. O'Neal, J.E. Neff, S.H. Saar, in Cool Stars,
Stellar Systems, and the Sun, ed. R. Pallavicini and A.K. Dupree, (ASP
Conf. Series 109), p. 621, 1996.
-
OH 1.563 micron Absorption From Starspots on Active
Stars, D. O'Neal, J.E. Neff, Astron. J., 113,
1129, 1997.
- II Peg: Spectroscopic Evidence for Multiple Spot Temperatures,
D. O'Neal, S.H. Saar, J.E. Neff, in Cool Stars, Stellar
Systems, and the Sun, ed. R.A. Donahue and J.A. Bookbinder, (ASP Conf.
Series 154), p. 1439, 1998.
- Spectroscopic
Evidence for Non-Uniform Starspot Properties on II Peg, D.
O'Neal, S.H. Saar, J.E. Neff, Astrophys. J. (Letters), 501, L73,
1998.
- Measurements
of Starspot Parameters on Active Stars using Molecular Bands in Echelle
Spectra, D. O'Neal, J.E. Neff, S.H. Saar, Astrophys. J., 507,
919, 1998.
- Starspot Temperature and Filling Factor Measurements for
Active Dwarfs, S.H. Saar, A. Peterchev, D. O'Neal, J.E. Neff, in
Cool Stars, Stellar Systems, and the Sun, eds. R.J. Garcia Lopes, R.
Rebolo, M.R. Zapatero Osorio, (ASP Conf. Series 223), p. CD-1057,
2001.
- Hydroxl
1.53 micron Absorption From Starspots on Active Stars, D.
O'Neal, J.E. Neff, S.H. Saar, J.K. Mines, Astron. J., 122, 1954, 2001.
James E. Neff ,
(neffj@cofc.edu)