PROPERTIES OF A POLAR CORONAL HOLE DURING THE SOLAR MINIMUM IN 2007
- Columbia Astrophysics Laboratory, Columbia University, MC 5247, 550 West 120th Street, New York, NY 10027 (United States)
- George Mason University, 4400 University Drive, Fairfax, VA 22030 (United States)
- US Naval Research Laboratory, Space Science Division, 4555 Overlook Avenue, SW, Code 76000A, Washington, DC 20375 (United States)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
We report measurements of a polar coronal hole during the recent solar minimum using the Extreme Ultraviolet Imaging Spectrometer on Hinode. Five observations are analyzed that span the polar coronal hole from the central meridian to the boundary with the quiet-Sun corona. We study the observations above the solar limb in the height range of 1.03-1.20 R{sub sun}. The electron temperature T{sub e} and emission measure (EM) are found using a geometric mean emission measure method. The EM derived from the elements Fe, Si, S, and Al are compared in order to measure relative coronal-to-photospheric abundance enhancement factors. We also studied the ion temperature T{sub i} and the non-thermal velocity v{sub nt} using the line profiles. All these measurements are compared to polar coronal hole observations from the previous (1996-1997) solar minimum and to model predictions for relative abundances. There are many similarities in the physical properties of the polar coronal holes between the two minima at these low heights. We find that the electron density, T{sub e}, and T{sub i} are comparable in both minima. T{sub e} shows a comparable gradient with height. Both minima show a decreasing T{sub i} with increasing charge-to-mass ratio q/M. A previously observed upturn of T{sub i} for ions above q/M>0.25 was not found here. We also compared relative coronal-to-photospheric elemental abundance enhancement factors for a number of elements. These ratios were {approx}1 for both the low first ionization potential (FIP) elements Si and Al and the marginally high FIP element S relative to the low FIP element Fe, as is expected based on earlier observations and models for a polar coronal hole. These results are consistent with no FIP effect in a polar coronal hole.
- OSTI ID:
- 21474426
- Journal Information:
- Astrophysical Journal, Vol. 725, Issue 1; Other Information: DOI: 10.1088/0004-637X/725/1/774; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
ABUNDANCE
ELECTRON DENSITY
ELECTRON TEMPERATURE
EXTREME ULTRAVIOLET RADIATION
ION TEMPERATURE
IONIZATION POTENTIAL
MEASURING METHODS
PHYSICAL PROPERTIES
SOLAR ACTIVITY
SOLAR CORONA
SPECTROMETERS
SUN
ATMOSPHERES
ELECTROMAGNETIC RADIATION
MAIN SEQUENCE STARS
MEASURING INSTRUMENTS
RADIATIONS
SOLAR ATMOSPHERE
STARS
STELLAR ACTIVITY
STELLAR ATMOSPHERES
STELLAR CORONAE
ULTRAVIOLET RADIATION