Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2011-07-12
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
42 pages, 15 figures, submitted to ApJ
Scientific paper
The velocity pattern of a fan loop structure within a solar active region over the temperature range 0.15-1.5 MK is derived using data from the EUV Imaging Spectrometer (EIS) on board the Hinode satellite. The loop is aligned towards the observer's line-of-sight and shows downflows (redshifts) of around 15 km/s up to a temperature of 0.8 MK, but for temperatures of 1.0 MK and above the measured velocity shifts are consistent with no net flow. This velocity result applies over a projected spatial distance of 9 Mm and demonstrates that the cooler, redshifted plasma is physically disconnected from the hotter, stationary plasma. A scenario in which the fan loops consist of at least two groups of "strands" - one cooler and downflowing, the other hotter and stationary -- is suggested. The cooler strands may represent a later evolutionary stage of the hotter strands. A density diagnostic of Mg VII was used to show that the electron density at around 0.8 MK falls from 3.2 x 10^9 cm^-3 at the loop base, to 5.0 x 10^8 cm^-3 at a projected height of 15 Mm. A filling factor of 0.2 is found at temperatures close to the formation temperature of Mg VII (0.8 MK), confirming that the cooler, downflowing plasma occupies only a fraction of the apparent loop volume. The fan loop is rooted within a so-called "outflow region" that displays low intensity and blueshifts of up to 25 km/s in Fe XII 195.12 A (formed at 1.5 MK), in contrast to the loop's redshifts of 15 km/s at 0.8 MK. A new technique for obtaining an absolute wavelength calibration for the EIS instrument is presented and an instrumental effect, possibly related to a distorted point spread function, that affects velocity measurements is identified.
Mason Harris E.
O'Dwyer B.
Young Paul R.
No associations
LandOfFree
Velocity measurements for a solar active region fan loop from Hinode/EIS observations does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Velocity measurements for a solar active region fan loop from Hinode/EIS observations, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Velocity measurements for a solar active region fan loop from Hinode/EIS observations will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-565970