IXO/CAT: Simulation: AB Dor


Simulations of AB Dor: detecting coronal Doppler signatures

(D.Huenemoerder Nov 2008 dph@space.mit.edu)

AB Dor is a rapidly rotating K0 dwarf with a strong corona. Here we investigate the possibility of detecting coronal spatial non-uniformities in line profile variability due to the rotational Doppler signature. AB Dor has rotational period of 0.5 days and a projected radial velocity of 93 km/s. It nearby (15 pc) and relatively bright in X-rays (3.5E-11 ergs/cm^2/s).

The model is comprised of a steady, uniform corona, with a superimposed idealized variable component which varies simusoidally in flux and velocity at the rotational period. The flux amplitude is 15% of the steady component, and the velocity amplitude is 90 km/s, which is the projected rotational velocity of the star.

We used a plasma model is based on Sans-Forcada et al (2003; A&A 408, 1087). The velocity model is loosely based on results in Hussain et al (2007, MNRAS 377, 1488).

Simulation Overview

Simulations were done with the Project quideline grating effective area of 3000 cm^2 and a resolving power of 3000, using our CAT response files.

This figure shows an overview of the spectral simulation for a 11 ks exposure. The black curve is from the zeroth order plus direct beam as detected by the microcalorimeter (XMS). The red is the CAT grating spectrum, detected by a grating readout.

AB Dor overview spectrum

The complementary nature of the combined instrument is more clearly seen in these figures:

The XMS has high efficiency and high resolving power at short wavelengths (below 10A; above 1.2 keV) AB Dor short wavelength xms

Above 10A, the CAT efficiency increases and the resolving power becomes larger than the XMS.

AB Dor 10A XMS and CAT

Here, at 13A, we can see the power of the grating spectrometer. Note the strong Fe blends in the Ne IX triplet at 13.5A.

AB Dor Ne IX XMS and CAT

Simulation Detail: O VII

To investigate the Doppler signature, we look at one line, O VII 21.6A, the resonance line in the He-like triplet. This figures gives an overview of the spectrum in this region.

AB Dor O VII region

To obtain phase sampling, we assumed that the total observation covered 5 stellar rotations, or 224 ks. Thus, in phase bins of 0.05, we have 11 ks exposure. These figures show the simulated O VII profiles from the CAT 3rd order for 11 ks in a phase bin of width 0.05 near phases 0.25 (left) and 0.75 (right). The black histogram is the simulated spectrum, and the red is a model of the steady component renormalized to match the line core. The Doppler signature of the variable compoenent is clear.

AB Dor O VII velocity profile phase 0.25 AB Dor O VII velocity profile phase 0.25

This animation shows the feature modulated in strength and velocity by rotation.

Simulation Script

This simulation was done in ISIS and used APED plasma models. The main simulation script is sim_abdor.sl. The initial plasma model is defined by this ISIS parameter file: AB_Dor_plaw_dem-1.par.

The script requires these utility files:

and CAT utility files in the IXO/CAT Software link.

This page was last updated Jan 8, 2010 by David P. Huenemoerder. To comment on it or the material presented here, send email to dph@space.mit.edu.
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