High-resolution X-ray spectra of the compact binary supersoft X-ray source CAL 87

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Volume 690 (October 2024)

A&A, 690 (2024) A9

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Table 2.

Best-fit parameters to the spectra of CAL 87.

	2001-08-13/14		2003-04-18/19

	Chandra ACIS+LETG		XMM-Newton RGS
Parameter	Model 1	Model 2	Model 1	Model 2
N(H) (10²¹ cm⁻²)	1.9 $_{- 0.3}^{+ 0.3}$ $^{+0.3}_{-0.3}$	2.1 $_{- 0.3}^{+ 0.3}$ $^{+0.3}_{-0.3}$	2.0 $_{- 0.4}^{+ 0.4}$ $^{+0.4}_{-0.4}$	2.1 $_{- 0.4}^{+ 0.4}$ $^{+0.4}_{-0.4}$
T_WD (K)	796619	801179	796596	800440
F_WD (abs.) (erg cm⁻² s⁻¹ × 10⁻¹³)	16.0 $_{- 1.1}^{+ 1.1}$ $^{+1.1}_{-1.1}$	16.7 $_{- 1.1}^{+ 1.1}$ $^{+1.1}_{-1.1}$	16.0 $_{- 1.4}^{+ 1.4}$ $^{+1.4}_{-1.4}$	16.3 $_{- 1.2}^{+ 1.3}$ $^{+1.3}_{-1.2}$
F_WD (unabs.) (erg cm⁻² s⁻¹ × 10⁻¹³)	112.9 $_{- 10.8}^{+ 11.1}$ $^{+11.1}_{-10.8}$	129.5 $_{- 12.0}^{+ 11.1}$ $^{+11.1}_{-12.0}$	119.4 $_{- 13.8}^{+ 13.6}$ $^{+13.6}_{-13.8}$	126.9 $_{- 14.8}^{+ 13.6}$ $^{+13.6}_{-14.8}$
L_WD (unabs.) (erg s⁻¹ × 10³⁵)	33.7 $_{- 3.5}^{+ 3.6}$ $^{+3.6}_{-3.5}$	38.7 $_{- 4.0}^{+ 3.7}$ $^{+3.7}_{-4.0}$	35.7 $_{- 4.4}^{+ 4.4}$ $^{+4.4}_{-4.4}$	37.9 $_{- 4.7}^{+ 4.4}$ $^{+4.4}_{-4.7}$
T_p (KeV)	0.24 $_{- 0.06}^{+ 0.05}$ $^{+0.05}_{-0.06}$	0.22 $_{- 0.05}^{+ 0.05}$ $^{+0.05}_{-0.05}$	0.23 $_{- 0.07}^{+ 0.08}$ $^{+0.08}_{-0.07}$	0.25 $_{- 0.07}^{+ 0.08}$ $^{+0.08}_{-0.07}$
Redshift_p (10⁻³)	3.7 $_{- 0.2}^{+ 0.1}$ $^{+0.1}_{-0.2}$	3.5 $_{- 0.1}^{+ 0.1}$ $^{+0.1}_{-0.1}$	2.7 $_{- 0.1}^{+ 0.1}$ $^{+0.1}_{-0.1}$	2.8 $_{- 0.1}^{+ 0.1}$ $^{+0.1}_{-0.1}$
Velocity_p (km s⁻¹)	754 $_{- 122}^{+ 118}$ $^{+118}_{-122}$	…	514 $_{- 94}^{+ 102}$ $^{+102}_{-94}$	…
F_p (abs.) (erg cm⁻² s⁻¹ × 10⁻¹³)	4.5 $_{- 0.6}^{+ 0.6}$ $^{+0.6}_{-0.6}$	3.5 $_{- 0.6}^{+ 0.5}$ $^{+0.5}_{-0.6}$	5.5 $_{- 0.6}^{+ 0.6}$ $^{+0.6}_{-0.6}$	5.0 $_{- 0.7}^{+ 0.7}$ $^{+0.7}_{-0.7}$
F_p (unabs.) (erg cm⁻² s⁻¹ × 10⁻¹³)	44.9 $_{- 9.7}^{+ 8.9}$ $^{+8.9}_{-9.7}$	53.5 $_{- 12.6}^{+ 10.4}$ $^{+10.4}_{-12.6}$	32.0 $_{- 13.3}^{+ 12.7}$ $^{+12.7}_{-13.3}$	33.5 $_{- 10.1}^{+ 9.8}$ $^{+9.8}_{-10.1}$
L_p (unabs.) (erg s⁻¹ × 10³⁵)	13.4 $_{- 3.0}^{+ 2.8}$ $^{+2.8}_{-3.0}$	16.0 $_{- 3.9}^{+ 3.2}$ $^{+3.2}_{-3.9}$	9.6 $_{- 4.0}^{+ 3.8}$ $^{+3.8}_{-4.0}$	10.0 $_{- 3.0}^{+ 2.9}$ $^{+2.9}_{-3.0}$
F_tot (abs.) (erg cm⁻² s⁻¹ × 10⁻¹³)	20.0 $_{- 1.5}^{+ 1.4}$ $^{+1.4}_{-1.5}$	20.3 $_{- 1.5}^{+ 1.5}$ $^{+1.5}_{-1.5}$	21.5 $_{- 1.9}^{+ 1.7}$ $^{+1.7}_{-1.9}$	21.3 $_{- 1.8}^{+ 1.8}$ $^{+1.8}_{-1.8}$
F_tot (unabs.) (erg cm⁻² s⁻¹ × 10⁻¹³)	155.4 $_{- 9.9}^{+ 9.4}$ $^{+9.4}_{-9.9}$	182.9 $_{- 12.5}^{+ 12.8}$ $^{+12.8}_{-12.5}$	151.9 $_{- 17.8}^{+ 18.8}$ $^{+18.8}_{-17.8}$	161.5 $_{- 14.0}^{+ 13.5}$ $^{+13.5}_{-14.0}$
L_tot (unabs.) (erg s⁻¹ × 10³⁵)	46.4 $_{- 3.6}^{+ 3.5}$ $^{+3.5}_{-3.6}$	54.6 $_{- 4.4}^{+ 4.5}$ $^{+4.5}_{-4.4}$	45.4 $_{- 5.7}^{+ 6.0}$ $^{+6.0}_{-5.7}$	48.2 $_{- 4.7}^{+ 4.5}$ $^{+4.5}_{-4.7}$
χ_red²	0.83	1.02	1.98	2.04

Notes. Physical parameters of the fits for the spectra of CAL 87 shown in Fig. 2 (model atmosphere + collisional ionization plasma model BVAPEC in XSPEC, Model 1) and Fig. 3 (model atmosphere + nonequilibrium ionization collisional plasma model VNEI in XSPEC, Model 2). N(H) is the hydrogen column density. T_WD is the WD effective temperature in the atmospheric model. The temperature grid in the atmospheric model is interpolated in steps of 100 000 K, which reflects the realistic value of the uncertainty. F_WD is the WD atmospheric flux. L_WD is the WD atmospheric luminosity. T_p is the plasma temperature in either the BVAPEC model or the VNEI model. The emission lines were also redshifted by around a few × 10⁻³. Velocity_p is the broadening velocity of BVAPEC, and the parameter broadening velocity does not exist in the VNEI model. F_p is the collisional ionization plasma flux or the nonequilibrium ionization collisional plasma flux. L_p is the collisional ionization plasma luminosity or the nonequilibrium ionization collisional plasma luminosity. F_tot is the total flux. L_tot is the total luminosity. Absorbed and unabsorbed fluxes in the 0.2−1.0 keV energy range are calculated with the cflux command in XSPEC. The distance of 49.97 ± 1.11 kpc was used in the luminosity calculation (Pietrzyński et al. 2013).

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