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Дата изменения: Sat Mar 11 12:22:26 2000
Дата индексирования: Sat Sep 11 20:55:17 2010
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Поисковые слова: crab nebula

H I 21 cm observations and data reduction

H I line observations were carried out in July 1998 and in February 1999 with the Nançay 300m radio telescope (NRT). The NRT has a half-power beam width of 37 (EW) $\times$ 22 (NS) at the declination Dec. = 0$^{\circ}$.

Since HS 0822+3542 had a known optical redshift, we split the 1024-channel autocorrelator in two halves and used a dual-polarization receiver to increase the S/N ratio. Each correlator segment covered a 6.4 MHz bandwidth, corresponding to a 1350 km s^-1 velocity coverage, and was centred at the frequency corresponding to the optical redshift. The channel spacing was 2.6 km s^-1 before smoothing and the effective resolution after averaging pairs of adjacent channels and Hanning smoothing was 10.6 km s^-1. The system temperature of the receiver was $\approx$ 40 K in the horizontal and vertical linear polarizations. The gain of the telescope was 1.1 K/Jy at the declination Dec. = 0$^{\circ}$. The observations were made in the standard total power (position switching) mode with 1-minute on-source and 1-minute off-source integrations.

The data were reduced using the NRT standard programs DAC and SIR, written by the telescope's staff. Both H and V polarization spectra were calibrated and processed independently, and were finally averaged together. Error estimates were calculated following Schneider et al. ([1986]). With an integration time of 210 minutes, the r.m.s. noise is of 1.4 mJy after smoothing. HS 0822+3542 is detected with S/N=11. The spectrum is presented in Fig. 3.

  

Table 2: Line intensities in HS 0822+3542

$\lambda_{0}$(Å) Ion	F($\lambda$)/F(H$\beta$)	I($\lambda$)/I(H$\beta$)
3727 [O II]	0.331 $\pm$0.013	0.331 $\pm$0.014
3835 H9	0.077 $\pm$0.005	0.080 $\pm$0.007
3868 [Ne III]	0.317 $\pm$0.018	0.318 $\pm$0.018
3889 H8 + He I	0.199 $\pm$0.009	0.203 $\pm$0.010
4026 He I	0.026 $\pm$0.005	0.026 $\pm$0.005
4101 H$\delta$	0.271 $\pm$0.011	0.274 $\pm$0.012
4340 H$\gamma$	0.479 $\pm$0.018	0.481 $\pm$0.018
4363 [O III]	0.123 $\pm$0.007	0.123 $\pm$0.008
4471 He I	0.039 $\pm$0.005	0.039 $\pm$0.005
4861 H$\beta$	1.000 $\pm$0.033	1.000 $\pm$0.034
4922 He I	0.009 $\pm$0.003	0.009 $\pm$0.003
4959 [O III]	1.192 $\pm$0.042	1.190 $\pm$0.042
5007 [O III]	3.550 $\pm$0.121	3.542 $\pm$0.121
5876 He I	0.098 $\pm$0.005	0.097 $\pm$0.005
6300 [O I]	0.004 $\pm$0.003	0.004 $\pm$0.003
6312 [S III]	0.010 $\pm$0.003	0.010 $\pm$0.003
6548 [N III]	0.005 $\pm$0.004	0.005 $\pm$0.004
6563 H$\alpha$	2.743 $\pm$0.087	2.729 $\pm$0.094
6584 [N II]	0.015 $\pm$0.012	0.015 $\pm$0.012
6678 He I	0.033 $\pm$0.004	0.033 $\pm$0.004
6717 [S II]	0.029 $\pm$0.004	0.028 $\pm$0.004
6731 [S II]	0.018 $\pm$0.004	0.018 $\pm$0.004
C(H$\beta$) dex	0.005$\pm$0.04
F(H$\beta$)	0.47 $\times10^{-14}$ erg s-1cm-2
EW(H$\beta$) Å	292$\pm$3
EW(abs) Å	0.6$\pm$0.7

  

Table 3: Abundances in HS 0822+3542, SBS 0335-052 and I Zw 18

Value	HS 0822+3542	SBS 0335-052E1,2	SBS 0335-052W3	I Zw 18NW4	I Zw 18SE4
$T_{\rm e}$(O III)(K)	20,360$\pm$850	20,300$\pm$300	17,200$\pm$500	19,700$\pm$200	18,800$\pm$400
$T_{\rm e}$(O II)(K)	15,790$\pm$600	15,800$\pm$200	14,700$\pm$400	15,600$\pm$150	15,300$\pm$300
$T_{\rm e}$(S III)(K)	18,600$\pm$700	18,500$\pm$200	16,000$\pm$400	18,000$\pm$200	17,300$\pm$350
$N_{\rm e}$(S II)(cm-3)	<10 $\pm^{40}_{10}$	524$\pm$204	10	90	10
O+/H+($\times$105)	0.247$\pm$0.025	0.20$\pm$0.1	0.60$\pm$0.05	0.22$\pm$0.01	0.49$\pm$0.03
O++/H+($\times$105)	1.967$\pm$0.190	1.70$\pm$0.1	1.08$\pm$0.08	1.16$\pm$0.03	1.04$\pm$0.06
O/H($\times$105)	2.214$\pm$0.191	1.90$\pm$0.1	1.68$\pm$0.10	1.45$\pm$0.03	1.54$\pm$0.07
12+log(O/H)	7.35$\pm$0.04	7.29$\pm$0.01	7.22$\pm$0.03	7.16$\pm$0.01	7.19$\pm$0.02
N+/H+($\times$107)	0.992$\pm$0.770	0.60$\pm$0.01	1.72$\pm$0.15	0.64$\pm$0.02	1.43$\pm$0.08
ICF(N)	8.962	8.66	2.81	6.59	3.14
log(N/O)	-1.40$\pm$0.34	-1.58$\pm$0.03	-1.54$\pm$0.06	-1.56$\pm$0.02	-1.53$\pm$0.04
Ne++/H+($\times$105)	0.355$\pm$0.041	0.27$\pm$0.05	0.24$\pm$0.03	0.19$\pm$0.01	0.23$\pm$0.03
ICF(Ne)	1.126	1.13	1.55	1.25	1.48
log(Ne/O)	-0.74$\pm$0.07	-0.80$\pm$0.03	-0.65$\pm$0.06	-0.80$\pm$0.01	-0.65$\pm$0.04
S+/H+($\times$107)	0.424$\pm$0.057	0.40$\pm$0.1	1.09$\pm$0.11	0.35$\pm$0.01	0.67$\pm$0.03
S++/H+($\times$107)	2.815$\pm$0.873	1.90$\pm$0.3	2.15$\pm$0.64	1.96$\pm$0.21	2.07$\pm$0.30
ICF(S)	2.26	2.21	1.29	1.82	1.32
log(S/O)	-1.48$\pm$0.09	-1.59$\pm$0.04	-1.60$\pm$0.08	-1.55$\pm$0.03	-1.63$\pm$0.04
Y(mean)	0.255$\pm$0.013	0.249$\pm$0.006	0.238$\pm$0.005	0.217$\pm$0.005	0.242$\pm$0.009
References: 1 Izotov et al. ([1997a]); 2 Izotov & Thuan ([1999]); 3 Lipovetsky et al. ([1999]); 4 Izotov & Thuan ([1998]).

  

Table 4: Structural properties of HS 0822+3542 in B,V,R-bands

Band	$\mu_{\rm E,0}$	$\alpha_{\rm E}$	$\mu_{\rm G,0}$	$\alpha_{\rm G}$	P25	E25	$m_{\rm LSB}\infty$	$m_{\rm SF}\infty$
	mag arcsec-2	arcsec	mag arcsec-2	arcsec	pc	pc	mag	mag
	(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)
B	20.96$\pm$0.04	1.41$\pm$0.02	20.40$\pm$0.02	1.58$\pm$0.02	118	318	18.22	19.46
V	20.86$\pm$0.04	1.42$\pm$0.03	19.92$\pm$0.02	1.61$\pm$0.03	126	333	18.10	18.68
R	20.57$\pm$0.08	1.38$\pm$0.04	19.79$\pm$0.03	1.61$\pm$0.03	129	342	17.88	18.60
(1) Central surface brightness of the LSB component obtained from the decomposition of each SB profile, weighted by its photometric uncertainties.
(2) Exponential scale length of the LSB component.
(3) Central surface brightness of the gaussian (SF burst) component.
(4) Effective size (FWHM) of the gaussian (SF burst) component.
(5) Linear extent of the luminous component in excess of the LSB component at a surface brightness level of 25 mag arcsec-2.
(6) Linear extent of the LSB component at a surface brightness level of 25 mag arcsec-2.
(7) Total apparent magnitude of the LSB component estimated by extrapolation of the exponential fitting law to R* = $\infty$ (equation 2).
(8) Total apparent magnitude of the SF component.

  

Figure: The surface brightness profiles of HS 0822+3542 in B, V and R-bands. Error bars correspond to 2$\sigma$ uncertainties.

  

Figure: The surface brightness profile of HS 0822+3542 in B-band. Error bars correspond to 2$\sigma$ uncertainties. By the solid lines the decomposition of SB profile is shown to the underlying exponential disc and the central gaussian component corresponding to the SF burst region. The decomposition was performed with the weights. Thick dashed line shows the PSF derived on nearby stars, with FWHM = 125. Two vertical dashed lines mark the region over which the decomposition was performed.

  

Figure 6: (B-V) and (V-R) radial colour profiles of HS 0822+3542. Radially averaged (B-V) and (V-R) colour profiles computed by subtraction of surface brightness profiles displayed in Fig. 4. The mean colours of the exponential disc are shown by the filled and open rectangulars with error bars. The isophotal radius E₂₅ of the LSB host at 25 B mag arcsec^-2 is indicated.