**Table 2:** Observed features of the X-ray dim radio-quiet isolated neutron stars $^{\ddag\ddag }$ .
ID	Period (s)	$\dot{P}_{-13}$ (s/s)	$B_{p\dot{p}}$	$L_{\rm x}$ (erg s^-1)	$kT_{\rm BB}$ (eV)	$E_{\rm EW}$ (eV)	$E_{\rm cen.}$ (eV)	Optical excess	$R_{\rm bb}$ (km)
RX J0420.0-5022	3.45	<92	-	$2.7\times 10^{30}$	44	-	-	<12	-
RX J0720.4-3125	8.39	0.69	3.93e13	$2.6\times 10^{31}$	85-95	40	280	5	4.4-4.8
RX J0806.4-4123	11.37	<18	-	$5.7\times 10^{30}$	96	-	306-430	-	-
RBS 1223	10.31	1.12	5.52e13	$5.1\times 10^{30}$	86	150	230-300	<5	-
RX J1605.3+3249	-	-	-	-	96	120	450-480	<14	-
RX J1856.5-3754	-	-	-	-	60	-	-	5-7	4.4
RBS 1774	9.44	-	-	-	101	-	$\sim$ 700	-	-

$^{\ddag\ddag }$ See Haberl (2005) and references therein.

Source LaTeX | All tables | In the text