Table 1: IUE spectra used in this work.

Spectrum	Exp. (s)	Aperture*	Obs. date	Spectrum	Exp. (s)	Aperture*	Obs. date
SWP02326	1200	L	18 Aug. 1978	SWP40148	900	L	20 Nov. 1990
SWP02334	6000	L	18 Aug. 1978	SWP40149	9000	L	20 Nov. 1990
SWP02953	2400	S	13 Oct. 1978	SWP43006	720	L	4 Nov. 1991
SWP05669	1800	S	29 Jun. 1979	SWP43007	13 980	L	4 Nov. 1991
SWP06353	1800	S	2 Sep. 1979	SWP46060	2700	L	5 Oct. 1992
SWP06355	4200	S	2 Sep. 1979	SWP46142	900	L	6 Nov. 1992
SWP06527	3960	L	15 Sep. 1979	SWP47697	720	L	20 May 1993
SWP06809	900	L	9 Oct. 1979	SWP50707	720	L	7 May 1994
SWP07406	1800	S	14 Dec. 1979	SWP52387	3600	L	12 Oct. 1994
SWP08760	1800	S	14 Apr. 1980	SWP55055	900	L	21 Jun. 1995
SWP09807	1440	L	23 May 1980	LWR02591	1200	S	13 Oct. 1978
SWP10454	1440	L	23 Oct. 1980	LWR06389	3600	S	14 Dec. 1979
SWP11004	900	L	9 Jan. 1981	LWR09130	2700	L	23 Oct. 1980
SWP13975	900	L	10 May 1981	LWR10571	840	L	10 May 1981
SWP15649	840	L	4 Dec. 1981	LWP09698	3000	L	12 Dec. 1986
SWP15651	6600	L	4 Dec. 1981	LWP16684	1800	L	28 Oct. 1989
SWP29862	10 800	L	12 Dec. 1986	LWP19253	1200	L	20 Nov. 1990
SWP29863	1500	L	13 Dec. 1986	LWP21635	1200	L	4 Nov. 1991
SWP37046	1800	L	16 Sep. 1989	LWP24280	1800	L	6 Nov. 1992
SWP37420	600	L	21 Oct. 1989	LWP25995	3600	L	25 Jul. 1993
SWP37476	1800	L	28 Oct. 1989	LWP28122	3900	L	13 May 1994
SWP37477	11 160	L	28 Oct. 1989	LWP30936	1080	L	21 Jun. 1995

^* L = Large aperture; S = Small aperture.