3 Searching for new DIBs

3.1 Average spectra

Since the publication of Kreowski & Walker ([1987]) it is clear that the strong diffuse bands at 5780 and 5797 Å are not of the same origin. Their strength ratio varies from object to object. In Table 1 we present 9 targets in which the 5780/5797 strength ratior resemble that of HD 147165 ($\sigma$ Sco) and 4 targets similar to HD 149757 ($\zeta$ Oph). These two types of objects can be classified as "sigma'' and "zeta'' type clouds (Kreowski & Sneden [1995]). The calculated average of $\lambda$5780 and $\lambda$5797 strength ratio is 2.2 for the "sigma'' cloud and 0.75 for "zeta'' type cloud. Our observational material involves only bright stars; such objects can be considered as nearby and thus very likely to be seen through single, individual clouds ("sigma'' or "zeta'' type). Adding up separately "sigma'' and "zeta'' type spectra we reach a very high signal-to-noise ratio, characteristic for two types of interstellar clouds (see Kreowski et al. [1997]).

Figure 2a presents the spectral region in the vicinity of $\lambda 5780$ for four "zeta'' type stars, which were used in procedure of adding up spectra. The weak features shortward of $\lambda$5780 are clearly seen in all four targets. The spectra seen in Fig. 2a were used to obtain average "zeta'' type spectrum, seen on the top of Fig. 2b. At the bottom of this figure we present the spectrum of HD 179406 and the next spectra to the top show the effect of adding up spectra of stars shown in Fig. 2a with the average zeta type spectrum seen at the top of this figure.

Figure 2: a) The spectra of four zeta type stars in the region of weak features shortward of $\lambda$5780

Figure 2: b) The effect of adding up the spectra seen in Fig. 2a. A--the spectrum of star HD 179406. Spectrum B corresponds to the sum of spectra HD 179406 and HD 148184 added up and normalized to unity. C involves the spectrum originating from the three bottom spectra seen in Fig. 2a. D--all considered spectra summarized. In each case we present measured S/N in the vicinity $\lambda$5762.69

Figure 3: a) Interstellar Li I line at 6707.9 Å seen in three program stars (spectrum of HD 23180 is not included as it has smaller S/N in this spectral range)

Figure 3: b) The effect of adding up the spectra seen in Fig. 4. A--the spectrum of star HD 179406. Spectrum B corresponds to the sum of spectra HD 179406 and HD 148184 added up and normalized to unity. C--all considered spectra summarized ("zeta" type spectrum)

The average spectra of "sigma'' and "zeta'' type are of very high signal-to-noise ratio (see the measured values of S/N in the vicinity $\lambda5762.69$ in Fig. 2b), which is very important for detection of weak interstellar features.

Figure 3a shows the spectral region of weak atomic doublet of interstellar Lithium at 6707.9 Å seen in three spectra of "zeta" type clouds. The spectrum of HD 23180 as of poorer quality in this spectral range was not included. In Fig. 3b we present the effect of adding up the spectra seen in Fig. 3a. In the vicinity of Li I line are seen three weak DIBs and one unidentified stellar line marked with the sign # (see Sect. 3.2). Interstellar Li I line seen only in several targets is too weak to be observed in most of individual targets and could not be used for shifting the wavelength scale of the spectra to the rest wavelength of these lines. The line is not detectable in any of our "sigma'' targets - only in the average spectrum (see Fig. 4).

The most heavily reddened star in Table 1, HD 210839, is a special target which is used to verify presence of weak interstellar features. This star was observed twice during one observational session at McDonald Observatory and these two spectra were averaged giving as a result a very high signal-to-noise ratio. It is also one of the most rapidly rotating targets which spectrum (O6) should contain only a few, broad lines and thus all observed narrow features (after the removal of telluric lines) are to be considered as interstellar.

3.2 Stellar lines

As an additional check of the interstellar origin of observed features, we have made identification of stellar lines in the available spectral range. To this purpose we have synthesized a number of spectra with temperatures characteristic for the observed spectral types and gravities. All calculations have been made with Hubeny's SYNSPEC code (Hubeny et al. [1986]; Hubeny et al. [1995]). As input atmospheric models we applied Kurucz's grid (Kurucz [1992]) using the list of lines from Kurucz's CD ROM No. 23 (Kurucz [1990]) and ocassionally the VALD database mailserver (Piskunov et al. [1995]). The procedure of dividing the spectra under consideration by the spectra of rapidly rotating standards and averaging of the stellar spectra of slightly different types and different radial velocities transforms the shapes of stellar features and leaves some complex structures in the resulting spectra. In such places the search for weak interstellar features is very difficult. Having this in mind we have identified the stellar lines being source of these features. Some features seen in the averaged spectrum of "zeta'' type originate in the binary object (o Per?) and their shapes are more complicated than one expects from the synthesized spectrum. At last, there are four features of stellar origin which remain unidentified. Both of them have been marked with the sign # in Fig. 4.

 

 

Table 2: List of certain DIBs. Codes: br: broad, bl: blended with stellar and/or telluric lines, a: very strong, b: strong, c: quite strong, d: weak, e: very weak, f: not detectable

$\lambda_{{\rm lab}}$	EW $\star$	In $\sigma$ cl.	In $\zeta$ cl.	references
Å	mÅ
5705.43:	25.4	c, br	d, br	H75 J94
5719.40	5.8	d	d	J94
5756.07		f	e	K97
5760.44	1.0:	e	d	K93 K95 K97
5762.69	3.0	e	d	K93 J94 K95
				K97
5766.15	8.4	d	d	Ch87 K93 K95
				K97
5769.03	0.5:	e	d	K93 K95 K97
5772.53	7.6	d	d	K93 J94 K95
				K97
5775.75	2.1:	d	d	K93 J94 K95
				K97
5780.50	245.2	a	a	H75 Ch87 K95
				J94
5785.11	2.1:	e	e	K97
5788.90	2.2:	f	e	K97
5793.19	7.6	e	d	K93 K95 K97
5795.20		d, br	d, br	K93 K95 K97
5796.97	bl	b	a	H75 Ch87 K93
				J94
5809.22	bl	e	d	K93 J94 K95
				K97
5811.57	bl	e	e	K97
5814.21	bl	e	d	K97
5815.78	bl	f	d	K97
5818.69	1.8:	f	d	K93 K95 K97
5821.22	1.7:	f	e	K97
5828.52	4.1	e	d	K93 K95 K97
5830.77	0.5:	f	e	K97
5832.88		f	e	K97
5835.00		f	e	K97
5837.26	0.8:	f	e	K97
5838.08	1.3:	e	d	K97
5840.72	4.4	e	d	K97
5842.49		e	d	K97
5843.42	2.5	d	d	K97
5844.15:		c, br	d, br	H75 H91 J94
5844.80	3.6	d	e	K97
5845.67		e	e	K97
5848.37	0.5:	e	e	new
5849.85	29.0	c	b	H75 Ch87 H91
				J94
5852.14	0.4:	e	e	K97
5854.54	1.9	e	d	K97
5855.72	0.7:	e	d	K97
5857.19		e	d	K97
5859.00	0.5:	e	e	new
5860.27	1.4:	e	e	K97
5861.89	1.2:	f	e	K97
5866.50	2.3	d	e	K97
5870.71	bl	d	d	new
5900.56	6.5	e	d	K95
5904.52	0.6:	e	d	K95
5908.33	0.6:	f	e	K95

$\lambda_{{\rm lab}}$	EW $\star$	In $\sigma$ cl.	In $\zeta$ cl.	references
Å	mÅ
5910.40	9.5	d	c	K95
5917.51	1.2:	e	e	K95
5922.31	1.8:	e	e	K95
5923.39	8.4	d	d	K95
5925.85	4.5	f	e	K95
5927.70	0.5:	e	d	K95
5928.96	1.2:	e	e	K95
5930.00	bl	f	d	K95
5932.84	1.0:	e	d	new
5942.30	2.8	e	d	new
5945.44	1.4:	e	d	K95
5947.25	6.4	e	d	K95
5948.88	1.4:	e	d	K95
5958.89	15.3:	e	d	new
5965.28	1.3:	e	e	new
5966.28	2.1	e	d	new
5967.63	2.0	d	d	new
5969.88	1.8:	e	e	new
5973.78	2.1	e	d	new
5975.58	2.6	f	d	K95
5982.83	10.4	e	d	H75 K95
5985.38	1.4:	f	e	new
5986.43	2.6	d	e	K95
5988.03	5.7	d	d	K95
5989.48	4.2	f	d	K95
5994.58	1.0:	e	e	new
5995.73	4.6	d	d	K95
5997.58	1.2:	e	e	new
5999.18	2.4	e	e	new
6004.93	10.8	e	e	H91 K95
6010.80:	14.1	e, br	e, br	H75 J94 K95
6017.53	0.5:	d	d	new
6019.23	2.6	d	d	J94 K95
6022.98	1.2:	f	e	K95
6023.88	1.7:	f	e	K95
6027.48	9.4	d	d	K95
6037.38	0.5:	d	d	J94 K95
6057.58	1.0:	e	d	new
6059.28:	3.2	e	f	J94
6060.10:	1.7:	e	e	J94
6065.23	8.2	d	e	J94
6068.23		e	e	new
6070.98:	1.7:	e	d	J94
6082.18	1.0:	f	e	new
6084.78	1.0:	e	d	new
6089.78	12.6	c	c	H91 J94
6093.18	0.9:	e	d	new
6098.53	1.4:	e	d	new
6102.33	1.6:	d	d	new
6108.13	5.9	d	d	K93 J94
6109.98	1.0:	e	d	K93
6113.18	14.9	d	d	H75 H91 K93
				J94
6116.83	3.4	e	d	K93 J94
6118.63	1.0:	e	d	K93
6140.03	6.3	d	d	K93 J94
6145.50	4.1	f	d	K93
6158.53		d	d	new
6161.96	4.8	d	d	K93

 

Table 2: continued

$\lambda_{{\rm lab}}$	EW $\star$	In $\sigma$ cl.	In $\zeta$ cl.	references
Å	mÅ
6181.25	0.8:	e	d	new
6182.60	0.9:	e	d	new
6185.98	2.7	e	d	new
6187.58	2.1	e	d	new
6189.47	0.5:	e	d	J94
6193.06	0.9:	e	d	new
6194.77	6.9	d	d	S81 Ch87 K93
				J94 K95
6196.05	34.2	c	c	H75 H91 K93
				J94
6196.96	1.2:	e	d	new
6199.04:	1.8:	f	e	new
6203.05	62.3	c	c	H75 Ch87 H91
				J94
6204.86	bl	e, br	d, br	J94
6211.73	2.4	e	d	K95
6212.87	2.1	d	d	K95
6220.77	1.4:	e	d	K95
6223.63	2.5	d	d	K95
6226.08:	1.3:	e	d	K95
6234.05	7.4	d	d	H75 J94 K95
6245.47	5.0	e	d	K95
6250.83	2.4	d	d	new
6289.86	73.8	c	b	H75 H91
6283.80	204.4:	a	a	H75 H91 J94
6287.54	8.4:	f	d	J94
6289.30	1.0:	e	d	J94
6350.70	4.4	e	d	new
6353.25	2.9	f	d	H91 J94 K95
6358.35	1.7:	f	d	H91 J94
6362.50	4.4	e	e	H91 J94 K95
6364.44	0.5:	e	d	H84 J94 K95
6367.41	6.7	e	d	H84 J94 K95
6376.10	16.1	d	c	H75 H91 J94
				K95
6379.46:	53.6	c	b	H75 H91 J94
6387.18		e	d	new
...
6396.63	bl	e	d	H91 K95
6400.25	2.7	e	d	K95
6414.18	3.1	e	d	H91 K95
6420.77	1.8:	e	d	new
6425.90	9.3	e	d	H75 H91 K95
6430.47	2.7	f	e	new
6439.50	8.7	e	d	H91 K95
6445.25	13.3	d	d	J94 K95
6449.28	5.2	e	d	H75 H91 J94
				K95
6455.86	8.6	d	d	new
6460.28	6.6	e	d	J94
6463.41	2.1	e	d	new
6465.44	1.5:	e	e	new
6466.65	6.1	e	d	new
6474.23	3.7	e	d	new
6486.75	1.1:	d	d	new
6489.62	3.6	e	d	new
6492.15	5.5	d	d	J94
6496.10	2.0	e	d	new

$\lambda_{{\rm lab}}$	EW $\star$	In $\sigma$ cl.	In $\zeta$ cl.	references
Å	mÅ
6497.82	3.0	e	d	J94
6501.23	2.5	e	d	new
6513.38	1.3:	e	d	new
6516.64	4.6	e	d	new
6518.76		e	e	new
6523.36	1.0:	e	d	new
6536.89	4.3	e	e	new
6627.88	1.0:	e	f	new
6660.70	2.5	e	e	new
6660.70	3.5	e	e	new
6672.39	1.7:	e	d	K95
6518.76	10.0	d	d	J94
6534.14	5.6	e	d	new
6536.89	0.8:	d	d	J94
6546.15	3.8	f	d	new
6548.93	5.2	d	e	new
6553.89	6.6	d	d	new
...
6597.34	13.3	d	d	H75 H91
6613.52	148.4	b	a	H75 H91 J94
6622.90	3.6	d	d	K95
6627.88	3.1	e	e	new
6632.65	3.4	d	e	J94 K95
6635.44	4.3	d	e	K95
6660.70	31.2	d	c	H75 H91 J94
				K95
6665.15	3.9	e	d	new
6672.39:	9.0	d	d	new
6694.50	5.4	f	e	K95
6697.01	1.5:	f	e	K95
6699.24	18.1	d	d	H75 F83 H91
				J94 K95
6701.95	11.0	d	d	F83 H91 K95
6709.44	0.9:	d	d	K95
6729.28	2.7	e	d	new
6737.14	1.8:	e	d	new
6740.96	2.6	d	d	J94
6767.58	0.9:	d	d	H88
6770.12	4.5	e	d	H88 J94
6779.04	4.0	d	e	H88
6788.66	2.3	e	d	H88
6792.42	3.1	d	c	H88
6795.20	4.7	d	d	H88 J94
6801.41	5.6	d	d	H88 J94
6803.26	2.9	d	d	H88
6811.27	9.7	d	e	H88
6820.80	1.3:	d	c	H88
6823.38	3.1	d	e	H88
6827.22	9.6	d	c	H88 J94
6834.53	1.3:	e	e	H88
6837.70	2.9	d	d	H88
6839.05	2.8	e	e	H88
6841.54	7.8	d	d	H88 J94
6843.69	10.7	d	d	H88 J94
6845.26	1.1:	e	e	H88
6846.53	2.2	e	d	H88
6852.91:	1.8:	d	d	H88 J94
6860.13	3.8	e	e	H88 J94
6862.47	1.5:	e	d	H88