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3. Discussion

DQ Serpentis

The star DQ Ser (l = tex2html_wrap_inline1032; b = tex2html_wrap_inline1036) is quoted in the 4th ed. of General Catalogue of Variable Stars-GCVS4 (Kholopov et al. 1987) as a slow irregular variable (type L) presenting a brightness variation from 13.9 to 16.0 mag. Our spectra show a late continuum with emission lines of Balmer series, HeI (tex2html_wrap_inline10385876, 6678, 7065), HeII tex2html_wrap_inline10404686, CIII-NIII tex2html_wrap_inline10424640-4650, [OIII] (tex2html_wrap_inline10464363, 4959, 5007), OI tex2html_wrap_inline10488446 and CaII triplet (tex2html_wrap_inline10508498, 8542, 8662). Lines of Paschen series in 8598 Å and 8751 Å, as well a large number of FeII lines are also seen (Figs. 1 (click here)a, b, c, d). The continuum of the late-type star is compatible with a type M3-M5 when compared with the spectra presented in Jacoby et al. (1984), Schulte-Ladbeck (1988) and Medina Tanco & Steiner (1995). The presence of a late-type continuum with emission lines of HI, [OIII] and HeII indicates DQ Ser as a symbiotic star.

The U-B and B-V colours presented by DQ Ser (Table 2) are somewhat bluer than those expected from a M3-M5 giant without emission lines. This is characteristic of symbiotic stars in which Htex2html_wrap_inline1060 + [OIII] lines enhance the emission in the filter B while the Balmer jump in emission, quite common in such variables, can affect the U-B colour by a significant amount (Munari et al. 1992; Kenyon 1986). The V-I index which is not strongly affected by emission lines is also consistent with symbiotic M giants (Munari et al. 1992).

DQ Ser also shows a double and asymmetric profile in the Htex2html_wrap_inline1068 line, whose peaks are centred in 6563.9 Å and in 6566.2 Å (see inserted box in Fig. 1 (click here)b). Such Htex2html_wrap_inline1070 profiles are quite common among symbiotic stars (Van Winckel et al. 1993).

DT Serpentis

DT Ser (l = tex2html_wrap_inline1078; b = tex2html_wrap_inline1082) appears in the GCVS4 as a probable irregular variable of type I, with a brightness variation in the range 13.2-13.9 mag. Due to its spectral type G0 with lines of [OIII] (tex2html_wrap_inline10864959, 5007), Bond (1978) suggested a classification as probable symbiotic.

Accurate measurements of DT Ser are difficult because of its close and bright companion star. This star, about 5 arcsec from the variable, has V magnitude of 12.8 and B-V of 0.76. Our spectra of this companion show the Balmer series in absorption. Other absorption lines, including the G band, are also present. DT Ser is tex2html_wrap_inline10942.6 mags fainter as estimated from our UBVRI photometry (Table 2). The extracted spectrum of the variable shows Balmer lines in emission as well as [OIII] (tex2html_wrap_inline10985007, 4959) and HeI tex2html_wrap_inline11005876. A weak emission of HeII tex2html_wrap_inline11024686 is also present (Figs. 1 (click here)e, f). The continuum is inconsistent with being a M or K giant as it does not display any band associated with these spectral types. We suggest this star to be a yellow symbiotic. We should, however, note that it is difficult to assign a specific spectral type because of the light contamination from bright G companion. This fact also makes the measurements of line fluxes and line ratios not reliable; so we do not included them in Table 3 (click here).

Figures 2 (click here)a and b show finding charts for these objects.


We would like to thank R. Baptista, F.J. Jablonski and G.R. Hickel for obtaining UBVRI photometry. We also thank the referee, R. Viotti, for his valuable comments and suggestions. D. Cieslinski and F. Elizalde thank for the support of CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), under contracts 140587/89-6 and 142589/92-6.

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